JPS63236269A - Control method for fuel cell - Google Patents

Abstract

PURPOSE:To obtain stable power generation efficiently by generating an electric current depending on fuel amount fed to a fuel cell stack. CONSTITUTION:In order to control the output current of a fuel cell depending on the modified gas feed, a central controller 18 controls pumps 3, 5 and a fan 7, consequently an intake of modified raw material, depending on instructions from the outside, which are determined by residual charging amounts detected from a storage battery 19 in series connected to the fuel cell stack 10. The instructions from the outside control the intake of modified raw material, increasing and decreasing when the residual charging amounts of the storage battery are small and large enough to 100%, respectively. By the arrangement, a long life of catalyst and an improved power generation efficiency are achieved, because no excessive fuel is required to waste the energy and, furthermore, no residual fuel overheats the catalyst returning to a modifier 1.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for operating a power generation system using a fuel cell;
In particular, it relates to a method of controlling a fuel cell.

(Prior Art) In a conventional power generation system using a fuel cell, hydrogen obtained by reforming hydrocarbons, for example, is used as fuel. - As an example, when methanol is reformed with steam, hydrogen is obtained by the following reaction.

CI+3011 + t120→ (:02+31-
12 This hydrogen containing carbon dioxide gas and air are combined into a phosphoric acid type fuel.
) When the fuel is sent to a t-4TL pond to generate electricity, the following reactions occur at each of the anode and cathode of this fuel cell.

Anode 112→ 211”+2e cathode l
/202+2e+211" →H20 That is, the oxidation reaction of hydrogen progresses at the anode, and the reduction reaction of oxygen in the air progresses at the cathode, and water is obtained as an overall reaction by an electrochemical reaction between hydrogen and oxygen. This reaction The chemical energy changes during the process are converted into electrical energy, which is then taken out as electrical output.

The current obtained in the above reaction is directly proportional to the amount of hydrogen and oxygen consumed, according to Faraday's law.

Here, FIG. 6 shows the configuration of this type of power generation system when methanol is used as the raw material for obtaining hydrogen fuel.

In FIG. 6, 1 is a reformer for reforming methanol to obtain hydrogen. This reformer 1 is supplied with methanol and water. That is, methanol is supplied to the reformer 1 from a methanol tank 2 through a methanol pump 3, and water is supplied from a water tank 4 through a water pump 5, respectively. The molar ratio of methanol and water supplied is methanol 1
water to 1.3 to 2. In this way, water is supplied in an amount greater than the theoretically calculated reaction amount, so that the reformed gas produced as a result of the reforming reaction contains water.

The methanol reforming reaction is generally carried out at a temperature of about 250°C. A ZnO-based or CuO-based catalyst is used as the catalyst, this reforming reaction catalyst is filled in the reforming tube IA, and the reforming reaction is performed by passing a mixed vapor of methanol and water through the catalyst. . Furthermore, since this reforming reaction is an endothermic reaction, it is carried out by heating the mixed vapor of methanol and water and the catalyst. Heat for this heating is obtained by supplying fuel to the reformer burner 6 and burning the fuel in air supplied from the reformer fan 7. Here, the fuel is
For example, it can be supplied in the following three ways. The first method is to supply methanol from the methanol tank 2 through the methanol pump 8. The second method is to supply off-gas discharged from the fuel cell stack 10, which will be described later.

The third method is to use the above-mentioned methanol and off-gas together.

The mixed fluid of methanol and water supplied to the reformer 1 is evaporated in the reforming tube IA in the reformer 1. In the reforming tube IA, reformed gas containing hydrogen and carbon dioxide gas is generated by the action of the catalyst. This reformed gas is sent to a fuel gas chamber 12 provided at an anode (ffl+) of a fuel electrode (anode) 11 in the fuel cell stack 10. Off-gas containing excess hydrogen, carbon dioxide, and water vapor that did not participate in the electromotive reaction is discharged from the fuel gas chamber 12 and supplied to the reformer burner 6. As described above, this combustion heat becomes heat for promoting endothermic reactions.

On the other hand, air is supplied from a fan 15 to the air chamber 14 on the side of the air electrode (cathode) 13 in the fuel cell stack 10, and excess air not involved in the reaction is removed from the stack 10.
is discharged outside.

16 is an electrolyte filled in the space between the fuel electrode 11 and the air electrode 12.

