AU2021463486B2

AU2021463486B2 - Combustion boiler control method, combustion boiler and boiler computation system

Info

Publication number: AU2021463486B2
Application number: AU2021463486A
Authority: AU
Inventors: Ari Kettunen; Jouni Miettinen
Original assignee: Sumitomo SHI FW Energia Oy
Current assignee: Sumitomo SHI FW Energia Oy
Priority date: 2021-09-09
Filing date: 2021-09-09
Publication date: 2025-06-26
Anticipated expiration: 2041-09-09
Also published as: JP7778227B2; WO2023036426A1; ZA202401678B; EP4222418C0; US20250109850A1; HUE071381T2; EP4222418B1; CN118318130A; AU2022344519B2; EP4222417C0; AU2022344519A1; JP2024535750A; JP7778228B2; JP2024533224A; EP4222418A1; EP4222417A1; PL4222417T3; KR20240065111A; HUE073502T2; PL4222418T3

Abstract

To improve boiler control, a combustion boiler control method is suggested, comprising the steps of: a) monitoring the current load (Qh) of a combustion boiler; b) finding such a numerical value (Qh, candidate) for a current computational maximum boiler momentary load (Qh, max) for which at least one flue gas factor (dfi) computed using currently monitored process data with a numerical model of the boiler fulfills an acceptance condition, and selecting the numerical value (Qh, candidate) as the current computational maximum boiler momentary load (Qh,max); c) indicating the current computational maximum boiler momentary load (Qh,max) to the operator and/or, if the current load (Qh) is c1) smaller than the current computational maximum boiler momentary load (Qh,max): c1i) indicating the boiler operator that the boiler load (Qh) may be increased, and/or c1ii) automatically increasing the boiler load (Qh), and/or c2) larger than the current computational maximum boiler momentary load (Qh,max): c2i) indicating the boiler operator that the boiler load (Qh) exceeds the current computational maximum boiler momentary load, and/or c2ii) automatically reducing the boiler load (Qh).

Description

WO 2023/036426 A9 Declarations under Rule 4.17: - as to as the identity to the identity of of the inventor the inventor (Rule (Rule 4.17(i)) 4.17(i))

- - as to as applicant's entitlement to applicant's to apply entitlement for for to apply and and be granted a be granted a

- patent (Rule 4.17(ii))

- of inventorship of inventorship(Rule 4.17(iv)) (Rule 4.17(iv))

- - as to as non-prejudicial disclosures to non-prejudicial or exceptions disclosures to lack or exceptions of of to lack

- novelty novelty (Rule (Rule 4.17(v)) 4.17(v))

Published: - withwith international search international search report report(Art. 21(3)) (Art. 21(3))

- (48) Date of publication of this corrected version: 19 May 2023 (19.05.2023)

(15) Information about Correction: see see Notice Notice of of 19 19 May May 2023 2023 (19.05.2023) (19.05.2023)

1 04 Jun 2025 04 Jun 2025

Combustion boiler Combustion boiler control control method, method, combustion combustion boiler boiler and and boiler boiler computation computation system system

Technical Field Technical Field The inventionrelates The invention relatesto to control control of combustion of combustion boilers, boilers, in particular in particular 5 fluidized bedboilers, fluidized bed boilers, such such as as circulating circulating fluidized fluidized bed (CFB) bed (CFB) boilersboilers 2021463486

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or bubblingfluidized or bubbling fluidized bed bed (BFB) (BFB) boilers. boilers.

Background Background Combustionboilers, Combustion boilers,such such as as grate grate boilers boilers and fluidized and fluidized bed boilers bed boilers are commonlyutilized are commonly utilized to to generate generate steam steam which which canused can be be for usedvariety for variety of purposes,such of purposes, suchasas forfor producing producing electricity electricity and heat. and heat.

In a fluidized In a fluidizedbed bedboiler, boiler, fuel fuel and and solid solid particulate particulate bed material bed material is is introduced intoa afurnace. introduced into furnace. TheThe bedbed material material and fuel and fuel is fluidized is fluidized by by introducing fluidizing introducing fluidizing gas gas from from a bottom a bottom portion portion offurnace. of the the furnace. Burning offuel Burning of fueltakes takes place place in in the the furnace. furnace. In combustion, In BFB BFB combustion, fluidization gasisispassed fluidization gas passed through through the the bed bed such such that that it forms it forms bubbles bubbles in the bed. in the bed.The Thefluidized fluidizedbedbed cancan in ainBFB a BFB be rather be rather conveniently conveniently controlled bycontrolling controlled by controllingthethe fluidization fluidization gas feed gas feed and feed. and fuel fuel In feed. In addition tofuel, addition to fuel,certain certain additives additives suchsuch as aluminum as aluminum silicates silicates (such (such as, non-hydratedclay) as, non-hydrated clay) andand alkali alkali alkaline alkaline earthearth metalmetal carbonates carbonates and and mixtures thereof mixtures thereof(such (such as,as, limestone limestone or calcium or calcium carbonate) carbonate) may bemay be added to the added to thecombustion combustionto to improve improve sorption sorption of possible of possible heavy heavy metals, metals, sulfur, andalso sulfur, and alsototoimprove improve alkali alkali sorption. sorption.

In CFB combustion, In CFB combustion,fluidization fluidization gas gas is passed is passed through through the bed the bed material.Most material. Mostbed bedparticles particles will will be entrained be entrained influidization in the the fluidization gas gas

and they will and they willbebecarried carried with with flue flue gas.gas. The The particles particles are separated are separated from the flue from the fluegas gasininatat least least oneone particle particle separator separator and circulated and circulated returning themback returning them backinto into thethe furnace. furnace. It common It is is common to arrange to arrange a a fluidized bedheat fluidized bed heatexchanger exchanger downstream downstream the the particle particle separator(s) separator (s) to to recover heatfrom recover heat fromthe the particles particles before before theythey are returned are returned into the into the

furnace. furnace.

In all boilers, In all boilers,regardless regardlessof of thethe combustion combustion technology, technology, the the combustion conditions, combustion conditions, such such as,as, the the mixing mixing of and of air air fuel, and fuel, may may not be not be ideal. ideal.

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International application International application published published under under WO 2016/202640 WO 2016/202640 A1 of A1 of Improbed ABdiscloses Improbed AB discloses a thermal a thermal load load control control method method for a for a combustion combustion boiler. In boiler. Inthe themethod, method, thethe thermal thermal loadload of aof a combustion combustion boilerboiler is is reduced if monitored reduced if monitoredflue flue gasgas velocity velocity inleast in at at least one location one location of the of the 5 boiler exceeds boiler exceedsa apre-determined pre-determined maximum maximum flueflue gas velocity gas velocity limit.limit. The The flue gas velocity velocityisiscomputed computed from volume flow flow of flue gas divided by 2021463486

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flue gas from volume of flue gas divided by the cross-sectionalarea the cross-sectional area of of thethe flue flue gas gas ductduct in location in the the location just just downstream thecyclone downstream the cyclone using using an an equation equation group. group.

SummaryA combustionboiler SummaryA combustion boiler traditionally traditionally is designed is designed for a for a given given load load that is the that is therespective respective boiler boiler maximum maximum continuous continuous rating rating (BMCR)(BMCR) of the of the boiler. This boiler. Thisisissometimes sometimes called called the the design design load load level. level.

The presentinvention The present inventionmaymay improve improve performance, performance, profitability, profitability, and and flexibility ofthe flexibility of theboiler, boiler, andand also also improve improve control control ofboiler of the the boiler load. In this load. In thisregard, regard, disclosed disclosed herein herein is acombustion is acombustion boilerboiler control control method according method accordingtoto claim claim 1 and 1 and withwith the the combustion combustion boilerboiler according according to claim 19. to claim 19.

The presentinvention The present inventionmaymay also also reduce reduce complexity complexity of control of control systemsystem of of a combustionboiler. a combustion boiler.InIn this this regard, regard, disclosed disclosed is a is a combustion combustion boiler boiler computation systemaccording computation system according to to claim claim 24. 24.

The dependentclaims The dependent claims describe describe advantageous advantageous aspects aspects ofcombustion of the the combustion boiler control boiler controlmethod, method, of of thethe combustion combustion boiler, boiler, and and of theofcombustion the combustion boiler computation boiler computationsystem. system.

The combustionboiler The combustion boiler control control method method comprises comprises the steps the steps of of

a) monitoringthe a) monitoring thecurrent current load load Qh of Qh of a combustion a combustion boiler; boiler; b) finding b) findingsuch sucha anumerical numerical value value for for a current a current computational computational maximum boiler maximum boilermomentary momentary load load for for which which at least at least one gas one flue flue gas factor computedusing factor computed using currently currently monitored monitored process process data data with awith a numerical modelofofthe numerical model the boiler boiler fulfills fulfills an acceptance an acceptance condition, condition,

and selectingthe and selecting thenumerical numerical value value as the as the current current computational computational maximum boiler maximum boilermomentary momentary load load Qh, Qmax h, max;

c) indicatingthe c) indicating thecurrent current computational computational maximum maximum boilerboiler momentary load momentary loadQh, Qh,max max to to the the operator and/or,ififthe operator and/or, the current current load Qh is load Qh is

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c1) c1) smaller smaller than than the the current current computational computational maximum maximum boiler momentary load: boiler momentary load: c1i) indicatingthe cli) indicating theboiler boiler operator operator thatthat the boiler load the boiler loadmay maybebe increased, increased, and/or and/or 5 c1ii) automaticallyincreasing clii) automatically increasing thethe boiler boiler load, 2021463486

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load, and/or and/or c2) c2) larger larger than than the the current current computational maximum computational maximum boiler momentary boiler momentaryload: load: c2i) indicatingthe c2i) indicating theboiler boiler operator operator thatthat the boiler load the boiler loadQhQhexceeds exceedsthethe current current computational maximum boiler computational maximum boiler momentary momentary load, and/or load, and/or c2ii) automaticallyreducing c2ii) automatically reducing thethe boiler boiler load Qh. load Oh.

With the With the method, method, instead instead of of having having a a fixed fixed boiler boiler maximum maximum load, load, with with the method of the method ofcomputing computing a flue a flue gasgas factor factor and selecting and selecting its acceptance its acceptance conditions suitable, conditions suitable, itit is is possible possible to safely to safely operate operate the combustion the combustion boiler at boiler at or or closer closer to to its its current current computational computational maximum maximum boiler boiler momentary load momentary load that that at at times may times may be be higher higher than than the the fixed fixed boiler boiler maximum load maximum load would would be. be. The current The current computational computational maximum maximum boiler boiler momentaryload momentary loadcan canbebe higher higher than than the the design design load load level. level. Therefore, Therefore, the overallperformance the overall performanceof of thethe boiler boiler may may be improved be improved and enabling and enabling

increased power/heatproduction. increased power/heat production. Further, Further, since since the current the current computational maximum computational maximum boiler boiler momentary momentary loadload may occasionally may occasionally be be smaller thanthe smaller than thedesign design load load level, level, boiler boiler wear wear resulting resulting from from exceeding exceeding the the current current computational computational maximum maximum boiler boiler momentary momentary load load may may be better be better reduced. In reduced. In other terms, other terms, the the current current computational computational maximum maximum

boiler momentary boiler momentary load load can can be be considered considered as as maximum maximum allowable allowable boiler boiler load and/orpreferable load and/or preferable boiler boiler load. load.

The presentapplicant The present applicanthashas been been able able to obtain to obtain in tests in the the tests performed, performed, in average,power in average, poweroutput output from from a combustion a combustion boiler boiler that that exceeds exceeds the the fixed boilermaximum fixed boiler maximumload. load. TheThe present present applicant applicant couldcould in theintests the tests

demonstrate demonstrate that that for for aa combustion combustion boiler boiler the the improvement improvement potential potential may may

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lie lie between between 2,5 2, -– 5% 5% which which corresponds, corresponds, for for example, example, 33 to to 66 MWth MWth for for aa 120 120 MWth combustion MWth boiler. combustion boiler.

In some embodiments, In some embodiments,inin thethe method: method:

5 i) the currently currentlymonitored monitored process datadata of boiler the boiler includes 2021463486

i) the process of the includes

ia) currentflue ia) current fluegas gasexit exit temperature temperature in ain a flue flue gas flow gas flow channel and channel and

ib) heat duty ib) heat dutyfor foreach each heat heat transfer transfer surface surface in flue in the the gas flue gas flow channel flow channel

and further: and further:

ii) monitoredprocess ii) monitored process data data from from both both ia) ia) and and ib)used ib) is is in used in computation computation ofofthe theflue flue gasgas factor factor and and whenwhen finding finding the numerical the numerical value for the value for thecurrent current computational computational maximum maximum boiler boiler momentary momentary load load Qh,max max .

Computation Computation ofofheat heatduty duty of of a heat a heat exchanger exchanger is known is known for skilled for skilled person in the person in theart artand and heat heat duty duty can can be obtained, be obtained, for instance, for instance, by by using the following using the followingequation equation

𝑄 𝑓𝑙𝑢𝑖𝑑,𝑖 = 𝑞𝑚,𝑓𝑙𝑢𝑖𝑑,𝑖 ∗ (ℎ𝑓𝑙𝑢𝑖𝑑,𝑜𝑢𝑡 − ℎ𝑓𝑙𝑢𝑖𝑑,𝑖𝑛 ) Qfluid,i = qm,fluid,i * (hfluid,out - hfluid,in)

whereinqm,fluid,i wherein 𝑞𝑚,𝑓𝑙𝑢𝑖𝑑,𝑖 is thefluid is the fluid flow flow in heat in ith ith transfer heat transfer surface, surface, hfluid,in ℎ𝑓𝑙𝑢𝑖𝑑,𝑖𝑛

is the enthalpy is the enthalpyofoffluid fluid entering entering to the to the ith ith heat heat transfer transfer surface surface and and ℎ𝑓𝑙𝑢𝑖𝑑,𝑜𝑢𝑡 is is hfluid,out thethe enthalpy enthalpyofoffluid fluid exiting from the exiting from theith ithheat heat transfer transfer surface. surface.

The findingmay The finding maybebeperformed performed such such that, that, if at if the theleast at least one gas one flue flue gas

factor computedusing factor computed using currently currently monitored monitored process process data data with awith a numerical modelofofthe numerical model the boiler boiler fails fails to fulfill to fulfill an acceptance an acceptance condition, condition, aanext nextnumerical numerical value value is automatically is automatically selected. selected. In some In some embodiments, thenext embodiments, the next numerical numerical value value can can be selected be selected iteratively. iteratively. This may enable This may enablethe theuse use of of computational computational library library functions, functions, and, inand, in

particularofofananiterative particular iterative solver solver (such (such as, Python as, Python FSOLVE FSOLVE function function which solvesroots which solves rootsofof function). function).

