JP5281998B2 - Load following operation method of fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high electric power generation efficiency by carrying out sure reforming at the time of an FC system load following operation. <P>SOLUTION: Two or more (i) reforming methods are determined, and Gi<SB>k</SB>corresponding to the maximum Ti<SB>k</SB>is adopted as Fi<SP>R</SP>. Pi<SP>*</SP>=P<SB>D</SB>and Fi<SP>*</SP>=Fi<SB>DS</SB>are settled at the time of Fi<SB>DS</SB>&le;Fi<SP>R</SP>, when P<SB>D</SB>&le;Pi<SB>Mi</SB>, in the case where the "i" bringing Fi<SP>R</SP>&ge;Fi<SB>min</SB>exists, Pi<SP>*</SP>=(maximum value of Pi<SB>j</SB>) and Fi<SP>*</SP>=(Fi<SB>j</SB>corresponding to Pi<SP>*</SP>) are settled at the time of Fi<SB>DS</SB>&gt;Fi<SP>R</SP>, when Pi<SB>j</SB>less than P<SB>D</SB>and corresponding to Fi<SB>j</SB>less than Fi<SP>R</SP>or less exists, and Pi<SP>*</SP>=0 and Fi<SP>*</SP>=Fi<SP>R</SP>are settled when not existing; Pi<SB>Mi</SB>=Pi<SB>Mi</SB>and Fi<SP>*</SP>=Fi<SB>Mi</SB>are settled at the time of Fi<SB>Mi</SB>&le;Fi<SP>R</SP>, when P<SB>D</SB>&gt;Pi<SB>Mi</SB>, and Pi<SP>*</SP>=(maximum value of Pi<SB>j</SB>corresponding to Fi<SB>j</SB>of Fi<SP>R</SP>or less), and Fi<SP>*</SP>=(Fi<SB>j</SB>corresponding to Pi<SP>*</SP>), are settled at the time of Fi<SB>Mi</SB>&gt;Fi<SP>R</SP>. Pi<SP>*</SP>, the reforming method and Fi<SP>*</SP>as to the "i" bringing &eta;i corresponding to Pi<SP>*</SP>into the maximum are adopted when the plurality of "i"s bringing Fi<SP>R</SP>&ge;Fi<SB>min</SB>exist. Fi<SP>R</SP>or the like is defined separately. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a load following operation method for a fuel cell system that generates power using a reformed gas obtained by reforming a hydrocarbon fuel such as kerosene.

  Solid oxide electrolyte fuel cell (Solid Oxide Fuel Cell, hereinafter referred to as SOFC in some cases) systems typically reform hydrocarbon-based fuels such as kerosene and city gas to produce hydrogen-containing gas (reformed gas). A reformer for generating and SOFC for electrochemically generating and reacting reformed gas and air are included.

  The SOFC is usually operated at a high temperature of 550 to 1000 ° C.

  Various reactions such as steam reforming (SR), partial oxidation reforming (POX), and autothermal reforming (ATR) are used for reforming, but in order to use a reforming catalyst, catalytic activity is manifested. Need to be heated to temperature.

  Steam reforming is a very large endothermic reaction, and the reaction temperature is relatively high at 550 to 750 ° C., which requires a high-temperature heat source. Therefore, an internal reforming SOFC is known in which a reformer (internal reformer) is installed in the vicinity of the SOFC, and the reformer is heated mainly using radiant heat from the SOFC as a heat source (Patent Document 1).

  Further, Patent Documents 2 and 3 make proposals regarding the load following operation of the fuel cell system.

JP 2004-319420 A JP 2001-185196 A JP 2006-32262 A

  If the hydrocarbon-based fuel is not reformed to a predetermined composition and the unreformed component is supplied to the SOFC, particularly when higher hydrocarbons such as kerosene are used as the hydrocarbon-based fuel, carbon deposition may occur. It may cause flow path blockage and anode deterioration.

  The SOFC system may perform load following operation. That is, there is a case where operation is performed in which the amount of power generated by the SOFC system is changed in accordance with fluctuations in power demand. For example, when the power generation amount is increased, the supply amount of hydrocarbon fuel to the SOFC system may be increased. Even in such a case, carbon may be deposited. Therefore, it is desirable to reliably reform the hydrocarbon fuel even during load following operation. In the techniques disclosed in Patent Documents 2 and 3, improvement is still desired in that reliable reform is performed.

  Also, higher power generation efficiency is required during load following operation.

  This is true not only for SOFC but also for fuel cell systems having high-temperature fuel cells such as molten carbonate fuel cells (MCFC).

  It is an object of the present invention to perform reforming more reliably when a fuel cell system having a reformer having a reforming catalyst layer and a high-temperature fuel cell is subjected to load following operation, and to prevent channel blockage and anode deterioration. It is an object to provide a method that can be surely prevented and that can achieve higher power generation efficiency.

According to the present invention,
A fuel cell comprising a reformer having a reforming catalyst layer for producing a reformed gas containing hydrogen by reforming a hydrocarbon fuel, and a high-temperature fuel cell for generating electric power using the reformed gas A load following operation method of the system,
At least two reforming methods selected from the group consisting of steam reforming method, partial oxidation reforming method and autothermal reforming method are defined as i-th reforming method, where i is an integer of 1 or more and L or less. L is 2 or 3,
For all i, when the reformed gas produced by the i-th reforming method is supplied to the fuel cell in advance to generate electric power, it corresponds to different Mi fuel cell electrical outputs Pi _j and each Pi _j . have set up a flow rate Fi _j of the hydrocarbon-based fuel, and, to previously obtain a power generation efficiency .eta.i _j in each Pi _j,
However, j is an integer of 1 or more and Mi or less, Mi is an integer of 2 or more,
Each Fi _j is the flow rate of the corresponding electrical output Pi _j need to be supplied to the reforming catalyst layer to perform reforming method of the i to output the fuel cell of the hydrocarbon-based fuel,
Each Pi _j is greater than or equal to 0, and Pi _j increases as _j increases, and each Fi _j is greater than 0,
Pi _i which is Pi _j when _j is ₁ is 0 for all i, and Pi Mi which is Pi _j when _j is _Mi is the value of the fuel cell in the case of performing the i-th reforming method. Maximum electrical output,
In each i, it represents the minimum value of the Fi _j for all j and Fi _min,
In addition, for all i, different Ni reforming catalyst layer temperatures Ti _k and hydrocarbon-based fuel flow rates Gi _k corresponding to the respective Ti _k are set in advance.
However, k is an integer of 1 or more and Ni or less, Ni is an integer of 2 or more,
Each Gi _k is a flow rate of the hydrocarbon-based fuel that can be reformed by the i-th reforming method in the reforming catalyst layer at the corresponding reforming catalyst layer temperature Ti _k , and each Gi _k is greater than 0 and increases by k Gi _k is increased or the same value with the,
A) a step of measuring the temperature T of the reforming catalyst layer,
B) For all i, the reformable flow rate Fi ^R that is the flow rate of the hydrocarbon-based fuel that can be reformed by the i-th reforming method in the reforming catalyst layer at the temperature T is the largest below the temperature T Adopting Gi _k corresponding to Ti _k ,
C) a step of stopping power generation in the fuel cell when the reformable flow rate Fi ^R is smaller than the minimum value Fi _min for all i;
If D) at least one of i the reformable flow rate Fi ^R about is the minimum value Fi _min or more, for each of the at least one i, the fuel cell output demand value P _D is equal to or less than the maximum electrical output Pi _Mi process performs step d1, the fuel cell output demand value P _D is a step d2 if exceeds the maximum electrical output Pi _Mi long,
d1) within the Pi _j for all j, if there is equal Pi _j to the fuel cell output demand value P _D, and Fi _j) corresponding to Fi _DS = (P _D equal Pi _j,
Among the Pi _j for all j, if there is equal Pi _j to the fuel cell output demand value P _D, and Fi _j corresponding to Fi _DS = (smallest Pi _j exceeding P _D, most in less than P _D The smaller one of Fi _j corresponding to large Pi _j ),
When Fi _DS is equal to or less than the reformable flow rate Fi ^R , Pi ^* = P _D and Fi ^* = Fi _DS ,
When Fi _DS exceeds the reformable flow rate Fi ^R ,
If there is Pi _j corresponding to Fi _j below Fi ^{R in} the range below the fuel cell output requirement value P _D , Pi ^* = (P _i of Pi _j corresponding to Fi _j below Fi ^{R in} the range below P _D the maximum value of the out), and, Fi ^* = a (Fi _j corresponding to the maximum value of the Pi _j corresponding to Fi ^R following Fi _j in the range of less than P _D),
If there is no Pi _j corresponding to Fi _j below Fi ^{R in} the range less than the fuel cell output required value P _D , Pi ^* = 0 and Fi ^* = Fi ^R ,
d2) When Fi _Mi which is Fi _j corresponding to the maximum electrical output Pi _Mi is equal to or less than the reformable flow rate Fi ^R , Pi ^* = Pi _Mi and Fi ^* = Fi _Mi ,
When Fi _Mi that is Fi _j corresponding to the maximum electrical output Pi _Mi exceeds the reformable flow rate Fi ^R , Pi ^* = (maximum value among Pi _j corresponding to Fi _j less than or equal to Fi ^R ) and, Fi ^* = step to (Fi _j corresponding to the maximum value of the Pi _j corresponding to Fi ^R following Fi _j),
E) When there are two or more i at which the reformable flow rate Fi ^R becomes the minimum value Fi _min or more, ηi corresponding to Pi ^* is obtained for each of the two or more i, and the most of the obtained ηi I that gives a large ηi is represented as I,
If PI ^* is zero, stop power generation in the fuel cell,
When PI ^* exceeds zero, the electric output of the fuel cell is PI ^* , the reforming method performed by the reformer is the first reforming method, and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is FI. ^The process ^*
F) When there is only one i at which the reformable flow rate Fi ^R is not less than the minimum value Fi _min , this only i is represented as I
If PI ^* is zero, stop power generation in the fuel cell,
When PI ^* exceeds zero, the electric output of the fuel cell is PI ^* , the reforming method performed by the reformer is the first reforming method, and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is FI. ^The process ^*
A load following operation method for a fuel cell system is provided.

