JP2003068344A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system which evaporates a raw material for reforming in high response to fluctuations of the load on a fuel cell. SOLUTION: The fuel cell system, equipped with a reformer 1 forming a reformed gas mainly of hydrogen from the raw material containing a liquid fuel, is equipped with plural sets (C1.V1 to Cn.Vn) of an evaporator to feed the raw material to the reformer 1 and a combustion apparatus to feed a heated gas as the heat source to the evaporator in such series that the heated gas discharged from an upstream evaporator is introduced to a downstream combustion apparatus. AT a minimum load, only the first combustion apparatus C1 and evaporator V1 are operated, and with load increased, the sets to be operated are increased. Since the combustion gas from an upstream combustion apparatus is introduced to the downstream evaporator, the evaporator of every set is always kept above the fuel evaporation temperature, thereby feeding the fuel vapor to the reformer 1 in a quick response to the fluctuations of the load.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a reformer for a fuel cell.

[0002]

2. Description of the Related Art In a fuel cell system having a reformer, hydrogen contained in anode exhaust gas discharged from a fuel cell is burned, and the heat of combustion burns hydrogen for reforming (hydrocarbon system). Energy efficiency can be improved by vaporizing the fuel or the mixed fuel of the fuel and water (the same applies hereinafter).

When a heat exchange type evaporator is applied as a method of vaporizing raw materials, for example, when the anode exhaust gas of a fuel cell is made into a combustible gas and a combustion reaction is caused with oxygen, the combustion energy is used to raise the temperature of the combustor itself. Then, the liquid fuel is supplied to the evaporator, and then the temperature of the evaporator is raised to some extent, and then vaporization of the liquid fuel is started. That is, in the vaporization method in which the combustor and the evaporator are combined, the heat capacity of the combustor and the evaporator is the main factor of the delay time until startup.

By the way, when the combustion gas containing the anode exhaust gas of the fuel cell as a combustible component is used as an energy source for fuel evaporation, the supplied heat amount must be substantially equal to or higher than the heat of vaporization. Due to the efficiency of the fuel cell energy system, a large amount of exhaust heat is not desirable. The fact that the surplus energy is small means that high-efficiency operation is established when a constant operating condition is maintained, but the operation itself becomes impossible, for example, when the operating load changes from low load to high load. Changing the operating load to the high load side means
This means that it is necessary to increase the evaporation amount of the reformed fuel.

However, there is a limit to the amount of heat that can be used for the heat of vaporization, and it is necessary to add energy from the outside or efficiently use the above-mentioned surplus energy to solve this problem. In the mechanism that burns the anode exhaust gas,
In the above method of supplying energy from the outside, this means that a mechanism for supplying energy from another path in order to vaporize the reformed fuel is provided, which leads to complication of the device and also in terms of energy efficiency. Not preferable. In addition, the method of using surplus energy generally causes a problem that the delay time from the heat capacity of the equipment to the load change request increases.

On the other hand, Japanese Unexamined Patent Publication No. 2000-100462 discloses a structure in which a plurality of vaporizers each having a compact combustion burner and an evaporator are combined in parallel.
In this case, when operating at low load, the delay time associated with the heat capacity mentioned above is improved by the effect of narrowing down the number of combustion burners to be operated to one or a few, and downsizing each combustor and evaporator. I am going to do it. However, when the load changes from low load to high load, it is necessary to heat the evaporator at a temperature much lower than the evaporation temperature of the liquid. Sex does not get faster. In addition, the combustion gas supplied to the evaporator is preferably the combustion gas obtained by catalytic combustion in order to reduce the temperature distribution in the evaporator, but the combustion catalyst has a temperature (Light
Off Temperature) is set, and even if fuel is supplied, it will not burn below this temperature.

