JPH02273466A - Fuel cell power generating system - Google Patents

Abstract

PURPOSE:To balance the respective exhaust gas side pressure losses of a fuel line and an air line with simple means so as to restrain differential pressure between anode and cathode inside a fuel cell by omitting a differential pressure control valve which is to be installed in the exhaust gas piping passage of the fuel cell, and installing a restricting member in another exhaust gas passage provided on the side of the cathode. CONSTITUTION:A fixed restrictor 13 serving as a pressure loss compensating restricting member for adding pipe resistance is installed inside the exhaust gas piping 32 of the air system drawn out from the exit of the cathode 1a of the fuel cell 1 of a fuel cell power generating system. Between the position P where a fuel exhaust gas piping 11 extended from a reformer 3 and a piping 12 are combined together, and the exist side of the battery 1, the restriction resistance of the fixed restrictor 13 corrects a difference between the pressure loss of the exhaust gas piping passage of the fuel system which passage is extended via the reformer 3 and that of the exhaust gas piping passage of the air system, so that the pressure losses of both piping passages are equalized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel cell power generation system for phosphoric acid fuel cells, t9 carbonate fuel cells, and the like.

[Conventional technology]

Regarding normal-phase fuel cell power generation systems, phosphoric acid fuel cells use a reformer to reform fuel such as natural gas, LPG, or methanol into hydrogen-rich fuel gas, which is then supplied to the anode of the fuel cell, and then to the cathode. generates electricity by supplying air taken in from the atmosphere through an air blower and compressor 5, and also sends the exhaust gas (including hydrogen) from the fuel system discharged from the anode to the burner of the reformer and burns it. The fuel is reformed using heat. In addition, in pressurized fuel cell power generation systems in which the operating pressure of the fuel cell is particularly high, high-temperature, high-pressure combustion exhaust gas from the reformer and cathode exhaust gas from the battery are effectively used to improve plant efficiency. A heat recovery method has been put into practical use in which a turbine/generator is driven and the power generated is supplied to auxiliary equipment such as air blowers and compressors for boosting air pressure.

On the other hand, in a power generation system using a molten carbonate fuel cell, fuel gas obtained through a fuel processing device that combines the fuel cell with coal gasification and a chemical refining process that removes harmful components is supplied to the fuel cell anode. However, the exhaust gas from the anode is pressurized and a mixed gas of carbon dioxide and air obtained by combustion is supplied to the cathode to generate electricity.

In addition, similar to the phosphoric acid fuel cell power generation system described above,
The system uses a heat recovery method that effectively utilizes the exhaust gas discharged from the cathode side of the molten carbonate fuel cell to generate power for the exhaust gas turbine.

On the other hand, inside the fuel cell, if gas crosses through the matrix and occurs between the anode and cathode, not only will the output characteristics of the cell decrease, but local heating will occur, shortening the battery life. For this purpose, it is necessary to suppress the differential pressure between the anode and cathode within a certain limit (usually around 200 mmHzO). Conventionally, as a means of controlling this differential pressure, the exhaust gas pipes of the anode and cathode are A method has been implemented in which a differential pressure control valve is installed to perform differential pressure control as in the next phase.

(1) The pressure of the nitrogen gas sealed in the containment pressure vessel of the fuel cell is maintained constant, and based on this nitrogen gas pressure, the differential pressure control valves installed in the anode and cathode outlet pipes of the fuel cell are used as a reference. A method of maintaining the anode/cathode differential pressure within acceptable limits.

(2) Based on the pressure of either air or fuel gas, the differential pressure between the anode and cathode is maintained within the permissible limit by a differential pressure control valve installed in the exhaust piping on the other side, and at the same time A pressure control method that maintains the pressure of the nitrogen gas sealed inside the pressure vessel at a predetermined value.

FIG. 3 shows a flowchart of a conventional phosphoric acid fuel cell power generation system that employs the differential pressure control method described in (1) above. In the figure, 1 is a pressurized fuel cell, 2 is a pressure vessel filled with nitrogen gas that stores the fuel cell 1, and 3 is a reformer for reforming fuel such as natural gas, LPG, methanol, etc. into hydrogen-rich fuel gas. 4 is an air blower that boosts the pressure of air taken in from the atmosphere, 5 is an exhaust gas turbine that recovers heat from exhaust gas, 6 is a generator, and 7.8 is an exhaust gas pipe drawn out from the outlet of the anode 1a + cathode 1b of the fuel cell 1. Differential pressure control valves 9 and 10 interposed and connected to the passage are a nitrogen gas-fuel gas differential pressure oscillator and a nitrogen gas-air differential pressure oscillator.