  The steps A to F can be repeated during the load following operation.

  The hydrocarbon fuel may include a hydrocarbon fuel having 2 or more carbon atoms.

  In this case, the concentration of the compound having 2 or more carbon atoms in the reformed gas is preferably 50 ppb or less on a mass basis.

  According to the present invention, when a fuel cell system having a reformer having a reforming catalyst layer and a high-temperature fuel cell is subjected to load following operation, reforming is performed more reliably, and channel blockage and anode deterioration are more reliably performed. There is provided a method that can be prevented and that can achieve higher power generation efficiency.

It is a schematic diagram which shows an outline | summary about the example of the indirect internal reforming type | mold SOFC system which can implement this invention. It is a flowchart for demonstrating the method of this invention.

  The fuel cell system used in the present invention includes a reformer that reforms a hydrocarbon-based fuel to produce a hydrogen-containing gas, and a high-temperature fuel cell. The reformer has a reforming catalyst layer. The hydrogen-containing gas obtained from the reformer is called reformed gas. The reforming catalyst layer is composed of a reforming catalyst that can promote the reforming reaction. A high-temperature fuel cell generates power using a hydrogen-containing gas (reformed gas) obtained from a reformer.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

[Indirect internal reforming SOFC]
FIG. 1 schematically shows an embodiment of an indirect internal reforming SOFC that can implement the present invention. Here, an indirect internal reforming SOFC system will be described, but the present invention can also be applied to an external reforming SOFC system or MCFC system.

  The indirect internal reforming SOFC has a reformer 3 that reforms a hydrocarbon-based fuel to produce a reformed gas (hydrogen-containing gas). The reformer has a reforming catalyst layer 4.

  The indirect internal reforming SOFC has an SOFC 6 that generates electric power using the reformed gas, and also has a combustion region 5 in which anode off-gas discharged from the SOFC (particularly its anode) is combusted.

  The indirect internal reforming SOFC has a housing 8 that houses a reformer, a solid oxide fuel cell, and a combustion region.

  The indirect internal reforming SOFC refers to a casing (module container) 8 and equipment included therein.

  In the indirect internal reforming SOFC of the form shown in FIG. 1, an igniter 7 that is an ignition means for igniting the anode off gas is provided, and the reformer includes an electric heater 9.

  Each supply gas is appropriately preheated as necessary and then supplied to the reformer or SOFC.

  A water vaporizer 1 including an electric heater 2 is connected to the indirect internal reforming SOFC, and a pipe for supplying hydrocarbon fuel to the reformer is connected in the middle of the connecting pipe. The water vaporizer 1 generates water vapor by heating with the electric heater 2. Water vapor can be superheated appropriately in the water vaporizer or downstream thereof and then supplied to the reforming catalyst layer.

  Air (for partial oxidation reforming reaction) can also be supplied to the reforming catalyst layer, but here, air can be supplied to the reforming catalyst layer after preheating with a water vaporizer. Water vapor can be obtained from the water vaporizer, and a mixed gas of air and water vapor can be obtained.

  Steam or a mixed gas of air and steam is mixed with a hydrocarbon fuel and supplied to the reformer 3, particularly the reforming catalyst layer 4. When liquid fuel such as kerosene is used as the hydrocarbon-based fuel, the hydrocarbon-based fuel can be appropriately vaporized and then supplied to the reforming catalyst layer.

  The reformed gas obtained from the reformer is supplied to the SOFC 6, particularly to the anode thereof. Although not shown, air is appropriately preheated and supplied to the SOFC cathode.

  The combustible component in the anode off gas (gas discharged from the anode) is burned by oxygen in the cathode off gas (gas discharged from the cathode) at the SOFC outlet. For this purpose, ignition can be performed using the igniter 7. The outlets of both the anode and the cathode are opened in the module container 8. The combustion gas is appropriately discharged from the module container.

  The reformer and SOFC are accommodated in one module container and modularized. The reformer is disposed at a position where heat can be received from the SOFC. For example, if the reformer is disposed at a position where it receives heat radiation from the SOFC, the reformer is heated by heat radiation from the SOFC during power generation.

  In the indirect internal reforming SOFC, the reformer is preferably arranged at a position where direct heat transfer from the SOFC to the outer surface of the reformer is possible. Therefore, it is preferable that a shielding object is not substantially disposed between the reformer and the SOFC, that is, a gap is provided between the reformer and the SOFC. Further, it is preferable to shorten the distance between the reformer and the SOFC as much as possible.

  The reformer 3 is heated by the combustion heat of the anode off gas generated in the combustion region 5. Further, when the SOFC is at a higher temperature than the reformer, the reformer is also heated by radiant heat from the SOFC.

  Furthermore, the reformer may be heated by heat generated by reforming. If the reforming is partial oxidation reforming or autothermal reforming (autothermal reforming) and the heat generation by the partial oxidation reforming reaction is greater than the endothermic reaction by the steam reforming reaction, Fever accompanies.

(Load following operation method)
According to the present invention, an appropriate flow rate of hydrocarbon fuel (supply flow rate to the reformer) and an electric output of the fuel cell are selected in order to surely perform reforming, and higher power generation efficiency is obtained. An appropriate reforming method can be selected. The procedure will be described in detail below.

[I-th modification method]
In the present invention, at least two reforming methods selected from the group consisting of a steam reforming method (SR), a partial oxidation reforming method (POX), and an autothermal reforming method () ATR are used as the i-th reforming method. Determine. However, i is an integer of 1 or more and L or less, and L is 2 or 3. When two kinds of reforming methods are selected (when L = 2), the first reforming method and the second reforming method are determined as the i-th reforming method. When three types of reforming methods are selected (when L = 3), the first, second, and third reforming methods are determined as the i-th reforming method. When i = 2, for example, SR is selected as the first reforming method and ATR is selected as the second reforming method. ATR may be selected as the first reforming method, and SR may be selected as the second reforming method. When i = 3, for example, SR is selected as the first reforming method, ATR is selected as the second reforming method, and POX is selected as the third reforming method.

[Pi _j, Fi _j and ηi corresponding to Pi _j]
In the present invention, for all i, when the reformed gas produced by the i-th reforming method is supplied to the fuel cell in advance to generate power, Mi different fuel cell electrical outputs Pi _j (j is 1). or Mi an integer, provided Mi and is an integer of 2 or more), and a flow rate Fi _j of the hydrocarbon-based fuel corresponding to each Pi _j, is set. Also, previously obtained the power generation efficiency .eta.i _j in each Pi _j.

Each Fi _j is a hydrocarbon that needs to be supplied to the reforming catalyst layer in order to output the corresponding electric output Pi _j by the fuel cell when the i-th reforming method is performed in the reforming catalyst layer. This is the flow rate of the system fuel. For example, so that even as much as possible the power generation efficiency increases while maintaining the SOFC preferably the temperature at which electricity can be generated, due preliminary experiment or simulation, by predetermining the current and the fuel utilization rate for each Pi _j, each Pi _j it is possible to set the flow rate Fi _j of the corresponding hydrocarbon fuel. At this time, at the same time, it is possible to obtain a power generation efficiency .eta.i _j in each Pi _j.

Each Pi _j is 0 or more. In other words, for all i and j, is 0 ≦ Pi _j. Pi _j increases as _j increases. That is, Pi _j <Pi _{j + 1} (where j is an integer from 1 to Mi−1).

Furthermore, each _Fij is greater than zero. That is, 0 <Fi _j for all i and j.

For all i, Pi ₁ which is Pi _j when _j is ₁ is 0, and Pi _j (ie Pi _Mi ) when j is Mi is the i-th reforming in the reforming catalyst layer. This is the maximum electrical output of the fuel cell when the method is used. Pi _Mi is predetermined as a specification of the fuel cell system.

In each i, it represents the minimum value Fi _min of Fi _j for all j, the maximum value and Fi _max. That is, if a i is given, indicating the among Fi _j for all j, the minimum value Fi _min, the maximum value and Fi _max.

