ABSTRACT
Abstract
A method of load following operation of a fuel cell system may include measuring a temperature of the reforming catalyst layer, obtaining a reformable flow rate of the hydrocarbon-based fuel capable of being reformed in the reforming catalyst layer at the temperature, and controlling electric power generation based on the relationship between the reformable flow rate and a minimum value.
Description
This is a U.S. national stage application of International Application No. PCT/JP2009/052744, filed on 18 Feb. 2009. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. JP2008-083634, filed 27 Mar. 2008 and Japanese Application No. JP2008-083635, filed 27 Mar. 2008, the disclosure of which is also incorporated herein by reference.
TECHNICAL FIELD
The present invention relates to a fuel cell system that generates electric power using a reformed gas obtained by reforming a hydrocarbon-based fuel, such as kerosene.
BACKGROUND ART
A solid oxide fuel cell (hereinafter sometimes referred to as SOFC) system usually includes a reformer for reforming a hydrocarbon-based fuel, such as kerosene and city gas, to generate a hydrogen-containing gas (reformed gas), and an SOFC for electrochemically reacting the reformed gas and air for electric power generation.
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, and heating to a temperature at which catalytic activity is exhibited is necessary for using a reforming catalyst.
Steam reforming is a very largely endothermic reaction. Also, the reaction temperature of the steam reforming is 550 to 750° C., which is relatively high, and the steam reforming requires a high temperature heat source. Therefore, an internal reforming SOFC is known in which a reformer (internal reformer) is installed near an SOFC, and the reformer is heated mainly using radiant heat from the SOFC as a heat source (Patent Document 1).
Also, proposals on the load following operation of a fuel cell system are made in Patent Documents 2 and 3.
Patent Document 1: JP2004-319420A
Patent Document 2: JP2001-185196A
Patent Document 3: JP2006-32262A
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
When a hydrocarbon-based fuel is not reformed to a predetermined composition, and an unreformed component is supplied to an SOFC, anode degradation and flow blockage due to carbon deposition may occur, particularly when a heavy hydrocarbon, such as kerosene, is used as the hydrocarbon-based fuel.
An SOFC system may be subjected to load following operation. In other words, an SOFC system may be subjected to an operation in which the amount of electric power generation of the SOFC system is varied according to the fluctuation of electric power demand. For example, when the amount of electric power generation is increased, the feed rate of the hydrocarbon-based fuel to the SOFC system may be increased. In such a case, carbon may be deposited. Therefore, it is desired to reliably reform the hydrocarbon-based fuel also in the load following operation. In the arts disclosed in Patent Documents 2 and 3, improvement is still desired in terms of performing reliable reforming.
This is true not only for the SOFC system, but also for a fuel cell system having a high temperature fuel cell, such as a molten carbonate fuel cell (MCFC).
It is an object of the present invention to provide a method in which, when performing load following operation of a fuel cell system including a reformer having a reforming catalyst layer and a high temperature fuel cell, reforming can be more reliably performed to more reliably prevent flow blockage and anode degradation.
It is another object of the present invention to provide a fuel cell system suitable for performing such a method.
Means for Solving the Problems
The present invention provides a method for performing load following operation of a fuel cell system including a reformer having a reforming catalyst layer, for reforming a hydrocarbon-based fuel to produce a reformed gas containing hydrogen, and a high temperature fuel cell for generating electric power using the reformed gas, wherein
a plurality of electrical outputs P i of the fuel cell (i is an integer of 1 or more and M or less, where M is an integer of 2 or more) and a flow rate F i of the hydrocarbon-based fuel that corresponds to each P i are set beforehand,
where each F i is a flow rate of the hydrocarbon-based fuel required to be supplied to the reforming catalyst layer in order to output a corresponding electrical output P i from the fuel cell, each P i is 0 or more, P i increases with an increase of i, and each F i is larger than 0,
P M that is P i when i is M is a maximum electrical output of the fuel cell, and
a minimum value of all F i is represented as F min ,
the method including:
A) measuring a temperature T of the reforming catalyst layer;
B) obtaining a reformable flow rate F R that is a flow rate of the hydrocarbon-based fuel that can be reformed in the reforming catalyst layer at the temperature T;
C) when the reformable flow rate F R is smaller than the minimum value F min , stopping electric power generation in the fuel cell; and
D) when the reformable flow rate F R is equal to or more than the minimum value F min ,
performing step d1 if a fuel cell output demand value P D is equal to or less than the maximum electrical output P M , and performing step d2 if the fuel cell output demand value P D exceeds the maximum electrical output P M ,
d1) if there exists, among all P i , a P i that is equal to the fuel cell output demand value P D , then setting F i , that corresponds to P i , that is equal to P D , as F DS ;
if there does not exist, among all P i , a P i that is equal to the fuel cell output demand value P D , then setting F i , that is the not smaller one of the two Fi, as F DS ; one of said two Fi corresponding to the smallest P i that exceeds P D , and the other one of said two F i corresponding to the largest P i that is less than P D ,
when F DS is equal to or less than the reformable flow rate F R , setting an electrical output of the fuel cell to P D , and setting a flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F DS , and
when F DS exceeds the reformable flow rate F R ,
if there exists a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that is less than P D and that corresponds to F i , that is equal to or less than F R ; and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then stopping electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R ,
d2) when F M that is F i , corresponding to the maximum electrical output P M , is equal to or less than the reformable flow rate F R , setting the electrical output of the fuel cell to P M , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F M , and
when F M that is F i , corresponding to the maximum electrical output P M , exceeds the reformable flow rate F R ,
if there exists a P i that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that corresponds to F i , that is equal to or less than F R , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that corresponds to F i , that is equal to or less than F R , then stopping the electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R .
