JP2003034501A - Fuel reforming system and fuel battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel reforming system which can produce hydrogen from a fuel such as methane with a high efficiency and, at the same time, can generate electricity. SOLUTION: This fuel reforming system is characterized in including a solid electrolyte-type reforming device in which reformed gas is produced in a solid electrolyte membrane on its fuel side by allowing fuel gas to flow into one side of the solid electrolyte membrane while allowing oxygen-containing gas to flow into the other side of the solid electrolyte membrane; a combustor for burning a part of the reformed gas to produce high-temp gas; a fuel high- temp heat exchanger for transferring heat from the high-temp gas produced in the combustor to the fuel before introduction into the reforming device; an air high-temp heat exchanger for transferring heat from high-temp oxygen- containing gas discharged from the reforming device to the oxygen-containing gas before introduction into the reforming device; and a reformed fuel gas circulation line for feeding a part of the reformed gas produced in the reforming device to the combustor and for making flow and feeding the remaining reformed gas together with externally introduced fuel gas into the reforming device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel reforming system using a solid electrolyte membrane, and in particular, it is suitably used as a reforming system in the front stage of a fuel cell system, and can efficiently produce hydrogen from a fuel such as methane. The present invention relates to a fuel reforming system that can be manufactured and simultaneously generate power.

[0002]

2. Description of the Related Art In a fuel cell system, how to supply hydrogen, which is a main fuel to be sent to a fuel cell body, is an important issue. It is not realistic to use hydrogen gas as a raw material of the fuel cell system as it is because the operation cost of the system is enormous. Therefore, it is practical to use a reformed gas produced from hydrocarbons. At present, the most promising method is to produce and supply hydrogen by a reformer using methane or methanol as a raw material. FIG. 6 shows a specific example of a chemical reactor for reforming that has been known so far.

To produce hydrogen from fuel, FIG. 6 (a)
As described above, there is a method of reforming by a partial oxidation method.
In this method, methane and air are circulated through the reforming catalyst 21 and burned, thereby promoting a partial oxidation reaction to obtain hydrogen H ₂ and carbon monoxide CO. However, in this method, the nitrogen N ₂ in the air also flows over the catalyst, and flows as it is in the downstream flow, so that the reformed gas mainly contains nitrogen gas. Therefore, although the reforming efficiency is deteriorated by this method, the hydrogen content of the produced reformed gas is usually as low as about 34 to 39%, which is not preferable as the fuel gas for the fuel cell.

There is also a method of reforming by a steam reforming method as shown in FIG. 6 (b). In this method, methane and water are circulated through the reforming catalyst 21 such as Ni and burned at a high temperature to promote a steam reforming reaction to obtain hydrogen and carbon monoxide. However, in order to carry out this reforming method, it is necessary to raise the temperature of the fuel up to about 1000 ° C., and the apparatus becomes large in size due to temperature control and the like, and a catalyst and a corrosion resistant metal are required. was there. In addition, the hydrogen content of the produced reformed gas is usually
It is about 50 to 60%, which is not a sufficient level as a fuel gas for fuel cells. Furthermore, in a system in which the fuel is heated to a high temperature by using a heat heater or the like, the operating cost is high and it is not realistic, and it is difficult to effectively use the thermal energy generated in the system, which is not an efficient method.

[0005]

In view of the above problems, the inventors of the present invention have less energy loss in the reforming system than the reforming catalyst device in the steam reforming method or the partial oxidation method, and can reduce the fuel cell of the fuel cell. The inventors have made earnest studies to develop a fuel reforming method capable of generating a high-concentration reformed gas as a fuel and improving power generation efficiency. As a result, the present inventors have used a reformer having a solid electrolyte membrane and effectively utilize the thermal energy generated in the system,
It has been found that the above problem can be solved by a system in which the temperature of the introduced fuel gas is high. In the present invention, a part of the reformed gas generated by the reformer is used for combustion to raise the temperature of the fuel, so that the generated thermal energy is effectively used, resulting in extremely efficient and continuous operation. The reformed gas can be generated. In addition, if fuel reforming is performed using this system, in a fuel cell system that supplies hydrogen and oxygen to the cell body to take out electricity, power can also be generated in the preceding stage, so power generation efficiency can be greatly improved. . The present invention has been completed from this point of view.