  From the viewpoint of power generation efficiency, Mi is preferably as large as possible within the allowable range of the memory of the control means.

[Ti _k and Gi _k corresponding to Ti _k]
Furthermore, for all i, different Ni reforming catalyst layer temperatures Ti _k (k is an integer of 1 or more and Ni or less, where Ni is an integer of 2 or more) and hydrocarbon systems corresponding to each Ti _k. and the flow rate Gi _k of fuel, setting the.

However, a flow rate of each Gi _k is the corresponding reforming hydrocarbon-based fuel that can be by reforming method of the i in the reforming catalyst layer in the reforming catalyst layer temperature Ti _k.

Each Gi _k is greater than zero. This means that for all i and k is 0 <Gi _k. Further, Gi _k is the same value or increases as _k increases. That is, Gi _k ≦ G _{i k} +1 (here, k is an integer from 1 to Ni−1).

Note that Gi _k (Gi _Ni ) when k is Ni is equal to or greater than Fi _max . That is, Gi _Ni ≧ Fi _max . Gi _Ni is the flow rate of the hydrocarbon-based fuel that can be reformed by the i-th reforming method in the assumed maximum temperature reforming catalyst layer, that is, the maximum value of the reformable hydrocarbon-based fuel. If Gi _Ni <Fi _max , the hydrocarbon-based fuel having a flow rate of Fi _max cannot be reformed, so the fuel cell system is naturally designed to satisfy Gi _Ni ≧ Fi _max .

[Operation conditions other than fuel flow and fuel cell electrical output]
Also, for each of the reforming process, if necessary, in advance, in correspondence with each Pi _j, the flow rate of the fluid supplied to the indirect internal reforming SOFC, other than the hydrocarbon-based fuel, indirect other than the output of the fuel cell Input / output of electricity to the internal reforming SOFC can be set in advance. For example, with respect to the flow rate of water supplied to the reformer, a steam / carbon ratio (ratio of the number of moles of water molecules to the number of moles of carbon atoms in the gas supplied to the reforming catalyst layer) is predetermined in order to suppress carbon precipitation. It can be set to be a value. The air flow rate supplied to the reformer is set so that the oxygen / carbon ratio (ratio of the number of moles of oxygen molecules to the number of moles of carbon atoms in the gas supplied to the reforming catalyst layer) becomes a predetermined value. be able to. Regarding the flow rate of the fluid supplied to the indirect internal reforming SOFC other than water and air supplied to the reformer and the input / output of electricity to the indirect internal reforming SOFC, the SOFC is preferably maintained at a temperature at which power can be generated. However, it can be set by preliminary experiments or simulations so that the power generation efficiency is as high as possible. In this way, when the output of the fuel cell is set to a certain value P, these flow rates and electrical input / output can be determined using a function obtained in advance.

  Alternatively, the flow rate of the fluid supplied to the indirect internal reforming SOFC other than the hydrocarbon fuel and the input / output of electricity to the indirect internal reforming SOFC other than the output of the fuel cell are used as a function of the flow rate of the hydrocarbon fuel. be able to. For example, the flow rate of water supplied to the reformer can be set to a flow rate at which the steam / carbon ratio becomes a constant value in order to suppress carbon deposition. The air flow rate supplied to the reformer can be a flow rate at which the oxygen / carbon ratio becomes a constant value.

  Alternatively, the flow rate of the fluid supplied to the indirect internal reforming SOFC other than the hydrocarbon fuel and the input / output of electricity to the indirect internal reforming SOFC other than the output of the fuel cell are appropriately controlled according to the control purpose. The value can be obtained by a technique.

  For example, the flow rate of air supplied to the cathode can be set so that the SOFC can be maintained at a temperature that can preferably generate power.

  The output of the electric heater attached to the reformer can be set so that the reforming catalyst layer can be maintained at a predetermined temperature (for example, the reforming catalyst layer can be maintained at a temperature preferable for reforming).

  When a catalyst layer heating burner is attached to the reformer, the fuel flow rate can be set so that the reforming catalyst layer can be maintained at a predetermined temperature, and the air ratio is set to a predetermined value ( For example, the flow rate can be a value preferable for combustion.

  The output of the electric heater attached to the vaporizer can be set so that the steam can be maintained at a predetermined temperature (for example, the steam temperature at the reformer inlet can be maintained at a temperature preferable for reforming).

  When a heating burner is attached to the vaporizer, the fuel flow rate can be set so that the steam can be maintained at a predetermined temperature, and the air flow rate should be a flow rate at which the air ratio becomes a predetermined value. it can.

  When a heating burner is attached in the vicinity of the SOFC, the fuel flow rate can be set so that the SOFC can be maintained at a temperature that can preferably generate power, and the air flow rate is a flow rate at which the air ratio becomes a predetermined value. be able to.

  When the SOFC cooling heat exchanger is arranged in the vicinity of the SOFC, the flow rate of the cooling fluid supplied to the heat exchanger can be set so that the SOFC can be preferably maintained at a temperature at which power generation is possible.

  In the vicinity of the reforming catalyst layer closest to the SOFC, the reforming catalyst layer cooling is performed to cool the SOFC by increasing the methane concentration in the reformed gas by an equilibration reaction and causing an endothermic reaction on the anode of the SOFC. When the heat exchanger is attached, the flow rate of the cooling fluid supplied to the heat exchanger can be set so that the SOFC can be preferably maintained at a temperature at which power can be generated.

[Steps A to F]
During the load following operation, the steps A to F are preferably repeated, that is, the steps A, B, C and D and the steps E or F are repeated in this order, thereby improving the reliability more reliably. As a result, the anode can be more reliably prevented from deteriorating and higher power generation efficiency can be obtained.

  In FIG. 2, the flowchart for demonstrating process AF is shown.

[Process A]
When actually performing the load fluctuation operation, the process A for measuring the temperature of the reforming catalyst layer is performed. This measurement can be performed continuously during the load following operation.

Step A is performed in order to know the temperature T of the reforming catalyst layer used when determining the reformable flow rate Fi ^R described later. It is preferable to start the process A within the shortest possible time from the start of the load following operation. It is preferable to start the process A immediately after starting the load following operation. If the temperature of the reforming catalyst layer is monitored (continuous measurement) before the start of the load following operation, the temperature may be monitored continuously.

  For temperature measurement, an appropriate temperature sensor such as a thermocouple can be used.

[Process B]
In step B, the flow rate of the hydrocarbon-based fuel that can be reformed in the reforming catalyst layer at the temperature T (temperature measured in step A) for all i (reformable flow rate Fi ^R ) Gi _k corresponding to large Ti _k is adopted. That is, among the preset Ti _k , the largest Ti _k in the range below the measured temperature T is selected. Then, from the relationship between the Ti _k and Gi _k which is set in advance, asked the Gi _k corresponding to the selected Ti _k, to the Gi _k and reformable flow rate Fi ^R.

[Process C]
When the reformable flow rate Fi ^R obtained in step B is smaller than the minimum value Fi _min for all i, power generation in the fuel cell is stopped. That is, when Fi ^R <Fi _min for all i, it is considered that the minimum required reformed gas cannot be reformed, and the electric output of the fuel cell is set to zero. At this time, the following operations can be performed. That is, among the plurality of reforming methods determined as the i-th reforming method, the reforming method having the largest ratio of the calorific value to the endothermic amount of the reaction is adopted. The flow rate of the hydrocarbon-based fuel supplied to the reformer is set to Fi ^R for this reforming method. Then, for at least one i, the temperature of the reforming catalyst layer is raised with a heater or a burner attached to the reformer until at least Fi ^R ≧ Fi _min (Fi ^R is obtained by steps A and B). Can do. If Fi ^R ≧ Fi _min for at least one i, step D and subsequent steps can be performed.

[Process D]
For at least one i, step D is performed when the reformable flow rate Fi ^R determined in step B is equal to or greater than the minimum value Fi _min . That is, if there is at least one i that satisfies Fi ^R ≧ Fi _min , for example, if F1 ^R ≧ F1 _min , the process D is performed.

In step D, for each of the at least one i, i.e. for each i as the Fi ^R ≧ Fi _min, the fuel cell output demand value P _D, the step d1 if less than the maximum electrical output Pi _Mi of the fuel cell Do. P _D ≦ Pi _Mi is considered to mean that the fuel cell output required value P _D means that the fuel cell can output when the i-th reforming method is performed in the reformer.

Alternatively, for each of the at least one i, i.e. for each i as the Fi ^R ≧ Fi _min, the fuel cell output demand value P _D, the step d2 if exceeds the maximum electrical output Pi _Mi of the fuel cell . P _D > Pi _Mi is considered to mean that the electric output of the fuel cell is insufficient with respect to the required fuel cell output value P _D when the i-th reforming method is performed in the reformer.

<Step d1>
In step d1, first, a value of Fi _DS is obtained for further determination. Here, Fi _DS is determined in order to determine the reforming whether the safe side, with a sense that the flow rate of the hydrocarbon-based fuel that corresponds to Pi _j close to the fuel cell output demand value P _D.

