JP5281997B2 - Load following operation method of fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high electric power generation efficiency by carrying out sure reforming at the time of an FC system load following operation. <P>SOLUTION: Two or more out of steam/partial oxidation/self-reforming methods are determined as the "i" reforming methods, and Gi<SB>k</SB>corresponding to the maximum Ti<SB>k</SB>is adopted at a reforming catalyst layer temperature or less, as Fi<SP>R</SP>. (1) is carried out at the time of P<SB>D</SB>&le;Pi<SB>M</SB>, when "i" bringing Fi<SP>R</SP>&ge;Fi<SB>min</SB>exists, and (2) is carried out at the time of P<SB>D</SB>&gt;Pi<SB>M</SB>, wherein (1): Pi<SP>*</SP>=P<SB>D</SB>and Fi<SP>*</SP>=fi(P<SB>D</SB>) are settled at the time of fi(P<SB>D</SB>)&le;Fi<SP>R</SP>, and Pi<SP>*</SP>=maximum fi<SP>-1</SP>(Fi<SP>R</SP>) less than Pi<SP>*</SP>=P<SB>D</SB>and Fi<SP>*</SP>=Fi<SP>R</SP>are settled at the time of fi(P<SB>D</SB>)&gt;Fi<SP>R</SP>, and (2): Pi<SP>*</SP>=Pi<SB>M</SB>and Fi<SP>*</SP>=fi(Pi<SB>M</SB>) are settled at the time of fi(Pi<SB>M</SB>)&le;Fi<SP>R</SP>, and Pi<SP>*</SP>=maximum fi<SP>-1</SP>(Fi<SP>R</SP>) and Fi<SP>*</SP>=Fi<SP>R</SP>are settled at the time of fi(Pi<SB>M</SB>)&gt;Fi<SP>R</SP>. Pi<SP>*</SP>, the reforming method and Fi<SP>*</SP>regarding the "i" bringing the maximum &eta;i=gi(Pi<SP>*</SP>) are adopted when the plurality of "i"s bringing Fi<SP>R</SP>&ge;Fi<SB>min</SB>exist. Fi<SP>R</SP>or the like is defined separately. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