Further, Japanese Patent Laid-Open No. 2000-203801 proposes a plate fin type heat exchanger in which a combustion catalyst is carried on the surface of a flow path through which a heating gas flows.
In this device, when combustible gas and oxygen pass through the evaporator,
The heat energy generated by combustion on the surface of the catalyst carried by the evaporator is utilized for vaporizing the reformed fuel via the plate fins. In this case, the heat capacity of the whole is reduced by integrating the combustor and the evaporator, and the delay time is shortened. However, even if a catalytic combustor is applied instead of the combustion burner in this way, the combustor that does not operate at low load will be at low temperature, so even if the load changes to high load, the catalytic combustor that has been stopped until then will not Does not work. Therefore, the effect of shortening the delay time when the load changes is insufficient. Although the plate fin of the heat exchanger originally uses a metal having good thermal conductivity, when the catalyst is carried on the plate fin, ceramics is used as a carrier, so the heat exchange performance should be reduced accordingly. Becomes On the other hand, catalytic combustion is a chemical reaction mainly occurring on the catalyst surface, and it can be considered that the amount of heat generated at that time is given to the gas, not the catalyst. Considering these facts, it is difficult for the structure in which the catalyst is supported on the evaporator to efficiently use the combustion energy in the evaporator.

The present invention has been made by paying attention to such a conventional problem, and provides a fuel cell system capable of evaporating a reforming raw material with good responsiveness to a load variation of the fuel cell. It is intended to be provided.

[0009]

A first aspect of the present invention is a fuel cell system including a reformer for producing a reformed gas containing hydrogen as a main component from a raw material containing a liquid fuel, and supplying the reformer with the reformed gas. A plurality of pairs of an evaporator for evaporating the raw material and a combustor for supplying a heating gas serving as a heat source to the evaporator, and the heating gas exhausted from the evaporator is provided on the downstream side of the plurality of evaporators and combustors. Connected in series so as to be introduced into the combustor.

A second invention is the same as the first invention,
The raw material supply device that supplies the raw material to the plurality of evaporators is configured to selectively supply the raw material to the number of evaporators according to the load of the fuel cell.

A third invention is the same as the first invention,
The combustor was composed of a catalytic combustor using a combustion catalyst.

According to a fourth aspect of the present invention, the combustor according to each of the above-described aspects contains a hydrocarbon component contained in the fuel cell anode exhaust gas as a combustible component and / or an oxygen contained in the fuel cell cathode exhaust gas as an oxidation aid. I was supposed to supply it.

In a fifth aspect of the invention, the plurality of combustors in the fourth aspect of the invention are set so that the total combustion capacity thereof is capable of burning substantially all combustible components of the fuel cell anode exhaust gas.

A sixth invention is the first invention or the third invention.
In the invention to the fifth invention, the combustion efficiency is set higher as the plurality of combustors are located on the downstream side.

A seventh invention is based on the sixth invention.
When the sum of the combustion capacities of a plurality of combustors is 1, the first stage from the upstream side is 0.1 to 0.3, the second stage is 0.2 to 0.4, and the third stage is It was composed of three combustors whose respective combustion capacities were set in the range of 0.3 to 0.7.

In an eighth aspect based on the fourth to seventh aspects, the flow rate of the fuel cell anode exhaust gas supplied to the combustor is measured, and the amount of oxygen supplied to the combustor is controlled.

In the ninth invention, in each of the above inventions, the fuel component in the raw material contains alcohols or lower hydrocarbons such as gasoline.

[0018]

According to each of the following inventions, by combining the combustor and the evaporator in multiple stages in series,
For example, when the fuel cell operates at an extremely low load, only the first stage of the combustors arranged in series operates. At this time, by disposing the evaporator adjacent to the combustor, the amount of heat obtained by the combustor can be efficiently given to the evaporator. In this case, 1
The heat quantity of the combustor located in the second stage does not need to give the heat quantity for raising the temperature of the combustor and the evaporator of the second and subsequent stages. In other words, according to this configuration, the combustor and the evaporator are required. It is possible to minimize the heat capacity of raising the temperature.

In the second aspect of the invention, the efficiency can be further improved by operating any number of the combustor and the evaporator combined in series. That is, when the operating load is low, only the first-stage combustor and evaporator located on the upstream side are operated, and when the load increases above a certain level, the combustibles that cannot be completely burned in the first-stage combustor are burned. Since the gas is supplied to the combustor in the second and subsequent stages, it is possible to generate the required amount of reformed gas by supplying the raw material in the second and subsequent stages. The same applies to the case where there are three or more stages of combustors and evaporators, and thus the amount of reformed gas corresponding to the operating load can be accurately supplied.

