JPS63207053A - Fuel cell power generation plant - Google Patents

Abstract

PURPOSE:To improve the battery performance by providing an oxygen concentration sensor in the immediate front of an oxidizer electrode in an air supply system and a nitrogen-oxygen separator further upper-streamwise in the system to control the oxygen concentration in the air supplied to the oxidizer electrode, whereby concentration polarization is reduced. CONSTITUTION:Fuel 1 is modified by a fuel modifier 5 and supplied to a fuel electrode 11A through a fuel gas flow rate control valve 12, adjusting the CO concentration and surplus steam by a transformer 7 and a fuel gas steam separator 8. Also, air is supplied to an oxidizer electrode 11B from an air feeder 19 and electrical energy is extracted from the electrochemical reaction generated between both electrodes. An oxygen concentration sensor 31, which detects oxygen amount in the air, is provided at the immediate front of an oxidizer electrode in an air supply system and a nitrogen-oxygen separator 30, which separates nitrogen and oxygen in the air, is provided upper-streamwise in the system. The sensor 31 controls the device 30 by checking the oxygen concentration at the inlet of the oxidizer electrode 11B, to keep the oxygen concentration at constant in a controlling loop 32, so that the concentration polarization is reduced and the battery performance can be improved.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention relates to a fuel cell power generation plant, and in particular to a fuel cell power generation plant with an improved air supply system supplied to the oxidizer electrode of the fuel cell. Regarding plan 1~.

(Problems to be Solved by the Invention) In recent years, fuel cell power generation plants have been known as plants that directly convert energy contained in fuel into electrical energy. In this fuel cell power generation plant, a fuel cell is usually constructed by arranging a pair of porous electrodes with an electrolyte sandwiched between them, and a fuel such as hydrogen is brought into contact with the back of one electrode, and a fuel such as hydrogen is brought into contact with the back of the other electrode. Electrical energy is extracted from between the two electrodes by bringing an oxidizing agent such as oxygen into contact and utilizing the electrochemical reaction that occurs. As long as the fuel and oxidizing agent are supplied, high conversion can be achieved. Electrical energy can be extracted efficiently.

FIG. 3 shows the basic configuration of typical fuel cell power generation plans 1 to 1 of this type. In the figure, steam from a fossil fuel J such as natural gas or coal gas, a fuel 1 and a steam supply device 2 is controlled by a fuel flow rate control valve 3 and a steam flow rate control valve 4, respectively, at a mixing molar ratio of steam and carbon. The fuel is introduced into the reforming contact tube 6 in the fuel reformer 5 while being controlled so that it is about 3 to 5. Here, the steam and fuel 1 are heated to about 500 to 600'C to undergo a reforming reaction, and then pass through the shift converter 7 to become fuel gas with a high hydrogen content. This fuel scum with a high hydrogen content is sent to a fuel scum steam/water separator 8 to remove surplus steam from reforming, and then sent to an auxiliary burner 9 by an auxiliary burner fuel flow control valve 10. Also, fuel cell 1
A fuel gas flow rate control valve 12 connects the fuel electrode 11A to the fuel electrode 1A.
The respective flow rates are controlled and sent.

Hydrogen in the fuel gas that has flowed into the fuel electrode 11A of the fuel cell 11 undergoes a catalytic reaction with oxygen in the air that has flowed into the oxidizer electrode 113, and as a result, a portion of the fuel is consumed and reacts with electrical energy. 19 of the produced water is removed. The fuel exhaust gas that exits the combustion electrode 11A and contains a part of the reaction product water generated in the fuel cell 11 is sent as fuel to the main burner 13 of the fuel reformer 5, but during this process, In order to recover moisture in the gas, the fuel exhaust gas passes through a steam/water separator 16.

The fuel waste sent to the main burner 13 is burned in the fuel reformer 5 and is discharged as high-temperature exhaust gas 17 after heating the reforming catalyst tube 6.

