JP2009295380A - Shutdown method of indirect internal reforming solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shutdown method of an indirect internal reforming SOFC capable of performing sure reformation, anode oxidation deterioration prevention, and cell crack prevention. <P>SOLUTION: In this method, a stepwise fuel flow rate Fk(j) is set in advance, while an anode temperature is at an oxidation deterioration point or higher, a calculated value FkCAL of a reformable fuel flow rate is calculated. In the case of FkCALC≥FkE, if there is an intermediate flow rate Fk(j) of lower than the fuel flow rate and over FkE to the reformer at the time of starting the shutdown method in Fk(j), processes C1 to C5 are carried out sequentially. (C1) j to give a maximum value out of the intermediate flow rate is made to be J, (C2) FkCALC is calculated, (C3) if FkCALC>Fk(J), this returns to the process C2, (C4) if FkCALC≤Fk(J), the fuel flow rate to the reformer is made to be Fk(J+1), and J increased by 1, (C5) if J≠M, this returns to the process C2, and if J=M, this moves to the process D, and in (D), this is made to wait until the anode temperature is lowered below the oxidation deterioration point. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for stopping an indirect internal reforming solid oxide fuel cell having a reformer in the vicinity of the fuel cell.

  Solid oxide electrolyte fuel cell (Solid Oxide Fuel Cell; hereinafter referred to as SOFC) systems are usually used to reform hydrocarbon fuels such as kerosene and city gas to generate reformed gas as hydrogen-containing gas. And a SOFC for electrochemically generating and reacting the reformed gas and air.

  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, a reformer (internal reformer) is installed in the vicinity of the SOFC, and the reformer is heated by using the heat of combustion from the radiant heat from the SOFC and the combustion heat of the anode offgas (gas discharged from the anode) of the SOFC. A modified SOFC is known (Patent Document 1).

In addition, when power generation is stopped, a fuel cell that reduces the stack temperature while maintaining the fuel electrode layer side in a reduced state by supplying the fuel cell while reducing the flow rate of water and hydrogen or hydrocarbon fuel. The operation stop method is disclosed in Patent Document 2.
JP 2004-319420 A JP 2006-294508 A

  If the method described in Patent Document 2 is used, it is considered that the anode can be held in a reducing atmosphere when the fuel cell is stopped, and oxidation deterioration of the anode can be prevented.

  However, in the method described in Patent Document 2, when the SOFC anode is maintained in a reduced state using a hydrogen-containing gas obtained by reforming a hydrocarbon fuel, reliable reforming is not ensured. That is, unreformed hydrocarbon fuel may be discharged from the reformer and flow into the anode.

  In particular, when using a higher order hydrocarbon such as kerosene, if the higher order hydrocarbon leaks from the reformer and flows into the SOFC, the performance of the SOFC may deteriorate due to carbon deposition.

  Furthermore, if the flow rate of the hydrocarbon-based fuel is suddenly changed when the temperature of the fuel cell is lowered, there is a possibility that cell cracking (damage of the fuel cell) may occur due to a sudden change in the internal pressure of the fuel cell. In addition, when the anode pressure rapidly decreases in a sealless stack (a stack in which the remaining gas that has not been used in the power generation reaction is discharged from the outer periphery), anode off-gas (gas discharged from the anode of the fuel cell) Oxygen-containing gas existing in the vicinity of the discharge part may enter the anode and cause oxidative deterioration of the anode.

  An object of the present invention is to provide an indirect internal reforming SOFC that can prevent oxidative deterioration of the anode with reformed gas and can prevent cell cracking while reliably reforming hydrocarbon fuel. It is to provide a stop method.

  The present invention provides the following method for stopping an indirect internal reforming solid oxide fuel cell.

1) a reformer having a reforming catalyst layer for reforming hydrocarbon fuel to produce reformed gas;
A solid oxide fuel cell that generates electric power using the reformed gas; and
A combustion region for burning anode off-gas discharged from the solid oxide fuel cell;
A method for stopping an indirect internal reforming solid oxide fuel cell comprising: a reformer, a solid oxide fuel cell, and a housing that houses a combustion region;
The following conditions i to iv,
i) The anode temperature of the solid oxide fuel cell is steady,
ii) the anode temperature is below the oxidative degradation point;
iii) In the reformer, the hydrocarbon-based fuel is reformed, and a reformed gas having a composition suitable for supplying to the anode is generated,
iv) The amount of the reformed gas generated is equal to or higher than the minimum flow rate necessary to prevent oxidative deterioration of the anode when the anode temperature of the solid oxide fuel cell is at or above the oxidative deterioration point.
FkE represents the flow rate of the hydrocarbon-based fuel supplied to the reformer in a state where all of the above are satisfied,
A stepwise hydrocarbon-based fuel flow rate Fk (j) is determined in advance (where j is an integer of 1 to M, and M is an integer of 2 or more), where Fk (j) is decreases with increasing j, and the smallest Fk (M) among Fk (j) is equal to FkE,
The flow rate of the hydrocarbon-based fuel that has been supplied to the reformer at the start of the stop method is expressed as Fk0,
When the calculated value of the flow rate of the hydrocarbon-based fuel that can be reformed by the type of reforming method performed after the start of the stopping method at the measured temperature of the reforming catalyst layer is expressed as FkCALC,
When the anode temperature falls below the oxidative degradation point, the supply of hydrocarbon fuel to the reformer is stopped and the stopping method is terminated.
While the anode temperature is not below the oxidation degradation point,
A) a step of measuring the reforming catalyst layer temperature, calculating FkCALC using the measured temperature, and comparing the values of FkCALC and FkE;
B) A step of sequentially performing the following steps B1 to B4 when FkCALC <FkE in step A,
B1) Step of heating the reforming catalyst layer
B2) measuring the reforming catalyst layer temperature, calculating FkCALC using the measured temperature, and comparing the values of FkCALC and FkE;
B3) A step of returning to step B1 when FkCALC <FkE in step B2,
B4) When FkCALC ≧ FkE in step B2, the flow rate of the hydrocarbon-based fuel supplied to the reformer is changed from Fk0 to FkE, and the process proceeds to step D.
C) When FkCALC ≧ FkE in step A,
If there is no intermediate flow rate Fk (j) that is smaller than Fk0 and larger than FkE among the predetermined hydrocarbon-based fuel flow rates Fk (j), the flow rate of the hydrocarbon-based fuel supplied to the reformer is changed from Fk0 to FkE. And go to step D,
A step of sequentially performing the following steps C1 to C5 if there is an intermediate flow rate Fk (j) that is smaller than Fk0 and larger than FkE among the predetermined hydrocarbon-based fuel flow rates Fk (j);
C1) j giving the largest Fk (j) among the intermediate flow rates is represented as J,
Reducing the flow rate of hydrocarbon-based fuel supplied to the reformer from Fk0 to Fk (J);
C2) measuring the reforming catalyst layer temperature, calculating FkCALC using the measured temperature, and comparing the value of FkCALC and Fk (J);
C3) If FkCALC> Fk (J) in step C2, returning to step C2;
C4) A step of decreasing the flow rate of the hydrocarbon-based fuel supplied to the reformer from Fk (J) to Fk (J + 1) and increasing J by 1 when FkCALC ≦ Fk (J) in step C2.
C5) Comparing J and M. If J ≠ M, return to step C2, and if J = M, go to step D, and D) wait for the anode temperature to fall below the oxidation degradation point. A method for stopping an indirect internal reforming solid oxide fuel cell.