As the combustor, a catalytic combustor can be applied as shown in the third invention.
If a configuration in which a combustor and an evaporator are combined in parallel is adopted as disclosed in JP 2000-100462 A, the combustor that is not operating at low load has a low temperature.
The catalyst activation temperature is not raised, combustion cannot be started immediately, and responsiveness is poor. On the other hand, in the present invention, by combining the combustor and the evaporator in series, the temperature of the combustion gas discharged from the upstream combustor corresponds to the vaporization temperature of the liquid to be evaporated. Generally, the vaporization temperature of the reformed fuel is 60 ° C to
In the configuration of the present invention, the inactive combustor and evaporator are warmed up at this temperature even under a low load condition, and the above-mentioned temperature of 60 to 120 ° C. is a normal combustion catalyst. Since the temperature is equal to or higher than the activation temperature of 1, the excellent responsiveness can be exhibited even when the load changes from a low load to a high load.

According to the fourth aspect of the invention, the combustible components burned in the combustor are obtained from the anode exhaust gas discharged from the fuel cell body. By burning the residual hydrogen component contained in the anode exhaust gas and supplying the amount of heat required for evaporation, the energy efficiency of the entire fuel cell can be improved.

According to the fifth aspect of the invention, the sum of the combustion efficiencies of the multiple-stage combustor in series burns almost all the combustible gas components contained in the anode exhaust gas discharged when the fuel cell is in rated operation. It is possible. For this, the capacity of the combustor is determined in advance according to the characteristics of the fuel cell. The combustible components in the exhaust gas are mainly hydrogen and other trace amounts, but also carbon monoxide and hydrocarbons. The present invention can reduce the emission of these harmful gases.

The combustion temperature and the calorific value generated by combustion are the combustible gas composition and flow rate, the concentration and flow rate of the oxidation aid (usually oxygen),
It depends on the concentration and flow rate of the noncombustible gas. When burning the anode exhaust gas of the fuel cell, it is possible to easily grasp the composition and concentration of each gas component by investigating with an analyzer or the like. If the amount of heat and the temperature generated in the combustor can be grasped, it is possible to supply the required amount of heat in each evaporator from each combustor. This feature relates to the invention of claim 6.

This is not the case unless the rated (maximum output) value of the fuel cell is extremely large, but it is practical for a vehicle, and generally, the combination of the combustor and the evaporator is about three stages. From the viewpoint of size and cost, and in addition to this, by distributing the combustion ability of each combustor as shown as the seventh invention, it is possible to efficiently perform combustion from low load to high load. It will be possible. Here, when the total number of combustors is N, the total combustion capacity of N combustors is R, and the combustion capacity of the Xth combustor (where 1 ≦ X ≦ N) is Rx, Rx is given by the following equation. expressed. It should be noted that R sets the combustion capacity capable of burning almost all exhaust gas discharged from the fuel cell during the rated operation as described above.

Rx = R (X!-(X-1)!) / N! (1) Depending on the capacity of the fuel cell, it is expected that even if the exhaust gas is combusted, the vaporization temperature of the fuel will not be reached, or conversely, the temperature of the combustion gas will become high and exceed the heat resistant temperature of the combustor. It On the other hand, according to the eighth aspect of the invention, the above problem can be solved by measuring the anode exhaust gas flow rate of the fuel cell, burning the combustible gas in the anode exhaust gas, and controlling the combustion temperature at that time. Is. Specifically, when the oxidation aid is insufficient, or when the combustion temperature becomes too high, air is introduced from the outside by a pump. On the other hand, when the amount of the oxidation aid is large or the combustion temperature is low, the relief valve or the like is used to control the cathode exhaust gas to escape.