A first embodiment of the present invention provides a method for performing load following operation of a fuel cell system including a reformer having a reforming catalyst layer, for reforming a hydrocarbon-based fuel to produce a reformed gas containing hydrogen, and a high temperature fuel cell for generating electric power using the reformed gas, wherein
a plurality of electrical outputs P i of the fuel cell (i is an integer of 1 or more and M or less, where M is an integer of 2 or more) and a flow rate F i of the hydrocarbon-based fuel that corresponds to each P i are set beforehand,
where each F i is a flow rate of the hydrocarbon-based fuel required to be supplied to the reforming catalyst layer in order to output a corresponding electrical output P i from the fuel cell, each P i is 0 or more, P i increases with an increase of i, and each F i is larger than 0,
P M that is P i when i is M is a maximum electrical output of the fuel cell, and
a minimum value of all F i is represented as F min ,
the method including:
1-A) measuring a temperature of the reforming catalyst layer; 1-B) calculating a reformable flow rate F R that is a 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; 1-C) when the calculated reformable flow rate F R is smaller than the minimum value F min , stopping electric power generation in the fuel cell; and 1-D) when the calculated reformable flow rate F R is equal to or more than the minimum value F min , performing step 1-d1 if a fuel cell output demand value P D is equal to or less than the maximum electrical output P M , and performing step 1-d2 if the fuel cell output demand value P D exceeds the maximum electrical output P M , 1-d1) if there exists, among all P i , a P i that is equal to the fuel cell output demand value P D , then setting F i , that corresponds to P i , that is equal to P D , as F DS ,
if there does not exist, among all P i , a P i that is equal to the fuel cell output demand value P D , then setting F i , that is the not smaller one of the two Fi, as F DS ; one of said two Fi corresponding to the smallest P i that exceeds P D and the other one of said two F i corresponding to the largest P i that is less than P D ,
when F DS is equal to or less than the calculated reformable flow rate F R , setting an electrical output of the fuel cell to P D , and setting a flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F DS , and when F DS exceeds the calculated reformable flow rate F R ,
if there exists a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that is less than P D and that corresponds to F i , that is equal to or less than F R ; and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then stopping electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R ,
1-d2) when F M that is F i , corresponding to the maximum electrical output P M , is equal to or less than the calculated reformable flow rate F R , setting the electrical output of the fuel cell to P M , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F M , and when F M that is F i , corresponding to the maximum electrical output P M , exceeds the calculated reformable flow rate F R ,
if there exists a P i that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that corresponds to F i , that is equal to or less than F R , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that corresponds to F i , that is equal to or less than F R , then stopping the electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R .
A second embodiment of the present invention provides a method for performing load following operation of a fuel cell system including a reformer having a reforming catalyst layer, for reforming a hydrocarbon-based fuel to produce a reformed gas containing hydrogen, and a high temperature fuel cell for generating electric power using the reformed gas, wherein
a plurality of electrical outputs P i of the fuel cell (i is an integer of 1 or more and M or less, where M is an integer of 2 or more) and a flow rate F i of the hydrocarbon-based fuel that corresponds to each P i are set beforehand,
where each F i is a flow rate of the hydrocarbon-based fuel required to be supplied to the reforming catalyst layer in order to output a corresponding electrical output P i from the fuel cell, each P i is 0 or more, P i increases with an increase of i, and each F i is larger than 0,
P M that is P i when i is M is a maximum electrical output of the fuel cell, and
a minimum value of all F i is represented as F min , and
a plurality of temperatures T j of the reforming catalyst layer (j is an integer of 1 or more and N or less, where N is an integer of 2 or more) and a flow rate G j of the hydrocarbon-based fuel that corresponds to each T j are set beforehand,
where each G j is a flow rate of the hydrocarbon-based fuel that can be reformed in the reforming catalyst layer at a corresponding reforming catalyst layer temperature T<sub
This is a U.S. national stage application of International Application No. PCT/JP2009/052744, filed on 18 Feb. 2009. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. JP2008-083634, filed 27 Mar. 2008 and Japanese Application No. JP2008-083635, filed 27 Mar. 2008, the disclosure of which is also incorporated herein by reference.
TECHNICAL FIELD
The present invention relates to a fuel cell system that generates electric power using a reformed gas obtained by reforming a hydrocarbon-based fuel, such as kerosene.
BACKGROUND ART
A solid oxide fuel cell (hereinafter sometimes referred to as SOFC) system usually includes a reformer for reforming a hydrocarbon-based fuel, such as kerosene and city gas, to generate a hydrogen-containing gas (reformed gas), and an SOFC for electrochemically reacting the reformed gas and air for electric power generation.
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, and heating to a temperature at which catalytic activity is exhibited is necessary for using a reforming catalyst.
Steam reforming is a very largely endothermic reaction. Also, the reaction temperature of the steam reforming is 550 to 750° C., which is relatively high, and the steam reforming requires a high temperature heat source. Therefore, an internal reforming SOFC is known in which a reformer (internal reformer) is installed near an SOFC, and the reformer is heated mainly using radiant heat from the SOFC as a heat source (Patent Document 1).
Also, proposals on the load following operation of a fuel cell system are made in Patent Documents 2 and 3.
Patent Document 1: JP2004-319420A
Patent Document 2: JP2001-185196A
Patent Document 3: JP2006-32262A
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
When a hydrocarbon-based fuel is not reformed to a predetermined composition, and an unreformed component is supplied to an SOFC, anode degradation and flow blockage due to carbon deposition may occur, particularly when a heavy hydrocarbon, such as kerosene, is used as the hydrocarbon-based fuel.
An SOFC system may be subjected to load following operation. In other words, an SOFC system may be subjected to an operation in which the amount of electric power generation of the SOFC system is varied according to the fluctuation of electric power demand. For example, when the amount of electric power generation is increased, the feed rate of the hydrocarbon-based fuel to the SOFC system may be increased. In such a case, carbon may be deposited. Therefore, it is desired to reliably reform the hydrocarbon-based fuel also in the load following operation. In the arts disclosed in Patent Documents 2 and 3, improvement is still desired in terms of performing reliable reforming.
This is true not only for the SOFC system, but also for a fuel cell system having a high temperature fuel cell, such as a molten carbonate fuel cell (MCFC).
It is an object of the present invention to provide a method in which, when performing load following operation of a fuel cell system including a reformer having a reforming catalyst layer and a high temperature fuel cell, reforming can be more reliably performed to more reliably prevent flow blockage and anode degradation.
It is another object of the present invention to provide a fuel cell system suitable for performing such a method.
