JPH1092451A - Fuel cell power generation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct smooth control so that pressure change in an exhaust gas pipe and in a reforming device is not allowed to exceed a permissible range by providing a variable type nozzle on an exhaust gas turbine, and controlling the variable type nozzle so as to take a proper nozzle opening in response to the operation load of a fuel cell power generation device. SOLUTION: A variable type nozzle 15 is provided at the exhaust gas inlet portion of an exhaust gas turbine 4. A nozzle opening control portion 18 controls so that proper opening corresponding to the operation load of a fuel cell power generation device is maintained according to a nozzle opening curve. The nozzle opening curve is obtained by selecting such nozzle opening as a pressure control valve 10 can conduct proper control in respective operation loads considering a pressure control property in the burning exhaust gas pipe 8 of the pressure control valve 10. Thereby, the proper pressure control valve 10 opening corresponding to the operation load change of the fuel cell power generation device is maintained, and smooth adjusting can be conducted without changing pressure in the exhaust pipe 8 excessively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressurized fuel cell power generator in which an exhaust gas turbine for heat recovery driven by exhaust gas from a fuel cell and combustion exhaust gas from a reformer is provided.

[0002]

2. Description of the Related Art In a fuel cell power generation system, natural gas,
LPG, methanol and other fuels are reformed into hydrogen-rich fuel gas by a reformer and supplied to the anode of the fuel cell, and the cathode is supplied with air taken in from the atmosphere through an air blower and compressor to generate electricity. In addition, the exhaust gas (including hydrogen) of the fuel system discharged from the anode side is sent to a burner of a reformer and burned, and the fuel is reformed by the heat of combustion. In particular, in a pressurized fuel cell power generator that operates at a operating pressure of 4 kg / cm ² G and an operating temperature of about 190 ° C. in a phosphoric acid fuel cell, the combustion discharged from the reformer is intended to improve plant efficiency. A method has been developed in which an exhaust gas turbine is driven by exhaust gas and air exhaust gas exhausted from a cathode of a fuel cell, and thermal energy possessed by the combustion exhaust gas is recovered as power.

On the other hand, in a fuel cell, when a gas cross is generated between the anode and the cathode through the internal matrix through the internal matrix, the output characteristics of the battery are reduced, and local heating is caused to shorten the battery life. For this purpose, it is necessary to suppress the anode-cathode electrode-to-electrode differential pressure within a certain range. Conventionally, as this differential pressure control means, a differential pressure control valve is provided in the exhaust gas piping system of the anode and the cathode at the outlet side of the fuel cell. Then, an inter-electrode differential pressure control method for maintaining the inter-electrode differential pressure within an allowable limit is generally adopted.

[0004] In such a fuel cell power generator,
As the operating load of the fuel cell increases or decreases, the flow rates of the fuel gas and air introduced into the fuel cell fluctuate, and accordingly, the flow rates of the exhaust gas from the cathode and the reformer flowing into the exhaust gas turbine change. Moreover, due to the characteristics of the exhaust gas turbine (the turbine outlet is open to the atmosphere), when the flow rate of the gas flowing into the exhaust gas turbine decreases, the gas expansion ratio in the exhaust gas turbine decreases, and the pressure on the inlet side of the exhaust gas turbine decreases. As a result, the gas pressure in the exhaust gas piping system of the fuel cell located upstream from the exhaust gas turbine decreases.

That is, the pressure of the exhaust gas piping system of the fuel cell is directly affected by the amount of gas flowing into the exhaust gas turbine, and the exhaust gas pressure is greatly reduced at a light load with a small gas flow, and conversely at a high load with a large gas flow. The exhaust gas pressure rises. For this reason, when comparing the operating conditions between the maximum load and the minimum load in the actual load range, the method in which the combustion exhaust gas from the reformer and the air-based exhaust gas from the fuel cell are directly introduced into the exhaust gas turbine is not used. The pressure fluctuation width in the system becomes extremely large, and the operating efficiency of the fuel cell decreases.

Japanese Patent Application Laid-Open No. 2-297866 describes a method for solving this problem by providing a pressure control valve near the upstream inlet of an exhaust gas turbine and controlling the pressure in an exhaust gas piping system to a predetermined pressure. . FIG. 5 is a system flow diagram of a conventional fuel cell power generator having such a configuration. In FIG. 5, 1 is a pressurized fuel cell, 2 is a fuel reformer for reforming a fuel such as natural gas into a hydrogen-rich fuel gas,
3 is an air blower that pressurizes air taken in from the atmosphere, 4
Is an exhaust gas turbine that performs heat recovery of exhaust gas, 5 is a generator,
Reference numerals 6 and 7 denote differential pressure control valves connected to an exhaust gas line of a fuel system and an air system drawn from outlets of an anode 1a and a cathode 1b of the fuel cell 1, respectively.