[0006]

That is, according to the present invention, a fuel gas is circulated on one side of a solid electrolyte membrane and an oxygen-containing gas is circulated on the other side of the solid electrolyte membrane to reform on the fuel side of the solid electrolyte membrane. Introduced into the solid electrolyte type reformer from the solid electrolyte type reformer that generates gas and the high temperature gas that burns part of the reformed gas to generate high temperature gas High temperature heat exchange of fuel, which transfers heat to the previous fuel gas, and high temperature heat of air, which transfers heat from the high-temperature oxygen-containing gas discharged from the solid electrolyte reformer to the oxygen-containing gas before introduction into the reformer And a part of the reformed gas generated from the solid electrolyte type reformer is sent to the combustor, the other reformed gas is circulated along with the fuel gas introduced from the outside, and is supplied to the solid electrolyte type reformer again. And a fuel reforming gas circulation line, There is provided a fuel reforming system. In the combustor, a part of the reformed gas is introduced and an oxygen-containing gas is introduced to make it a fuel. At this time, it is preferable to use the oxygen-containing gas discharged from the reformer cooled by the high temperature air heat exchange from the viewpoint of the efficiency of the entire system.

When the reformed gas is obtained as a hydrogen-containing product, in addition to the above system, the fuel is obtained from the reformed gas discharged from the solid electrolyte reformer before the high temperature fuel heat exchange. It is preferred to include refueling heat exchange, which transfers thermal energy to the gas. As a result, when the reformed gas is taken out as a product from the fuel reformed gas circulation line,
The temperature of the reformed gas taken out can be sufficiently cooled, and the thermal energy at that time can be used for increasing the temperature of the fuel reformed gas whose temperature has been lowered by newly adding the fuel gas. When the high-temperature reformed gas is used as it is, for example, when the fuel reforming system is used by connecting to the fuel cell system, it is not necessary to incorporate such fuel regeneration heat exchange into the system, and It is preferable that the reformed gas is allowed to flow down to the fuel cell main body at the subsequent stage. In the present invention, in addition to the above system, a low-temperature air heat exchanger for transferring heat from the high-temperature gas discharged from the high-temperature heat exchanger for fuel to the upstream air-containing gas that becomes high temperature in the high-temperature heat exchanger for air You can Further, similarly, in addition to the above, a condenser for condensing and removing water in the reformed gas can be included in a stage before the reformed gas is taken out from the fuel reformed gas circulation line.

Further, the present invention is a fuel cell system for reforming a fuel gas into a hydrogen-containing gas and supplying it to the fuel cell main body, wherein the fuel gas is reformed by using any one of the above fuel reforming systems. The present invention also provides a fuel cell system characterized in that the hydrogen-containing gas is introduced into the solid polymer membrane fuel cell body from the hydrogen gas supply unit of the solid polymer membrane fuel cell body to generate electricity after the hydrogen-containing gas is qualified. . In the solid electrolyte type reformer, since it is possible to generate power with the reforming of the fuel gas, in addition to the power generated by the fuel cell body,
Power can be generated in the reforming stage. Therefore, by providing the fuel reforming system in the preceding stage of the fuel cell main body, it is possible to generate electric power in two stages including the electric power generation in the fuel cell main body, and remarkably improve the power generation efficiency of the entire fuel cell system. You can

As described above, according to the system of the present invention, the fuel gas of the fuel cell can be produced as the reformed gas containing hydrogen, and electricity can be generated. Suitable fuels include hydrocarbons such as methane, propane and butane, and gases containing alcohols such as methanol and ethanol. These are reformed by a solid electrolyte type reformer to generate hydrogen gas as a power generation raw material of the fuel cell body.