Means for Solving the Problems
The present invention provides a method for performing load following operation of a fuel cell system including a reformer having a reforming catalyst layer, for reforming a hydrocarbon-based fuel to produce a reformed gas containing hydrogen, and a high temperature fuel cell for generating electric power using the reformed gas, wherein
a plurality of electrical outputs P i of the fuel cell (i is an integer of 1 or more and M or less, where M is an integer of 2 or more) and a flow rate F i of the hydrocarbon-based fuel that corresponds to each P i are set beforehand,
where each F i is a flow rate of the hydrocarbon-based fuel required to be supplied to the reforming catalyst layer in order to output a corresponding electrical output P i from the fuel cell, each P i is 0 or more, P i increases with an increase of i, and each F i is larger than 0,
P M that is P i when i is M is a maximum electrical output of the fuel cell, and
a minimum value of all F i is represented as F min ,
the method including:
A) measuring a temperature T of the reforming catalyst layer;
B) obtaining a reformable flow rate F R that is a flow rate of the hydrocarbon-based fuel that can be reformed in the reforming catalyst layer at the temperature T;
C) when the reformable flow rate F R is smaller than the minimum value F min , stopping electric power generation in the fuel cell; and
D) when the reformable flow rate F R is equal to or more than the minimum value F min ,
performing step d1 if a fuel cell output demand value P D is equal to or less than the maximum electrical output P M , and performing step d2 if the fuel cell output demand value P D exceeds the maximum electrical output P M ,
d1) if there exists, among all P i , a P i that is equal to the fuel cell output demand value P D , then setting F i , that corresponds to P i , that is equal to P D , as F DS ;
if there does not exist, among all P i , a P i that is equal to the fuel cell output demand value P D , then setting F i , that is the not smaller one of the two Fi, as F DS ; one of said two Fi corresponding to the smallest P i that exceeds P D , and the other one of said two F i corresponding to the largest P i that is less than P D ,
when F DS is equal to or less than the reformable flow rate F R , setting an electrical output of the fuel cell to P D , and setting a flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F DS , and
when F DS exceeds the reformable flow rate F R ,
if there exists a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that is less than P D and that corresponds to F i , that is equal to or less than F R ; and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then stopping electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R ,
d2) when F M that is F i , corresponding to the maximum electrical output P M , is equal to or less than the reformable flow rate F R , setting the electrical output of the fuel cell to P M , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F M , and
when F M that is F i , corresponding to the maximum electrical output P M , exceeds the reformable flow rate F R ,
if there exists a P i that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that corresponds to F i , that is equal to or less than F R , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that corresponds to F i , that is equal to or less than F R , then stopping the electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R .
A first embodiment of the present invention provides a method for performing load following operation of a fuel cell system including a reformer having a reforming catalyst layer, for reforming a hydrocarbon-based fuel to produce a reformed gas containing hydrogen, and a high temperature fuel cell for generating electric power using the reformed gas, wherein
a plurality of electrical outputs P i of the fuel cell (i is an integer of 1 or more and M or less, where M is an integer of 2 or more) and a flow rate F i of the hydrocarbon-based fuel that corresponds to each P i are set beforehand,
where each F i is a flow rate of the hydrocarbon-based fuel required to be supplied to the reforming catalyst layer in order to output a corresponding electrical output P i from the fuel cell, each P i is 0 or more, P i increases with an increase of i, and each F i is larger than 0,
P M that is P i when i is M is a maximum electrical output of the fuel cell, and
a minimum value of all F i is represented as F min ,
the method including:
1-A) measuring a temperature of the reforming catalyst layer; 1-B) calculating a reformable flow rate F R that is a 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; 1-C) when the calculated reformable flow rate F R is smaller than the minimum value F min , stopping electric power generation in the fuel cell; and 1-D) when the calculated reformable flow rate F R is equal to or more than the minimum value F min , performing step 1-d1 if a fuel cell output demand value P D is equal to or less than the maximum electrical output P M , and performing step 1-d2 if the fuel cell output demand value P D exceeds the maximum electrical output P M , 1-d1) if there exists, among all P i , a P i that is equal to the fuel cell output demand value P D , then setting F i , that corresponds to P i , that is equal to P D , as F DS ,
if there does not exist, among all P i , a P i that is equal to the fuel cell output demand value P D , then setting F i , that is the not smaller one of the two Fi, as F DS ; one of said two Fi corresponding to the smallest P i that exceeds P D and the other one of said two F i corresponding to the largest P i that is less than P D ,
when F DS is equal to or less than the calculated reformable flow rate F R , setting an electrical output of the fuel cell to P D , and setting a flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F DS , and when F DS exceeds the calculated reformable flow rate F R ,
if there exists a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that is less than P D and that corresponds to F i , that is equal to or less than F R ; and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then stopping electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R ,
1-d2) when F M that is F i , corresponding to the maximum electrical output P M , is equal to or less than the calculated reformable flow rate F R , setting the electrical output of the fuel cell to P M , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F M , and when F M that is F i , corresponding to the maximum electrical output P M , exceeds the calculated reformable flow rate F R ,
if there exists a P i that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that corresponds to F i , that is equal to or less than F R , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that corresponds to F i , that is equal to or less than F R , then stopping the electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R .
