JPH0221103B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a fuel cell power generation method and equipment using a fuel cell that uses hydrogen gas produced by steam reforming of raw material gas containing methanol as a fuel and pressurized air as an oxidizing agent. Regarding improvements. More specifically, the present invention relates to the simplification of fuel cell power generation equipment and the effective use of low-temperature waste heat by changing the heat source of steam reforming.

Since fuel cells have high power generation efficiency and almost no pollution problems such as air pollution, they have recently attracted attention as portable and stationary power generation equipment, and research on improving them has been actively conducted. Currently, the systems that are considered to be highly practical as stationary power generation equipment are a reformer that generates hydrogen by steam reforming of raw material gas containing hydrocarbons, methanol, etc., and a reformer that uses this hydrogen as fuel and generates air. It has a fuel cell as an oxidizer and a pressurized air generator. As an electrolyte for fuel cells,
For example, an aqueous phosphoric acid solution is used, and natural gas, naphtha, methanol, petroleum gas, etc. are used as raw material hydrocarbons for reforming, but methanol is more difficult to steam reform at a low temperature than other hydrocarbons. It is attracting attention because it is easy to store and handle because it is liquid at room temperature.

In order for power generation by fuel cells to be economically comparable to power generation by other methods, it is important to thoroughly increase its overall thermal efficiency, and various methods for this purpose have been studied. When using hydrogen gas obtained by steam reforming of hydrocarbons etc. as the fuel gas for a fuel cell, this fuel gas usually contains inert gases such as carbon dioxide and methane, so the battery In order to maintain the partial pressure of hydrogen within the cell at the required level, it is necessary to continuously discharge a portion of the fuel gas supplied to the cell to the outside of the cell. Combustion and utilization of this discharged gas (hereinafter abbreviated as fuel residual gas) as fuel gas for a re-former is generally adopted as a method of increasing the overall thermal efficiency of power generation.

In addition, the efficiency of the fuel cell itself, that is, the ratio of the electrical output of the fuel cell to the effective energy of the hydrogen consumed in the fuel cell, increases as the operating temperature of the fuel cell increases, and the hydrogen content on the fuel electrode (hydrogen electrode) side increases. The higher the pressure, and the higher the oxygen partial pressure on the air electrode (oxygen electrode) side, the higher it becomes. Therefore, the operating conditions for the fuel cell are selected to be high temperature and high pressure within the range permitted by its structure and device materials. For example, in a fuel cell using an aqueous phosphoric acid solution as an electrolyte, it is usually 150~
Approximately 220°C and approximately 1 to 10 atmospheres are selected as the operating conditions. In fuel cells, part of the energy from the consumed hydrogen is converted into heat, so heat removal is necessary to maintain constant operating conditions. During this heat removal, a large amount of heat is generally recovered in the form of steam. Although some of this heat is used for preheating the reforming raw materials, etc., a considerable amount of surplus steam is currently generated. It is.

The present inventors focused on this surplus steam and conducted various studies on its effective use, and as a result, they found that by carrying out the reforming reaction at a relatively low temperature, it is possible to use this surplus steam as a heat source for the reformer. Therefore, the present inventors have discovered that it is possible to reduce the consumption of the qualitatively superior fuel residual gas, which was conventionally used as a heat source for a re-former, and to improve the overall thermal efficiency of the fuel cell, thereby completing the present invention.

That is, when the present invention generates electricity using a fuel cell that uses air as an oxidizing agent and hydrogen produced by steam reforming of methanol as fuel, the present invention provides at least a portion of the heat source of the reformer that performs the steam reforming. , a power generation method using a fuel cell, characterized in that exhaust heat generated in the fuel cell is used.

Another aspect of the present invention is a fuel cell power generation facility having a reformer that generates hydrogen by steam reforming methanol, and a fuel cell that uses hydrogen as a fuel and air as an oxidant. The fuel cell power generation equipment is characterized in that a heat recovery device for recovering heat and using it as a heat source for the refohmer is attached to the fuel cell, and the heat recovery device is connected to the refohmer.