  2) The method according to 1), wherein the hydrocarbon fuel includes a hydrocarbon fuel having 2 or more carbon atoms.

  3) The method according to 2), 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.

  INDUSTRIAL APPLICABILITY According to the present invention, a method for stopping an indirect internal reforming SOFC that can prevent oxidative deterioration of an anode with a reformed gas while reliably reforming a hydrocarbon-based fuel, and further prevent cell cracking Is provided.

  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.

  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 is also supplied to the reforming catalyst layer. Here, air is preheated by a water vaporizer and then supplied to the reforming catalyst layer. 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.

[Reforming stoppage possible state]
In the present specification, a state where all of the following conditions i to iv are satisfied is referred to as a reforming stoppable state.
i) The anode temperature of the SOFC is steady.
ii) The anode temperature is lower than the oxidation deterioration point.
iii) A reformed gas having a composition suitable for supply to the anode is generated in the reformer.
iv) The amount of the reformed gas generated is equal to or higher than the minimum flow rate necessary to prevent oxidative degradation of the anode when the SOFC anode temperature is at or above the oxidation degradation point.

<Conditions i and ii>
The anode temperature means the temperature of the anode electrode. When it is difficult to directly measure the temperature of the anode electrode directly, it can be the temperature of a stack component such as a separator in the vicinity of the anode. As the anode temperature measurement position, it is preferable to adopt a location where the temperature is relatively high, more preferably a location where the temperature is highest, from the viewpoint of safety control. The position where the temperature rises can be known through preliminary experiments and simulations.

  The oxidation deterioration point is a temperature at which the anode is oxidized and deteriorated. For example, the electrical conductivity of the anode material is measured by the direct current four-terminal method by changing the temperature in a reducing or oxidizing gas atmosphere, and in an oxidizing gas atmosphere. The minimum temperature at which the electrical conductivity at is lower than the value in the reducing gas atmosphere can be set as the oxidation deterioration point.

<Condition iii>
The condition iii means that the hydrocarbon-based fuel is reformed in the reformer and a reformed gas having a composition suitable for supplying to the anode is obtained. For example, when the hydrocarbon-based fuel contains a hydrocarbon-based fuel having 2 or more carbon atoms, the reformed gas is reducible, and the C2 + component (compound having 2 or more carbon atoms) in the reformed gas flows due to carbon deposition. This means that the concentration is below the concentration that does not cause a problem with respect to path blockage or anode deterioration. The concentration of the C2 + component at this time is preferably 50 ppb or less as a mass fraction in the reformed gas.

<Condition iv>
The minimum necessary reformed gas flow rate for preventing oxidative deterioration of the anode is the smallest flow rate among the flow rates at which the anode electrode is not oxidized and deteriorated due to diffusion of the cathode off gas from the anode outlet to the inside of the anode. This reformed gas flow rate can be known in advance by performing experiments and simulations by changing the reformed gas flow rate while maintaining the anode temperature at or above the oxidation deterioration point. The anodic oxidation degradation can be judged by, for example, measuring the electrical conductivity of the anode electrode in an experiment and comparing it with an anode electrode that has not undergone oxidation degradation. Alternatively, the gas composition partial pressure of the anode can be calculated by simulation using an equation including an advection diffusion term, and can be determined by comparison with the equilibrium partial pressure in the oxidation reaction of the anode electrode. For example, when the anode electrode material is Ni, the equilibrium partial pressure of oxygen in the anode electrode oxidation reaction represented by the following formula is 1.2 × 10 ⁻¹⁴ atm (1.2 × 10 ⁻⁹ Pa) at 800 ° C. If the calculated value of the oxygen partial pressure of the anode is smaller than this value, it can be determined that the anode electrode is not oxidized and deteriorated.

  The reformed gas flow rate (the amount of reformed gas generated by the reformer) supplied to the SOFC to prevent oxidative deterioration of the anode can be combusted when the reformed gas passes through the SOFC and is discharged from the anode. The flow rate is preferably as follows. When the smallest flow rate among the combustible reformed gas flow rates is larger than the above-mentioned minimum required reformed gas flow rate, the smallest flow rate among the combustible reformed gas flow rates is referred to as “required minimum flow rate in condition iv Thus, the reformed gas flow rate can be obtained. Whether combustion is possible can be determined by, for example, sampling the gas in the combustion gas discharge line by experiment and performing composition analysis, or calculating by simulation.

  The flow rate of the hydrocarbon-based fuel supplied to the reformer (particularly the reforming catalyst layer) in a state where the reforming can be stopped is represented as FkE.

  FkE can be obtained in advance by experiments or simulations. Water flow (including steam) for steam reforming or autothermal reforming supplied to the reformer, air flow for autothermal reforming or partial oxidation reforming, cathode air flow, fuel and air flow for supplying to the burner , The flow rate of the fluid supplied to the indirect internal reforming SOFC, such as the flow rate of the fluid such as water or air supplied to the heat exchanger; the reformer, the evaporator of water or liquid fuel, the SOFC, the fluid supply piping The electric input / output to the indirect internal reforming SOFC, such as the electric heater output for heating etc., the electric input extracted from the thermoelectric conversion module, etc., is changed, that is, the operating conditions of the indirect internal reforming SOFC are changed. Thus, FkE can be known by conducting an experiment or simulation and searching for FkE that regularly satisfies the conditions i to iv. FkE may be any value as long as the conditions i to iv are satisfied, but it is preferable to use the smallest FkE from the viewpoint of thermal efficiency. The operation condition of the indirect internal reforming SOFC including the FkE is determined in advance as the operation condition in a state where the reforming can be stopped.

[Flow rate Fk (j) of different hydrocarbon fuels]
M different stepwise hydrocarbon fuel flow rates Fk (j) are determined in advance. Here, j is an integer of 1 or more and M or less, and M is an integer of 2 or more.

  However, Fk (j) decreases as j increases. That is, Fk (j)> Fk (j + 1). In addition, the smallest Fk (M) in Fk (j) is set equal to FkE.

  The largest fuel flow rate among the predetermined stepwise fuel flow rates Fk (j), that is, Fk (1) is preferably set to be equal to or greater than the maximum value of the fuel flow rates to be supplied before the stop method is started.

  The stepped fuel flow rate Fk (j) can be set, for example, at equal intervals.

  From the viewpoint of excellently preventing the cathode electrode from flowing and diffusing rapidly from the anode outlet to the inside of the anode due to a rapid decrease in the reformed gas, M is made as large as possible and Fk (j ) It is preferable to reduce the distance between them. For example, M is increased as much as possible and the interval of Fk (j) is decreased within the allowable range of memory consumption of the flow rate control unit and within the range exceeding the accuracy of the boosting unit and the flow rate control / measurement unit. it can.

  The flow rate of the hydrocarbon-based fuel that has been supplied to the reformer at the start of the stop method is represented as Fk0.

