JPH05266909A - Fuel cell system - Google Patents

Abstract

PURPOSE:To provide a fuel cell system provided with a simple detection system for oxygen concentration in the exhausted gas of a reformer, by which stable power supply is possible even at the time of rapid increase in the load. CONSTITUTION:In a fuel cell system provided with a reformer for reforming a fuel gas and a turbo compressor serving as an air source for supplying air, a zirconia oxygen concentration meter 55 is directly mounted on the reformer main body, while the discharged air of the turbo compressor 41 is used as an air for comparison for the zirconia oxygen concentration meter. Stable power supply is possible even at the time of rapid increasing of the load, and a fuel cell system provided with a simple detection system of oxygen concentration in the exhausted gas of the reformer is thus provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell system capable of supplying stable electric power against load fluctuations.

[0002]

2. Description of the Related Art A fuel system in a conventional fuel cell system will be described with reference to FIG. In the figure, natural gas as a fuel flows through the fuel flow rate control valve 30, and is introduced into the fuel preheater 5 together with the fuel gas having a high hydrogen gas concentration flowing from the fuel recycle system to be heated. The fuel gas leaving the fuel preheater 5 is guided to the desulfurization tower 1 to remove the sulfur content in the natural gas. The fuel gas leaving the desulfurization tower 1 is steam separator 1
The steam generated in 3 is mixed with the steam through the steam superheater 8 and the steam flow rate control valve 32, and is introduced into the reformer 2 through the reformer inlet preheater 6. In the reformer 2, it is heated by the reformer burner and reformed into a fuel gas containing a large amount of hydrogen gas by a chemical reaction. At the same time, carbon dioxide and a small amount of carbon monoxide are generated. This fuel gas containing hydrogen gas, carbon dioxide and a small amount of carbon monoxide is introduced into the high temperature carbon monoxide shift converter 3 to transform harmful carbon monoxide into carbon dioxide.

However, since all the carbon monoxide cannot be converted to carbon dioxide in the high temperature carbon monoxide shift converter 3, the fuel gas containing hydrogen gas, carbon dioxide and carbon monoxide is fed into the low temperature carbon monoxide shift converter inlet. It is introduced into the low temperature carbon monoxide shift converter 4 through the cooler 7, and the remaining carbon monoxide is transformed into carbon dioxide. A fuel gas mainly composed of hydrogen gas obtained by converting carbon monoxide into carbon dioxide is introduced into a fuel cooler 9 through a steam superheater 8 and vapor mixed with the fuel gas for reforming natural gas. Cooled to remove the residue. A part of the fuel gas leaving the fuel cooler 9 is sent to the inlet of the fuel preheater 5 via the fuel system recycle compressor 15. The remaining fuel gas is sent to the fuel cell 40 via the reformed gas flow rate control valve 31. The fuel cell 40 consumes hydrogen in the fuel gas to generate electricity.
Not all the hydrogen content is consumed in the fuel cell 40, but there is a residual content.

A part of the fuel exhaust gas discharged from the fuel cell 40 is returned to the inlet of the fuel cell 40 via the anode recycle compressor 16 to form an anode recycle system. The remaining fuel exhaust gas is returned to the reformer 2 and used as a fuel for the burner of the reformer 2 and serves as a heat source when reforming natural gas into hydrogen gas. The fuel exhaust gas burned by the burner of the reformer 2 is sent to the auxiliary burner 22 via the reformer burner air preheater 10 for heating the combustion air of the reformer burner as combustion exhaust gas, and the fuel cell It is sent to a turbo compressor device 41 which is an air source for generating the cathode air 40, the combustion air of the auxiliary burner 22 and the combustion air of the burner of the reformer 2. The turbo compressor device 41 includes a high pressure compressor 21 and a low pressure turbo compressor 20.

Explaining the other air system, the air generated in the turbo compressor device 41 is sent to the bypass air flow rate control valve 36 in order to maintain the partial pressure difference of the fuel cell system at a certain constant value. Further, the remaining part is used as combustion air for the burner of the reformer 2 through the reformer burner air flow rate control valve 33 and the cathode exhaust of the fuel cell 40 and the reformer burner air preheater 10 and the reformer 2
It is sent as fuel air for the burner. Further, the air leaving the remaining turbo compressor device 41 is sent to the fuel cell 40 via the air flow rate control valve 35, and oxygen is consumed in the fuel cell 40 to generate electricity.