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The findingmay The finding maybebecarried carried outout with with performing performing the computational the computational steps steps of: of:

- I: computing - I: computingananestimate estimateforfor boiler boiler flueflue gas exit gas exit temperature thatresults temperature that resultsin in a computational a computational boiler boiler modelmodel when when 5 the thermalload the thermal loadofofthe the boiler boiler corresponds corresponds to numerical to the the numerical 2021463486

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value; value;

- - II: II: computing computing flue flue gas gas mass mass flow flow

- III: computing - III: computinga aheat heat duty duty forfor eacheach heatheat transfer transfer surface surface in in the flue gas the flue gasflow flowchannel channel with with itsits current current heat heat duty duty that is that is corrected byusing corrected by usinga a numerical numerical boiler boiler model; model;

- IV: using - IV: usingthe thecomputed computed heat heat duties duties for for each each heat heat transfer transfer surface in the surface in theflue fluegas gas flow flow channel channel to compute to compute flue flue gas gas temperatures temperatures atateach each heat heat transfer transfer surface surface in flue in the the flue gas flow gas flow channel inthe channel in theupstream upstream direction direction of flue of flue gas flow, gas flow, starting starting from the heat from the heattransfer transfer surface surface thatthat is closest is closest to flue to the the gas flue gas exit usingthe exit using theestimate estimate forfor thethe boiler boiler flueflue gas exit gas exit temperature; temperature;

- V: computing - V: computinga aflue flue gas gas factor factor for for eacheach heat heat transfer transfer surface surface in the flue in the fluegas gasflow flowchannel. channel.

With this With thisapproach, approach, the the situation situation of each of each heat heat transfer transfer surface surface (here (here and hereinafter,"heat and hereinafter, “heat transfer transfer surface” surface" means means a heat a heat exchanger, exchanger, a a heat exchanger heat exchangertube, tube, heat heat exchanger exchanger tubetube bundle, bundle, heat heat exchanger exchanger packages and/or packages and/ora aconstructive constructive group group of heat of heat exchangers, exchangers, such as such as economizer) economizer) ininthe theflue flue gasgas flow flow channel channel canestimated can be be estimated numerically numerically

with the with the flue flue gas gas factor factor in in the the situation situation where where the the thermal thermal load load of of the boilercorresponds the boiler correspondsto to thethe numerical numerical value. value. In some In some embodiments, embodiments, the term "heat the term “heattransfer transfer surface” surface" means means a constructive a constructive group group of heat of heat exchangers, exchangers, such such as as economizer. So,we economizer. So, wecan cannow nowtest testwhether whetheraagiven given numerical value numerical valuethat that is is a candidate a candidate for for a current a current computational computational

maximum boiler maximum boiler momentary momentary load load would would produce produce an an acceptable acceptable situation situation at at the heat transfer the heat transfersurface. surface.

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According to According toananembodiment embodiment of of thethe invention, invention, in step in step III) the III) the numerical boiler numerical boiler modelmodel is of is theof the form form i, Qfluid, Qfluid, i, candidate candidate = Qfluid,i,current = Qfluid, i, current ++  (On, ,i j,i (Q candidate) j h,candidate) j -  par(On, - par, j,i (Q j h,current) . current)

The The fitting fitting of of the the parameters parameters (par j,i) can (par,) can be be done done manually manually by by human human or or 5 automatically automatically bybycomputer computer utilizing utilizing historical historical data.data. Automatic Automatic update update 2021463486

of the parameters of the parametersmay may be be done done e.g.e.g. onceonce per per month. month. AIneural AI and and neural network basedalgorithms network based algorithms cancan be be utilized utilized in automatic in automatic update. update.

On one hand, On one hand,this thisenables enables predicting predicting the the maximum maximum computational computational allowable currentboiler allowable current boiler momentary momentary loadload without without goinggoing to thetolimit the limit with the with the current currentboiler boiler load, load, in contrast in contrast to method to the the method disclosed disclosed in in WO 2016/202640 WO 2016/202640A1, A1,and and on on thethe other other hand, hand, and even and even more importantly, more importantly, enables goingtotothe enables going the limit limit without without exceeding exceeding the maximum the maximum computational computational allowable currentboiler allowable current boiler momentary momentary load. load.

In some embodiments, In some embodiments,the the flue flue gasgas factor factor includes includes or is: or is:

df i=k df=k i(qm,fluegas fluegas /(ρfluegas,i / (Ofluegas, *Across,i) )n i Across,

where where

k is aa non-zero ki is non-zero parameter parameter that that may may be be chosen chosen combustion-boiler combustion-boiler specifically, specifically, ininsome some embodiments embodiments positive positive (non-zero) (non-zero) numbernumber

qm,fluegas qm, is isa aflue fluegas flue gas massflow gas mass flow

n n is is a a model model parameter parameter that that may may be be chosen chosen combustion-boiler combustion-boiler specifically, specifically, ininsome some embodiments embodiments positive positive (non-zero) (non-zero) numbernumber

ρfluegas,i is Pfluegas, i the density is the ofofthe density theflue flue gas gas at at the ith heat the ith transfer heat transfer surface; surface; andand

Across,i is Across, thethe i is cross-sectional cross-sectional area area of the flue of the fluegas gasflow flow path path at at the ith heat the ith transfersurface. heat transfer surface.

This This is is particularly particularly convenient convenient since since choosing choosing this this functional functional form form for the flue gas factor, it becomes very flexible and can be for the flue gas factor, it becomes very flexible and can be easilyeasily adapted to suit adapted to suitdifferent different combustion combustion boiler boiler needs, needs, suchbased such as, as, based on on

the conditionsininthe the conditions the current current fuel. fuel.

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Particularly advantageously, Particularly advantageously, thethe model model parameter parameter n mayn be may be selected selected to to include at least include at leastone oneofof thethe following: following:

i) in the i) in the range rangeofof0,9 0,9to to 1,1, 1,1, in in somesome embodiments embodiments equivalent equivalent or about 1.0, or about 1.0,forforusing using computed computed flueflue gas gas velocity; velocity;

5 ii) in the the range rangeofof2,9 2,9 to to 3,5, in some embodiments between 3,2 2021463486

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ii) in 3,5, in some embodiments between 3,2 and 3,35, for and 3,35, forusing usingcomputed computed flue flue gas gas caused caused erosion; erosion; or or

iii) in the iii) in therange rangeofof1,8 1,8 to to 2,2, 2,2, in some in some embodiments embodiments equivalent equivalent or about 2.0, or about 2.0,for forusing using pressure pressure loss. loss.

The value for The value forn nmay maybebe changed changed over over time. time. This This is advantageous is advantageous for thefor the reason thatthe reason that theflue fluegas gas flow flow conditions conditions at heat at the the heat transfer transfer surfaces surfaces may change may change over over time, time, such such as as because because ofof slagging, slagging, ash ash agglomeration agglomeration or fuel or or fuel orbed bedconditions. conditions. Thus, Thus, the the flueflue gas factor gas factor may bemay be shifted shifted over time, to over time, tobetter better reflect reflect thethe actual actual boiler boiler situation. situation.

According to According toananembodiment embodiment of of thethe invention, invention, when when n=2flue n=2 and and gas flue gas factor representsa apressure factor represents pressure loss, loss, the the comparison comparison between between thegas the flue flue gas factor dfi and factor dfi and aapredetermined predetermined maximum maximum value value for for the flue the flue gas factor gas factor dfmax,i can dfmax,i can be be carried out for carried out foreach eachheat heat transfer transfer surface. surface. According According to to an embodimentthe an embodiment theacceptance acceptance condition condition is substantially is substantially dfi= dfmax,i. dfi= dfmax,i.

According to According toananembodiment embodiment of of thethe invention, invention, when when n=2flue n=2 and and gas flue gas factor representsa apressure factor represents pressure loss, loss, the the comparison comparison can can be be between done done between the sum of the sum of the theflue fluegas gas factors factors dfi dfi

𝑑𝑝 dp𝑡𝑜𝑡 == ∑df 𝑑𝑓𝑖

and sum of and sum of the thepredetermined predetermined flue flue gas gas factors factors dfmax,i dfmax,i or simply or simply predetermined fluegas predetermined flue gas factor factor represents represents totaltotal pressure pressure drop drop and and hence hence

the comparisonrepresents the comparison represents thethe comparison comparison of total of total pressure pressure drops drops between the between thefurnace furnace and and stack. stack. According According toembodiment to an an embodiment the the acceptance conditionisis acceptance condition substantially substantially dptot dptot= = dp dp, max,tot. tot.

According to According toananembodiment embodiment of of thethe invention, invention, the flue the flue gas factor gas factor represents anash represents an ashloading loading factor factor and and can can be written be written inform in the the form

n

df dfii ==kphC kphC(d)q m_favp (d) qm_faVp

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where Kph where kph is is particle particlehardness hardness factor, factor, C(d) C (d) is is particle particle diameter diameter function, qm_fa is function, qm_fa fly ash is fly ash mass massflow flowrate, rate, vp particle V is is particle velocity velocity and n and n is exponent(0,3 is exponent (0,3- –4). 4). In In such such case, case, the the predetermined predetermined fluefactor flue gas gas factor represents maximumash represents maximum ash loading loading value. value. It can It can also also be adjustable be adjustable based based 5 on the ash on the ash properties properties (softness, (softness, etc.). etc.) 2021463486

According to According to an an embodiment embodiment of of the the invention, invention, the the acceptance acceptance condition condition is substantiallydfi is substantially dfi= =dfmax,i dfmax,i but but in in practical practicalcircumstances circumstances the the acceptance condition acceptance condition can can be be defined defined as as

dfmax,i – dfmax,i - δ< <dfi dfidfmax,i ≤ dfmax,i

wherein >0 wherein δ>0and anddepends dependsononthe thenumerical numericalaccuracy accuracyand/or and/ormethod. method.When When dfmax,i – -δ < dfmax,i < dfi dfi ≤dfmax,i, dfmax,i, it it means means that thatatatleast least oneone flue flue gas gas factor factor computed usingcurrently computed using currently monitored monitored process process data data with with a numerical a numerical model model of the boiler of the boilerfulfills fulfillsthethe acceptance acceptance condition condition and inand in asuch such casea case maximum allowable maximum allowableboiler boiler load load has has beenbeen found found andthe and so sonumerical the numerical value Qh, candidate value Qn, candidate is is selected selectedasasthe the current current computational maximum computational maximum boiler momentary boiler momentaryload loadQh,Qh,max max.

According to According to an an embodiment embodiment of of the the invention, invention, the the acceptance acceptance condition condition is is substantially  (df= substantially (dfi) i) =  (dfmax,ibut (dfmax,i) ) but in practical in practical circumstances circumstances the acceptancecondition the acceptance conditioncancan be be defined defined as utilizing as utilizing the following the following sums sums

(df δ <<  (dfi) max,i)– - (dfmax,i)  (dfmax,i) (dfi) ≤ (dfmax,i)

wherein >0 wherein δ>0and anddepends dependsononthe thenumeric numericaccuracy accuracyand/or and/ormethod. method.When When (dfmax,i) < (dfi) (dfmax,i)– -δ <  (dfmax,i), (dfi) ≤(dfmax,i), it it means means thatthat at least at least one gas one flue flue gas factor computedusing factor computed using currently currently monitored monitored process process data data with awith a

numerical modelofofthe numerical model the boiler boiler fulfills fulfills the the acceptance acceptance condition condition and in and in such such aa case casemaximum maximumallowable allowable boiler boiler loadload has been has been foundfound and soand theso the numerical valueQh, numerical value Qh,candidate candidate isisselected selected as as the current computational the current computational maximum boiler maximum boilermomentary momentary load load Qn, Qmax . According h, maxAccording to embodiment to an an embodiment the the summation indexi igoes summation index goes over over allall of the of the heatheat transfer transfer surfaces. surfaces.

According to According to another another aspect aspect of of the the invention, invention, the the summation summation index index i i goes over only goes over onlya apart part of of thethe heat heat transfer transfer surfaces, surfaces, preferably preferably in a in a flue gas channel. flue gas channel.

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It may be It may be particularly particularly useful useful if if the the value value for for n is ndetermined is determined from a from a group of boilers group of boilerscomprising comprising at at least least two two separate separate boilers boilers using using operational datamonitored operational data monitored forfor each each of the of the boilers. boilers. Using Using a larger a larger number of boilers number of boilers(two, (two, three, three, four, ...) four, ...) gives gives aa larger largerdata dataset. set. 5 Hence, therewill Hence, there willbebe more more operational operational datadata monitored. monitored. Thisproduce This may may produce better results,which which maymay be be especially goodgood in a in a situation where the 2021463486

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better results, especially situation where the determination usesinterpolation determination uses interpolation and/or and/or extrapolation extrapolation of experimental of experimental data. data.

For the computation For the computationinin step step I),I), the the flueflue gas exit gas exit temperature temperature may be may be substantially estimated substantially estimated by by equation equation

Tboiler, exit Tboiler, = =0 ++ Qiicandidate exit Qih,candidate

or may be or may be its itsfirst, first, second, second, or or third third (or (or higher) higher) degree degree approximation. approximation. The coefficients may The coefficients maybebeobtained obtainedbybyfitting fittingafter after measuring flue measuring flue gas gas exit exit values values for for aa number number of of discrete discrete steam steam load load values. This values. Thisdata datamay may be be collected collected overover timetime and refreshed and refreshed from time from time to time, such to time, suchas, as,periodically. periodically. Alternatively, Alternatively, or inor in addition, addition, it may it may be collectedininone be collected oneoror more more calibration calibration runsruns of combustion of the the combustion boiler.boiler.

The The fitting fitting of of the the coefficients coefficients () can be () can be done done manually manually byby human human or or automatically automatically bybycomputer computer utilizing utilizing historical historical data.data. Automatic Automatic update update of the coefficients of the coefficientsmay maybe be done done e.g. e.g. onceonce per month. per month. AI andAIneural and neural network basedalgorithms network based algorithms cancan be be utilized utilized in automatic in automatic update. update.

According to According toananembodiment embodiment of of thethe invention, invention, in step in step I),flue I), the thegas flue gas exit temperaturemay exit temperature may bebe substantially substantially estimated estimated by utilizing by utilizing artificial intelligence artificial intelligence tools. tools. According According to another to another embodiment embodiment of the of the

invention, instep invention, in stepI), I), thethe flue flue gas gas exitexit temperature temperature may bemay be substantially estimated substantially estimated by by utilizing utilizing neural neural network. network.

According to According toananembodiment embodiment of of thethe invention, invention, in step in step I),flue I), the thegas flue gas exit temperaturemay exit temperature may bebe estimated estimated by equation by equation

𝑇𝑏𝑜𝑖𝑙𝑒𝑟,𝑒𝑥𝑖𝑡 = 𝛼 = + Qh,candidate + * Qh,candidate² 2 + 𝛼* ∗ 1 𝑄ℎ,𝑐𝑎𝑛𝑑𝑖𝑑𝑎𝑡𝑒 + 𝛼2 ∗ 𝑄ℎ,𝑐𝑎𝑛𝑑𝑖𝑑𝑎𝑡𝑒 Tboiler,exit 0

wherein , wherein α0, and α1 and α2 be can canpredefined be predefined constants. constants. Alternatively Alternatively or inor in addition, addition, the the fitting fitting ofof the the coefficients coefficients () can be () can be done done manually manually by by human or automatically human or automaticallyby by computer computer utilizing utilizing historical historical data. data.

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Automatic update Automatic updateofof the the coefficients coefficients may may be done be done e.g. e.g. oncemonth. once per per month. AI and AI and neural neural network network based based algorithms algorithms can can be be utilized utilized in in automatic automatic update. update.