Further, this high-temperature exhaust gas 17 is combined with the air exhaust gas sent from the oxidizer electrode 113 of the fuel cell 11, and then sent to the mixer 18, where it is sent to the air supply device (turbo compressor) 1.
It is used as part of the driving energy of 9. On the other hand, the fuel gas sent to the auxiliary burner 9 is combusted within the auxiliary burner 9, and the fuel gas passes through the mixer 18 to drive the turbine 19A of the air supply device (turbo compressor 19).

On the other hand, the air discharged from the compressor 19B connected to and driven by the turbine 19A is sent to the auxiliary burner 9 and the main burner 13 with the air-fuel ratio adjusted by the auxiliary burner air flow control valve 20 and the main burner air flow control valve 21, respectively. At the same time, it is sent to the oxidizer electrode 11B of the fuel cell 11 by the air flow control valve 22, and the surplus is sent to the mixer 18 as part of the energy for driving the air supply device (turbo compressor) 19.

A part of the air sent to the oxidizer electrode 1iB is consumed by reacting with the above fuel (hydrogen in the image 11A), and then the air is transferred to the oxidizer electrode 11B.
It is discharged containing the water produced inside. Similar to the fuel exhaust gas, this discharged air exhaust gas is partially removed from the steam component in the air exhaust gas by the air exhaust gas separator 25, and then merges with the high temperature exhaust gas 17 from the fuel reformer 5.

As mentioned above, in the fuel A'4 battery 11, the oxidizer electrode 11B becomes the positive electrode and the fuel electrode 11A becomes the negative electrode due to the catalytic reaction between the hydrogen in the fuel electrode 11A and the oxygen in the oxidizer electrode 11B.
Generate electrical energy. Both electrodes 11A, 1iB
The hydrogen supplied to both electrodes 11A and 118 reacts with the 1!2 element approximately in proportion to the current value absorbed by the electric load 26 connected between them, and 1q of water produced by the reaction is produced, and this steam is The unreacted gas containing
will be discharged from the outlet.

On the other hand, a recycle pipe 14 connected to a fuel recirculation device is branched from the outlet of the fuel electrode 11A, and a portion of the fuel exhaust gas is returned to the fuel electrode 11A via a fuel recirculation fan 15. Alternatively, an air recycle pipe 23 connected to an air recirculation device is branched from the outlet of the oxidizer electrode 11B, and a part of the air exhaust gas is passed through an air recirculation fan 24 to the oxidizer electrode 11B.
returned to the entrance. These poles and the recirculation device adjust the hydrogen temperature of the fuel exhaust gas and the oxygen concentration of the air exhaust gas, adjust the cell generated voltage through the temperature separation effect of the fuel cell, and reuse the unreacted gas after the cell reaction. As a result, more reaction gas can be supplied to the battery, which allows operation at a higher load and increases the efficiency of the single-fuel cell plant.

Under such operating conditions of a fuel cell power generation plant,
Since the fuel cell 11 does not maintain a stable output voltage, in order to continue outputting load power according to the load command, the fuel electrode 1
It is necessary that the amount of hydrogen gas contained in the fuel gas supplied to the inlet 1A and the amount of oxygen gas contained in the air supplied to the oxidizer electrode 11 [3] are adjusted to appropriate levels. Here, the appropriate amount is the amount of reaction gas consumed in the cell reaction plus a certain amount of surplus unreacted waste ω, and in general, in the case of hydrogen gas, this surplus is the amount of reaction gas ( In contrast, it is desirable that the amount be about 20% or more, and in the case of oxygen gas, about 40% or more based on the amount of reaction gas.

Furthermore, carbon monoxide (Co) contained in the fuel gas must also be adjusted to below a permissible value. This is generally referred to as catalyst poisoning because CO reduces the ionization effect, which is a reaction on the catalyst surface, and lowers the voltage generated by the battery. here,
Generally, in the case of a phosphoric acid fuel cell, this CO allowable value is approximately 1 to 2% at an operating temperature of 200°C, and the fuel gas reformed by the fuel reformer 5 is passed through the shift converter 7. By passing through it, it is adjusted to below the allowable value.

