JPH01134871A - Fuel cell power generating device - Google Patents

Abstract

PURPOSE:To enhance the rate of fuel utilization by introducing fuel electrode exhaust gas to a film separator device, separating into CO enriched gas and hydrogen enriched fuel gas, and mixing the hydrogen enriched fuel gas with conversion gas to accomplish a fuel gas. CONSTITUTION:Fuel electrode exhaust gas 105 generated from a fuel cell body 3 is introduced into a film separator device 7 and separated into two streams of hydrogen enriched fuel gas 106 and CO enriched gas 107 by a hydrogen/CO separating film. The hydrogen enriched fuel gas is mixed with a conversion gas 103 given by a CO transformer 2 and used in circulation as a fuel electrode supply gas 104. The hydrogen gas concentration of the hydrogen enriched fuel gas is enriched to around 40-70vol.% by selecting an appropriate hydrogen/CO separating film. Mixing this with the conversion gas drops the hydrogen concentration in the fuel gas to approx. 60-75vol.%, while there is little drop of the power generating efficiency. Thus the rise of the rate of fuel utilization due to utilization of hydrogen enrichment of the fuel electrode exhaust gas overwhelms the drop in the power generating efficiency, wherein the rate of fuel utilization amounts to approx. 90%.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a fuel cell power generation device, and in particular, to a fuel cell power generation device, in particular a method for converting or reforming fuel by steam reforming (steam reforming).
The present invention relates to a fuel cell power generation device that supplies the hydrogen-containing gas obtained by this process and air as an oxidizing agent to a fuel cell, generates electrical energy through an electrochemical reaction, and obtains electric power.

[Prior Art] Conventional fuel cells use fuel such as natural gas, methanol, propane, naphtha, or coal gas in a steam reforming reactor (
A fuel reformer unit that produces a hydrogen-containing gas (herein referred to as converted gas) that is converted or reformed by a shift converter to produce a hydrogen-containing gas, and the hydrogen concentration is increased by a carbon monoxide shift reaction in a shift converter. This converted gas is used as the fuel electrode (hydrogen electrode) supply gas, air is used as the oxygen electrode gas, and a fuel cell main body that directly converts chemical energy into electrical energy through an electrochemical reaction and a power converter that converts electrical energy into electricity It consists of a device section.

In the above configuration, 70 to 85% by volume of hydrogen in the conversion gas supplied to the fuel cell main body is used for power generation, and the remainder is not used and flows out from the fuel cell main body as fuel electrode exhaust gas. For example, it is used as fuel (thermal energy) for a steam reforming reactor (reformer).

[Problems to be solved by the invention] As described above, in the conventional technology, 70 to 8
Only 5% by volume is used for power generation, and 15-30% by volume of the supplied hydrogen is limited by concentration polarization within the fuel electrode and gas flow rate, so it is difficult to increase the utilization rate further, and it is difficult to increase the utilization rate beyond that. It cannot be offered to

As a technique to improve this drawback, Japanese Patent Application Laid-Open No. 59-1844
No. 68 proposes a method in which carbon dioxide is extracted and removed from the fuel electrode exhaust gas using an alkaline solvent, and the recovered hydrogen-containing gas is again supplied to the fuel cell body as fuel.

However, this device for removing carbon dioxide gas using a solvent requires a device for absorbing and removing carbon dioxide gas using a solvent, a regeneration device for the solvent that has absorbed carbon dioxide gas, and a circulation device for the solvent, making the device complicated. This causes problems in the stability of the necessary equipment, simplification of maintenance management, and load response as a power generation device.

Therefore, the first object of the present invention is to separate fuel electrode exhaust gas into a carbon dioxide-enriched gas stream and a hydrogen-enriched fuel gas stream using a simple membrane separation device whose working mechanism is only a pressure difference in a fuel cell power generation device. The second purpose is to improve the utilization rate of fuel energy for power generation by separating the latter into two flows and using the latter as fuel electrode raw material gas.The second purpose is to improve the utilization rate of fuel energy for power generation. The purpose is to reduce changes in hydrogen concentration, and the third purpose is to increase the gas flow rate at the exit of the fuel cell main body, thereby making it possible to improve the uniformity of temperature distribution, etc. in the fuel cell main body.

Conventionally, in a membrane separation device, it has been difficult to separate hydrogen, which is the fuel, and carbon dioxide, which is the main impurity, in the fuel cell body because both are highly permeable gases.