5 2021463486

According to According to an an embodiment embodiment of of the the invention, invention, αterm 0 term maybebesolved may solved based on based on the thecurrent current state state values values

𝛼=0 Tboiler,exit,current = 𝑇𝑏𝑜𝑖𝑙𝑒𝑟,𝑒𝑥𝑖𝑡,𝑐𝑢𝑟𝑟𝑒𝑛𝑡 −- 𝛼1* ∗Q,current ∗ 𝑄ℎ,𝑐𝑢𝑟𝑟𝑒𝑛𝑡 2 𝑄ℎ,𝑐𝑢𝑟𝑟𝑒𝑛𝑡-− *𝛼2Qh,current²

whereinTboiler,exit,current wherein 𝑇𝑏𝑜𝑖𝑙𝑒𝑟,𝑒𝑥𝑖𝑡,𝑐𝑢𝑟𝑟𝑒𝑛𝑡 represents represents measured flue measured flue gasgas exitexit temperature. temperature.

According to According toananembodiment embodiment of of thethe invention, invention, in step in step II),flue II), the thegas flue gas mass flow mass flowis iscomputed computed using using boiler boiler massmass and energy and energy balance balance equations. equations.

In step II), In step II),the thecomputation computation of of flue flue gas gas massmass flow flow may include may include taking taking into into account account mass mass flow flow of of components components CO 2, HO, CO, H2O,N,N2,SO, SO2O. , OThe 2. The

concentration concentration ofofthese these components components can can be measured be measured reliably reliably with rather with rather simple equipment. simple equipment.

In step II), In step II),the thecomponent component values values may may include include fuel fuel parameters. parameters. This This enables reflectingchanges enables reflecting changes in in thethe fuelfuel properties properties or/oror/or in theinkind theofkind of fuel that is fuel that isused usedininthe the combustion combustion boiler. boiler. For example, For example, for fuels for fuels that tend to that tend tocause causemore more erosion, erosion, the the acceptance acceptance condition condition may bemay be

stricter, whilea amore stricter, while more relaxed relaxed acceptance acceptance condition condition may may be be for used used for fuels that tend fuels that tendtotocause cause less less erosion. erosion.

The step b) The step b)may maybebeperformed performed remotely remotely to combustion to the the combustion boiler, boiler, in in some embodimentsinina a some embodiments cloud-based cloud-based computation computation service. service. This helps This helps to to simplify themaintenance simplify the maintenanceof of thethe combustion combustion boiler, boiler, sincesince the remote the remote

computation computation equipment, equipment, such such asas configured configured to to run run the the cloud-based cloud-based computation service,can computation service, can be be maintained maintained separately separately from from the combustion the combustion boiler. The boiler. The computational computational software software updates, updates, for for example, example, can can thus thus be be performed centrally performed centrally at at one one or or a a few few locations, locations, instead instead of of updating updating software ateach software at eachcombustion combustion boiler. boiler.

Alternatively,the Alternatively, thestep step b) b) maymay be performed be performed locally locally at theatcombustion the combustion boiler, in boiler, insome someembodiments embodiments at at an edge an edge server. server. This This may speed may speed up the up the

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computation sincenonodata computation since data needs needs to transferred to be be transferred to a to a remote remote computation location. computation location.

Any of Any of the the currently currently monitored monitored process process data data and/or and/or current current load load may may be be obtained fromreal-time obtained from real-time measurements. measurements. Instead Instead of this, of this, or in or in addition addition 5 to it, the to it, the currently currently monitored monitored process process datadata and/or and/or current current load load may be may be 2021463486

treated byfiltering, treated by filtering, treated treated by by averaging, averaging, computing computing trendstrends or anyor any combination ofthese. combination of these. This This helps helps to avoid to avoid noise noise or outlier or outlier measurements to measurements to impact impact the the outcome outcome of of the the computation, computation, and and thus thus facilitates toincrease facilitates to increase stability stability of the of the current current computational computational maximummaximum boiler momentary boiler momentaryload. load.

The acceptancecondition The acceptance condition maymay include include a hysteresis a hysteresis condition, condition, requiring requiring a predefinedminimum a predefined minimum change change before before changing changing the current the current computational computational maximum boiler maximum boiler momentary momentary load. load. This This may may increase increase the the stability stability of of the the current computational current computational maximum maximum boiler boiler momentary momentary load,load, in some in some embodiments helpingtoto embodiments helping avoid avoid changing changing the the current current computational computational maximum boiler maximum boiler momentary momentary load load up up and and down down within within a a short short period period of of time. time.

Even thoughthe Even though themethod method cancan be be utilized utilized in sort in any any sort of combustion of combustion boiler, the boiler, thepresent present applicant applicant finds finds it particularly it particularly usefuluseful if theif the combustion boilerisisa circulating combustion boiler a circulating fluidized fluidized bed (CFB) bed (CFB) or a bubbling or a bubbling fluidized bed(BFB) fluidized bed (BFB)boiler, boiler, andand the the stepstep b)carried b) is is carried outthe out for for the combustion combustion boiler boiler heat heat transfer transfer surfaces. surfaces. The The method method is is particularly particularly convenient for CFB or BFB boilers. convenient for CFB or BFB boilers.

According to According toananembodiment embodiment thethe step step b) carried b) is is carried outthe out for for the combustion boilerheat combustion boiler heat transfer transfer surfaces surfaces between between a furnace a furnace and stack. and stack.

A combustion A combustionboiler boiler comprises: comprises:

- a furnace - a furnaceandandassociated associated passes passes defining defining a flue a flue gas path gas flow flow path a flue gas a flue gas flow flowpath pathand and having having a number a number of heat of heat transfer transfer

surfaces; surfaces;

- measurementinstrumentation - measurement instrumentation to to monitor monitor current current load load of theof the combustion boiler; combustion boiler;

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- further measurement - further measurement instrumentation instrumentation to currently to currently monitor monitor process data; process data; and and

- a control - a controlsystem systemconfigured configured to to carry carry out out the boiler the boiler control control method. method.

5 According to to an an embodiment embodiment combustion combustion boiler boiler comprises comprises aa furnace furnace and and 2021463486

2021463486

According associated passesdefining associated passes defining a flue a flue gas gas flowflow path path a flue a flue gas path gas flow flow path and and having having a a number number of of heat heat transfer transfer surfaces surfaces in in the the flue flue gas gas flow flow path. path.

Such Such aa combustion combustionboiler, boiler,thethe boiler boiler control control canimproved. can be be improved. The The advantages aresame advantages are sameasas thethe advantages advantages of method. of the the method.

The The control control system system may may comprise comprise an an edge edge server server which which may may be be configured configured to process the real-time measurement results for currently monitored to process the real-time measurement results for currently monitored process data process dataand/or and/or current current load, load, namely namely by filtering, by filtering, averaging, averaging, and/or computingtrends. and/or computing trends. TheThe edge edge server server willwill facilitate facilitate cutting cutting down down the amount of the amount ofcurrently currently monitored monitored process process data. data. In certain In certain installations thismay installations this maybe be particularly particularly useful useful especially especially in of in view view of the fact that the fact thatthere theremay may be be 60 60 to to 90 gigabytes 90 gigabytes of monitored of monitored process process data each day. data each day.

The controlsystem The control systemmay may be be configured configured to carry to carry out method out the the method step b) step b) to determinethe to determine thecurrent current computational computational maximum maximum boiler boiler momentary momentary load load locally. Thisfacilitates locally. This facilitatesto to have have fastfast decision decision making making at theat the combustion combustion boiler boiler since since less less or or no no data data may may need need to to be be transferred transferred from the combustion boiler system. from the combustion boiler system.

Alternatively, or Alternatively, or in in addition, addition, the the control control system system may may be be configured configured to to

send data to send data toa aremote, remote,in in some some embodiments embodiments cloud-based, cloud-based, computing computing system whichmay system which maybebeconfigured configured to to carry carry out out the method the method step step b) andb) and return the current return the currentcomputational computational maximum maximum boiler boiler momentary momentary load load to the to the control system.This control system. This facilitates facilitates to have to have a combustion a combustion boilerboiler simpler simpler and makes updating and makes updatingthe the computing computing system system easier. easier. The updating The updating can incan in

this situationbebeperformed this situation performed centrally centrally and and noteach not at at each and every and every combustion boiler. combustion boiler.

The edge server The edge servermay maybebe configured configured to reduce to reduce amount amount of measurement of measurement data data that is passed that is passedtotothe the remote remote computing computing system. system. In this In this manner, manner, a a

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smaller bandwidthfor smaller bandwidth for transferring transferring datadata may may suffice. suffice. In certain In certain installations thismay installations this may be be particularly particularly useful useful especially especially in of in view view of the fact that the fact thatthere theremay may be be 60 60 to to 90 gigabytes 90 gigabytes of monitored of monitored process process data each day. data each day.

5 A combustion A combustionboiler boiler computation computation system system comprises comprises 2021463486

- a group - a group of ofcombustion combustion boilers, boilers, eacheach boiler boiler comprising comprising a a boiler control boiler controlsystem system comprising comprising an edge an edge server server system system which which is is configured toprocess configured to process the the real-time real-time measurement measurement results results for for currently monitoredprocess currently monitored process data data and/or and/or current current load,load, namelynamely by by filtering, averaging, filtering, averaging, and/or and/or computing computing trends, trends, and send and send the the processed real-timemeasurement processed real-time measurement results results to ato a remote remote computing computing system; system;

- a remote - a remote computing computing system system which which in some in some embodiments embodiments is a is a cloud-based computing cloud-based computing system, system, configured configured to receive to receive data data processed fromreal processed from realtime time measurement measurement results results andcompute and to to compute data usingaanumerical data using numerical boiler boiler model model for for eacheach of boilers, of the the boilers, and return computation and return computation results results forfor eacheach of boilers. of the the boilers.

Further, inthe Further, in thecombustion combustion boiler boiler computation computation system, system, the boiler the boiler control systemisisconfigured control system configured to to adapt adapt its its function function basedbased on theon the computation results. computation results.

The advantagefor The advantage forthis this arrangement arrangement is that is that the need the need of computation of computation devices atthe devices at thecombustion combustion boiler boiler can can be reduced, be reduced, stillstill obtaining obtaining effective andfast effective and fastcomputation computation results results fromfrom the remote the remote computing computing system. system.

The computingsystem The computing system may may be be configured configured to find to find such such a numerical a numerical value value or or aa current currentcomputational computational maximum maximum boiler boiler momentary momentary loadwhich load for for at which at least one flue least one fluegas gasfactor factor computed computed using using currently currently monitored monitored process process data with aanumerical data with numerical model model of of the the boiler boiler that that fulfills fulfills an acceptance an acceptance condition andselecting condition and selectingthethe numerical numerical value value as current as the the current

computational maximum computational maximum boiler boiler momentary momentary load. load. This This basically basically enables enables using the method using the methodofofthe the invention invention alsoalso in ain a distributed distributed environment. environment.

The boilercomputation The boiler computation system system maymay be configured be configured to adapt to adapt or calibrate or calibrate a numericalmodel, a numerical model,such such as,as, thethe flue flue gas gas factor factor numerical numerical model,model, for a for a

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boiler using boiler usingprocessed processed measurement measurement datadata for boiler. for the the boiler. This it This makes makes it easier to remotely easier to remotelyadapt adapt or or calibrate calibrate the the numerical numerical model model for boiler for boiler control. control.

The boilercomputation The boiler computation system system maymay be configured be configured to adapt to adapt or calibrate or calibrate 5 a numericalmodel a numerical modelfor for a boiler a boiler using using processed processed measurement measurement data data 2021463486

collected alsofrom collected also fromother other boilers. boilers. ThisThis enables enables usingusing a larger a larger collection ofdata collection of datatoto adjust adjust thethe numerical numerical modelmodel for boiler for boiler control. control.

Brief Description Brief Descriptionofof Figures Figures The combustionboiler The combustion boiler andand itsits control control method method are explained are explained in more in more detail belowininthe detail below thecontext contextof of thethe embodiments embodiments shownshown in theinappended the appended drawings inFIG drawings in FIG1 1toto 9, 9, of of which: which:

FIG FIG 11 illustrates illustrates aaCFB CFBboiler; boiler;

FIG FIG 22 illustrates illustrates aaBFB BFBboiler; boiler;

FIG FIG 33 illustrates theflow illustrates the flowofof measurement measurement datadata fromfrom sensors; sensors;

FIG FIG 44 is a flow is a flow diagram diagramillustrating illustrating a first a first method method for for finding the current finding the currentcomputational computational maximum maximum boiler boiler momentary momentary load load Qn, Qmaxi h, max;

FIG FIG 55 is a flow is a flow diagram diagramillustrating illustrating a second a second method method for for finding the current finding the currentcomputational computational maximum maximum boiler boiler momentary momentary load load Qn, Qmaxi h, max;

FIG FIG 66 illustrates howthe illustrates how thecurrent current computational computational maximum maximum boiler momentary boiler momentaryload load Qh,Qh,max canbe max can bepresented presentedto to thethe boiler operator; boiler operator;

FIG FIG 77 shows boilermomentary shows boiler momentary load load Qn Qand h and computed computed current current computational maximum computational maximum boiler boiler momentary momentary loadload Qh, max, Qn, max/ as well as as well as the theeffect effectof of using using thethe method method according according to the invention to the inventionduring during a test a test period; period;

FIG FIG 88 a closer look a closer lookatatthe the data data of of FIGFIG 7, showing 7, showing boiler boiler

momentary load momentary loadQnQhcomputed computed current current computational computational maximum boiler maximum boilermomentary momentary load load Qn,Qmax where h, maxwhere the the effect effect

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of using the of using themethod methodaccording according to to the the invention invention during the10 during the 10day daytest test period period is is better better visible. visible.

Same referencenumerals Same reference numerals refer refer to to samesame technical technical features features in allin all FIG. FIG.

Detailed description Detailed description 5 FIG FIG 11 shows showsa acombustion combustion boiler 10 that is aisCFBa boiler CFB boiler and comprises 2021463486

2021463486

boiler 10 that and comprises a furnace 12 a furnace 12that thathas has tube tube walls walls 13 connected 13 connected to water-steam to water-steam circuit circuit of the combustion of the combustionboiler boiler 10.10. Water Water is fed is fed from from waterwater tank shown) tank (not (not shown) to economizerand to economizer andfrom from thethe economizer economizer via via a steam a steam drum drum to evaporative to evaporative heat transfer heat transfer surfaces surfaces such such as as the the tube tube walls walls 13 13 and and then then guided guided via via the steam drum the steam drumtotosuperheaters superheaters andand thenthen to ato a turbine. turbine. Fluechannel Flue gas gas channel may be may be provided providedwith with economizer economizer and/or and/or superheater/s. superheater/s.

