JP3969976B2 - Fuel reforming system and fuel cell system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel reforming system using a solid electrolyte membrane, and is particularly suitable for use as a reforming system in the previous stage of a fuel cell system, which produces hydrogen from fuel such as methane with high efficiency and simultaneously generates power. The present invention relates to a fuel reforming system that is capable of operating.
[0002]
[Prior art]
In a fuel cell system, how to supply hydrogen, which is a main fuel to be sent to the fuel cell body, is an important problem. It is not practical to use hydrogen gas as a raw material for a fuel cell system as it is because the operation cost of the system is enormous, and 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, methanol or the like as a raw material. A specific example of a chemical reaction apparatus for reforming known so far is shown in FIG.
[0003]
In order to produce hydrogen from fuel, there is a method of reforming by a partial oxidation method as shown in FIG. In this method, methane and air are circulated through the reforming catalyst 21 and burned, thereby causing a partial oxidation reaction to proceed to obtain hydrogen H ₂ and carbon monoxide CO. However, in this method, nitrogen N ₂ in the air also circulates on the catalyst and flows as it is to the downstream, so that the reformed gas mainly contains nitrogen gas. Therefore, in this method, the reforming efficiency is deteriorated. On the other hand, 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.
[0004]
Further, there is a method of reforming by a steam reforming method as shown in FIG. In this method, methane and water are passed through the reforming catalyst 21 such as Ni and burned at a high temperature, whereby the steam reforming reaction is advanced to obtain hydrogen and carbon monoxide.
However, in order to perform this reforming method, it is necessary to raise the temperature of the fuel to about 1000 ° C., and the size of the apparatus increases with temperature control, and a catalyst and a corrosion-resistant metal are required. was there. Further, the hydrogen content of the produced reformed gas is usually about 50 to 60%, which is not yet a sufficient level as the fuel gas for the fuel cell. Furthermore, in a system in which the fuel is heated to a high temperature using a heat heater or the like, the operation cost is high and it is not realistic, and it is difficult to effectively use the heat energy generated in the system, which is not an efficient method.
[0005]
[Problems to be solved by the invention]
In view of the above problems, the present inventors have a high concentration reformed gas that is a fuel for fuel cells with less energy loss of the reforming system compared to reforming catalyst devices in the steam reforming method and the partial oxidation method. At the same time, we have intensively studied to develop a fuel reforming method that can improve power generation efficiency.
As a result, the present inventors use the reformer having a solid electrolyte membrane and effectively utilize the heat energy generated in the system to increase the temperature of the introduced fuel gas. Has been found to be resolved. In the present invention, a part of the reformed gas generated by the reformer is used for combustion for increasing the temperature of the fuel, so that the generated thermal energy is effectively used to achieve extremely efficient and continuous. The reformed gas can be generated. In addition, when fuel reforming is performed using this system, power generation efficiency can be greatly improved because power can be generated at the front stage of the fuel cell system in which hydrogen and oxygen are supplied to the battery body to extract electricity. . The present invention has been completed from such a viewpoint.
[0006]
[Means for Solving the Problems]
That is, the present invention is a solid electrolyte type modified type in which a reformed gas is generated on the fuel side of a solid electrolyte membrane by flowing a fuel gas on one side of the solid electrolyte membrane and an oxygen-containing gas on the other side. The combustor and a part of the reformed gas are burned to generate a high-temperature gas, and the heat is transferred from the combustor and the high-temperature gas generated in the combustor to the fuel gas before being introduced into the solid electrolyte reformer. Fuel high temperature heat exchanger and air high temperature heat exchanger that 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 the solid electrolyte type reformer Fuel reformed gas circulation in which part of the reformed gas generated from the gasifier is sent to the combustor and other reformed gas is circulated together with the fuel gas introduced from the outside and supplied to the solid oxide reformer again. And a fuel reforming system characterized by comprising: It is intended to provide.