(Problem to be solved by the invention) This J: Sea urchin If the hydrogen gas m supplied to the fuel cell and the oxygen scum or CO mixed with the hydrogen gas are not maintained at appropriate values, the fuel cell will overvoltage or abnormally drop. This makes it difficult to continue stable power generation operation.

When extracting load current from a battery, polarization at both poles (
The rate of voltage loss) is much larger at the oxidizer electrode (cathode) 1113 than at the fuel electrode (anode) 11A. This is because the reduction reaction of air (oxygen) is significantly more irreversible than the oxidation reaction of hydrogen, and the reaction occurs smoothly in less than 1q.

For this reason, in a normal battery, the platinum supported amount of the carbon-supported platinum catalyst used as the electrode catalyst of the cathode 11[3 is 3 to 50 times higher than that of the anode 11A to facilitate the reaction.

In order to reduce polarization in this J: eel cathode 11A,
Highly active electrode catalysts such as alloy catalysts have been developed, but efforts are being made to make further improvements.

In order to reduce the polarization of the cathode 11B, a half cell was assembled and its polarization characteristics were investigated by varying the platinum content in the electrode stone ts layer, and the following results were obtained.

In FIG. 2, it can be seen that as the platinum base increases, the oxygen gain (the difference in voltage value when pure oxygen is used as the oxidant gas and when air is used as the oxidant gas) decreases. This indicates that the cathode reaction (oxygen reduction reaction) at an electrode with a small amount of platinum in the ts layer shows that the difference in voltage at a constant current value is large between when the reaction gas is oxygen and when the reaction gas is air. It means that.

However, when the price of platinum exceeds a certain value, this difference means that it can almost be tax-free. In the case of platinum □ (approximately 10% Pt by weight) as a catalyst normally used for the cathode, the constant current value is, for example, 17.5 m^/cm.
When flowing, this difference is as much as 20 mV. In actual power plants, air is used as the oxidant gas, so this! Iiii'I! It is necessary to take measures to minimize the difference in voltage loss between oxygen and air.

When air is used as the reaction gas, as electrochemically active oxygen gas is consumed by the reaction, electrochemically inactive nitrogen gas accumulates in the catalyst layer, and this causes unused gas in the catalyst layer. Since diffusion of reaction air and produced water is inhibited, so-called concentration polarization may occur, resulting in voltage loss.

Therefore, reducing the thickness of the cathode catalyst layer
This is an important measure to reduce volume and at the same time increase high performance batteries. However, from the viewpoint of battery life characteristics, it is
There is also a problem in making the layer too thin, and it is difficult to reduce the concentration polarization of the oxidant gas.

The object of the present invention is to reduce concentration polarization when air is used as an oxidant gas as described above, and to improve cathode performance and eventually battery performance.
- to provide.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides an oxygen/nitrogen separation device at the inlet of the oxidizer electrode (cathode) of a fuel cell to remove oxygen from the air. ) Increase the agricultural degree to about 50 to 80% and supply this as a reaction gas. Furthermore, an oxygen gas sensor is installed at the cathode inlet, and the acid Mm concentration at the cathode inlet is constantly checked. This patent is characterized by controlling the oxygen concentration by applying feedback to the oxygen/nitrogen separation device.

(Function) According to the oxygen reduction reaction rate equation, the partial pressure of oxygen gas at the cathode is linearly proportional to the current value. As the pressure increases, the current value generated at a constant potential in the activated polarization region increases by 2 to 3 times, and battery performance can be improved.

(Embodiment) Hereinafter, an embodiment of the present invention will be described in detail based on FIG. 1. In addition, the same parts in FIG. 1 and FIG. 3 are denoted by the same reference numerals.