Fluidization gas(such Fluidization gas (suchas,as, airair and/or and/or oxygen-containing oxygen-containing gas) gas) is fedis fed from fluidizationgas from fluidization gas supply supply 153153 to below to below the grate the grate (the grate (the grate not not shown in FIG shown in FIG1)1)via viaa a windbox windbox (not (not shown), shown), wherefrom wherefrom the primary the primary fluidization airenters fluidization air enters into into thethe furnace furnace through through nozzles nozzles (not shown) (not shown) (to (to fluidize thebed), fluidize the bed),and and secondary secondary fluidization fluidization gas feed gas feed 152 (to 152 (to feed oxygencontaining feed oxygen containinggasgas to to control control combustion). combustion). The effect The effect is thatis that the bed materials the bed materialswill will be be fluidized fluidized and and alsoalso oxygen oxygen required required for the for the combustion isprovided combustion is provided into into thethe furnace furnace 12. 12. Further, Further, fuel fuel is fedis fed into into the furnace1212via the furnace viathe the fuel fuel feed feed 22. 22. The The combustion combustion can can be be adjusted adjusted by by controlling thefuel controlling the fuelfeed feed22 22 (such (such as, as, by reducing by reducing or increasing or increasing fuel fuel feed), and by feed), and bycontrolling controllingthethe fluidization fluidization gas feed gas feed (such (such as, byas, by reducing orincreasing reducing or increasing amount amount of of oxygen oxygen supply supply into into the furnace the furnace 12). 12). Fuel can be Fuel can befed fedtogether together with with additives, additives, in particular in particular with such with such

additives thatact additives that actasas alkali alkali sorbents, sorbents, suchsuch as CaCO as CaCO3 3 and/or and/or clay for clay for example. Inaddition example. In additionor or alternatively, alternatively, NOx NOx reduction reduction agents, agents, such as such as ammonium orurea ammonium or ureacan can be be fedfed into into the the combustion combustion zone zone of theoffurnace the furnace 12, or above 12, or abovethe thecombustion combustion zone zone of the of the furnace furnace 12. 12.

Bed Bed material material is is also also fed fed into into the the furnace, furnace, which which bed bed material material may may

comprise sand, limestone, and/or clay, that in particular may comprise comprise sand, limestone, and/or clay, that in particular may comprise kaolin. Oneeffect kaolin. One effectofof the the bedbed and, and, generally, generally, of combustion, of the the combustion, is is that in the that in thewater-steam water-steam circuit, circuit, water water and and steamsteam is heated is heated in thein the tube tube walls 13 walls 13 and andwater waterisis converted converted to steam. to steam.

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Ash may Ash may fall fall to to the the bottom bottom of of the the furnace furnace 12 12 and and be be removed removed via via an an ash ash chute (omittedfrom chute (omitted fromFIG FIG 1 for 1 for thethe sakesake of clarity) of clarity) and of and part part theof the ash, so-calledfly ash, so-called flyash, ash, will will be be carried carried along along flue flue gas. gas.

Combustionproducts, Combustion products, such such as as flue flue gas,gas, unburnt unburnt fuel fuel andmaterial and bed bed material 5 proceed from proceed from the the furnace furnace 12 12 to to a a particle particle separator separator 17 17 that that may may 2021463486

2021463486

comprise comprise aa vortex vortexfinder finder 103. 103. TheThe particle particle separator separator 17 separates 17 separates flue flue gases fromsolids. gases from solids.Especially Especially in in larger larger combustion combustion boilers boilers 10, there 10, there may be may be more morethan thanone one (two, (two, three, ...) three, ...) separators 17preferably separators 17 preferably arranged inparallel arranged in paralleltoto each each other. other.

Solids separatedbybythe Solids separated the separator separator 17 pass 17 pass through through a seal a loop loop 160 seal 160 that that preferablyisislocated preferably located at at thethe bottom bottom of the of the separator separator 17. the 17. Then Then the solids passtotofluidized solids pass fluidizedbedbed heat heat exchanger exchanger (FBHE) (FBHE) 100 is 100 that that isa also a also heat transfer heat transfersurface surfaceso so that that thethe FBHEFBHE 100 100 collects collects heat the heat from from the solids to further solids to furtherheat heat thethe steam steam in the in the water-steam water-steam circuit. circuit. The The chamber in which chamber in whichthe the FBHE FBHE 100100 is is located located mayfluidized may be be fluidized and and the the FBHE FBHE 100 itself comprises 100 itself comprisesheat heat transfer transfer tubes tubes or other or other kindskinds of heat of heat transfer surfaces.FBHE transfer surfaces. FBHE100100 maymay be arranged be arranged as a as a reheater reheater or as or a as a superheater. Fromthe superheater. From the FBHE FBHE outlet outlet 101,101, steam steam is passed is passed into ainto a high- high- pressure turbine pressure turbine (if (if the the FBHE FBHE 100 is 100 is superheater) superheater) or or medium-pressure medium-pressure turbine turbine (if (if the the FBHE FBHE 100 100 is is a a reheater). Forthe reheater) For thesake sakeof ofclarity, clarity,the the turbines turbines are are not not illustrated illustrated inin FIG FIG 1. 1. The The solids solids may may be be returned returned from from the FBHE 100 via the FBHE 100 via a areturn return channel 102 into channel 102 into the the furnace 12. Especially furnace 12. Especially in larger combustion in larger combustionboilers boilers 10,10, there there may may be more be more than than one (two, one (two, three, three, ...) loop seals ...) loop seals160 160and and FBHE FBHE 100, 100, and and return return channels channels 102, 102,

preferably arranged preferably arranged in in parallel parallel toto each each other, other, such such that that for for each each separator 17,there separator 17, therewill will be be respective respective looploop seal seal 160, 160, FBHEand FBHE 100 100 and return channel102. return channel 102.InIn practice, practice, somesome of the of the FBHE FBHE 100bemay 100 may be arranged arranged as superheaterswhile as superheaters while some some others others may may be arranged be arranged as reheaters. as reheaters.

The flue gases The flue gasesare arepassed passed from from the the separator separator 17 to17horizontal to horizontal pass 15pass 15

and from there and from therefurther furtherto to backpass backpass 16 (that 16 (that advantageously advantageously may bemay a be a vertical pass) vertical pass)and andfrom from there there viavia flueflue gas gas conduit conduit 18 to 18 to stack stack 19. 19.

The backpass1616comprises The backpass comprises a number a number of heat of heat transfer transfer surfaces surfaces 21i (where 21i (where i i == 1, 1, 2, 2, 3, 3, …, k, k, where where k is k is thethe number number of of heat heat transfer transfer surfaces). surfaces) In FIG 1, In FIG 1, heat heattransfer transfer surfaces surfaces 211,21212, 1, 21213, 2, 213, ..., 21k-1, 21k 21-, 21k are are

illustrated. Heattransfer illustrated. Heat transfer surface surface 21k 21 k depicts depicts air preheater. air preheater. Heat Heat

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transfer transfer surfaces surfaces 21 k-1, 21 21-, 212depict depictsuperheaters superheatersandandheat heattransfer transfer surfaces surfaces 211, 21 211, depict reheaters. 213 depict reheaters. The The actual actual number number of of different different heat heat transfer surfacesinin transfer surfaces eacheachof of these these components, components, for example, for example, may bemay be selected foreach selected for eachcombustion combustion boiler boiler differently differently according according to actual to actual 5 needs. Andthere needs. And theremay may be be further further components components as well, as well, comprising comprising a heat a heat transfer surface21. 21. 2021463486

transfer surface

Flue Flue gas gas exiting exiting the the last last heat heat transfer transfer surface surface 21 will be 21k will be in in flue flue gas exit temperature gas exit temperature TFG,exit. TFG, exit. This temperatureisismeasured This temperature measuredwithwith temperature temperature sensor sensor 20 20.k.

According to According toone oneaspect, aspect, thethe temperatures temperatures before before and after and after each heat each heat transfer surface21i transfer surface 21i(TFG,in,i, (TFG,in,i, TFG,in,i+1, respectively) TFG,in,i+1, respectively)can can be be measured measured with respective with respectivetemperature temperature sensors sensors 20i 20 i (where (where i =2,1, i = 1, 3,2, 3, k-1, ..., …, k-1, k). k).

According to According toanother another aspect, aspect, andand advantageously, advantageously, thesethese temperatures temperatures however do however donot notnecessarily necessarily need need to measured. to be be measured. It suffice It will will suffice to to know the flue know the fluegas gasexit exit temperature temperature TFG,TFG, exit.The exit. Thetemperatures temperatures before before and and after eachpreceding after each preceding heat heat transfer transfer surface surface 21i (TFG,in,iTFG,in,i+1) 21i (TFG,in,i, , TFG,in,i+1) can can be be obtained numerically. obtained numerically. This This will will be explained be explained further further below.below.

A combustion A combustion boiler boiler 10 10 is is equipped equipped with with aa plurality plurality ofof sensors sensors and and computer units.Actually, computer units. Actually,oneone middle-size middle-size (100 (100 - 150– MWth) 150 MWth) combustion combustion boiler 10 boiler 10 may may produce produce 100 100 million million measurement measurement results results / / day, day, which which needs 25 GB needs 25 GBofofstorage storage space. space. FIGFIG 1, 21,and 2 and 3 illustrate 3 illustrate some some of the of the sensors andcomputer sensors and computer units. units. Examples Examples of sensors of sensors are combustion are combustion gas gas (usually combustionair) (usually combustion air) volume volume flow flow sensors sensors 30 (for 30 (for measuring measuring primary primary

and secondaryfluidizing and secondary fluidizinggasgas feeds), feeds), fuelfuel feed feed sensors sensors 650 and 650 and temperature sensors20i temperature sensors 20(i i (i = 1, = 1, 2, 2, ..., k), temperaturesensor k), temperature sensor in in FBHE FBHE and pressuresensor and pressure sensor116 116in in thethe return return channel channel 102 (both 102 (both only only in in a CFB a CFB boiler), and boiler), andsensors sensors40 40 in in thethe furnace furnace 12. 12.

Process datamay Process data maybebecollected collected from from the the sensors sensors by distributed by distributed control control

system (DCS)201. system (DCS) 201.The The data data collection collection may may most most conveniently conveniently be be arranged overa afield arranged over field bus bus 290, 290, for for example. example. DCS may DCS 201 201have may ahave a display/monitor display/monitor 202202for for displaying displaying operational operational status status information information to to the operator.AnAnEDGE the operator. EDGE server server 203203 may may process process measurement measurement datathe data from from the

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obtained fromsensors, obtained from sensors, such such as,as, filter filter and and smooth smooth it. There it. There may bemay a be a local storage204 local storage 204for for storing storing data. data.

The DCS 201, The DCS 201,display/monitor display/monitor 202, 202, EDGEEDGE server server 203, 203, local local storage storage 204 204 may be may be in incombustion combustion boiler boiler network network 280 280 (local (local storage storage 204 204 5 advantageously directly advantageously directly connected connected to the to the EDGEEDGE server). server). The combustion The combustion 2021463486

boiler network boiler network280 280isis advantageously advantageously separate separate from from the field the field bus 290 bus 290 that is used that is usedtotocommunicate communicate measurement measurement results results from from the sensors the sensors to to the DCS 201 the DCS 201and/or and/orthethe EDGE EDGE server server 203.203. Between Between the201 the DCS DCSand 201EDGE and EDGE server 203 there server 203 theremay maybebe an an open open platform platform communications communications serverserver 210 210 (cf. FIG 3) (cf. FIG 3) to tomake makethe thesystems systems better better interoperable. interoperable.

Combustionboiler Combustion boilernetwork network 280280 maymay be connection be in in connection withinternet with the the internet 200, preferablyvia 200, preferably viaa a gateway gateway 290. 290. In this In this situation, situation, measurement measurement results maybebetransferred results may transferred from from the the combustion combustion boiler boiler network network 280 to 280 a to a cloud service,such cloud service, suchasas process process intelligence intelligence system system 205 located 205 located in a in a computation computation cloud cloud 206. 206. The The applicant applicant currently currently operates operates aa cloud cloud service running an analysis platform. The cloud service may service running an analysis platform. The cloud service may be be operated operated on on aa virtualized virtualized server server environment, environment, such such as as on on Microsoft® Microsoft® Azure® which is a virtualized, easily scalable environment Azure® which is a virtualized, easily scalable environment for for distributed distributed computing computing and and cloud storage cloud storage for for data. data. Other Other cloud cloud computing computing services may be services may be suitable suitable for for running running the the analysis analysis platform platform too. Further,instead too. Further, instead of of a cloud a cloud computing computing service, service, or in or in addition addition thereto, thereto, aa local localororremote remote server server can can be used be used for running for running the analysis the analysis platform. platform.

FIG FIG 22 illustrates illustratesa acombustion combustion boiler boiler 10 that 10 that is a is BFBa boiler. BFB boiler. BFB BFB

boiler differs boiler differs from from CFB CFB boiler boiler in in that that the the fluidized fluidized bed bed is is not not aa circulating bedbut circulating bed buta a bubbling bubbling bed. bed. Thus,Thus, there there is nois no for need needthe for the separator 17,loop separator 17, loopseal seal 160, 160, FBHE FBHE 100 100 and and return return channel channel 102. 102.

There is normally There is normallyatat least least oneone superheater superheater 14 located 14 located in theinfurnace the furnace 12, preferablyonontop 12, preferably topof of thethe furnace furnace 12. 12. Superheater Superheater 14 inlet 14 inlet 141 is 141 is

preferablythe preferably thesteam steam drum drum or or from from another another superheater superheater andoutlet and the the outlet 142 is to 142 is to high highpressure pressure turbine. turbine.

FIG FIG 44 illustrates illustratesthe the combustion combustion boiler boiler control control method: method:

a) the current a) the currentload loadQhQof h of combustion combustion boiler boiler 10monitored 10 is is monitored in in step K1 (in step K1 (inthe themethod method illustrated illustrated in FIG in FIG 4, also 4, also flue flue gas exit gas exit

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temperature TFG, exit temperature TFG, exit is is monitored and heat monitored and heatduty dutyQfluid, Qfluid,i for foreach each heat transfer heat transfersurface surface 21i21i in in thethe flueflue gas gas flow flow channel channel (vertical pass16). (vertical pass 16).

b) a anumerical b) numerical value value Qn, Qcandidate h, candidate is selected(step is selected (stepK3), K3), after after 5 which heat which heatduties dutiesatat heat heat transfer transfer surfaces surfaces 21i computed 21i are are computed 2021463486

and flue gas and flue gastemperatures temperatures in in relation relation to candidate to Qn, Qh, candidate.The The numerical valueQn, numerical value Qh,candidate candidate isisthen thenused used to to compute (stepK7) compute (step K7)atat least one flue least one fluegas gasfactor factor dfidfusing i using currently currently monitored monitored process process data with aanumerical data with numerical model model of of the the boiler boiler fulfills fulfills an an acceptance condition acceptance condition (which (which is is tested tested in step in step K9), K9), and and selecting thenumerical selecting the numerical value value Qn,Qcandidate h, candidate as as the current the current computational maximum computational maximum boiler boiler momentary momentary loadload Qh, max Qn, max (step (step K11); K11);

c) the current c) the currentcomputational computational maximum maximum boiler boiler momentary momentary load Qh, load Qn, max is max is indicated to the indicated to theoperator operator (such (such as,as, by displaying by displaying on the on the monitor/screen202) monitor/screen 202) and/or, and/or, if if the the current current load load Qn isQh is

c1) smallerthan c1) smaller thanthe the computational computational boiler boiler maximum maximum momentary momentary load load Qh, Qmax h,max:

c1i) indicatingthe cli) indicating theboiler boiler operator operator thatthat the boiler the boiler load Qh may load Qn may be be increased, increased, and/or and/or

c1ii) automaticallyincreasing clii) automatically increasing thethe boiler boiler load load On, Qh,

and/or and/or

c2) c2) larger larger than than the the computational computational boiler boiler maximum maximum momentary load Q h,max momentary load Qh, max :

c2i) indicatingthe c2i) indicating theboiler boiler operator operator thatthat the boiler the boiler

load Qh exceeds load Qn exceedsthe theboiler boiler maximum maximum momentary momentary load, load, and/or and/or

c2ii) automaticallyreducing c2ii) automatically reducing thethe boiler boiler loadload Qh. Qh.

