JP2001126748A - Operating method for fuel cell electricity generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an operating method for a fuel cell electricity generator that improves generation efficiency by carrying out temperature control of the reformer that minimizes required calories to be supplied to the reformer. SOLUTION: In a method of operating fuel cell electricity generator, having a reformer 7 for providing a reformed gas rich in hydrogen by reforming reaction of an original fuel gas with vapor, and a burner 17 for performing combustion of hydrogen exhausted from the fuel cell 10 with air, the method comprises the step of controlling the flow rate of the original fuel gas, so as to change the measured value 32 of temperature in the reformer 7 into the predetermined reformer set temperature 33, where during the operation of the fuel cell electricity generator, correcting the predetermined reformer set temperature 33 by means of a reformer set temperature correction circuit 40 so as to allow reforming rate in the reformer 7 to be approximately uniform, based on correlation pre-obtained between anticipated set temperature of the reformer 7 and accumulated operation time of he fuel cell electricity generator taking into consideration the catalytic activity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of operating a fuel cell power generator having a reformer for converting a raw fuel into a hydrogen-rich reformed gas by a steam reforming reaction.

[0002]

2. Description of the Related Art There are various types of fuel cells which are incorporated in a fuel cell power generator, depending on the type of electrolyte, the type of reforming material, and the like. The phosphoric acid type fuel cell and the polymer electrolyte fuel cell used are well known.

[0003] Phosphoric acid type fuel cells and solid polymer type fuel cells generally include hydrogen in a reformed gas obtained by steam reforming a hydrocarbon reforming raw fuel such as natural gas or methanol, and
Oxygen in the air is supplied to the fuel electrode and the air electrode of the fuel cell, respectively, and power is generated based on the electrochemical reaction. It is well known to use a steam reforming reaction in which water is added and heated to reform steam and raw fuel gas using a catalyst.

[0004] In the case of the above-mentioned fuel cell power generator, the raw fuel gas flowing through the reforming catalyst layer includes city gas, natural gas and natural gas.
Raw fuel gas such as methane gas, methanol, ethanol,
A raw fuel gas obtained by vaporizing a liquid fuel obtained by mixing a liquid hydrocarbon such as gasoline with water is used.

FIG. 4 shows a case where methanol is used as a raw fuel,
Shows an example of a fuel cell power generator using a fuel reformer reforming by steam reforming, fuel cell, reformer, evaporator,
FIG. 2 is a schematic flow diagram showing a CO remover, an exhaust hydrogen combustor, and a piping of a raw fuel supply system connecting them;

A raw fuel (here, methanol and water are shown as being already mixed at an appropriate ratio) is supplied from a raw fuel tank 1 by a raw fuel pump 2 to a vaporizer 4 through a raw fuel supply pipe 3. Is done. The raw fuel gas exiting the evaporator 4 is supplied to the reformer 7 through the raw fuel gas supply pipe 6.

In the reformer 7, a hydrogen-rich fuel gas is generated by a steam reforming reaction. The reformed gas exiting the reformer 7 enters the CO remover 9 through the reformed gas supply pipe 8 and is
After the O concentration is reduced to a level that does not adversely affect the performance of the cell, the O concentration is supplied to the fuel cell 10. Fuel cell 10
Then, for example, after the hydrogen utilization rate of 80%, that is, 80% of the hydrogen is consumed, the hydrogen is supplied to the exhaust hydrogen combustor 12 using, for example, a catalytic combustor through the exhaust hydrogen supply pipe 11. Exhaust air is simultaneously supplied to the exhaust hydrogen combustor 12 through an exhaust air supply pipe 13.

[0008] The flue gas discharged from the exhaust hydrogen combustor 12 is supplied to the evaporator 4 through a flue gas supply pipe 14 and becomes an energy source for evaporating the raw fuel. Reaction air to the fuel cell is supplied by a blower 15 through a reaction air supply pipe 16.

In the above fuel cell power generator, when city gas is used as the raw fuel gas, for example, the evaporator 4 becomes unnecessary, but steam for reforming is separately injected into the reformer. Further, many of the exhaust hydrogen combustors are burners for direct combustion, and many of such burners are configured to be incorporated in the reformer body.

FIG. 3 shows a conventional system diagram mainly related to the present invention, which relates to the operation method of the fuel cell power generator. In FIG. 3, reference numeral 10 denotes a fuel cell;
Is a reformer, 17 is a reformer burner as an exhaust hydrogen combustor,
Reference numeral 18 denotes a raw fuel gas flow control valve. Reference numeral 19 denotes a flow meter for raw fuel gas, reference numeral 20 denotes a reformer temperature measuring device, reference numeral 21 denotes an ammeter for measuring the output current of the fuel cell, reference numeral 22 denotes a necessary raw fuel gas flow rate calculation circuit, and reference numerals 23 and 24 denote feedback control. , For example, a PID controller for performing a PID operation. Further, reference numerals 30 to 35 denote various set values or measured values. SV in each block indicates Set Point Value, and PV indicates Process Value.

