JPS5851079B2 - Pulp Senjiyoki no Seigiyosouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a pulp washer.

When producing paper from pulp, the paper is passed through a continuous digester (
digester) to multiple washing drums, where it is
The spent liquor or black liquor resulting from the cooking process is washed out of the pulp.

This black liquor contains alkali and lignin, and if this alkali is not effectively washed away, it is carried away with the paper and is consumed.

If black liquor remains in the pulp, this black liquor will also have an adverse effect on the subsequent bleaching process.

Therefore, in order to maximize the efficiency of the washing process, it is desirable to remove as much black liquor as possible from the pulp during the washing process.

The black liquor removed from the pulp in the washer undergoes evaporation treatment,
The black liquor residue is burned to regenerate the alkaline content which is recycled to the digester.

This black liquor removed from the pulp in the washer contains most of the total alkali that goes into the digester.

Most of the alkalis in black liquor contain sodium sulfide or sodium inorganic compounds.

The total solids content of black liquor usually averages about 20 percent.

This black liquor is first concentrated in an evaporator to a total solids content of about 45 to 70 percent, depending on the type of recovery unit used.

Removal of moisture is necessary to produce a liquid that heats and burns when blown into the furnace.

In order for alkali recovery to be effective, the ratio of liquid to solids (original material) of black liquor must be as low as possible.

That is, if the black liquor contains too much water, the evaporator and furnace will be overloaded, thereby reducing the efficiency of the alkali recovery process.

The water content of diluted black liquor is also a function of the wash water used in the wash equipment.

PRIOR ART A common pulp washing machine consists of three vacuum drums through which the pulp passes in succession.

The outer cylindrical surface of each drum is a sieve or mesh through which the pulp-laden liquid is sucked into the vat when a vacuum is created in the drum.

Pure water or white water (bleaching solution) from the concentrator is sprinkled onto the pulp mat and passes through the third drum.

This filtrate, which has passed through the third drum, is then discharged into a vat and is then sprinkled onto the mat of the second drum,
The filtrate from the second drum is discharged into the second vat.

Finally, the filtrate from the second vat is sprinkled onto the mat of the first drum, and the filtrate from the first drum is discharged to a pump, which transfers a portion of the filtrate to the digester as diluted black liquor. attributed to.

Meanwhile, the remaining filtrate is fed to the aforementioned evaporator and furnace to regenerate the alkali fraction.

As previously mentioned, the only additional pure water provided in the washing step is that provided to the third drum.

Therefore, the solids content of the filtered water returned to the evaporator and furnace is primarily a function of the flow rate of the water sprayed into the third drum.

The solids content of the filtrate returned to the evaporator and furnace can thus be controlled as a function of the flow rate of the wash water sprayed onto the third drum.

DISCLOSURE OF THE INVENTION According to the present invention, the flow rate of wash water applied to the third drum is controlled to maintain a constant desired liquid-to-solids ratio of the black liquor returned to the evaporator.

In the embodiment of the invention shown here, pure water is sprayed into the third drum at a rate controlled by the operator, while white water from the concentrator controls the liquid-to-solids ratio of the recycled black liquor. controlled for.

However, the pure water and white water may be controlled in the opposite manner to the above, and when only one washing machine is used, it is controlled in this way.

A set of simultaneous equations was programmed to solve a test value of the washer flow rate such that the filtrate returned to the evaporator had the expected solids concentration in the filtrate tank for the first drum at steady state. Control is preferably performed by a multi-purpose computer.

Change the test value of the washer flow rate to a larger value little by little,
The calculation is repeated about 5 times.

This test value signal is such that the difference between the predicted solids content of the filtrate tank of the first drum and the desired solids content of that filtrate tank becomes progressively smaller, and is It has a size that changes the sign of .

As this difference changes sign, a linear interpolation method is used to calculate the washer flow rate corresponding to the desired solids content in the filtrate tank of the first drum.

From this washer flow rate value, the desired ratio of water flow rate to solids content is calculated.

The calculated ratio is held within certain limits, and the change in the ratio from one calculation to the next is held within certain limits.

Control of the white water flow rate into the third drum white water washer is based on the desired measurement of the storage flow rate into the knotter and the storage consistency into the knotter to calculate the desired total washer flow rate. This is done by a subloop that uses the ratio as an input.

The desired white water washer flow rate is the total desired washer flow rate minus the measured pure water washer flow rate determined by the operator.

When the set point controller is switched to the computer position, the computer provides an output that corrects the actual white water washer flow rate to equal the desired white water washer flow rate every minute, if necessary.