The step b) The step b)isispreferably preferably carried carried out out for for the combustion the combustion boilerboiler 10 10 heat transfer heat transfersurfaces surfaces21i21between i between furnace furnace 12 stack 12 and and stack 19. 19.

In the method, In the method,the thecurrently currently monitored monitored process process data data of the ofboiler the boiler may may include a) current include a) currentflue flue gasgas exit exit temperature temperature TFG, Texit FG,exitinina a flue flue gasgas flow flow

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channel andb)b)heat channel and heatduty duty Qfluid,i for Qfluid,i for each eachheat heattransfer transfer surface surface 21i 21 ini in the flue gas the flue gasflow flowchannel channel (back (back pass pass 16).16).

Further, inthe Further, in themethod method monitored monitored process process datadata from from both both a) anda)b)and may b) may be used be used in incomputation computationof of thethe flue flue gas gas factor factor dfi when dfi and and finding when finding the the 5 numerical valueQn, numerical value Qh,candidate candidate for forthe thecurrent current computational maximumboiler computational maximum boiler 2021463486

momentary momentary load load Qn, Qmax. h,max.

The findingisisperformed The finding performed such such that, that, if the if the at least at least one gas one flue flue gas factor dfi computed factor dfi computedusing using currently currently monitored monitored process process data data with awith a numerical modelofofthe numerical model the boiler boiler that that fails fails to fulfill to fulfill an acceptance an acceptance condition, condition, aanext nextnumerical numerical value value Qh, Qcandidate h, candidate is automatically is automatically selected.. The automatic selected. The automatic selection selection isis advantageously advantageously done done iteratively. iteratively.

As aa specific As specificexample, example,thethe finding finding may may be carried be carried out performing out with with performing the computationalsteps the computational steps of:of:

- I: computing - I: computingananestimate estimateforfor boiler boiler flueflue gas exit gas exit temperature Tboiler, exit temperature Tboiler, that exit thatresults resultsin in aa computational boiler computational boiler model when model whenthe thethermal thermal load load of of the the boiler boiler corresponds corresponds to theto the numerical value numerical value Qh, Qcandidate; h, candidate;

- II:computing - II: computingflueflue gas flow gas mass massqm, flow qm,fluegas fluegas; ; ;;

- III:computing - III: computing a heat a heat duty Qfluid, duty Qfluid, forfor i, candidate i, candidate eacheach heat heat transfer surface21i transfer surface 21iininthe the flue flue gasgas flowflow channel channel (back(back pass pass 16) withits 16) with its current current heat heat duty Qfluid, duty Qfluid, thatthat i, current i, current is corrected is corrected by using by using a numerical a numerical boiler boiler model model Qfluid, Qfluid, i,= candidate i, candidate Qfluid, i,= current Qfluid,i,current + +  (Q,(Q ,ij,i h,candidate) candidate)  par j j- - parj, (Qn, Qh,currentj)j j,i (current)

- IV:using - IV: using thethe computed computed heat duties heat duties Qfluid, Qfluid, i, i, candidate candidate for each for each

heat transfersurface heat transfer surface 21i21in i in thethe flue flue gas gas flowflow channelchannel (back (back pass 16) pass 16) to tocompute compute flue flue gasgas temperatures temperatures at each at each heat transfer heat transfer surface (Tfluegas,in,i surface fluegas, , Tfluegas,out,i in, i, Tfluegas, out, i;; ii = =1,1, ... , , k) in the k) in the flue fluegas gas flow channel(back flow channel (backpasspass16)16)in in thethe upstream upstream direction direction of flueof flue gas gas flow, flow, starting starting from from the the heat heat transfer transfer surface surface 21 that is 21k that is

closest to the closest to theflue fluegas gas exit exit i.e. i.e. using using the the estimate estimate for the for the boilerflue boiler flue gasgas exitexit temperature temperature Tfluegas,out,m Tfluegas,out, = TFG,=exit; TFG, exit;

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- - V: V: computing computinga aflue fluegas gasfactor dfi df factor , i, =i1 =, 1..., , k kfor for each each heat transfersurface heat transfer surface21i21in i in thethe flue flue gas gas flowflow channel channel (back (back pass 16). pass 16).

Step II) may Step II) mayinclude include computing computing flue flue gas gas massmass flow flow qm,fluegas,mm for qm, fluegas, for selected fluegas selected flue gascomponents. components.

The flue gas The flue gastemperatures temperaturesat at each each heatheat transfer transfer surface surface can becan be computed, forinstance, computed, for instance,

𝑄𝑓𝑙𝑢𝑖𝑑,𝑖 Tfluegas,in,i = Tfluegas,out,i + qm,fluegas Qfluid,i * c 𝑇𝑓𝑙𝑢𝑒𝑔𝑎𝑠,𝑖𝑛,𝑖 = 𝑇𝑓𝑙𝑢𝑒𝑔𝑎𝑠,𝑜𝑢𝑡,𝑖 + 𝑞𝑚,𝑓𝑙𝑢𝑒𝑔𝑎𝑠 ∗ 𝑐𝑝 𝑇𝑓𝑙𝑢𝑒𝑔𝑎𝑠,𝑖𝑛,𝑖 is is wherein Tfluegas,in,i wherein the theflue flue gas temperature gas temperature at at the the inlet inlet of ithof ith heat heat transfer transfer surface, is specific surface, 𝑐c𝑝 is specific heat heat capacity, capacity, and and 𝑇𝑓𝑙𝑢𝑒𝑔𝑎𝑠,𝑜𝑢𝑡,𝑖 is the Tfluegas,out,i flue is the fluegas gas temperature temperature atatthethe outlet outlet ofheat of ith ith heat transfer surface.The transfer surface. Theflue flue gasgas temperatures temperatures could could be determined be determined with artificialintelligence with artificial intelligence tools. tools. The The flueflue gas temperatures gas temperatures could could be be determined determinedwith with neural neural network. network.

Preferably, theflue Preferably, the fluegas gas factor factor dfi dfi can can include include or is: or is:

df dfi i= =ki k(q, i (q fluegas /(ρfluegas,I / (Pfluegas, m,fluegas Across,i I Across, ) ))n

where ki is where ki is aa predetermined predetermined non-zero non-zero parameter parameter that that may may be be chosen chosen combustion-boiler specifically, combustion-boiler specifically, preferably preferably positive positive (non-zero) (non-zero) number,number,

qm,fluegas qm, is isa aflue fluegas flue gas massflow, gas mass flow,

n is aa positive n is positivenumber number (which (which maymay be selected be selected as a as a natural natural number, number, rational number,real rational number, real number, number, or or even even as complex as complex number), number),

ρfluegas,i is Pfluegas, isflue flue gas gas density obtainablefrom density obtainable fromflue flue gasgas temperature temperature th T in,i iat FG, in, TFG, at iith heat transfersurface heat transfer surface 21i 21 andi and

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th A is A is aa cross crosssection sectionof of flue flue gasgas channel channel at heat at ith i heat transfer transfer surface surface 21 i. 21i.

Advantageously,inn may Advantageously, maybebeselected selected to to include include at least at least onethe one of of the following: following:

5 i) in the the range rangeofof0,9 0,9 to to 1,1, preferably equivalent or about 2021463486

i) in 1,1, preferably equivalent or about 1.0, for using 1.0, for usingcomputed computed flue flue gasgas velocity; velocity;

ii) in the ii) in the range rangeofof2,9 2,9 to to 3,5, 3,5, preferably preferably between between 3,2 and 3,2 and 3,35, 3, 35, for for using computedflue using computed fluegas gas caused caused erosion; erosion; or or

iii) in the iii) in therange rangeofof1,8 1,8 to to 2,2, 2,2, preferably preferably equivalent equivalent or about or about 2.0, for using 2.0, for usingpressure pressure loss. loss.

The value for The value forn nmay maybebe changed changed over over time. time. In particular, In particular, the for the value value for n may be n may be determined determinedfromfrom a group a group of combustion of combustion boilers, boilers, the group the group comprising atleast comprising at leasttwo two separate separate combustion combustion boilers boilers 10, that 10, such such that using operationaldata using operational data monitored monitored for for eacheach of combustion of the the combustion boilers boilers 10 10 is used in is used in the thedetermination. determination.

In the computation In the computationinin step step I),I), thethe computational computational valuevalue for gas for flue flue gas exit temperature exit temperature TFG,TFG, exitexit under under any any chosen chosen numerical numerical value value Qh, Qh, candidate candidate for for boiler load boiler loadcan canbebeestimated estimated by by equation equation

T TFG, FG, exit == exit +0 +(Q, candidate, j(Qh, candidate ) j )j

or preferablyits or preferably itsfirst, first, second, second, third third or higher or higher degree degree approximation. approximation. The coefficients  The coefficients ,,,have   have been been obtained obtained beforehand beforehand by fitting by fitting after measuringflue after measuring fluegasgasexit exit temperature temperature TFG, Texit FG, exit values values forfor a number a number of discreteboiler of discrete boilerload load Qsteamvalues. Qsteam values.

In step II), In step II),the thecomputation computation of of the the components components qm,fluegas,mm preferably qm, fluegas, preferably

includes includes atat least least some, some, most most preferably preferably allall of of the the following: following: m m = = CO2, CO, H2O, N, HO, N2,SO, SO2, O O 2 so so as as to to determine determine flue flue gasgas mass mass flow. flow. In In other other words, words, in step IV) in step IV)of ofthethecomputation, computation, as qfluegas, as qm, m,fluegas,m values values somesomeor orallallofof q m,fluegas,CO2 qm, fluegas, CO2, qm, qm,fluegas,H20 fluegas, H20 , qm,qfluegas, m,fluegas,N2 ,qfluegas, N2 qm, m,fluegas,SO2 ,qfluegas, S02 qm, 02 maymay m,fluegas,O2 be used. be used.

They are preferably They are preferablymeasured measured in in flueflue gas gas conduit conduit 18 or18 in or in flute flute 19, 19,

for which reason for which reasonsuitable suitable sensors sensors are are installed installed in flue in the the gas flue gas passage. In passage. Instep stepII), II), thethe component component values values may further may further include include fuel fuel parameters. parameters.

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Flue gas mass Flue gas massflow flowmay may be be based based on computation on computation of sums of sums of gas of flue flue gas component massflows component mass flowsqm, qm,fluegas,m fluegas,whichwhich are are calculated basedononfuel calculated based fuel analysis (proximateand analysis (proximate and ultimate ultimate analysis analysis of fuel), of fuel), combustion combustion air air flow and/orrecirculation flow and/or recirculationgasgas flow flow according according to boiler to boiler massenergy mass and and energy 5 balance calculation. balance calculation. 2021463486

Preferably, theflue Preferably, the fluegas gas mass mass flow flow may may be computed: be computed:

qm,fluegas = qm,fluegas,i 𝑞𝑚,𝑓𝑙𝑢𝑒𝑔𝑎𝑠 = ∑ 𝑞𝑚,𝑓𝑙𝑢𝑒𝑔𝑎𝑠,𝑖 i.e., for example, i.e., for example,the the sums sums of of thethe following following flue flue gas flow gas mass mass flow components components CO 2, H2O, N2, SO2 and O2: CO, HO, N, SO and O: 𝑀𝐶𝑂2 𝑞𝑚,𝑓𝑙𝑢𝑒𝑔𝑎𝑠,𝐶𝑂2 = 9m,fluegas,C02 𝑥𝐶,𝑓𝑢𝑒𝑙 ∗* = XC,fuel Mc * ∗ 𝑞𝑚,𝑓𝑢𝑒𝑙 𝑀𝐶 𝑀𝐻2𝑂 qm,fluegas,H20 = 0.5 * XH,fuel * MH MH * 9m,fuel + XH20,fuel * 9m,fuel + Xmoist,air * qm,air 𝑞𝑚,𝑓𝑙𝑢𝑒𝑔𝑎𝑠,𝐻2𝑂 = 0.5 ∗ 𝑥𝐻,𝑓𝑢𝑒𝑙 ∗ ∗ 𝑞𝑚,𝑓𝑢𝑒𝑙 + 𝑥𝐻2𝑂,𝑓𝑢𝑒𝑙 ∗ 𝑞𝑚,𝑓𝑢𝑒𝑙 + 𝑥𝑚𝑜𝑖𝑠𝑡,𝑎𝑖𝑟 ∗ 𝑞𝑚,𝑎𝑖𝑟 𝑀𝐻 𝑞 qm,fluegas,N2 = = 𝑚,𝑓𝑙𝑢𝑒𝑔𝑎𝑠,𝑁2 0.50.5 ∗ 𝑥𝑁,𝑓𝑢𝑒𝑙 * XN,fuel ∗ 𝑞𝑚,𝑓𝑢𝑒𝑙 * 9m,fuel + 𝑥𝑁2,𝑎𝑖𝑟 + XN2,air ∗ 𝑞𝑚,𝑎𝑖𝑟 * qm,air

qm,fluegas,S02 = X,fuel * M 𝑀M𝑆𝑂2* 9m,fuel 𝑞𝑚,𝑓𝑙𝑢𝑒𝑔𝑎𝑠,𝑆𝑂2 = 𝑥𝑆,𝑓𝑢𝑒𝑙 ∗ ∗ 𝑞𝑚,𝑓𝑢𝑒𝑙 𝑀𝑆 𝑀𝑂2 𝑞𝑚,𝑓𝑙𝑢𝑒𝑔𝑎𝑠,𝑂2= = 𝑥𝑂2,𝑎𝑖𝑟 ∗ 𝑞𝑚,𝑎𝑖𝑟 − 𝑞𝑚,𝑓𝑙𝑢𝑒𝑔𝑎𝑠,𝐶𝑂2 ∗ 9m,fluegas,02 X02,air

-0.25 * XH,fuel * 𝑀 * qm,air - 9m,fluegas,C02 *

M MH * 9m,fuel - qm,fluegas,S02 * M 𝑀 MH𝐻2𝑂 𝑀𝐶𝑂2 M 𝑂2 −0.25 ∗ 𝑥𝐻,𝑓𝑢𝑒𝑙 ∗ 𝑀𝐻 M ∗ 𝑞𝑚,𝑓𝑢𝑒𝑙 − 𝑞𝑚,𝑓𝑙𝑢𝑒𝑔𝑎𝑠,𝑆𝑂2 ∗ 𝑀𝑆𝑂2

where, where, for for instance, 𝑥𝐶,𝑓𝑢𝑒𝑙 represents instance, XC,fuel carbon in represents carbon in fuel fueli.e. i.e.first first subscript denotescomponent subscript denotes component andand second second subscript subscript is either is either fuel fuel or combustionair or combustion airreferred, referred, isa afuel 𝑞𝑚,𝑓𝑢𝑒𝑙 is 9m,fuel fuelflow, flow, is 𝑞𝑚,𝑎𝑖𝑟 is qm,air

combustion airflow combustion air flowand and Mx denotes M denotes molarmolar mass.mass. Advantageously, Advantageously, fuel propertiesasasutilized fuel properties utilized in in flue flue gas gas massmass flowflow components components and and combustion airproperties. combustion air properties. Fuel Fuel moisture moisture may may be measured be measured or or calculated. calculated.

The step b) The step b)may maybebeperformed performed remotely remotely to combustion to the the combustion boiler, boiler, such such

as, in the as, in the process processintelligence intelligence system system 205.205. Alternatively, Alternatively, theb)step b) the step may be may be performed performedlocally locally at at thethe combustion combustion boiler, boiler, preferably preferably at the at the EDGE server203. EDGE server 203.