A second embodiment of the present invention provides a method for performing load following operation of a fuel cell system including a reformer having a reforming catalyst layer, for reforming a hydrocarbon-based fuel to produce a reformed gas containing hydrogen, and a high temperature fuel cell for generating electric power using the reformed gas, wherein
a plurality of electrical outputs P i of the fuel cell (i is an integer of 1 or more and M or less, where M is an integer of 2 or more) and a flow rate F i of the hydrocarbon-based fuel that corresponds to each P i are set beforehand,
where each F i is a flow rate of the hydrocarbon-based fuel required to be supplied to the reforming catalyst layer in order to output a corresponding electrical output P i from the fuel cell, each P i is 0 or more, P i increases with an increase of i, and each F i is larger than 0,
P M that is P i when i is M is a maximum electrical output of the fuel cell, and
a minimum value of all F i is represented as F min , and
a plurality of temperatures T j of the reforming catalyst layer (j is an integer of 1 or more and N or less, where N is an integer of 2 or more) and a flow rate G j of the hydrocarbon-based fuel that corresponds to each T j are set beforehand,
where each G j is a flow rate of the hydrocarbon-based fuel that can be reformed in the reforming catalyst layer at a corresponding reforming catalyst layer temperature T j , each G j is larger than 0, and G j is the same value or increases with an increase of j,
the method including:
2-A) measuring a temperature T of the reforming catalyst layer; 2-B) adopting G j corresponding to a largest T j that is equal to or less than the temperature T as a reformable flow rate F R that is a flow rate of the hydrocarbon-based fuel that can be reformed in the reforming catalyst layer at the temperature T; 2-C) when the reformable flow rate F R is smaller than the minimum value F min , stopping electric power generation in the fuel cell; and 2-D) when the reformable flow rate F R is equal to or more than the minimum value F min , performing step 2-d1 if a fuel cell output demand value P D is equal to or less than the maximum electrical output P M , and performing step 2-d2 if the fuel cell output demand value P D exceeds the maximum electrical output P M ,
2-d1) if there exists, among all P i , a P i that is equal to the fuel cell output demand value P D , then setting F i , that corresponds to P i , that is equal to P D , as F DS ;
if there does not exist, among all P i , a P i that is equal to the fuel cell output demand value P D , then setting F i , that is the not smaller one of the two Fi, as F DS ; one of said two Fi corresponding to the smallest P i that exceeds P D , and the other one of the two F i corresponding to the largest P i that is less than P D ,
when F DS is equal to or less than the reformable flow rate F R , setting an electrical output of the fuel cell to P D , and setting a flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F DS , and when F DS exceeds the reformable flow rate F R ,
if there exists a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that is less than P D and that corresponds to F i , that is equal to or less than F R ; and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then stopping electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R ,
2-d2) when F M that is F i , corresponding to the maximum electrical output P M , is equal to or less than the reformable flow rate F R , setting the electrical output of the fuel cell to P M , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F M , and
when F M that is F i , corresponding to the maximum electrical output P M , exceeds the reformable flow rate F R ,
if there exists a P i that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that corresponds to F i , that is equal to or less than F R , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that corresponds to F i , that is equal to or less than F R , then stopping the electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R .
Steps A to D, steps 1-A to 1-D, or steps 2-A to 2-D may be repeatedly performed during the load following operation.
The hydrocarbon-based fuel may include a hydrocarbon-based fuel(s) with a carbon number of two or more.
The concentration of a compound(s) with a carbon number of two or more in the reformed gas may be 50 ppb or less on a mass basis.
The present invention provides a fuel cell system including a reformer having a reforming catalyst layer, for reforming a hydrocarbon-based fuel to produce a reformed gas containing hydrogen, and a high temperature fuel cell for generating electric power using the reformed gas, wherein
a plurality of electrical outputs of the fuel cell are represented as P i (i is an integer of 1 or more and M or less, where M is an integer of 2 or more), and a flow rate of the hydrocarbon-based fuel that corresponds to each P i is represented as F i ,
where each F i is a flow rate of the hydrocarbon-based fuel required to be supplied to the reforming catalyst layer in order to output a corresponding electrical output P i from the fuel cell, each P i is 0 or more, P i increases with an increase of i, and each F i is larger than 0,
P M that is P i when i is M is a maximum electrical output of the fuel cell, and
a minimum value of all F i is represented as F min ,
the system including:
I) a means for measuring a temperature T of the reforming catalyst layer;
II) a means for obtaining a reformable flow rate F R that is a flow rate of the hydrocarbon-based fuel that can be reformed in the reforming catalyst layer at the temperature T;
III) a means for, when the reformable flow rate F R is smaller than the minimum value F min , stopping electric power generation in the fuel cell; and
IV) a means for, when the reformable flow rate F R is equal to or more than the minimum value F min ,
performing step d1 if a fuel cell output demand value P D is equal to or less than the maximum electrical output P M , and performing step d2 if the fuel cell output demand value P D exceeds the maximum electrical output P M ,
d1) if there exists, among all P i , a P i that is equal to the fuel cell output demand value P D , then setting F i , that corresponds to that is equal to P D , as F DS ;
if there does not exist, among all P i , a P i that is equal to the fuel cell output demand value P D , then setting F i , that is the not smaller one of the two Fi, as F DS ; one of said two Fi corresponding to the smallest P i that exceeds P D , and the other of said two F i corresponding to the largest P i that is less than P D ,
when F DS is equal to or less than the reformable flow rate F R , setting an electrical output of the fuel cell to P D , and setting a flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F DS , and
when F DS exceeds the reformable flow rate F R ,
if there exists a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that is less than P D and that corresponds to F i , that is equal to or less than F R ; and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then stopping electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R ,
d2) when F M that is F i , corresponding to the maximum electrical output P M , is equal to or less than the reformable flow rate F R , setting the electrical output of the fuel cell to P M , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F M , and
when F M that is F i , corresponding to the maximum electrical output P M , exceeds the reformable flow rate F R ,
if there exists a P i that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that corresponds to F i , that is equal to or less than F R , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that corresponds to F i , that is equal to or less than F R , then stopping the electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R .
Advantages of the Invention
The present invention provides a method in which, when performing load following operation of a fuel cell system including a reformer having a reforming catalyst layer and a high temperature fuel cell, reforming can be more reliably performed to more reliably prevent flow blockage and anode degradation.
Also, the present invention provides a fuel cell system suitable for performing such a method.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram showing the outline of an example of an indirect internal reforming SOFC system that can perform the present invention; and
FIG. 2 is a schematic diagram showing the outline of another example of the indirect internal reforming SOFC system that can perform the present invention.
DESCRIPTION OF SYMBOLS
1
water vaporizer
2
electrical heater annexed to water vaporizer
3
reformer
4
reforming catalyst layer
5
thermocouple
6
SOFC
7
igniter
8
module container
9
electrical heater annexed to reformer
10
computer
11
flow rate control valve
12
flowmeter
13
thermocouple
14
electric power conditioner
BEST MODE FOR CARRYING OUT THE INVENTION
A fuel cell system used in the present invention includes a reformer for reforming a hydrocarbon-based fuel to produce a hydrogen-containing gas, and a high temperature fuel cell. The reformer includes a reforming catalyst layer. The hydrogen-containing gas obtained from the reformer is referred to as reformed gas. The reforming catalyst layer is composed of a reforming catalyst that can promote a reforming reaction. The high temperature fuel cell generates electric power, using the hydrogen-containing gas (reformed gas) obtained from the reformer.