In the present invention, as shown in FIG. 5, a solid electrolyte membrane 20 is used to flow a fuel gas such as methane on one side and an oxygen-containing gas such as air on the other side. , The fuel gas and oxygen react to obtain hydrogen gas. That is, the solid electrolyte reformer 1 of the present invention is provided with the solid electrolyte membrane 20, and the membrane 20 is required to have conductivity so that ions can easily move. Examples of the solid electrolyte membrane 20 include a zirconia membrane in which crystals are stabilized by adding 3 to 10 mol% of yttria. Its features include oxygen ions (O ₂ ^-) is that of transmitting only. In other words, the air introduced is about 80% nitrogen and about 20%
However, as shown in FIG. 5, nitrogen does not permeate through the membrane 20 at all, and only oxygen permeates as ions. The proportion of oxygen that permeates is determined by the conductivity of the fixed electrolyte membrane 20, and during operation is determined by the effective area of the membrane and temperature conditions. When the temperature is lowered, the permeation rate of oxygen ions is decreased, which is not preferable, and is usually about 800 ° C. or higher and 1300 ° C. or lower, preferably about 900 to 1
It is preferably in the range of 100 ° C. The permeated activated oxygen reacts with the fuel such as methane CH ₄ supplied from the fuel side to generate the target hydrogen H ₂ . The amount of hydrogen in the reformed gas on the fuel side obtained is usually 60% or more, and a high-concentration hydrogen-containing gas of about 66% can be obtained.

When air is used as the oxygen-containing gas, most of the nitrogen gas is used. Therefore, if the reaction is performed without using the electrolyte membrane 20, only the reformed gas containing nitrogen gas as the main component can be produced. Therefore, in the present invention, by using the electrolyte membrane 20 in the solid electrolyte reformer 1, only oxygen is selectively permeated to the fuel side through which methane or the like flows. Then, on the fuel side of the membrane 20, the oxygen and the fuel that have permeated the membrane are burned and reacted,
A hydrogen-rich reformed gas containing no nitrogen gas can be obtained.

The combustion reaction of methane CH _{4 as} a fuel and oxygen O ₂ includes a partial oxidation reaction (incomplete combustion reaction) and a complete combustion reaction as follows. 2CH ₄ + O ₂ → 2CO + 4H ₂ (partial oxidation reaction) CH ₄ + 2O ₂ → CO ₂ + 2H ₂ O 〔2CH ₄ + 2H ₂ O → 2CO + 6
H ₂ ] (Complete combustion reaction) Since the solid electrolyte membrane 20 is used in the present invention, the amount of oxygen that permeates is limited as described above, and a reaction that generates as much hydrogen gas as possible from this limited amount of oxygen. Is preferred. For example, if the amount of methane is reduced according to the limited amount of oxygen, a complete combustion reaction occurs, but a large amount of oxygen is required compared with the partial oxidation reaction to obtain the same amount of hydrogen, which is not preferable. Therefore, by always controlling the flow rate of methane to a large amount in accordance with the amount of oxygen that permeates,
The partial oxidation reaction is allowed to proceed selectively.

From the above, in the solid electrolyte reformer 1, one side of the membrane 20 is the fuel side and the other side is the air (oxygen-containing gas) side, but no reaction occurs on the air side and the air It only has a function of allowing the oxygen content in the fuel to permeate to the fuel side at a constant rate. Usually, electrodes are connected to both sides of the electrolyte membrane 20 in the reformer 1, and oxygen is dissociated and permeates as oxygen ions. The oxygen ions that have permeated to the fuel side react with the fuel as active oxygen molecules that have returned to oxygen molecules. At the same time, the solid electrolyte membrane 2
Since the movement of ions occurs within 0, power can be generated by connecting the outside with a wire.
The current control is performed by increasing or decreasing the amount of oxygen ions that permeate.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on embodiments with reference to the accompanying drawings. Embodiment (No. 1) FIG. 1 shows an example of the configuration of a fuel reforming system including a solid electrolyte type reformer having an electrolyte membrane according to the present embodiment. Here, first, the fuel introduction stage to the fuel reformed gas circulation line will be described. When the fuel such as the city gas 13A is normally introduced into the system line at room temperature, it is sent to the fuel recirculation fan 6 and then to the fuel regeneration heat exchanger 4 to rise in temperature. From there, it is further sent to the high temperature fuel heat exchanger 7 from * 1 in the figure, and the temperature rises to about 900 to 1200 ° C. This high-temperature fuel is introduced into the solid electrolyte type reformer 1 from * 2 in FIG. When a low-temperature fuel is introduced into the solid electrolyte reformer 1, the reformer 1 does not operate. Therefore, a method of circulating the fuel at a high temperature through the two-stage heat exchange is effective. In the present invention, the thermal energy generated in the system is effectively utilized to raise the temperature of the fuel gas (methane or the like) introduced into the reformer 1 having the solid electrolyte membrane to a high temperature (about 1000 ° C.).