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

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

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

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

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

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

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

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

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

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

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

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

According to the present invention,
A fuel cell comprising a reformer having a reforming catalyst layer for producing a reformed gas containing hydrogen by reforming a hydrocarbon fuel, and a high-temperature fuel cell for generating electric power using the reformed gas A load following operation method of the system,
At least two reforming methods selected from the group consisting of steam reforming method, partial oxidation reforming method and autothermal reforming method are defined as i-th reforming method, where i is an integer of 1 or more and L or less. L is 2 or 3,
For all i, the reforming catalyst layer for outputting the electric output P of the fuel cell in advance and the electric output P of the fuel cell when the reformed gas produced by the i-th reforming method is supplied to the fuel cell. The functions Fi = fi (P) and P = fi ⁻¹ (Fi) with the flow rate Fi of the hydrocarbon-based fuel that needs to be supplied to
However, P = fi ⁻¹ (Fi) is an inverse function of Fi = fi (P),
The power generation efficiency of the fuel cell when the electric output P of the fuel cell and the reformed gas produced by the i th reforming method are supplied to the fuel cell in advance and the electric output P is output by the fuel cell for all i Obtain a function ηi = gi (P) with ηi,
The maximum electrical output of the fuel cell when the reformed gas produced by the i-th reforming method is supplied to the fuel cell is denoted as Pi _M.
When P is in the range of 0 or more Pi _M, the minimum value of the flow rate of the hydrocarbon-based fuel determined by the function Fi = fi (P) expressed as Fi _min,
In addition, for all i, different Ni reforming catalyst layer temperatures Ti _k and hydrocarbon-based fuel flow rates Gi _k corresponding to the respective Ti _k are set in advance.
However, k is an integer of 1 or more and Ni or less, Ni is an integer of 2 or more,
Each Gi _k is a flow rate of the hydrocarbon-based fuel that can be reformed by the i-th reforming method in the reforming catalyst layer at the corresponding reforming catalyst layer temperature Ti _k , and each Gi _k is greater than 0 and increases by k Gi _k is increased or the same value with the,
A) measuring the temperature of the reforming catalyst layer,
B) For all i, the reformable flow rate Fi ^R that is the flow rate of the hydrocarbon-based fuel that can be reformed by the i-th reforming method in the reforming catalyst layer at the temperature T is the largest below the temperature T Adopting Gi _k corresponding to Ti _k ,
C) a step of stopping power generation in the fuel cell when the reformable flow rate Fi ^R determined in step B is smaller than the minimum value Fi _min for all i;
D) for at least one i, reformable flow rate Fi ^R determined in step B is, if the it is the minimum value Fi _min or more, for each of the at least one i, the fuel cell output demand value P _D is the maximum if the electrical output Pi _M or less performs step d1, the fuel cell output demand value P _D is a step d2 if exceeds the maximum electrical output Pi _M step,
d1) wherein the function Fi = with fi (P), the fuel cell output demand value P _D need be supplied to the reforming catalyst layer to perform reforming method of the i to output the fuel cell hydrocarbon Calculate the flow rate fi (P _D ) of the system fuel,
If fi (P _D ) is equal to or less than the reformable flow rate Fi ^R determined in step B, Pi ^* = P _D , Fi ^* = fi (P _D ),
If fi (P _D ) exceeds the reformable flow rate Fi ^R determined in step B, Pi ^* = {less than P _D among the values of P calculated from the function P = fi ⁻¹ (Fi ^R ) The maximum value}, and Fi ^* = Fi ^R ,
d2) A reforming catalyst that needs to be supplied to the reforming catalyst layer that performs the i-th reforming method in order to output the maximum electrical output Pi _M by a fuel cell using the function Fi = fi (P). Calculate the flow rate fi (Pi _M ) of the hydrocarbon-based fuel supplied to the bed,
If fi (Pi _M ) is less than or equal to the reformable flow rate Fi ^R determined in step B, Pi ^* = Pi _M , Fi ^* = fi (Pi _M ),
If fi (Pi _M ) exceeds the reformable flow rate Fi ^R determined in step B, Pi ^* = {the maximum value of P values calculated from the function P = fi ⁻¹ (Fi ^R ). a value}, Fi ^* = step to Fi ^R,
E) When there are two or more i in which the reformable flow rate Fi ^R determined in the step B is equal to or greater than the minimum value Fi _min , the function ηi = gi (P) is used for each of the two or more i. Then, the power generation efficiency ηi = gi (Pi ^* ) at the electrical output Pi ^* is calculated, and i that gives the largest ηi among the calculated ηi is expressed as I,
If PI ^* is zero, stop power generation in the fuel cell,
When PI ^* exceeds zero, the electric output of the fuel cell is PI ^* , the reforming method performed by the reformer is the first reforming method, and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is FI. ^{* The} process, and
F) When there is only one i where the reformable flow rate Fi ^R determined in step B is equal to or greater than the minimum value Fi _min , this single i is represented as I,
If PI ^* is zero, stop power generation in the fuel cell,
When PI ^* exceeds zero, the electric output of the fuel cell is PI ^* , the reforming method performed by the reformer is the first reforming method, and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is FI. A load following operation method for a fuel cell system having a process of ^* is provided.

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

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

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

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

It is a schematic diagram which shows an outline | summary about the example of the indirect internal reforming type | mold SOFC system which can implement this invention. In order to explain the method of the present invention, the electric output P of the fuel cell and the reformed gas produced by the i-th reforming method are modified so that the electric output P is output by the fuel cell when supplied to the fuel cell. 3 is a schematic graph showing a correlation with a flow rate Fi of a hydrocarbon-based fuel that needs to be supplied to a porous catalyst layer. In order to explain the method of the present invention, the electric output P of the fuel cell and the reformed gas produced by the i-th reforming method are modified so that the electric output P is output by the fuel cell when supplied to the fuel cell. 3 is a schematic graph showing a correlation with a flow rate Fi of a hydrocarbon-based fuel that needs to be supplied to a porous catalyst layer. In order to explain the method of the present invention, the electric output P of the fuel cell and the reformed gas produced by the i-th reforming method are modified so that the electric output P is output by the fuel cell when supplied to the fuel cell. 3 is a schematic graph showing a correlation with a flow rate Fi of a hydrocarbon-based fuel that needs to be supplied to a porous catalyst layer. In order to explain the method of the present invention, the electric output P of the fuel cell and the reformed gas produced by the i-th reforming method are modified so that the electric output P is output by the fuel cell when supplied to the fuel cell. 3 is a schematic graph showing a correlation with a flow rate Fi of a hydrocarbon-based fuel that needs to be supplied to a porous catalyst layer. In order to explain the method of the present invention, the electric output P of the fuel cell and the reformed gas produced by the i-th reforming method are modified so that the electric output P is output by the fuel cell when supplied to the fuel cell. 3 is a schematic graph showing a correlation with a flow rate Fi of a hydrocarbon-based fuel that needs to be supplied to a porous catalyst layer. Fuel cell for explaining the method of the present invention, when the fuel cell electrical output P and the reformed gas produced by the i-th reforming method are supplied to the fuel cell and the fuel cell outputs the electrical output P It is a typical graph which shows the correlation with the power generation efficiency (eta) i. It is a flowchart for demonstrating the method of this invention.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[Functions Fi = fi (P) and P = fi ⁻¹ (Fi)]
In the present invention, for all i, the electric output P of the fuel cell and the electric output P are output by the fuel cell when the reformed gas produced by the i-th reforming method is supplied to the fuel cell in advance. Functions Fi = fi (P) and P = fi ⁻¹ (Fi) with the flow rate Fi of the hydrocarbon-based fuel that needs to be supplied to the reforming catalyst layer are obtained. P = fi ⁻¹ (F) is an inverse function of Fi = fi (P). For example, when L = 2, the following function is obtained in advance.
Function F1 = f1 (P) and its inverse function P = f1 ⁻¹ (F1). Here, F1 is a flow rate of the hydrocarbon-based fuel that needs to be supplied to the reforming catalyst layer that performs the first reforming method in order to output the electric output P by the fuel cell.
Function F2 = f2 (P) and its inverse function P = f2 ⁻¹ (F2). Here, F2 is a flow rate of the hydrocarbon-based fuel that needs to be supplied to the reforming catalyst layer that performs the second reforming method in order to output the electric output P by the fuel cell.