  Calculation of the flow rate of the hydrocarbon-based fuel that can be reformed by the type of reforming method performed after the stop method is started at the measured reforming catalyst layer temperature (hereinafter, this flow rate is referred to as “reformable flow rate”). The value is expressed as FkCALC. That is, FkCALC can be obtained by measuring the temperature of the reforming catalyst layer and calculating the flow rate of the hydrocarbon-based fuel that can be reformed by the reforming catalyst layer when the reforming catalyst layer is at that temperature. it can. At this time, the reforming catalyst layer is subjected to the kind of reforming method performed after the start of the stop method (hereinafter, the type of reforming method is referred to as the reforming type). The reforming type is, for example, steam reforming, autothermal reforming, or partial oxidation reforming.

  Specifically, when a certain type of reforming is performed before the start of the stopping method, the same type of reforming can be performed after the starting of the stopping method. In this case, the flow rate (calculated value) of the hydrocarbon-based fuel that can be reformed when the type of reforming is performed by the reformer is FkCALC. For example, if steam reforming was performed before the start of the stop method, steam reforming can be continued after the start of the stop method. The flow rate of the hydrocarbon-based fuel that can be reformed at temperature is FkCALC.

  Alternatively, if a certain type of reforming (first type of reforming) has been performed before the start of the stopping method, a different type of reforming (second type of reforming) is started. Can be done later. In this case, the flow rate of the hydrocarbon-based fuel that can be reformed when the second type reforming is performed by the reformer is FkCALC. For example, when autothermal reforming has been performed before the start of the stop method, switching to steam reforming can be performed after the start of the stop method. At this time, when steam reforming is performed, the flow rate (calculated value) of the hydrocarbon-based fuel that can be reformed at the reforming catalyst layer measurement temperature is FkCALC.

  For the calculation of FkCALC, the measured value of the reforming catalyst layer temperature is used. For this purpose, the reforming catalyst layer temperature is measured. For example, the reforming catalyst layer temperature can be monitored (continuously measured).

  When the temperature of the reforming catalyst layer is monitored before the start of the stop method, the temperature may be continuously monitored as it is.

  If the anode temperature falls below the oxidative deterioration point, reducing gas is no longer necessary, so the supply of hydrocarbon fuel to the reformer can be stopped and the stopping method can be terminated. Therefore, the temperature monitoring of the reforming catalyst layer may be continued until the anode temperature falls below the oxidation deterioration point.

  An appropriate temperature sensor such as a thermocouple can be used for measuring the reforming catalyst layer temperature.

  In the present invention, the following steps A to D are performed while the anode temperature is not below the oxidation deterioration point. When the anode temperature falls below the oxidative deterioration point, the supply of hydrocarbon fuel to the reformer can be stopped and the stopping method can be terminated regardless of the implementation status of steps A to D. When the supply of hydrocarbon fuel to the reformer is stopped, water for steam reforming or autothermal reforming (including steam), autothermal reforming or partial oxidation reforming to be supplied to the reformer Supply of fluid supplied to indirect internal reforming SOFC, such as air, cathode air, fuel and air supplied to burner, fluid such as water and air supplied to heat exchanger, reformer and water and liquid fuel It is possible to stop the input / output of electricity to the indirect internal reforming SOFC, such as the electric heater output for heating the evaporator, cell stack, fluid supply piping, etc., the electric input taken out from the thermoelectric conversion module, etc. .

  FIG. 9 is a flowchart showing steps A to D in the stopping method of the present invention. In addition to the procedure shown in this flowchart, the anode temperature is monitored, and when the anode temperature falls below the oxidative deterioration point of the anode, the hydrocarbon fuel is supplied to the reformer regardless of the steps A to D. To stop.

[Process A]
In the stopping method according to the present invention, first, the reforming catalyst layer temperature T is measured. Based on this temperature T, a reformable flow rate FkCALC is calculated. Further, the magnitude relationship between the supply flow rate FkE of the hydrocarbon-based fuel to the reformer in the above-described reforming stoppable state and the FkCALC is examined.

[Process B]
In step A, when FkCALC <FkE, the following steps B1 to B4 are sequentially performed. Note that “FkCALC <FkE” means that a hydrocarbon-based fuel having a flow rate of FkE cannot be reformed in the reformer (if the reforming type is changed, depending on the reforming type after the change). .

・ Process B1
First, step B1 is performed. That is, a step of raising the temperature of the reforming catalyst layer is performed.

  For example, the temperature of the reforming catalyst layer is raised using an appropriate heat source such as a heater or a burner attached to the reformer.

・ Process B2
And process B2 is performed. That is, a step of measuring the reforming catalyst layer temperature T, calculating FkCALC using this T, and comparing the values of FkCALC and FkE is performed.

・ Process B3
If FkCALC <FkE in step B2, a step returning to step B1 is performed. That is, steps B1 to B3 are repeated while FkCALC <FkE. During this time, the temperature of the reforming catalyst layer rises.

・ Process B4
If FkCALC ≧ FkE in step B2, the flow rate of hydrocarbon-based fuel supplied to the reformer (represented as Fk) is changed from Fk0 to FkE, and the process proceeds to step D. “FkCALC ≧ FkE” means that a hydrocarbon-based fuel having a flow rate of FkE can be reformed in the reforming catalyst layer (depending on the reforming type after the change when the reforming type is changed).

  At this time, when the reforming type is changed before and after the start of the stopping method, the fuel flow rate is changed from Fk0 to FkE and the reforming type is changed. By this method, it is possible to prevent oxidative deterioration of the anode by the reformed gas while reliably reforming the hydrocarbon fuel.

  In performing steps B2 and B3, the temperature rise in step B1 may be temporarily stopped, but step B1 may be continued while steps B2 and B3 are performed.

[Process C]
In the case of FkCALC ≧ FkE in the process A, if there is no intermediate flow rate Fk (j) smaller than Fk0 and larger than FkE among the predetermined hydrocarbon fuel flow rate Fk (j), it is supplied to the reformer. The flow rate of the hydrocarbon-based fuel is changed from Fk0 to FkE, and the process proceeds to Step D. At this time, when the reforming type is changed before and after the start of the stop method, the fuel flow rate can be changed from Fk0 to FkE and the reforming type can be changed.

  The intermediate flow rate is a value that satisfies FkE <Fk (j) <Fk0 among predetermined M Fk (j). There may or may not be an intermediate flow rate. As a case where there is no intermediate flow rate, there are a case where Fk0 is less than or equal to FkE, a case where Fk0 is greater than FkE and less than or equal to Fk (M−1).

  On the other hand, when FkCALC ≧ FkE in step A, if there is an intermediate flow rate Fk (j) that is smaller than Fk0 and larger than FkE among the predetermined hydrocarbon fuel flow rate Fk (j), the following steps C1 to C1 are performed. C5 is sequentially performed.

・ Process C1
J which gives the largest Fk (j) among the intermediate flow rates is represented as J, and the flow rate of the hydrocarbon-based fuel supplied to the reformer is reduced from Fk0 to Fk (J). At this time, when changing the reforming type before and after the start of the stopping method, the flow rate Fk of the hydrocarbon-based fuel is decreased from Fk0 to Fk (J), and the reforming type is changed.

・ Process C2
Measurement of the reforming catalyst layer temperature T and calculation of FkCALC based on this T are performed, and the values of FkCALC and Fk (J) are compared.

・ Process C3
If FkCALC> Fk (J) in step C2, the process returns to step C2. That is, steps C2 and C3 are repeated while FkCALC> Fk (J). During this time, the reforming catalyst layer temperature decreases. Therefore, the value of FkCALC decreases and eventually FkCALC ≦ Fk (J).

