JPH0419964A - Method and device for controlling air amount for cathode of molten carbonate fuel cell - Google Patents

Abstract

PURPOSE:To enhance cell efficiency under light loads and also enable a differential pressure controlling high-temperature valve to be omitted by using a flow rate control valve to adjust the amount of air flow sucked into a compressor, and also adjusting the differential pressure between a fuel cell cathode and a box body using the variable pitch blade of a turbine. CONSTITUTION:When the load of a fuel cell 1 is fluctuated the rate of opening of a flow rate control valve 30 on the suction side of a compressor 4 is adjusted according to this load fluctuation. When the load of the battery 1 is reduced below its rating the valve 30 is adjusted according to the load and the amount of air sucked into the compressor 4 is restricted. Therefore the amount of by-pass air from the compressor 4 to a turbine 5 is decreased and the amount of air supplied to a cathode 2 is also decreased. Under those circumstances the inlet pressure of the turbine 5 i.e., cathode pressure can be reduced but, the differential pressure between the cathode and a box body 25 being detected by a differential pressure detector 27, the variable pitch blade 32 of the turbine 5 is adjusted according to the differential pressure to control the inlet pressure of the turbine 5, thereby holding constant the differential pressure between the cathode 2 and the box body 25.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is directed to a fuel cell that is supplied to the cathode of a molten carbonate fuel cell, which is used in the energy sector that directly converts the chemical energy of fuel into electrical energy. The present invention relates to a cathode air control method and device for adjusting the air flow rate.

[Prior Art] A molten carbonate fuel cell uses tiles (electrolyte plates) made by impregnating a porous material with molten carbonate as an electrolyte.
It is sandwiched between the cathode (oxygen electrode) and anode (fuel electrode) from both sides, and by supplying oxidizing gas to the cathode side and supplying fuel residue to the anode side, the reaction between the cathode side and the anode side causes a gap between the cathode and the anode. One cell is configured to generate electricity by the potential difference generated between the two, and each cell is laminated in multiple layers via a separator to form a stack.

Among the power generation systems using molten carbonate fuel cells as described above, in those that use natural scum as fuel, as shown in an example in FIG. , after compressing air A with compressor 4,
While being supplied to the inlet side of the cathode 2 through the air supply line 6, some air A is guided to the combustion chamber side of the reformer 9 after passing through the air preheater 8 provided on the branch line Z, where it is combusted. The scum is mixed with the air in the air supply line 6 through the air preheater 8 and supplied to the cathode 2, and the cathode scum discharged from the cathode 2 is sent to the cando gas outlet line 11 for auxiliary combustion. The air is introduced into the turbine 5 through a vessel 12, and is discharged from the turbine 5 through a superheater 13 and an evaporator 14 to the atmosphere. Furthermore, the anode 3 of the fuel cell 1 contains natural scum N.
After being desulfurized in the desulfurizer 15 and preheated in the natural scum preheater 16, it is generated by the evaporator 14 and superheater 13,
mixed with superheated steam supplied via steam line 23;
The fuel gas is introduced into the reforming chamber of the reformer 9, reformed there, and supplied to the anode 3 from the fuel gas supply line 17 as fuel gas, and the anode gas discharged from the anode 3 is the natural gas. Preheater 16, heat exchanger 18
, through a condenser 19 to a gas-liquid separator 20, where H2O in the anode gas is separated, and the gas is pressurized by a blower 21 and enters a heat exchanger 18, where it is heated and then In addition to being supplied to the combustion chamber of the reformer 9, the separated H2O is pressurized by the pump 22 and sent to the evaporator 14, where it becomes steam and is superheated by the superheater 13. The natural waste NG is mixed with the reformer 9 through the steam line 23. 24 is cathode 2
and the anode 3 differential pressure control valve.

In the molten carbonate fuel cell power generation system as described above, the air flow rate control method for the compressor 4 is constant air flow control that keeps the air flow rate flowing through the compressor 4 constant regardless of load fluctuations of the fuel cell 1. There are two methods: one method is to provide a flow rate control valve 30 on the suction side of the compressor 4, and the other method is to change the flow rate of air flowing into the compressor with load fluctuations.

In any of the air flow rate control methods, the cathode gas flow rate changes as the load on the fuel cell 1 changes, so the differential pressure between the cathode 2 and the housing 25 will change if no measures are taken. In the past, it was necessary to control the cathode pressure in order to keep the differential pressure within a certain range, and conventionally, the cathode 2 and the housing 2
5, a dedicated differential pressure control valve 26 is provided in the cathode scum outlet line 11, and the differential pressure between the cathode outlet and the casing 25 is detected by a differential pressure detector 27 and controlled by the differential pressure control valve 26. ing.