FIG. 1 is a block diagram of a fuel cell power generation plant according to the present invention, in which fuel 1 is reformed in a fuel reformer 5, and a shift converter 7 is used.
001 degrees and surplus steam are adjusted by the fuel gas steam water separator 8 and supplied to the fuel electrode 11A via the fuel gas flow rate control valve 12. In addition, the air supply device 19
Air is supplied to the oxidizer electrode 11B from the oxidizer electrode 11B, and at this time, electric energy is extracted from between the two electrodes by an electrochemical reaction.

In this embodiment, 20 to 60% of the nitrogen gas in the compressed air sent from the air supply device 19 is discharged, and the highly concentrated oxygen gas is passed through the oxygen/nitrogen separation device 30 to the oxidizer electrode (cathode) 11B. supply to. Semiconductor force sensor using materials such as T i O2, COO or ZrO2Ca
4. such as O1Th02-Y2O2. j Solid-state IIS' using M'l? Oxygen gas sensor 31 such as quality sensor
is provided at the inlet of the oxidizer electrode 11B.

Next, the operation of this embodiment configured as described above will be explained.

When the fuel cell power generation plant is in power generation operation, the oxidizer electrode 11
An air recycle pipe 23 connected to an air supply device is branched from the outlet of 30, and a part of the air exhaust gas is sent to the inlet of the oxidizer electrode 11B via an air recirculation fan 24 to the oxygen/nitrogen separation device 30. It is returned via the oxygen gas sensor 31. Air is separated into oxygen and nitrogen by the oxygen/nitrogen valve IT device 30, and the oxygen concentration in the supplied air is increased to about 50 to 80% and then supplied to the cathode 11B.

Then, an oxidizing gas sensor 31 checks the oxygen concentration immediately before the cathode 11B, and a control loop 32 controls the oxygen/nitrogen separation device 30 so that the oxygen concentration is constant.

[Effects of the Invention] As explained above, according to the present invention, since a reactant gas having a high oxygen concentration is always supplied to the cathode at a constant rate,
It is possible to reduce temperature polarization for cathode reactions without increasing the platinum temperature in the electrode catalyst layer, and to assemble high-performance batteries.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a fuel cell power generation plan I according to an embodiment of the present invention, and Fig. 2 shows changes in oxygen gain when the polarization current value is kept constant and the platinum-containing matrix in the electrode catalyst layer is changed. Figure 3 is a block diagram of a conventional fuel cell power generation plant. 1... Fuel 2... Steam supply device 3... Fuel flow rate control valve 4... Steam flow rate control valve 5... Fuel 1 reformer 6... Reforming contact duplex 7... Transformer 8...Fuel gas steam separator 9...Auxiliary burner 10...Auxiliary burner fuel flow control valve 11...Fuel cell 11A...Fuel electrode 11B...Oxidizer electrode 12...・Fuel gas flow rate control valve 13...Main burner 14...Fuel recycle piping 15...Fuel recirculation fan 16...Fuel exhaust gas air/moisture 1iSlt device 17...High temperature exhaust gas 18...Mixer 19 ...Air supply device (turbo compressor) 19A
...Turbine 19[3...Compressor 20...Auxiliary burner air flow control valve 21...Main burner air flow control valve 22...Air flow control valve 23...Air recycle piping 24...・Air recirculation fan 25...Air exhaust gas water separator 26...Electrical load 27...Transformer 30...Oxygen/nitrogen separation device 31...Oxygen gas sensor 32...Control loop (8733 ) Agent Patent Attorney Yoshiaki Inomata (Baka 1
name) 1st leap 2nd figure

Claims (1)

[Claims] (1) A fuel reformer for reforming raw fuel as a mixed component into a fuel gas containing hydrogen as a main component; an air supply device for supplying compressed air; In a fuel cell power generation plant consisting of a fuel cell that outputs current through a reaction, an oxygen concentration sensor that detects the amount of oxygen in the air is installed in the air supply system just before the oxidizer electrode inlet of the fuel cell, and an air 1. A fuel cell power generation plant, comprising: a nitrogen/oxygen separation device for separating nitrogen and oxygen therein, and configured to control the oxygen concentration in the air supplied to the oxidizer electrode.