・ Process C4
When FkCALC ≦ Fk (J) in Step C2, the flow rate of the hydrocarbon-based fuel supplied to the reformer is decreased from Fk (J) to Fk (J + 1), and J is increased by 1. FkCALC ≦ Fk (J) means that the hydrocarbon fuel at the flow rate Fk (J) cannot be completely reformed by the reformer.

・ Process C5
J (the value after incrementing by 1 in step C4) is compared with M. If J ≠ M, the process returns to step C2, and if J = M, the process proceeds to step D.

  For example, when M = 3, that is, when three different Fk (j) are set in advance and Fk (1) and Fk (2) exist as intermediate flow rates, Fk0> Fk (1)> Fk (2)> FkE = Fk (3) is satisfied. At this time, the largest Fk (j) in the intermediate flow rate is Fk (1), and j giving Fk (1) is 1, so that J = 1 and the hydrocarbon system supplied to the reformer The fuel flow rate Fk is changed from Fk0 to Fk (J), that is, Fk (1) (step C1). When FkCALC ≦ Fk (J), that is, FkCALC ≦ Fk (1), the flow rate of the hydrocarbon-based fuel supplied to the reformer is changed from Fk (J), that is, Fk (1), to Fk (J + 1), that is, Fk (2). ) And 1 is added to J to make J = 2 (step C4). J is 2 and M is 3. Since J ≠ M at this stage, the process returns to the process C2 (process C5). When the reforming catalyst layer temperature is measured and FkCALC is calculated, and FkCALC ≦ Fk (J), that is, FkCALC ≦ Fk (2), the flow rate of the hydrocarbon-based fuel supplied to the reformer is Fk (J), that is, Fk ( From 2), Fk (J + 1), that is, Fk (3) is set, and 1 is added to J to set J = 3 (step C4). Since J is 3 and M is 3 at this stage, the process proceeds to process D (process C5).

  Alternatively, for example, when M = 4, that is, when four different Fk (j) are set, and Fk (2) and Fk (3) exist as intermediate flow rates, Fk ( 1) Assume that ≧ Fk0> Fk (2)> Fk (3)> FkE = Fk (4). At this time, the largest Fk (j) in the intermediate flow rate is Fk (2), and j giving Fk (2) is 2, so that J = 2 and the hydrocarbon system supplied to the reformer The fuel flow rate Fk is changed from Fk0 to Fk (J), that is, Fk (2) (step C1). When FkCALC ≦ Fk (J), that is, FkCALC ≦ Fk (2), the flow rate of the hydrocarbon-based fuel supplied to the reformer is changed from Fk (J), that is, Fk (2), to Fk (J + 1), that is, Fk (3). ) And 1 is added to J to make J = 3 (step C4). J is 3 and M is 4. Since J ≠ M at this stage, the process returns to the process C2 (process C5). The reforming catalyst layer temperature is measured and FkCALC is calculated. When FkCALC ≦ Fk (J), that is, FkCALC ≦ Fk (3), the flow rate of the hydrocarbon-based fuel supplied to the reformer is Fk (J), that is, Fk ( From 3), Fk (J + 1), that is, Fk (4) is set, and 1 is added to J to set J = 4 (step C4). Since J is 4 and M is 4 at this stage, the process proceeds to process D (process C5).

  Thus, instead of changing the flow rate of the hydrocarbon-based fuel supplied to the reformer from Fk0 to FkE at once, the fuel flow rate is changed from Fk0 to FkE via the reformable flow rate among the intermediate flow rates. Since it can be gradually reduced, cell cracking and anode deterioration can be prevented while reliably reforming.

  It is assumed that the hydrocarbon fuel (flow rate is Fk0) supplied to the reformer is reliably reformed at the start of the stop method. Otherwise, the unreformed hydrocarbon-based fuel is discharged from the reformer before the time when the stopping method is started, and a malfunction occurs. Of course, this situation should be avoided. Therefore, when the reforming type is not changed before and after the start of the stop method, the hydrocarbon fuel having an intermediate flow rate smaller than Fk0 can inevitably be reformed at the start of the stop method.

  When the reforming type is changed before and after the start of the stop method, the hydrocarbon-based fuel (flow rate is Fk0) supplied to the reformer at the start of the stop method (when the reforming type has not been changed yet). Even if the fuel is reliably reformed, the hydrocarbon fuel having a flow rate of Fk0 is not necessarily reformed reliably in the reforming type performed after changing the reforming type. Therefore, at the start of the stopping method, the hydrocarbon-based fuel having an intermediate flow rate is not always reformable depending on the reforming type after the change.

  In preparation for such a case, when the reforming type is changed before and after the start of the stopping method, the following step C0 can be performed.

・ Process C0
In Step C, if there is an intermediate flow rate Fk (j) that is smaller than Fk0 and greater than FkE among the predetermined hydrocarbon fuel flow rate Fk (j), Step C0 is performed before Step C1 is performed. Can do.

  Step C0: Check whether an intermediate flow rate equal to or lower than FkCALC exists, and if it exists, sequentially perform Steps C1 to C5, and if not, change the flow rate Fk of hydrocarbon-based fuel supplied to the reformer from Fk0 to FkE. And changing the reforming type and moving to step D.

  In step C0, the fact that there is no intermediate flow rate below FkCALC means that there is no intermediate flow rate that can be reformed after changing the reforming type, in other words, there is an intermediate flow rate to be adopted. It means not. Therefore, in such a case, the flow rate of the hydrocarbon-based fuel supplied to the reformer is changed from Fk0 to FkE and the reforming type is changed.

[Process D]
In step D, the process waits for the anode temperature to fall below the oxidation deterioration point. During this time, the flow rate of the hydrocarbon-based fuel is maintained at FkE, the flow rate of water for steam reforming or autothermal reforming (including steam) supplied to the reformer, air for autothermal reforming or partial oxidation reforming The flow rate of the fluid supplied to the indirect internal reforming SOFC, such as the flow rate, the cathode air flow rate, the fuel and air flow rate supplied to the burner, the flow rate of the fluid such as water and air supplied to the heat exchanger, the reformer and water Input and output of electricity to the indirect internal reforming SOFC, such as an electric heater output for heating an evaporator of liquid fuel, a cell stack, a fluid supply pipe, etc., an electric input taken from a thermoelectric conversion module, etc. The operating condition is maintained in a predetermined reforming stoppable state. That is, the operating conditions of the indirect internal reforming SOFC in a predetermined reforming stoppable state are maintained. Since the anode temperature decreases with time, the anode temperature eventually falls below the oxidation degradation point. The anode temperature can be appropriately monitored (continuously measured) using a temperature sensor such as a thermocouple.

  The monitoring of the anode temperature is preferably started immediately after starting the shutdown method. If these temperatures are monitored before the stop method is started, the temperature may be continuously monitored even when the stop method is performed.

When the anode temperature falls below the oxidative deterioration point, the supply of hydrocarbon fuel to the reformer can be stopped to end the stopping method.
[Case 1]
The case where FkCALC calculated in step A is equal to or higher than the flow rate FkE of the hydrocarbon-based fuel to the reformer in a state where the reforming can be stopped and one intermediate flow rate exists will be described with reference to FIG. To do. That is, a case will be described in which step B is not performed, but step C, particularly steps C1 to C5 are performed.