During operation of the power generator having such a configuration, exhaust gas from the anode 1a of the fuel cell 1 and air sent from the air blower 3 are supplied to the burner 2a of the reformer 2 and burned, and the fuel is converted into fuel by the heat of combustion. The fuel is reformed to a hydrogen-rich fuel gas by causing a catalytic reaction with the high quality catalyst. In addition, reformer 2
An air exhaust pipe 9 drawn from the cathode 1b of the fuel cell 1 is connected to a flue gas pipe 8 drawn out of the fuel cell 1, and the flue gas of the reformer 2 and the exhaust gas of the air system are merged and then led to the exhaust gas turbine 4. To drive the exhaust gas turbine 4 and supply electric power obtained from a generator 5 connected thereto to, for example, a drive motor 3 a of the air blower 3.

On the other hand, during normal operation of the fuel cell 1, the differential pressure control valves 6 and 7 are controlled based on the gas pressure of nitrogen sealed in a pressure vessel (not shown) of the fuel cell 1, and the anode in the fuel cell 1 is controlled. The differential pressure control is performed so that the differential pressure between the electrode 1a and the cathode 1b falls within an allowable limit. Further, a pressure control valve 10 is provided near the inlet of the exhaust gas turbine 4. Downstream of the differential pressure control valves 6, 7, pressure detectors 11, 12 are provided, and their detection signals are given to a pressure control valve control unit 14 via a signal switch 13. On the other hand, the pressure control valve controller 14 controls the pressurized fuel cell 1
A predetermined constant pressure determined in accordance with the operating pressure or a pressure corresponding to a pressure curve obtained for the load is given as a set value, and the combustion exhaust gas is detected based on the detection values of the pressure detectors 11 and 12. The pressure control valve 10 is feedback-controlled so that the gas pressure in the piping 8 system maintains the set pressure.

In this way, by maintaining the gas pressure in the flue gas piping 8 system at the set pressure by the pressure control valve 10, the pressure fluctuation width of the flue gas piping system due to the load fluctuation can be reduced. Within the controllable range.

[0010]

However, in the conventional system, the pressure downstream of the pressure control valve 10 fluctuates greatly depending on the gas flow rate flowing into the exhaust gas turbine 4, and the operating load of the fuel cell 1 is small and the exhaust gas When the flow rate of the gas flowing into the turbine 4 is also small, the pressure at the exhaust gas turbine 4 inlet decreases, and the power recovery amount of the exhaust gas turbine 4 also decreases. Further, since the gas pressure difference before and after the pressure control valve 10 is large, the opening of the pressure control valve 10 may be very small, or in the worst case, ON-OFF control. Then, the poor controllability causes a disadvantage that the pressure in the flue gas pipe 8 and the reformer 2 fluctuates. As described above, the controllability of the pressure control valve 10 when the gas pressure in the flue gas pipe 8 is finely adjusted by adjusting the opening of the pressure control valve 10 still has a problem.

The present invention has been made in view of the above points, and the power of the exhaust gas turbine 4 is maintained even if the flow rate of the exhaust gas flowing into the exhaust gas turbine 4 changes due to a change in the operating load of the fuel cell 1. It is an object of the present invention to provide a fuel cell power generation device capable of effectively recovering the energy of an inflow gas without lowering it, having excellent controllability of a pressure control valve 10, and capable of precisely controlling the pressure in an exhaust gas piping system. .

[0012]

In order to achieve the above object, the present invention provides an exhaust gas turbine driven by exhaust gas from a fuel cell and combustion exhaust gas from a fuel reformer, and a method for introducing exhaust gas into the exhaust gas turbine. An exhaust gas piping system, wherein a pressure control valve for maintaining a gas pressure in the exhaust gas piping system at a predetermined value is provided upstream of the exhaust gas turbine. A variable nozzle was provided at the entrance. The variable nozzle and the pressure control valve are located in series. The variable nozzle is controlled so as to take an appropriate nozzle opening in accordance with a nozzle opening curve indicating the nozzle opening determined with respect to the operating load of the fuel cell.

As a result, the gas pressure difference before and after the pressure control valve provided upstream of the nozzle is reduced, so that the pressure control valve is gradually changed to one of a fully opened state and a fully closed state as in the prior art. Rather than performing appropriate control, maintain the appropriate opening of the pressure control valve according to the fluctuation of the operating load of the fuel cell, and smooth the fluctuation of pressure in the exhaust gas piping system and the reformer without exceeding the allowable range. It is now possible to make adjustments.

