JPS6139369A - Fuel cell power generation plant - Google Patents

Abstract

PURPOSE:To facilitate controlling of the temperature of a fuel cell by installing a heat exchanger for cooling and condensing surplus steam in a cooling water loop for cooling the fuel cell and controlling the amount of steam fed into the heat exchanger according to the load variation of the fuel cell. CONSTITUTION:A fuel cell 1 is constituted by stacking unit cells and installing several cooling pipes 8. A cooling system is constituted by supplying cooling water from a circulation pump 16 into the cooling pipes 8 and separating the steam flowing out from the cell 1 by means of a steam separator 17 before the separated steam is condensed by a heat exchanger 22 to produce water which is then returned back to the pump 16. The flow rate of steam is controlled by drawing a control valve 21 installed in a surplus steam conduit 20 during a load decrease and opening the valve 21 during a load increase according to the output of a detector 19 installed in a load 7. Accordingly, it is possible to improve the efficiency of the fuel cell power generation plant by accurately and easily controlling the temperature of the fuel cell during the time when the plant is being partially loaded or before its operation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel cell power generation plant in which the temperature of a fuel cell is adjusted by adjusting the pressure of a cooling water loop in accordance with load fluctuations of the fuel cell.

FIG. 1 is a system diagram showing an example of a fuel cell power generation plant. Here, only the main components of the power plant flow scheme are shown, and the numerous heat exchangers for heat recovery are omitted.

The fuel cell main body 1 is a single-cell fuel cell composed of a large number of stacked fuel cells 4, a fuel electrode gas space 5, and an air electrode gas space 6.

Since the current obtained from the fuel cell is direct current, this direct current is normally converted to alternating current via an inverter, then converted to a predetermined voltage by a transformer, and then connected to the existing power system. In the following description, the circuit after the inverter will be simply referred to as the load 7. The current generated from the fuel cell passes through the air electrode 3, an external circuit load 7, and returns to the fuel electrode 2, forming a closed circuit. In addition, a cooling loop is configured to cool the fuel cell main body 1, and inside the fuel cell main body 1, the flow is divided into many cooling pipes 8 (only one is shown in the figure) to cool each part of the fuel cell main body. ing. This cooling pipe 8 is buried as a large number of thin tubes in order to absorb and cool the heat generated by the fuel cells, and constitutes a cooling plate to enable cooling by flowing water, and is arranged for each of a plurality of fuel cells. Ru.

In such a fuel cell main body 1, hydrogen-rich fuel gas supplied from the outside, oxygen and carbon in the air as oxidants
The following reaction, which is well known in the art, delivers electricity to the external circuit load 7 and produces water.

Fuel electrode reaction H2→2H+ 2e Air electrode reaction 2 H++ 1/202+ 2e--H2
0 Comprehensive Reaction H2+ l/202-H20 In a fuel cell power generation plant, various reactors are provided to supply the hydrogen-rich fuel gas necessary for the above reaction.

Fuel (hydrocarbon or hydrogen-rich gas, etc.) supplied from a fuel tank or supply device (not shown) through the fuel supply pipe 9 is removed from harmful impurities by a fuel pretreatment system (not shown), and then reformed into a fuel. quality equipment 10.

In the fuel reformer 10, a reforming reaction is caused between hydrocarbon fuel and steam to produce hydrogen-rich gas.

The following example shows methane (CH4) as a representative example of fuel.

CH, + H20→Co + 3H2 A hydrogen-rich gas is produced by this known reaction. The necessary steam for the reforming reaction (2) is supplied by a steam supply pipe 11.

Since the reformed gas that has passed through the fuel reformer lO still contains a large amount of CO gas, the high temperature shift reactor 12 is generally used.
and a low-temperature shift reactor 13, and the CO gas is converted into 002 gas by the following shift reaction.

CO+H20→C02+I (2) Since the hydrogen-rich gas leaving both shift reactors 12 and 13 contains a large amount of water vapor, it is dehumidified by a dehumidifier (not shown) and then supplied to the fuel electrode gas space 5.

Here, water is produced by the electrochemical reaction described above.

Since the gas flow flowing out from the fuel electrode gas space 5 contains unreacted combustible gas, it is sent to the combustion chamber of the fuel reformer 10 and burned. This serves as a heating source necessary for the above-mentioned reforming reaction.

The combustion exhaust gas from the fuel reformer 10 is sent to the turbine 14 to do work. The work of the turbine 14 is the air compressor 15
The air is then pressurized and sent to the air electrode gas space 6 of the fuel cell main body 1 and the combustion chamber of the fuel reformer 10.