The calculation of the desired ratio is performed by the operator entering hourly values of the measured solids content in the first washer vat and the measured solids content in the first filtrate tank, and then During the hour, the calculation of the ratio is performed every 10 minutes.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and particularly to FIG. 1, the illustrated system includes a continuous digester 10 in which the pulp flows to a broken knock 12 and then to a knock 14.

This pulp enters the first v1 of the washer itself from the knock 14 via a flow meter 16, a consistency meter 18 and a valve 20.

Inside the vat V1 is a rotating drum D1 having a sieve on its outer periphery.

The drum D1 rotates with its peripheral portion immersed in the pulp inside the bat.

When the drum D1 rotates, the filtrate that has passed through the sieve passes through the conduit 22 by gravity to the first filtrate tank FL1.
fall into.

This creates a vacuum in the drum D1 which draws the black liquor in the pulp through the sieve around the drum and down into the conduit 22.

As is common practice, when the drum makes approximately half a revolution around its periphery, the pulp is scraped off by a scraper 24, and this pulp is then transferred to a second drum D2 within which the drum is rotated. Fall into the butt.

The pulp around the drum D2 is scraped off by the scraper 26 in the same way as the pulp around the drum D1, and the pulp around the drum D2 is scraped off by the scraper 26.
Bat with 3 ■ Falls within 3.

The filtrate passing through the sieve of drum D2 is transferred to conduit 2 by gravity.
8 to the second filtrate tank FL2, and the filtrate passing through the sieve of drum D3 flows via conduit 30 to the third filtrate tank FL3.

The pulp around the drum D3 is scraped by a scraper 32 and enters a collection tank 34 from where it goes to the next processing unit, such as a continuous bleaching plant.

The filtrate in the third filtrate tank FL3 is controlled by a level controller 38 and transferred by a pump 36 to a spreader 40, where it is spread around the drum D2.

Similarly, the filtrate from the second filtrate tank FL2 is controlled by a level controller 44 and is transferred to the sprayer 4 by a pump 42.
6, where it is spread around drum D.

The filtrate in the first filtrate tank FL1 is directly returned to the digester 10 by the pump 48 as diluted black liquor.

On the other hand, the excess filtrate in the first filtrate tank FL1 is returned directly to the digester 10 as diluted black liquor, which is not sold in mass quantities, and is saved as a drip pan by a pump 50 controlled by a level controller 51. ) is transferred to tank 52.

Finally, the filtrate in this save-all tank 52 is controlled by a level controller 56 and flows through a valve 54 to an evaporator and furnace 58 where the alkaline value is regenerated before being fed to the digester 10. Mixed with chips (wood chips).

As explained above, it is desirable to maintain a predetermined solid content ratio of the black liquor flowing from the first filtrate tank FL1 to the evaporator and furnace 58.

That is, if the black liquor contains too much water, too much heat will be required to evaporate it before it is combusted in order to regenerate the alkaline value.

Water in conduit 60 leading to first spreader 66 via flow meter 62 and valve 64 is spread around drum D3.

Valve 64 is controlled by a flow control device 68, the set point of which is manually set by the operator in the embodiment of the invention shown. It flows through the meter 72 and valve 74 to the second spreader 76 .

Valve 74 is controlled by flow controller T8.

However, the set point of this flow controller is determined by the output from a computer, generally designated 80, which controls the flow of white liquor to the second spreader 76 in accordance with the control system of the present invention.

Thus, in the embodiment of the invention described herein, the first
Although the water sprayed by the sprayer 66 remains approximately constant, the flow rate of the white liquor sprayed by the second sprayer 76 is such that the solid content ratio of the black liquor that is returned to the evaporator and the furnace 58 is maintained constant. can be changed to

However, the flow rate of water in conduit 60 may also be controlled by said computer, or the water may be replenished only once, in which case this single replenishment is controlled by computer 80. You will find that it will be done.

The system in Figure 1 has 5 areas: 1, 1; 1, 2; 1.3; 1
, 4; and 1, 5.

These include the various flow rates, consistency, solids content and flow rate at various points in the system, designated by the letter "F" and measured in gallons per minute.

Consistency is designated by the letter "C" and is measured in percent by weight.

Solids content is represented by the letter “S” and is expressed in pounds (solids)/
Measured in pounds (solution).

In this way, the flow rate of the broken tank 12 is F1*1s
The flow rate from the knotter 14 is F.

