JPH0812782B2 - Fuel cell generator - Google Patents

Description

The present invention relates to a pressurized fuel cell power generator, particularly an exhaust gas turbine for heat recovery driven by combustion exhaust gas of a reformer and exhaust gas of a fuel cell, The present invention relates to a fuel cell power generator in combination with an air booster compressor independently installed without being connected to the turbine.

[Conventional technology]

In the fuel cell power generator described above, fuel such as natural gas, LPG, and methanol is reformed into a hydrogen-rich fuel gas by a reformer and supplied to the anode of the fuel cell. The air taken in from the anode is supplied to generate electricity, and the exhaust gas (including hydrogen) of the fuel system discharged from the anode side is sent to the burner of the reformer for combustion, and the combustion heat is used to reform the fuel. ing. Also, especially with phosphoric acid fuel cells, the operating pressure is 4 kg /
In a pressurized fuel cell power generator set to about cm ² G and 190 ° C, the exhaust gas turbine is driven by combustion exhaust gas discharged from the reformer and air exhaust gas discharged from the fuel cell cathode in order to improve plant efficiency. A method of recovering the thermal energy of combustion exhaust gas as a power source has been developed.

On the other hand, in a fuel cell, when gas crosses through the internal matrix and occurs between the anode and the cathode, the output characteristics of the cell deteriorate, and in addition, local heating occurs and the cell life decreases. Therefore, it is necessary to keep the anode / cathode inter-electrode differential pressure within a certain limit (usually about 50 to 100 mmH ₂ O). As a means for controlling this differential pressure, conventionally, the anode and cathode of the fuel cell on the outlet side are used. A differential pressure control system between poles is generally adopted in which a differential pressure control valve is provided in the exhaust gas piping system to maintain the differential pressure between poles within an allowable limit.

FIG. 3 is a system flow diagram of a conventional phosphoric acid fuel cell power generator employing the above-mentioned inter-electrode differential pressure control system. In the figure, 1 is a pressurized fuel cell and 2 is a fuel such as natural gas. Reformer for reforming hydrogen gas into hydrogen-rich fuel gas, 3 compressor for boosting the air taken in from the atmosphere, 4 exhaust gas turbine for heat recovery of exhaust gas, 5 generator, 6 and 7 fuel cell 1 Is a differential pressure control valve connected to the exhaust lines of the fuel system and the air system drawn from the outlets of the anode 1a and the cathode 1b.

With this configuration, the reformer 2 is operated when the power generation system is operating.
The burner 2a of the fuel cell 1 is supplied with the anode exhaust gas (containing hydrogen) of the fuel cell 1 and the air sent from the air blower 3 for combustion, and the combustion heat causes the fuel and the reforming catalyst to react with each other to produce the fuel. Reforms into hydrogen-rich fuel gas. Also,
Combustion exhaust gas pipe 8 drawn from reformer 2 is connected to air exhaust gas pipe 9 drawn from cathode 1b of fuel cell 1, and the combustion exhaust gas of reformer 2 and the exhaust gas of the air system are combined to form an exhaust gas turbine. 4 to drive the exhaust gas turbine 4 to supply power to the drive motor 3a of the air blower 3, for example, and to supply power from an external power supply system when the power generation amount is insufficient.

On the other hand, during normal operation of the fuel cell 1, the differential pressure control valves 6 and 7 are controlled on the basis of the gas pressure of nitrogen sealed in the pressure container (not shown) of the fuel cell 1, and the anode 1a in the fuel cell 1 is controlled.
The differential pressure control is performed so that the inter-electrode differential pressure between the cathode and the cathode 1b falls within the allowable limit pressure.

[Problems to be Solved by the Invention]

By the way, in the above-described fuel cell power generation system, the flow rate of fuel gas and air introduced into the fuel cell and the flow rate of combustion exhaust gas of the reformer fluctuate due to an increase / decrease in load. The amount of gas flowing in changes. Moreover, due to the characteristics of the exhaust gas turbine, when the flow rate of the gas flowing into the turbine decreases, the gas expansion ratio in the turbine becomes smaller, and the pressure on the inlet side of the exhaust gas turbine decreases. The gas pressure in the exhaust gas piping system of the battery drops.

In other words, 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 drops significantly when the gas flow rate is small and the load is high. The pressure rises. Therefore, comparing the operating conditions of the maximum load and the minimum load in the actual load range, the combustion exhaust gas of the reformer and the air system exhaust gas of the fuel cell are directly introduced into the exhaust gas turbine as shown in FIG. In the conventional power generation system described above, the fluctuation range of pressure in the exhaust gas piping system of the fuel cell becomes extremely large, and the operating efficiency of the fuel cell decreases.

Further, this means that in the system in which the differential pressure control valve is provided in the exhaust gas piping system of the fuel cell, a wide range of pressure control function is required for the differential pressure control valve. However, the practical control range of the differential pressure control valve is generally narrow, and under the present circumstances, it is almost impossible to perform pressure control in response to a wide range of pressure fluctuations from the maximum load operation to the minimum load operation as described above. is there.

On the other hand, as a measure to deal with the above problem, an operating system in which the operating pressure of the fuel cell is changed according to the load fluctuation can be considered. However, the power generation characteristics of the fuel cell are as follows: Since it depends on the partial pressure of oxygen, if the operating pressure of the fuel cell is lowered below the rated pressure when the load is low, the power generation efficiency of the fuel cell is significantly reduced.

In view of the above points of the present invention, a fuel cell power generation system in which an exhaust gas turbine installed independently without being connected to a compressor is combined, and a fuel cell is used in a load variation range from low load to high load. It is an object of the present invention to provide a fuel cell power generation device capable of maintaining an appropriate operating pressure at all times for high-efficiency operation and at the same time keeping the pressure fluctuation range within a practical control range of a differential pressure control valve. And

[Means for solving the problem]

In order to solve the above problems, the present invention provides a pressurized fuel cell, a fuel reformer, an exhaust gas turbine for heat recovery driven by exhaust gas of a fuel cell and combustion exhaust gas of the reformer, and the turbine. In a fuel cell power generator combined with an air boosting compressor independently installed without being connected, each fuel gas exhaust gas outlet pipe portion of the fuel cell is provided with a differential pressure control valve in the outlet pipe portion. The fuel cell includes a pressure detector arranged on the downstream side of the valve, a pressure control valve provided at the inlet of the exhaust gas turbine, and a control unit for controlling the opening degree of the pressure control valve. The unit inputs the detection signal of the pressure detector, and takes into account the pressure loss between the fuel cell and the pressure detector, depending on a predetermined constant pressure determined according to the operating pressure of the fuel cell or depending on the load. Pressure corresponding to the pressure curve The given as a set value, it is assumed that a feedback control based on the valve opening degree of the control valve so that the detected value of said pressure detector matches the set value of the detected value of said pressure detector.

[Action]

In the above configuration, the control system is configured as a process control system including a pressure control valve provided on the inlet side of the exhaust gas turbine, a pressure detector provided on the exhaust gas piping system of the fuel cell, and its control unit. .

Here, by giving a pressure set value corresponding to a pressure curve that depends on a constant pressure or load to the control unit and controlling the pressure control valve based on the pressure detection value, the gas flow rate from a low load with a small gas flow rate is changed. Through a range of high loads,
The gas pressure in the exhaust gas piping system of the fuel cell, and hence the operating pressure of the fuel cell, can always be maintained at an appropriate pressure for highly efficient operation.

Also, by controlling the pressure on the inlet side of the exhaust gas turbine, the pressure fluctuation range of the exhaust gas piping system due to the load fluctuation of the fuel cell within the range from low load to high load is within the practical control range of the differential pressure control valve. This makes it possible to keep the pressure difference between the electrodes constant, which allows stable control of the differential pressure between poles.

〔Example〕

1 and 2 are system flow charts of different embodiments of the present invention, and the same reference numerals are attached to the same devices corresponding to FIG.

First, the embodiment shown in FIG. 1 is an embodiment in which the anode 1a and the cathode 1b of the fuel cell 1 are provided with differential pressure control valves 6 and 7 in the exhaust gas piping system to perform inter-electrode differential pressure control. Yes,
According to the present invention, a pressure control valve is provided on the inlet side of the exhaust gas turbine 4.
Ten is provided. Further, a differential pressure control valve arranged in the exhaust gas piping section drawn from the anode 1a and the cathode 1b of the fuel cell 1.
Pressure transmitters 11 and 12 as pressure detectors are installed on the downstream side of 6 and 7, and detection signals thereof are given to a control unit 14 via a signal switch 13. On the other hand, the control unit 14 determines a predetermined constant pressure determined in consideration of the pressure loss between the fuel cell outlet and the pressure detector corresponding to the operating pressure of the pressurized fuel cell 1, or a pressure curve depending on the load. Is applied as a set value, and feedback control is performed so that the gas pressure of the exhaust gas piping system of the fuel cell maintains the set pressure based on the detected values of the pressure transmitters 11 to 12.

The control signal switch 13 selects one of the detected values of the pressure transmitters 11 and 12. That is, although not shown, the exhaust gas piping system drawn from the anode 1a and the cathode 1b in the fuel cell 1 is provided with heat exchangers at various places as necessary to recover the thermal energy of the exhaust gas. Moreover, the pressure loss of the piping system is different between the fuel system and the air system. Therefore, by selecting one of the pressure transmitters 11 to 12 as in the illustrated example, it is possible to perform optimum pressure control as a system.

With the above configuration, it is possible to maintain the pressure of the exhaust gas piping system of the fuel cell 1, that is, the operating pressure of the fuel cell itself, at an appropriate pressure at all times and to operate in response to load changes from low load to high load. Further, by performing pressure control with the pressure control valve 10 disposed on the downstream side of the differential pressure control valves 6 and 7, the pressure fluctuation width of the exhaust gas piping system due to load fluctuations can be adjusted by the differential pressure control valves 6 and 7. Within the practical control range, it becomes possible to perform the inter-electrode differential pressure control corresponding to the load fluctuation from the minimum load to the maximum load. The above reason will be described in detail below. For example, the operating pressure of the fuel cell is 4 kg / cm ² G. The planned pressure loss of the differential pressure control valve is 0.5 kg / cm ² G, and the piping pressure loss from the fuel cell to the differential pressure control valve is short because the piping length is short, so the predetermined set pressure given to the control unit 14 is 3.5 kg / cm 2. ² G
Becomes

In order to increase the recovery power of the exhaust gas turbine,
I want to increase the inlet pressure. In the case of a power generation system with a large load fluctuation range and a large change in the flow rate of the reaction gas, the pressure loss from the downstream part of the differential pressure control valve to the exhaust gas turbine inlet increases, so the pressure set value or control Part 14
The predetermined set pressure to be applied to may be changed depending on the load. That is, in order to increase the recovery power in the exhaust gas turbine, the pressure setting curve downstream of the differential pressure control valve is determined so that the pressure in the downstream portion of the differential pressure control valve is increased when the pressure loss of the system is large under high load. For example, the operating pressure of a fuel cell is 4 kg / cm ² G
The pressure loss of the differential pressure control valve is 0.5 (minimum load) to 0.3 (maximum load) kg / cm ^{2 for} (the fuel cell has a constant pressure in all load zones).
If so, the pressure set value downstream of the differential pressure control valve, that is, the control unit 14
The predetermined set pressure to be applied to is 3.5 (minimum load) to 3.7 (maximum load) kg / cm ² G.

By the way, in planning the differential pressure control valve, it is common to design the pressure loss in the differential pressure control valve to be small so that the amount of power recovery by the downstream exhaust gas turbine does not decrease. As is well known, the relationship between the flow rate of a gas turbine and the expansion ratio becomes smaller as the flow rate decreases. In the case of a fuel cell power generator, the exhaust gas turbine outlet is open to the atmosphere and its pressure is constant at atmospheric pressure. Therefore, the exhaust gas turbine inlet pressure decreases as the flow rate decreases.

For example, at the design point of the exhaust gas turbine rating, the inlet pressure is planned to be 3 kg / cm ² G (in this case, the pressure detector 11
It is planned that the pressure loss of the piping from the pressure control valve to the pressure control valve 10 is 0.5 kg / cm ² ), and when the flow rate decreases under partial load, it will drop to around ² kg / cm ² G.

When there is no pressure control valve at the inlet of the exhaust gas turbine as in the prior art, the pressure drop is borne by the differential pressure control valve as its pressure loss. That is, the planned differential pressure of 0.5 kg / cm ² in the differential pressure control valve is operated at 1.5 kg / cm ² . In this case, the opening of the differential pressure control valve is considerably narrowed to be small, and since the opening is close to the closed state, delicate pressure control cannot be performed, and it becomes difficult to normally maintain the battery differential pressure.