In the combustor, a part of the reformed gas is introduced and an oxygen-containing gas is introduced and fueled. At this time, it is preferable from the viewpoint of the efficiency of the entire system to use the oxygen-containing gas discharged from the reformer cooled by the high-temperature air heat exchanger .
[0007]
Here, when the reformed gas is obtained as a hydrogen-containing product, the reformed gas discharged from the solid oxide reformer is further converted into fuel gas in the preceding stage of the fuel high-temperature heat exchanger in addition to the above system. It is preferable to include a fuel regeneration heat exchanger that transfers thermal energy. As a result, when the reformed gas is taken out from the fuel reformed gas circulation line as a product, the temperature of the taken out reformed gas can be sufficiently cooled, and the thermal energy at that time can be replaced with new fuel gas. In addition, it can be used to increase the temperature of the fuel reformed gas whose temperature has decreased. When using the high-temperature reformed gas as it is, for example, when using the fuel reforming system connected to the fuel cell system, it is not necessary to incorporate such a fuel regeneration heat exchanger in the system. It is preferable that the reformed gas is allowed to flow down to the subsequent fuel cell main body.
In the present invention, further addition to the system, from the hot gas discharged from the fuel high-temperature heat exchanger, to heat transfer to the air-containing gas before stream comprising a high temperature in high-temperature air heat exchanger, an air low-temperature heat exchanger Can be included. Similarly, in addition, a condenser for condensing and removing moisture in the reformed gas may be included in a stage before taking out the reformed gas from the fuel reformed gas circulation line.
[0008]
The present invention also provides a fuel cell system for supplying a fuel cell main body after reforming the fuel gas into a hydrogen-containing gas, wherein the fuel gas is reformed using any one of the fuel reforming systems described above. It is another object of the present invention to provide a fuel cell system characterized in that after the hydrogen-containing gas is used, the hydrogen-containing gas is introduced from the hydrogen gas supply unit of the solid polymer membrane fuel cell main body to generate power.
Since the solid electrolyte reformer can generate electric power as the fuel gas is reformed, it can generate electric power in the reforming stage separately from the electric power generated by the fuel cell main body. Therefore, by providing the fuel reforming system in the front stage of the fuel cell main body, two-stage power generation combined with power generation in the fuel cell main body is possible, and the power generation efficiency of the entire fuel cell system is remarkably improved. Can do.
[0009]
Thus, 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 also be generated.
Suitable fuels include gases containing hydrocarbons such as methane, propane and butane, or alcohols such as methanol and ethanol. These are reformed by a solid electrolyte reformer to generate hydrogen gas that serves as a power generation raw material for the fuel cell body.
[0010]
In the present invention, as shown in FIG. 5, by using a solid electrolyte membrane 20, a fuel gas such as methane is circulated on one side and an oxygen-containing gas such as air is circulated on the other side. And oxygen react to obtain hydrogen gas.
That is, the solid electrolyte reformer 1 of the present invention is provided with a solid electrolyte membrane 20, and the membrane 20 needs to be conductive so that ions can easily move.
Examples of the solid electrolyte film 20 include a zirconia film in which 3 to 10 mol% of yttria is added to stabilize crystals. Its feature is that only oxygen ions (O ₂ ⁻ ) are transmitted. In other words, the introduced air is composed of about 80% nitrogen and about 20% oxygen. However, as shown in FIG. 5, nitrogen does not permeate the membrane 20 at all, and only oxygen is permeated as ions. To do. The percentage of oxygen that permeates is determined by the conductivity of the fixed electrolyte membrane 20, and is determined by the effective area of the membrane and the temperature conditions during operation. Lowering the temperature is not preferable because the permeation rate of oxygen ions decreases, and it is usually in the range of about 800 ° C. to 1300 ° C., preferably about 900 to 1100 ° C. The permeated oxygen in the activated state reacts with a fuel such as methane CH ₄ supplied from the fuel side to produce target hydrogen H ₂ . The amount of hydrogen in the resulting reformed gas on the fuel side is usually 60% or more, and a high-concentration hydrogen-containing gas of about 66% is obtained.