The air supplied to the air electrode gas space 6 of the fuel cell main body 1 causes a stain flow to be caused by the above-mentioned electrochemical reaction to the external circuit load 7.
As it flows into the atmosphere, some of that oxygen becomes water. Unreacted air (a large amount of nitrogen and unreacted oxygen) and reaction product water flow out of the air electrode gas space 6, join with the combustion exhaust gas of the fuel reformer 10, and are sent to the turbine 14 to do work. A part of the air supplied from the air compressor 15 is branched,
The fuel is sent to the combustion chamber of the fuel reformer 10 and undergoes a combustion reaction with the unreacted fuel discharged from the fuel electrode gas space 5 of the fuel cell main body 1, thereby serving as a heat source for advancing the aforementioned reforming reaction.

The cooling system of the fuel cell body 1 is as follows.

The cooling water supplied from the fuel cell cooling water circulation pump 16 is branched and supplied to a large number of cooling pipes 8 of the fuel cell main body 1 to cool each part of the fuel cell main body 1, and a part of the cooling water evaporates and becomes steam. , flows out of the fuel cell main body 1.

This steam is separated by a steam separator 17, sent to the fuel reformer 10 via the steam supply pipe 11, and used as steam in the reforming reaction.

Moreover, the water separated by the steam-water separator 17 is sent to the pump 16 and circulated again. Water that has passed through a water treatment device upstream of the pump 16 (- is not shown in Figure C) is replenished by a replenishment pipe 18.

In this way, in a fuel cell power generation plant, in order to keep the fuel cell temperature constant (2) cooling water is circulated, a part of the cooling water is evaporated to create steam while passing through the fuel cell main body 1. This steam is used as the steam necessary for the reforming reaction.

The above is an overview of a fuel cell power generation plant.The amount of power generated from the fuel cell main body 1 changes at partial loads below the rated value, and although power is not supplied to the external system, the electrical output of the plant as a whole is If the plant is to be kept in a standby state where it can be pumped out at any time, it is necessary to keep the temperature of the fuel cell in the fuel cell body 1 as constant as possible. Despite the difficulty, this adjustment method was desired.

The fuel cell body 1 is used to adjust the fuel cell temperature.

One possible method is to branch off a portion of the supply of cooling water to adjust the flow rate. However, in this method, when the amount of cooling water to the fuel cell main body 1 is small, the flow rate distribution to the multiple cooling pipes 8 changes, and some cooling pipes have a high flow rate and others have a low flow rate. It has been difficult to uniformly cool the fuel cells, and therefore it has been difficult to maintain the fuel cell temperature constant.

An object of the present invention is to provide a fuel cell power generation plant in which the fuel cell temperature can be easily adjusted when the fuel cell power generation plant is under partial load or in a standby state.

□ The present invention will be explained below using the drawings. FIG. 2 is a diagram showing essential parts of an embodiment of the present invention. The same equipment as in FIG. 1 is given the same number, and the explanation will be limited to only the differences from FIG. 1.

In the figure, the steam separated by the steam separator 17 is branched by the steam supply pipe 11 to be supplied to the reforming reaction, and the excess steam is passed through the conduit 2o and regulated by the control valve 21C2 to produce steam. The water is condensed by the condensing heat exchanger 22 and supplied to the pump 16.

The cooling side of the steam condensing heat exchanger 22 passes through a cooling device 23 and is cooled by a refrigerant supplied by a pump 24. The cooling device 23 is a well-known cooling tower, and may be air-cooled or water-cooled. If a fuel cell power plant is characterized by not requiring make-up water from outside the plant, an air-cooled system is a desirable cooling system.

The control valve 21 measures the temperature of the fuel cell by a method not shown, or receives a signal obtained by measuring other physical quantities representing the temperature of the cell, such as air electrode outlet gas temperature or fuel electrode outlet gas temperature. The opening degree is controlled by the modified signal. Further, as will be described later, the amount of heat to be discharged from the fuel cell main body 1 is a function of the electrical output of the fuel cell main body 1. Therefore, the control valve 21 is operated as shown in FIG. A signal obtained by modifying the signal detected by the detector 19 of the current or electrical output of the main body 1 (secondary control is performed).

In the present invention C2 having the piping system as described above, in order to maintain the fuel cell temperature at a constant temperature, the amount of heat generated at each partial load of the fuel cell main body l is cooled by cooling water to fuel the fuel. All it has to do is release it outside the battery body 1.