The present invention will be explained in more detail. Methanol has a low steam reforming temperature, and it is possible to obtain hydrogen through the reaction CH ₃ OH + H ₂ O→CO ₂ +3H ₂ at temperatures above about 130°C.
However, the higher the reaction temperature, the higher the hydrogen conversion rate of methanol and the better the fuel gas to be supplied to the fuel cell. Conventionally, a temperature of 250°C or higher was selected for methanol steam reforming. The re-former was heated to the temperature required for the reaction by burning residual fuel gas or direct raw material gas. In the present invention, waste heat generated in the fuel cell, generally heat in the form of steam recovered by a heat recovery device attached to the fuel cell, is used as a heat source for the reformer of the methanol steam reforming reaction. Therefore, the steam reforming temperature is 130 to 220°C, particularly preferably 150 to 200°C. Temperatures below 130°C are unsuitable because the reaction hardly progresses. In order to increase the reaction rate of steam reforming, it is advantageous to raise the temperature, but if you try to raise the reaction temperature to 200℃ or higher using only the steam obtained by heat removal from the fuel cell as a heat source, the fuel cell It has become difficult to design a heat recovery device to transfer heat from the heat to the rifoma, and currently it is difficult to raise the temperature above 220℃.

The heat source of the reformer as used in the present invention refers to a heat source for supplying the heat required for the steam reforming reaction in the reformer equipment. This does not preclude its use as raw material steam for the reaction, and it is also a preferable method to use it in combination.

The molar ratio of H ₂ O and methanol used in the steam reforming reaction is 0.8/1 to 10/1, preferably 1/1 to 5/1. If the molar ratio is less than 0.8/1, a large amount of CO will be produced as a by-product, which will have an adverse effect on the fuel cell itself, and at the same time, the methanol conversion rate will decrease. The methanol conversion rate increases as the molar ratio of H ₂ O to methanol increases, but as the molar ratio increases, the increasing curve of the conversion rate becomes gradual. Although the upper limit of the molar ratio is not restrictive,
Even if the molar ratio is increased beyond 10/1, there is almost no effect on the methanol conversion rate, so it is appropriate to set the upper limit around this range.

There are no particular restrictions on the catalysts used for steam reforming, but examples include Cr, Mn, Fe, Co, Ni,
Base metal elements such as Cu, Zn, Al, Si, Ag, Sn or
If necessary, metals or compounds of noble metal elements such as Pt, Rh, Ru, Re, Pd, etc. are supported on a carrier. Among them, Cu-Cr, Cu-Zn-Al,
Combinations such as Cu-Zn-Mn have high activity and are preferably used. The amount of methanol treated per unit volume of the catalyst layer is 0.5 to 200 Kg-mole/m ³ , hr, preferably 2 to 50 Kg-mole/m ³ hr.

In the present invention, since the methanol reforming reaction temperature is low, in order to obtain a methanol conversion rate equivalent to that obtained when the reaction is carried out at a higher temperature, it is necessary to increase the size of the reformer and increase the amount of catalyst packed. If it is supplied to the fuel cell as fuel gas at a low level, unreacted methanol will not react effectively within the fuel cell and its chemical energy cannot be directly converted into electrical energy, resulting in a decrease in overall power generation efficiency. Connect. However, one preferred embodiment of the present invention comprises an absorption tower for absorbing methanol with water and a stripping tower for dissipating the absorbed methanol with steam, in order to recover unreacted methanol in the rifoma. A methanol recovery facility is attached to the rifoma. The recovery equipment can utilize the steam generated by the fuel cell, and can simultaneously reduce the load on the reflomer and prevent methanol loss. In addition, methanol recovered by steam dissipation in the methanol recovery equipment is accompanied by steam, but this entrained steam can be used as raw material steam for reforming, so the recovered methanol can be supplied to the reformer as it is without separating the steam. It can be used repeatedly.