Among the Pi _j for all j, see if there is equal Pi _j to the fuel cell output demand value P _D.

If there is equal Pi _j to P _D, using the correspondence relationship between Pi _j and Fi _j that is set in advance, obtains the Pi _j (= P _D) corresponding to Fi _j, the value of the Fi _j Is substituted into Fi _DS . In the following, when obtaining the Pi _j corresponding to Fi _j and Fi _j corresponding to Pi _j uses the correspondence between the predetermined Pi _j and Fi _j.

Among the Pi _j for all j, if there is equal Pi _j to P _D, to determine reforming whether safer side, and Fi _j corresponding to "the smallest Pi _j exceeding P _D", " Of Fi _j corresponding to “the largest Pi _j less than P _D ”, the larger one (if these two values are equal, the value thereof) is defined as Fi _DS .

Next, this Fi _DS is compared with the calculated reformable flow rate Fi ^R.

When Fi _DS ≦ Fi ^R When Fi _DS is equal to or less than the reformable flow rate Fi ^R , Pi ^* = P _D and Fi ^* = Fi _DS . Fi _DS ≦ Fi ^R is considered to mean that the hydrocarbon-based fuel having the flow rate Fi _DS can be reformed in the reforming catalyst layer when the i-th reforming method is performed in the reformer.

Pi ^* and Fi ^* are variables that are candidates for the electric output of the fuel cell to be finally set and the supply flow rate to the hydrocarbon-based fuel reformer, respectively.

When Fi _DS > Fi ^R When Fi _DS exceeds the reformable flow rate Fi ^R , the following step (1) or (2) is performed. Fi _DS > Fi ^R is considered to mean that the hydrocarbon-based fuel having the flow rate Fi _DS cannot be completely reformed in the reforming catalyst layer.

(1) When Pi _j corresponding to Fi _j equal to or less than Fi ^R exists in a range less than the fuel cell output requirement value P _{D In} this case, PI ^* = P _{i j} (Fi less than P _{D and} less than Fi ^R). _Let the maximum value of Pi _j ) corresponding to _j , FI ^* = (Fi _j corresponding to this maximum value).

(2) When Pi _j corresponding to Fi _j below Fi ^R does not exist in the range less than the fuel cell output required value P _{D In} this case, PI ^* = 0 (zero) and Fi ^* = Fi ^R.

<Step d2>
As mentioned above, step d2, to the fuel cell output demand value P _D, performed when the electrical output of the fuel cell is judged to be insufficient.

In this step, Fi _Mi (Fi _j corresponding to the maximum electric output Pi _Mi ) is compared with the reformable flow rate Fi ^R.

When Fi _Mi ≦ Fi ^R When Fi _Mi is equal to or less than the reformable flow rate Fi ^R , Pi ^* = Pi _Mi and Fi ^* = Fi _Mi. Fi _Mi ≦ Fi ^R is considered to mean that a hydrocarbon-based fuel having a flow rate Fi _Mi can be reformed in the reforming catalyst layer.

When Fi _Mi > Fi ^R When Fi _Mi exceeds the reformable flow rate Fi ^R ,
Pi ^* = (maximum value of Pi _j corresponding to Fi _j equal to or less than Fi ^R ),
Fi ^* = (Fi _j corresponding to this maximum value)
And Fi _Mi > Fi ^R is considered to mean that the hydrocarbon-based fuel having the flow rate Fi _Mi cannot be reformed in the reforming catalyst layer.

[Process E]
When there are two or more i in which the reformable flow rate Fi ^R determined in the process B is equal to or greater than the minimum value Fi _min, ηi corresponding to Pi ^* determined in the process D is set for each of the two or more i. Ask. I that gives the largest ηi among the two or more ηi thus obtained is represented by I.

For example, if i satisfying Fi ^R ≧ Fi _min is two of 1 and 2, that is, if F1 ^R ≧ F1 _min and F2 ^R ≧ F2 _min and i can be 3, F3 ^R <F3 _min In this case, η1 corresponding to P1 ^* determined in step D and η2 corresponding to P2 ^* determined in step D are obtained. If the largest ηi of these η1 and η2 is η1, i (expressed as I) giving the largest ηi is 1, that is, I = 1.

In the case where there are a plurality of the largest ηi among the two or more ηi obtained as described above, among those ηi (these are equal values), i giving an arbitrary ηi can be expressed as I. it can. For example, among the two or more reforming methods in which the reformable flow rate Fi ^R determined in the step B is equal to or greater than the minimum value Fi _min , i having a larger electrical output Pi ^* can be set to I.

If PI ^* exceeds zero, the electric output of the fuel cell is PI ^* , the reforming method performed in the reformer is the first reforming method, and the hydrocarbon-based fuel supplied to the reforming catalyst layer Let the flow rate be FI ^* .

When PI ^* is zero, power generation in the fuel cell is stopped. That is, the electric output of the fuel cell is set to zero. At this time, the following operations can be performed. That is, among the plurality of reforming methods determined as the i-th reforming method, the reforming method having the largest ratio of the calorific value to the endothermic amount of the reaction is adopted. The flow rate of the hydrocarbon-based fuel supplied to the reformer is set to Fi ^R for this reforming method. Then, for at least one i, the temperature of the reforming catalyst layer is raised with a heater or a burner attached to the reformer until at least Fi ^R ≧ Fi _min (Fi ^R is obtained by steps A and B). Can do. If Fi ^R ≧ Fi _min for at least one i, step D and subsequent steps can be performed again.

[Process F]
When there is only one i at which the reformable flow rate Fi ^R determined in the step B is equal to or greater than the minimum value Fi _min , this only i is represented as I.

For example, if i satisfying Fi ^R ≧ Fi _min is only 1, that is, F1 ^R ≧ F1 _min and F2 ^R <F2 _min , even if i can be 3, F3 ^R If <F3 _min , I = 1.

If PI ^* exceeds zero, the electric output of the fuel cell is PI ^* , the reforming method performed in the reformer is the first reforming method, and the hydrocarbon-based fuel supplied to the reforming catalyst layer Let the flow rate be FI ^* .

When PI ^* is zero, power generation in the fuel cell is stopped. That is, the electric output of the fuel cell is set to zero. At this time, the following operations can be performed. That is, among the plurality of reforming methods determined as the i-th reforming method, the reforming method having the largest ratio of the calorific value to the endothermic amount of the reaction is adopted. The flow rate of the hydrocarbon-based fuel supplied to the reformer is set to Fi ^R for this reforming method. Then, for at least one i, the temperature of the reforming catalyst layer is raised with a heater or a burner attached to the reformer until at least Fi ^R ≧ Fi _min (Fi ^R is obtained by steps A and B). Can do. If Fi ^R ≧ Fi _min for at least one i, step D and subsequent steps can be performed again.

[Example of load following operation]
Hereinafter, how to operate under a variety of conditions when performing a load following operation of a certain fuel cell system will be described with specific examples. However, the present invention is not limited thereby.

<Determination of Pi ^* and Fi ^* >
First, the procedure for determining Pi ^* and Fi ^* in step D will be described. However, only the first reforming method will be specifically described here. For the second reforming method, and when the third reforming method exists, Pi ^* and Fi ^* can be obtained by the same procedure for the third reforming method.

First, as shown in Table 1, for the fuel cell system, when the first reforming method is performed, the electric output P1 _j and the flow rate F1 _j of the hydrocarbon fuel corresponding to each P1 _j are as follows. Suppose that it is set. Here, P1 _M1 = 700 W and F1 _min = 1 g / min, which are values inherent to this fuel cell system. Meanwhile P _D are those that may vary depending upon the power demand, F1 ^R are those which may vary depending on the reforming catalyst layer temperature. Further, M1 = 7, that is, seven different P1 _j are set.

Further, as shown in Table 2 in advance for the same fuel cell system, the temperature T1 _k of the reforming catalyst layer and the flow rate of hydrocarbon fuel corresponding to each T1 _k when the first reforming method is performed. Assume that G1 _k is set. Here, T1 _N1 = 700 ° C. and G1 _N1 = 15 g / min, which are values specific to the fuel cell system. Ni = 5, that is, five different T1 _k are set.

Note that G1 _Ni = 15 g / min ≧ 5 g / min = F1 _M1 = F1 _max .

  In step A, the temperature T of the reforming catalyst layer is measured.

(Case 1)
Consider the case where P _D = 450 W and T = 660 ° C.

Step B is performed. From Table 2, the largest T1 _{k in} the range of T (660 ° C.) or less is T1 ₃ (650 ° C.). G1 _k (G1 ₃ ) corresponding to T1 ₃ is 6 g / min. As reformable flow rate F1 ^R, adopt a G1 _3. Therefore, F1 ^R = 6 g / min.

Since F1 ^R = 6 g / min ≧ 1 g / min = F1 _min , the process D is performed without performing the process C.

Since P _D = 450W ≦ 700W = P1 _M1 , step d1 is performed instead of step d2.