  In this case, M = 2, that is, Fk (1) and Fk (2) are determined in advance (Fk (2) is equal to FkE). Further, it is assumed that the flow rate Fk0 of the hydrocarbon-based fuel at the time of starting the stopping method is larger than Fk (1). Therefore, Fk0> Fk (1)> Fk (2) = FkE.

  2 (a) and 2 (b), the horizontal axis represents the elapsed time from the start of the stopping method of the present invention. In FIG. 6A, the vertical axis represents temperature, and in FIG. 5B, the vertical axis represents the flow rate of hydrocarbon fuel (the flow rate Fk of hydrocarbon-based fuel supplied to the reformer or the calculated reformable flow rate FkCALC. ). 3 to 8 are basically the same, but there are also diagrams in which the graph of the vertical axis is omitted.

  As shown in FIG. 2, step A is performed immediately after the stop method is started. That is, the reforming catalyst layer temperature T is measured, and the reformable flow rate FkCALC is calculated using this T. At this time, since FkCALC ≧ FkE, it is checked whether an intermediate flow rate exists.

  Among the predetermined stepwise fuel flow rates Fk (1) and Fk (2), there exists Fk (j), that is, Fk (1), that is smaller than Fk0 and larger than FkE, that is, Fk (2).

  Therefore, in step C1, since the intermediate flow rate is only Fk (1), the largest of the intermediate flow rates is Fk (1), and j giving Fk (1) is 1. Therefore, J = 1, and the flow rate of the hydrocarbon-based fuel supplied to the reformer is reduced from Fk0 to Fk (J), that is, Fk (1).

  Next, in step C2, the reforming catalyst layer temperature T is measured, the reformable flow rate FkCALC is calculated based on this T, and this FkCALC is compared with Fk (J), that is, Fk (1).

  Since FkCALC is larger than Fk (1) at the beginning of the stop method, step C2 is performed again according to step C3. Steps C2 and C3 are repeated for a while, while FkCALC decreases with time.

  When FkCALC is equal to or lower than Fk (1), the flow rate of the hydrocarbon-based fuel supplied to the reformer is decreased from Fk (J) to Fk (J + 1) according to step C4. That is, Fk (1) is decreased to Fk (2), that is, FkE. Then, 1 is added to J, and J = 2.

  Next, J and M are compared according to step C5. Since J = 2 and M = 2, the process proceeds to step D.

  In step D, the process waits for the anode temperature to fall below the oxidation deterioration point.

  When the anode temperature is lower than the oxidation deterioration point, the supply of hydrocarbon fuel to the reformer is stopped, and the stopping method is terminated.

  When the reforming type is changed before and after the stop method is started, the flow rate of the hydrocarbon-based fuel is decreased from Fk0 to Fk (1) and the reforming type is changed in step C1. When the reforming type is not changed, as shown in FIG. 2, it is possible to reform the hydrocarbon-based fuel whose flow rate is Fk0 at the start of the stopping method. Therefore, a hydrocarbon fuel with an intermediate flow rate (less than Fk0) can be reformed (FkCALC ≧ Fk0> Fk (1)). However, this may not be the case when changing the reforming type. That is, there may be a case where the hydrocarbon fuel at the flow rate Fk (1) cannot be reformed after the reforming type is changed. In preparation for such a case, the process C0 can be performed before the process C1 after determining whether or not an intermediate flow rate exists in the process C.

  In the case shown in FIG. 2, when the process C0 is performed, after confirming that the intermediate flow rate Fk (1) exists in the process C, it is checked whether an intermediate flow rate equal to or less than FkCALC exists. Since Fk (1) is below FkCALC, such an intermediate flow rate exists. Therefore, steps C1 to C5 are performed as described above.

[Case 2]
In the present invention, if the anode temperature is lower than the oxidation deterioration point at any time, the supply of hydrocarbon fuel to the reformer can be stopped and the stopping method can be terminated. Such a case will be described with reference to FIG. In FIG. 3, it is shown in contrast with FIG. 2, and therefore M = 2, stepped flow rates Fk (1) and Fk (2) are determined in advance, and Fk0> Fk (1)> Fk (2) = FkE. Suppose that

  First, the reforming catalyst layer temperature T is measured in step A, and FkCALC is calculated using the T. Before the FkCALC becomes equal to or lower than Fk (1) in Step C, the anode temperature becomes lower than the oxidation deterioration point, so the flow rate of the hydrocarbon-based fuel supplied to the reformer at that time is set to zero. That is, in this case, the step of reducing the flow rate of the hydrocarbon-based fuel supplied to the reformer from Fk (1) to Fk (2), that is, FkE, and increasing j by 1 to 2 is not necessary.

[Case 3]
A case where the reforming type is changed before and after the start of the stopping method will be described with reference to FIG. The reforming type (first reforming type) that was performed before the stop method was started and the reforming type (second reforming type) that was performed after the stop method was started are different. C1). Similar to case 1, in this case, M = 2, that is, Fk (1) and Fk (2) are determined in advance (Fk (2) is equal to FkE). Further, it is assumed that the flow rate Fk0 of the hydrocarbon-based fuel at the time of starting the stopping method is larger than Fk (1). Therefore, it is assumed that Fk0> Fk (1)> Fk (2) = FkE. However, the first reforming type is performed at the start of the stopping method, and the hydrocarbon fuel having a flow rate of Fk0 can be reformed for the first reforming type. The FkCALC calculated as the quality type is below Fk0.

  In the case shown in FIG. 4, in step A, the reforming catalyst layer temperature T is measured and FkCALC is calculated. Since FkCALC ≧ FkE, the process proceeds to step C. The only intermediate flow that exists is Fk (1).

  At this time, Step C0 can be performed to check whether there is an intermediate flow rate below FkCALC. Since Fk (1) is equal to or less than FkCALC, steps C1 to C5 can be performed.

  Next, the process C1 and subsequent steps are performed as in the case shown in FIG. As in this case, even when the reforming type is switched, if there is a flow rate below FkCALC among the intermediate flow rates, it is possible to decrease Fk0 to Fk (1) as in the case of FIG. it can. In this case, the fuel flow rate is decreased from Fk0 to Fk (1) and the reforming type is changed.

  That is, when the reforming type is not changed before and after the start of the stop method and Fk (1) exists as an intermediate flow rate, FkCALC ≧ Fk0 should be satisfied, and therefore FkCALC ≧ Fk (1). However, even when the reforming type is changed before and after the start of the stop method, if FkCALC ≧ Fk (1), the fuel flow rate can be gradually decreased through the intermediate flow rate.

[Case 4]
Referring to FIG. 5, FkCALC calculated in step A is equal to or higher than the reformable flow rate FkE (FkCALC ≧ FkE), and there are two intermediate flow rates among the predetermined stepwise fuel flow rates Fk (j). The case will be described. In this case, M = 3, and stepped flow rates Fk (1), Fk (2), and Fk (3) are determined in advance. Fk (3) is set equal to FkE. It is assumed that Fk0> Fk (1)> Fk (2)> Fk (3) = FkE.

  After starting the stopping method, the reforming catalyst layer temperature T is measured immediately in step A, and FkCALC is calculated based on this T.

  Since this FkCALC is equal to or higher than FkE, the process C is performed without performing the process B.

  In Step C, it can be confirmed that intermediate flow rates Fk (1) and Fk (2) are present.