Referring to FIG. 3, a method of operating a conventional fuel cell power generator for controlling a raw fuel gas flow rate based on a reformer temperature and a hydrogen utilization rate of a fuel cell fuel electrode will be described below.

In the fuel cell 10, the following reaction takes place:
2 Faraday charges flow with 1 mol of hydrogen and 0.5 mol of oxygen.

[0013]

[Formula 1] ^{_{anode: H 2 → 2H + +}} 2e -

[0014]

Cathode: 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O Therefore, the theoretical hydrogen flow required for power generation can be obtained from the output of the ammeter 21 as follows.

Required theoretical hydrogen amount (mol / s) = [battery current (A) ×
The number of cells] ÷ [the number of electrons x the Faraday constant] When the supplied hydrogen amount falls below the required theoretical hydrogen amount, the carbon that is the catalyst carrier corrodes. Supplying hydrogen. The degree of excess at this time is indicated by the hydrogen utilization rate, and the actual required amount of hydrogen is obtained as follows.

Required hydrogen amount (mol / s) = Required theoretical hydrogen amount (mol / s)
s) / ([hydrogen utilization (%)] / 100) When the hydrogen utilization is 80%, the required amount of hydrogen is 1.25 times the required theoretical amount of hydrogen. Hydrogen used for power generation by fuel cells is generally obtained by reforming city gas, natural gas, methane gas, methanol, ethanol, gasoline, and the like using a reformer. Taking CH ₄ as an example, the reaction formula in the reformer is as follows.

[0017]

Embedded image CH ₄ + H ₂ O → 3H ₂ + CO ΔH ₂₉₈ = 205.75 kJ / mol (1)

[0018]

Embedded image CO + H ₂ O → CO ₂ + H ₂ ΔH ₂₉₈ = −41.12 kJ / mol (2) In the steam reforming reaction, the equation (1), which is an endothermic reaction, is dominant. The reforming rate of CH ₄ increases, and the amount of generated hydrogen also increases. In the fuel cell power generator, the reformer temperature is controlled so that the ratio of the amount of hydrogen generated per unit of fuel (city gas, natural gas, methane gas, methanol, ethanol, gasoline, etc.) can be kept constant. The following reforming rates are used as indices for the porcelain performance.

Reforming rate (%) = (C _CO2 + C _CO ) / (C _CH4 +
C _CO2 + C _CO ) × 100 where C _CO2 : CO ₂ concentration at the outlet of the reformer (%), C _CO : CO concentration at the outlet of the reformer (%), C _CH4 : at the outlet of the reformer CH ₄ concentration (%) In FIG. 3, the raw fuel gas flow rate for battery power generation before reforming was 30
(F _FC -SV) is obtained by calculating the required hydrogen amount obtained from the battery output current 31 (I _FC -PV) from the relationship between the fuel gas supply amount and the generated hydrogen amount at a preset reforming rate. It is determined by the fuel gas flow rate calculation circuit 22.

In the reformer 7, the measured reformer temperature 32 (T _RF
-PV) for controlling the combustion amount of the reformer burner 17 so that the reformer set temperature 33 (T _RF -SV) corresponding to the preset reforming rate. The raw fuel gas flow rate 34 (F _RF -SV) is calculated. In FIG. 3, P
Although the example in which the ID controller 23 is used has been described, the PID controller may be a simple comparator.

Since the reforming rate is determined by the temperature of the reforming catalyst, the control point of the reformer temperature is determined by taking into account the reforming catalyst temperature or the delay in the temperature at the reforming catalyst. Nearby furnace wall temperatures, or both, are used. Raw fuel gas flow supplied to the fuel cell power generation system 35 (F-PV)
Is such that the flow rate obtained by adding the battery power generation raw fuel gas flow 30 (F _FC -SV) to the reformer temperature adjusting raw fuel gas flow 34 (F _RF -SV), flow meter 19 and the raw fuel gas Feedback control is performed by the flow control valve 18.

[0022]

The above-described conventional method of operating a fuel cell power generator has the following problems.

[0023] Due to the decrease in the catalyst activity over time with the operation of the fuel cell power generator, the reforming rate decreases with an increase in the cumulative operation time. Therefore, in the conventional control method of maintaining the reformer at a certain temperature or a certain temperature range, the reforming rate is high at the beginning of the operation and the reforming rate is low at the end of the operation. Since the hydrogen utilization of the battery increases as the reforming rate decreases when the raw fuel gas flow rate is the same, the raw fuel gas flow rate remains at the upper limit even at the end of operation when the reforming rate is the lowest. It is set not to exceed.