2. The flow rate to the sprayer 46 is expressed as F2.2. The flow rate to the sprayer 40 is expressed as F2.3.

Three tacho generators or pulse generators T1.
F2. and three drums D1 derived from each of F3
．． The speeds of D2 and D3 are provided to computer 80 as input electrical signals.

In addition, the knock-14 determined by the flow meter 16
The pulp consistency C ( determined by the flow rate F (1, 2) and the consistency meter 18 from
1, 2) are also applied to the computer 80.

The flow rate of water in conduit 60 leading out from flow meter 62, together with the flow rate of white liquor in conduit 70 leading out from flow meter 72,
It is given to the computer 80.

The computer output from lead 82 is the set point signal for flow controller 18.

In accordance with this invention, the model used to calculate the solids content of the solutions in the various parts of the system requires the following inputs:

P-knotter flow rate F1.2 and consistency C
S3. for 177 days with the pulp flow rate calculated from 1 and 2. ．． - the solids content of the first vat (2), which is determined manually by the operator once every hour and entered by the lead 84 into the computer 80;

84.2 - Solids content of first filtrate tank FL1, also determined manually by the operator and entered into computer 80 by lead 86 once every hour.

N2. N3 and N4 - tachometer T0. T2 and F
Drum D1: R at the speed of D2 and D3, PlM C1°2 - weight percent at the consistency of the first batt 1, which is calculated as described below.

C1,3 and C1,4 - Weight percentage in consistency of second vat 2 and third vat 3, which is calculated from the consistency of the first vat and the vat yield as described below. .

C3°2 s C3,3 and C3,4 - Drum D1.
The mud consistencies of D2 and D3 are produced experimentally and entered into computer 80 by lead 88.

F2.4 and F2. , -a is the flow rate of water sent to the purifiers 76 and 66, respectively, and exits from the flowmeters 72 and 62.

The unit is gallons/minute. S2.4 and S2. , - the solids content in pounds per gallon of the liquids sent to the washers 76 and 66, respectively, which are determined by the computer 8 by the lead 90.
It is an experimentally derived constant that is set to 0.

The conditions to which the pulp is subjected as it passes through the washer are believed to be the primary factor in determining the solids content of the solutions in the various parts of the system.

In this cleaning area, the two important cleaning mechanisms are the same.

The first of these is the thorough mixing that occurs at the outer surface of the mat between a certain amount of cleaning liquid and the solution collected in the pulp.

The second mechanism is that the actual solution collected in the pulp is continuously replaced by a constant volume by adding wash liquid.

This displacement occurs particularly towards the inner surface of the mat.

Assume that these two mechanisms operate and that a distribution of their effects is created, and that this distribution is simulated by carefully chosen coefficients that are entered into a mathematical model.

The assumption is that the washing liquid supplied to 1 pound of pulp is 1
This is particularly confirmed by the fact that the solids content in the solution collected in the pulp of the pound is greater than the solid content in the solution collected in the pulp.

Therefore, the process must not only be a process of displacement of solution and solids, but also a process combined with mixing, if the data are correct.

The cleaning theory can be understood by considering FIG.

The washer in Fig. 2 rotates at Nr pm and P pump 1
Consider that the washer receives a flow rate of F2 lbs/min of wash liquor having a solids content of 82 lbs solids/1 lb solution.

The pulp in the vat has a consistency of 0.1 weight percent, and the solution solids content of this vat is S1
pounds per gallon.

The pulp coming out of the washing machine has a consistency of C3, and the solid content in the solution together with this pulp is S.
It is 3.

Furthermore, C3 remains approximately constant while the pulp is on the sieve mesh, so it is believed that both the weight and volume of solution collected with the pulp remain constant over this time.

First, let us consider the case of complete mixing in a constant volume.

The amount of washing fluid F2 used per minute for one pound of pulp is:
F22F'! /P ・・・・・・(
1) Here, F'2 is the amount of cleaning solution used for P-bond pulp per minute, and F3 is the amount of solution collected in one pound of pulp and in this pulp. First, considering the vat, Volume F3 of solution with solids content S1
is subjected to an increment ΔF of wash liquid with solids content S2.

The new mixture has a solids content S.

Considering the solid content balance: F3S1+ΔF-82=(
F3+ΔF)S-F3S+ΔF・S Then ΔF・(82
5)=Fs (S S,)=F3・△S-F2 subordinate-, 82 S3-(S, St).../F
・-FV'F3 i.e. %S3282+(81-82)・e...
-(3) Now consider 1 pound of pulp that collects the total amount of liquid F3.

K, K3 is the amount of this liquid that has undergone the mixing operation,
And (1-Kl)·K3 is the quantity subjected to the substitution operation.