Any of Any of the thecurrently currently monitored monitored process process datadata and/or and/or current current load load may be may be obtained fromreal-time obtained from real-time measurements, measurements, treated treated by filtering, by filtering, treated treated by by

averaging, computing averaging, computing trends trends or or any any combination combination of these. of these.

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The acceptancecondition The acceptance condition maymay include include a hysteresis a hysteresis condition, condition, requiring requiring a predefinedminimum a predefined minimum change change before before changing changing the current the current computational computational maximum boiler maximum boilermomentary momentary load load Qh, Qmax h,max.

The acceptancecondition The acceptance condition preferably preferably includes includes comparing comparing the computed the computed at at 5 least one flue least one fluegas gasfactor factor dfidfagainst i against a respective a respective maximum maximum value value 2021463486

2021463486

df dfmax,i The . maximum The maximum valuevalue dfmax,i dfmax,i is is a preset a preset value value andand preferably preferably boiler specific. boiler specific.The The numerical numerical value value Qh, Qcandidate is rejected h, candidate is rejectedififthe the maximum value maximum valuedfmax,i dfmax,i is is exceeded. exceeded.

In the combustion In the combustionboiler boiler 10,10, thethe furnace furnace 12 associated 12 and and associated passespasses (horizontal pass1515and (horizontal pass andback back pass pass 16)16) define define a flue a flue gas path. gas flow flow path. The The furnace 12 and furnace 12 andthe thepasses passes 15,15, 16 16 have have a number a number of heat of heat transfer transfer surfaces 21i in surfaces 21i inthe theflue fluegas gas flow flow path. path. The The combustion combustion boiler boiler 10 also 10 also has measurementinstrumentation has measurement instrumentation to monitor to monitor current current load load Qn of Qthe h of the

combustion boiler,and combustion boiler, and further further measurement measurement instrumentation instrumentation to to currently monitorprocess currently monitor process data. data.

The controlsystem The control system(DCS (DCS 201, 201, andand EDGEEDGE server server 203, 203, or201 or DCS DCSremote 201 remote process intelligence process intelligence system system 205, 205, possibly possibly underunder the participation the participation of of the EDGE server the EDGE server203) 203) isis configured configured to carry to carry out boiler out the the boiler control control method. method.

The EDGE server The EDGE server203 203may may be be configured configured to process to process the real-time the real-time measurement results measurement results for for currently currently monitored monitored process process data data and/or and/or current load,namely current load, namelybyby filtering, filtering, averaging, averaging, and/or and/or computing computing trends.trends.

The controlsystem The control systemmay may be be configured configured to carry to carry out method out the the method step b) step b) to determinethe to determine thecurrent current computational computational maximum maximum boiler boiler momentary momentary load load

Qh,maxmax Qn, locally locallyatatthe the combustion boiler 10, combustion boiler 10,and/or and/orto to send send data data to ato a remote, preferablycloud-based remote, preferably cloud-based (such (such as, as, computation computation cloud cloud 206), 206), computing system(such computing system (such as,as, process process intelligence intelligence system system 205) which 205) which is is configured tocarry configured to carryout out thethe method method stepstep b) return b) and and return the current the current computational maximum computational maximum boiler boiler momentary momentary loadload Qh,maxtoto Qh, max thethe control control

system. Thecontrol system. The controlsystem system maymay then then use use the the display/monitor display/monitor to to indicate theinformation, indicate the information, such such as as in method in method step step c), c), to thetoboiler the boiler operator, suchas, operator, such as,byby displaying displaying the the information. information.

The EDGE server The EDGE server203 203may maybe be configured configured to reduce to reduce amount amount of measurement of measurement data that is data that ispassed passedtoto thethe remote remote computing computing system. system.

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A combustion A combustion boiler boiler computation computation system system comprises comprises aa group group of of combustion combustion boilers 10, boilers 10,each eachcombustion combustion boiler boiler 10 comprising 10 comprising a boiler a boiler control control system (CS)comprising system (CS) comprisingan an EDGE EDGE server server (203) (203) system system whichwhich is configured is configured to processthe to process thereal-time real-time measurement measurement results results for currently for currently monitored monitored 5 process data process dataand/or and/or current current load, load, namely namely by filtering, by filtering, averaging, averaging, and/or computingtrends, trends, andand send the the processed real-time measurement 2021463486

2021463486

and/or computing send processed real-time measurement results to aaremote results to remotecomputing computing system. system. The The remote remote computing computing systemsystem is is preferablya acloud-based preferably cloud-based computing computing system, system, configured configured to receive to receive data data processed from processed from real real time time measurement measurement results and results and to to compute compute data data using using a numericalboiler a numerical boilermodel model forfor each each of of the the combustion combustion boilers boilers 10, 10, and to and to return computationresults return computation resultsforfor each each of the of the combustion combustion boilers boilers 10. The 10. The boiler control boiler controlsystem system maymay be be configured configured to adapt to adapt its function its function based on based on the computationresults. the computation results.

The computingsystem The computing systemis is preferably preferably configured configured to find to find such asuch a numerical numerical value Qh, candidate value Qn, candidate forfor a current a currentcomputational computational maximum boilermomentary maximum boiler momentary load Qh,max for load Qh,max for which at least which at least one oneflue fluegas gas factor factor dfidf i computed computed using using currently monitoredprocess currently monitored process data data withwith a numerical a numerical modelmodel of theofboiler the boiler that fulfillsananacceptance that fulfills acceptance condition, condition, and and selecting selecting the numerical the numerical value Qh, candidate value Qn, candidate as as thethe current currentcomputational maximum boiler computational maximum boilermomentary momentary load Qh,max load Qn, max .

The boilercomputation The boiler computation system system maymay be configured be configured to adapt to adapt or calibrate or calibrate a numericalmodel a numerical modelfor for a boiler a boiler using using processed processed measurement measurement data for data for the combustionboiler the combustion boiler 10. 10. Alternatively Alternatively oraddition, or in in addition, the boiler the boiler computation systemmay computation system maybe be configured configured to adapt to adapt or calibrate or calibrate a numerical a numerical

model for model foraacombustion combustion boiler boiler 10 using 10 using processed processed measurement measurement data data collected alsofrom collected also fromother other combustion combustion boilers boilers 10. 10.

FIG FIG 55 shows showsa amodification modificationof of thethe method method shownshown in 4. in FIG FIG 4. Steps Steps L1, L3,L1, L3, L7, L9 are L7, L9 arethe thesame sameasas steps steps K1,K1, K3, K3, K9, K9, K11, K11, respectively, respectively, but inbut in step L5, the step L5, theflue fluegas gas factors factors dfidf i can can be directly be directly computed computed for all for all

heat transfer heat transfer surfaces surfaces 20i: 20i: if if the the temperatures temperatures TTFG, aremeasured FG,in,iare measured using the respective using the respective temperature temperature sensors sensors 21i, 21 i, back-calculation the the back-calculation will not will not be benecessary necessaryandand thus thus the the stepstep K7 be K7 can canomitted be omitted in thein the method illustrated method illustratedinin FIGFIG 5. 5.

FIG FIG 66 shows showsininstep stepN1N1 thethe useuse of possible of possible inputs inputs tonumerical to the the numerical

boiler model. boiler model.InInstep step N3 N3 thethe Qh,maxisiscomputed Qh,max computed numerically numerically using using the the

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boiler model, boiler model,and andinin step step N5,N5, thethe estimated estimated maximum maximum loadmax load Qh, Qh,max is is presented to presented toboiler boiler operator operator viavia a specific a specific user user interface interface (UI), (UI), preferablyvia preferably viadisplay/monitor display/monitor 202. 202.

FIG FIG 77 shows showsboiler boilermomentary momentary load load Qh and Qh and computed computed currentcurrent 5 computational maximum computational maximum boiler boiler momentary momentary loadload Qh, maxas Qn, max, , as well well as the as the 2021463486

effect of using effect of usingthe themethod method according according to the to the invention invention duringduring a testa test period. During period. Duringthe the1010 dayday test test period, period, the the 120 MW 120 MWth th boiler boiler power power obtained inaverage obtained in averagea a 3 to 3 to 6 MWhigher 6 MWth th higher loadload as outside as outside the test the test period. FIG period. FIG8 8illustrates illustratesthethe 10 day 10 day testtest period period in detail. in more more detail.

In other words, In other words,ininthe the boiler boiler control control method, method, the current the current computational maximum computational maximum boiler boiler momentary momentary loadload Qh,maxofof Qh, max thethe combustion combustion boiler is boiler is estimated estimated using using aa numerical numerical model model using using determined determined fluidized fluidized bed combustion bed combustionboiler boiler operating operating parameters. parameters. The current The current boilerboiler load Qnload Qh is computedusing is computed usingsteam steam circuit circuit measurement measurement data.data.

Then, if the Then, if theboiler boilerload load Qn Qis h is smaller smaller thanthan the the current current computational computational maximum boiler maximum boilermomentary momentary load load Qh, Qmax, h,max, it itisisi)i)indicated indicated to to the the boiler boiler operator thatthe operator that theboiler boiler load load maymay be increased, be increased, and/or and/or ii)boiler ii) the the boiler load is automatically load is automatically increased. increased. Alternatively Alternatively or inoraddition, in addition, if the if the boiler load boiler loadQhQhisislarger larger than than thethe boiler boiler maximum maximum momentary momentary load load Qh, maxQh,max, it is i) it is i) indicated indicatedtoto the the boiler boiler operator operator that that the boiler the boiler load exceeds load exceeds the boiler maximum the boiler maximummomentary momentary load, load, and/or and/or ii) boiler ii) the the boiler load is load is automatically reduced. automatically reduced.

It is obvious It is obvioustotothe theskilled skilled person person that, that, along along with with the technical the technical progress, the progress, the basic basic idea idea of of the the invention invention can can be be implemented implemented in in many many

ways. The ways. The invention invention and and itsits embodiments embodiments are thus are thus not limited not limited to the to the examples andsamples examples and samples described described above above but but they they may vary may vary withinwithin the the contents ofpatent contents of patentclaims claims andand their their legal legal equivalents. equivalents.

In addition,ororinstead In addition, instead of of using using above above mentioned mentioned specific specific empirical empirical equations, itisispossible equations, it possible to to utilize utilize artificial artificial intelligence intelligence tools tools

and/or neuralnetwork and/or neural networkin in thethe numerical numerical model model computations. computations.

In the claims In the claimswhich whichfollow followandand in in the the preceding preceding description description of theof the invention, exceptwhere invention, except where thethe context context requires requires otherwise otherwise due todue to express express language ornecessary language or necessary implication, implication, the the wordword “comprise” "comprise" or variations or variations such as "comprises" such as “comprises”oror “comprising” "comprising" is used is used in anininclusive an inclusive sense,sense,

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i.e. to specify i.e. to specifythe thepresence presenceof of the the stated stated feature feature buttonot but not to preclude preclude the presenceororaddition the presence additionof of further further features features in various in various embodiments embodiments of of the invention. the invention.

5 2021463486

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List of List of reference referencenumbers numbers used: used:

T FG, in, TFG, in, ii flue gas temperature flue gas temperatureatat inlet inlet of of heat heat exchanger exchanger 21i 21i (i (i = 1, 2, = 1, 2, ... k) k)

5 T FG, exit TFG, exit flue flue gas gas temperature temperature at at outlet outlet of of heat heat exchanger exchanger 21 21k 2021463486

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Sensors: Sensors: 20 20 temperature sensor(FBHE) temperature sensor (FBHE) 20 20ii temperature sensor(i(i temperature sensor = 1, = 1, 2, 2, ... k) k) ... 30 30 gas volumeflow gas volume flowsensor sensor 40 40 sensor in the sensor in thefurnace furnace 116 116 pressure sensor pressure sensor 165 165 pressure sensor pressure sensor(loop (loop seal) seal) 650 650 fuel feed sensor fuel feed sensor

10 10 combustion boiler combustion boiler 12 furnace 12 furnace 13 13 tube wall tube wall 14 14 superheater superheater 15 15 horizontalpass horizontal pass 16 16 back pass back pass 17 17 particle separator particle separator 18 18 flue gas conduit flue gas conduit 19 19 flute flute

21 21ii heat transfersurface heat transfer surface(i (i = 1, = 1, 2, 2, ... k) k) ... 22 22 fuel feed fuel feed 100 fluidized bed 100 fluidized bed heat heat exchanger exchanger (FBHE) (FBHE) 101 FBHE outlet 101 FBHE outlet 102 102 return channel return channel

103 103 vortex finder vortex finder

141 superheater inlet 141 superheater inlet 142 superheater outlet 142 superheater outlet 151 primary fludization 151 primary fludization gas gas feed feed 152secondary 35 152 secondary fludization fludization gasgas feed feed 153 fludization gas 153 fludization gas supply supply 161 reheateroutput 161 reheater output

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200 internet 200 internet 201 distributed control 201 distributed control system system 202 display // monitor 202 display monitor 5 203 EDGE server 203 EDGE server 204 local storage storage 2021463486

204 local 205 process intelligence 205 process intelligence system system 206 computation cloud 206 computation cloud 210 open platform 210 open platformcommunications communications server server 280 combustionboiler 280 combustion boiler network network 290 field bus 290 field bus

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Claims: Claims:

1. 1. AA combustion combustionboiler boiler control control method, method, comprising comprising the steps the steps of: of:

a) monitoringthe a) monitoring thecurrent current load load (Qof (Qh) h) a ofcombustion a combustion boiler; boiler;

b) finding b) findingsuch sucha anumerical numerical value value (Q, (Q h, candidate)for candidate) fora acurrent current 2021463486

5 computational maximum computational maximum boiler boiler momentary momentary loadload (Qh, max (Q, max) for) for whichwhich at least one at least oneflue fluegas gas factor factor (dfcomputed (dfi) i) computed using using currently currently monitored process monitored process data data with with aa numerical numerical model model of of the the boiler boiler fulfills an acceptance fulfills an acceptance condition, condition, and and selecting selecting the numerical the numerical value (Qh,candidate) value (Q, candidate) asasthe the current current computational maximum computational maximum boiler boiler momentary momentary load load (Qh,max;); (Qh,max)

c) indicatingthe c) indicating thecurrent current computational computational maximum maximum boiler boiler momentary load momentary load(Oh,max) (Qh,max) to to the theoperator operator and/or, and/or, if if the the current current load load (Qh) is (Q) is

c1) c1) smaller smaller than than the the current current computational computational maximum maximum boiler momentary load (Qh,max boiler momentary load (Oh,max) : ):

c1i) indicatingthe cli) indicating theboiler boiler operator operator thatthat the boiler load the boiler load(Qh) (Qh)may may bebe increased, increased, and/or and/or

c1ii) automaticallyincreasing clii) automatically increasing thethe boiler boiler load (Qh), load (Qh),

and/or and/or

c2) c2) larger larger than than the the current current computational computational maximum maximum boiler momentary load (Qh,max boiler momentary load (Qh,max) : ):

c2i) indicatingthe c2i) indicating theboiler boiler operator operator thatthat

the boiler load the boiler load(Qh) (Qh)exceeds exceeds thethe current current computational maximum computational maximum boiler boiler momentary momentary load, and/or load, and/or

c2ii) automaticallyreducing c2ii) automatically reducing thethe boiler boiler load (Qh). load (Qh).