[0011]
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 a reformed gas mainly composed of nitrogen gas 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 is circulated. A hydrogen-rich reformed gas that does not contain nitrogen gas can be obtained by causing a combustion reaction between the oxygen that has permeated the membrane and the fuel on the fuel side of the membrane 20.
[0012]
In addition, a partial oxidation reaction (incomplete combustion reaction) and a complete combustion reaction coexist in the combustion reaction between methane CH _{4 as} a fuel and oxygen O ₂ 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 + 6H 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 preferable. For example, if the amount of methane is decreased in accordance with the limited amount of oxygen, a complete combustion reaction occurs, but a large amount of oxygen is required to obtain the same amount of hydrogen compared to the partial oxidation reaction, which is not preferable. Therefore, the partial oxidation reaction is allowed to proceed selectively by always controlling the flow rate of methane so as to be in accordance with the amount of oxygen that permeates.
[0013]
For this reason, 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 takes place on the air side, and oxygen in the air It only has the effect of allowing the minute 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 separates and permeates as oxygen ions. The oxygen ions permeated to the fuel side react with the fuel as active oxygen molecules that have returned to oxygen molecules.
At the same time, the movement of ions occurs in the solid electrolyte membrane 20, so that power generation can be performed by connecting the outside with a line. Current control is performed by increasing or decreasing the amount of oxygen ions that permeate.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments with reference to the accompanying drawings.
Embodiment (Part 1)
FIG. 1 shows an example of a configuration of a fuel reforming system including a solid electrolyte reformer having an electrolyte membrane according to the present embodiment. First, the fuel introduction stage to the fuel reformed gas circulation line will be described.
When fuel such as city gas 13A is introduced into the system line at normal room temperature, it is sent to the fuel recirculation fan 6 and then sent to the fuel regeneration heat exchanger 4 to increase the temperature. From there, it is further sent from * 1 in the figure to the high-temperature fuel heat exchanger 7 where the temperature rises to about 900 to 1200 ° C. This high-temperature fuel is introduced into the solid electrolyte reformer 1 from * 2 in FIG. When the low temperature fuel is introduced into the solid electrolyte reformer 1, the reformer 1 does not operate. Thus, a method of circulating the fuel at a high temperature through the two-stage heat exchanger is effective. In the present invention, the thermal energy generated in the system is effectively used to raise the temperature of the fuel gas (methane or the like) introduced into the reformer 1 having a solid electrolyte membrane (about 1000 ° C.).
[0015]
A part of the reformed gas containing hydrogen and carbon monoxide generated by the solid electrolyte reformer 1 is input to the combustor 2 provided in the downstream, and the other reformed gas is used for fuel regeneration heat exchange. Sent to vessel 4. Here, the ratio of the reformed gas sent to the combustor 2 is not particularly limited as long as it is an amount of gas necessary 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 subjected to moisture removal by the downstream condenser 5. A part of the reformed gas containing hydrogen thus cooled is taken out from the line as a product. The other reformed gas flows again into 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 because the solid electrolyte reformer 1 has a certain limit in the amount of fuel that reacts with oxygen that has permeated through the electrolyte membrane 20, so that the gas once circulated through the reformer 1 can also be circulated again. This is because it is taken out as a high-concentration hydrogen-containing gas that has been reformed at a certain ratio or more.
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 continuous operation is performed with methane fuel, the ratio of the reformed gas taken out is usually about 5 to 30% by volume of the reformed gas flowing.