  However, for each reforming method, that is, for each i, Fi is uniquely determined for a certain electric output P, and one or a plurality of P can exist for a certain Fi. For example, it is inevitable that the current and the fuel utilization rate for a certain electric output P are determined in advance by preliminary experiments or simulations so that the power generation efficiency is as high as possible while maintaining the SOFC at a temperature at which power generation is preferable. Fi for a certain electric output P is uniquely determined. Further, for example, in order to maintain the SOFC at a temperature at which power generation can be preferably performed even when the electric output is small (including when it is zero), the flow rate of the hydrocarbon fuel with respect to a certain electric output P or less as shown in FIG. May be set to a constant value, in which case there are a plurality of Ps for a certain Fi.

[Operation conditions other than fuel flow and fuel cell electrical output]
For each reforming method, the flow rate of fluid supplied to the indirect internal reforming SOFC other than the hydrocarbon-based fuel and the input of electricity to the indirect internal reforming SOFC other than the output of the fuel cell are preliminarily necessary. The output can be determined as a function of the electrical output P. For example, with respect to the flow rate of water supplied to the reformer, a steam / carbon ratio (ratio of the number of moles of water molecules to the number of moles of carbon atoms in the gas supplied to the reforming catalyst layer) is predetermined in order to suppress carbon precipitation. It can be determined to be a value. The air flow rate supplied to the reformer should be determined 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) is a predetermined value. Can do. 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, P> 0 is obtained through preliminary experiments and simulations. In this case, it is required that the power generation efficiency be as high as possible while maintaining the SOFC at a temperature at which power generation is preferable. When P = 0, the input energy is reduced as much as possible while the SOFC is preferably maintained at a temperature at which power generation is possible. You can ask for it. In this way, when the output of the fuel cell is set to a certain value P, these flow rates and electrical input / output can be determined using a function obtained in advance.

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

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

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

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

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

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

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

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

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

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

[Function ηi = gi (P)]
The power generation efficiency of the fuel cell when the electric output P of the fuel cell and the reformed gas produced by the i th reforming method are supplied to the fuel cell in advance and the electric output P is output by the fuel cell for all i A function ηi = gi (P) with ηi is obtained. For example, when L = 2, the following function is obtained in advance.
Η1 = g1 (P). Here, η1 is the power generation efficiency of the fuel cell when the reformed gas produced by the first reforming method is supplied to the fuel cell and the electric output P is output by the fuel cell.
Η2 = g2 (P). Here, η2 is the power generation efficiency of the fuel cell when the reformed gas produced by the second reforming method is supplied to the fuel cell and the electric output P is output by the fuel cell.

The function ηi = gi (P) can be obtained at the same time as the above functions Fi = fi (P) and P = fi ⁻¹ (Fi). For example, it is inevitable that the current and the fuel utilization rate for a certain electric output P are determined in advance by preliminary experiments or simulations so that the power generation efficiency is as high as possible while maintaining the SOFC at a temperature at which power generation is preferable. In this case, Fi for a certain electric output P is uniquely determined. At that time, ηi for the electric output P is uniquely determined at the same time.