The pressure energy of the oxygen-diluted air (hereinafter referred to as residual air) discharged from the oxygen electrode of the fuel cell is recovered by a gas turbine and used as part of the compressor power for supplying pressurized air. This has been known for a long time. In addition, as mentioned above, the residual fuel gas generated from the hydrogen electrode of the fuel cell was used as a fuel for the heat source of the rifohmer, but the pressure energy and thermal energy of the combustion exhaust gas discharged from the refohmer can be used by a gas turbine. Recovery has also been known for a long time. Also in the present invention,
Combustion equipment is installed to burn the residual fuel gas generated from the hydrogen electrode of the fuel cell, and the energy of the combustion gas generated by burning the residual fuel gas is recovered by a gas turbine and used as an oxidizing agent at the oxygen electrode of the fuel cell. One preferred embodiment is to use the supplied air as part of the energy for compressing and pressurizing. In that case, using at least a portion of the pressurized residual air discharged from the oxygen electrode of the fuel cell as an oxygen source for fueling the residual fuel gas is a method of This is a preferred method for reducing air and increasing overall power generation efficiency.

Generally, the waste heat generated by the fuel cell is recovered as steam and used as a heat source for reforming, but other methods such as using other heat carriers or directly exchanging heat between the reforming raw material and the fuel cell can also be used. .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the method and apparatus of the present invention as well as preferred embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a schematic diagram showing the flow of conventional fuel cell power generation equipment. FIG. 2 is a schematic diagram showing the flow of the fuel cell power generation equipment according to the present invention. Since these are schematic diagrams for explaining the differences between the conventional power generation equipment and the power generation equipment of the present invention, unnecessary equipment and flows for explanation are omitted.

In the example of the conventional fuel cell power generation equipment shown in FIG.
01. The hydrogen-containing generated gas 4 from the reformer 101 is separated from water by a separator 109 if necessary, and then transferred to the hydrogen electrode 104 of the fuel cell 102.
supplied to The residual fuel gas 7 discharged from the hydrogen electrode 104 is supplied to the refoamer 101 as fuel. On the other hand, air 1 compressed by the compressor 105
5 is branched into two, and the fuel cell oxidant air 5 is supplied to the oxygen electrode 103 of the fuel cell 102. The remainder of the compressed air 8 is used as combustion air to be used as combustion air.
01. The remaining fuel gas 7 is used as combustion air 8
The raw material gas 3 is combusted in the reformer 101 and is discharged as reformer exhaust gas 9 after giving the raw material gas 3 the thermal energy necessary for steam reforming. Reformer exhaust gas 9 is supplied to raw material preheater 107
After a portion of the remaining thermal energy is recovered, further energy is recovered by the gas turbine 106. In order to remove the heat generated in the fuel cell 102, the cooling water 14 is supplied to the heat exchange device 113 attached to the fuel cell, and the heat is recovered as steam 20, but a part of this is used as the reforming raw material steam 2 and the raw material preheating. In addition to being used as steam 21, most of the heat is radiated by a cooler or the like.

In such a fuel cell power generation facility, it is necessary that the remaining fuel gas and remaining air after passing through the fuel cell have energy equivalent to the air compression power and the reheater heating energy. Adjustment of this energy balance can be performed by increasing or decreasing the amount of residual fuel gas 7 discharged from the fuel cell 102. In other words, when the energy consumed by the gas turbine and the reformer increases, it is necessary to generate extra fuel residual gas, and if the amount of power generation in the fuel cell 102 is to be kept constant, a large amount of raw material methanol must be supplied. This relationship exists.

In the example of the power generation equipment according to the present invention, the remaining fuel gas that has passed through the fuel cell 102 is directly supplied to a gas turbine or the like after combustion to recover energy. As shown in FIG. 2, the fuel residual gas 7 is burned in the combustion equipment 112 and the energy of the generated fuel gas 16 is recovered by the gas turbine 106.
This is one preferred method. On the other hand, fuel cell 10
The steam generated in step 2 is used as a heat source for the reformer 101, and a portion is used for preheating the raw material gas 3 in the raw material preheater 108. In addition, the fuel cell 10
It has been conventionally known to use a part of the steam generated in step 2 as it is as steam 2 for reforming, and the combined use of such a method is also included in the scope of the present invention.

