JP2003197236A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the response at the time of evaporating methanol and water, which are introduced into a reformer, using the combustion heat of off-gas in a burner with respect to the reform system of the fuel cell. <P>SOLUTION: If the load of the fuel cell increases, the amount of hydrogen consumption in the fuel cell is temporarily reduced for example, by reducing the introduced amount of hydrogen to a fuel electrode, or by reducing the introduced amount of air to an air electrode, the consumption amount of hydrogen is made drop down temporally to make the combustion amount of heat in the burner increase, and to make the combustion heat amount in the burner increase. By this, it becomes possible to supply the fuel supplied to a reform part, and the quantity of heat required for evaporating water promptly without making problems, such as a temperature fall in the combustion part, and the like. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a reforming type fuel cell system, and more particularly to vaporizing hydrocarbon fuel and water introduced into a reformer by utilizing combustion heat of surplus hydrogen rich gas. It is related to the improvement of responsiveness in the case.

[0002]

2. Description of the Related Art As a conventional fuel reformer, there is one disclosed in Japanese Patent Laid-Open No. 2000-178001.
This is a means for supplying heat necessary for the reaction to a reformer that reforms a hydrocarbon-based fuel such as methanol or gasoline to generate a hydrogen-rich fuel gas. Combustible gas containing hydrogen (hereinafter referred to as "off gas") used is burned in the combustor, and the combustion heat is supplied to the reformer to maintain and control the reforming reaction. When it becomes necessary to control the reaction in the reformer in response to changes in the fuel cell load, especially when the load increases, the amount of reformed fuel to be processed in the reformer and the corresponding amount of water are increased. Let In this case, the amount of heat to be supplied to the reformer must be increased according to the amount of the reformed fuel and the amount of water corresponding to it, so that the reforming reaction cannot be maintained and the desired amount of hydrogen-rich gas cannot be obtained. The load on the battery cannot be increased. Therefore, in the conventional device, when the load of the fuel cell increases, the supply amount of either off-gas or hydrocarbon-based fuel to be burned in the combustion section is increased according to the increase amount, and the heat amount is still insufficient. in case of,
We are trying to increase the supply of the other.

However, in the above-mentioned prior art, when the load increases and the amount of off-gas supplied to the combustion section first becomes maximum, the hydrocarbon fuel is supplied to the combustion section early due to insufficient heat quantity. Will be. In this case, if methanol or gasoline is supplied as a fuel in a liquid state, the amount of heat required to vaporize it is deprived from the combustion part, and the temperature distribution in the combustion part changes rapidly. In the case of the above configuration, this effect is large, and the delay in the supply of the required amount of heat becomes large, causing the problem that the vaporization of fuel and water to be supplied to the reformer cannot be performed sufficiently.

This point will be described in more detail. Figure 1
Shows the temperature distribution of the combustion part in the steady state. In the steady state, the fuel supplied to the combustion section is only the excess hydrogen-rich gas discharged from the fuel cell, that is, the off gas.
In this case, although there is a difference depending on the load, the temperature distribution is roughly as shown in the figure in the longitudinal direction of the combustion section, and the air-fuel ratio of the combustion section is controlled so that the outlet gas temperature becomes a predetermined value. . The load increases from this steady state,
Assuming that the hydrocarbon-based fuel is directly supplied to the combustion section so as to correspond thereto, the temperature distribution in the combustion section will be in the state shown in FIG. That is, in the vicinity of the inlet of the combustion section, a large decrease in temperature occurs because the amount of heat required for the vaporization of the hydrocarbon-based fuel is taken from the combustion section, and the vaporized fuel then burns, resulting in the highest temperature on the downstream side of the combustion section. The temperature point shifts.

When the hydrocarbon fuel is directly supplied to the combustion section in this way, first, in the process in which the temperature distribution in the combustion section changes from the state shown in FIG. 2 to the state shown in FIG. Rapidly decreases, and then vaporized fuel burns until there is a desired temperature in that part, there is a time when the outlet temperature of the combustion part becomes lower than the target temperature, and as a result, reforming occurs. The supply of the amount of heat required to vaporize the fuel and water supplied to the parts is delayed, and the response of the entire system to an increase in load is delayed. This phenomenon of response delay becomes more significant as the load increase width increases, that is, as the amount of hydrocarbon-based fuel directly supplied to the combustion section increases.