Here, 1 is a value between O and 1, and this is called the mixing ratio.

S'3 is the amount of mixed liquid leaving the washer in this mixing zone, 1・F.
Let's assume the solids content is 3.

Then s%=s2+ (sl-82)e (4) Equation (4) also gives the solids content of the liquid entering the displacement zone such that F2 increases.

If equation (4) is changed to F22F2(total)・−(IK
By integrating over the interval I)·F3, the total solid content in the substitution region can be obtained.

To obtain a final solids content of 83F, (4), (5
), the solids content at the bottom of the washer is smaller than the solids content when exiting the sieve mesh, so multiply F3 by 3 to a factor close to 1.1.

To adjust the thickness, multiply 1 by a factor calculated by the following formula.

E--E-ni, 4-shi 1 1 2 P Here, is the coefficient.

N1 is the speed of the drum, P is the pulp flow rate, and N1/P
is the amount of filtask carbon, ie, the thickness of the pulp mat on the face of the drum.

This means that as the speed increases for a given pulp flow rate, the thickness of the mat decreases and the mixing effect increases.

On the other hand, if the pulp flow rate increases at a given speed,
The thickness of the mat increases and the mixing effect decreases.

In equation (6), if we set '1' and F3 as 3F3, (6) becomes as follows.

83F-82 ten'1 (Sl-82)・e, that is, 8
3F=820′,・(st 82)・f (M)・
(7A) Next, consider a washing machine 66 that is moved by a car.

Let F2.4 and S2.4 be the flow rate (in pounds) of the washing water sent to the washer 76 and the solids content (in pounds), respectively.

F2. , and S2.5 are the flow rate (in pounds) of the washing water sent to the washer 66 and the solids content (in pounds), respectively.

83.4 is the solid content in the pulp liquid in the mixing zone at the boundary between these two washers, and S3. Let , be the solids content in the pulp liquor exiting the third washer.

Instead of equation (4), it can be written as follows.

F2.4 to'1・F3 83.4= 82.4 + (81,4-82,4)
e -” (8) F2.5 < (I KS
)・Let's assume F3.

If this is not corrected, only the displacement below the washer 66 needs to be considered.

During the period when the main washer is working, the solids flow rate inserted into the displacement zone is F2.4 and F2.4 + F2.5- (
It is obtained by the integral equation (8) in the interval I K'l )·F3.

That is, here, if F2. , <(1-to'1), then equation (8A) must be integrated between the limits F2.5 and O.

If this does not hold, then F2. . and “2.5 (
I K't ) must be integrated over the interval with Ps.

Considering the first case, we add the equation (9X10) and αυ and divide by F3, then the following formula%Proof: S2.4" 82.5 and 82.4 = 82°,
By substituting =-iF, equation (6) is obtained.

If F2.5>(1-to'1)・F3, set the limit of equation (IOA) to F2. , and F2.5(I
K'1) By replacing F3, the following equation is obtained.

Adding equations (9) and (13) and dividing by F3, this equation becomes equation (6) as before if it is proven that the same cleaning liquid is divided into two washers.

The following points must be noted.

(a) The flow rate entering each washer is a function of the solids content of the vat.

(b) The flow rate entering each vat is equal to the total inflow minus the flow rate collected by the pulp coming from the immediately preceding vat.

(c) All solids in the liquid circulating from the filtrate tank FL1 to the digester returns to the first vat.

The objective now is to create seven simultaneous equations for the seven unknown solids contents with unique solutions obtained by matrix transposition and multiplication.

Let us assume for a moment that the net liquid flow rate F l-1 downstream of the digester from the pulp extraction zone to the blow zone is calculated by the flow equilibrium around the bottom of the digester.

Flow rate downstream of digester: Ft, t Here, 8.34 is the number of pounds per gallon of water.

Also, in some installations, additional liquor is added before the knotter so that the total volume going to the knotter is not equal to that calculated from the consistency of the pulp leaving the blow tank.
Between the extraction zone and the blowing zone, the solids content of the first vat containing the additional solution volume notter is 83.1 and the solids content of the diluted black liquor to the first filtrate tank is 84.2. The solids content of the solution downstream of the digester S1. , is calculated as follows.

This calculation considers solid content balance and S2. ,=S4.
2, that is, F3.1・s3. , F2.1・S4.2F
1. You can do this if you know S.