[Pi _M ]
Let Pi _{M be} the maximum electrical output of the fuel cell when the reformed gas produced by the i-th reforming method is supplied to the fuel cell. Pi _M is predetermined as a specification of the fuel cell system. For example, representative of the maximum electrical output of the fuel cell when the reformed gas produced in the first reforming process is supplied to the fuel cell and P1 _M.

[Fi _min ]
Further, Fi _min is a minimum value of the flow rate of the hydrocarbon fuel determined by the function Fi = fi (P) when P is in the range of 0 to Pi _M. For example, the minimum value of the flow rate F1 of the hydrocarbon fuel determined by the function F1 = f1 (P) when P is in the range of 0 to P1 _M is represented as F1 _min .

Further, Fi _max is set to the maximum value of the flow rate of the hydrocarbon fuel determined by the function Fi = fi (P) when P is in the range of 0 to Pi _M. For example, the maximum value of the flow rate of the hydrocarbon-based fuel determined by the function F1 = f1 (P) when P is in the range of 0 to P1 _M is represented as F1 _max .

At this time, the functions Fi = fi (P) and P = fi ⁻¹ (Fi) are
0 may Sadamare in the range of ≦ P ≦ Pi _M and Fi _min ≦ Fi ≦ Fi _max.

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

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

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

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

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

  In FIG. 8, the flowchart for demonstrating process AF is shown.

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

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

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

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

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

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

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

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

・ Process d1
Wherein the function Fi = with fi (P), the fuel cell output demand value P _D hydrocarbon fuel need be supplied to the reforming catalyst layer to perform reforming method of the i to output the fuel cell The flow rate fi (P _D ) is calculated.

If the calculated fi (P _D ) is equal to or less than the reformable flow rate Fi ^R obtained in step B, Pi ^* = P _D and Fi ^* = fi (P _D ). fi (P _D ) ≦ Fi ^R is the carbonization of the flow rate fi (P _D ) necessary for outputting the electric output of the fuel cell output required value P _D when the i-th reforming method is performed in the reformer. The hydrogen-based fuel is considered to mean that it can be reformed in the reforming catalyst layer.

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

On the other hand, if the calculated fi (P _D ) exceeds the reformable flow rate Fi ^R obtained in step B, Pi ^* = {P value calculated from the function P = fi ⁻¹ (Fi ^R ) of out, the maximum value} is less than P _D, Fi ^* = and Fi ^R. fi (P _D )> Fi ^R is the carbonization of the flow rate fi (P _D ) necessary for outputting the electric output of the fuel cell output required value P _D when the i-th reforming method is performed in the reformer. This is considered to mean that the hydrogen-based fuel cannot be reformed in the reforming catalyst layer. There may be only one value of P calculated from P = fi ⁻¹ (Fi ^R ), or there may be a plurality of values. In the case of only one, the electrical output of the fuel cell is Pi ^* . If there are a plurality of values of a plurality of P, and P _D below and largest values, and Pi ^*.

・ Process d2
As described above, when P _D > Pi _M (when the reformer performs the i-th reforming method, the electric output of the fuel cell is regarded as insufficient with respect to the required fuel cell output value P _D ). Step d2 is performed.

Using the function Fi = fi (P), a reforming catalyst layer that needs to be supplied to the reforming catalyst layer that performs the i-th reforming method in order to output the maximum electrical output Pi _M by a fuel cell. The flow rate fi (Pi _M ) of the hydrocarbon-based fuel to be supplied is calculated.

If fi (Pi _M ) is equal to or less than the reformable flow rate Fi ^R obtained in step B, Pi ^* = Pi _M and Fi ^* = fi (Pi _M ). fi (Pi _M ) ≦ Fi ^R indicates that the hydrocarbon fuel at the flow rate fi (Pi _M ) can be reformed in the reforming catalyst layer when the i-th reforming method is performed in the reformer. Consider it to mean.

On the other hand, if fi (Pi _M ) exceeds the reformable flow rate Fi ^R obtained in step B, Pi ^* = {of P values calculated from the function P = fi ⁻¹ (Fi ^R ) the maximum value}, Fi ^* = and Fi ^R. The maximum value of P calculated from P = fi ⁻¹ (Fi ^R ) is necessarily less than P _D. If fi (Pi _M )> Fi ^R means that the reforming catalyst layer cannot reform the hydrocarbon-based fuel at the flow rate fi (Pi _M ) when the i-th reforming method is performed in the reformer. I reckon.

[Process E]
When there are two or more i in which the reformable flow rate Fi ^R obtained in step B is equal to or greater than the minimum value Fi _min , for each of the two or more i, using the function ηi = gi (P), The power generation efficiency ηi = gi (Pi ^* ) at the electrical output Pi ^* is calculated. I that gives the largest ηi among the two or more ηi calculated in this way is represented by I.