However, some of the oxygen in the air is not consumed and some remains. The cathode exhaust discharged from the fuel cell 40 is sent to the cathode exhaust cooler 12 through the cathode exhaust reheater 11, removes the water generated in the fuel cell 40, and is sent to the cathode exhaust reheater 11 again to partially Returns to the downstream of the air flow rate control valve 35 via the cathode recycle compressor 17 and constitutes a cathode recycle system. The remaining cathode exhaust gas is mixed with the air generated by the turbo compressor device 41 downstream of the reformer burner air flow rate control valve 33 as described above through the low temperature carbon monoxide shift converter inlet cooler 7. It is sent to the reformer burner air preheater 10 to be heated, and sent to the reformer 2 as reformer burner combustion air to be used for combustion. Next, the combustion control of the reformer will be described.

As shown in the reformer burner fuel control algorithm of FIG. 3, the reformer reformer upper temperature 50 and the reformer reformer upper temperature set value are calculated by the temperature PI calculator 52, and the flow rate is calculated. Set the flow rate set value of the PI calculator 53 to the fuel cell inlet flow rate of 5
1 and the flow rate PI are calculated and used as a control signal for the reformed gas flow rate control valve 31. In this way, the reformed gas flow rate control valve 31 controls the fuel flow rate at the fuel cell inlet so that the reformer upper reforming temperature becomes constant.

Further, as shown in the reformer burner flow rate control algorithm of FIG. 4, the reformer combustion exhaust gas oxygen concentration 55 and the reformer combustion exhaust gas oxygen concentration set value are set to the oxygen PI calculator 57.
Is calculated by the reformer burner air flow meter 56 and the flow PI calculator 58 as a flow set value of the flow PI calculator 58, and is used as a control signal of the reformer burner air flow control valve 33. In this way, the reformer burner air flow rate control valve 33 controls the flow rate of air sent from the turbo compressor device 41 to be mixed with the cathode exhaust gas of the fuel cell so that the oxygen concentration of the reformer combustion exhaust gas becomes constant.

[0009]

By the way, in the conventional fuel cell system, the reformer combustion exhaust gas oxygen concentration detector 55 is required to have a high-speed reaction, and the reformer combustion exhaust gas oxygen concentration is accurately measured. Wet sampling method (concentration analysis including water vapor content in exhaust gas) is required for measurement. In order to satisfy this, the reformer combustion exhaust gas oxygen concentration is detected with the configuration shown in FIG. That is, the sample gas is taken out from the reformer 2 and the sample pressure is reduced by the oxygen concentration meter pressure-reducing valve 71 that reduces the pressure to a sample pressure suitable for the oxygen concentration meter through the oxygen concentration meter automatic stop valve 70. It is led to the oxygen concentration meter 55 through an oxygen concentration meter flow rate control valve 72 provided for flowing a sample amount suitable for the concentration meter. Here, the oxygen concentration meter detection pipe heating heater 74 is heating so that the temperature of the sample gas does not fall below the dew point of the sample gas.
Further, the drain separator 73 is for discharging the drain out of the system so that the drain does not collect in the detection pipe in the event that drain occurs.

On the other hand, since the comparative air pressure reducing valve 75 for the oxygen concentration meter uses the zirconia type oxygen concentration detector for the reformer combustion exhaust gas oxygen concentration meter 55, the comparative air is required. And to reduce the pressure.

By the way, for example, when there is a sudden load change, the output of the reformer oxygen concentration meter 55 does not change immediately and it takes time until the sample in the detection pipe constituting the reformer oxygen concentration detection device is replaced. Be late. Furthermore, a response delay of the reformer oximeter 55 itself is added, which causes a further delay, but this delay time is about 30 to 7 compared with a pressure detector generally used as a control element when performing pressure control.
It is about 0 times slower and limits the load change rate of the fuel cell system. Then, the advantage of the fuel cell system, that is, it is possible to stably supply electric power against a rapid load change, is lost. Further, since the wet sampling method is used, it is necessary to install a heating heater in the detector, which complicates the detector.

The present invention has been made in view of the above circumstances, and an object thereof is to enable stable power supply even with a sudden load increase, and to have a simple reformer exhaust gas oxygen concentration detection system. It is to provide a fuel cell system.

[0013]

To achieve the above object, the present invention provides a fuel cell system comprising a reformer for reforming a fuel gas and a turbo compressor as an air source for generating air. A zirconia oximeter is directly attached to the reformer main body, and the discharge air of the turbo compressor is used as reference air for the zirconia oximeter.

[0014]

According to the present invention, the oxygen concentration meter is directly attached to the reformer main body, and the air for comparison of the oxygen concentration meter is the air discharged from the turbo compressor, so that stable power supply can be achieved even when the load is suddenly increased. Therefore, a fuel cell system having a simple reformer exhaust gas oxygen concentration detection system can be provided.