Given the consistency C12 of the first vat ■1 and calculating the consistency of vats ■2 and ■3, the consistency of the second vat ■2: C1,3-C2,2+ is 7×pulp Consistency of production amount 3rd vat ■3: Cl-4-C1,2+ KB・×Pulp production amount For each washing machine, the flow rate of washing liquid at the entrance to the main washing machine of the 3rd washing machine, F2.4 and Cleaning liquid flow rate F2 to the washer 66 of the third washer. , are both known.

Therefore, the following order from the third washer is expressed as follows.

F4.4=F,,,+F2,4+F2. ．． -F3.4F
2.3-F4.4 Fl, 44F3.3F4.3”F
l, 3+F2.3 F3.3F2,2”F4.3
Fl, 3+F3.2F4,2-Fl, 2+F2.2
The formula for F3.2 washer solid content is derived as follows, where the above ■ is 2 or 3 depending on the washer 1 or 2.

Considering a washer vat, the solids balance is expressed as:

FII"5II=F3-I-・s3.I-1+(FI
I-F3 I-1) "SKI..."
The solid content balance of the entire bag is given by the following formula.

FtI・SII"F2I"52I-F, 9I-s3□
- F4
Remembering F s-I:1・S3. I-1+(FI I
Fa I-t)・S4I+F2l54-I◆t
F3IS3I F4IS4I=0 Then F3-I-1
・83-)1+(Fl□-Fs-I-tF4I)S4I
F3IS3I+F2l54. I+1=0・・・・・・
・(17) Next, let's consider cleaning with a washing machine.

From (7), the right-hand side of this equation (22) is known, as are all of the flow rates on the left-hand side, and only 833? 844
and 835 are unknown.

From the solution of these simultaneous equations, the total washer flow rate (82,4+
82.5) is calculated, and the total fiber (pulp) flow rate Fib is calculated from:

F□b=F1.2×C1□X8.34 lb/min From this, the ratio of washer flow rate to fiber flow rate is calculated by the following equation.

F2,4+F2. , -RXFi,XK Here, R is a ratio, and K is a conversion constant.

Using the calculated values of this ratio R and Fib, which are calculated once per hour, the total washer flow rate can be calculated once per minute.

Since the flow rate to the washer 66 is kept constant, the flow rate to the washer 76, which is changed once per minute, is calculated from the following equation.

F2,4= (F2.4 +F2.5) F2.5
This F2.4 is then the set point signal applied to the flow controller 78 which maintains the total washer flow rate to obtain the desired solids ratio of the black liquor returned to the digester.

Effects As mentioned above, this invention filters the black liquor in the pulp by the washer and returns it to the evaporator and recovery furnace (alkaline value regeneration) in order to keep the concentration of the black liquor constant. The dilution water that is sprayed is controlled by a computer, and this computer controls the flow rate and concentration of the pulp liquid entering the washer, the rotation speed of the drum, and the raw material concentration of the filtered water at the outlet of the washer.

Using the actual flow rate of cleaning water sprayed onto the drum as input, the flow rate of the cleaning water is determined, and the effect is that optimal control can be performed so that the ratio of water to raw material in the black liquor is constant.

[Brief explanation of drawings]

Figure 1 is an overall schematic illustration of a drum-type vacuum pulp washer showing its connection to a computer to control the solids content of the black liquor; Figure 2 is used here to explain the cleaning theory. FIG. 3 is a table showing a complete simultaneous equation matrix used for the control of the present invention. In Figure 1, the drum on which cleaning water is sprayed...
D3, Drum where the filtrate is sprayed...Dl, D
2. Device/song for creating electrical signals proportional to pulp flow rate and consistency 16, 18. A device that generates an electric signal proportional to the rotational speed of the drum...T1°F2. F3. A device that generates an electrical signal proportional to the solid content of the filtrate...86. A device that generates an electrical signal proportional to the flow rate of washing water...62. Responds to all electrical signals. Equipment for...80°

Claims (1)

[Claims] 1. In the controller of a continuous drum type vacuum pulp washer of the type in which the wash water is sprayed on a drum and the filtrate is sprayed on at least one other drum, the flow rate of pulp flowing into this washer and the controller are controlled. a device for generating electrical signals proportional to the respective rotational speeds of said drums, and a device for generating electrical signals proportional to the measured solids content of the filtrate exiting said washer; a device for producing an electrical signal proportional to the measured solids content of pulp entering the washer; a device for producing at least one electrical signal proportional to the flow rate of wash water applied to the drum; and a plurality of calculates a desired flow rate of wash water to be sprayed on the drum in response to all of the electrical signals of A control device for a pulp washing machine, which is equipped with a device for controlling the desired ratio.