The reformed gas containing hydrogen and carbon monoxide generated by the solid electrolyte reformer 1 is introduced into the combustor 2 provided in the downstream side, and the other reformed gas is the fuel. It is sent to the regeneration heat exchanger 4. Here, the ratio of the reformed gas sent to the combustor 2 is not particularly limited, and may be the amount of gas required for combustion. For example, the generated reformed gas is usually 1 to 10% by volume, preferably 4 ~ 8% by volume.
The gas cooled by the heat exchange in the fuel regeneration heat exchanger 4 is further moisture-removed by the condenser 5 in the downstream. A part of the reformed gas containing hydrogen thus cooled is
Taken from the line as a product. The other reformed gas is made to flow again in the fuel reformed gas circulation line, and is sent to the fuel recirculation ejector drive fan 6 together with the newly introduced fuel. This is the solid electrolyte reformer 1.
Since the amount of fuel that reacts with oxygen that has permeated the electrolyte membrane 20 has a certain limit, the gas that once circulated in the reformer 1 was reformed at a certain ratio or more by being circulated again. This is because it is taken out as a high-concentration hydrogen-containing gas. Here, the ratio of the reformed gas taken out as a product from the gas line flowing through the system is arbitrarily determined depending on the type of fuel, operating conditions, etc., and is not particularly limited. Specifically, when performing continuous operation with methane fuel, the ratio of the reformed gas taken out is usually about 5 to 30% by volume of the reformed gas flowing.

Next, the reformed gas branched from the fuel reformed gas circulation line and introduced into the combustor 2 will be described.
A part of the reformed gas generated by the solid electrolyte reformer 1 is supplied to the combustor 2 provided in the downstream and is burned,
The thermal energy generated in the combustor 2 is used as a heat source for the entire system. A part of the reformed gas introduced into the combustor 2 is burned together with the exhausted gas on the air side to reach a high temperature and then sent to the high temperature fuel heat exchanger 7 to be used for raising the temperature of the fuel gas. To be done. Therefore, the ratio of the reformed gas sent to the combustor 2 is usually 1 of the gas generated from the reformer 1.
It is about 10 to 10% by volume, preferably about 4 to 8% by volume. The gas discharged from the combustor 2 is further sent to the low temperature air heat exchanger 8 and used to raise the temperature of the air at room temperature, and then discharged from the exhaust equipment 9 into the atmosphere.

Next, the supply of oxygen-containing gas such as air sent to the solid electrolyte reformer 1 will be described. In the present embodiment, similar to the above fuel gas, the reformer 1 having the solid electrolyte membrane 20 is normally provided with a temperature of about 800 ° C. or higher and 1300 ° C. or lower,
Air having a high temperature of 900 to 1100 ° C. is preferably introduced. Therefore, the thermal energy generated in the system is effectively used to transfer heat to the air introduced into the reformer 1 having the solid electrolyte membrane. Specifically, the air introduced from the air fan 10 to the air line in the system is
It is heated by using waste heat in the low temperature air heat exchanger 8. Then, it is introduced into the high temperature air heat exchanger 3, and it is about 800 ° C or higher 13
It is introduced into the reformer 1 after being made into a high temperature gas of 00 ° C. or lower. In the reformer 1, a part of the oxygen content, for example 0.01
About 50% by volume is permeated and used for the reforming reaction, and the entire nitrogen content and the remaining oxygen content are exhausted from the reformer 1. These are introduced into the combustor 2 after being cooled by the high temperature air heat exchanger 3.