The fuel cell stack 10 has a pair of a fuel electrode (anode) 11 and an air electrode (cathode) 12. However, the output voltage of a single cell with a pair of electrodes is only a little less than 17, and the output per unit area of the electrode is several hundred mA/am2.
It is. Therefore, a large output can be obtained by using a plurality of stacks in which a plurality of large-area single cells are connected in series and by arbitrarily combining the series and parallel connections of these stacks.

The theoretical amount of hydrogen and oxygen in the air consumed by such a stack is determined by the number of single cells in the stack n and the output current T
is directly proportional to

In general, a fuel cell power generation system is operated by supplying hydrogen and oxygen in excess of the amounts theoretically consumed by the stack. The ratio of the consumption of hydrogen and oxygen to the supply of each is called the utilization rate. In fuel cell power generation systems, the hydrogen utilization rate is 70%.
~80% Oxygen utilization rate (also called air utilization rate in the case of air supply consumption) is operated at 50-60%.

In the power generation system as described above, the temperature of the reformer 1,
The water and methanol feed rates, the stack 10 temperature, and the air feed rate are controlled by a central controller 18. Further, the output voltage from the stack 10 is controlled by the output controller 17 under the control of the central controller 18 and is supplied to the storage battery 19. 20 is storage battery 1
This is a load that is supplied with power from 9.

Note that the signal lines indicated by broken lines in the figure are used to send and receive control signals.

The utilization rates of hydrogen and oxygen are controlled by setting the output current of the stack 10 and supplying water and methanol, which are reforming raw materials, to the reformer 1 in proportion to the set current.

When performing such control, water and methanol are supplied to the reformer 1 through the respective pumps 5 and 3 to become reformed gas, and there is a time delay and reformation until that gas is supplied to the stack 10. If the reforming reaction temperature is not properly controlled, the reforming reaction will not proceed sufficiently. Therefore, the output of the fuel cell power generation system must be controlled in consideration of the above-mentioned time delay. If such control is not performed, for example, when starting up the fuel cell or increasing output, the stack 10 will run out of hydrogen gas, making it impossible to generate electricity.

Such a lack of hydrogen gas causes a lack of hydrogen gas in the off-gas, which may lead to a misfire of the reformer burner 6, making the reformer 1 inoperable.

Furthermore, in the case of a gas shortage that is milder than the above-mentioned hydrogen gas shortage, an off-gas shortage occurs even if the stack 10 does not run out of gas. Therefore, the temperature of the reformer I decreases, the amount of reformed gas decreases, and eventually the fuel cell power generation system will stop operating.

Furthermore, when the output is reduced or stopped, the amount of reformed gas becomes excessive, which may cause the amount of off-gas to become excessive and the temperature of the reformer 1 to exceed.

In order to overcome the above-mentioned drawbacks, the operation of fuel cells has conventionally been controlled by the following method.

FIG. 7 is a time chart showing temporal changes in the fuel cell output current (FC current) and the amount of reformed gas supplied.

In the figure, 50 indicates a change in the FC current over time, and 51 indicates a change in the amount of reformed gas supplied over time. Δt indicates a control delay between the time of changing the reformed gas supply amount and the time of changing the FC output power setting.

Δt is on the order of a few minutes.

As shown in FIG. 7, conventionally, when increasing the output current, first, before increasing the output current,
Methanol, which is the fuel in the reformer burner 6, is combusted. Next, water and methanol as reforming raw materials are increased, and a delay time Δt is set to increase the output current. When decreasing the output current, the method used is to first decrease the output current and then lower the output of the reformer 1, contrary to the case where the output current is increased.

[Problem that the invention seeks to solve]

However, in the conventional operation control method of a fuel cell power generation system as described above, an excessive amount of fuel is required to be burned in the reformer burner, which has the disadvantage of wasting energy. Moreover, since excess fuel is combusted, the reformer heats up and the reforming catalyst deteriorates, resulting in the problem that the reforming reaction may not proceed normally.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a fuel cell control method that eliminates the above-mentioned drawbacks and allows efficient operation of a fuel cell power generation system.

