JP4014730B2 - Fuel cell system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell system, and more particularly to a fuel cell system using a reformed gas from a reformer as fuel.
[0002]
[Prior art]
As a method of supplying fuel (hydrogen gas) supplied to automobile fuel cell systems such as automobiles, hydrogen stored in hydrogen cylinders, hydrogen storage alloys, etc. may be used. There are cases where hydrogen-rich reformed gas is generated from fossil fuel and used as hydrogen gas.
In a fuel cell system using such a reformer, the start-up time of the reformer system (that is, the time until reformed gas is generated) is determined by the temperature rise time of the reformer having the longest start-up time. This is because the fuel for generating hydrogen cannot be supplied until the vaporizer, the reforming catalyst, etc. constituting the reformer rise to a certain temperature and are activated. In order to shorten the start-up time, a method for raising the reformer temperature by incorporating a heater or an electric heater inside the reformer (Japanese Patent Laid-Open No. 9-63618), Methods for increasing the temperature of the reformer with thermal energy obtained by burning fuel (JP-A-3-192661, JP-A-5-3043) have been proposed.
[0003]
[Problems to be solved by the invention]
As described above, various methods for shortening the start-up time of the reformer have been proposed in the past. However, in the reformer of a fuel cell system mounted on a vehicle such as an automobile, the conventional method is still insufficient. There is a need to further reduce the time.
[0004]
The present invention has been made to solve the problems of the prior art as described above, and an object thereof is to provide a fuel cell system including a reformer having a short start-up time.
[0005]
[Means for Solving the Problems]
In the present invention, as described in claim 1, air sent from an air compressor that supplies air to the fuel cell is controlled to a desired air temperature and supplied to the reformer. It is used as a heating means.
There are the following methods for controlling the temperature of the air sent from the air compressor. First, as a first method, as described in claim 2, the compressor is not necessarily at the highest efficiency point for fuel cell system operation, but is operated at an operating point shifted to a higher pressure side. This is a method of obtaining the air temperature. That is, by adiabatic compression of air, a high air temperature can be obtained by increasing the internal energy.
[0006]
As a second method, as described in claim 3, a circulation flow path that connects the discharge path and the suction path of the air compressor is provided, and when the reformer is started, the circulation flow path is opened to discharge the discharge air. by returning a portion to the suction passage, it is possible to raise the temperature of the ejection exit air.
The above two methods can be performed simultaneously by combining them. In addition, each of them can be obtained by conventional reformer start-up heating means, that is, a method of increasing the reformer temperature by incorporating a heater or an electric heater inside the reformer, or burning the fuel for raising the temperature in the internal combustor. It can also be carried out in combination with a method in which the temperature of the reformer is raised by the thermal energy.
[0007]
Further, as described in claim 4, after the temperature of the reformer is raised to a desired operating temperature, the air is controlled to a desired temperature value by a cooling means (intercooler) provided between the switching means and the fuel cell. Is switched to the fuel cell side and supplied to the cathode electrode of the fuel cell, so that the normal fuel cell operation mode can be set.
[0008]
【The invention's effect】
In the present invention, in the fuel cell system using a reformer, the temperature of the reformer is started by increasing the temperature of the air sent from the air compressor when the reformer is started and using the high-temperature air. The effect that the rise can be promoted and the startup time can be shortened is obtained.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 is a schematic diagram showing a first embodiment of the present invention. This embodiment is an example of a reformer type fuel cell system having a turbo compressor as an air compressor, a steam reformer as a reformer, and a polymer membrane fuel cell as a fuel cell. In addition to the present invention, the start-up preheating means uses a method of increasing the temperature of the reformer with heat energy obtained by burning fuel for raising the temperature with an internal combustor.
[0010]
In FIG. 1, 1 is a turbo type air compressor, 2 is a steam reformer, 3 is a fuel cell body, 4 is switched from the air compressor 1 to the fuel cell body 3 and the reformer 2. The flow path switch 5 to be supplied is a valve provided in the flow path from the air compressor 1 to the reformer 2, and 6 is a fuel cell which cools the air whose temperature has risen from the air compressor 1 to an appropriate temperature. This is an intercooler supplied to the main body 3. Reference numeral 7 denotes control means for controlling the fuel cell system, and is constituted by a microcomputer comprising, for example, a CPU, ROM, RAM and the like. A temperature sensor is provided for measuring the air temperature delivered by the air compressor 1, the temperature of the reformer 2 (particularly the catalyst temperature), the air inlet (outlet of the intercooler 6) temperature of the fuel cell body 3, and the like. However, they omit the display.