The representative temperature of the fuel cell is T1, the cooling water temperature is T2, the representative heat transfer area between the fuel cell and the cooling water is 8, the overall heat transfer coefficient is K, and the amount of heat generated from the fuel cell is Q.
If H and the amount of heat absorbed by the cooling water are Qo, then Qo = KS (TI - T2) '''
(1)=3ΔT Here, ΔT3(Ts-Tz) is the temperature difference between the representative temperature T1 of the fuel cell and the cooling water temperature T2.

Here, depending on the magnitude relationship between Qn and Qo, the following three types of changes in cell temperature occur. QH changes depending on the output of the fuel cell main body, that is, as the output increases, q becomes larger, and as the output decreases, q becomes smaller.

(i) When QH=Qo In this case, the amount of heat generated is the amount of heat absorbed by the cooling water, and the fuel cell temperature does not change, and the temperature is kept constant.

(II) Case of QH>Qo In this case (2), since the amount of heat generated is large, the fuel cell temperature will gradually rise.

(Iff) Q+(< QO In this case, since the amount of heat generated is small, the fuel cell temperature gradually decreases.

Fuel cell temperature is one of the important factors that determines the efficiency of a fuel cell power generation plant.In general, the higher the temperature, the higher the plant efficiency. It also causes shortening of life span and deterioration of cell characteristics.

Therefore, as in the cases (II) and (iii) above, the solution to the problem is how to multiply C2 to make Qo-QH in the case of Qo ``e QH. That is, (1)
By changing any or all of K, S, T, and T2 in the equation, Qo=QH
It is sufficient to do this.

Let us now consider the meaning of equation (1). T is the fuel cell temperature, which must be kept as constant as possible, so T is assumed to remain unchanged. T2 is the temperature of the cooling water, which can be changed by some means.

However, since it is assumed that part of the cooling water evaporates while passing through the fuel cell main body 1 and generates steam, T
2 becomes equal to the saturated steam temperature To determined by the pressure po of the cooling water. Therefore, even if the amount of evaporation changes, To does not change. To change To, it is necessary to change pressure Po. S is a representative heat transfer area, and when considering the state of load change in the same fuel cell power generation plant, S is constant because the fuel cell main body is the same.

K is the overall heat transfer coefficient, and considering its contents, (a)
(2) Due to conduction within the fuel cell, (2) Due to the flow of cooling water, (2) Due to conduction in the insulating layer on the surface of the cooling pipe.
The contribution of species is considered.

However, the contribution of the cooling water flow is small, and (
A) and (c) have a large contribution. (A) and (C) do not change due to load fluctuations, and in the end, they do not change much due to load fluctuations and can be considered constant.

Therefore, the only thing that can change Qc is the temperature difference △T, and since T1 is constant, only T2, that is, the fuel cell cooling water temperature, can change. Also, since this temperature is the saturation temperature of steam, it can be changed. The only thing that exists is pressure.

From another perspective, when the load on the fuel cell is large and the amount of heat generated from the fuel cell body is large, T2 is made small. That is, the pressure is controlled to decrease.

When the load is small and the amount of heat generated from the fuel cell body is small, T2 is increased. In other words, it is sufficient to control the pressure so as to increase it.

In FIG. 2, it is assumed that under a constant load, the control valve 21 has a certain valve opening degree, and the cooling system is balanced.

When a load decrease occurs, it is necessary to increase the pressure of the fuel cell cooling water system to raise the temperature of the cooling water. In order to achieve this, the detector 19 detects a decrease in the load, and the detection signal is used to throttle the control valve 21 to reduce the flow rate of steam to the steam condensing heat exchanger 22. Reduce the amount of heat exchange.

Then, the amount of surplus steam increases and the pressure rises, so the control valve 21 may be adjusted so that the fuel cell temperature is balanced.

Furthermore, when an increase in load occurs, the detector 19 detects this and reduces the pressure of the fuel cell cooling water system.
It is necessary to lower the cooling water temperature. To achieve this, the control valve 21 is opened in response to a detection signal from the detector 19, the flow rate of steam is increased, and the amount of heat exchanged by the steam condensing heat exchanger 22 is increased. Then, the amount of surplus steam decreases and the pressure decreases, so the control valve 21 may be adjusted so that the fuel cell temperature is balanced.

In the case of an increase or a decrease in load (in both cases, the flow rate of cooling water passing through the fuel cell main body 1 is approximately constant and does not change, so there is almost no change in the distribution of cooling water flowing through the many cooling thin tubes 8) This makes it possible to uniformly control the battery cell temperature within a certain range.