However, as a result of intensive research, the inventors of the present invention discovered that it is possible to separate carbon dioxide gas from fuel electrode exhaust gas using a membrane separation device, and recover and use the hydrogen-containing gas as hydrogen-enriched fuel gas. It is something. In other words, even if the hydrogen concentration of the supplied fuel gas and therefore the partial pressure of hydrogen introduced into the fuel electrode decreases by mixing the hydrogen-enriched fuel gas obtained from the membrane separation device with the converted gas, the power generation efficiency will decrease due to this. It was found that the improvement in fuel utilization rate by reusing hydrogen-enriched fuel gas greatly exceeds this, and as a result, the overall efficiency of the fuel cell power generation device increases.Based on this, the present invention was developed. This is the completed version.

[Structure of the Invention] The fuel cell power generation device of the present invention that achieves the above object is a device that obtains electric power by supplying hydrogen-containing gas obtained by converting fuel by steam reforming and air to a fuel cell. In the fuel cell power generation device, the fuel electrode exhaust gas is collected from the fuel cell main body, carbon dioxide gas is removed, and the fuel electrode exhaust gas is again supplied to the fuel cell main body as fuel for the fuel cell. The hydrogen-enriched fuel gas is introduced into a fuel cell to be separated into a carbon dioxide-enriched gas and a hydrogen-enriched fuel gas, and the hydrogen-enriched fuel gas is mixed with a converted gas and supplied to the fuel cell main body as a fuel for the fuel cell.

Here, the gas separation membrane used in the membrane separation device should have better hydrogen and carbon dioxide separation performance.In general, the index showing this separation performance is the permeability coefficient of high permeability gas and the permeability coefficient of low permeability gas. It is expressed as a ratio of transmission coefficients. The larger the permeability coefficient ratio is, the more preferable it is, and in principle, the permeability coefficient ratio is infinite in a hydrogen permeable metal thin film such as a special palladium alloy film.

On the other hand, hydrogen and carbon dioxide gas are highly permeable gases in the membrane used for boat fishing, and their permeability coefficient ratio is small, generally 1.4~
It is about 5. Therefore, membrane separation is not used as a method for separating hydrogen and carbon dioxide gas. In the present invention, due to the characteristics of the fuel cell power generation device, we have found that the fuel utilization rate can be greatly improved by using these membranes, and the lower limit of the permeability coefficient ratio is about 2, preferably 3 or more. For example, an inorganic porous membrane having pores with a pore diameter of 20 to 2000 pores, preferably 40 to 490 pores;
Specifically, organic polymer membranes with a hydrogen to carbon dioxide permeability coefficient ratio of 2 or more, such as porous glass membranes, porous alumina membranes, porous zirconia membranes, porous titania membranes, etc., specifically silicone thin membranes, polyimide membranes. , cellulose acetate membrane, polysulfone membrane, etc. In addition, the aforementioned hydrogen-permeable metal thin film can also be used.

[Function] In the fuel cell power generation device according to the present invention, the fuel electrode exhaust gas generated from the fuel cell main body is introduced into the membrane separation device,
The hydrogen/carbon dioxide gas separation membrane separates the fuel gas into two streams: hydrogen-enriched fuel gas and carbon dioxide-enriched gas. The hydrogen-enriched fuel gas is mixed with the conversion gas from the carbon oxide shift converter (shift converter) and recycled as fuel electrode supply gas.

The hydrogen gas concentration of the hydrogen-enriched fuel gas can be enriched to about 40 to 0% by volume by selecting an appropriate hydrogen/carbon dioxide separation membrane. By mixing this into the conversion gas, the hydrogen concentration in the fuel gas decreases to about 60-75% by volume, but the decrease in power generation efficiency due to the decrease in the partial pressure of hydrogen in the fuel gas within the fuel cell body is minimal. As shown in Figure 1, it is faint. Therefore, the increase in fuel utilization rate due to the hydrogen-enriched use of fuel electrode exhaust gas greatly exceeds the decrease in power generation efficiency, and the fuel utilization rate reaches approximately 90%.

In addition, the hydrogen concentration of hydrogen-enriched fuel gas is 40 to 70% by volume.
The impurity carbon dioxide dilutes the excess hydrogen gas concentration in the fuel electrode supply gas, making the distribution of hydrogen partial pressure within the fuel cell body more uniform, and increasing the gas flow rate at the outlet of the fuel cell body. The operation of the battery power generator becomes stable.

Furthermore, since the carbon dioxide enriched gas usually contains 20 to 30% by volume of hydrogen and a small amount of methane, it can be used as a heat source for a steam reforming reactor if necessary.