[0011]
The steam reformer is a reformer of a type that generates hydrogen by reacting a mixture of fuel (for example, methanol) and water with a catalyst. The reformer 2 includes an internal combustor, and a part (excess) of hydrogen sent from the reformer 2 to the fuel cell main body 3 or methanol is returned to the internal combustor for combustion, thereby reforming. It also has a function to raise the temperature of the vessel. An example of a reformer provided with such an internal combustor is disclosed in Japanese Patent Laid-Open No. 9-63618. When hydrogen generated by the reformer 2 is sent out, it is cooled to a temperature suitable for the fuel cell and then supplied to the fuel cell main body 3.
[0012]
In the present embodiment, the air compressor 1 is controlled at the time of startup to increase the temperature of the air to be sent out, and the flow path switching device 4 is switched to the reformer side, and the valve 5 is opened to open the high-temperature air. Is supplied to the reformer 2, thereby rapidly increasing the temperature of the reformer 2.
[0013]
As a method for raising the temperature of the air sent from the air compressor 1, the following method is used. In other words, the air compressor 1 is operated at an operating point shifted to a higher pressure side, which is not necessarily the highest efficiency point for the fuel cell system operation, thereby obtaining a high discharge air temperature. As described above, by adiabatic compression of air, it is possible to increase internal energy and obtain a high air temperature. By supplying this high-temperature air to the reformer 2 (details will be described later), the reformer start-up time can be shortened.
[0014]
The discharge air temperature T2 from the air compressor 1 is given by the following (Equation 1).
T2 = Tl [(1 / η) (π ^{( κ- 1) / κ-} 1) +1] (Equation 1)
However, π = P2 / Pl
π: pressure ratio, P1: intake air pressure, P2: discharge air pressure, T1: intake air temperature, κ: specific heat ratio, η: adiabatic efficiency of air compressor, for example, intake air temperature T1 = 30 ° C., pressure ratio π = When it is about 3, the efficiency of the air compressor 1 is about 70%, and the discharge air temperature T2 is about 200 ° C. The operating temperature of the catalyst in the reformer 2 is, for example, 300 to 350 ° C. in a steam reformer using methanol as a fuel. It can be used, and the temperature raising rate of the reformer 2 can be increased. In order to achieve a desired start-up time, the operating point may be determined by monitoring the temperature rise of the reformer 2 and setting the pressure ratio of the air compressor 1 to a desired temperature. The above control is performed by a control signal from the control device 7.
[0015]
FIG. 2 is a performance curve diagram showing the relationship between the pressure ratio and the flow rate when the air compressor used is a turbo compressor. As shown in FIG. 2, the operating ratio of the air compressor can be changed by increasing the rotation speed of the motor to increase the compression ratio.
As shown in FIG. 2, the operating point of the air compressor is changed to the high pressure side, and for comparison, the air compressor is operated when the pressure ratio π = 1.5 and the pressure ratio π = 3. Then, when the time until the reformer temperature rises to 300 ° C., which is the reaction temperature for allowing the reformer 2 to generate the mixed gas, is compared, the time required when operating at the pressure ratio π = 3 Was shortened by about 30% compared with the case of operating at a pressure ratio π = 1.5.
[0016]
When the air compressor to be used is a variable stroke type piston compressor, the operating point (compression ratio) of the air compressor can be changed by changing the stroke amount of the piston according to the partition plate angle or the like. .
[0017]
FIG. 3 is a schematic diagram showing an outline of a steam method reformer. As shown in FIG. 3, the steam reformer sends a mixed liquid of methanol and water to the vaporization section 13 to vaporize it, and sends the vaporized gas to the reforming section (catalyst) 12 for reaction, thereby obtaining it. The mixed gas of H ₂ and CO thus obtained is passed through the gas generator 11 to obtain a hydrogen-rich gas. As described in the description of the conventional example, normally, heat obtained by burning methanol as a fuel at the time of start-up with an oxidation catalyst is introduced into each unit of the gas generating unit 11, the reforming unit 12, and the vaporizing unit 13. The temperature of the entire reformer is raised to start the reformer. In the present invention, the high-temperature air obtained by changing the operating point of the air compressor 1 as described above is supplied to each unit of the gas generator 11, the reformer 12, and the vaporizer 13 in the reformer 2. It is introduced to increase the temperature of the entire reformer and start the reformer.