[0006]

A first invention is a fuel reformer for producing a hydrogen-rich fuel gas using a hydrocarbon fuel and water, and a fuel cell for generating electricity using the fuel gas. And a combustor for combusting off-gas containing hydrogen discharged without being consumed by the fuel cell, the hydrocarbon heat for reforming and the fuel adapted to be vaporized by the combustion heat generated in the combustor. In the battery system, when the required load on the fuel cell is increased, the hydrogen consumption amount in the fuel cell is temporarily reduced and the combustion heat amount in the combustor is increased.

A second invention is the same as the first invention,
By reducing the amount of hydrogen introduced into the fuel electrode of the fuel cell, the amount of hydrogen consumed in the fuel cell is reduced.

A third invention is the same as the first invention,
By reducing the amount of air introduced into the air electrode of the fuel cell, the amount of hydrogen consumed in the fuel cell is reduced.

A fourth invention is the same as the first invention,
It is configured to directly supply the reforming hydrocarbon-based fuel amount to the combustor, and is provided with temperature detecting means for detecting the combustor outlet gas temperature, and the outlet gas temperature reduces hydrogen consumption in the fuel cell. The ratio between the amount and the amount of the hydrocarbon-based fuel directly supplied is controlled.

A fifth aspect of the invention is the same as the fourth aspect of the invention.
The amount of decrease in hydrogen consumption in the fuel cell was set to the latent heat of vaporization of the hydrocarbon-based fuel that is directly supplied to the combustor that burns surplus hydrogen-rich gas.

A sixth invention is the same as the first invention,
A secondary battery was provided to supplement the output shortage with respect to the required load when the hydrogen consumption in the fuel cell was temporarily reduced.

[0012]

According to each of the following inventions,
When the load on the fuel cell increases, the hydrogen consumption in the fuel cell is temporarily reduced and the combustion heat in the combustor is increased. It is possible to quickly supply the amount of heat required to vaporize the fuel and water supplied to the section. In order to reduce the amount of hydrogen consumed in the fuel cell, for example, as shown in the second invention, the amount of hydrogen introduced into the fuel electrode is reduced, or
Alternatively, as shown as the third invention, the amount of air introduced into the air electrode is reduced.

According to the fourth or fifth aspect of the invention, it is possible to minimize the power generation amount reduction time in the fuel cell and to improve the system responsiveness.

According to the sixth aspect of the invention, the load can be promptly dealt with by the secondary battery under the condition that the required load cannot be dealt with due to the output reduction of the fuel cell.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention configured as a vehicle-mounted fuel cell system will be described below with reference to the drawings. In FIG. 3, reference numeral 1 is a fuel cell, and an electromotive force is generated by an electrochemical reaction by a gas containing hydrogen supplied to the fuel electrode 1A and air which is an oxidant supplied to the air electrode 1B. 2 is a rechargeable secondary battery,
When the amount of power generation from the fuel cell 1 is insufficient, the fuel cell 1 is discharged, and when it is excessive, it is charged. 3 are motors 3 and 4 for driving the vehicle
Is a power controller that controls the flow of electricity from the fuel cell 1 and the secondary battery 2 to the motor 3. A control unit 5 controls the fuel cell system, and is configured as a microcomputer including a CPU and its peripheral devices.