Further, in order to keep the pressure on the outlet side of the compressor 4 constant, the pressure is detected by a pressure regulator 28 and excess air is caused to flow into the auxiliary combustor 12 by a flow rate regulating valve 29. The auxiliary combustor 1
In No. 2, the temperature of the waste entering the turbine 5 is maintained constant by burning fuel.

[Problems to be Solved by the Invention] However, in the constant air flow rate control method described above, in order to keep the air temperature of the turbine 5 constant, the auxiliary combustor 1
There is a problem in that the partial load efficiency of the system decreases because 2 ton more fuel is flowing, and there is a desire to improve the efficiency at low loads. On the other hand, in the system in which the amount control valve 30 is provided on the suction side of the compressor 4, the flow rate of waste flowing into the turbine during partial load is reduced, which lowers the inlet pressure, leading to a decrease in turbine output. . Further, a high temperature valve for differential pressure control is required to control the differential pressure between the cathode 2 and the housing 25.

Therefore, the present invention improves efficiency at low loads by reducing the fuel in the auxiliary combustor to keep the turbine inlet temperature constant, and also improves the differential pressure control between the cathode and the casing by increasing the high temperature for differential pressure control. The idea is to make it possible to do it without a valve.

[Means for Solving the Problems] In order to solve the above problems, the present invention supplies air compressed by a compressor to the cathode of a fuel cell, and sends cathode scum discharged from the cathode through an auxiliary combustor. In a configuration in which a part of the air compressed by the compressor is bypassed to the turbine via an auxiliary combustor, the flow rate of the air introduced to the compressor is controlled by a flow rate control valve number. Therefore, the pressure is adjusted according to the load fluctuation of the fuel cell, and the differential pressure between the cathode of the fuel cell and the casing housing the fuel cell is maintained constant by controlling the pressure on the upstream side of the turbine using the variable stator vanes of the turbine. A method for controlling the amount of air for the cathode of a molten carbonate fuel cell, in which a flow control valve is provided on the suction side of the compressor, and the flow control valve is controlled by a command from a master based on a load signal of the fuel cell. In this cathode air amount control device, the first stage stator vane of the turbine is a variable vane, and the variable vane can be adjusted according to the differential pressure between the cathode and the casing.

[Effect] When the amount of air sucked into the compressor is reduced during partial load, the amount of air bypassed from the compressor to the turbine is reduced. Therefore,
Since the turbine inlet temperature decreases less than in the past, the amount of auxiliary combustor fuel needed to keep the turbine inlet temperature constant can be reduced accordingly, improving efficiency at low loads. In addition, the turbine inlet pressure can be maintained constant by adjusting the variable blades of the turbine based on the differential pressure between the cathode and the casing, so the conventional differential pressure control valve can be omitted.
Turbine efficiency can be maintained at low loads.

[Implementation example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the main parts of a molten carbonate fuel cell power generation system according to an embodiment of the present invention.The anode 3 of the fuel cell 1 is supplied with fuel gas reformed by a reformer 9. On the other hand, the air compressed by the compressor 4 is supplied to the cathode 2 of the fuel cell 1 via the air supply line 6, and the cathode sludge discharged from the cathode 2 is sent to the auxiliary combustor 12 from the cathode scum outlet line 11. In the molten carbonate fuel cell power generation system, the flow rate control valve 30 is installed on the suction side of the compressor 4, and the flow rate control valve 30 is connected to the load signal of the fuel cell 1. It is connected to a master 31 which inputs and issues commands in accordance with load fluctuations, and the opening degree of the flow rate control valve 30 is adjusted according to the commands from the master 31, so that the amount of air sucked into the compressor 4 can be changed. Further, the first stage stationary blade in the turbine 5 is separated from other stationary blades to form a variable blade 32, and the variable blade 32 is adjusted by a command from a pressure regulator 33 provided in the cathode scum outlet line 11 on the upstream side of the turbine 5. At the same time, a differential pressure detector 27 for detecting the differential pressure between the cathode 2 of the fuel cell 1 and the casing 25 is connected to the pressure regulator 33,
Further, a part of the natural waste NG is supplied to the auxiliary combustor 12 from a natural waste line 34, and a flow rate control valve 35 provided in the natural waste line 34 is used as a temperature regulator for detecting the temperature on the inlet side of the turbine 5. 36 so that it can be adjusted. Of course, the other configurations are the same as those shown in FIG. 2, and the same components are given the same reference numerals.