According to the present invention, the pressure decrease at the exhaust gas turbine inlet due to the decrease in the flow rate is borne by the pressure control valve provided at the exhaust gas turbine inlet, that is, 3 kg / cm ² G is 2 kg / cm in the above example.
^The pressure control valve bears the amount of pressure drop to around ² G, and bears 0.5 kg / cm ^{2 due} to the pressure loss in the above-mentioned piping, and the remaining 0.5 kg / cm ²
Since the battery pressure is maintained at 4 kg / cm ² G by bearing the differential pressure control valve, the differential pressure control valve can operate with the pressure loss as planned, and it is possible to properly control the battery differential pressure. Become.

FIG. 2 shows another embodiment of the present invention, in which the differential pressure control valve in the embodiment of FIG. 1 is omitted and instead the cathode 1b is used.
The exhaust gas pipe 9 pulled out from the exhaust gas pipe 9 is provided with a throttle member 15 for providing a fixed flow path resistance in the middle, and other configurations are the same as those in FIG.

In such a configuration, by setting the flow path resistance corresponding to the pressure loss of the burner 2a of the reformer 2 connected to the exhaust gas piping system of the anode 1a by the throttle member 15, the fuel system and the air system of the fuel cell are set. By matching so that the pressure loss of the exhaust gas pipe in the fuel cell is almost the same, the inter-electrode differential pressure between the anode 1a and the cathode 1b inside the fuel cell can be suppressed within the allowable pressure limit. Further, the pressure loss in the system can be reduced by omitting the differential pressure control valve, and the power recovery in the exhaust gas turbine 4 is improved.

Moreover, as in the embodiment of FIG. 1, by selecting the pressure detectors 11 to 12 to control the pressure control valve 10 provided on the inlet side of the exhaust gas turbine 4, the load fluctuation from the minimum load to the maximum load can be controlled. The operating pressure of the fuel cell 1 can be maintained at an appropriate pressure within the range. As a result, high efficiency operation of the fuel cell 1 can be realized even during low load operation.

According to a calculation by the inventor, a power control efficiency is improved by about 5% as a single fuel cell by providing a pressure control valve on the inlet side of the exhaust gas turbine to maintain the operating pressure of the fuel cell. You can

〔The invention's effect〕

Since the fuel cell power generator of the present invention is configured as described above, it has the following effects.

(1) By controlling the control valve installed at the inlet of the exhaust gas turbine against the load change from low load to high load,
Highly efficient operation can be realized by always maintaining the operating pressure of the fuel cell at an appropriate pressure.

(2) In particular, when the differential pressure control valve is connected to the exhaust gas piping system of the fuel cell to perform the inter-electrode differential pressure control of the fuel cell,
It is possible to reduce the pressure fluctuation range of the exhaust gas piping system due to a wide range of load fluctuations and keep it within the practical control range of the differential pressure control valve to perform stable inter-electrode differential pressure control.

[Brief description of drawings]

1 and 2 are system flow charts of different embodiments of the present invention, and FIG. 3 is a flow chart of a conventional fuel cell power generation system. In the figure, 1: fuel cell, 1a: anode, 1b: cathode, 2: reformer, 4:
Exhaust gas turbine, 6, 7: Differential pressure control valve, 10: Pressure control valve, 11,
12: Pressure detector, 13: Control part.

Claims (1)

[Claims] 1. A pressurized fuel cell, a fuel reformer, an exhaust gas turbine for heat recovery driven by the exhaust gas of the fuel cell and the combustion exhaust gas of the reformer, and installed independently without being connected to the turbine. In a fuel cell power generator combined with a compressor for air boosting, in a fuel cell equipped with a differential pressure control valve disposed at each reaction gas exhaust gas outlet pipe portion of the fuel cell, the valve A pressure detector provided on the downstream side, a pressure control valve provided at the exhaust gas turbine inlet, and a control unit for controlling the opening of the pressure control valve, the control unit being the pressure detector of the pressure detector. Input the detection signal,
A predetermined constant pressure determined corresponding to the operating pressure of the fuel cell in consideration of the pressure loss between the fuel cell and the pressure detector,
Or, the pressure corresponding to the pressure curve depending on the load is given as a set value, and the valve opening of the control valve is based on the detector of the pressure detector so that the detected value of the pressure detector matches the set value. A fuel cell power generator characterized by feedback control.