The embodiments of the present invention will be described below, using drawings, but the present invention is not limited thereto.
[Indirect Internal Reforming SOFC System]
One embodiment of an indirect internal reforming SOFC that can perform the present invention is schematically shown in FIG. 1 . Here, the indirect internal reforming SOFC system will be described, but the present invention can also be applied to an external reforming SOFC system or an MCFC system.
The indirect internal reforming SOFC includes a reformer 3 for reforming a hydrocarbon-based fuel to produce a reformed gas (hydrogen-containing gas). The reformer includes a reforming catalyst layer 4 .
The indirect internal reforming SOFC includes an SOFC 6 for generating electric power using the above reformed gas, and also includes a combustion region 5 for combusting an anode off-gas discharged from the SOFC (particularly the anode of the SOFC).
The indirect internal reforming SOFC includes an enclosure 8 for housing the reformer, the solid oxide fuel cell, and the combustion region.
The indirect internal reforming SOFC refers to the enclosure (module container) 8 and equipment included in the interior of the enclosure.
In the indirect internal reforming SOFC in the embodiment shown in FIG. 1 , an igniter 7 that is an ignition means for igniting the anode off-gas is provided, and also, the reformer is equipped with an electrical heater 9 .
Each supply gas is supplied to the reformer or the SOFC, after being appropriately preheated as required.
A water vaporizer 1 equipped with an electrical heater 2 is connected to the indirect internal reforming SOFC, and piping for supplying the hydrocarbon-based fuel to the reformer is connected to the midstream of connection piping for the water vaporizer 1 . The water vaporizer 1 generates steam by heating with the electrical heater 2 . The steam may be supplied to the reforming catalyst layer after being appropriately superheated in the water vaporizer or downstream thereof.
Also, air (for a partial oxidation reforming reaction) may be supplied to the reforming catalyst layer, and here, air can be supplied to the reforming catalyst layer after being preheated in the water vaporizer. Steam or a mixed gas of air and steam can be obtained from the water vaporizer.
The steam or the mixed gas of air and steam is mixed with the hydrocarbon-based fuel and supplied to the reformer 3 , particularly to the reforming catalyst layer 4 of the reformer 3 . When a liquid fuel, such as kerosene, is used as the hydrocarbon-based fuel, the hydrocarbon-based fuel may be supplied to the reforming catalyst layer after being appropriately vaporized.
The reformed gas obtained from the reformer is supplied to the SOFC 6 , particularly to the anode of the SOFC 6 . Although not shown, air is appropriately preheated and supplied to the cathode of the SOFC.
Combustible components in the anode off-gas (gas discharged from the anode) are combusted by oxygen in a cathode off-gas (gas discharged from the cathode) at the SOFC outlet. In order to do this, ignition using the igniter 7 is possible. The outlets of both the anode and the cathode are open in the module container 8 . The combustion gas is appropriately discharged from the module container.
The reformer and the SOFC are housed in one module container and modularized. The reformer is disposed at a position where it can receive heat from the SOFC. For example, when the reformer is located at a position where it receives thermal radiation from the SOFC, the reformer is heated by thermal radiation from the SOFC during electric power generation.
In the indirect internal reforming SOFC, the reformer is preferably disposed at a position where radiation heat can be directly transferred from the SOFC to the outer surface of the reformer. Therefore, it is preferred that there is substantially no obstacle between the reformer and the SOFC, that is, it is preferred to make the region between the reformer and the SOFC be an empty space. Also, the distance between the reformer and the SOFC is preferably as short as possible.
The reformer 3 is heated by the combustion heat of the anode off-gas generated in the combustion region 5 . Also, when the temperature of the SOFC is higher than that of the reformer, the reformer is also heated by radiation heat from the SOFC.
Further, the reformer may be heated by heat generation by reforming. When the reforming is partial oxidation reforming, or when the reforming is autothermal reforming and heat generation by a partial oxidation reforming reaction is larger than endothermic heat by a steam reforming reaction, heat is generated with the reforming.
[Load Following Operation Method (First Embodiment)]
In the present invention, a plurality of electrical outputs P i of the fuel cell (i is an integer of 1 or more and M or less, where M is an integer of 2 or more) and a flow rate F i of the hydrocarbon-based fuel that corresponds to each Rare beforehand set.
Each F i is a flow rate of the hydrocarbon-based fuel required to be supplied to the reforming catalyst layer in order to output the corresponding electrical output P i from the fuel cell. For example, the flow rate F i of the hydrocarbon-based fuel that corresponds to each P i may be set by beforehand determining an electric current and a fuel utilization rate for each P i by preliminary experiment, simulation, or the like so that the electric power generation efficiency is as high as possible, while the SOFC is maintained at a temperature at which electric power can be preferably generated.
Also, the flow rates of fluids supplied to the indirect internal reforming SOFC, other than the hydrocarbon-based fuel, and the input and output of electricity to and from the indirect internal reforming SOFC, other than the output of the fuel cell, may be beforehand set correspondingly to each P i , as required. For example, in order to suppress carbon deposition, the flow rate of water supplied to the reformer may be set so that the 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 a predetermined value. The flow rate of air supplied to the reformer may be 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) is a predetermined value. The flow rate of fluids supplied to the indirect internal reforming SOFC, other than the water and air supplied to the reformer, and the input and output of electricity to and from the indirect internal reforming SOFC may be set by preliminary experiment, simulation, or the like so that the electric power generation efficiency is as high as possible, while the SOFC is maintained at a temperature at which electric power can be preferably generated. By doing so, these flow rates and electrical input and output may be determined using beforehand obtained functions, when the output of the fuel cell is set to a certain value P.
Each P i is 0 or more. In other words, for all i, 0â¦P. Also, P i increases with the increase of i. In other words, P i <P i+1 (here, i is an integer of 1 or more and Mâ1 or less). Therefore, P i that may be actually zero is only P 1 .
Further, each F i is larger than 0. In other words, for all i, 0<F i .