  Therefore, step C1 is performed. The largest Fk (j) among the intermediate flow rates is Fk (1). Since j giving Fk (1) is 1, J = 1, and the flow rate Fk of the hydrocarbon-based fuel supplied to the reformer is decreased from Fk0 to Fk (1).

  Next, in step C2, the reforming catalyst layer temperature T is measured and FkCALC is calculated based on this T. While this FkCALC is larger than Fk (J), that is, Fk (1), the process returns to Step C2 (Step C3).

  When FkCALC calculated in step C2 is equal to or lower than Fk (J), that is, Fk (1), the flow rate of the hydrocarbon-based fuel supplied to the reformer is decreased from Fk (J) to Fk (J + 1), and J is Increase by one. That is, Fk (1) is changed to Fk (2), and then J = 2 is set (step C4).

  Next, according to Step C5, since J = 2 and M = 3, the process returns to Step C2. Steps C2 to C5 are repeated. In step C5, which is performed a second time, J = M = 3, so that the process proceeds to step D.

  In step D, the process waits for the anode temperature to fall below the oxidation degradation point. When the anode temperature falls below the oxidation degradation point, the flow rate of the hydrocarbon-based fuel supplied to the reformer is made zero, and the stopping method can be terminated.

  Of course, also in this case, if the anode temperature falls below the oxidative deterioration point before FkCALC falls below Fk (2), and further below Fk (1), Step D may be performed at that point. Thereafter, step C need not be performed.

  In the case shown in FIG. 2, two stepped flow rates are set. In this case, three stepped flow rates are set. Therefore, in this case, the flow rate of the hydrocarbon fuel can be decreased little by little. For this reason, it is possible to further reduce the possibility that the cathode offgas rapidly flows and diffuses from the anode outlet to the inside of the anode due to the sudden decrease in the flow rate of the reformed gas, thereby further oxidatively degrading the anode electrode.

[Case 5]
The case where the process C0 is performed when the reforming type is changed before and after the start of the stopping method will be described with reference to FIG.

  Here, M = 2, and stepped flow rates Fk (1) and Fk (2) are determined in advance. It is assumed that Fk0> Fk (1)> Fk (2) = FkE.

  Immediately after the start of the stop method, step A is performed to measure the reforming catalyst layer temperature T and calculate FkCALC based on this T. Since FkCALC ≧ FkE, step C is not performed and step C is performed.

  In the process C, an intermediate flow rate (Fk (1)) exists in the predetermined stepwise fuel flow rate Fk (j).

  In step C0, since FkCALC <Fk (1), it is determined that there is no intermediate flow rate equal to or lower than FkCALC. Therefore, the flow rate Fk of the hydrocarbon-based fuel supplied to the reformer is reduced from Fk0 to FkE, the reforming type is changed, and the process D is started.

  Thereafter, when the anode temperature falls below the oxidative deterioration point, the flow rate of the hydrocarbon-based fuel supplied to the reformer can be made zero, and the stopping method can be terminated.

[Case 6]
A case where it is determined in step C that there is no intermediate flow rate among the predetermined stepwise fuel flow rates Fk (j) will be described with reference to FIG.

  Here, M = 2, and stepped flow rates Fk (1) and Fk (2) are determined in advance. It is assumed that Fk (1)> Fk0> Fk (2) = FkE.

  Immediately after the start of the stop method, step A is performed to measure the reforming catalyst layer temperature T and calculate FkCALC based on this T. Since FkCALC ≧ FkE, step C is not performed and step C is performed.

  Step C checks whether an intermediate flow rate exists, but in this case there is no intermediate flow rate.

  In this case, as shown in FIG. 7, the flow rate Fk of the hydrocarbon-based fuel supplied to the reformer is changed from Fk0 to FkE. Then, the process proceeds to step D and waits for the anode temperature to become lower than the oxidation deterioration point.

  When changing the reforming type before and after the start of the stop method, the fuel flow rate is changed from Fk0 to FkE and the reforming type is changed.

  When the anode temperature becomes lower than the oxidation deterioration point, the flow rate of the hydrocarbon-based fuel supplied to the reformer can be made zero, and the stopping method can be terminated.

[Case 7]
A case where FkCALC calculated in step A is smaller than the flow rate FkE of the hydrocarbon-based fuel supplied to the reformer in a state where the reforming can be stopped, that is, a case where FkCALC <FkE will be described with reference to FIG. That is, the case where the process B is performed will be described.

  Here, M = 2, and stepped flow rates Fk (1) and Fk (2) are determined in advance. It is assumed that Fk (1)> Fk (2) = FkE> Fk0.

  Immediately after the start of the stop method, step A is performed to measure the reforming catalyst layer temperature T and calculate FkCALC based on this T. Since FkCALC <FkE, step B is not performed but step B is performed.

  In this case, as shown in FIG. 8, the reforming catalyst layer is formed with an appropriate heat source such as a burner or a heater attached to the reformer until FkCALC ≧ FkE so that the hydrocarbon fuel at the flow rate FkE can be reformed. Raise the temperature.

  When FkCALC ≧ FkE, the flow rate Fk of the hydrocarbon-based fuel supplied to the reformer is changed from Fk0 to FkE. When changing the reforming type before and after the start of the stop method, the fuel flow rate is changed from Fk0 to FkE and the reforming type is changed.

  Then, the process proceeds to step D and waits until the anode temperature falls below the oxidation deterioration point.

  When the anode temperature becomes lower than the oxidation deterioration point, the flow rate of the hydrocarbon-based fuel supplied to the reformer can be made zero, and the stopping method can be terminated.

[Calculation of reformable flow rate (calculation of FkCALC)]
Hereinafter, a method for calculating the flow rate of the hydrocarbon-based fuel that can be reformed in the reforming catalyst layer based on the measured temperature of the reforming catalyst layer will be described.

  When the type of the reforming method is changed before and after the start of the stop method, FkCALC is calculated assuming that the reforming method after the change is performed.

  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 SOFC. The flow rate that results in a composition 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 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 Ni 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, calculation of the reformable flow rate in the reforming catalyst layer is performed based on the measured temperature of the reforming catalyst layer.

  The reformable flow rate FkCALC in the reforming catalyst layer can be obtained by an experiment in advance as a function of the temperature T of the reforming catalyst layer (represented as FkCALC (T) when explicitly indicating that the function is a function of temperature). . Further, the reformable flow rate can be obtained after multiplying the function obtained by the experiment by the safety factor or correcting the temperature to the safe side. The unit of FkCALC (T) is, for example, mol / s.

<When there is one temperature measurement point>
-Temperature measurement location When the temperature measurement point of the reforming catalyst layer is one point, the temperature measurement location used for calculating the reformable flow rate is preferably relative to the reforming catalyst layer from the viewpoint of safety control. In particular, it is preferable to employ a place where the temperature is lowered, more preferably a place where the temperature is lowest in the reforming catalyst layer. When the heat of reaction in the reforming catalyst layer is endothermic, the vicinity of the center of the catalyst layer can be selected as the temperature measurement location. When the heat of reaction in the reforming catalyst layer is exothermic, and the end portion becomes cooler than the center portion due to heat dissipation, the end portion of the catalyst layer can be selected as the temperature measurement location. The position where the temperature is lowered can be known by preliminary experiments and simulations.

