JP2002175828A - Fuel-reforming system for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize carbon monoxide selection oxidation reaction equipment, which is equipped in a fuel-reforming system for a fuel cell, and a improve energy efficiency of the fuel reforming system. SOLUTION: In the fuel-reforming system for fuel cell, a reforming device (6) generates a reformed gas from hydrocarbon system fuel, water, and air, and the fuel cell (10) generates electricity using the reformed gas, exhausted reformed gas from the fuel cell (10) is burned using a burner (11), and the reforming device (6) is heated by this combustion gas. Since the hydrocarbon system fuel, other than methanol, water, and air are introduced into the above reforming device, and further both hydrogen and methane generate rich reform gas by a steam reform reaction or combined using of the steam reforming reaction and a partial oxidation reaction, carbon monoxide selection oxidation reaction equipment (8) can have a simple composition, similar to the reforming system using methanol. Thus, the energy efficiency of the system can be improved, without causing the output of the fuel cell to be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in a fuel reforming system for a fuel cell.

[0002]

2. Description of the Related Art As a fuel reforming system for generating a hydrogen-rich reformed gas by using a hydrocarbon-based fuel other than methanol as a fuel, a technology of a gasoline reformed fuel cell vehicle issued by the Petroleum Industry Activation Center Investigation Report on Development Trends and Issues "found on page 43 (see Figure 5), which removes carbon monoxide in hydrogen-rich reformed gas generated in the reformer. High temperature shift reactor (HTS), low temperature shift reactor (LTS), carbon monoxide selective oxidation reactor (shown as CO removal in the figure) and heat exchangers for controlling the temperature of these reactors It is composed of

[0003]

However, in these conventional systems, the reformer is usually operated at 800 ° C. or higher, and even at a low temperature of about 700 ° C., the carbon monoxide concentration in the reformed gas increases, There is a problem that the carbon monoxide selective oxidation reactor becomes very large. Also, it is necessary to introduce a large amount of water into the reformer in order to avoid coking which is a problem in operation at high temperatures, and introduce water that does not contribute to such a reforming reaction into the reformer, and heat, There is also a problem that the energy efficiency of the system is significantly reduced due to the necessity of cooling.

Accordingly, an object of the present invention is to provide a fuel reforming system for a fuel cell which solves such a problem.

[0005]

According to a first aspect of the present invention, a reformer generates a reformed gas from a hydrocarbon-based fuel, water and air, and a fuel cell uses the reformed gas to generate electric power and generate a combustion gas. In the fuel reforming system for a fuel cell in which the reformed gas discharged from the fuel cell is burned using the reformer and the reformed gas is heated by the combustion gas, a hydrocarbon-based fuel other than methanol and water are supplied to the reformer. Air is introduced, and both hydrogen and methane generate a reformed gas rich in steam by a steam reforming reaction or a combination of a steam reforming reaction and a partial oxidation reaction.

A second invention is characterized in that, in the first invention, a temperature range in which the reformed gas is generated is set to a low temperature range of about 500 ° C.

According to a third aspect, in the first or second aspect, the flow rate of at least one of hydrocarbon fuel other than methanol, water and air supplied to the reformer is adjusted,
Control the methane content in the reformed gas.

In a fourth aspect based on the first or second aspect, the introduction flow rate of the combustion gas for heating the reformer is controlled.

In a fifth aspect based on the first aspect, a hydrocarbon-based fuel other than methanol is supplied to the combustion gas for heating the combustor.

[0010]

According to the first and second aspects of the present invention, a reforming reaction is performed in a low temperature range of about 500 ° C. using a hydrocarbon fuel other than methanol. In such a low-temperature reforming reaction, the formation of carbon monoxide in the reformer can be suppressed, and the amount of introduced air for causing the reformer to self-generate heat in the partial oxidation reaction and water not involved in the reaction. Therefore, the selective oxidation reactor for carbon monoxide can be as simple as a reforming system using methanol, and the energy efficiency of the system can be improved without lowering the output of the fuel cell. be able to.

In the third aspect of the invention, the flow rate of at least one of the hydrocarbon fuel other than methanol, water and air supplied to the reformer is controlled, so that the methane contained in the exhaust reformed gas of the fuel cell is controlled. The content, that is, the calorific value supplied by the reformer can be adjusted, and the energy efficiency of the system can be improved without lowering the output of the fuel cell.

According to the fourth aspect of the present invention, since the flow rate of the combustion gas introduced into the reformer is directly controlled, the temperature of the reformer can be changed quickly, and the responsiveness of the system is improved. Can be.