Furthermore, as described above, it is also a preferable method to recycle raw methanol by providing methanol recovery equipment without forcing the methanol conversion rate in the reformer 101 to be high. That is, the hydrogen-containing generated gas 4 leaving the reformer 101 passes through the separator 109 and then passes through the absorption tower 110, where unreacted methanol is absorbed and removed by water. The gas 13 after methanol separation is sent to the hydrogen electrode 104 of the fuel cell 102 as a fuel gas. The methanol aqueous solution produced in the absorption tower 110 is sent to the stripping tower 111 together with the methanol aqueous solution produced in the separator 109, and methanol is recovered using steam produced in the fuel cell 102. The recovered methanol 11 is mixed with unused methanol 1 and reused as a reforming raw material. Air 15 is used as a fuel cell oxidant at the oxygen electrode 10 of the fuel cell 102.
3. A portion of the residual air 6 that has left the fuel cell is supplied to the combustion equipment 112 as combustion air 10 for the residual fuel gas 7.

The effect of the present invention is that the overall thermal efficiency of the fuel cell power generation equipment is improved by using exhaust heat generated in the fuel cell, which has not been effectively used in the past, as at least a part of the heat source of the reflow generator. In other words, the amount of raw material methanol supplied can be reduced by the amount of residual fuel gas required for heating the reformer that is no longer needed. Therefore, from the standpoint of overall thermal efficiency, it is desirable to supplement all of the heat source of the re-former with the exhaust heat generated by the fuel cell, but it is also possible to partially utilize the combustion heat of residual fuel gas.

In addition, when using fuel residual gas as a heat source for the refohmer as in the past, it is necessary to install the combustion chamber in contact with or very close to the refohmer reaction tube in order to effectively transfer the heat generated by combustion to the refohmer. However, since the combustion temperature of residual fuel gas reaches 800 to 1000°C, there were major restrictions on the material and shape of the re-former. but,
In the method of the present invention, when the heat source of the re-former is provided only by the exhaust heat generated in the fuel cell, the combustion equipment for residual fuel gas may be provided separately, so that restrictions on the re-former material are significantly reduced.

Examples of the present invention will be comparatively shown below to quantitatively illustrate the effects of the present invention, but the present invention is not limited to the following examples.

Comparative Example 1 The conventional fuel cell power generation system shown in Figure 1
Tests were conducted in a 4.8MW experimental facility. Methanol 1916 heated to 134℃ in preheater 108
Kg/hr is mixed with 2154Kg/hr of the 180℃ steam generated by the fuel cell, and further heated in the preheater 107.
After raising the temperature to 250°C, a reforming reaction was carried out in a reformer 101 at a reaction temperature of 250°C and a pressure of 4.2 Kg/cm ² G. CuO-
Filled with 3 m ³ of ZnO-Al ₂ O ₃ catalyst, practically 100
% rehoming reaction was completed. fuel cell 1
02 was operated at 195°C and 2.8Kg/cm ² G, and 80.0% of the supplied hydrogen was consumed at the hydrogen electrode. At the same time, 10Kg/cm ² G180℃ steam is generated from the fuel cell.
7400 Kg/hr was generated via heat exchanger 113. On the other hand, 17,700 kg/hr of compressed air was supplied from the compressor 105, of which 15,000 kg/hr was used as an oxidizing agent for the fuel cell oxygen electrode, and 2,700 kg/hr was used as combustion air for the residual fuel gas 7. The exhaust gas from the refoamer and the remaining air after passing through the fuel cell oxygen electrode were supplied to the gas turbine for energy recovery.
The overall power generation efficiency of this fuel cell system is 39.76%
It was hot. Note that the overall power generation efficiency refers to the ratio of electric power generated by the fuel cell to the total calorific value of consumed methanol.

Example 1 In the 4.8 MW experimental equipment for the fuel cell power generation system of the present invention shown in FIG.
The test was conducted with the reaction temperature at 170° C. and the operating conditions of the fuel cell 102 being the same as in the comparative example.