In the present invention, when using a pressurized type fuel cell 3, it is not necessary, but when using an ordinary pressure type, there is a pressure l
It is preferable to provide an i1 machine, that is, when the fuel cell main body is a pressurized type, the hydrogen-enriched fuel gas is recovered by membrane separation using the fuel electrode exhaust gas pressure as the working power, and then,
By pressurizing the gas and mixing it into the fuel electrode supply gas, it is possible to omit or downsize the pressure device. In this case, although it is possible to dispense with the compressor for supplying gas to the membrane separation device, it is preferable to provide a compressor for mixing hydrogen-enriched fuel gas.

Note that the steam reforming reactor used in the present invention may be an internally heated reformer or an externally heated reformer, and pressurized air may be used as the oxygen electrode air. Furthermore, it is also possible to perform heat exchange within any system of the present invention, or to apply known fuel cell power generation device technology (for example, see Japanese Patent Publication No. 38828/1983).

[Example] The present invention will be described in detail below with reference to FIG. 2 through examples, but the present invention is not limited to these examples in any way.

Embodiment l Fuel such as naphtha is supplied to the supply pipe 10 along with steam (steam).
1, the gas is introduced into a steam reforming reactor, where it is reformed into a mixed reformed gas of carbon monoxide, carbon dioxide gas, water, and methane containing hydrogen as its main component. converter) 2. - In the carbon oxide shift converter 2, the shift reaction between carbon monoxide and water converts the -carbon oxide concentration to 1% by volume or less, and increases the hydrogen concentration. An example of its composition is a hydrogen concentration of approximately 75% by volume on a dry basis.
, a carbon dioxide concentration of 22 to 25% by volume, a -carbon oxide concentration of 1% by volume or less, and a methane concentration of 2% by volume or less. The converted gas passes through a line 103 and is mixed with a hydrogen-enriched fuel gas whose hydrogen concentration has been enriched in a membrane separator 7, which will be described later, and passes through a fuel cell fuel introduction line 104 to the fuel electrode 31 of the fuel cell main body 3. be introduced.

As an example of the composition of the introduced gas, in the case of compression@5 pressure or 4.5 kg/cm''G as described later, on a dry basis, the hydrogen concentration is 71 to 73% by volume, the carbon dioxide concentration is 25 to 27% by volume, - Carbon oxide concentration 1% by volume or less, methane concentration 2% by volume
It is as follows.

Air is introduced into the air electrode 32 of the fuel cell main body 3 through the introduction line 109, and the fuel gas and air react electrochemically in the fuel cell main body 3, and the chemical energy is directly converted into electrical energy and is converted into direct current. Generated electricity. This DC current is outputted as electric power through a power converter 4.

Fuel electrode exhaust gas is compressed by compressor 5 to a pressure of 1 to 50 Kg/cm''G.
5 After the pressure is increased to preferably 1 to 10 Kg/crn'G, the heat is recovered by a heat exchanger 6. An example of m composition of this fuel electrode exhaust gas is that the pressure 1i1115 is 4.5Kg/cm.
Examples of 'G' include hydrogen concentration of 33 to 37% by volume, carbon dioxide concentration of 58 to 65% by volume, -carbon oxide concentration of 2% by volume or less, and methane concentration of 4% by volume or less. This compressed fuel electrode exhaust gas is heated to a temperature of 120°C or higher using the Cerabel alumina membrane, an inorganic porous membrane made of alumina (pore size 40-40).
Hydrogen enriched fuel gas 106 and carbon dioxide enriched gas 10
7 into two streams. The pressure of the compression a5 is 4
．． For example, in the case of 5 Kg/ctfG, the former composition has a hydrogen concentration of about 45% by volume, a carbon dioxide concentration of about 54% by volume, and a carbon oxide and methane concentration of 1% by volume or less, and the line 106 is used as a hydrogen-enriched fuel gas. The gas is mixed with the conversion gas in line 103 and reused as fuel electrode supply gas. Similarly, the latter composition example has a hydrogen concentration of about 25% by volume and a carbon dioxide concentration of 7.
0 to 75% by volume, - carbon oxide concentration of 2% by volume or less, methane concentration of 1 to 6% by volume, mixed with fuel oil such as naphtha or kerosene through line 107, and used as a heat source for steam reforming reactor 1. be done.

By introducing this membrane separation device 7, the fuel utilization rate has been reduced to 89% compared to the 80% of a normal fuel cell power generation device.
% and an improvement of approximately 10%.