P i when i is M (that is, P M ) is the maximum electrical output of the fuel cell. P M is beforehand determined as one of the specifications of the fuel cell system.
The minimum value among all F i is represented as F min .
It is preferred to make M as large as possible within the allowable range of the memory of a control means, in terms of electric power generation efficiency.
By preferably repeatedly performing steps 1-A to 1-D, that is, repeatedly performing the step 1-A, the step 1-B, and the step 1-C or 1-D in this order, during load following operation, reforming can be more reliably performed to more reliably prevent the degradation of the anode.
[Step 1-A]
When load fluctuation operation is actually performed, the step 1-A of measuring the temperature of the reforming catalyst layer is performed. This measurement may be continuously performed while the load following operation is performed.
The step 1-A is performed to find the temperature T of the reforming catalyst layer used when a reformable flow rate F R described later is calculated. The step 1-A is preferably started in a time as short as possible from the point of time of the start of the load following operation. The step 1-A is preferably started immediately after the load following operation is started. When the monitoring (continuous measurement) of the temperature of the reforming catalyst layer has been performed since before the start of the load following operation, the temperature monitoring may be continuously performed as it has been.
An appropriate temperature sensor, such as a thermocouple, may be used for the temperature measurement.
[Step 1-B]
In the step 1-B, the flow rate of the hydrocarbon-based fuel that can be reformed in the reforming catalyst layer (reformable flow rate F R ) is calculated based on the measured temperature of the reforming catalyst layer. The calculation method will be described in detail later.
[Step 1-C]
When the reformable flow rate F R calculated in the step 1-B is smaller than the minimum value F min , electric power generation in the fuel cell is stopped. In other words, when F R <F min , the requisite minimum reformed gas cannot be reformed, and therefore, the electrical output of the fuel cell is set to zero. In this case, it is possible to supply the hydrocarbon-based fuel at the flow rate F R to the reformer and increase the temperature of the reforming catalyst layer by a heater annexed to the reformer, a burner, or the like until at least F R â§F min is satisfied. When F R â§F min , the step 1-D and the subsequent steps may be performed.
[Step 1-D]
When the reformable flow rate F R calculated in the step 1-B is equal to or more than the minimum value F min , the step 1-D is performed.
In the step 1-D, when a fuel cell output demand value P D is equal to or less than the maximum electrical output P M of the fuel cell, step 1-d1 is performed. P D â¦P M means that the fuel cell can output the fuel cell output demand value P D .
Or, when the fuel cell output demand value P D exceeds the maximum electrical output P M of the fuel cell, step 1-d2 is performed. P D >P M means that the electrical output of the fuel cell is insufficient for the fuel cell output demand value P D .
<Step 1-d1>
In the step 1-d1, first, in order to make a further judgment, a value of F DS is obtained. Here, F DS has a meaning of a flow rate of the hydrocarbon-based fuel corresponding to a P i which is close to the fuel cell output demand value P D , obtained for judging on the safe side whether reforming is possible or not.
Whether there is, among all P i beforehand set, a P i that is equal to the fuel cell output demand value P D is checked.
When there is a P i that is equal to P D , F i that corresponds to the P i (=P D ) is obtained using the correspondence relationship between P i and F i , which has been beforehand set, and this F i is set as F DS . Also in the following descriptions, when obtaining F i that corresponds to P i , or P i that corresponds to F i , the correspondence relationship between P i and F i beforehand determined is used.
When there is, among all P i , no P i that is equal to P D , the larger one of F i corresponding to âthe smallest P i that exceeds P D â and F i corresponding to âthe largest P i that is less than P D â (when these two values are equal, the very value) is set as F DS in order to judge on the safer side whether reforming is possible or not.
Next, this F DS is compared with the above calculated reformable flow rate F R .
Case where F DS â¦F R
When F DS is equal to or less than the reformable flow rate F R , the electrical output of the fuel cell is set to P D , and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is set to F DS . F DS â¦F R means that the hydrocarbon-based fuel at the flow rate F DS can be reformed in the reforming catalyst layer.
Case where F DS >F R
When F DS exceeds the above calculated reformable flow rate F R , the following step (1-1) or (1-2) is performed. F DS >F R means that the hydrocarbon-based fuel at the flow rate F DS cannot be totally reformed in the reforming catalyst layer.
(1-1) Case where there is a P i Corresponding to F i , that is Equal to or Less than F R , within a Range of Less than Fuel Cell Output Demand Value P D
In this case, the electrical output of the fuel cell is set to the maximum value among the P i (P i that is less than P D and that corresponds to F i , that is equal to or less than F R ), and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is set to F i that corresponds to this maximum value. This operation is intended to output an electrical output as much as possible from the fuel cell.
(1-2) Case where there is No P i Corresponding to F i , that is Equal to or Less than F R , within a Range of Less than Fuel Cell Output Demand Value P D
In this case, the electric power generation of the fuel cell is stopped, and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is set to the reformable flow rate F R . Here, the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is set to the reformable flow rate F R in order to continue running the system. After this operation, it is possible to increase the temperature of the reformer (reforming catalyst layer) by a heater annexed to the reformer, a burner, or the like and wait for F R to increase (become F DS â¦F R ). When F DS â¦F R , the step 1-D and the subsequent steps may be performed.
<Step 1-d2>
As described above, the step 1-d2 is performed when it is judged that the electrical output of the fuel cell is insufficient for the fuel cell output demand value P D .
In this step, F M (F i corresponding to the maximum electrical output P M ) is compared with the above calculated reformable flow rate F R .