FIG. 3 is a diagram showing a main piping system of another embodiment of the present invention, in which the same parts as in FIG. 2 are given the same reference numerals. This embodiment uses a steam condensing heat exchanger 22 for regulating surplus steam.
This is an example in which a control valve 21 is provided at the heating side outlet, that is, on the downstream side of the condensed water outlet.

FIG. 4 is a system diagram of a main part of still another embodiment of the present invention, in which a bypass loop 27 is provided in the cooling side loop of the steam condensing heat exchanger 22, and a cooling water inlet of the steam condensing heat exchanger 22 is provided. This is an example in which a control valve 25 is provided on the side.

Furthermore, although not shown, a bypass loop may be provided in the cooling side loop of the steam condensing heat exchanger 22 and a control valve may be provided on the cooling water outlet side of the steam condensing heat exchanger 22, as in the case of FIG. good.

Similarly, a bypass loop may be provided in the cooling side loop of the steam condensing heat exchanger 22, and a control valve may be provided in this bypass loop.

Similarly, a bypass loop is provided on the cooling side loop of the two-steam condensing heat exchanger 22, and a control valve is provided in this bypass loop, so that the cooling water inlet side of the steam condensing heat exchanger 22 is A control valve may also be provided in the control valve, and these two control valves may be controlled in conjunction with each other.

Furthermore, similarly to the above, a control valve may be provided in the bypass loop, and a control valve may also be provided on the cooling water outlet side of the steam condensing heat exchanger 22, and these two control valves may be controlled in conjunction with each other.

FIG. 5 is a system diagram of main parts of still another embodiment of the present invention,
A bypass loop 2 is provided in the cooling loop of the steam condensing heat exchanger 22.
A control valve 25 is installed on the cooling water inlet side of the heat exchanger 22, and a control valve 21 is installed in the excess steam conduit 20 of the cooling water circulation loop of the fuel cell main body 1. The control valve 26 is controlled in conjunction with the control valve 26.

Although the example in which the control valve for the surplus steam loop is provided on the inlet side of the steam condensing heat exchanger 22 is shown, this control valve may also be a control valve on the condensed water outlet side.
Although the control valve of the second cooling loop is shown as the control valve 25 on the cooling water inlet side, this may be a control valve on the cooling water outlet side or a control valve provided in the bypass loop 27.

The present invention has been described in detail above. According to the present invention, the fuel cell temperature, which is an important factor governing the efficiency of a fuel cell power generation plant, can be easily controlled during partial load or standby. It is possible to obtain a fuel cell power generation plant that is capable of producing two types of power.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a fuel cell power generation plant, Fig. 2 is a system diagram showing main parts of an embodiment of the present invention, and Fig. 3 is a block diagram showing an example of a fuel cell power generation plant.
5 to 5 are system diagrams showing main parts of different embodiments of the present invention. 1...Fuel cell main body 289. Fuel electrode 3...Air electrode 7-...External circuit load 8...Fuel cell cooling pipe 10...Reformer 16...Pump
17... Steam water separator 22... Steam condensing heat exchanger 2311. Cooling device 24...pump (7317) Agent: Patent attorney Noriyuki Chika (
1 other person) Figure 2

Claims (3)

[Claims] (1) A plurality of fuel cells each having a fuel electrode, an air electrode, and an electrolyte disposed between these two electrodes and electrically connected in series with a load, with a plurality of tubes buried in the plurality of fuel cells. a fuel cell main body composed of a plurality of cooling plates disposed between the pipes and absorbing heat generated by the fuel cell by passing water through the pipes; and a cooling water loop for passing cooling water through the cooling plates. , a fuel processing device that processes fuel supplied to the fuel cell main body, and a device that supplies unprocessed fuel and steam to the fuel processing device, and the cooling water A fuel cell power generation plant characterized in that the pressure of the loop is controlled and the temperature of the fuel cell is controlled. (2) A heat exchanger for cooling and condensing excess steam in the cooling water loop is provided, and the amount of steam flowing into the heat exchanger is controlled according to fluctuations in the load of the fuel cell main body. A fuel cell power generation plant according to scope 1. (3) A heat exchanger for cooling and condensing excess steam in the cooling water loop is provided, and the flow rate of the cooling medium of the heat exchanger is controlled according to fluctuations in the load of the fuel cell main body. The fuel cell power generation plant according to item 1 or 2.