During steady operation, the amount of electric power to be output to the motor 3 is calculated based on the load signal from the accelerator sensor 6 and the vehicle speed, and the amount of electric power to be generated by the fuel cell 1 is determined accordingly. When the amount of power to be generated by the fuel cell 1 is determined, the amount of hydrogen rich gas to be supplied to the fuel cell 5 is calculated by the control unit 5, and the amount of hydrocarbon fuel, in this case methanol, to be supplied to the reforming side is calculated. Is determined. A command is sent to the methanol and water supplier 16 according to the amount, and methanol and water are introduced into the vaporizer 14 from the respective tanks 18 and 17. The required amount of heat is supplied to the introduced methanol and water from the combustion gas from the combustor 13, which will be described later, to form the reforming fuel gas at a predetermined temperature. The generated reforming fuel gas is guided to the reformer 11 through the fuel introduction pipe 21. Reformer 11
Has a structure in which air is introduced as necessary or heat is externally supplied through a heat exchanger (not shown). The reforming fuel gas supplied to the reformer 11 causes a reforming reaction inside the reformer 11 in accordance with the supplied fuel amount, water amount, air amount, and external heat amount to generate a hydrogen-rich gas. To generate. The produced hydrogen-rich gas is introduced into the CO remover 12 through the passage 22. The gas before entering the CO remover 12 contains a considerable amount of carbon monoxide determined by the reaction conditions in the reformer 11, such as temperature and pressure. This is removed by the CO remover 12 to prepare a gas composition that can be introduced into the fuel cell 1. The adjusted hydrogen-rich gas is introduced into the fuel electrode 1A through the gas passage 23. On the other hand, air as the oxidant is supplied to the air electrode 1B through the air introduction passage 24 according to the amount of gas supplied to the fuel electrode 1A. The fuel cell 1 does not consume all the amount of hydrogen supplied, but the amount of hydrogen supplied is approximately 1
5-20% is not consumed but is discharged to the off-gas passage 25 as excess hydrogen-rich gas, that is, off-gas. The discharged off-gas is also used in the exhaust air passage 26 of the fuel cell 1.
It is guided to the combustor 13 together with the surplus air discharged from the. The combustor 13 is loaded with a catalyst for reacting excess hydrogen in the introduced off-gas with oxygen in the air to burn, and further has an air introduction passage 20 for adjusting the air-fuel ratio to control the combustion temperature. It is connected. Reference numeral 15 is an injection valve for directly supplying methanol to the combustor 13. The combustion gas discharged from the combustor 13 is introduced into the above-described vaporizer 14 through the passage 25 and vaporizes methanol and water.

Here, the operation in the case where the command for increasing the output request from the accelerator sensor 6 to the motor 3 is input to the control unit 5 will be described. First, in order to increase the output from the motor 3, it is necessary to increase the power supply to the motor 3. Now, if it is attempted to supplement the power increase request only by increasing the output of the fuel cell 1, the hydrogen gas supply amount to the fuel cell 1 must be increased accordingly. In this case, the control unit 5 is the feeder 1
6 to increase the supply amount of methanol and water supplied to the vaporizer 14. However, since there is a delay before the amount of heat generated in the combustor 13 increases, the vaporizer 14 is in a state of insufficient amount of heat, and the supplied fuel and water cannot be vaporized sufficiently or is raised to a predetermined temperature. I can't. Therefore, the reforming reaction in the reformer 11 is not sufficiently performed, and the required hydrogen cannot be supplied to the fuel cell 1 as well, so that the response of the entire system is delayed,
As a result, the acceleration required by the driver cannot be obtained.

On the other hand, in the present invention, when it is determined that the load increases from the accelerator opening, the amount of hydrogen consumed in the fuel cell 1 is reduced and the amount of exhaust hydrogen introduced into the combustor 13 and the fuel cell are reduced. By reducing the amount of hydrogen consumed in 1,
The amount of exhaust air increasing at the same rate, that is, the amount of air containing unused oxygen exhausted from the fuel cell 1 is increased. By doing so, since the air-fuel ratio in combustion does not change in the combustor 13, it is possible to change only the amount of heat generated without changing the combustion temperature, and it is possible to increase the amount of heat supplied to the carburetor 14 with good response. Further, the shortage of electric power with respect to the required load can be compensated by the supply from the secondary battery 2.

As a result, the responsiveness of the entire system is improved, and it becomes possible to accurately meet the driver's acceleration request. Further, the supplementary power from the secondary battery 2 can be reduced due to the quick response of the reforming system, and the capacity of the secondary battery 2 can be suppressed to the necessary minimum.