Case where F M â¦F R
When F M is equal to or less than the above calculated reformable flow rate F R , the electrical output of the fuel cell is set to P M , and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is set to F M . F M â¦F R means that
CLAIMS
Claims ( 13 )
The invention claimed is:
1. A method of load following operation of a fuel cell system comprising a reformer having a reforming catalyst layer, for reforming a hydrocarbon-based fuel to produce a reformed gas containing hydrogen, and a high temperature fuel cell for generating electric power using the reformed gas, wherein
a plurality of electrical outputs P i of the fuel cell (i is an integer of 1 or more and M or less, where M is an integer of 2 or more) and a flow rate F i of the hydrocarbon-based fuel that corresponds to each P i are set beforehand,
where each F i is a flow rate of the hydrocarbon-based fuel required to be supplied to the reforming catalyst layer in order to output a corresponding electrical output P i from the fuel cell,
each P i is 0 or more, P i increases with an increase of i, and each F i is larger than 0,
P M that is P i when i is M is a maximum electrical output of the fuel cell, and
a minimum value of all F i is represented as F min ,
the method comprising:
A) measuring a temperature T of the reforming catalyst layer;
B) obtaining a reformable flow rate F R that is a flow rate of the hydrocarbon-based fuel capable of being reformed in the reforming catalyst layer at the temperature T;
C) when the reformable flow rate F R is smaller than the minimum value F min , stopping electric power generation in the fuel cell; and
D) when the reformable flow rate F R is equal to or more than the minimum value F min ,
performing step d1 if a fuel cell output demand value P D is equal to or less than the maximum electrical output P M , and performing step d2 if the fuel cell output demand value P D exceeds the maximum electrical output P M ,
d1) if there exists, amongst all P i values, a P i that is equal to the fuel cell output demand value P D , then setting F i , that corresponds to P i , that is equal to P D , as F DS ;
if there does not exist, amongst all P i values, a P i that is equal to the fuel cell output demand value P D , then setting F i , that is the not smaller value of the two Fi values, as F DS ; one of said two Fi values corresponding to the smallest P i that exceeds P D , and the other of said two F i values corresponding to the largest P i that is less than P D ,
when F DS is equal to or less than the reformable flow rate F R , setting an electrical output of the fuel cell to P D , and setting a flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F DS , and
when F DS exceeds the reformable flow rate F R ,
if there exists a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that is less than P D and that corresponds to F i , that is equal to or less than F R ; and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then stopping electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R ,
d2) when F M that is F i , corresponding to the maximum electrical output P M , is equal to or less than the reformable flow rate F R , setting the electrical output of the fuel cell to P M , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F M , and
when F M that is F i , corresponding to the maximum electrical output P M , exceeds the reformable flow rate F R ,
if there exists a P i that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that corresponds to F i , that is equal to or less than F R , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i corresponding to this maximum value, and
if there does not exist a P i that corresponds to F i , that is equal to or less than F R , then stopping the electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R .
2. A method of load following operation of a fuel cell system comprising a reformer having a reforming catalyst layer, for reforming a hydrocarbon-based fuel to produce a reformed gas containing hydrogen, and a high temperature fuel cell for generating electric power using the reformed gas, wherein
a plurality of electrical outputs P i of the fuel cell (i is an integer of 1 or more and M or less, where M is an integer of 2 or more) and a flow rate F i of the hydrocarbon-based fuel that corresponds to each P i are set beforehand,
where each F i is a flow rate of the hydrocarbon-based fuel required to be supplied to the reforming catalyst layer in order to output a corresponding electrical output P i from the fuel cell,
each P i is 0 or more, P i increases with an increase of i, and each F i is larger than 0,
P M that is P i when i is M is a maximum electrical output of the fuel cell, and
a minimum value of all F i is represented as F min ,
the method comprising:
1-A) measuring a temperature of the reforming catalyst layer;
1-B) calculating a reformable flow rate F R that is a flow rate of the hydrocarbon-based fuel capable of being reformed in the reforming catalyst layer, based on the measured temperature of the reforming catalyst layer;
1-C) when the calculated reformable flow rate F R is smaller than the minimum value F min , stopping electric power generation in the fuel cell; and
1-D) when the calculated reformable flow rate F R is equal to or more than the minimum value F min ,
performing step 1-d1 if a fuel cell output demand value P D is equal to or less than the maximum electrical output P M , and performing step 1-d2 if the fuel cell output demand value P D exceeds the maximum electrical output P M ,
1-d1) if there exists, amongst all P i values, a P i that is equal to the fuel cell output demand value P D , then setting F i , that corresponds to P i , that is equal to P D , as F DS ;
if there does not exist, amongst all P i , a P i that is equal to the fuel cell output demand value P D , then setting F i , that is the not smaller value of the two Fi values, as F DS ; one of said two Fi values corresponding to the smallest P i that exceeds P D , and the other of said two F i values corresponding to the largest P i that is less than P D ,
when F DS is equal to or less than the calculated reformable flow rate F R , setting an electrical output of the fuel cell to P D , and setting a flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F DS , and
when F DS exceeds the calculated reformable flow rate F R ,
if there exists a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that is less than P D and that corresponds to F i , that is equal to or less than F R ; and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then stopping electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R ,
1-d2) when F M that is F i , corresponding to the maximum electrical output P M , is equal to or less than the calculated reformable flow rate F R , setting the electrical output of the fuel cell to P M , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F M , and
when F M that is F i , corresponding to the maximum electrical output P M , exceeds the calculated reformable flow rate F R ,
if there exists a P i that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that corresponds to F i , that is equal to or less than F R , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i corresponding to this maximum value, and
if there does not exist a P i that corresponds to F i , that is equal to or less than F R , then stopping the electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R .