As mentioned above, in the reforming system of the present invention, it is preferable to cause a partial oxidation reaction.
When water is generated due to the flow rate adjustment of the fuel gas and the relationship with the temperature in the device, it flows through the fuel reformed gas circulation line, and in the reformer 1, the generated water reacts with methane to perform a steam reforming reaction. Occurs. CH ₄ + 3H ₂ O → CO + 3H ₂ + 2H ₂ O The simultaneous occurrence of such reactions is a factor that reduces the hydrogen content of the reformed gas taken out as a product and makes efficient reforming difficult. It is not preferable because it cannot be performed. For this reason, it is preferable to provide a condenser 5 for condensing and removing water in the reformed gas before the reformed gas is taken out from the fuel reformed gas circulation line as required in this embodiment.

Further, as the solid electrolyte reformer 1, various types of devices can be used as long as they are devices having one or more solid electrolyte membranes 20, and although not particularly limited, for example, a flat plate is used. A device generally used in the field of fuel cells, such as a laminated product or a cylindrical product, can be used. In such a reformer 1, hydrogen is produced by a reforming reaction on or near the membrane, and only oxygen is selectively permeated from the air side. Furthermore, in order to improve the power generation efficiency also in the reformer 1,
A mode in which a certain or more electric power is obtained is also possible by a structure in which two or more solid electrolyte membranes 20 are stacked, a structure in which the solid electrolyte membranes 20 are connected in parallel, or the like.

Embodiment (No. 2) FIG. 2 shows another example of the configuration of the fuel reforming system according to this embodiment. In the present embodiment, a fuel recirculation ejector 11 is provided in the fuel reformed gas circulation line, and a part of the reformed gas immediately after being generated in the solid electrolyte reformer 1 is sent to the high temperature fuel heat exchanger 7. . The present embodiment is a mode in which the reforming reaction is promoted by circulating the reformed gas in the high temperature gas state using the fuel recirculation ejector 11. This makes it easier for the solid electrolyte reformer 1 to maintain the high temperature state, and facilitates the reforming reaction.

Embodiment (Part 3) FIG. 3 shows another example of the configuration of the fuel reforming system according to the present embodiment. In the present embodiment, the air recirculation ejector 12 is provided in the oxygen-containing gas supply line, and a part of the oxygen-containing gas immediately after being discharged from the solid electrolyte type reformer 1 is again supplied to the solid electrolyte type reformer. Send to 1. In this form,
In addition to the fuel recirculation ejector 11, air is also recirculated as a high temperature gas to reduce heat loss and improve oxygen utilization efficiency.

Embodiment (No. 4) FIG. 4 shows another example of the configuration of the fuel reforming system according to this embodiment. In addition to the system of the embodiment (part 3), the exhaust heat steam generator 13 is added to the exhaust gas system, and the generated steam is added to the fuel circulation system to increase the reforming efficiency. In the present embodiment, an exhaust heat steam generator 13 that transfers heat from the high temperature gas to the water introduced from the outside in the wake of the combustor 2 is provided, and the generated steam together with the fuel gas is used as a fuel reformed gas circulation line. Supply to. The timing of introducing the steam into the circulation line is not particularly limited, but it is preferable that the steam is mixed with the fuel gas in the preceding stage of the fuel regeneration heat exchange 4 and the temperature is raised in the two stages of heat exchange. Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and changes can be made without departing from the scope of the present invention. is there.

[0023]

According to the present invention, compared with the steam reforming method or partial oxidation method in which a fuel is passed through a reforming catalyst, according to the method using the solid electrolyte membrane of the present invention, the amount of reformed gas produced is The hydrogen concentration can be maintained high. The apparatus can be made compact as compared with a reformer using a steam reforming method. Further, when used as a part of the fuel cell system, electricity can be taken out from the reforming system to generate electricity, so that power generation efficiency is improved when the same amount of fuel gas is used.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a system according to an embodiment (part 1).