[0018]
3, (A) shows a configuration in which high-temperature air is supplied in series in the order of the gas generation unit 11, the reforming unit 12, and the vaporization unit 13, and (B) shows a configuration in which high-temperature air is supplied in parallel to the above units. Since the high-temperature air introduced from the air compressor 1 is for heating each unit, it is natural that the high-temperature air does not come into contact with methanol or gas flowing through each unit. For example, a flow path of high-temperature air may be provided in contact with the outer wall of the reaction part such as a catalyst.
[0019]
Also, as described above, conventional reformer start-up heating means, that is, a method of increasing the reformer temperature by incorporating a heater or an electric heater inside the reformer, or a fuel for raising the temperature in the internal combustor. It can be carried out in combination with a method of increasing the temperature of the reformer with the heat energy obtained by burning.
[0020]
Further, the cooling water supply for cooling the fuel cell main body is stopped when the reformer is started, and the air supply path that bypasses the fuel cell is covered with a heat insulating material so as not to lower the air temperature.
[0021]
(Second Embodiment)
FIG. 4 is a schematic diagram showing an air compressor used in the second embodiment of the present invention. As shown in FIG. 4, a circulation flow path connecting the air suction path 8 and the discharge path 9 of the air compressor 1 is provided, and the circulation valve 10 provided in the flow path is opened to change the discharge side to the suction side. The circulating air temperature can be raised by circulating the air. What the reformer needs when starting up the reformer is high temperature air, not high pressure air. Therefore, it is possible to use a method of increasing the discharge air temperature by temporarily reducing the efficiency temporarily. As a specific method for temporarily reducing the efficiency, as shown in FIG. 4, the discharge passage 9 and the suction passage 8 are connected by a bypass passage, and the circulation valve 10 provided there is opened. Hot air recirculates from the inlet to the suction side. At this time, the compressor temperature decreases, but the discharge temperature increases. Thereby, the high temperature air for heating the reformer can be supplied, and the temperature raising rate of the reformer can be increased. As a matter of course, when the circulation valve 10 is closed, it operates as a normal air compressor.
[0022]
Note that the method of raising the discharge air temperature by changing the operating point of the air compressor 1 shown in the first embodiment and the method described in the second embodiment are simultaneously performed. You can also. The matters described with reference to FIG. 3 are the same in the second embodiment.
[0023]
In addition, the method described in the first and second embodiments, the conventional reformer start-up heating means, that is, the method of increasing the reformer temperature by incorporating a heater or an electric heater inside the reformer, A method of raising the temperature of the reformer with the thermal energy obtained by burning the fuel for raising the temperature in the combustor (described in FIG. 1) can also be implemented in combination.
[0024]
Next, FIG. 5 is a flowchart showing a part of the control contents in the control device 7, and after raising the reformer 2 to a desired operating temperature, between the air compressor 1 and the fuel cell main body 3. The control when supplying air controlled to a desired temperature value to the cathode electrode of the fuel cell main body 3 by cooling by the intercooler 6 provided in FIG.
[0025]
In FIG. 5, first, in step S1, it is determined whether or not the temperature of the reformer 2 has reached a desired operating temperature t1. In case of “no”, the temperature raising operation at the time of starting is continued. In case of “yes”, it is determined whether or not a mixed gas (reformed gas) is generated in step S2. In step S3, the operating point of the air compressor 1 is changed to a normal operating point. In addition, said operating temperature t1 is a value of about 300-350 degreeC, for example. In step S2, it is desirable not to simply determine the generation of the mixed gas, but to “yes” when the mixed gas flow rate corresponding to the desired power generation amount is confirmed.
[0026]
Next, in step S4, it is made to circulate through the cooling water of the intercooler 6 provided between the air compressor 1 and the fuel cell main body 3, and prepares the state which can cool the air sent to the fuel cell main body 3. To do. It is also possible to control the air temperature to the optimum temperature by controlling the cooling circulating water amount of the intercooler 6.