Further, the nozzle of the exhaust gas turbine has a function of converting thermal energy of the exhaust gas into velocity energy. By adjusting the opening degree of the variable type nozzle according to the operating load, the exhaust gas turbine at the time of low load is used. Even when the flow rate of the gas flowing into the turbine is small, it is possible to suppress the pressure drop of the gas flowing into the exhaust gas turbine and effectively recover the energy of the exhaust gas.

However, even with the above-described configuration having the variable nozzle whose opening degree is controlled in accordance with the operating load, the variable nozzle can be controlled by factors other than the operating load, such as a change in gas flow rate due to a change in fuel cell characteristics over time. The pressure difference before and after the pressure control valve also fluctuates. According to a second aspect of the present invention, a fuel cell power generator having a nozzle provided in the exhaust gas turbine described above includes a differential pressure detector for detecting a pressure difference before and after a pressure control valve in order to cope with the fluctuation of the differential pressure. This is a configuration provided. If the detected pressure difference continues to be equal to or greater than the set value larger than the standard pressure difference for a certain period of time, the opening degree of the exhaust gas turbine nozzle is reduced by a certain amount, and the detected pressure difference is smaller than the standard pressure difference. If the value equal to or less than the set value is continued for a predetermined time or more, the opening of the nozzle of the exhaust gas turbine is increased by a certain amount.

By performing such fine adjustment, the differential pressure across the pressure control valve is always kept within a predetermined range. Therefore, the pressure controllability of the pressure control valve in the exhaust gas piping system is further improved, and Also in the turbine, the energy of the exhaust gas can be effectively recovered without waste, and the efficiency of the entire fuel cell power generator can be increased.

[0017]

FIG. 1 is a system flow chart showing an embodiment of the present invention. For the sake of simplicity, the same parts as those in FIG. As shown in FIG. 1, the fuel cell power generation device of the present invention is provided with a variable nozzle 15 at the inlet of the exhaust gas turbine 4 provided downstream of the pressure control valve 10 and in series. Pressure control valve 10
Is introduced into the exhaust gas turbine 4 through the variable nozzle 15, and the thermal energy of the exhaust gas is converted into rotational energy, drives the generator 5, and is collected as electric power.

The pressure control valve 10 is controlled so that the pressure in the flue gas pipe 8 is maintained at a predetermined value so as to maintain a predetermined value.
0 controls the pressure of the pressure control valve 10 and the variable nozzle 15 so that the pressure in the flue gas piping 8 system can be controlled while maintaining an appropriate opening degree. This nozzle opening is set according to the nozzle opening curve shown in FIG. 2 according to the operating load.

In consideration of the pressure controllability of the pressure control valve 10 in the flue gas pipe 8 system, the nozzle opening degree curve is such that the pressure control valve 10 can perform appropriate pressure control at each operation load. It was obtained by selecting. When the value of the operating load is given to the nozzle opening degree controller 18, the nozzle opening degree controller 18 follows the nozzle opening degree curve shown in FIG.
Control is performed so as to maintain an appropriate nozzle opening degree according to the operation load.

FIG. 3 is a system flow chart showing an embodiment of the second invention. FIG. 3 shows a configuration in which a differential pressure detector 16 for detecting a differential pressure across the pressure control valve 10 is provided in the fuel cell power generator shown in FIG. 1 described above, and a detection signal of the differential pressure detector 16 is provided. Is the nozzle opening correction controller 17
And a control signal is output to the variable nozzle 15 to correct the nozzle opening. With such a configuration, the correction is performed so that the change in the pressure difference between the front and rear of the pressure control valve 10 due to the change in the exhaust gas flow rate caused by a reason other than the change in the operation load of the fuel cell 1 is always within a predetermined range. It is possible to do. FIG. 4 shows the relationship between the differential pressure across the pressure control valve 10 and the nozzle opening when such control is performed.

FIG. 4 schematically shows the relationship between the differential pressure across the pressure control valve 10 and the opening correction of the variable nozzle 15. FIG. 4B shows a case where the operating load is constant.
(C) shows the correction of the nozzle opening when the load is rising. Here, as an example, the planned value of the differential pressure before and after the pressure control valve 10 is 0.2 kg / cm ² , and the differential pressure is 0.3 kg continuously from t ₀ to t ₁ after a lapse of a certain time (for example, 10 seconds).
If the pressure exceeds 10 cm / cm ² , the opening of the variable nozzle 15 is reduced by a fixed amount (for example, 1%), and the differential pressure across the pressure control valve 10 is reduced to 0.
If the pressure falls below 1 kg / cm ² continuously for a certain period of time (for example, 10 seconds), the opening degree of the variable nozzle 15 becomes a certain amount (for example, 1%).
The case where it is made to increase is shown.