In the above control method, the reformer is controlled at the temperature or the temperature range at the end of the operation even in the early stage of the operation in which the activity of the reforming catalyst is high. It will be driven. Since the reforming reaction in the reformer is an endothermic reaction as described above, it is necessary to give the reforming catalyst an amount of heat corresponding to the amount of heat absorbed. In the fuel cell power generation system, the calorific value corresponding to the endothermic amount is obtained by burning the fuel electrode off-gas not consumed by the fuel cell, for example, in a reformer burner section. It is done by adjusting. When the reforming rate is high, the amount of heat absorbed becomes larger, so it is necessary to increase the flow rate of the raw fuel gas, and as a result, the power generation efficiency decreases.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel cell having a reformer for converting a raw fuel into a hydrogen-rich reformed gas by a steam reforming reaction. In the operation method of the power generator, by performing the temperature control of the reformer to minimize the amount of heat supplied to the reformer,
The purpose is to improve the power generation efficiency.

[0026]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention relates to a method for converting raw fuel gas such as city gas, natural gas and methane gas or liquid hydrocarbon such as methanol, ethanol and gasoline with water. The raw fuel gas, which is the vaporized liquid fuel that has been mixed, flows through the reforming catalyst layer, and is converted into a hydrogen-rich reformed gas by a steam reforming reaction. The reformed gas is supplied to a fuel cell. And an exhaust hydrogen combustor for burning exhaust hydrogen discharged from the fuel cell together with air, so that the measured reformer temperature in the reformer becomes a preset reformer set temperature. In the operating method of the fuel cell power generator for controlling the flow rate of the raw fuel gas, the reformer set temperature is corrected so that the reforming rate in the reformer becomes substantially constant during the operation of the fuel cell power generator. (To be Section 1).

The method of correcting the set temperature of the reformer is as follows.
According to a second aspect of the present invention, in the operating method according to the first aspect, the desired reformer set temperature in consideration of the catalyst activity and the fuel cell power generation device for keeping the reforming rate substantially constant. The reformer set temperature is corrected on the basis of a correlation obtained in advance with the accumulated operation time.

As described above, by changing the reformer temperature so that the reforming rate becomes substantially constant, it is possible to suppress an increase in the amount of heat absorption due to the high reforming rate, and it is necessary to use a reformer burner. Since the amount of combustion can be suppressed, the flow rate of the raw fuel gas is reduced, and the power generation efficiency is improved.

Further, in the operating method according to claim 2, the fuel cell power generation system is operated based on operation information obtained by analyzing a gas composition of reformed gas at a reformer outlet during operation of the fuel cell power generation device. Correction of a previously determined correlation with the cumulative operation time of the device is performed, and the reformer set temperature is corrected based on the corrected correlation. Appropriate correction control according to the state becomes possible.

According to a fourth aspect of the present invention, in the operating method according to any one of the first to third aspects, a predetermined upper limit value is set within a range where the hydrogen utilization rate in the fuel cell does not exceed a predetermined upper limit value. By determining the reforming rate so as to be near, the flow rate of the raw fuel gas can be reduced to the maximum, and the power generation efficiency is most improved.

[0031]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of a method of operating a fuel cell power generator according to the second aspect of the present invention. FIG.
In FIG. 7, the same reference numerals are given to functional members, measured values, and set values equivalent to those in FIG. 3, and description thereof is omitted. The difference between the system diagram of FIG. 1 and the system diagram shown in FIG. 3 is that, in the system of FIG. 1, a reformer temperature set value correction calculation is performed between the reformer set temperature 33 and the PID controller 23. The point is that a circuit 40 and a cumulative operation time meter 41 (Time Counter) are provided.

In FIG. 1, the reformer temperature (T _RF ) at which the preset reforming rate is obtained can be obtained from the operation time (Time) of the cumulative operation time meter 41 so that the reformer temperature can be obtained. Operation time (Time) in the set value correction arithmetic circuit 40
Is calculated from a relational expression between the temperature of the reformer and the reformer temperature (T _RF ) to correct the reformer temperature set value 33 (T _RF -SV). Reformer temperature measurement 3
In accordance with the difference between 2 (T _RF -PV) and the corrected reformer temperature set value, the reformer temperature control raw fuel gas flow rate 34 (F _RF -SV) is set to PI
It is calculated by the D controller 23. The raw fuel gas flow rate for battery power generation was increased to 30 (F _RF -SV) for the reformer temperature control raw fuel gas flow rate.
(F _FC -SV) plus the raw fuel gas flow rate 35 (F-SV) to the reformer 7
Is controlled by the flow meter 19, the PID controller 24, and the raw fuel gas flow control valve 18.