30 2.2.The Themethod methodaccording accordingtotoclaim claim1,1,wherein: wherein:

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i) the currently i) the currentlymonitored monitored process process datadata of boiler of the the boiler includes includes

ia) currentflue ia) current fluegas gasexit exit temperature temperature (T flue gas,exit,current (Tflue ) in a flue gas, exit, current) gas gas in a flue flow channel flow channel and and

ib) heat duty ib) heat duty(Qfluid,i) (Qfluid,i) for for each heat transfer each heat transfersurface surface 5 (i) (i) in the flue fluegas gasflow flow channel 2021463486

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in the channel

and furtherwherein: and further wherein:

ii) monitoredprocess ii) monitored process data data from from both both ia) ia) and and ib)used ib) is is in used in computation computation ofofthe theflue flue gasgas factor factor and and whenwhen finding finding the the numerical value(Q, numerical value (Qh, candidate) for candidate) for the current computational the current computational maximum boiler maximum boilermomentary momentary loadload (Qh,max). (Qh,max)

3. The method 3. The methodaccording according to to claim claim 1 or1 2, or wherein: 2, wherein: the finding the finding is is performed suchthat, performed such that,if if thethe at at least least one one flue flue gas factor gas factor (dfi) (dfi) computed computed using currentlymonitored using currently monitored process process datadata withwith a numerical a numerical model model of the of the boiler that boiler thatfulfills fulfillsan an acceptance acceptance condition condition for numerical for the the numerical value value (Q (Q,h, candidate candidate)) forfor the current the currentcomputational maximumboiler computational maximum boilermomentary momentary load load (Q h,max) fails (Oh,max) failsto to fulfill an acceptance fulfill an acceptancecondition, condition, a next a next numerical numerical valuevalue (Q (Q, candidate) is h, candidate) is automatically selected. automatically selected.

4. The method 4. The methodaccording accordingto to claim claim 3, wherein: 3, wherein: the next the next numerical numerical value value (Q h, candidate (On, ) isisselected candidate) iteratively. selected iteratively.

5. The method 5. The methodaccording accordingto to anyany oneone of claims of claims 1 to 14,towherein: 4, wherein: the finding the finding is carried out is carried outwith withperforming performingthethe computational computational stepssteps of: of:

- I: computing - I: computingananestimate estimate forfor boiler boiler flueflue gas exit gas exit temperature (Tboiler, exit temperature (Tboiler, ) that exit) thatresults results in in aa computational boiler computational boiler model when model when the the thermal thermal loadload ofof the the boiler boiler corresponds corresponds to to the the

numerical value numerical value (On,(Qh, candidate); candidate) ;

- II:computing - II: computingflueflue gas flow gas mass mass(qm, flow (qm,fluegas fluegas) ; );

- III:computing - III: computing a heat a heat duty (Qfluid, duty (Qfluid, ) for i, candidatefor i, candidate) eacheach heat heat transfer surfaceininthe transfer surface the flue flue gasgas flowflow channel channel with with its current its current heat duty(Qfluid, heat duty (Qfluid,i,i, current) current) that is corrected that is corrected by using by using a numerical a numerical

boiler boiler model model (Qfluid, (Qfluid, i, candidate i, candidate = Qfluid,i,current = Qfluid,i i, current ++

 (Qsteam,max) ,I j,I (Qsteam,max j)  j,i (Q -j ,i- (Qsteam, j) ;)j); steam,current current)

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- IV:using - IV: using thethe computed computed heat duties heat duties (Qfluid, (Q i,fluid, candidate) for) each i, candidate for each heat transfersurface heat transfer surface in in thethe flue flue gas gas flowflow channelchannel to compute to compute flue flue gasgastemperatures temperatures at heat at each eachtransfer heat transfer surface (T surface (Tfluegas,i fluegas,in,i, in, T out, ; fluegas,out,i Tfluegas, i; i i ==1,1, ... ,, k) in the k) in the flue fluegas gasflow flow channel channel in the in the 5 upstream directionofof upstream direction flue flue gasgas flow, flow, starting starting from from the heat the heat transfer transfer surface surface 21 that is 21k that is closest closest to to the the flue flue gas gas exit exit using using 2021463486

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the estimatefor the estimate forthe the boiler boiler flueflue gas gas exitexit temperature temperature (T out, k = = fluegas,out,k (Tfluegas, TFG,Texit) FG, exit) ; ;

- V: computing - V: computinga aflue flue gas gas factor factor (dfii , (dfi, i ,= 1 , ..., k) = 1 for k) for each heat transfer each heat transfersurface surfacein in thethe flueflue gas gas flow flow channel. channel.

6. The method 6. The methodaccording accordingto to claim claim 5, wherein: 5, wherein: the flue the flue gas factor gas factor includes includes or is: or is: 𝑞𝑚,𝑓𝑙𝑢𝑒𝑔𝑎𝑠 df = k Pfluegas,i qm,fluegas * Across,i )

𝑑𝑓𝑖 = 𝑘𝑖 ( )𝑛 𝞺𝑓𝑙𝑢𝑒𝑔𝑎𝑠,𝑖 ∗ 𝐴𝑐𝑟𝑜𝑠𝑠,𝑖

where k where ki is is aa non-zero non-zero parameter parameter that that may may be be chosen chosen combustion-boiler combustion-boiler specifically, specifically,

q m,fluegas qm, is isflue fluegas flue gas massflow, gas mass flow,

n is aa model n is modelparameter parameter that that maymay be chosen be chosen combustion-boiler combustion-boiler specifically, specifically, , , 𝞺𝑓𝑙𝑢𝑒𝑔𝑎𝑠,𝑖 isisflue Pfluegas,i fluegas gas density density at ith heat at ith transfersurface heat transfer surfaceand and A is A is a a crosssection ZU cross sectionofofflue fluegas gaschannel ith heat channelatatith heat transfer transfer surface. surface.

7. The method 7. The methodaccording accordingto to claim claim 6, wherein: 6, wherein: n is nselected is selected to include to include at at least one of least one ofthe thefollowing: following:

i) in the i) in the range rangeofof0,9 0,9 to to 1,1, 1,1, forfor using using computed computed flue flue gas gas velocity; velocity;

ii) in the ii) in the range rangeofof2,9 2,9 to to 3,5, 3,5, for for using using computed computed flue flue gas gas caused erosion;oror caused erosion;

iii) in the iii) in the range rangeofof1,8 1,8 to to 2,2, 2,2, for for using using pressure pressure loss.loss.

8. The method 8. The methodaccording accordingto to claim claim 7, wherein: 7, wherein: the value the value for n for n is changed is changed over time. over time.

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9. The method 9. The methodaccording accordingto to claim claim 7 or7 8, or wherein: 8, wherein: the value the value for n for is n is determined froma agroup determined from group of of boilers boilers comprising comprising at least at least two separate two separate boilers using boilers usingoperational operational data data monitored monitored for each for each ofboilers. of the the boilers.

10. The method 10. The methodaccording accordingto to anyany one one of claims of claims 5 to 59,to 9, wherein: wherein: the the 5 computation instep computation in stepI), I), thethe flue flue gas gas exitexit temperature temperature is substantially is substantially 2021463486

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estimated byequation estimated by equation

T boiler, exit Tboiler, = =0 ++ (Q, exit j(Q )j h, candidatej candidate)

or its first, or its first,second, second, third third or or higher higher degree degree approximation, approximation, and wherein and wherein the the respective respective coefficients coefficients ((,,,) have ) have been been obtained obtained beforehand beforehand by by fitting aftermeasuring fitting after measuring flue flue gasgas exitexit temperature temperature (TFG,(TFG, exit exit) ) values values for for a a number of discrete number of discreteboiler boiler load load (Qsteam)values. (Qsteam) values.

11. The method 11. The methodaccording according to to anyany one one of claims of claims 5 to 510, to wherein: 10, wherein: in stepin step II), computationofofflue II), computation flue gasgas mass mass flowflow utilizes utilizes mass mass flow fluegas,m) flow (qm, (qm,fluegas,m)ofof flue flue gas gas components, components, wherein wherein the the components components include include CO2, H CO2, 2O, N, HO, N2, SO, SO2,O.O2.

12. The method 12. The methodaccording accordingto to anyany one one of claims of claims 5 to 511, to wherein: 11, wherein: in stepin step II), the computation II), the computationofof flue flue gasgas massmass flowflow includes includes fuel parameters. fuel parameters.

13. The method 13. The methodaccording accordingto to anyany one one of the of the preceding preceding claims, claims, wherein: wherein: the the step b) is step b) is performed performedremotely remotelyto to the the combustion combustion boiler. boiler.

14.The 20 14. Themethod methodaccording accordingtotoany anyone oneofofthe thepreceding precedingclaims claims1 1toto12, 12, wherein: the wherein: thestep stepb)b) is is performed performed locally locally at combustion at the the combustion boiler. boiler.

15. The method 15. The methodaccording according to to anyany one one of the of the preceding preceding claims, claims, wherein: wherein: any any of the currently of the currentlymonitored monitored process process datadata and/or and/or current current load load is is obtained obtained from real-timemeasurements, from real-time measurements, treated treated by filtering, by filtering, treated treated by averaging, by averaging, computingtrends 25 computing trendsororany anycombination combinationofofthese. these.

16. The method 16. The methodaccording accordingto to anyany one one of the of the preceding preceding claims, claims, wherein: wherein: the the acceptance condition acceptance condition includes includes a hysteresis a hysteresis condition, condition, requiring requiring a a predefinedminimum predefined minimumchange change before before changing changing the current the current computational computational maximum boiler maximum boiler momentary momentary load load (Q, (Qh,max).

17.The 30 17. Themethod methodaccording accordingtotoany anyone oneofofthe thepreceding precedingclaims, claims,wherein: wherein:the the acceptance condition acceptance condition includes includes comparing comparing the the computed computed at least at least one flue one flue

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gas factor(dfi) gas factor (dfi)against against a respective a respective design design value, value, and wherein and wherein in thein the method, the method, thenumerical numerical value value (Q,(Q h, candidate) is candidate) is rejected rejectedifif thethe design design value value is exceeded. is exceeded.

18. The method 18. The methodaccording accordingto to anyany one one of the of the preceding preceding claims, claims, wherein: wherein: the the 5 combustion boilerisis combustion boiler a circulating a circulating fluidized fluidized bed (CFB) bed (CFB) or a bubbling or a bubbling 2021463486

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fluidized bed(BFB) fluidized bed (BFB)boiler, boiler, andand the the stepstep b)carried b) is is carried outthe out for for the combustion boilerheat combustion boiler heat transfer transfer surfaces, surfaces, between between the furnace the furnace and the and the stack, optionallyincluding stack, optionally including thethe furnace. furnace.

19. 19. AA combustion combustionboiler, boiler, comprising: comprising:

- a furnace - a furnaceand andassociated associated passes passes defining defining a flue a flue gas path gas flow flow path and and having having aa number number of of heat heat transfer transfer surfaces surfaces that that are are located located in the flue in the flueflow flowpath; path;

- measurementinstrumentation - measurement instrumentation to to monitor monitor current current load load (Qh) of (Qh) of the combustionboiler; the combustion boiler;

- further measurement - further measurement instrumentation, instrumentation, suchsuch as sensors, as sensors, to to currently monitorprocess currently monitor process data; data; and and

- a control - a controlsystem systemconfigured configuredto to carry carry out out the boiler the boiler control control method according method accordingtoto anyany oneone of of the the preceding preceding claims. claims.

20. The combustion 20. The combustionboiler boiler according according to claim to claim 19, wherein: 19, wherein: the control the control system comprisesananedge system comprises edge server server which which is configured is configured to process to process real-time real-time measurementresults measurement results for for currently currently monitored monitored process process data and/or data and/or currentcurrent load, namelybybyfiltering, load, namely filtering, averaging, averaging, and/or and/or computing computing trends. trends.

21. The combustion 21. The combustionboiler boiler according according to claim to claim 19 or1920, orwherein: 20, wherein: the the control systemisisconfigured control system configured to to carry carry out out the method the method step step b) to b) to determine determine the 25 the current current computational computational maximum maximum boilerboiler momentary momentary load (Q load (Qh,max) h,max)locally. locally.

22. The combustion 22. The combustionboiler boiler according according to claim to claim 19 or1920, orwherein: 20, wherein: the the control control system system isis configured configured to to send send data data to to a a remote remote computing computing system system which is which is configured configuredtoto carry carry outout the the method method step step b)return b) and and return the the current computational current computational maximum maximum boiler boiler momentary momentary load load (Qh,max (Qh,max) to) the to the controlsystem. 30 control system.

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23. The combustion 23. The combustionboiler boiler according according to claim to claim 22, wherein: 22, wherein: theserver the edge edge server is configuredtotoreduce is configured reduce amount amount of of measurement measurement data data that that is passed is passed to the to the remote computingsystem. remote computing system.

24. 24. AA combustion combustionboiler boiler computation computation system system comprising: comprising:

5 - - a a group group of of combustion combustion boilers boilers , comprisingatat least two 2021463486

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comprising least two separate boilersaccording separate boilers accordingto to anyany one one of claims of the the claims 19 to 19 22,to 22, each boilercomprising each boiler comprising a boiler a boiler control control system system (DCS)(DCS) comprising comprising an edge server an edge serversystem system which which is is configured configured to process to process the real- the real- time measurementresults time measurement results forfor currently currently monitored monitored process process data data and/or currentload, and/or current load, namely namely by by filtering, filtering, averaging, averaging, and/orand/or computing trends,and computing trends, and send send thethe processed processed real-time real-time measurement measurement results to aaremote results to remotecomputing computing system system (205); (205) ;

- a remote - a remote computing computing system system configured configured to receive to receive data data processed from processed from real-time real-time measurement measurement results results and and to to compute compute data usinga anumerical data using numerical boiler boiler model model for for eacheach of combustion of the the combustion boilers, and boilers, andtotoreturn return computation computation results results for each for each of theof the combustion boilers, combustion boilers,

- and wherein - and wherein

- the boiler - the boilercontrol control system system is is configured configured to adapt to adapt its function its function based on based on the the computation computation results, results, and and

the computingsystem the computing systemisis configured configured to find to find such such a numerical a numerical value (Qh, candidate value (On, candidate)) forfor a current a currentcomputational maximum boiler computational maximum boiler momentaryload momentary load(Qh,max) (Qh,max) for for which whichatatleast least oneone flue flue gas gas factor factor (dfi) computed (dfi) usingcurrently computed using currently monitored monitored process process datadata with with a a

numerical modelofofthe numerical model the boiler boiler that that fulfills fulfills an acceptance an acceptance condition, andselecting condition, and selectingthethe numerical numerical value value (Qh, candidateas (Q, candidate) ) as thethe current computational current computational maximum maximum boiler boiler momentary momentary load load (Qh,max). (Qh,max).

25. The combustion 25. The combustionboiler boiler computation computation system system according according to claim to claim 24, 24, wherein: the wherein: the combustion combustion boiler boiler computation computation system system is is configured configured toto adapt adapt

30 ororcalibrate calibratea anumerical numericalmodel modelfor fora acombustion combustionboiler boilerusing usingprocessed processed measurementdata measurement datafor for the the combustion combustion boiler. boiler.