[0022]

As described above, according to the present invention, a variable nozzle is provided in an exhaust gas turbine connected to a fuel cell power generator, and the variable nozzle is controlled so as to have a nozzle opening corresponding to an operation load. I decided that. As a result, since the gas pressure difference before and after the pressure control valve provided upstream of the variable nozzle became small, an appropriate opening degree of the pressure control valve corresponding to the fluctuation of the operating load of the fuel cell was maintained, and the exhaust gas piping system It has become possible to perform a smooth adjustment without excessively changing the pressure.

Further, even when the flow rate of the gas flowing into the exhaust gas turbine at a low load is small, it is possible to suppress the pressure drop of the gas flowing into the exhaust gas turbine and to recover the energy of the exhaust gas as effectively as possible. Further, as a second invention, in the fuel cell power generator having a configuration in which a variable nozzle is provided in the exhaust gas turbine, a configuration is provided in which a differential pressure detector for detecting a pressure difference before and after the pressure control valve is provided, and the detected pressure is If the difference is greater than the set value greater than the standard pressure difference and continues for a certain period of time, the exhaust gas turbine nozzle opening is reduced by a fixed amount, and the detected pressure difference is less than the set value smaller than the standard pressure difference. Is continued for a certain time or longer, the nozzle opening is increased by a certain amount. This allows
It is possible to fine-tune the differential pressure across the pressure control valve to always fall within a predetermined range in response to changes in gas flow rate due to reasons other than operating load fluctuations such as changes in fuel cell characteristics over time. It has become possible. Therefore, the pressure control in the exhaust gas piping system by the pressure control valve is further improved, and the energy of the exhaust gas can also be effectively collected in the exhaust gas turbine without waste, thereby increasing the efficiency of the entire fuel cell power generator. Can be done.

[Brief description of the drawings]

FIG. 1 is a system flow chart showing an embodiment of the present invention.

FIG. 2 is a nozzle curve diagram showing a relationship between an operation load and a nozzle opening degree.

FIG. 3 is a system flow chart showing a second embodiment of the present invention.

FIG. 4 is a diagram schematically showing a relationship between a differential pressure across the pressure control valve and correction of a nozzle opening.

FIG. 5 is a system flow diagram of a conventional fuel cell power generator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fuel cell, 1a ... Anode, 1b ... Cathode, 2 ...
Reformer, 3 ... Air blower, 4 ... Exhaust gas turbine, 5 ... Generator, 6, 7 ... Differential pressure control valve, 8 ... Combustion exhaust gas piping, 9 ...
Air exhaust gas piping, 10 pressure control valves, 11 and 12 pressure detectors, 13 signal switchers, 14 pressure control valve control units,
15 ... variable nozzle, 16 ... differential pressure detector, 17 ... nozzle opening correction control unit, 18 ... nozzle opening control unit.

Claims (3)

[Claims] An exhaust gas turbine driven by exhaust gas of a fuel cell and combustion exhaust gas of a fuel reformer, and an exhaust gas piping system for introducing exhaust gas to the exhaust gas turbine, wherein a gas pressure in the exhaust gas piping system is provided. In a fuel cell power generator provided with a pressure control valve for maintaining a predetermined value upstream of the exhaust gas turbine, a variable nozzle provided in series between the pressure control valve and the exhaust gas turbine; A fuel cell power generator, comprising: a nozzle opening controller that controls the opening of the variable nozzle in accordance with the operating load of the fuel cell. 2. The control device according to claim 1, wherein the nozzle opening control unit controls the variable nozzle by giving a set value according to a nozzle opening curve determined according to an operation load of the fuel cell. The fuel cell power generator according to claim 1, wherein 3. The fuel cell power generator according to claim 1, wherein a differential pressure detector for detecting a pressure difference between before and after the pressure control valve and a pressure detection signal from the differential pressure detector are provided. When the pressure difference continues a value equal to or greater than the first set value for a predetermined time or more, the opening degree of the variable nozzle is reduced by a predetermined amount,
The nozzle opening control is performed so as to increase the opening of the variable nozzle by a predetermined amount when the pressure difference continues to be a value equal to or less than a second set value lower than the first set value for a predetermined time or more. And a control unit for correcting a nozzle opening degree instructing the unit.