According to the fifth aspect of the present invention, since a hydrocarbon-based fuel other than methanol is also supplied to the combustor in addition to the exhaust reformed gas, the calorific value of the combustion gas is changed to adjust the reaction temperature of the reformer. , A predetermined reforming rate can be secured.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an overall configuration diagram of a fuel reforming system to which the present invention is applied.

From the water tank 1 and the fuel tank 2 to the pump 3,
The hydrocarbon fuel excluding water and methanol supplied to the combustor 5 via the heater 4 is heated in the combustor 5, vaporized and mixed, and supplied to the reformer 6. In the reformer 6, the mixed gas of water and fuel is reformed into hydrogen and methane-rich reformed gas by a low-temperature reforming reaction at a temperature of about 500 ° C., which will be described later. Is required, the flow control valve 13 is opened and air is supplied to the reformer 6 if necessary.
To promote the partial oxidation reaction.

The reformed gas generated in the reformer 6 is cooled to a predetermined temperature in a heat exchanger 7 and sent to a carbon monoxide selective oxidation reactor (hereinafter referred to as a CO reactor) 8, and at the same time, a flow rate is controlled. Under a small amount of air introduced into the CO reactor 8 through the regulating valve 14, carbon monoxide in the reformed gas is selectively oxidized to be converted into carbon dioxide, and the carbon monoxide in the reformed gas is converted into carbon dioxide. Decrease concentration.

The reformed gas from which carbon monoxide has been removed is introduced into a heat exchanger 9 and cooled to a predetermined temperature.
0 is supplied to the anode electrode. On the other hand, air is supplied from an air supply source (not shown) to the cathode of the fuel cell 10, and the reformed gas and air are used for power generation.

The exhaust reformed gas at the anode contains methane and hydrogen not consumed by the power generation in the fuel cell 10, and the exhaust reformed gas is supplied to the combustor 11 and burned.
The combustion gas from the combustor 11 is introduced into the reformer 6, and the amount of heat is used for the reforming reaction. Further, the combustion gas discharged from the reformer 6 is supplied to the evaporator 5, used as heat for vaporizing water and fuel, and then released to the atmosphere.

The fuel reforming system uses a temperature detector (not shown) for detecting a reforming reaction temperature and a combustible gas concentration detector 12 installed at the outlet of the exhaust reformed gas at the anode of the fuel cell 10. , The reforming reaction temperature and the flammable gas concentration are detected, and when the detected values are not within a predetermined range, the flow rate of water or air supplied to the reformer 6 is changed to change the methane amount in the reformed gas. Is controlled within a certain range. This allows
In order to operate the fuel reforming system independently, it is possible to secure a sufficient amount of methane to supply the heat required for the reforming.

Next, the operation will be described with reference to FIG.

FIG. 2 shows the temperature dependence of the composition of the reformed gas. At a reaction temperature of 750 ° C., the carbon monoxide concentration accounts for nearly 20% of the components excluding water and nitrogen. But 5
It can be seen that at about 00 ° C., the concentration drops to 5% or less. That is, by performing the reforming reaction in the low-temperature reforming region of about 500 ° C. as in the present embodiment, generation of carbon monoxide can be suppressed, and the influence of coking in the reformer 6 is extremely small. Since the flow rate of water that does not contribute to the reforming reaction can be reduced, the energy efficiency can be improved, and the CO reactor 8 can be formed in the same size as when methanol is reformed.

Further, the energy efficiency can be further improved as compared with the case of reforming at a high temperature of about 750 ° C.
When the reforming reaction is carried out at a temperature of about 500 ° C., methane which is hardly produced by the reforming reaction at a high temperature is generated together with hydrogen, and both hydrogen and methane become rich reformed gas. Is not poisoned by methane and is not consumed by the fuel cell 10, so methane is discharged from the fuel cell 10 as it is.
Therefore, the calorific value of the exhaust reformed gas can be made sufficiently large by the calorific value of methane, and the heat of combustion of the exhaust reformed gas can cover the heat required for the reformer 6, the evaporator 5, and the like. For this reason, the flow rate of the air introduced for the heat supply of the reformer 6 can be reduced as much as possible, and the rate of the steam reforming reaction can be increased.

Here, in a conventional reforming reaction in a high temperature region using both a partial oxidation reaction and a steam reforming reaction, the flow rate of air supplied to the reformer is large. Then, the reformed gas is diluted, and the hydrogen concentration decreases. On the other hand, in the reforming in a low-temperature region using a hydrocarbon-based fuel other than methanol according to the present invention, the amount of methane generated increases, so that the hydrogen concentration in the reformed gas decreases similarly to the reforming in a high-temperature region. The same hydrogen concentration can be ensured as compared with the high-temperature reforming, the output of the fuel cell 10 does not decrease, and the energy efficiency is improved by using the calorific value of methane instead of nitrogen.