With this configuration, when the power generation system is in operation, the fuel exhaust gas (containing hydrogen) from the fuel cell 1 and the air sent from the air blower 4 are supplied to the burner 3a of the reformer 3 and combusted, and the combustion heat is generated. The fuel and the reforming catalyst undergo a catalytic reaction to reform the fuel into hydrogen-rich fuel gas. Further, the air exhaust gas pipe 12 drawn from the cathode 1b of the fuel cell is connected to the combustion exhaust gas pipe 11 drawn from the reformer 3, and the combustion exhaust gas and the air exhaust gas are combined and guided to the exhaust gas turbine 5. /The generator 6 is driven, and the generated power is supplied to the air blower 4 for operation. On the other hand, during normal operation of the fuel cell 1, the pressure vessel 2
Differential pressure oscillator 9.1 using the nitrogen gas sealed in as the reference pressure
0 to control the differential pressure control valve 78 to control the differential pressure so that the differential pressure between the anode 1a and the cathode 1b inside the fuel cell is within an allowable limit.

[Problem to be solved by the invention]

By the way, in the conventional differential pressure control method in which differential pressure control is performed by interposing a differential pressure control valve in the exhaust gas piping of the anode cathode of a fuel cell as described above, a complicated differential pressure control system is required. Furthermore, due to differential pressure control, it is inevitable that a large pressure loss will occur inside the control valve during the process in which the exhaust gas passes through the differential pressure control valve. For this reason, when a heat recovery method is adopted to power the exhaust gas turbine using the energy contained in the combustion exhaust gas and air exhaust gas of the reformer as described above, the pressure loss caused by the differential pressure control valve described above is The enthalpy drop of adiabatic expansion in the exhaust gas turbine decreases, the recovered power also decreases, and the overall plant efficiency of the power generation system decreases accordingly.

In addition, in molten carbonate fuel cells, the operating temperature of the cell is 5
50 to 650"C, and for this reason, the pressure control valve used for differential pressure control has the same problems as the phosphoric acid fuel cell power generation system described above, as well as a higher heat resistance temperature and large capacity. Specifications are required for the flow rate (particularly on the air electrode side, the air flow rate is large due to the air cooling system, and the volumetric flow rate increases due to the high operating temperature), which makes the differential pressure control valve extremely expensive.

The present invention has been developed in consideration of the above points, and eliminates the differential pressure control valve used in conventional systems, which causes increased pressure loss in the exhaust gas system and increases costs, and instead uses a pipe line. By using a simple throttle member that adds resistance, the pressure difference between the anode and cathode can be kept within the permissible limit, and at the same time, for pressurized fuel cells, the pressure loss in the exhaust gas piping route can be kept low. The object of the present invention is to provide a fuel cell power generation system that increases the recovery power of an exhaust gas turbine and thereby improves overall plant efficiency.

[Means to solve the problem]

In order to solve the above problems, in the fuel cell power generation system of the present invention, the air system exhaust gas piping led out from the cathode side outlet of the fuel cell is connected to the fuel system exhaust gas piping and the air system exhaust gas piping. A throttle member shall be interposed to match the pressure loss.

[Effect]

In the above-mentioned fuel cell power generation system, regarding the exhaust gas piping of the fuel cell, the gas density and piping route are different between the fuel system and the air system, and the configuration of the piping route differs between the fuel system and the air system.
The inherent pressure loss of the air system exhaust gas piping is also determined automatically.

In this case, in a typical power generation system configuration, devices such as the reformer burner (phosphoric acid fuel cell), blower 3 combustor (molten carbonate fuel cell), etc. are installed in the exhaust gas piping of the fuel system. Because of this, the pressure loss in the piping route is greater than that in an air system. Therefore, a restriction member that adds resistance to the exhaust gas piping in the cathode example, such as a fixed restriction, is inserted, and the difference in pressure loss inherent in the exhaust gas piping between the fuel system and the air system is reduced. By setting the throttling resistance of the throttling member to compensate, the gas pressure between the anode and cathode inside the fuel cell can be balanced and the difference between the electrodes can be reduced without employing a differential pressure control method using a differential pressure control valve. The pressure can be kept below the permissible limit.

Moreover, the pressure loss due to the throttle member inserted in the pipe line for pressure loss correction is extremely small, and the provision of the throttle member eliminates the need for a pressure control valve for differential pressure control. Therefore, the large pressure loss that occurs with the differential pressure control method is eliminated, and especially when heat is recovered from the exhaust gas, such as in a pressurized fuel cell power generation system, the recovery power of the exhaust gas turbine is also improved, which improves the power generation system. Overall plant efficiency will be improved.

〔Example〕

1 and 2 are flowcharts of a phosphoric acid fuel cell power generation system 1 and a molten carbonate fuel cell power generation system according to embodiments of the present invention, respectively, and the same members corresponding to FIG. The same symbols are attached.