[0015]

Embodiments of the present invention will be described with reference to the drawings. Figure 1
FIG. 1 is a configuration diagram of an embodiment of the present invention. As shown in the figure, in the fuel cell system of the present invention, the reformer combustion exhaust gas oxygen concentration meter 55 is directly installed in the reformer 2, and the reformer combustion exhaust gas oxygen concentration meter is installed from the outlet pipe of the turbo compressor device 41. A line for supplying the reference comparative air to the reformer combustion exhaust gas oxygen concentration meter 55 is provided, and a flow control valve 80 for the reformer combustion exhaust gas oxygen concentration meter is provided.

As the reformer combustion exhaust gas oxygen concentration meter 55, a zirconia type oxygen concentration meter is used. Explaining the principle of this zirconia oximeter, a solid electrolyte (zirconia porcelain) exhibits conductivity with respect to oxygen ions at high temperature, and a platinum-based electrode is attached to the inner and outer surfaces of the zirconia element to heat it, and oxygen Contacting gases with different partial pressures causes the oxygen concentration cell action. That is, the oxygen concentration is measured by the ratio of the oxygen partial pressures inside and outside the zirconia element. Therefore, accurate measurement cannot be performed unless the pressures of the sample gas and the comparative air are equal.

In the fuel cell system of this embodiment, by using the outlet air of the turbo-compressor device 41 as the reference air, the reference air equivalent to the pressure of the reformer combustion exhaust gas as the sample gas can be obtained. Further, by directly attaching the reformer oxygen concentration meter 55, which is a zirconia-type oxygen concentration meter, to the reformer 2, it is possible to omit a device for adjusting the pressure of the sample gas, the flow rate, and the temperature, and therefore the configuration is simple. .. Regarding the detection delay,
Since the reformer exhaust gas oxygen concentration meter 55 is installed directly in the reformer 2, the reformer oxygen concentration detection system can be detected without delay in detection.

Since this embodiment is constructed as described above, the output of the reformer exhaust gas oxygen concentration meter 55 is directly output to the reformer 2 when the load changes suddenly. Since the densitometer 55 is attached, the densitometer 55 starts to change immediately, and cannot limit the load change rate of the fuel cell system. As a result, stable power supply can be achieved even with rapid load changes, which is a feature of fuel cell systems. Further, the reformer 2 has a reformer exhaust gas oxygen concentration meter 5
Since 5 is directly attached, the structure for detecting the oxygen concentration of the reformer exhaust gas becomes simple.

[0019]

As described above, according to the present invention,
By attaching the reformer exhaust gas oxygen concentration meter directly to the reformer and supplying the reference air of the reformer exhaust gas oxygen concentration meter from the turbo compressor device, stable power supply even with rapid load changes It is possible to provide a fuel cell system having a simple reformer exhaust gas oxygen concentration detection system.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a system configuration diagram of a conventional fuel cell system.

FIG. 3 is a diagram showing a reformer burner fuel control algorithm of FIG. 2.

FIG. 4 is a diagram showing a reformer burner flow rate control algorithm of FIG. 2;

5 is a block diagram of the reformer combustion exhaust gas oxygen concentration detection system of FIG.

[Explanation of symbols] 1 ... desulfurization tower, 2 ... reformer, 3 ... high temperature carbon monoxide shift converter,
4 ... Low temperature carbon monoxide shift converter, 5 ... Fuel preheater, 6 ... Reformer inlet preheater, 7 ... Low temperature carbon monoxide shift inlet cooler,
8 ... Steam superheater, 9 ... Fuel cooler, 10 ... Reformer burner air preheater, 11 ... Cathode exhaust reheater, 12 ... Cathode exhaust cooler, 13 ... Steam separator, 15 ... Fuel system recycle compressor, 16 ... Anode recycling compressor, 17 ... Cathode recycling compressor,
18 ... Battery cooling water pump, 20 ... Low pressure turbo compressor, 21 ... High pressure turbo compressor, 22 ... Auxiliary burner, 30 ... Fuel flow rate control valve, 31 ... Reformed gas flow rate control valve, 32 ... Steam flow rate control valve, 33 ... Modified Pneumatic burner Air flow control valve, 34 ... Cathode exhaust gas reformer bypass cutoff valve, 35 ... Air flow control valve, 36 ... Bypass flow control valve, 40 ... Fuel cell, 41 ... Turbo compressor device, 55 ... Reformer Combustion exhaust gas oxygen concentration meter, 56 ... Reformer burner air flow meter.

Claims (1)

[Claims] 1. A fuel cell system comprising a reformer for reforming fuel gas and a turbo compressor as an air source for generating air, wherein a zirconia-type oxygen concentration meter is directly attached to the reformer main body. A fuel cell system, wherein discharge air of the turbo compressor is used as comparative air for an oximeter.