In step d1, first, F1 _DS is obtained. From Table 1, it can be seen that there is no P _i equal to P _D (450 W). Therefore, finding a "F1 _j corresponding to the smallest P1 _j exceeding P _D", and "F1 _j corresponding to the largest P1 _j is less than P _D" in Table 1. The smallest P1 _j exceeding P _D is 500 W (P1 ₅ ), and F1 _j (F1 ₅ ) corresponding to P1 ₅ is 3 g / min. The largest P1 _j less than P _D is 400 W (P1 ₄ ), and F1 _j (F1 ₄ ) corresponding to P1 ₄ is 4 g / min. The lesser of F1 ₅ and F1 ₄ , that is, F1 ₄ is defined as F1 _DS . Therefore, F1 _DS = 4 g / min.

Compare F1 _DS with F1 ^R. Since F1 _DS = 4 g / min ≦ 6 g / min = F1 ^R ,
P1 ^* = P _D = 450 W, F1 ^* = F1 _DS = 4 g / min.

(Case 2)
Consider the case where P _D = 400 W and T = 660 ° C.

Step B is performed. From Table 2, the largest T1 _{k in} the range of T (660 ° C.) or less is T1 ₃ (650 ° C.). G1 _k (G1 ₃ ) corresponding to T1 ₃ is 6 g / min. As reformable flow rate F1 ^R, adopt a G1 _3. Therefore, F1 ^R = 6 g / min.

Since F1 ^R = 6 g / min ≧ 1 g / min = F1 _min , the process D is performed without performing the process C.

Since P _D = 400W ≦ 700W = P1 _M1 , step d1 is performed instead of step d2.

In step d1, first, F1 _DS is obtained. From Table 1, since there is P1 _i (P1 ₄ ) equal to P _D (400 W), F1 ₄ is defined as F1 _DS . Therefore, F1 _DS = 4 g / min.

Compare F1 _DS with F1 ^R. Since F1 _DS = 4 g / min ≦ 6 g / min = F1 ^R ,
P1 ^* = P _D = 400 W, F1 ^* = F1 _DS = 4 g / min.

(Case 3)
Consider the case of P _D = 350 W and T = 630 ° C.

Step B is performed. From Table 2, the largest T1 _{k in} the range of T (630 ° C.) or less is T1 ₂ (625 ° C.). G1 _k (G1 ₂ ) corresponding to T1 ₂ is 3 g / min. As reformable flow rate F1 ^R, adopt a G1 _2. Therefore, F1 ^R = 3 g / min.

Since F1 ^R = 3 g / min ≧ 1 g / min = F1 _min , the process D is performed without performing the process C.

Since P _D = 350W ≦ 700W = P1 _M1 , step d1 is performed instead of step d2.

In step d1, first, F1 _DS is obtained. From Table 1, it can be seen that there is no P1 _j equal to P _D (350 W). Therefore, finding a "F1 _j corresponding to the smallest P1 _j exceeding P _D", and "F1 _j corresponding to the largest P1 _j is less than P _D" in Table 1. The smallest P1 _j exceeding P _D is 400 W (P1 ₄ ), and F1 _j (F1 ₄ ) corresponding to P1 ₄ is 4 g / min. The largest P1 _j less than P _D is 300 W (P1 ₃ ), and F1 _j (F1 ₃ ) corresponding to P1 ₃ is 3 g / min. The smaller one of F1 ₄ and F1 ₃ , that is, F1 ₄ is defined as F1 _DS . Therefore, F1 _DS = 4 g / min.

Compare F1 _DS with F1 ^R. Since F1 _DS = 4 g / min> 3 g / min = F1 ^R , the above-described step (1) or (2) is performed depending on the situation. Specifically, since there is P1 _j corresponding to F1 _j less than P _D and F1 ^R or less, step (1) is performed.

In P _D below i.e. the range of less than 350 W, P1 _j corresponding to F1 ^R i.e. 3 g / min following F1 _j is, P1 ₁ (0W), a P1 ₂ (200 W) and P1 ₃ (300W). The maximum value of these is P1 ₃ (300 W). F1 _j (F1 ₃ ) corresponding to the maximum value P1 ₃ is 3 g / min.

Therefore, PI ^* = P1 ₃ = 300 W and FI ^* = F1 ₃ = 3 g / min.

(Case 4)
Consider the case where P _D = 350 W and T = 610 ° C.

Step B is performed. From Table 2, the largest T1 _{k in} the range of T (610 ° C.) or less is T1 ₁ (600 ° C.). G1 _k (G1 ₁ ) corresponding to T1 ₁ is 1 g / min. G1 ₁ is adopted as the reformable flow rate F1 ^R. Therefore, F1 ^R = 1 g / min.

Since F1 ^R = 1 g / min ≧ 1 g / min = F1 _min , the process D is performed without performing the process C.

Since P _D = 350W ≦ 700W = P1 _M1 , step d1 is performed instead of step d2.

In step d1, first, F1 _DS is obtained. From Table 1, it can be seen that there is no P1 _j equal to P _D (350 W). Therefore, finding a "F1 _j corresponding to the smallest P1 _j exceeding P _D", and "F1 _j corresponding to the largest P1 _j is less than P _D" in Table 1. The smallest P1 _j exceeding P _D is 400 W (P1 ₄ ), and F1 _j (F1 ₄ ) corresponding to P1 ₄ is 4 g / min. The largest P1 _j less than P _D is 300 W (P1 ₃ ), and F1 _j (F1 ₃ ) corresponding to P1 ₃ is 3 g / min. The smaller one of F1 ₄ and F1 ₃ , that is, F1 ₄ is defined as F1 _DS . Therefore, F1 _DS = 4 g / min.

Compare F1 _DS with F1 ^R. Since F1 _DS = 4 g / min> 1 g / min = F1 ^R , the above-described step (1) or (2) is performed depending on the situation. Specifically, since there is no P1 _j corresponding to F1 _j less than P _D and F1 ^R or less, step (2) is performed. Specifically, F1 _j corresponding to P1 _j in a range less than P _D is F1 ₁ , F1 ₂ and F1 ₃ , all of which are greater than F1 ^R (1 g / min). Therefore, there is no P1 _j corresponding to F1 _j less than P _{D and} less than or equal to F1 ^R.

Therefore, in step (2), P1 ^* = 0 (zero) W and F1 ^* = F1 ^R (1 g / min).

(Case 5)
Consider the case where P _D = 800 W and T = 660 ° C.

Step B is performed. From Table 2, the largest T1 _{k in} the range of T (660 ° C.) or less is T1 ₃ (650 ° C.). G1 _k (G1 ₃ ) corresponding to T1 ₃ is 6 g / min. As reformable flow rate F1 ^R, adopt a G1 _3. Therefore, F1 ^R = 6 g / min.

Since F1 ^R = 6 g / min ≧ 1 g / min = F1 _min , the process D is performed without performing the process C.

Since P _D = 800W> 700W = P1 _M1 , step d2 is performed instead of step d1.

In step d2, F1 _M1 and F1 ^R are compared. Since F1 _M1 = 5 g / min ≦ 6 g / min = F1 ^R ,
P1 ^* = P1 _M1 = 700 W, F1 ^* = F1 _M1 = 5 g / min.

(Case 6)
Consider the case where P _D = 800 W and T = 630 ° C.

Step B is performed. From Table 2, the largest T1 _{k in} the range of T (630 ° C.) or less is T1 ₂ (625 ° C.). G1 _k (G1 ₂ ) corresponding to T1 ₂ is 3 g / min. As reformable flow rate F1 ^R, adopt a G1 _2. Therefore, F1 ^R = 3 g / min.

Since F1 ^R = 3 g / min ≧ 1 g / min = F1 _min , the process D is performed without performing the process C.

Since P _D = 800W> 700W = P1 _M1 , step d2 is performed instead of step d1.

In step d2, F1 _M1 and F1 ^R are compared. Since F1 _M1 = 5 g / min> 3 g / min = F1 ^R , the next step is performed.

P1 _j corresponding to F1 ^R, that is, F1 _j of 3 g / min or less is P1 ₁ (0 W), P1 ₂ (200 W), P1 ₃ (300 W), P1 ₅ (500 W), and P1 ₆ (600 W). The maximum value of these is P1 ₆ (600 W). F1 _j (F1 ₆ ) corresponding to the maximum value P1 ₆ is 1 g / min.

Therefore, PI ^* = P1 ₃ = 600 W and FI ^* = F1 ₃ = 1 g / min.

The correspondence shown in Table 1 is extreme for explanation. However, in practice, it is considered that there are many cases that are close to the correspondence shown in Table 3. In Table 3, in the range where the electric output Pi _j is small, that is, the electric output Pi _j is in the range of 0 W or more and 300 W or less, the flow rate Fi _j of the hydrocarbon-based fuel is set to 1.0 g in order to maintain the SOFC at a preferable power generation temperature. / Min is constant. Further, in order to increase the power generation efficiency in the range where the electrical output Pi _j is large, that is, the range where the electrical output Pi _j is 400 W or more and the maximum electrical output Pi _Mi (1000 W) or less, it corresponds to the increase of the electrical output Pi _j. flow rate Fi _j of the hydrocarbon-based fuel is to increase from 1.5 g / min until 4.5 g / min.

<Determination of fuel cell electrical output and fuel flow rate supplied to reformer>
The procedure for determining the electric output of the fuel cell and the flow rate of the hydrocarbon-based fuel supplied to the reformer in step E or F will be described in detail below.

In the following description, it is assumed that the following values are obtained considering the case of L = 2.
F1 _min = 1 g / min, F2 _min = 2 g / min.

  As shown in Tables 4 and 5, for each of the first reforming method and the second reforming method, it is assumed that correspondence between the fuel cell electrical output and the power generation efficiency at the output is required. For the same electrical output, the first reforming method has a higher power generation efficiency than the second reforming method, but the magnitude relationship of the power generation efficiency differs for different electrical outputs. For example, in some cases, the second reforming method has a higher maximum electric output that can be generated in a state in which complete reforming is ensured and the power generation efficiency is higher than the first reforming method. In the present invention, in order to determine the reforming method in which the electric output, the hydrocarbon fuel flow rate, and the power generation efficiency are ensured in a state in which complete reforming is ensured in real time, the electric output during the load following operation is increased as much as possible. The power generation efficiency can be kept high.

(Case 7)
here,
P _D = 600W
In step B, F1 ^R = 2 g / min, F2 ^R = 5 g / min
It is assumed that Further, in step D,
P1 ^* = 500 W, F1 ^* = 2 g / min,
P2 ^* = 600W, F2 ^* = 4g / min
It is assumed that

Since F1 ^R = 2 g / min ≧ 1 g / min = F1 _min and F2 ^R = 5 g / min ≧ 2 g / min = F2 _min , there are two i and 1 that satisfy Fi ^R ≧ Fi _min. To do. Therefore, process E is performed instead of process F.

Η1 corresponding to P1 ^* (500 W) is 30% from Table 4. Η2 corresponding to P2 ^* (600 W) is 33% from Table 5.

  The largest ηi among these ηi is η2, and I (i giving η2) is 2.

PI ^* = P2 ^* = 600 (W) ≠ 0. Therefore, the electric output of the fuel cell is PI ^*, that is, P2 ^* (600 W), the reforming method is the second reforming method, and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is F2 ^* = 4 g / min. And

(Case 8)
Here, P _D = 600W
In step B, F1 ^R = 2 g / min, F2 ^R = 1.5 g / min
It is assumed that Further, in step D,
P1 ^* = 500W, F1 ^* = 2g / min
It is assumed that

While F1 ^R = 2 g / min ≧ 1 g / min = F1 _min , F2 ^R = 1.5 g / min <2 g / min = F2 _min , so there is only 1 as i where Fi ^R ≧ Fi _min. To do. Therefore, I (this only i) = 1.

PI ^* = P1 ^* = 500 (W) ≠ 0. Therefore, the electric output of the fuel cell is PI ^*, that is, P1 ^* (500 W), the reforming method is the first reforming method, and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is F1 ^* = 2 g / min. And

(Case 9)
Here, P _D = 600W
In process B, F1 ^R = 0.5 g / min, F2 ^R = 5 g / min
It is assumed that Further, in step D,
P2 ^* = 600W, F2 ^* = 4g / min
It is assumed that

While F2 ^R = 5 g / min ≧ 2 g / min = F2 _min , while F1 ^R = 0.5 g / min <1 g / min = F1 _min , there is only 2 as i where Fi ^R ≧ Fi _min. To do. Therefore, I (this only i) = 2.

PI ^* = P2 ^* = 600 (W) ≠ 0. Therefore, the electric output of the fuel cell is PI ^*, that is, P2 ^* = 600 W, the reforming method is the second reforming method, and the flow rate of the hydrocarbon fuel supplied to the reforming catalyst layer is F2 ^* = 4 g / min. To do.

<Example of performing step C>
(Case 10)
Here, in step B, F1 ^R = 0.5 g / min, F2 ^R = 1.5 g / min
It is assumed that

At this time, since F1 ^R = 0.5 g / min <1 g / min = F1 _min and F2 ^R = 1.5 g / min <2 g / min = F2 _min , that is, since Fi ^R <Fi _min for all i, D is not performed, but process C is performed, and the electric output of the fuel cell is made zero.

At this time, if the reforming method having the largest ratio of the calorific value to the endothermic amount among the first and second reforming methods is the second reforming method, the second reforming method is adopted and F2 ^R Is supplied to the reformer, and the temperature of the reforming catalyst layer is raised with a heater or a burner attached to the reformer until at least Fi ^R ≧ Fi _{min for} at least one i. can do. If the temperature of the reforming catalyst layer rises while steps A to C are repeated and Fi ^R ≧ Fi _min for at least one i, step D and subsequent steps can be performed.

[Way of Gi _k of settings corresponding to Ti _k and Ti _k]
-How to set Ti _{k When} the measured temperature T of the catalyst layer is smaller than the minimum value of Ti _k , step B cannot be performed. Therefore, the minimum value of Ti _k is preferably as small as possible. The lowest temperature among the temperatures at which the flow rate of the hydrocarbon-based fuel that can be reformed by the i-th reforming method exceeds zero can be achieved.

From the viewpoint of power generation efficiency, Ni is preferably as large as possible within the allowable range of the memory of the control means. In particular, when the rate of increase in the flow rate of the hydrocarbon-based fuel that can be reformed by the i-th reforming method increases as the catalyst layer temperature increases, the interval between Ti _k decreases as the temperature increases. Is preferred.

· Gi _k setting way Gi _k of a flow rate of reforming hydrocarbon-based fuel that can be by reforming method of the i in the reforming catalyst layer at the corresponding reforming catalyst layer temperature Ti _k. Therefore, when the temperature of the reforming catalyst layer is the temperature Ti _k , the flow rate Gi _k of the hydrocarbon-based fuel that can be reformed in the reforming catalyst layer by the i-th reforming method is _obtained in advance, and Ti _k and Gi _k Is set in advance. Hereinafter, how to obtain Gi _k will be described.

  The flow rate of the hydrocarbon-based fuel that can be reformed in the reforming catalyst layer is such that when the hydrocarbon-based fuel at that flow rate is supplied to the reforming catalyst layer, the composition of the gas discharged from the reforming catalyst layer is the fuel cell. The flow rate at which the composition is suitable for supply to the anode.

For example, the reformable flow rate in the reforming catalyst layer can be an arbitrary flow rate that is not more than the maximum value of the flow rate at which the supplied hydrocarbon fuel can be decomposed to the C1 compound (compound having 1 carbon atom). That is, the reforming catalyst layer is modified until the C2 + component (the component having 2 or more carbon atoms) in the reforming catalyst layer outlet gas has a concentration that does not cause a problem with respect to channel blockage or anode deterioration due to carbon deposition. When the quality can proceed, the flow rate can be set to an arbitrary flow rate that is not more than the maximum value of the supply flow rate of the hydrocarbon-based fuel to the reforming catalyst layer. The reformable flow rate can be the maximum value, or can be a value obtained by dividing the maximum value by a safety factor (a value exceeding 1; for example, 1.4). The concentration of the C2 + component at this time is preferably 50 ppb or less as a mass fraction in the reformed gas. At this time, the reforming catalyst layer outlet gas only needs to be reducible. It is allowed that methane is contained in the reforming catalyst layer outlet gas. In the reforming of hydrocarbon-based fuels, methane usually remains in equilibrium. Even if the reforming catalyst layer outlet gas contains carbon in the form of methane, CO, or CO ₂ , carbon deposition can be prevented by adding steam as necessary. When methane is used as the hydrocarbon-based fuel, reforming may be advanced so that the reforming catalyst layer outlet gas becomes reducible.

Regarding the reducing property of the reforming catalyst layer outlet gas, even if this gas is supplied to the anode, it only needs to be capable of suppressing oxidative deterioration of the anode. For this purpose, for example, the partial pressure of oxidizing O ₂ , H ₂ O, CO _{2 and the} like contained in the reforming catalyst layer outlet gas can be made lower than the equilibrium partial pressure in the oxidation reaction of the anode electrode. For example, when the anode electrode material is nickel and the anode temperature is 800 ° C., the O ₂ partial pressure contained in the reforming catalyst layer outlet gas is less than 1.2 × 10 ⁻¹⁴ atm (1.2 × 10 ⁻⁹ Pa). , less than 1.7 × 10 ² partial pressure ratio of H ₂ O for H _2, the partial pressure ratio of CO ₂ to CO may be less than 1.8 × 10 ^2.

  The reformable flow rate depends on the temperature of the reforming catalyst layer. Therefore, the reformable flow rate in the reforming catalyst layer is obtained based on the temperature of the reforming catalyst layer.

The reformable flow rate Gi _k can be _obtained in advance by experiments as a value corresponding to the temperature Ti _k of the reforming catalyst layer. In addition, it is possible to obtain the reformable flow rate after dividing the value obtained by the experiment by the safety factor or correcting the temperature to the safe side. The unit of Gi _k is, for example, g / min or mol / s. The reformable flow rate Gi _k can be a value corresponding only to the temperature Ti _k . However, the reformable flow rate Gi _k may be a value corresponding to a variable other than Ti _k such as the catalyst layer volume and the concentration of the gas component in addition to the temperature Ti _k . In this case, when obtaining a reformable flow rate Gi _k is appropriately determined variables other than Ti _k, and variables other than Ti _k, it is possible to obtain the reformable flow rate Gi _k from the measured Ti _k.

In preliminary experiment for obtaining the gi _k, the temperature measuring portion of the reforming catalyst layer, in one point, or at a plurality of points. In addition, as the temperature of the reforming catalyst layer, a representative temperature such as an average value of a plurality of points can be used.

  Considering a plurality of divided regions obtained by dividing the reforming catalyst layer along the gas flow direction, measuring temperatures at a plurality of points at different positions in the gas flow direction of the reforming catalyst layer, and based on those temperatures, The flow rate of fuel that can be reformed in at least a part of the plurality of divided regions may be obtained, and the total value of the obtained flow rates may be used as the flow rate of fuel that can be reformed in the reforming catalyst layer.

When obtaining the temperature T of the reforming catalyst layer in actual operation in step A, it is desirable to measure the temperature of the reforming catalyst layer in the same manner as the preliminary experiment for obtaining Gi _k . That is, it is desirable to measure the temperature of the reforming catalyst layer at the same location as in the preliminary experiment. When the representative temperature is used in the preliminary experiment, it is desirable that the same representative temperature is set as the temperature T of the reforming catalyst layer in the process A.

[Others]
In addition, by connecting the fuel cell with the system power supply, the shortage of the electrical output of the fuel cell with respect to the power load can be supplied from the system power supply.

Fuel cell output demand value P _D may be the value of the power load measured by an appropriate power meter. Alternatively, in the case of other generators and battery and interconnection, a portion of the measured electric power load may be a fuel cell output demand value P _D.

When determining the flow rate of the hydrocarbon fuel in the processes E, F, etc., the flow rate of the fluid supplied to the indirect internal reforming SOFC other than the hydrocarbon fuel and the indirect other than the output of the SOFC as necessary The electric input / output to / from the internal reforming SOFC is a value set in advance corresponding to each Pi _j (the same j-th flow rate as the determined hydrocarbon fuel flow rate in the i-th reforming method). Value).

  The present invention is particularly effective when the hydrocarbon fuel supplied to the reforming catalyst layer contains a hydrocarbon fuel having 2 or more carbon atoms. According to the present invention, even during load following operation, the concentration of the compound having 2 or more carbon atoms in the reformed gas can be reduced to 50 ppb or less on the mass basis. Can be more reliably prevented.

  In order to perform the method of the present invention, an appropriate instrumentation control device including a calculation means such as a computer can be used.

[Hydrocarbon fuel]
The hydrocarbon-based fuel is appropriately selected from compounds or mixtures thereof containing carbon and hydrogen (may contain other elements such as oxygen) known in the field of high-temperature fuel cells as a reformed gas raw material. Compounds having carbon and hydrogen in the molecule such as hydrocarbons and alcohols can be used. For example, hydrocarbon fuels such as methane, ethane, propane, butane, natural gas, LPG (liquefied petroleum gas), city gas, gasoline, naphtha, kerosene, light oil, etc., alcohols such as methanol and ethanol, ethers such as dimethyl ether, etc. is there.

  Of these, kerosene and LPG are preferred because they are readily available. Moreover, since it can be stored independently, it is useful in areas where city gas lines are not widespread. Furthermore, a high-temperature fuel cell power generator using kerosene or LPG is useful as an emergency power source. In particular, kerosene is preferable because it is easy to handle.

[High-temperature fuel cell]
The present invention can be suitably applied to a system including a high-temperature fuel cell that may cause channel blockage or anode deterioration due to carbon deposition. Such fuel cells include SOFC and MCFC.

  As the SOFC, various known shapes such as a flat plate type and a cylindrical type can be appropriately selected and used. In the SOFC, oxygen ion conductive ceramics or proton ion conductive ceramics are generally used as an electrolyte.

  The MCFC can be appropriately selected from known MCFCs.

  The SOFC or MCFC may be a single cell, but in practice, a stack in which a plurality of single cells are arranged (in the case of a cylindrical type, it may be called a bundle, but the stack referred to in this specification also includes a bundle) Is preferably used. In this case, one or more stacks may be used.

  Among high temperature fuel cells, the indirect internal reforming SOFC is superior in that it can increase the thermal efficiency of the system. The indirect internal reforming SOFC includes a reformer that produces a reformed gas containing hydrogen from a hydrocarbon fuel using a reforming reaction such as steam reforming, and the SOFC. In this reformer, a steam reforming reaction can be performed, and a partial oxidation reaction or autothermal reforming accompanied by a partial oxidation reaction in the steam reforming reaction may be performed. Then, heat necessary for the reforming reaction is supplied from the SOFC. The reformer and SOFC are accommodated in one module container and modularized. The reformer is disposed at a position that receives heat radiation from the SOFC. By doing so, the reformer is heated by heat radiation from the SOFC during power generation. In addition, the SOFC can be heated by burning the anode off-gas discharged from the SOFC at the cell outlet.

  In the indirect internal reforming SOFC, the reformer is preferably arranged at a position where direct heat transfer from the SOFC to the outer surface of the reformer is possible. Therefore, it is preferable that a shielding object is not substantially disposed between the reformer and the SOFC, that is, a gap is provided between the reformer and the SOFC. Further, it is preferable to shorten the distance between the reformer and the SOFC as much as possible.

  Each supply gas is appropriately preheated as necessary and then supplied to the reformer or SOFC.

  As the module container, an appropriate container capable of accommodating the SOFC and the reformer can be used. As the material, for example, an appropriate material having resistance to the environment to be used, such as stainless steel, can be used. The container is appropriately provided with a connection port for gas exchange and the like.

  In particular, when the cell outlet is open in the module container, the module container is preferably airtight so that the inside of the module container and the outside (atmosphere) do not communicate with each other.

  The combustion region is a region where the anode off gas discharged from the anode of the SOFC can be combusted. For example, the anode outlet can be opened in the housing, and the space near the anode outlet can be used as a combustion region. This combustion can be performed using, for example, a cathode off gas as the oxygen-containing gas. For this purpose, the cathode outlet can be opened in the housing.

  An ignition means such as an igniter can be appropriately used to burn the combustion fuel or anode off gas.

[Reformer]
The reformer produces a reformed gas containing hydrogen from a hydrocarbon fuel.

  In the reformer, any of steam reforming, partial oxidation reforming, and autothermal reforming accompanied by a partial oxidation reaction in the steam reforming reaction may be performed.

  An autothermal reforming catalyst having both partial oxidation reforming ability and steam reforming ability can be used for the reformer.

  As the structure of the reformer, a structure known as a reformer can be appropriately adopted. For example, it is possible to have a structure having a region for accommodating the reforming catalyst in a sealable container and having an inlet for fluid necessary for reforming and an outlet for reforming gas.

  The material of the reformer can be appropriately selected and adopted from materials known as reformers in consideration of resistance in the use environment.

  The shape of the reformer can be an appropriate shape such as a rectangular parallelepiped or a circular tube.

  Supply hydrocarbon-based fuel (pre-vaporized if necessary), water vapor, and oxygen-containing gas such as air, if necessary, individually or appropriately mixed to the reformer (reforming catalyst layer) can do. The reformed gas is supplied to the anode of the SOFC.

[Reforming catalyst]
As the reforming catalyst used in the reformer, for example, a known autothermal reforming catalyst such as a rhodium catalyst can be used.

[Reformer operating conditions]
Hereinafter, the conditions at the time of load follow-up operation in the reformer will be described for each of steam reforming, autothermal reforming, and partial oxidation reforming.

In steam reforming, steam is added to reforming raw materials such as kerosene. The reaction temperature of the steam reforming can be performed, for example, in the range of 400 ° C to 1000 ° C, preferably 500 ° C to 850 ° C, more preferably 550 ° C to 800 ° C. The amount of steam introduced into the reaction system is defined as the ratio of the number of moles of water molecules to the number of moles of carbon atoms contained in the hydrocarbon fuel (steam / carbon ratio), and this value is preferably 1 to 10, more preferably 1.5-7, more preferably 2-5. When the hydrocarbon fuel is liquid, the space velocity (LHSV) at this time is A / B when the flow rate in the liquid state of the hydrocarbon fuel is A (L / h) and the catalyst layer volume is B (L). This value is preferably set in the range of 0.05 to 20 h ⁻¹ , more preferably 0.1 to 10 h ⁻¹ , and still more preferably 0.2 to 5 h ⁻¹ .