If the amount of increase in load required is large and the hydrogen rich gas is supplied to the combustor 13 in its entirety (the amount of power generated by the fuel cell 1 becomes zero at this time), but the amount of heat is insufficient, methanol is directly fed to the combustion section. Additional supply. In this case, the effect is minimized, although there is a slight delay with respect to the increase in heat quantity. Further, in this case, when the reformed gas amount increases, first, the supply of the additionally supplied methanol is gradually reduced, and then the hydrogen consumption amount in the fuel cell 1 is increased, and finally the steady state is reached. Move to.

FIG. 4 is a flow chart showing the control procedure described above. The numbers shown with the reference symbol S in FIG. 4 and other flowcharts and the following description are process step numbers. The processing represented by the flow chart is periodically executed at predetermined time intervals. In the following, with reference to FIG. 4, step by step, first, in S1, the load state is detected by the signal from the accelerator sensor 6. Next, in S2, the required reformed fuel amount according to the load increase is calculated, and in S3, the required increased heat amount in the combustor 13 according to the reformed fuel amount is calculated. In S4, the hydrogen consumption reduction required amount required to obtain the required increased heat amount is calculated, and in S5, it is determined whether the required increased heat amount can be satisfied by the hydrogen consumption reduction. If the required amount of increased heat can be satisfied, the process proceeds to S6 and below, and if not, the process proceeds to S10 and below.

In S6 to S7, the hydrogen consumption is reduced, and methanol and water are added to cope with the increase in load. Next, in S8 to S9, the reduction amount of hydrogen consumption is gradually reduced according to the response time of the carburetor 14 until the reforming system reaches the target load corresponding to the load increase, and when the target load is reached, the present processing is performed. finish. On the other hand, S10
At ~ S12, since it is a condition that the combustor necessary increase heat quantity cannot be satisfied due to the decrease in hydrogen consumption quantity, first, the hydrogen consumption quantity is decreased within a possible range, and then the additional methanol fuel for satisfying the necessary increase heat quantity is added. It is directly charged into the combustor 13 until the amount of reformed gas increases. Next, when the reformed gas amount increases in S13 to S14, the supply of additional methanol is reduced until the supply amount becomes unnecessary (supply amount = zero), and then the process proceeds to S8 and subsequent steps.

FIG. 5 shows a second embodiment of the present invention. Explaining the parts different from the first embodiment, in this embodiment, a control valve 31 for controlling the flow rate of the fuel gas is provided at the inlet of the fuel electrode 1A of the fuel cell 1 and is branched from the control valve 31. A bypass line 32 communicating with the off-gas passage 25 is provided. When reducing the amount of hydrogen consumed in the fuel cell 1, the opening of the control valve 32 is adjusted to reduce the amount of hydrogen introduced into the fuel electrode 1A.

FIG. 6 shows a third embodiment of the present invention. First
Is different from that of the first embodiment in that a control valve 33 for controlling the air flow rate is provided at the inlet of the air electrode 1B of the fuel cell 1, and a bypass line 34 that branches from the control valve 33 and communicates with the exhaust air passage 26 is provided. There is a point. When reducing the hydrogen consumption in the fuel cell 1, the opening of the control valve 33 is adjusted,
The amount of air introduced into the air electrode 1B is reduced to suppress the reaction in the fuel cell 1, and as a result, the hydrogen consumption amount is reduced.

7 and 8 show other embodiments of the control method of the present invention, respectively. 7 differs from FIG. 4 in the processing of S7 to S9 and S13 to S14.
In summary, when a load increase request is input to the control unit 5, the fuel cell 1 first reduces the hydrogen consumption amount, and while observing the outlet temperature of the combustor 13, this temperature is allowed from the set value T1. While not decreasing the capacity ΔT or more, the decrease amount of hydrogen consumption is gradually reduced and the amount Gf1 of methanol directly supplied to the combustor 13 is increased. As a result, the power generation amount reduction time of the fuel cell 1 can be minimized.