[Means for solving problems]

In order to achieve such an object, the present invention, when controlling a fuel cell having a fuel cell stack supplied with reformed fuel, changes the output current of the fuel cell stack in accordance with the amount of fuel supplied. It is characterized by

(Function) In the present invention, stable power generation output can be efficiently obtained by outputting current in accordance with the amount of fuel supplied to the fuel cell stack.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 2 shows an IV curve representing the relationship between the output voltage V and the output current I of the fuel cell stack. 30°31.32 shows 1-V curves with different fuel utilization rates. Among these curves, the IV curve 32 has the highest fuel utilization rate. 30A, 3IA, 32A are the lowest voltage curves 36 and I
- respective intersections x, y with V curve 30.31.32,
Indicates the portion of the curve that is at a higher voltage than z. These curved portions result from the flat portion of the fuel utilization curve shown in FIG. 30B, 31B.

32B indicates a curved portion having a lower voltage than the above-mentioned intersections x, y, and z. These curved portions correspond to characteristic curve 3 in Fig. 3.
This corresponds to the part where the voltage suddenly drops from the flat part of 3.34.35.

Figure 3 shows the fuel utilization characteristics. Here, 33.34.
35 shows the relationship between the fuel utilization rate and the output voltage of the stack at different fuel supply amounts. The fuel utilization rate is the ratio between the theoretical consumption amount and the supply amount of fuel, and is a value smaller than 1. The theoretical consumption of fuel is calculated from the electrician's output current. However, in reality, due to unreacted gas components within the fuel or electrode structure, the ability of the fuel to diffuse to the reaction site, ie, the anode, is reduced. Therefore, in order to obtain stable electrical output from the stack when the fuel utilization rate is 75% or less, at least 13 times the theoretical fuel consumption must be supplied when the fuel utilization rate is 75% or less. Must be.

As can be seen from the above, the IV curve in Figure 2 and the
The fuel utilization rate curves in the figure all change depending on the fuel supply amount, that is, the reformed gas supply amount, so by using this characteristic, it is possible to make the output current of the fuel cell stack follow the reformed gas supply amount. . That is, a minimum voltage curve 36 is provided that is several volts lower than the IV curve 30 in FIG.
6, the fuel cell stack voltage is maintained at the lowest voltage curve 36 or higher by lowering the fuel stack current. Conversely, when the amount of reformed gas supplied increases, the fuel cell stack current increases.

Therefore, in the present invention, the fuel cell stack is controlled by 11□1 by making the fuel cell output current follow the amount of reformed gas supplied.

FIG. 1 shows an embodiment of a fuel cell power generation system operated by implementing the control method of the present invention. In the figure, the same parts as in FIG. 6 are given the same reference numerals. In FIG. 1, 21 is a voltage measuring device, for example a voltmeter, for detecting the output voltage of the fuel cell, and is the voltage vr between the fuel electrode 11 and the air electrode 13.
Detect c. The detected voltage is detected by the central controller 18.
supply to.

In order to control the output current of the fuel cell to follow the reformed gas supply amount, the central controller 18 determines the amount of charge remaining in the 8Ti pond 19 connected in parallel with the fuel cell stack 10. Pumps 3 and 5 and fan 7 are controlled in accordance with external commands to control reforming raw material input. This external command controls to increase the input raw material when the remaining charge of the storage battery 19 is small, and to decrease the input raw material amount when the charge is close to 100%.

The fuel cell output current is set by an output controller 17 controlled by a central controller 18 to a value that follows the reformed amount. Is the voltage measured here? '521, the central controller 18 and the output controller 17 form a closed loop, and the fuel cell output voltage V measured by the voltage measuring device 21
The FC is fed back to the central controller 18 to control the output controller 17.

FIG. 4 shows a time chart showing an example of a control form in the present invention. Here, the output current 40 of the fuel cell is made to follow the reformed gas supply amount 41. In FIG. 4, Δt is the time delay from when the reforming raw material is first introduced into the reformer 1 until the fuel enters the fuel cell stack lo.

FIG. 5 is a flowchart showing an example of a control procedure that is stored in advance in the central controller 18 in order to execute control in accordance with the time chart shown in FIG. here,
An example will be explained in which the increase/decrease in the fuel cell output current FC in the output controller 17 for obtaining the set vehicle flow value is IA.