For example, if i satisfying Fi ^R ≧ Fi _min is two of 1 and 2, that is, if F1 ^R ≧ F1 _min and F2 ^R ≧ F2 _min and i can be 3, F3 ^R <F3 _min Η1 = g1 (P1 ^* ) and η2 = g2 (P2 ^* ) are calculated. If the largest ηi of these η1 and η2 is η1, i (expressed as I) giving the largest ηi is 1, that is, I = 1.

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

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

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

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

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

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

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

[Example of load following operation]
Hereinafter, with reference to FIGS. 2 to 5 and 7, how to operate under a variety of conditions when performing a load following operation of a certain fuel cell system will be described with specific examples. However, the present invention is not limited thereby.

  FIG. 7 shows the correlation between the electrical output and the power generation efficiency when L = 2. For the same electrical output, the first reforming method has a higher power generation efficiency than the second reforming method, but the magnitude relationship of the power generation efficiency differs for different electrical outputs. For example, in some cases, the second reforming method has a higher maximum electric output that can be generated in a state in which complete reforming is ensured and the power generation efficiency is higher than the first reforming method. In the present invention, the electric output and the hydrocarbon fuel flow rate in a state in which complete reforming is ensured are calculated in real time, and a reforming method that increases power generation efficiency is selected. The power generation efficiency can be kept high while increasing the size.

<Pi ^* , Fi ^* calculation example>
First, the procedure for calculating Pi ^* and Fi ^* in step D will be described. However, only the first reforming method will be specifically described here. Pi ^* and Fi ^* can be calculated in the same procedure for the second reforming method, and also for the third reforming method when the third reforming method exists.

Hydrocarbons that need to be supplied to the reforming catalyst layer in advance in order to obtain the electric output P when the electric output P of the fuel cell and the reformed gas produced by the first reforming method are supplied to the fuel cell. Assume that the correlation with the flow rate F1 of the system fuel, that is, the functions F1 = f1 (P) and P = f1 ⁻¹ (F1) are obtained as shown in FIG. 2 (the same correlation is also applied in FIGS. 3 to 5).

Further, as shown in Table 1 in advance for the same fuel cell system, the temperature T1 _k of the reforming catalyst layer and the flow rate of the hydrocarbon fuel corresponding to each T1 _k when the first reforming method is performed. Assume that G1 _k is set. Here, T1 _N1 = 700 ° C. and G1 _N1 = 8 g / min, which are values inherent to the fuel cell system. Ni = 5, that is, five different T1 _k are set.

Note that G1 _Ni = 8 g / min ≧ 7 g / min = F1 _max .

Further, it is assumed that P1 _M = 1000 W and F1 _min = 1 g / min.

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

(Case 1)
Consider the case where P _D = 600 W as shown in FIG. 2 and T = 660 ° C.

Step B is performed. From Table 1, the largest T1 _{k in} the range of T (660 ° C.) or less is T1 ₃ (650 ° C.). G1 _k (G1 ₃ ) corresponding to T1 ₃ is 3 g / min. As reformable flow rate F1 ^R, adopt a G1 _3. Therefore, F1 ^R = 3 g / min.

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

Since P _D = 600W ≦ 1000W = P1 _M , step d1 is performed instead of step d2.

In step d1, using function F1 = f1 (P), to output power P _D, the flow rate of the hydrocarbon-based fuel required to be supplied to the reforming catalyst layer to perform the first reforming f1 (P _D ) is calculated. This value is 2 g / min.

Since f1 (P _D ) = 2 g / min ≦ 3 g / min = F1 ^R , P1 ^* = P _D = 600 W and F1 ^* = f1 (P _D ) = 2 g / min. In FIGS. 2 to 5, asterisks are added to the points indicating the conditions thus obtained.

(Case 2)
Consider the case where P _D = 900 W and T = 640 ° C. as shown in FIG. The fuel cell output demand value P _D is intended to vary in load following operation, F1 ^R is to vary the temperature of the reforming catalyst layer. Since P1 _M = 1000 W and F1 _min = 1 g / min are values inherent to the fuel cell system, they are the same as the above example.

Step B is performed. From Table 1, the largest T1 _{k in} the range of T (640 ° C.) or less is T1 ₂ (625 ° C.). G1 _k (G1 ₂ ) corresponding to T1 ₂ is 2 g / min. As reformable flow rate F1 ^R, adopt a G1 _2. Therefore, F1 ^R = 2 g / min.

At this time, since F1 ^R = 2 g / min ≧ 1 g / min = F1 _min , the process D is performed without performing the process C.