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26. The boiler 26. The boilercomputation computation system system according according to one to any anyofone of claims claims 24 to 24 to 25, wherein:the 25, wherein: theboiler boiler computation computation system system is configured is configured to adapt to adapt or or calibrate calibrate a a numerical numerical model model for for a a combustion combustion boiler boiler using using processed processed measurement measurement data collected also data collected also from other combustion boilers . from other combustion boilers 2021463486

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2023/036426 oM PCT/EP2021/074838 1/8

200 Internet Internet

206 205

153 Gateway Gateway

19 CS 290 201 202 203 204

161

TFG, T FG, in, k-1 K-118 21 21 18 boiler boiler network network FG, in, k-1

TFG, T FG, in, 2 FG, in, 2 TFG, T FG, FG, in, in, 33

combustion

21 211 G K-1 FG, in, k

TFG, T

16 20 201 T T T TFG, FG, exit exit DCS DCS

T 16 TK 20k 20K 290 280 TFG, in, 1 in, 1 T FG, in, 1

202 202 2 20 K-1

101 203 21 20 213 20 K-1 20k. 20 20 21 21k 21K 212 21 20 15 15 165 103 20 20 100 30

160 17 102 30 30

116

152 151

12 40

132 13 131 22 FIG 1 10 10 650 wo 2023/036426 PCT/EP2021/074838 2/8

200 Internet Internet

206 205 205

206 153 153 19 Gateway Gateway

290 201 201202 202203 203204 204

FG, in, k-1 TFG, in, k-1

TFG, FG, in,in, 2 2 TFG,FG,in, in, 3 3 boiler boilernetwork network

K-1 TTFG, FG, in, k in, k 18 combustion combustion

21 21 1 21 21 TFG, in, 1 16 20,

201 6 T T T TFG,FG,exit exit DCS DCS

16 T 20k 20 290 FG, in, 1 280 280

152K-1 20

20 2 21 20 21 20, 21, 203 21. 3 20 20K-1 20 30 T 21 K 21 152

15 30 a 12

151

142 40 650 14

131 10 141 13 22

FIG 2

Storage Storage

Local EDGE EDGE

203 203

204 210 210 OPC OPC

201 DCS

20, 40, 20, 30, 30, 116, 40, 116, 140, 140, 650 650

280 290 Sensors Sensors

FIG 33 FIG

FIG 4

Monitor: Qh, TFG, Q, TFG, exit' exit'Qfluid, Qfluid,i i

K1

Qh, candidate Q, candidate

K3 Calculate heat duties at heat transfer

surfaces and flue gas temperatures in in relation relationtoto Qh,Q,candidate candidate

K5 K5

Compute flue gas factor (df;) (df) in in relation relationtoto Qh,Q,candidate candidate

K7 K9 K9

Compare flue gas (df;)to factor (df) topredetermined predetermined

flue gas factor value (dt max, i) not not acceptable, acceptable,df; dfdiffers differsdf df, i (df, ) max, i new Qh, candidate' Q, candidate'

iterate iterate until df 1 df until dt ~ maydf, max,ii

acceptable, dfjdf acceptable, ~ df ~ max, df, ii

K11 Q, maxfound Qh, found max

FIG 5

Monitor: Qh, Qh, TTFG, FG, exit' exit'Qfluid, i i Qfluid,

L1

Qh h, Q, candidate candidate

L3

L5

L7

Compare flue gas factor (df;) topredetermined (df) to predetermined

flue gas factor value (d f max. max, i)

not not acceptable, acceptable,dfj dfdiffers df df, i differs (df,) max, i new Qh, candidate' Q, candidate'

interate interate until df; ~df until df ~max, df,i i

acceptable, df;df acceptable, 1 d~f df, max, ii

Qh,max Q maxfound found

L9

FIG 6

Inputs Fuel Fuel N1 Current operation

Boiler load, operation paramenters

Q, h, Q maxEstimation Estimation max Adjustment of digital twin parameters based

on measured state Estimation of the effect of boiler load on

limiting process variables (temperature, N3 pressure loss, velocity) by digital twin

Comparison of estimated variables to max load limit values

Iteration until estimated variables match with

Estimated maximum load Presented to boiler operator via specific UI N5

WO 2023/036426 2023/03442 OM PCT/EP2021/074838 7/8

Q, max

Test period (10d)

Q

Boiler power (MW)

FIG 7

130 128 126 124 122 120 118 116 114 112 110 wo 2023/036426 PCT/EP2021/074838 8/8 8/8 ov

1

100

Test period

0

"40

"O

100% 8 DH MCR

Claims

Claims:

1. A combustion boiler control method, comprising the steps of:

a) monitoring the current load (Qh) of a combustion boiler;

b) finding such a numerical value (Qh, candidate) for a current

computational maximum boiler momentary load (Qh, max) for which at least one flue gas factor (dfi) computed using currently monitored process data with a numerical model of the boiler fulfills an acceptance condition, and selecting the numerical value (Qh, candidate) as the current computational maximum boiler

momentary load (Qh,max) ;

c) indicating the current computational maximum boiler momentary load (Qh,max) to the operator and/or, if the current load (Qh) is

cl) smaller than the current computational maximum boiler momentary load (Qh,max):

cli) indicating the boiler operator that the boiler load (Qh) may be increased,

and/or

clii) automatically increasing the boiler load (Qh),

and/or

c2) larger than the current computational maximum boiler momentary load (Qh,max):

c2i) indicating the boiler operator that the boiler load (Qh) exceeds the current

computational maximum boiler momentary load, and/or

c2ii) automatically reducing the boiler load (Qh).

2. The method according to claim 1, wherein:

21807516_1 (GHMatters) P123789.AU i) the currently monitored process data of the boiler includes ia) current flue gas exit temperature (Tflue gas,exit, current) in a flue gas flow channel and ib) heat duty (Qfnua,i) for each heat transfer surface

(i) in the flue gas flow channel

and further wherein:

ii) monitored process data from both ia) and ib) is used in computation of the flue gas factor and when finding the numerical value (Qh, candidate) for the current computational maximum boiler momentary load (Qh,max).

3. The method according to claim 1 or 2, wherein: the finding is performed such that, if the at least one flue gas factor (dfi) computed using currently monitored process data with a numerical model of the boiler that fulfills an acceptance condition for the numerical value (Qh, candidate) for the current computational maximum boiler momentary load (Qh,max) fails to fulfill an acceptance condition, a next numerical value (Qh, candidate) is automatically selected.

4. The method according to claim 3, wherein: the next numerical value (Qh, candidate) is selected iteratively.

5. The method according to any one of claims 1 to 4, wherein: the finding is carried out with performing the computational steps of:

- I: computing an estimate for boiler flue gas exit temperature (Tboier, exit) that results in a computational boiler model when the thermal load of the boiler corresponds to the numerical value (Qh, candidate) ;

- II: computing flue gas mass flow (qm,fnuegas);

- III: computing a heat duty (Qfnia, i, candidate) for each heat transfer surface in the flue gas flow channel with its current heat duty (Qf1ia, i, current) that is corrected by using a numerical boiler model (Qf1ia, i, candidate = Qfliiad,a,current +

I ], I (Qsteam,max) j,i (Qsteam, current) )

21807516_1 (GHMatters) P123789.AU

- IV: using the computed heat duties (Qfia, i, canaiate) for each heat transfer surface in the flue gas flow channel to compute flue gas temperatures at each heat transfer surface (Tficegas,in,i,

Tfiuegas,out,i; i = 1, .. . , k) in the flue gas flow channel in the upstream direction of flue gas flow, starting from the heat 21 transfer surface k that is closest to the flue gas exit using the estimate for the boiler flue gas exit temperature (Tfluegas,out,k = FG, exit);

- V: computing a flue gas factor (dfi, i = 1 , ... , k) for

each heat transfer surface in the flue gas flow channel.

6. The method according to claim 5, wherein: the flue gas factor includes or is:

qm,fluegas )n

Pfluegas,i * Across,i

where ki is a non-zero parameter that may be chosen combustion-boiler specifically,

qm,fiuegas is flue gas mass flow,

n is a model parameter that may be chosen combustion-boiler specifically,

pfluegas,i is flue gas density at ith heat transfer surface and A is a cross section of flue gas channel at ith heat transfer surface.

7. The method according to claim 6, wherein: n is selected to include at least one of the following:

i) in the range of 0,9 to 1,1, for using computed flue gas velocity;

ii) in the range of 2,9 to 3,5, for using computed flue gas caused erosion; or

iii) in the range of 1,8 to 2,2, for using pressure loss.

8. The method according to claim 7, wherein: the value for n is changed over time.

21807516_1 (GHMatters) P123789.AU

9. The method according to claim 7 or 8, wherein: the value for n is determined from a group of boilers comprising at least two separate boilers using operational data monitored for each of the boilers.

10. The method according to any one of claims 5 to 9, wherein: the computation in step I), the flue gas exit temperature is substantially estimated by equation

Tboiler, exit = U-0 + I Uj (Qh, candidate)j

or its first, second, third or higher degree approximation, and wherein the respective coefficients (UUiU2,...))have been obtained beforehand by

fitting after measuring flue gas exit temperature (TFG, exit) values for a number of discrete boiler load (Qsteam) values.

11. The method according to any one of claims 5 to 10, wherein: in step II) , computation of flue gas mass flow utilizes mass flow (qm,fnuegas,m) of flue gas components, wherein the components include C0 2 , H 2 0, N2 , SO 2 , 02.

12. The method according to any one of claims 5 to 11, wherein: in step II), the computation of flue gas mass flow includes fuel parameters.

13. The method according to any one of the preceding claims, wherein: the step b) is performed remotely to the combustion boiler.

14. The method according to any one of the preceding claims 1 to 12, wherein: the step b) is performed locally at the combustion boiler.

15. The method according to any one of the preceding claims, wherein: any of the currently monitored process data and/or current load is obtained from real-time measurements, treated by filtering, treated by averaging, computing trends or any combination of these.

16. The method according to any one of the preceding claims, wherein: the acceptance condition includes a hysteresis condition, requiring a predefined minimum change before changing the current computational maximum boiler momentary load (Qh,max).

17. The method according to any one of the preceding claims, wherein: the acceptance condition includes comparing the computed at least one flue

21807516_1 (GHMatters) P123789.AU gas factor (dfi) against a respective design value, and wherein in the method, the numerical value (Qh, candidate) is rejected if the design value is exceeded.

18. The method according to any one of the preceding claims, wherein: the combustion boiler is a circulating fluidized bed (CFB) or a bubbling fluidized bed (BFB) boiler, and the step b) is carried out for the combustion boiler heat transfer surfaces, between the furnace and the stack, optionally including the furnace.

19. A combustion boiler, comprising:

- a furnace and associated passes defining a flue gas flow path and having a number of heat transfer surfaces that are located in the flue flow path;

- measurement instrumentation to monitor current load (Qh) of the combustion boiler;

- further measurement instrumentation, such as sensors, to currently monitor process data; and

- a control system configured to carry out the boiler control method according to any one of the preceding claims.

20. The combustion boiler according to claim 19, wherein: the control system comprises an edge server which is configured to process real-time measurement results for currently monitored process data and/or current load, namely by filtering, averaging, and/or computing trends.

21. The combustion boiler according to claim 19 or 20, wherein: the control system is configured to carry out the method step b) to determine the current computational maximum boiler momentary load (Qh,max)locally.

22. The combustion boiler according to claim 19 or 20, wherein: the control system is configured to send data to a remote computing system which is configured to carry out the method step b) and return the current computational maximum boiler momentary load (Qh,max) to the control system.

21807516_1 (GHMatters) P123789.AU

23. The combustion boiler according to claim 22, wherein: the edge server is configured to reduce amount of measurement data that is passed to the remote computing system.

24. A combustion boiler computation system comprising:

- a group of combustion boilers , comprising at least two separate boilers according to any one of the claims 19 to 22, each boiler comprising a boiler control system (DCS) comprising an edge server system which is configured to process the real time measurement results for currently monitored process data and/or current load, namely by filtering, averaging, and/or computing trends, and send the processed real-time measurement results to a remote computing system (205);

- a remote computing system configured to receive data processed from real-time measurement results and to compute data using a numerical boiler model for each of the combustion boilers, and to return computation results for each of the combustion boilers,

- and wherein

- the boiler control system is configured to adapt its function based on the computation results, and

the computing system is configured to find such a numerical value (Qh, candidate) for a current computational maximum boiler momentary load (Qh,max) for which at least one flue gas factor (dfi) computed using currently monitored process data with a numerical model of the boiler that fulfills an acceptance condition, and selecting the numerical value (Qh, candidate) as the current computational maximum boiler momentary load (Qh,max).

25. The combustion boiler computation system according to claim 24, wherein: the combustion boiler computation system is configured to adapt or calibrate a numerical model for a combustion boiler using processed measurement data for the combustion boiler.

21807516_1 (GHMatters) P123789.AU

26. The boiler computation system according to any one of claims 24 to 25, wherein: the boiler computation system is configured to adapt or calibrate a numerical model for a combustion boiler using processed measurement data collected also from other combustion boilers

21807516_1 (GHMatters) P123789.AU

Internet

206 205

153 Gateway

19 CS 290 201 202 203 204

161

21 K-1 18 boiler network FG, in, k-1

FG, in, 2 FG, in, 3

combustion

211 G FG, in, k

201 T T T FG, exit DCS

T 16 TK 20k 290 280 T FG, in, 1

202 2 203 K-1

101 213 20k. 20 K-1 21k 212

15 165 20 103 100 30

160 17 102 30

116

152 151

12 40

132 13 131 22 FIG 1 10 650

Internet

205

206 153 19 Gateway

290 201 202 203 204

FG, in, k-1

FG, in, 2 FG, in, 3 boiler network

K-1 T FG, in, k 18 combustion

211 21

201 6 T T T FG, exit DCS

16 T 20k 290 FG, in, 1 280

K-1

2 20, 21, 203 21. 3 20K-1 20 30 T K 21 152

15 30

a 12

151

142 40 650 14

131 10 141 13 22

FIG 2

205

200

290

Storage

Local EDGE

203

204 210 OPC

201 DCS

20, 30, 40, 116, 140, 650

280 290 Sensors

FIG 3

FIG 4

Monitor: Qh, TFG, exit' Qfluid, i

K1

Qh, candidate

K3 Calculate heat duties at heat transfer

surfaces and flue gas temperatures in relation to Qh, candidate

K5 Compute flue gas factor (df;) in relation to Qh, candidate

K7 K9

Compare flue gas factor (df;) to predetermined

flue gas factor value (dt max, i) not acceptable, df; differs df max, i new Qh, candidate'

iterate until df 1 dt may max, i

acceptable, dfj ~ df max, i

K11 Qh, found max

FIG 5

Monitor: Qh, T FG, exit' Qfluid, i

L1

Qh h, candidate

L3

Compute flue gas factor (df;) in relation to Qh, candidate

L5

L7

Compare flue gas factor (df;) to predetermined

flue gas factor value (d f max. max, i)

not acceptable, dfj differs df max, i new Qh, candidate'

interate until df; ~ df max, i

acceptable, df; 1 d f max, i

Qh, max found

L9

FIG 6

Inputs Fuel N1 Current operation

Boiler load, operation paramenters

Q h, Estimation max Adjustment of digital twin parameters based

on measured state Estimation of the effect of boiler load on

Comparison of estimated variables to max load limit values

Iteration until estimated variables match with

Estimated maximum load Presented to boiler operator via specific UI N5