On the other hand, as shown in Figure 1, the decrease in output voltage due to a decrease in the partial pressure of hydrogen in the fuel gas in the fuel cell body has little dependence on the hydrogen partial pressure, and the hydrogen partial pressure decreases from 75% to 65%. However, the effect on the output voltage is less than 5 mV. That is, the decrease in efficiency due to the decrease in output voltage due to this decrease in partial pressure is less than 1%, and the improvement in the hydrogen utilization rate greatly exceeds this.

Similar results were also obtained using a membrane separation device incorporating a Vycor glass porous membrane (pore diameter: 40 to 400 pores) instead of the alumina inorganic porous membrane.

Example 2 The gas membrane separation device of Example 1 was changed only in that a polyimide-based organic polymer non-porous membrane manufactured by Ube Industries, Ltd. was used instead of an inorganic porous membrane as the separation membrane. This polyimide-based organic polymer non-porous membrane has a high hydrogen/carbon dioxide gas permeability coefficient ratio, and the pressure of the gas supplied to the membrane separator is approximately 5 Kg/c.
In the case of GoG, the hydrogen concentration of the hydrogen-enriched fuel gas in line 106 is about 56% by volume, the carbon dioxide concentration of the carbon dioxide-enriched gas in line 107 is about 80% by volume, and the fuel utilization rate is about 9%.
2%, which is an improvement of about 15% compared to a normal fuel cell power generation device.

Example 3 The gas membrane separation device of Example 1 was changed only in that a silicone-based organic polymer membrane manufactured by Asahi Glass Co., Ltd. was used instead of an inorganic porous membrane as the separation membrane. The feature of this silicone-based organic polymer membrane is that the permeation rate of carbon dioxide gas is higher than the permeation rate of hydrogen, and since the hydrogen-enriched fuel gas is recovered as a non-permeable gas, there is no pressure loss in the membrane. In a membrane separator using this membrane, when the pressure of the gas supplied to the membrane separator is about 3 g/cm''G, hydrogen enrichment with a hydrogen concentration of about 40% by volume is obtained from the fuel electrode exhaust gas with a hydrogen concentration of about 27%. The fuel gas can be recovered and carbon dioxide can be removed as carbon dioxide enriched gas with a carbon dioxide concentration of about 75 to 77% by volume, and the overall hydrogen utilization rate of the fuel cell power generation device is about 90%.

[Effects of the Invention] The fuel cell power generation device according to the present invention separates fuel electrode exhaust gas into two flows, hydrogen-enriched fuel gas and carbon dioxide-enriched gas, using a membrane separation device, and reuses the hydrogen-enriched fuel gas as fuel. Since the gas is recycled to the electrode supply gas, the fuel usage rate is greatly improved. Furthermore, the moderate carbon dioxide gas dispersion effect equalizes the gas flow rate and temperature distribution within the fuel cell body, resulting in a remarkable effect on stabilizing the fuel cell operation. Furthermore, the use of a membrane separation device has the advantage of being simpler in operation and maintenance than conventional carbon dioxide removal devices.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between hydrogen partial pressure and output voltage at a constant output current at the fuel electrode, and FIG. 2 is a flow scheme showing an embodiment of the present invention. 1...Steam reforming reactor 2...-carbon oxide shift converter 3...Fuel cell main body 4...Power converter 5...Compressor 6...Heat exchanger 7...Membrane Separation device 31... fuel electrode (hydrogen electrode) 32... air electrode (oxygen electrode) 33... electrolytic layer 101... fuel or its line 102... reformed gas or its line 103... Conversion gas or its line 104...Fuel electrode supply gas or its line 105...
-Fuel electrode exhaust gas or its line 106...Hydrogen enriched fuel gas or its line 107-...Carbon dioxide enriched gas or its line 108...Steam reforming reactor fuel 109...Oxygen electrode air 111... ...Fuel cell DC current 112...Output power

Claims (1)

[Claims] A device for generating electricity by supplying hydrogen-containing gas and air obtained by converting fuel by steam reforming to a fuel cell, which collects fuel electrode exhaust gas from the fuel cell body and removes carbon dioxide gas, In a fuel cell power generation device that supplies the fuel cell main body as fuel for the fuel cell again, the fuel electrode exhaust gas from the fuel cell main body is introduced into a membrane separation device and separated into carbon dioxide enriched gas and hydrogen enriched fuel gas. , A fuel cell power generation device characterized in that the hydrogen-enriched fuel gas is mixed with a conversion gas and supplied to the fuel cell main body as a fuel for the fuel cell.