In the control of FIG. 8, when a load increase request is input to the control unit 5 in S1 to S3,
The combustion heat increase amount ΔQ1 in the combustor 13 required for this is calculated. Next, in S4 to S6, the amount of methanol necessary for that purpose, which should be directly charged into the combustor 13, is calculated, and then the amount of heat Q2 required to vaporize the amount of methanol is calculated, and hydrogen corresponding to Q2 is calculated. Calculate the amount. Next, in S7, the reduction amount of the hydrogen consumption amount in the fuel cell 1 required to supply the hydrogen amount to the combustor 13 is calculated and executed, and in S8, the direct supply of methanol to the combustor 13 is executed. . S9 and S10 are the same as S8 and 9 in FIG. By doing so also, the amount of decrease in the power generation amount of the fuel cell 1 can be suppressed to the necessary minimum.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a combustion part temperature distribution when an off gas is supplied to a combustor.

FIG. 2 is an explanatory diagram of a combustion part temperature distribution when a liquid fuel is supplied to the combustor.

FIG. 3 is a schematic configuration diagram of a first embodiment of a fuel cell system to which the present invention has been applied.

FIG. 4 is a flowchart showing a first example of a control method for the combustion cell system.

FIG. 5 is a schematic configuration diagram of a second embodiment of a fuel cell system to which the present invention has been applied.

FIG. 6 is a schematic configuration diagram of a third embodiment of a fuel cell system to which the present invention is applied.

FIG. 7 is a flowchart showing a second example of the control method of the combustion cell system.

FIG. 8 is a flowchart showing a third example of the control method of the combustion cell system.

[Explanation of symbols]

1 fuel cell 1A Fuel cell fuel electrode 1B Fuel cell air electrode 3 motor 4 Power controller 5 control unit 6 Accelerator sensor 11 reformer 12 CO remover 13 Combustor 14 Vaporizer 16 Methanol and water feeder 17 Water tank 18 Methanol tank 20 Air introduction passage 21 Fuel introduction pipe 23 gas passage 24 Air introduction passage 25 Off-gas passage 26 Exhaust air passage

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 8/00 H01M 8/00 AZ F term (reference) 4G040 EA02 EA03 EA06 EB43 5H027 AA02 BA01 BA09 BA16 DD00 DD03 KK41 MM04 MM09 5H115 PA01 PA11 PC06 PG04 PI16 PI18 PU01 SE06 TI00 TO21 TU17

Claims (6)

[Claims] 1. A fuel reforming apparatus for producing a hydrogen-rich fuel gas using a hydrocarbon fuel and water, a fuel cell for generating electric power using the fuel gas, and a fuel cell for exhausting without being consumed by the fuel cell. And a combustor for combusting off-gas containing hydrogen, and the combustion heat generated in the combustor vaporizes the reforming hydrocarbon fuel and water. The fuel cell system is characterized in that the hydrogen consumption amount in the fuel cell is temporarily reduced when the fuel consumption increases and the combustion heat amount in the combustor is increased. 2. The fuel cell system according to claim 1, wherein hydrogen consumption in the fuel cell is reduced by reducing the amount of hydrogen introduced into the fuel electrode of the fuel cell. 3. The fuel cell system according to claim 1, wherein hydrogen consumption in the fuel cell is reduced by reducing the amount of air introduced into the air electrode of the fuel cell. 4. A structure for directly supplying a reforming hydrocarbon-based fuel quantity to a combustor, and a temperature detecting means for detecting a combustor outlet gas temperature, which is provided in the fuel cell according to the outlet gas temperature. 2. The fuel cell system according to claim 1, wherein the ratio between the amount of decrease in hydrogen consumption and the amount of hydrocarbon-based fuel directly supplied is controlled. 5. The fuel cell system according to claim 4, wherein the reduced amount of hydrogen consumption in the fuel cell is used as the latent heat of vaporization of the hydrocarbon-based fuel directly supplied to the combustor for combusting the excess hydrogen-rich gas. 6. The fuel cell system according to claim 1, further comprising a secondary battery that compensates for the output shortage with respect to the required load when the hydrogen consumption in the fuel cell is temporarily reduced.