First, in step S1, the fuel cell output voltage VFC
However, it is determined whether or not it is a dog based on a preset minimum voltage VD. If V, , < V, the process proceeds to step S2, where the output controller 17 decreases the fuel cell output current FC by IA, and then returns to step S1.
Proceed to. On the other hand, in step Sl, if VFC≧Vo, the process proceeds to step S3, where it is determined whether vrc is smaller than the maximum output voltage Vp. vr
If c≧Vo, the process advances to step S4, where the output controller 17 increases the FC current by IA, and then
Return to step S1 again. In step s3, vr
If it is less than VP, the process proceeds to step S5, where the FC current is maintained without increasing or decreasing, and then the process returns to step s1. The output controller 17 is controlled by the central controller 18 according to the control procedure as described above,
By controlling the FC current thereby, VPC is controlled to be between VD and V.

Here, ■2 and ■. is determined within a range of about 70 to 90% fuel utilization. In other words, VP has a fuel utilization rate of 7.
It is close to 0% and is determined by power generation efficiency. on the other hand,
vo is determined based on the higher fuel utilization rate. In determining this high utilization rate, the unreacted reformed gas in the fuel cell is reused as fuel for the reformer burner, that is, as reforming energy, so at least the amount necessary for this is calculated as the theoretical consumption. The utilization rate corresponding to the voltage VP is determined from the added supply amount.

Note that the output of the fuel cell stack 10 is also greatly influenced by the composition of the supplied fuel. For example, there is a decrease in the amount of hydrogen supplied due to a decrease in the reforming rate caused by deterioration of the reforming catalyst. Furthermore, when methanol is used as a reforming raw material, co is also generated along with H2 and CO2, and if these are returned without being consumed in the fuel cell, the amount of CO that poisons the TL electrode catalyst increases. However, in the embodiment of the present invention, control is performed so that power is generated only for the amount of hydrogen gas supplied to the fuel cell stack 10.
0 will never run out of gas.

(Effects of the Invention) As explained above, in the present invention, a current corresponding to the amount of fuel supplied to the fuel cell stack is output,
Further, power generation is performed with the fuel utilization rate set to, for example, 70 to 90%. Therefore, according to the present invention, no excess fuel is required, so no energy is wasted, and the excess fuel does not return to the reformer and overheat the catalyst, resulting in a long catalyst life. In turn, this has the effect of contributing to improving power generation efficiency.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of a fuel cell power generation system implementing the present invention, Fig. 2 is a characteristic diagram showing the relationship between the output current and output voltage from the fuel cell stack, and Fig. 3 is the fuel utilization rate. A characteristic diagram showing the characteristics, FIG. 4 is a time chart showing temporal changes in the fuel cell output current and reformed gas supply amount in the present invention, and FIG. 5 is an example of a control procedure for executing the control form shown in FIG. 4. 6 is a block diagram showing a configuration example of a conventional fuel cell power generation system. FIG. 7 is a time chart showing temporal changes in fuel cell output current and reformed gas supply amount in a conventional operating method. . 1... Reformer, IA... Reforming pipe, 2... Methanol tank, 3... Methanol pump, 4... Water tank, 5... Water pump, 6... Reforming 7... Reformer fan, 8... Methanol pump, 10... Fuel cell stack, 11... Fuel electrode (anode), 12... Fuel gas chamber, 13... Air Pole (cathode), 14... Air chamber, 15... Fan, 16... Electrolyte, 17... Output controller, 18... Central controller, 19... Storage battery, 20... Load, 21... Voltage measuring device. Jōran 4-ring 2-stack t-kami 5L and output power h-Q Saiji・
Figure 2: 4-engine special grade for fuel storage Figure 3, Quimchard Figure 4 showing ``af'' masu sankake +: 'b' Aro Hayabusa Figure 5: Flowchart around ゛J荏p+1

Claims (1)

[Claims] 1) In controlling a fuel cell having a fuel cell stack supplied with reformed fuel, the output current of the fuel cell stack is changed to follow the supply amount of the fuel. Characteristic fuel cell control method. 2) A fuel cell control method according to claim 1, characterized in that the output voltage of the fuel cell stack is controlled so as not to fall below a preset minimum voltage of the fuel cell stack. 3) In the method according to claim 1 or 2, the fuel utilization rate of the fuel cell stack is set to 70 to 9.
A fuel cell control method characterized by maintaining the fuel cell at 0%. 4) In the fuel cell control method according to any one of claims 1 to 3, the fuel cell stack is controlled depending on the amount of charge of a backup battery connected in parallel with the fuel cell. A fuel cell control method characterized by setting a fuel supply amount.