JPS5975571A - Method for operating power generating system with fuel cell - Google Patents

Abstract

PURPOSE:To improve the overall efficiency of the power generating system at the time of partial load operation, by operating the fuel cell then at lower operating pressure than that at the full load operation through the variable pressure and variable airflow operation of the air compressor. CONSTITUTION:A fuel 2 is reformed with steam and denatured by a reforming apparatus 4 into hydrogen fuel and the same is supplied to the fuel cell 8. Air is also supplied to the cell through a compressor 22 equipped with a heat recovery turbine 40, and the air is adapted to react there with the hydrogen to generate electricity. At the time of partial load operation, auxiliary fuel 3 to be supplied to a burner 28 installed at the inlet line of the turbine 40 is so adjusted that the airflow measured by a flowmeter installed in the discharge line of the compressor 22 indicates such a value that corresponds to the load value, whereby the compressor 22 can be operated to provide varied pressure and airflow. Thus, it becomes possible to operate the cell 8 under varied pressure conditions provided by the compressor 22, and the improvement of the overall efficiency of the power generating system at the partial load operation can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention produces a hydrogen fuel gas by steam reforming and carbon oxide transformation of a raw material gas, for example, natural gas whose main component is methane. The present invention relates to a method of operating a fuel cell power generation system that generates electricity by supplying it to a battery. - In order to increase the power generation efficiency of fuel cells, the operating pressure of fuel cells has recently been increasing from 1 to 8 #/caG.
The air supplied to the conventional batteries is pressurized by a compressor equipped with an exhaust heat recovery turbine to improve power generation efficiency.
As a heat source, high-temperature exhaust gas generated from a power generation system or subboom is used.

Even in such a pressurized fuel Φ1 pond power generation system, operation at partial load is frequently performed due to demands from the demand side, and even in this case, it is necessary to establish a highly efficient operating method. It came as I expected.

JP-A-51-105551 discloses a method of partial load operation in a pressurized fuel cell power generation system, but the method is limited to operating only the fuel cell with high efficiency.

The present inventors studied a method for highly efficient operation of the entire system without using only a fuel cell, and obtained results contrary to the conventional understanding that high pressure is highly efficient during dual-part load operation, and completed the present invention. I ended up doing it. That is, two aspects of the present invention are as follows.

A fuel processing device that generates hydrogen fuel by steam reforming and converting raw material gas, a fuel cell that generates electricity by receiving the hydrogen fuel and an oxidizing agent such as air, and an oxidizing agent such as air that is supplied to the fuel cell. A pressurized fuel cell power generation system comprising a compression device equipped with an exhaust heat recovery turbine for compressing the fuel, characterized in that the fuel cell is operated at a pressure lower than the operating pressure at full load during one partial load. A method of operating a battery power generation system is provided.

A detailed explanation will be given below based on one drawing and the like.

First, full load operation will be explained with reference to FIG.

FIG. 1 is a flow sheet showing a typical power generation system in which the operating method of the present invention is to be implemented. Fuel cell8. The compressor 22 and the exhaust heat recovery turbine 40 are the main components.

The reformer 4 is composed of a known steam reformer, a high-temperature shift converter, and a low-temperature shift converter, respectively, and here, the fuel 2 (
A gas containing hydrogen as a main component obtained by the reaction between natural gas (natural gas) and fuel reforming steam (described later) is sent to the fuel chamber IO of the fuel cell 8 via a line 6.

The fuel cell 8 is a hydrogen-oxygen (air) type fuel cell,
By the electrode 16, the fuel chamber]0. It is separated into an air chamber 12 and an electrolyte chamber 14, and further includes a battery cooler 32 for controlling heat generation of the battery. Reference numeral 18 indicates a DC/AC converter.

Air 2 is supplied to the air chamber 12 of the fuel cell 8 by a compressor 22.
0 is pressurized and sent, and electricity is generated by reaction with the hydrogen gas.

Both the hydrogen gas 26 and the air 24 that have completed the reaction are sent to the reformer 4 and burned, thereby being used as a heat source for the reforming reaction, and the reforming reaction proceeds. The steam necessary for the reforming reaction comes from makeup water 30, which is used to control heat generation in the fuel cell.

Steam 3 obtained by evaporation while passing through the battery cooler 32
A portion of 4 is used. The remaining steam 3B is taken out of the system and used.

Combustion exhaust gas 36 from the reformer and auxiliary fuel 3 are transferred to the combustor 2.
8 and is used as driving power for the exhaust heat recovery turbine 40, which drives the compressor 22 coaxial therewith.

Next, in the case of one partial load, the conversion efficiency ηC of the battery into electricity is expressed as, and it is known that this improves when the power generation wind is reduced because the current density becomes sparse. . Furthermore, as mentioned above, the higher the operating pressure, the higher the efficiency, and a graph of this is shown in FIG. The solid line shows the pressure change (Pi > P
2>P3) shows the relationship between the load and ηC.

A diagram showing the characteristics of the compressor is shown in Figure 3, and the curve P in Figure 2 represents the case of constant air flow and constant pressure operation at point A (100%) regardless of the power generation load. shown. That is, since η0 increases as the power generation load decreases, constant air volume and constant pressure operation is considered preferable.