Methanol heated to 160℃ in preheater 108
1768 Kg/hr was mixed with the reforming raw material steam 2 and the recovered raw material 11, and a reforming reaction was performed in the reformer 101 at a reaction temperature of 170° C. and a pressure of 4.2 Kg/cm ² . CuO is used for rifoma 101.
-ZnO- _Al2O3 -based catalyst ( _15m3 ⁾ was packed, and the methanol conversion rate was 90.2%. The generated hydrogen-containing gas passed through methanol recovery equipment 109, 110 and was then supplied to the hydrogen electrode 104 of the fuel cell 102. 10Kg/cm ² generated by the fuel cell heat recovery device
G, 180℃ steam 7400Kg/hr, 100Kg/hr as reforming raw material steam 2, 800Kg/hr as heat source of preheater 108, reformer 10
3000Kg as a heat source for 1, methanol recovery equipment 11
The remainder was used for stripping No. 1.
Methanol at 164℃ is produced from the methanol recovery equipment.
186 Kg/hr and entrained steam 1900 Kg/hr were recovered and recycled as part of the reaction raw material together with reforming raw material steam 2. On the other hand, compressor 10
15,000 kg/hr of air at 2.6 kg/cm ² G was supplied from No. 5, and the entire amount was used as an oxidizing agent in the fuel cell.
Remaining air after passing through oxygen electrode 103 12800Kg/hr
Of the total (dry gas basis), 7500 Kg/hr was used as combustion air 10 for residual fuel gas, and the remainder was directly recovered by the gas turbine. The overall power generation efficiency of this fuel cell system was 43.08%.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing an example of conventional fuel cell power generation equipment, and FIG. 2 is a flow sheet showing an example of the fuel cell power generation equipment of the present invention. 1: Methanol, 2: Steam (raw material), 3:
Raw material gas, 4: Fuel gas, 5: Oxidizing air,
6: Oxygen electrode residual air, 7: Fuel residual gas, 8: Combustion air (refoamer), 9: Refoamer exhaust gas, 1
0: Combustion air (combustion equipment), 11: Recovered methanol, 12: Fuel gas, 13: Fuel gas, 14:
Cooling water, 15: Compressed air, 16: Combustion gas, 2
0: Steam (for re-forming), 21: Steam (for preheating raw materials), 101: Re-forming, 10
2: Fuel cell, 103: Oxygen electrode, 104: Hydrogen electrode, 105: Compressor, 106: Gas turbine, 1
07: Preheater, 108: Preheater, 109: Separator, 110: Absorption tower, 111: Stripping tower, 112: Combustion equipment, 113: Heat exchange device.

Claims (1)

[Claims] 1. When generating electricity using a reformer that generates hydrogen by steam reforming methanol and a fuel cell that uses the hydrogen as fuel and air as an oxidizing agent, exhaust heat generated in the fuel cell. of,
A power generation method using a fuel cell, characterized in that the steam is recovered as steam, and the steam is used as at least a part of the heat source of a re-former that performs the steam re-forming. 2 The temperature of the steam re-forming is 130~
The method according to claim 1, wherein the temperature is within the range of 220°C. 3 The temperature of the steam re-forming is 150~
The method according to claim 2, wherein the temperature is within the range of 200°C. 4. Claim 1, wherein the unreacted methanol after the steam reforming is absorbed by water, and the absorbed methanol is recovered by dissipating it with steam.
2 or the method described in 3. 5 In equipment that has a reformer that generates hydrogen by steam reforming methanol and a fuel cell that uses hydrogen as a fuel and air as an oxidizing agent, heat generated in the fuel cell is recovered as steam to generate hydrogen in the reformer. The fuel cell is characterized in that a heat recovery device for use as a heat source is attached to the fuel cell, and the heat recovery device is connected to the reheater so that at least a part of the heat source of the reheater is supplied by the steam. Fuel cell power generation equipment. 6. The equipment according to claim 5, wherein a methanol recovery equipment comprising an absorption tower for absorbing methanol with water and a stripping tower for dissipating the absorbed methanol with steam is attached to the reformer.