3. A method of load following operation of a fuel cell system comprising a reformer having a reforming catalyst layer, for reforming a hydrocarbon-based fuel to produce a reformed gas containing hydrogen, and a high temperature fuel cell for generating electric power using the reformed gas, wherein
a plurality of electrical outputs P i of the fuel cell (i is an integer of 1 or more and M or less, where M is an integer of 2 or more) and a flow rate F i of the hydrocarbon-based fuel that corresponds to each P i are set beforehand,
where each F i is a flow rate of the hydrocarbon-based fuel required to be supplied to the reforming catalyst layer in order to output a corresponding electrical output P i from the fuel cell,
each P i is 0 or more, P i increases with an increase of i, and each F i is larger than 0,
P M that is P i when i is M is a maximum electrical output of the fuel cell, and
a minimum value of all F i is represented as F min , and
a plurality of temperatures T j of the reforming catalyst layer (j is an integer of 1 or more and N or less, where N is an integer of 2 or more) and a flow rate G j of the hydrocarbon-based fuel that corresponds to each T j are set beforehand,
where each G j is a flow rate of the hydrocarbon-based fuel capable of being reformed in the reforming catalyst layer at a corresponding reforming catalyst layer temperature T j , each G j is larger than 0, and G j is the same value or increases with an increase of j,
the method comprising:
2-A) measuring a temperature T of the reforming catalyst layer;
2-B) adopting G j corresponding to a largest T j that is equal to or less than the temperature T as a reformable flow rate F R that is a flow rate of the hydrocarbon-based fuel capable of being reformed in the reforming catalyst layer at the temperature T;
2-C) when the reformable flow rate F R is smaller than the minimum value stopping electric power generation in the fuel cell; and
2-D) when the reformable flow rate F R is equal to or more than the minimum value F min ,
performing step 2-d1 if a fuel cell output demand value P D is equal to or less than the maximum electrical output P M , and performing step 2-d2 if the fuel cell output demand value P D exceeds the maximum electrical output P M ,
2-d1) if there exists, amongst all P i values, a P i that is equal to the fuel cell output demand value P D , then setting F i , that corresponds to P i , that is equal to P D , as F DS ;
if there does not exist, amongst all P i , a P i that is equal to the fuel cell output demand value P D , then setting F i , that is the not smaller value of the two Fi values, as F DS ; one of said two Fi values corresponding to the smallest P i that exceeds P D , and the other of said two F i values corresponding to the largest P i that is less than P D ,
when F DS is equal to or less than the reformable flow rate F R , setting an electrical output of the fuel cell to P D , and setting a flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F DS , and
when F DS exceeds the reformable flow rate F R ,
if there exists a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that is less than P D and that corresponds to F i , that is equal to or less than F R ; and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then stopping electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R ,
2-d2) when F M that is F i , corresponding to the maximum electrical output P M , is equal to or less than the reformable flow rate F R , setting the electrical output of the fuel cell to P M , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F M , and
when F M that is F i , corresponding to the maximum electrical output P M , exceeds the reformable flow rate F R ,
if there exists a P i that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that corresponds to F i , that is equal to or less than F R , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i corresponding to this maximum value, and
if there does not exist a P i that corresponds to F i , that is equal to or less than F R , then stopping the electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R .
4. The method according to claim 1 , wherein steps A to D are repeatedly performed during the load following operation.
5. The method according to claim 1 , wherein the hydrocarbon-based fuel comprises a hydrocarbon-based fuel with a carbon number of two or more.
6. The method according to claim 5 , wherein the concentration of a compound with a carbon number of two or more in the reformed gas is 50 ppb or less on a mass basis.
7. A fuel cell system comprising a reformer having a reforming catalyst layer, for reforming a hydrocarbon-based fuel to produce a reformed gas containing hydrogen, and a high temperature fuel cell for generating electric power using the reformed gas, wherein
a plurality of electrical outputs of the fuel cell are represented as P i (i is an integer of 1 or more and M or less, where M is an integer of 2 or more), and a flow rate of the hydrocarbon-based fuel that corresponds to each P i is represented as F i ,
where each F i is a flow rate of the hydrocarbon-based fuel required to be supplied to the reforming catalyst layer to output a corresponding electrical output P i from the fuel cell, each P i is 0 or more, P i increases with an increase of i, and each F i is larger than 0,
P M that is P i when i is M is a maximum electrical output of the fuel cell, and
a minimum value of all F i is represented as F min ,
the system comprising:
I) a means for measuring a temperature T of the reforming catalyst layer;
II) a means for obtaining a reformable flow rate F R that is a flow rate of the hydrocarbon-based fuel capable of being reformed in the reforming catalyst layer at the temperature T;
III) a means for, when the reformable flow rate F R is smaller than the minimum value F min , stopping electric power generation in the fuel cell; and
IV) a means for, when the reformable flow rate F R is equal to or more than the minimum value F min ,
performing step d1 if a fuel cell output demand value P D is equal to or less than the maximum electrical output P M , and performing step d2 if the fuel cell output demand value P D exceeds the maximum electrical output P M ,
d1) if there exists, amongst all P i values, a P i that is equal to the fuel cell output demand value P D , then setting F i , that corresponds to P i , that is equal to P D , as F DS ;
if there does not exist, amongst all P i values, a P i that is equal to the fuel cell output demand value P D , then setting F i , that is the not smaller value of the two Fi values, as F DS ; one of the said two Fi values corresponding to the smallest P i that exceeds P D , and the other of said two F i values corresponding to the largest P i that is less than P D ,
when F DS is equal to or less than the reformable flow rate F R , setting an electrical output of the fuel cell to P D , and setting a flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F DS , and
when F DS exceeds the reformable flow rate F R ,
if there exists a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that is less than P D and that corresponds to F i , that is equal to or less than F R ; and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i that corresponds to this maximum value, and
if there does not exist a P i that is less than the fuel cell output demand value P D and that corresponds to F i , that is equal to or less than F R , then stopping electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R ,
d2) when F M that is F i , corresponding to the maximum electrical output P M , is equal to or less than the reformable flow rate F R , setting the electrical output of the fuel cell to P M , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F M , and
when F M that is F i , corresponding to the maximum electrical output P M , exceeds the reformable flow rate F R ,
if there exists a P i that corresponds to F i , that is equal to or less than F R , then setting the electrical output of the fuel cell to the maximum value of P i that corresponds to F i , that is equal to or less than F R , and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to F i corresponding to this maximum value, and
if there does not exist a P i that corresponds to F i , that is equal to or less than F R , then stopping the electric power generation of the fuel cell, and setting the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer to the reformable flow rate F R .
8. The method according to claim 2 , wherein steps A to D are repeatedly performed during the load following operation.
9. The method according to claim 2 , wherein the hydrocarbon-based fuel comprises a hydrocarbon-based fuel with a carbon number of two or more.
10. The method according to claim 9 , wherein the concentration of a compound with a carbon number of two or more in the reformed gas is 50 ppb or less on a mass basis.
11. The method according to claim 3 , wherein steps A to D are repeatedly performed during the load following operation.
12. The method according claim 3 , wherein the hydrocarbon-based fuel comprises a hydrocarbon-based fuel with a carbon number of two or more.
13. The method according to claim 12 , wherein the concentration of a compound with a carbon number of two or more in the reformed gas is 50 ppb or less on a mass basis.
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Fuel cell system and method for load following operation of the same
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