[0016]
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 introduced into the combustor 2 provided in the downstream and burned, and the heat energy generated in the combustor 2 is used as a heat source for the entire system. The A part of the reformed gas charged into the combustor 2 is combusted together with the exhaust gas on the air side to become high temperature, and then sent to the fuel high temperature heat exchanger 7 to raise the temperature of the fuel gas. Used. Therefore, the ratio of the reformed gas sent to the combustor 2 is usually about 1 to 10% by volume, preferably about 4 to 8% by volume of the gas generated from the reformer 1. The gas discharged from the combustor 2 is further sent to the air low-temperature heat exchanger 8 where it is used to raise the temperature of normal temperature air and then released from the exhaust facility 9 into the atmosphere.
[0017]
Next, supply of oxygen-containing gas such as air sent to the solid electrolyte reformer 1 will be described.
In the present embodiment, similarly to the fuel gas, air having a high temperature of about 800 ° C. to 1300 ° C., preferably 900 to 1100 ° C. is introduced into the reformer 1 having the solid electrolyte membrane 20. Therefore, heat 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 heated by the air low-temperature heat exchanger 8 using waste heat. Next, the high temperature gas is introduced into the air high temperature heat exchanger 3 to obtain a high temperature gas of about 800 ° C. or higher and 1300 ° C. or lower, and then introduced into the reformer 1. In the reformer 1, a part of oxygen content, for example, 0.01 to 50% by volume permeates through the membrane and is used for the reforming reaction, and the entire nitrogen content and the remaining oxygen content are exhausted from the reformer 1. Is done. These are introduced into the combustor 2 after being cooled by the air high temperature heat exchanger 3.
[0018]
As described above, in the reforming system of the present invention, it is preferable to cause a partial oxidation reaction. However, if water is generated due to the flow rate adjustment of the fuel gas, the temperature in the apparatus, or the like, the fuel reforming gas circulation In the reformer 1, the produced water reacts with methane and a steam reforming reaction occurs in the reformer 1.
CH ₄ + 3H ₂ O → CO + 3H ₂ + 2H ₂ O
It is not preferable that such reactions occur at the same time because it causes anxiety reduction in the hydrogen content of the reformed gas taken out as a product, and efficient reforming cannot be performed. For this reason, it is preferable to provide a condenser 5 that condenses and removes moisture in the reformed gas before the reformed gas is taken out from the fuel reformed gas circulation line as required in the present embodiment.
[0019]
Further, as the solid electrolyte reformer 1, various types of apparatuses can be used as long as the apparatus has one or more solid electrolyte membranes 20, and are not particularly limited. Alternatively, a general device such as a cylindrical one in the field of fuel cells 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 in the reformer 1 as well, a structure in which two or more solid electrolyte membranes 20 are stacked, or a structure in which the solid electrolyte membranes 20 are connected in parallel, or the like is used. It is also possible to obtain an aspect in which
[0020]
Embodiment (2)
FIG. 2 shows another example of the configuration of the fuel reforming system according to the present 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 transferred to the fuel high temperature heat exchanger 7. send. In this embodiment, the reforming reaction is promoted by circulating the reformed gas in a high-temperature gas state using the fuel recirculation ejector 11. This makes it easier for the solid electrolyte reformer 1 to maintain a higher temperature and facilitates the reforming reaction.
[0021]
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, an air recirculation ejector 12 is provided in the supply line of the oxygen-containing gas, and a part of the oxygen-containing gas immediately after being discharged from the solid electrolyte reformer 1 is again converted into the solid electrolyte reformer. Send to 1. In this embodiment, in addition to the fuel recirculation ejector 11, air is also recirculated as a high-temperature gas to reduce heat loss and increase oxygen utilization efficiency.
[0022]
Embodiment (part 4)
FIG. 4 shows another example of the configuration of the fuel reforming system according to the present embodiment. In addition to the system of the third embodiment (No. 3), an 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 is provided which heat-transfers from a high-temperature gas to water introduced from the outside in the downstream of the combustor 2, and the generated steam is combined with the fuel gas in the fuel reformed gas circulation line. To supply. The timing of charging the steam into the circulation line is not particularly limited, but it is preferable to mix the fuel gas in the previous stage of the fuel regeneration heat exchanger 4 and raise the temperature in the two-stage heat exchanger .