In autothermal reforming, an oxygen-containing gas is added to the reforming raw material in addition to steam. The oxygen-containing gas may be pure oxygen, but air is preferred because of its availability. An oxygen-containing gas can be added so that the endothermic reaction accompanying the steam reforming reaction is balanced, and a heat generation amount capable of maintaining the temperature of the reforming catalyst layer and SOFC or raising the temperature thereof can be obtained. The addition amount of the oxygen-containing gas is preferably 0.005 to 1, more preferably 0.01 to 0.00 as the ratio of the number of moles of oxygen molecules to the number of moles of carbon atoms contained in the hydrocarbon fuel (oxygen / carbon ratio). 75, more preferably 0.02 to 0.6. The reaction temperature of the autothermal reforming reaction is set, for example, in the range of 400 ° C to 1000 ° C, preferably 450 ° C to 850 ° C, and more preferably 500 ° C to 800 ° C. When the hydrocarbon fuel is a liquid, the space velocity (LHSV) at this time is preferably 0.05 to 20 h ⁻¹ , more preferably 0.1 to 10 h ⁻¹ , further preferably 0.2 to 5 h ^−1. Is selected within the range. The amount of steam introduced into the reaction system is preferably 1 to 10, more preferably 1.5 to 7, and still more preferably 2 to 5 as a steam / carbon ratio.

In partial oxidation reforming, an oxygen-containing gas is added to the reforming raw material. The oxygen-containing gas may be pure oxygen, but air is preferred because of its availability. In order to secure a temperature for proceeding the reaction, the amount added is appropriately determined in terms of heat loss and the like. The amount is preferably 0.1 to 3, more preferably 0.2 to 0.7 as the ratio of the number of moles of oxygen molecules to the number of moles of carbon atoms contained in the hydrocarbon fuel (oxygen / carbon ratio). . The reaction temperature of the partial oxidation reaction can be set, for example, in the range of 450 ° C to 1000 ° C, preferably 500 ° C to 850 ° C, and more preferably 550 ° C to 800 ° C. When the hydrocarbon fuel is a liquid, the space velocity (LHSV) at this time is preferably selected in the range of 0.1 to 30 h ⁻¹ . Steam can be introduced to suppress the generation of soot in the reaction system, and the amount thereof is preferably 0.1 to 5, more preferably 0.1 to 3, more preferably 1 to 1, as a steam / carbon ratio. 2.

[Other equipment]
In the high-temperature fuel cell system used in the present invention, known components of the high-temperature fuel cell system can be appropriately provided as necessary. Specific examples include desulfurizers that reduce sulfur content in hydrocarbon fuels, vaporizers that vaporize liquids, pumps for pressurizing various fluids, compressors, boosters such as blowers, and the flow rate of fluids. Flow adjustment means such as valves for controlling or shutting off / switching the flow of fluid, flow path shutting / switching means, heat exchangers for heat exchange and heat recovery, condensers for condensing gas, steam, etc. Heating / heat-retaining means for externally heating various equipment, storage means for hydrocarbon fuels and combustibles, instrumentation air and electrical systems, control signal systems, control devices, output and power electrical systems, etc. is there.

  The present invention can be applied to, for example, a stationary or mobile power generation system, and a high-temperature fuel cell system used for a cogeneration system.

DESCRIPTION OF SYMBOLS 1 Water vaporizer 2 Electric heater attached to water vaporizer 3 Reformer 4 Reforming catalyst layer 5 Combustion zone 6 SOFC
7 Igniter 8 Module container 9 Electric heater attached to reformer

Claims (4)

A fuel cell comprising a reformer having a reforming catalyst layer for producing a reformed gas containing hydrogen by reforming a hydrocarbon fuel, and a high-temperature fuel cell for generating electric power using the reformed gas A load following operation method of the system,
At least two reforming methods selected from the group consisting of steam reforming method, partial oxidation reforming method and autothermal reforming method are defined as i-th reforming method, where i is an integer of 1 or more and L or less. L is 2 or 3,
For all i, when the reformed gas produced by the i-th reforming method is supplied to the fuel cell in advance to generate electric power, it corresponds to different Mi fuel cell electrical outputs Pi _j and each Pi _j . have set up a flow rate Fi _j of the hydrocarbon-based fuel, and, to previously obtain a power generation efficiency .eta.i _j in each Pi _j,
However, j is an integer of 1 or more and Mi or less, Mi is an integer of 2 or more,
Each Fi _j is the flow rate of the corresponding electrical output Pi _j need to be supplied to the reforming catalyst layer to perform reforming method of the i to output the fuel cell of the hydrocarbon-based fuel,
Each Pi _j is greater than or equal to 0, and Pi _j increases as _j increases, and each Fi _j is greater than 0,
Pi _i which is Pi _j when _j is ₁ is 0 for all i, and Pi Mi which is Pi _j when _j is _Mi is the value of the fuel cell in the case of performing the i-th reforming method. Maximum electrical output,
In each i, it represents the minimum value of the Fi _j for all j and Fi _min,
In addition, for all i, different Ni reforming catalyst layer temperatures Ti _k and hydrocarbon-based fuel flow rates Gi _k corresponding to the respective Ti _k are set in advance.
However, k is an integer of 1 or more and Ni or less, Ni is an integer of 2 or more,
Each Gi _k is a flow rate of the hydrocarbon-based fuel that can be reformed by the i-th reforming method in the reforming catalyst layer at the corresponding reforming catalyst layer temperature Ti _k , and each Gi _k is greater than 0 and increases by k Gi _k is increased or the same value with the,
A) a step of measuring the temperature T of the reforming catalyst layer,
B) For all i, the reformable flow rate Fi ^R that is the flow rate of the hydrocarbon-based fuel that can be reformed by the i-th reforming method in the reforming catalyst layer at the temperature T is the largest below the temperature T Adopting Gi _k corresponding to Ti _k ,
C) a step of stopping power generation in the fuel cell when the reformable flow rate Fi ^R is smaller than the minimum value Fi _min for all i;
If D) at least one of i the reformable flow rate Fi ^R about is the minimum value Fi _min or more, for each of the at least one i, the fuel cell output demand value P _D is equal to or less than the maximum electrical output Pi _Mi process performs step d1, the fuel cell output demand value P _D is a step d2 if exceeds the maximum electrical output Pi _Mi long,
d1) within the Pi _j for all j, if there is equal Pi _j to the fuel cell output demand value P _D, and Fi _j) corresponding to Fi _DS = (P _D equal Pi _j,
Among the Pi _j for all j, if there is equal Pi _j to the fuel cell output demand value P _D, and Fi _j corresponding to Fi _DS = (smallest Pi _j exceeding P _D, most in less than P _D The smaller one of Fi _j corresponding to large Pi _j ),
When Fi _DS is equal to or less than the reformable flow rate Fi ^R , Pi ^* = P _D and Fi ^* = Fi _DS ,
When Fi _DS exceeds the reformable flow rate Fi ^R ,
If there is Pi _j corresponding to Fi _j below Fi ^{R in} the range below the fuel cell output requirement value P _D , Pi ^* = (P _i of Pi _j corresponding to Fi _j below Fi ^{R in} the range below P _D the maximum value of the out), and, Fi ^* = a (Fi _j corresponding to the maximum value of the Pi _j corresponding to Fi ^R following Fi _j in the range of less than P _D),
If there is no Pi _j corresponding to Fi _j below Fi ^{R in} the range less than the fuel cell output required value P _D , Pi ^* = 0 and Fi ^* = Fi ^R ,
d2) When Fi _Mi which is Fi _j corresponding to the maximum electrical output Pi _Mi is equal to or less than the reformable flow rate Fi ^R , Pi ^* = Pi _Mi and Fi ^* = Fi _Mi ,
When Fi _Mi that is Fi _j corresponding to the maximum electrical output Pi _Mi exceeds the reformable flow rate Fi ^R , Pi ^* = (maximum value among Pi _j corresponding to Fi _j less than or equal to Fi ^R ) and, Fi ^* = step to (Fi _j corresponding to the maximum value of the Pi _j corresponding to Fi ^R following Fi _j),
E) When there are two or more i at which the reformable flow rate Fi ^R becomes the minimum value Fi _min or more, ηi corresponding to Pi ^* is obtained for each of the two or more i, and the most of the obtained ηi I that gives a large ηi is represented as I,
If PI ^* is zero, stop power generation in the fuel cell,
When PI ^* exceeds zero, the electric output of the fuel cell is PI ^* , the reforming method performed by the reformer is the first reforming method, and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is FI. ^The process ^*
F) When there is only one i at which the reformable flow rate Fi ^R is not less than the minimum value Fi _min , this only i is represented as I
If PI ^* is zero, stop power generation in the fuel cell,
When PI ^* exceeds zero, the electric output of the fuel cell is PI ^* , the reforming method performed by the reformer is the first reforming method, and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is FI. ^The process ^*
A load following operation method for a fuel cell system.   The method according to claim 1, wherein the steps A to F are repeated during the load following operation.   The method according to claim 1 or 2, wherein the hydrocarbon fuel includes a hydrocarbon fuel having 2 or more carbon atoms.   The method according to claim 3, wherein the concentration of the compound having 2 or more carbon atoms in the reformed gas is 50 ppb or less on a mass basis.

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