First, in the embodiment shown in FIG. 1, an exhaust gas pipe 12 of the air system led out from the outlet side of the cathode la of the fuel cell 1 is provided with a restrictor member for pressure loss correction that adds pipe resistance, for example, a fixed restrictor. 13 is interposed. here,
The aperture resistance of the fixed aperture 13 is set as follows. In other words, there is a point P where the combustion exhaust gas pipe 11 and the air exhaust gas pipe 12 discharged from the reformer 3 and 4 merge (at this meeting point, the exhaust gas pressures of the fuel system and the air system become the same) and the fuel cell 1.
The difference between the pressure loss in the fuel system exhaust gas piping via the reformer 3 and the pressure loss in the air system exhaust gas piping is corrected to ensure that the pressure loss in both piping is approximately the same. Set it so that

As a result, inside the fuel cell 1, the anode 1a is
The reaction gas pressure becomes balanced between the electrode 1b and the cathode 1b, and the pressure difference between the electrodes can be suppressed within an allowable limit, thereby preventing gas cross from occurring. Moreover, by omitting the differential pressure control valve, a large pressure loss occurring in the differential pressure control valve is eliminated, and the recovered power in the exhaust gas turbine 5 is increased by several percent compared to the configuration shown in FIG. 3.

The fixed throttle 13 is set in such a way that when the power generation plant is installed on site, orifices with different hole diameters are replaced while gas is actually flowing into the system to add the optimum pipe resistance.

On the other hand, FIG. 2 shows an example of a power generation system using a molten carbonate fuel cell, and 14 is a fuel processing device that gasifies fuel such as coal and removes harmful components to obtain fuel gas; 15 is a blower for boosting the pressure of the fuel exhaust gas discharged from the anode 1a of the fuel cell 1; 16 is an air compressor that takes in air from the atmosphere; 17 is its drive motor; and 18 is a combustion engine that burns the fuel exhaust gas and air to produce carbon dioxide and air. a combustor for producing a component cathode reaction gas; 19 is a cathode 1;
The heat exchanger 20 installed in the gas circulation circuit between the inlet and outlet of b is a circulating gas blower.

With this configuration, a fixed throttle 13 is interposed as a throttle member in the exhaust gas pipe 12 led out from the outlet of the cathode 1a of the fuel cell 1, similar to the embodiment shown in FIG. The restricting resistance of the fixed throttle 13 is set so as to balance the pressure loss of the exhaust system drawn from the outlet side of the cathode 1b with the pressure loss of the exhaust system of the anode Ia. As a result, the anode 1 inside the fuel cell 1 is similar to the embodiment shown in FIG.
The differential pressure between the poles a and cathode Ib can be suppressed within the permissible limit.

Moreover, the pressure loss of the throttle member is lower than that of the differential pressure control valve used in the conventional differential pressure control method, and the recovered power in the exhaust gas turbine 5 can be increased accordingly.

〔Effect of the invention〕

Since the fuel cell power generation system according to the present invention is configured as described above, it achieves the following effects.

(1) By omitting the differential pressure control valve that was installed in the exhaust gas piping of the fuel cell in the conventional differential pressure control method, a simple means was adopted in which a throttle member was inserted in the exhaust gas piping on the cathode side. ,
By balancing the pressure loss on the exhaust gas side of the fuel system and the air system, it is possible to suppress the differential pressure between the anode and cathode within the fuel cell to within an allowable limit, thereby preventing the occurrence of gas cross.

(2) In particular, for pressurized fuel cells, which are equipped with an exhaust gas turbine to recover the energy held in exhaust gas within the power generation system, compared to the conventional differential pressure control method, It is possible to reduce the pressure loss in the plant, increase the recovery power, and improve the overall efficiency of the plant.

[Brief explanation of drawings]

Figures 1 and 2 are system flow diagrams of an embodiment of the present invention targeting a phosphoric acid fuel cell and a molten carbonate fuel cell, respectively, and Figure 3 is a system flow diagram of a phosphoric acid fuel cell using a conventional differential pressure control method. It is a system flow diagram of a battery power generation system. In the figure, 1: fuel cell, 1a: anode, Xb: cathode, 3:
Reformer, 4: Air blower, 5: Exhaust gas turbine, 12:
Cathode side exhaust gas piping, 13: Fixed throttle (throttle member)
, 1.4. :Fuel processing device.

Claims (1)

[Claims] 1) In a fuel cell power generation system that generates electricity by supplying fuel gas obtained from a fuel processing device and air to the anode and cathode of a fuel cell, an exhaust gas piping line of the air system drawn out from the cathode side outlet of the fuel cell, A fuel cell power generation system characterized by interposing a throttle member to match pressure loss between a fuel system exhaust gas piping path and an air system exhaust gas piping path.