[0027]
Next, in steps S5 and S6, it is determined whether or not the air inlet temperature of the cathode electrode of the fuel cell body 3 has become a predetermined safe temperature t2 or less, and the air inlet temperature of the fuel cell cathode electrode exceeds a predetermined value t2. In step S7, the flow path switching unit 4 is switched to the fuel cell main body 3 side as shown in step S7. To supply air. By performing such an operation, high-temperature air can be prevented from flowing into the fuel cell, and normal operation can be prevented.
[0028]
As described above, by performing the control of FIG. 5, the temperature-controlled hot air can be switched from the reformer side to the fuel cell side, and the fuel cell system can be operated safely.
Note that the temperature of the air supplied to the cathode electrode of the fuel cell main body 3 is cooled in order to prevent thermal damage to the solid polymer film as an electrolyte, and the supply air is higher than the operating temperature of the fuel cell main body. In such a case, condensation of moisture in the air is caused, and as a result, performance deterioration (voltage drop) due to water clogging inside the fuel cell gas flow path is prevented. In a normal polymer electrolyte membrane fuel cell, the above operating temperature is about 90 ° C.
[0029]
The fuel cell used in the present invention includes a polymer electrolyte fuel cell, a phosphoric acid fuel cell, and the like. In consideration of the power density and portability, the polymer electrolyte fuel cell is used. A battery is suitable.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an overall configuration in a first embodiment of the present invention.
FIG. 2 is a performance curve diagram showing the relationship between the pressure ratio and the flow rate when the air compressor is a turbo compressor.
FIG. 3 is a schematic diagram showing an example of a configuration for supplying high temperature air to a reformer.
FIG. 4 is a schematic diagram showing a configuration of an air compressor according to a second embodiment of the present invention.
FIG. 5 is a flowchart showing control when switching the high-temperature air of the air compressor from the reformer side to the fuel cell side in the fuel cell system of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Turbo type air compressor 2 ... Reformer 3 ... Fuel cell main body 4 ... Flow path switcher 5 ... Valve 6 ... Intercooler 7 ... Control device 8 ... Air suction path 9 ... Air discharge path 10 ... Circulation valve DESCRIPTION OF SYMBOLS 11 ... Gas production | generation part 12 ... Reformation part 13 ... Vaporization part

Claims (4)

A fuel cell system comprising: a reformer for subjecting a hydrocarbon compound to a reforming reaction to reform it into a hydrogen-rich gas; and an air compressor for supplying air to the fuel cell body,
A flow path for blowing air from the air compressor to the reformer;
Switching means for switching and blowing air discharged from the air compressor to either the fuel cell main body or the reformer;
When starting the reformer, the air compressor is controlled so that the temperature of the air discharged from the air compressor rises to a predetermined temperature, and the switching means sends air to the reformer side. Control means for switching control to
And a high temperature air from the air compressor is used to promote a temperature rise at the start of the reformer and shorten the start-up time.   The control means increases the discharge air temperature by changing the operating point of the air compressor at a higher pressure ratio direction than at the time of normal operation when the reformer is started. The fuel cell system according to claim 1. A fuel cell system comprising: a reformer for subjecting a hydrocarbon compound to a reforming reaction to reform it into a hydrogen-rich gas; and an air compressor for supplying air to the fuel cell body,
A flow path for blowing air from the air compressor to the reformer;
Switching means for switching and blowing air discharged from the air compressor to either the fuel cell main body or the reformer;
A circulation passage connecting the discharge passage and the suction passage of the air compressor;
At the start of the reformer, the switching means and the switching control to send air to the reformer side, and by returning a portion of the discharge air by opening the circulation flow path to the intake path, ejection Control means for controlling the temperature of the outlet air to rise;
And a high temperature air from the air compressor is used to promote a temperature rise at the start of the reformer and shorten the start-up time. A cooling means provided between the switching means and the fuel cell main body,
The control means detects that the reformer has been heated to a desired operating temperature at the time of starting the reformer, then changes the air compressor to a normal operation state and operates the cooling means. it is, on the Symbol switching means by cooling the discharge air is switched to the fuel cell main body side, and controls the air controlled at a desired temperature value to supply to the cathode of the fuel cell body, The fuel cell system according to any one of claims 1 to 3, wherein

Images