Further, the reforming reaction temperature and the exhaust reformed gas concentration are detected, and if these detected values are not within the predetermined ranges, the reformer 6
The amount of methane in the reformed gas is controlled within a certain range by changing the flow rate of the water or the flow rate of the air supplied to the fuel cell. As a result, in order to make the fuel reforming system operate independently, it is possible to secure a sufficient amount of methane necessary to supply the heat required for reforming.

FIG. 3 shows a second embodiment.
This has a function of adjusting the flow rate of the combustion gas supplied to the reformer 6 in addition to the configuration of the first embodiment.

In the first embodiment, the amount of methane in the reformed gas is adjusted by changing the flow rates of water and air supplied to the reformer 6. In this case, the flow rates of water and air are changed. After that, the reforming temperature changes with a delay, and the demand for quick response of the system cannot be met.

Therefore, in this embodiment, in addition to the configuration of the first embodiment, a flow control valve 15 capable of adjusting the flow rate of the combustion gas from the combustor 11 to the reformer 6 is provided. The temperature of the reformer 6 is adjusted by adjusting the flow rate of the combustion gas without having to adjust the flow rate of the air and the air. Therefore, in addition to the operation of the first embodiment, the direct reformer 6
Can be adjusted, and the responsiveness of the system can be greatly improved.

Next, a third embodiment shown in FIG. 4 will be described. In the present embodiment, a function of supplying fuel to the combustor 11 is added to the configuration of the first embodiment.

In this embodiment, when the reforming reaction temperature of the reformer 6 is low and the reforming rate is low, fuel is supplied from the fuel tank 2 to the combustor 11 to increase the temperature of the combustion gas. The higher temperature combustion gas is supplied to the reformer 6 to raise the reforming reaction temperature of the reformer 6 to secure a predetermined reforming rate. Therefore, even when the reforming rate of the system is low and the hydrogen concentration in the reformed gas is low, a predetermined reforming rate, that is, a hydrogen concentration can be secured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing the overall configuration of the present invention.

FIG. 2 is a diagram showing the temperature dependence of a composition component in a reformed gas.

FIG. 3 is a configuration diagram illustrating an overall configuration of a second embodiment.

FIG. 4 is a configuration diagram illustrating an overall configuration of a third embodiment.

FIG. 5 is a configuration diagram showing a configuration of a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Water tank 2 Fuel tank 3 Pump 4 Pump 5 Evaporator 6 Reformer 7 Heat exchanger 8 Carbon monoxide selective oxidation reactor 9 Heat exchanger 10 Fuel cell 11 Combustor 12 Combustible gas concentration detector 13 Flow control valve 14 Flow control valve

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takashi Aoyama 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture Inside Nissan Motor Co., Ltd. (72) Inventor Hiroshi Komatsu 2 Takaracho, Kanagawa-ku, Yokohama City, Kanagawa Prefecture Nissan Motor Co., Ltd. Terms (reference) 4G040 EA03 EA06 EB03 EB43 4G140 EA03 EA06 EB03 EB43 5H027 AA02 BA09 BA17 KK21 KK31 KK42 MM12 MM13 MM14

Claims (5)

[Claims] 1. A reformer generates a reformed gas from a hydrocarbon fuel, water, and air, a fuel cell generates power using the reformed gas, and a fuel cell is discharged from the fuel cell using a combustor. In a fuel reforming system for a fuel cell, which burns a reformate gas and heats a reformer with the combustion gas, a hydrocarbon-based fuel other than methanol, water and air are introduced into the reformer, and a steam reforming reaction or A fuel reforming system for a fuel cell, wherein both hydrogen and methane generate a reformed gas rich by a combination of a steam reforming reaction and a partial oxidation reaction. 2. A temperature range in which a reformed gas is generated is 500 ° C.
The temperature is set in a low temperature range of about 1 degree.
3. The fuel reforming system for a fuel cell according to 1. 3. The methane content in the reformed gas is controlled by adjusting the flow rate of at least one of hydrocarbon fuel other than methanol, water and air supplied to the reformer. The fuel reforming system for a fuel cell according to claim 1. 4. The fuel reforming system for a fuel cell according to claim 1, wherein the flow rate of the combustion gas for heating the reformer is controlled. 5. The fuel reforming system for a fuel cell according to claim 1, wherein a hydrocarbon-based fuel other than methanol is supplied to the combustion gas for heating the combustor.