FIG. 2 shows an embodiment according to the third aspect of the present invention. The difference between the system diagram of FIG. 2 and the system diagram shown in FIG. 1 is that, in the system of FIG. 2, the gas composition of the reformed gas at the outlet of the reformer is measured during the operation of the fuel cell power generator. The correlation between the operation time (Time) and the reformer temperature (T _RF ) is corrected by a correlation correction circuit 52 based on the operation information measured by the analyzer 51 and analyzed. The point is that a reformer temperature set value correction arithmetic circuit 50 for correcting the reformer set temperature based on the corrected correlation is provided. The point of providing the cumulative operation time meter 41 (Time Counter) and the supply control of the raw fuel gas flow rate are the same as those in FIG.

In FIG. 2, the reformed gas composition data at the outlet of the reformer obtained by arbitrarily analyzing during the operation is taken into the control, and the relationship between the preset cumulative operation time and the reformer temperature is set. Since the equation is automatically corrected, appropriate correction control based on actual operation can be performed as compared with the control in FIG.

[0036]

As described above, according to the present invention, a raw fuel gas such as city gas, natural gas, and methane gas, and a liquid fuel formed by mixing a liquid hydrocarbon such as methanol, ethanol, gasoline, and water with water are vaporized. The raw fuel gas flows through the reforming catalyst layer and is converted into a hydrogen-rich reformed gas by a steam reforming reaction. The reformed gas is supplied from the fuel cell to the reformer for supplying the reformed gas to the fuel cell. An exhaust hydrogen combustor for burning exhaust hydrogen together with air, and controlling the flow rate of the raw fuel gas such that a measured reformer temperature in the reformer becomes a preset reformer set temperature. In the operating method of the fuel cell power generator, the reformer set temperature is corrected so that the reforming rate in the reformer becomes substantially constant during the operation of the fuel cell power generator. Reforming in porcelain It is possible to suppress the amount of heat absorption that occurs in response to a minimum, it is possible to improve the reduction and the power generation efficiency of the raw fuel gas flow rate to be supplied to the reformer.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an operation method of a fuel cell power generator according to the present invention.

FIG. 2 is a diagram showing an example of a different operation method of the fuel cell power generator according to the present invention.

FIG. 3 is a diagram showing an operation method of a conventional fuel cell power generator.

FIG. 4 is a diagram showing an example of a system system of a conventional fuel cell power generator.

[Explanation of symbols]

7: reformer, 10: fuel cell, 17: burner, 18: raw fuel gas flow control valve, 19: flow meter, 20: reformer temperature measuring device, 21: ammeter, 22: required raw fuel gas flow rate Arithmetic circuits, 23, 24: PID controller, 40, 50: Reformer temperature set value correction arithmetic circuit, 41: Cumulative operation time meter, 5
1: Gas composition measuring device, 52: Correlation correction circuit based on operation information.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H027 AA02 BA01 KK28 KK31 KK42 MM13

Claims (4)

[Claims] 1. A reforming catalyst layer for converting a raw fuel gas such as city gas, natural gas, or methane gas or a raw fuel gas obtained by vaporizing a liquid fuel obtained by mixing a liquid hydrocarbon such as methanol, ethanol, gasoline, and water with water. And a reformer for supplying the reformed gas to the fuel cell by a steam reforming reaction, and a wastewater for combusting the hydrogen discharged from the fuel cell together with the air. Elementary combustor and
In the operating method of the fuel cell power generator, which controls the flow rate of the raw fuel gas such that the measured value of the reformer temperature in the reformer is a preset reformer set temperature, A method of operating the fuel cell power generator, wherein the set temperature of the reformer is corrected so that the reforming rate in the reformer becomes substantially constant. 2. The operating method according to claim 1, wherein an intended reformer set temperature considering catalyst activity and a cumulative operating time of the fuel cell power generator for keeping the reforming rate substantially constant. A method for operating the fuel cell power generator, wherein the set temperature of the reformer is corrected based on a correlation obtained in advance with the fuel cell power generator. 3. The operating method according to claim 2, wherein the correlation is corrected based on operating information obtained by analyzing a gas composition of the reformed gas at the outlet of the reformer during operation of the fuel cell power generator. Then, based on the corrected correlation, the operating method of the fuel cell power generator, wherein the set temperature of the reformer is corrected. 4. The operating method according to claim 1, wherein the hydrogen utilization in the fuel cell is close to a predetermined upper limit within a range not exceeding a predetermined upper limit. A method for operating a fuel cell power generator, comprising determining a rate.