This is further calculated as the heat rate (W/KVW) of the raw natural gas required per reservoir at each load.
).

They are abbreviated as H and R. ) is shown by the solid line F in FIG.

Up to now, we have explained the compression device including the compressor and the exhaust heat recovery turbine on the assumption that it is self-sustaining, that is, it is possible to increase the pressure only with the recovery power of the turbine without inputting power from outside the string. It is necessary to maintain a turbine inlet temperature commensurate with the pressure. The higher the discharge pressure of the compressor, the more high temperature gas is required to be guided to the turbine.

Even under full load, the compressor can currently support itself by burning a certain amount of auxiliary fuel. However, when the power generation load is lowered, the amount of heat handled by the reformer decreases in proportion to the power generation load, but the amount of air coming out of the air chamber remains almost the same, so the amount of heat obtained from the reformer is proportional to the load. and decreased.

The temperature of combustion exhaust gas decreases. Therefore, a large amount of auxiliary fuel is required for self-support. i of auxiliary fuel at each load
(H, R,) is shown by solid line A in FIG.

Above, we have explained constant air volume and constant pressure operation.

What will happen if the air volume of the compressor is reduced?

When the compressor air volume is reduced according to the power generation load.

As shown in the characteristic diagram of FIG. 3, the operating pressure decreases from A and B to C, and ηC at each load changes as shown by the broken line in FIG. Comparing the ηC of this variable air volume variable pressure operation and the previous constant air volume constant pressure operation, it appears that the constant air volume constant pressure operation is superior. The broken line F in FIG. 4 shows H and R in the variable air volume and variable pressure operation, but compared to the solid line ^, the constant air volume and constant pressure operation appears to be superior.

Next, regarding auxiliary fuel, in variable air volume variable pressure operation.

Even if the power generation load is reduced, the amount of air coming out of the air chamber is reduced, so the temperature of the combustion exhaust gas remains almost constant regardless of the reduction in the amount of heat received from the reformer. Therefore, auxiliary fuel can be reduced. (Dotted line A in Figure 4).

The solid line T and the broken line T in FIG. 4 indicate the respective sums of raw material and auxiliary fuel in both operations. It can be seen that variable air volume variable pressure operation can generate electricity with a small amount of heat at partial load.

Note that if the solid line T and broken line T in FIG. 4 are converted into total power generation efficiency, the result will be as shown in FIG. 5.

As already mentioned, the characteristics of the compressor are 1. Normal.

A wide driving range is often not possible. In that case.

It is sufficient to operate at the rated minimum air volume and a power generation load lower than that.

In the figure, the broken line indicates variable air volume operation at 50 = 100% load, and constant air volume operation where the air volume at 50% is ensured from 25 to 50%. In 25% operation with constant air volume and constant pressure operation, the generating end efficiency becomes extremely poor and is not practical, but in variable air volume and variable pressure operation, even 25% is sufficient for practical use.

The variable air volume variable pressure operation during partial load according to the present invention is as follows.

Specifically, by adjusting the amount of auxiliary fuel to the combustor installed on the turbine inlet line, so that the flow rate measured by the flow meter installed on the compressor discharge line becomes a value commensurate with the load. Do J.

Note that the load response of the compression device is slower than the load fluctuation speed of the battery, so if a sudden load reduction is required,
It is no problem to first respond with constant air volume and constant pressure operation, and then gradually shift to variable air volume and variable pressure operation.

Furthermore, in the case of a sudden load increase, it is no problem to first increase the load on the compression device to a value commensurate with the increased load and then increase the battery load.

In order to understand the present invention, when designing with the goal of generating power of 100 OKW, the result will be as follows.

At 100% load, natural gas for reforming 8.43 Kfmot
/'hx With auxiliary fuel 0.5 Kf mat / hr, 110 Kf mot/h3, s Ky /iG
of air and can generate 100 kW of electricity.

The efficiency at that time is 30.5%.

For each partial load, the conventional method (constant air volume, constant air volume) and 9
Calculations and comparisons will be made regarding the methods according to the present invention (variable pressure, variable air volume).

Operating the compressed air ζ under variable pressure and variable wind speed means operating the fuel cell itself under the changed pressure conditions.

As is clear from the above description, according to the present invention, it is possible to improve the overall power generation efficiency at partial load, and this efficiency increases as the efficiency of the compression device decreases.

The difference is remarkable.

[Brief explanation of drawings]

Fig. 1 is a flow sheet showing a typical power generation system in which the operating method of the present invention is to be implemented; FIG. 4 is a diagram showing the Heat Rate with respect to the power generation load, and FIG. 5 is a diagram showing the total power generation efficiency with respect to the power generation load. Agent Patent Attorney Ao Asa Shoji1] Figure 0 25 50 75
Missed 100 shots (%) Figure 2 Q 25 50 75
Fig. 3

Claims (1)

[Claims] (1) A fuel processing device that generates hydrogen fuel by steam reforming/transforming raw material gas, a fuel cell that generates electricity by receiving the hydrogen fuel and an oxidizing agent such as air, and air that is supplied to the fuel cell. A pressurized fuel cell power generation system consisting of a compression device equipped with an exhaust heat recovery turbine for compressing the oxidizer of An operating method for a fuel cell power generation system.