When the load on the fuel cell 1 fluctuates, the opening degree of the flow rate control valve 3o on the suction side of the compressor 4 is adjusted by a command from the master 31 in accordance with this load fluctuation.

When the load on the fuel cell 1 becomes less than the rated value, the flow rate control valve 3o is adjusted according to the load, and the amount of air sucked into the compressors 11 and 4 is reduced. As a result, from the compressor 4 to the turbine 5
The amount of air bypassed to the cathode 2 is reduced compared to the constant air flow rate control method, and the amount of air supplied to the cathode 2 is also reduced.

If this continues, the inlet pressure of the turbine 5, that is, the cathode pressure will decrease, or the differential pressure between the cathode pressure and the pressure of the housing 25 will be detected by the differential pressure detector 27.
The variable blades 32 of the turbine 5 are adjusted according to the differential pressure, and the inlet pressure of the turbine 5 is controlled.
The differential pressure of 5 is kept constant.

Note that the variable blades 32 do not have to be only the first-stage stationary blades of the turbine 5.

[Effects of the Invention] As described above, according to the present invention, the compressor that compresses and supplies air to the cathode of the fuel cell is driven by a turbine, and the cathode scum discharged from the cathode is passed through the auxiliary combustor and direct it to the turbine,
In a configuration in which air is bypassed from the compressor to the turbine, the flow rate of air sucked into the compressor is regulated by a flow rate control valve whose opening degree is adjusted according to the load of the fuel cell, and The differential pressure between the fuel cell cathode and the housing that houses the fuel cell is kept constant by adjusting the first stage stator vanes of the turbine as variable vanes, so as the load on the fuel cell becomes low, the compressor By throttling the amount of air sucked in, the amount of air bypassed to the turbine can be reduced compared to the conventional system using a compressor with constant air flow control, and as a result, the turbine inlet temperature can be kept constant. The auxiliary combustor fuel can be reduced to improve efficiency at low loads, and variable vanes at the turbine inlet can control turbine inlet pressure (cathode pressure) to improve turbine efficiency at low loads. The present invention has excellent effects such as being able to maintain the pressure difference even at different times, controlling the differential pressure between the cathode and the casing, and omitting the conventional high temperature valve for controlling the differential pressure.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of essential parts showing an embodiment of the present invention, and FIG. 2 is a system configuration diagram showing an example of a molten carbonate fuel cell power generation system employing a conventional method. DESCRIPTION OF SYMBOLS 1... Fuel cell, 2... Cathode, 3... Anode, 4... Compressor, 5... Turbine, 6... Air supply line, 11... Cathode gas outlet line, 12
... Auxiliary combustor, 25 ... Housing, 27 ... Differential pressure detector, 30 ... Flow rate control valve, 31 ... Master, 32
...Variable wings.

Claims (2)

[Claims] (1) Supplying air compressed by a compressor to the cathode of the molten carbonate fuel cell, bypassing the compressed air to the turbine via an auxiliary combustor, and directing the cathode gas discharged from the cathode to the In a method for controlling the amount of air for a cathode of a molten carbonate fuel cell which is guided to a turbine via an auxiliary combustor, the amount of air sucked into the compressor is adjusted according to load fluctuations of the fuel cell; The molten carbonate is characterized in that the differential pressure between the cathode and the casing housing the fuel cell, which is generated by adjusting the amount of air sucked into the fuel cell, is maintained within a certain level by controlling the turbine inlet pressure using variable stator blades of the turbine. A method for controlling the amount of air for the cathode of a type fuel cell. (2) Supplying air compressed by a compressor to the cathode of the molten carbonate fuel cell, bypassing the compressed air to the turbine via an auxiliary combustor, and directing the cathode gas discharged from the cathode to the In a device for controlling the amount of air for the cathode of a molten carbonate fuel cell, which is guided to the turbine via an auxiliary combustor, a flow rate control valve is provided on the suction side of the compressor, and the flow rate control valve is connected to the load of the fuel cell. connected to a master that issues commands in response to fluctuations, and at least the first-stage stator vane of the turbine is a variable vane, and the variable vane is adjusted based on the differential pressure between the cathode and a casing housing the fuel cell. 1. An air amount control device for a cathode of a molten carbonate fuel cell, characterized by having a configuration consisting of: