JPH0831324B2 - Fuel cell power generation system Fuel system recirculation device - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a fuel system recirculation device for a fuel cell (hereinafter referred to as FC) power generation system.

[Technical Background of the Invention and Problems Thereof] A conventional FC power generation system fuel system is a system for supplying hydrogen-rich fuel gas to FC, and as shown in FIG. Reformer 1 that changes the mixed gas of raw fuel gas and steam into a gas containing hydrogen as the main component
Then, steam acts on carbon monoxide generated in the reformer,
A predetermined fuel gas is supplied to the fuel cell 4 by the shift converter 2 that converts hydrogen and carbon dioxide and the fuel gas flow rate control valve 3. Further, since the above-mentioned reforming reaction in the reformer 1 is an endothermic reaction, the residual hydrogen in the fuel gas discharged from FC4 is burned in the reformer burner 5 and used as the heat source of the above reaction.

Moreover, the structure of FC is as shown in FIG.
FC stack 6 in which fuel cells and air are supplied to and exhausted from the FC stack, and FC
It is composed of a pressure vessel 8 and the like that stores the stack and the entire manifold.

In this way, the FC stack is formed by stacking many unit cells in series, so if there is a unit cell that does not provide sufficient output, even if it is a very small unit, the output of the entire FC stack is transferred to this defective cell. I have no choice but to match. Therefore, when the fuel gas is distributed to each unit cell in a biased manner, the output current of the stack is limited by the capacity of the unit cell through which the least amount of fuel flows, and the fuel gas becomes excessive in the unit cells other than the above, resulting in power generation. It is discharged without being used. Therefore, the fuel gas must be evenly distributed to each unit cell.

However, as shown in FIG. 4, the FC has a structure in which the fuel gas is supplied through piping that passes through the manifold. Therefore, when the fuel gas flow rate is small, the pressure loss in each unit cell flow path is small, so the manifold The fuel gas flowing into the fuel cell proceeded in almost the same direction, and a large amount of fuel gas flowed into the unit cell near the inflowing fuel pipe, resulting in a deviation that the number of ends was small. In particular, the fuel gas consists of carbon dioxide and hydrogen, and when used for power generation, only hydrogen decreases, so the specific gravity of the fuel gas after use of FC is
Remarkably large. As a result, when the fuel gas flow rate is low,
After the FC is used, the fuel gas tends to stay in the lower part of the FC stack and hinder the supply of new fuel gas to the lower unit cell.

Due to the above reasons, in the conventional FC power plant, the fuel utilization rate cannot be increased due to the non-uniformity of the fuel gas at a low flow rate, and most of the fuel gas is discarded. Therefore, the power generation cost of FC was high.

[Object of the Invention] An object of the present invention is to eliminate the above-mentioned inconvenience and to provide a fuel system recirculation device capable of uniformly supplying a fuel gas to unit cells constituting an FC stack.

SUMMARY OF THE INVENTION In order to eliminate the non-uniformity of fuel gas flow at low load, the present invention provides a fuel cell and a fuel gas recirculation system for re-supplying exhaust fuel gas from the fuel cell to the fuel cell. A differential pressure detecting means for measuring the differential pressure between the pressure of the fuel gas supplied to the fuel cell and the pressure of the exhausted fuel gas discharged from the fuel cell; and a difference between the measured value by the differential pressure detecting means. Calculating means for calculating a flow rate target value of the fuel gas recirculation system based on a pressure target value, flow rate measuring means for measuring a flow rate of exhaust fuel gas flowing through the fuel gas recirculation system, and the calculating means Flow rate adjusting means for calculating an opening signal of the flow rate adjusting valve of the fuel gas recirculation system based on the flow rate target value from the flow rate measuring means and the flow rate measured value from the flow rate measuring means. It is a thing. As a result, when the load is low and the amount of hydrogen required for FC is small and the amount of fuel supplied from the outside is small accordingly, a sufficient flow rate is secured in the FC stack.

[Effects of the Invention] Since the fuel recirculation device described above can ensure a substantially uniform fuel flow in each unit cell, the fuel utilization rate of all unit cells becomes substantially the same, and therefore, at the time of low load, that is, A high fuel utilization rate is possible even when the flow rate of the fuel gas is low. As a result, the economic efficiency of the FC power generation system is significantly improved.

In addition, since the hydrogen partial pressure in the FC stack decreases as the recirculation amount of the fuel gas increases, this phenomenon can also be used for voltage control. In addition, the lower the load, the larger the amount of recirculation required to secure the flow rate in the FC stack, but this also cures the voltage at the low load.
When the load is low, it is necessary to lower the cell voltage in order to protect the catalyst. Therefore, adjustment by the recirculation amount of fuel gas is extremely effective.

[Embodiment of the Invention] An embodiment of an FC power plant fuel system recirculation apparatus according to the present invention will be described in detail below with reference to FIG. In this embodiment, a fuel gas recirculation line 9 from the exhaust fuel gas line of FC4 to the supply line is provided, and a blower 10 for flowing the exhaust fuel gas to this line and a valve 11 for adjusting the flow rate thereof are used for FC4 Pressure loss of fuel gas inside the differential pressure gauge 12
The control unit 13 controls the flow rate meter 14 to detect the recirculation amount so that the pressure loss reaches a target value.

As shown in FIG. 2, the algorithm of the controller 13 obtains the fuel gas recirculation flow rate target value by PI calculation from the difference between the differential pressure target value and its measured value, and determines this target value and the recirculation flow rate. The opening of the recirculation flow valve is obtained from the difference between the measured value and the measured value by the PI calculation, and is output to the valve 11 which is a flow rate adjusting means for adjusting the flow rate of the fuel gas recirculation system.

According to this embodiment, it is possible to constantly generate a pressure loss of a predetermined value or more in the FC stack, and to make the fuel flow of each unit cell in the stack uniform.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a fuel gas recirculation system according to the present invention, FIG. 2 is a block diagram of a calculation algorithm of a controller, and FIG. 3 is a conventional FC power plant fuel system. FIG. 4 is a structural diagram of the FC stack. 1 ... Reformer, 2 ... Shift converter 3 ... Valve, 4 ... Fuel cell 5 ... Reformer burner, 6 ... Fuel cell stack 7 ... Manifold, 8 ... Pressure vessel 9 ... Fuel Gas recirculation line 10 …… Blower, 11 …… Valve 12 …… Differential pressure gauge, 13 …… Controller 14 …… Flowmeter, 15 …… Fuel gas flowmeter 16 …… Computer

Claims (1)

[Claims] 1. A fuel cell, a fuel gas recirculation system for re-supplying exhaust fuel gas from the fuel cell to the fuel cell, a pressure of the fuel gas supplied to the fuel cell, and an exhaust from the fuel cell. The differential pressure detection means for measuring the differential pressure with the pressure of the exhausted fuel gas, and the flow rate target value of the fuel gas recirculation system based on the measured value and the differential pressure target value by the differential pressure detection means. Based on the flow rate target value from the calculation means and the flow rate measurement value from the flow rate measurement means, the flow rate measurement means for measuring the flow rate of the exhaust fuel gas flowing through the fuel gas recirculation system, A flow rate adjusting means for calculating an opening signal of a flow rate adjusting valve of the fuel gas recirculation system, and a recirculation device for a fuel system of the fuel cell power generation system.