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]
【The invention's effect】
According to the present invention, compared with the steam reforming method and the partial oxidation method in which fuel is circulated through the reforming catalyst, the method using the solid electrolyte membrane of the present invention maintains the hydrogen concentration of the reformed gas to be generated high. can do.
The apparatus can be made more compact than a reformer using a steam reforming method.
Furthermore, when used as part of the fuel cell system, electricity can be generated by taking out electricity from the reforming system, so that the power generation efficiency when the same amount of fuel gas is used is improved.
[Brief description of the 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]
DESCRIPTION OF SYMBOLS 1 Solid electrolyte type reformer 2 Combustor 3 Air high temperature heat exchanger 4 Fuel regeneration heat exchanger 5 Condenser 6 Fuel recirculation fan 7 Fuel high temperature heat exchanger 8 Air low temperature heat exchanger 9 Chimney 10 Air fan 11 Fuel Recirculation ejector 12 Air recirculation ejector 13 Waste heat steam generator 20 Solid electrolyte membrane 21 Reforming catalyst

Claims (8)

A solid electrolyte reformer for generating a reformed gas on the fuel side of the solid electrolyte membrane by flowing a fuel gas on one side of the solid electrolyte membrane and an oxygen-containing gas on the other side;
A combustor for burning a part of the reformed gas to generate a high-temperature gas;
A fuel high-temperature heat exchanger for transferring heat from the high-temperature gas generated in the combustor to the fuel gas before being introduced into the solid electrolyte reformer;
An air high-temperature heat exchanger for transferring heat from a high-temperature oxygen-containing gas discharged from the solid electrolyte reformer to an oxygen-containing gas before being introduced into the reformer;
A part of the reformed gas generated from the solid electrolyte reformer is sent to the combustor, and other reformed gases are circulated together with the fuel gas introduced from the outside, and supplied to the solid electrolyte reformer again. , Fuel reforming gas circulation line,
A fuel reforming system comprising: In addition, it further includes a fuel regeneration heat exchanger that transfers heat from the reformed gas discharged from the solid oxide reformer to the fuel gas upstream of the high-temperature fuel heat exchanger. Item 4. The fuel reforming system according to Item 1. Furthermore, the present invention includes an air low-temperature heat exchanger for transferring heat from a high-temperature gas discharged from the fuel high-temperature heat exchanger to an air-containing gas upstream of the air high-temperature heat exchanger. The fuel reforming system according to 1 or 2.   Furthermore, the condenser which condenses and removes the water | moisture content in reformed gas in the front | former stage which takes out reformed gas from the said fuel reformed gas circulation line is further included in any one of Claims 1-3 characterized by the above-mentioned. Fuel reforming system. A fuel recirculation ejector is provided in the fuel reformed gas circulation line, and a part of the reformed gas generated immediately after the solid oxide reformer is sent to the fuel high temperature heat exchanger. Item 5. The fuel reforming system according to any one of Items 1 to 4.   An oxygen 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 reformer is sent to the solid electrolyte reformer again. The fuel reforming system according to any one of claims 1 to 5.   An exhaust heat steam generator is provided for transferring heat from a high-temperature gas to water introduced from the outside in the downstream of the combustor, and the generated steam is supplied to the fuel reformed gas circulation line together with fuel gas. The fuel reforming system according to any one of claims 1 to 6. A fuel cell system for reforming a fuel gas into a hydrogen-containing gas and supplying the fuel gas to a fuel cell body,
The fuel reforming system according to any one of claims 1 to 7, wherein the fuel gas is reformed to form a hydrogen-containing gas, and then the hydrogen-containing gas is supplied from a hydrogen gas supply unit of the solid polymer membrane fuel cell main body. A fuel cell system for generating power by introducing gas.

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