The reformable flow rate FCALC (T) can be a function of temperature T only. However, the reformable flow rate FkCALC may be a function having variables other than T such as the catalyst layer volume and the concentration of the gas component in addition to the temperature T. In this case, when calculating the reformable flow rate may suitably determine the variables other than T, and variables other than T, it is possible to calculate the reformable flow rate F ^R from the measured T.

<When there are multiple temperature measurement points>
The temperature measurement point used for calculating the reformable flow rate FkCALC need not be one point. In order to calculate the reformable flow rate in the reforming catalyst layer more accurately, it is preferable that the temperature measurement points are two or more. For example, the inlet temperature and outlet temperature of the reforming catalyst layer are measured, and the average of these can be used as the aforementioned reforming catalyst layer temperature T.

Or, for example, the reforming catalyst layer to N divided regions Z _i (N is an integer of 2 or more, i is an integer 1 or more N) thinking, knowing the temperature T _i of each divided region Z _i, the temperature T _i Thus, the reformable flow rate FkCALC _i (T _i ) in each divided region is calculated, and a value obtained by integrating them can be calculated as the reformable flow rate FkCALC in the reforming catalyst layer.

When N divided regions Z _i are considered, the reformable flow rates of all the divided regions may be integrated, or a value obtained by integrating only a part of the N divided regions is used as the reforming catalyst layer. The reformable flow rate FkCALC may be employed. Depending on the amount of hydrocarbon fuel supplied, the catalyst layer region to be integrated can be changed as appropriate.

As the temperature of the divided region Z _i , the actually measured temperature can be used as it is, but an appropriately calculated value such as an average value of the inlet temperature and the outlet temperature of the divided region can also be used as a representative value.

Further, it is not necessary to measure the temperature for all the divided regions Z _i . Further, the catalyst layer division number N and the number of temperature measurement points can be set independently.

  It is also possible to know the temperature by measuring the temperature of a part of the N divided regions and supplementing the remaining divided regions as appropriate from the measured temperatures.

  For example, as the temperature of the divided area where the temperature sensor is not installed, the temperature of the divided area closest to the divided area can be used. When there are two closest divided regions, the temperature of one of the two divided regions can be used, or the average value of the temperatures of the two divided regions can be used.

  Regardless of the divided region, the temperature of a plurality of points (at different positions in the gas flow direction) of the reforming catalyst layer can be measured, and the temperature of each divided region can be known from the measured temperatures of the plurality of points. For example, the temperature at the inlet and outlet of the reforming catalyst layer is measured (and the temperature at an arbitrary position in the middle portion may be measured), and the reforming catalyst layer is measured from these measured temperatures by an approximation method such as the least square method. It is possible to interpolate the temperature and know the temperature of the divided area from the interpolation curve.

(Example of temperature measurement location used to calculate reformable flow rate)
In order to know the temperature of all the divided areas, the temperature of the following points can be measured.
-Entrance and exit of each divided area.
-Inside each divided area (inside from the entrance and exit) (one or more points).
-Entrance, exit and inside of each divided area (one or more points for one divided area).

In order to know the temperature of some of the divided regions, the temperature at the following locations can be measured.
-Entrance and exit of some divided areas.
-Inside of some divided areas (inside from the inlet and outlet) (one or more points).
-Entrances, exits, and interiors of some divided areas (one or more points for one divided area).

[Others]
When the flow rate Fk of hydrocarbon-based fuel is set to FkE, the flow rate of water for steam reforming or autothermal reforming (including steam) supplied to the reformer according to the flow rate, if necessary, self-thermal reforming Or the fluid supplied to the indirect internal reforming SOFC, such as the air flow rate for partial oxidation reforming, the cathode air flow rate, the fuel and air flow rate supplied to the burner, the flow rate of fluid such as water or air supplied to the heat exchanger Indirect internal reforming SOFC, such as the flow rate of air, the reformer and the electric heater output to heat the water and liquid fuel evaporator, cell stack, fluid supply piping, etc., the thermoelectric conversion module etc. The input / output of electricity to the operation condition is set in a predetermined reforming stoppable state. That is, the operation condition of the indirect internal reforming SOFC in a predetermined reforming stoppable state is set.

  When changing the flow rate of the hydrocarbon-based fuel supplied to the reformer in step C1 and step C4, the flow rate of the fluid supplied to the indirect internal reforming SOFC according to the necessity as described above, indirect internal Input / output of electricity to the reforming SOFC can be set to predetermined operating conditions. 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. To maintain the value, the water flow rate can be reduced as the fuel flow rate decreases. Regarding the air flow rate supplied to the reformer, the fuel flow rate is maintained 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 fed to the reforming catalyst layer) maintains a predetermined value. The air flow rate can be reduced with a decrease in. 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, operating conditions in a predetermined reforming stoppable state Or predetermined operating conditions as a function of fuel flow rate.

  When changing the reforming type, if necessary, the flow rate of fluid supplied to the indirect internal reforming SOFC and the input / output of electricity to the indirect internal reforming SOFC are determined in advance, as necessary. Can be a condition. For example, the flow rate of water supplied to the reformer can be changed to a flow rate with a predetermined steam / carbon ratio in order to suppress carbon deposition. The air flow rate supplied to the reformer can be changed to a flow rate that provides a predetermined oxygen / carbon ratio. 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, operating conditions in a predetermined reforming stoppable state Or predetermined operating conditions as a function of fuel flow rate.

  When a steam reforming reaction is performed, that is, when steam reforming or autothermal reforming is performed, steam is supplied to the reforming catalyst layer. When performing a partial oxidation reforming reaction, that is, when performing partial oxidation reforming or autothermal reforming, an oxygen-containing gas is supplied to the reforming catalyst layer. As the oxygen-containing gas, a gas containing oxygen can be used as appropriate, but air is preferable because it is easily available.

  The present invention is particularly effective when the hydrocarbon fuel has 2 or more carbon atoms. This is because such fuel is particularly required to be reformed.

[Hydrocarbon fuel]
As the hydrocarbon-based fuel, as a reformed gas raw material, a compound known from the field of SOFC, containing carbon and hydrogen (may contain other elements such as oxygen) or a mixture thereof, or a mixture thereof may be used as appropriate. And 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, SOFC power generators using kerosene or LPG are useful as emergency power supplies. In particular, kerosene is preferable because it is easy to handle.

[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.

  The reformer is appropriately equipped with a steam reforming catalyst having steam reforming ability, a partial oxidation reforming catalyst having partial oxidation reforming ability, and a self-thermal reforming catalyst having both partial oxidation reforming ability and steam reforming ability. Can be used.

  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.

[SOFC]
The reformed gas obtained from the reformer is supplied to the anode of the SOFC. On the other hand, an oxygen-containing gas such as air is supplied to the cathode of the SOFC. During power generation, the SOFC generates heat with power generation, and the heat is transmitted from the SOFC to the reformer by radiant heat transfer or the like. Thus, the SOFC exhaust heat is used to heat the reformer. Gas exchange and the like are appropriately performed using piping or the like.

  As the SOFC, a known SOFC can be appropriately selected and employed. In the SOFC, oxygen ion conductive ceramics or proton ion conductive ceramics are generally used as an electrolyte.

  The SOFC 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, sometimes referred to as a bundle, but the stack in this specification includes a bundle) is preferable. Used. In this case, one or more stacks may be used.

  The shape of the SOFC is not limited to the cubic stack, and an appropriate shape can be adopted.

  For example, oxidation deterioration of the anode may occur at about 400 ° C.

[Case]
As the casing (module container), an appropriate container capable of accommodating the SOFC, the reformer, and the combustion region 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.

  The module container is preferably airtight so that the interior of the module container does not communicate with the outside (atmosphere).

(Combustion area)
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.

[Reforming catalyst]
Any of the steam reforming catalyst, partial oxidation reforming catalyst, and autothermal reforming catalyst used in the reformer can be a known catalyst. Examples of the partial oxidation reforming catalyst include platinum-based catalysts, examples of the steam reforming catalyst include ruthenium-based and nickel-based catalysts, and examples of the autothermal reforming catalyst include rhodium-based catalysts. Examples of reforming catalysts that can promote combustion include platinum-based and rhodium-based catalysts.

  The temperature at which the partial oxidation reforming reaction can proceed is, for example, 200 ° C. or higher, and the temperature at which the steam reforming reaction can proceed is, for example, 400 ° C. or higher.

[Operation conditions of reformer]
Hereinafter, the conditions during rated operation and stop 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, more preferably 500 ° C to 800 ° C. When the hydrocarbon fuel is liquid, the space velocity (LHSV) at this time is preferably selected in the range of 0.05 to 20, more preferably 0.1 to 10, and further preferably 0.2 to 5. 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 0.1-30. 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]
Known components of the indirect internal reforming SOFC can be appropriately provided as necessary. Specific examples include a vaporizer for vaporizing liquid, a pump for pressurizing various fluids, a pressure increasing means such as a compressor and a blower, a valve for adjusting the flow rate of the fluid, or for blocking / switching the flow of the fluid. Such as flow rate control means, flow path blocking / switching means, heat exchanger for heat exchange / recovery, condenser for condensing gas, heating / heat-retaining means for externally heating various devices with steam, etc., hydrocarbon system Fuel (reforming raw materials) and combustion fuel storage means, instrumentation air and electrical systems, control signal systems, control devices, output and power electrical systems, desulfurization to reduce the concentration of sulfur in the fuel Such as a vessel.

  The present invention can be applied to, for example, an indirect internal reforming SOFC used in a stationary or moving power generator or a cogeneration system.

It is a schematic diagram which shows the outline | summary about one form of the indirect internal reforming type | mold SOFC which can apply this invention. It is a conceptual graph for demonstrating the method of this invention, (a) shows the relationship between elapsed time and temperature, (b) shows the relationship between elapsed time and hydrocarbon fuel flow rate. It is a conceptual graph for demonstrating the method of this invention, (a) shows the relationship between elapsed time and temperature, (b) shows the relationship between elapsed time and hydrocarbon fuel flow rate. It is a conceptual graph for demonstrating the method of this invention, and shows the relationship between elapsed time and hydrocarbon fuel flow volume. It is a conceptual graph for demonstrating the method of this invention, and shows the relationship between elapsed time and hydrocarbon fuel flow volume. It is a conceptual graph for demonstrating the method of this invention, and shows the relationship between elapsed time and hydrocarbon fuel flow volume. It is a conceptual graph for demonstrating the method of this invention, and shows the relationship between elapsed time and hydrocarbon fuel flow volume. It is a conceptual graph for demonstrating the method of this invention, and shows the relationship between elapsed time and hydrocarbon fuel flow volume. It is a flowchart for demonstrating the method of this invention.

Explanation of symbols

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 Case (module container)
9 Electric heater attached to the reformer

Claims (3)

A reformer having a reforming catalyst layer for reforming hydrocarbon fuel to produce reformed gas;
A solid oxide fuel cell that generates electric power using the reformed gas; and
A combustion region for burning anode off-gas discharged from the solid oxide fuel cell;
A method for stopping an indirect internal reforming solid oxide fuel cell comprising: a reformer, a solid oxide fuel cell, and a housing that houses a combustion region;
The following conditions i to iv,
i) The anode temperature of the solid oxide fuel cell is steady,
ii) the anode temperature is below the oxidative degradation point;
iii) In the reformer, the hydrocarbon-based fuel is reformed, and a reformed gas having a composition suitable for supplying to the anode is generated,
iv) The amount of the reformed gas generated is equal to or higher than the minimum flow rate necessary to prevent oxidative deterioration of the anode when the anode temperature of the solid oxide fuel cell is at or above the oxidative deterioration point.
FkE represents the flow rate of the hydrocarbon-based fuel supplied to the reformer in a state where all of the above are satisfied,
A stepwise hydrocarbon-based fuel flow rate Fk (j) is determined in advance (where j is an integer of 1 to M, and M is an integer of 2 or more), where Fk (j) is decreases with increasing j, and the smallest Fk (M) among Fk (j) is equal to FkE,
The flow rate of the hydrocarbon-based fuel that has been supplied to the reformer at the start of the stop method is expressed as Fk0
When the calculated value of the flow rate of the hydrocarbon-based fuel that can be reformed by the type of reforming method performed after the start of the stopping method at the measured temperature of the reforming catalyst layer is expressed as FkCALC,
When the anode temperature falls below the oxidative degradation point, the supply of hydrocarbon fuel to the reformer is stopped and the stopping method is terminated.
While the anode temperature is not below the oxidation degradation point,
A) a step of measuring the reforming catalyst layer temperature, calculating FkCALC using the measured temperature, and comparing the values of FkCALC and FkE;
B) A step of sequentially performing the following steps B1 to B4 when FkCALC <FkE in step A,
B1) Step of heating the reforming catalyst layer
B2) measuring the reforming catalyst layer temperature, calculating FkCALC using the measured temperature, and comparing the values of FkCALC and FkE;
B3) A step of returning to step B1 when FkCALC <FkE in step B2,
B4) When FkCALC ≧ FkE in step B2, the flow rate of the hydrocarbon-based fuel supplied to the reformer is changed from Fk0 to FkE, and the process proceeds to step D.
C) When FkCALC ≧ FkE in step A,
If there is no intermediate flow rate Fk (j) that is smaller than Fk0 and larger than FkE among the predetermined hydrocarbon-based fuel flow rates Fk (j), the flow rate of the hydrocarbon-based fuel supplied to the reformer is changed from Fk0 to FkE. And go to step D,
A step of sequentially performing the following steps C1 to C5 if there is an intermediate flow rate Fk (j) that is smaller than Fk0 and larger than FkE among the predetermined hydrocarbon-based fuel flow rates Fk (j);
C1) j giving the largest Fk (j) among the intermediate flow rates is represented as J,
Reducing the flow rate of hydrocarbon-based fuel supplied to the reformer from Fk0 to Fk (J);
C2) measuring the reforming catalyst layer temperature, calculating FkCALC using the measured temperature, and comparing the value of FkCALC and Fk (J);
C3) If FkCALC> Fk (J) in step C2, returning to step C2;
C4) A step of decreasing the flow rate of the hydrocarbon-based fuel supplied to the reformer from Fk (J) to Fk (J + 1) and increasing J by 1 when FkCALC ≦ Fk (J) in step C2.
C5) Comparing J and M. If J ≠ M, return to step C2, and if J = M, go to step D, and D) wait for the anode temperature to fall below the oxidation degradation point. A method for stopping an indirect internal reforming solid oxide fuel cell.   The method according to claim 1, wherein the hydrocarbon fuel includes a hydrocarbon fuel having 2 or more carbon atoms.   The method according to claim 2, 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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