Since P _D = 900W ≦ 1000W = P1 _M , step d1 is performed instead of step d2.

In step d1, using function F1 = f1 (P), to output power P _D, the flow rate of the hydrocarbon-based fuel required to be supplied to the reforming catalyst layer to perform the first reforming f1 (P _D ) is calculated. This value is 3 g / min.

Since f1 (P _D ) = 3 g / min> 2 g / min = F1 ^R, let P1 ^* be the maximum value less than P _D among the values of P calculated from P = f1 ⁻¹ (F1 ^R ), ^Let F1 ^* = F1 ^R = 2 g / min.

The values of P calculated from P = f1 ⁻¹ (F1 ^R ) are 30 W, 600 W and 800 W. Among these values, the maximum value less than P _D (900 W) is 800 W. Therefore, P1 ^* = 800W.

(Case 3)
Consider the case where P _D = 1200 W and T = 680 ° C. as shown in FIG. P1 _M = 1000 W and F1 _min = 1 g / min are the same as in the above example.

Step B is performed. From Table 1, the largest T1 _{k in} the range of T (680 ° C.) or less is T1 ₄ (675 ° C.). G1 _k (G1 ₄ ) corresponding to T1 ₄ is 5 g / min. As reformable flow rate F1 ^R, adopt a G1 _4. Therefore, F1 ^R = 5 g / min.

At this time, since F1 ^R = 5 g / min ≧ 1 g / min = F1 _min , the process D is performed without performing the process C.

Since P _D = 1200W> 1000W = P1 _M , the process d2 is performed instead of the process d1.

In step d2, the function F1 = f1 (P) is used to supply the reforming catalyst layer that performs the first reforming method in order to output the electric output of the maximum electric output P1 _M (1000 W). The flow rate f1 (P1 _M ) of the hydrocarbon fuel supplied to the reforming catalyst layer is calculated. This value is 4.5 g / min.

Since f1 (P1 _M ) = 4.5 g / min ≦ 5 g / min = F1 ^R , P1 ^* = P1 _M = 1000 W and F1 ^* = f1 (P1 _M ) = 4.5 g / min.

(Case 4)
Consider the case where P _D = 1200 W and T = 640 ° C. as shown in FIG. P1 _M = 1000 W and F1 _min = 1 g / min are the same as in the above example.

Step B is performed. From Table 1, the largest T1 _{k in} the range of T (640 ° C.) or less is T1 ₂ (625 ° C.). G1 _k (G1 ₂ ) corresponding to T1 ₂ is 2 g / min. As reformable flow rate F1 ^R, adopt a G1 _2. Therefore, F1 ^R = 2 g / min.

At this time, since F1 ^R = 2 g / min ≧ 1 g / min = F1 _min , the process D is performed without performing the process C.

Since P _D = 1200W> 1000W = P1 _M , the process d2 is performed instead of the process d1.

In step d2, the function F1 = f1 (P) is used to supply the reforming catalyst layer that performs the first reforming method in order to output the electric output of the maximum electric output P1 _M (1000 W). The flow rate f1 (P1 _M ) of the hydrocarbon fuel supplied to the reforming catalyst layer is calculated. This value is 4.5 g / min.

Since f1 (P1 _M ) = 4.5 g / min> 2 g / min = F1 ^R , _let P1 ^* be the maximum value of P values calculated from P = f1 ⁻¹ (F1 ^R ), and F1 ^* = F1 ^R = 2g / min.

The values of P calculated from P = f1 ⁻¹ (F1 ^R ) are 30 W, 600 W and 800 W. The maximum value among these is 800W. Therefore, P1 ^* = 800W.

In the description using FIGS. 2 to 5, the correlation between F1 and P is assumed to be extreme for the sake of explanation. However, in practice, it is considered that there are many cases where the correlation is close to that shown in FIG. In FIG. 6, the flow rate F1 of the hydrocarbon-based fuel is set to 1.5 g / min in order to maintain the SOFC at a preferable power generation temperature in a range where the electrical output P is small, that is, in a range where the electrical output P is 0 W or more and 300 W or less. It is constant. Further, in the range where the electrical output P is large, that is, in the range where the electrical output P is greater than 300 W and the maximum electrical output P1 _M (1000 W) or less, in order to increase the power generation efficiency, the hydrocarbon fuel is increased as the electrical output P increases. It is assumed that the flow rate F1 increases from 1.5 g / min to 4.5 g / min.

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

In the following description, it is assumed that the following values are obtained considering the case of L = 2.
P1 _M = 1000 W, P2 _M = 900 W,
F1 _min = 1 g / min, F2 _min = 2 g / min.

(Case 5)
here,
P _D = 900W
In step B, F1 ^R = 2 g / min, F2 ^R = 5 g / min
It is assumed that In addition, for the first and second reforming methods, it is assumed that functions η1 = g1 (P) and η2 = g2 (P) are obtained as shown in FIG. Further, it is assumed that P1 ^* , F1 ^* , P2 ^*, and F2 ^* are obtained as follows.
P1 ^* = 800 W, F1 ^* = 2 g / min,
P2 ^* = 900 W, F2 ^* = 4 g / min.

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

For each of these two i (1 and 2), from the functions η1 = g1 (P) and η2 = g2 (P), ie from FIG.
η1 = g1 (P1 ^* ) = 43%,
η2 = g2 (P2 ^* ) = 45%
It is obtained.

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

Therefore, the electric output of the fuel cell is PI ^*, that is, P2 ^* (900 W), the reforming method is the second reforming method, and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is F2 ^* = 4 g / min. And

(Case 6)
Here, P _D = 900 W
In step B, F1 ^R = 2 g / min, F2 ^R = 1.5 g / min
It is assumed that Further, it is assumed that P1 ^* and F1 ^* are obtained as follows. Here, P2 ^* and F2 ^* are not used.
P1 ^* = 800 W, F1 ^* = 2 g / min.

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

Therefore, the electric output of the fuel cell is PI ^*, that is, P1 ^* (800 W), the reforming method is the first reforming method, and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is F1 ^* = 2 g / min. And

(Case 7)
Here, P _D = 900 W
In process B, F1 ^R = 0.5 g / min, F2 ^R = 5 g / min
It is assumed that Further, it is assumed that P2 ^* and F2 ^* are obtained as follows. Here, P1 ^* and F1 ^* are not used.
P2 ^* = 900 W, F2 ^* = 4 g / min.

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

Therefore, the electric output of the fuel cell is PI ^*, that is, P2 ^* = 900 W, the reforming method is the second reforming method, and the flow rate of the hydrocarbon fuel supplied to the reforming catalyst layer is F2 ^* = 4 g / min. To do.

<Case where process C is performed>
(Case 8)
Although not shown, in step B, F1 ^R = 0.5 g / min, F2 ^R = 1 g / min
Consider the case where it is determined.

At this time, since F1 ^R = 0.5 g / min <1 g / min = F1 _min and F2 ^R = 1 g / min <2 g / min = F2 _min , that is, for all i, since Fi ^R <Fi _min , step D is performed. Without performing the step C, the electric output of the fuel cell is made zero.

At this time, if the reforming method having the largest ratio of the calorific value to the endothermic amount among the first and second reforming methods is the second reforming method, the second reforming method performed in the reformer is the second reforming method. the flow rate hydrocarbon fuel F2 ^R while adopting the reforming process is supplied to the reformer, at least for one i, until at least Fi ^R ≧ Fi _min, a heater or a burner that is attached to the reformer Thus, the temperature of the reforming catalyst layer can be increased. If the temperature of the reforming catalyst layer rises while steps A to C are repeated and Fi ^R ≧ Fi _min for at least one i, step D and subsequent steps can be performed.

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

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

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

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

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

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

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

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

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

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

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

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

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

  When determining the flow rate of the hydrocarbon fuel in the processes E, F, etc., the flow rate of the fluid supplied to the indirect internal reforming SOFC other than the hydrocarbon fuel and the indirect other than the output of the SOFC as necessary The input / output of electricity to the internal reforming SOFC can be determined by calculating from the function of the electrical output P obtained in advance.

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

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

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

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

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

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

  The MCFC can be appropriately selected from known MCFCs.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Claims (4)

A fuel cell comprising a reformer having a reforming catalyst layer for producing a reformed gas containing hydrogen by reforming a hydrocarbon fuel, and a high-temperature fuel cell for generating electric power using the reformed gas A load following operation method of the system,
At least two reforming methods selected from the group consisting of steam reforming method, partial oxidation reforming method and autothermal reforming method are defined as i-th reforming method, where i is an integer of 1 or more and L or less. L is 2 or 3,
For all i, the reforming catalyst layer for outputting the electric output P of the fuel cell in advance and the electric output P of the fuel cell when the reformed gas produced by the i-th reforming method is supplied to the fuel cell. The functions Fi = fi (P) and P = fi ⁻¹ (Fi) with the flow rate Fi of the hydrocarbon-based fuel that needs to be supplied to
However, P = fi ⁻¹ (Fi) is an inverse function of Fi = fi (P),
The power generation efficiency of the fuel cell when the electric output P of the fuel cell and the reformed gas produced by the i th reforming method are supplied to the fuel cell in advance and the electric output P is output by the fuel cell for all i Obtain a function ηi = gi (P) with ηi,
The maximum electrical output of the fuel cell when the reformed gas produced by the i-th reforming method is supplied to the fuel cell is denoted as Pi _M.
When P is in the range of 0 or more Pi _M, the minimum value of the flow rate of the hydrocarbon-based fuel determined by the function Fi = fi (P) expressed as Fi _min,
In addition, for all i, different Ni reforming catalyst layer temperatures Ti _k and hydrocarbon-based fuel flow rates Gi _k corresponding to the respective Ti _k are set in advance.
However, k is an integer of 1 or more and Ni or less, Ni is an integer of 2 or more,
Each Gi _k is a flow rate of the hydrocarbon-based fuel that can be reformed by the i-th reforming method in the reforming catalyst layer at the corresponding reforming catalyst layer temperature Ti _k , and each Gi _k is greater than 0 and increases by k Gi _k is increased or the same value with the,
A) measuring the temperature of the reforming catalyst layer,
B) For all i, the reformable flow rate Fi ^R that is the flow rate of the hydrocarbon-based fuel that can be reformed by the i-th reforming method in the reforming catalyst layer at the temperature T is the largest below the temperature T Adopting Gi _k corresponding to Ti _k ,
C) a step of stopping power generation in the fuel cell when the reformable flow rate Fi ^R determined in step B is smaller than the minimum value Fi _min for all i;
D) for at least one i, reformable flow rate Fi ^R determined in step B is, if the it is the minimum value Fi _min or more, for each of the at least one i, the fuel cell output demand value P _D is the maximum if the electrical output Pi _M or less performs step d1, the fuel cell output demand value P _D is a step d2 if exceeds the maximum electrical output Pi _M step,
d1) wherein the function Fi = with fi (P), the fuel cell output demand value P _D need be supplied to the reforming catalyst layer to perform reforming method of the i to output the fuel cell hydrocarbon Calculate the flow rate fi (P _D ) of the system fuel,
If fi (P _D ) is equal to or less than the reformable flow rate Fi ^R determined in step B, Pi ^* = P _D , Fi ^* = fi (P _D ),
If fi (P _D ) exceeds the reformable flow rate Fi ^R determined in step B, Pi ^* = {less than P _D among the values of P calculated from the function P = fi ⁻¹ (Fi ^R ) The maximum value}, and Fi ^* = Fi ^R ,
d2) A reforming catalyst that needs to be supplied to the reforming catalyst layer that performs the i-th reforming method in order to output the maximum electrical output Pi _M by a fuel cell using the function Fi = fi (P). Calculate the flow rate fi (Pi _M ) of the hydrocarbon-based fuel supplied to the bed,
If fi (Pi _M ) is less than or equal to the reformable flow rate Fi ^R determined in step B, Pi ^* = Pi _M , Fi ^* = fi (Pi _M ),
If fi (Pi _M ) exceeds the reformable flow rate Fi ^R determined in step B, Pi ^* = {the maximum value of P values calculated from the function P = fi ⁻¹ (Fi ^R ). a value}, Fi ^* = step to Fi ^R,
E) When there are two or more i in which the reformable flow rate Fi ^R determined in the step B is equal to or greater than the minimum value Fi _min , the function ηi = gi (P) is used for each of the two or more i. Then, the power generation efficiency ηi = gi (Pi ^* ) at the electrical output Pi ^* is calculated, and i that gives the largest ηi among the calculated ηi is expressed as I,
If PI ^* is zero, stop power generation in the fuel cell,
When PI ^* exceeds zero, the electric output of the fuel cell is PI ^* , the reforming method performed by the reformer is the first reforming method, and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is FI. ^{* The} process, and
F) When there is only one i where the reformable flow rate Fi ^R determined in step B is equal to or greater than the minimum value Fi _min , this single i is represented as I,
If PI ^* is zero, stop power generation in the fuel cell,
When PI ^* exceeds zero, the electric output of the fuel cell is PI ^* , the reforming method performed by the reformer is the first reforming method, and the flow rate of the hydrocarbon-based fuel supplied to the reforming catalyst layer is FI. ^* The load following operation method of the fuel cell system which has the process of ^* .   The method according to claim 1, wherein the steps A to F are repeated during the load following operation.   The method according to claim 1 or 2, wherein the hydrocarbon fuel includes a hydrocarbon fuel having 2 or more carbon atoms.   The method according to claim 3, wherein the concentration of the compound having 2 or more carbon atoms in the reformed gas is 50 ppb or less on a mass basis.

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