FIG. 2 is a diagram showing a schematic configuration of a system according to an embodiment (part 2).

FIG. 3 is a diagram showing a schematic configuration of a system according to an embodiment (part 3).

FIG. 4 is a diagram showing a schematic configuration of a system according to an embodiment (part 4).

FIG. 5 is a diagram schematically showing the principle of hydrogen generation when a solid electrolyte membrane is used.

FIG. 6 is a diagram schematically showing a reforming reaction using a reforming catalyst.

[Explanation of symbols]

1 Solid electrolyte reformer 2 Combustor 3 Air high temperature heat exchange 4 Fuel Regeneration Heat Exchange 5 condenser 6 Fuel recirculation fan 7 Fuel high temperature heat exchange 8 Air low temperature heat exchange 9 chimney 10 air fans 11 Fuel recirculation ejector 12 Air recirculation ejector 13 Waste heat steam generator 20 Solid electrolyte membrane 21 reforming catalyst

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 4G040 EA03 EA07 EB03 EB13 EB18                       EB44                 5H026 AA06                 5H027 AA06 BA01 BA16

Claims (8)

[Claims] 1. A solid electrolyte type reformer, wherein a fuel gas is circulated to one side of a solid electrolyte membrane and an oxygen-containing gas is circulated to the other side to generate a reformed gas on the fuel side of the solid electrolyte membrane. And a combustor for combusting a part of the reformed gas to generate a high-temperature gas, and a heat from the high-temperature gas generated in the combustor to a fuel gas before being introduced into the solid electrolyte reformer. Moving, high temperature fuel heat exchange, from the high temperature oxygen-containing gas discharged from the solid electrolyte reformer, heat transfer to the oxygen-containing gas before introduction into the reformer, high temperature air heat exchange, A part of the reformed gas generated from the solid electrolyte reformer is sent to the combustor, another reformed gas is circulated together with the fuel gas introduced from the outside, and is supplied to the solid electrolyte reformer again. And a fuel reforming gas circulation line, Fee reforming system. 2. In addition to the above, the fuel cell system further comprises a fuel regeneration heat exchanger for transferring heat from the reformed gas discharged from the solid electrolyte reformer to a fuel gas upstream of the fuel high temperature heat exchanger. The fuel reforming system according to claim 1. 3. In addition, a low-temperature air heat exchanger for transferring heat from the high-temperature gas discharged from the high-temperature fuel heat exchanger to the air-containing gas upstream of the high-temperature heat exchanger for air is further included. The fuel reforming system according to claim 1 or 2. 4. In addition, a condenser for condensing and removing water in the reformed gas is included in a stage before the reformed gas is taken out from the fuel reformed gas circulation line. 5. The fuel reforming system according to any one of 1. 5. A fuel recirculation ejector is provided in the fuel reformed gas circulation line to send a part of the reformed gas generated immediately after the solid electrolyte type reformer to the fuel high temperature heat exchanger. The fuel reforming system according to any one of claims 1 to 4, which is characterized. 6. An air recirculation ejector is provided in the oxygen-containing gas supply line, and a part of the oxygen-containing gas immediately after being discharged from the solid electrolyte type reformer is supplied to the solid electrolyte type reformer again. The fuel reforming system according to any one of claims 1 to 5, wherein the fuel reforming system is sent. 7. An exhaust heat steam generator is provided, which transfers heat from hot gas to water introduced from the outside in the downstream of the combustor, and the generated steam is introduced into the fuel reformed gas circulation line together with fuel gas. It supplies, The fuel reforming system in any one of Claims 1-6 characterized by the above-mentioned. 8. A fuel cell system for reforming a fuel gas into a hydrogen-containing gas and supplying the hydrogen-containing gas to a fuel cell main body, wherein the fuel reforming system according to claim 1 is used. A fuel cell system characterized by reforming a gas into a hydrogen-containing gas, and then introducing the hydrogen-containing gas from a hydrogen gas supply unit of a solid polymer membrane fuel cell body to generate electricity.