As shown in the ninth invention, alcohols such as methanol, lower hydrocarbons such as gasoline, or a mixture of these with water can be applied as the raw material.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a fuel cell system to which the present invention is applied. In the figure, 1 is a reformer, which is an air and fuel vapor passage 5 from the air supply passage 10.
The reformed gas containing hydrogen as a main component is generated by receiving the supply of the raw material vapor from. Reference numeral 2 is a CO remover for removing carbon monoxide in the reformed gas, and 3 is a reformed gas and air supply passage 1 sent from the CO remover 2 through a reformed gas passage 6.
1 is a fuel cell stack that receives the supply of air from 1 to generate power. The reformed gas is supplied to the anode electrode of the fuel cell stack 3, the air is supplied to the cathode electrode, and the surplus gas of each is passed through the anode exhaust gas passage 7 and the cathode exhaust gas passage 8 to the multistage combustor and evaporator. Supplied.

Reference symbols C and V in the drawing respectively denote the above-mentioned combustor and evaporator, and subscripts 1 to n indicate the number of stages thereof. Combustors C1 to Cn are catalytic combustors, evaporators V1 to Vn
Is a heat exchange type evaporator. As shown in the figure, the combination of the second-stage combustor C2 and the evaporator V2 is connected in series downstream of the combination of the first-stage combustor C1 and the evaporator V1. The combustor Cn up to the n-th stage and the evaporator Vn are connected in series. The fuel cell stack 3 is provided in the first stage combustor C1 located at the most upstream side.
The anode exhaust gas passage 7 and the cathode exhaust gas passage 8 are connected to each other to burn unreacted hydrogen and oxygen contained in each exhaust gas to heat the evaporators V1 to Vn. Each of the evaporators V1 to Vn receives supply of a liquid material from a fuel tank (not shown) via fuel cocks FC1 to FCn connected to the material passage 4, and the combustion gas is heated to evaporate in the evaporators V1 to Vn. The obtained raw material is supplied to the reformer 1 via the fuel vapor passage 5 as described above. The exhaust gas that has completed the heat exchange in each evaporator is discharged from the final-stage evaporator Vn through the exhaust gas passage 9 to the outside.

The respective cocks FC1 to FCn are controlled by a control device (not shown) as shown in Table 1 according to the load state. The load increases from load 1 to load 3 to the rated load in the table. The left column of each load column is the combustor C1-
The combustion state of Cn and the right column show the open / close states of the fuel cocks FC1 to FCn, respectively.

[0030]

[Table 1] By the way, the amount of combustible exhaust gas supplied from the fuel cell stack 3 depends on the amount of fuel that can be evaporated under a low load, and even if the raw material is excessively supplied to the evaporator, the total amount cannot be vaporized. . Therefore, as the operating load increases, it is necessary to increase the fuel supply amount to the evaporators V1 to Vn, that is, the number of operated evaporators.
A problem at this time is a delay time from when the combustor, which has not been operated until then when the load is increased, is supplied with the combustible gas until the combustion is started. In this respect, according to the present invention, even when only the first-stage combustor C1 is operating, the temperature of the gas discharged from the evaporator V1 is equal to or higher than the vaporization temperature of the fuel, and this temperature is the latter stage. Combustor C
A temperature sufficient to warm up the catalyst from 2 to Cn,
Therefore, when the load increases and the combustible gas and the oxygen that is the oxidation aid reach the combustor, it is possible to start the operation without delay.

Although not shown, each combustor C1 to Cn
Any or all of the above may be provided with a fuel / air supply device for additionally supplying combustion air and fuel, if necessary.

FIG. 2 shows a second embodiment of the present invention. In this embodiment, the combustor and the evaporator are provided in three stages to facilitate control and reduce costs.
Further, in the first stage combustor C1, the heat capacity of the combustor itself is made small in order to quickly supply the combustion heat quantity to the first stage evaporator V1 when the load is low.

At rated load, the combustion temperatures are C1, C2
The order is C3, but when the ability to burn combustible gas in the first stage combustor C1 is large, this temperature difference becomes even larger. The same applies to the relationship between the second-stage combustor C2 and the third-stage combustor C3.
It is preferable to increase in the order of 2 and C3. For example, if the combustion capacity ratio of the combustors C1, C2, C3 is 20%, 30
%, It is possible to reduce the possibility of becoming an abnormally high temperature in the upstream portion, and to achieve both combustion characteristics and evaporation characteristics.

FIG. 3 shows a third embodiment of the present invention. This is based on the first embodiment and is further provided with a flow rate sensor 12 for detecting the anode exhaust gas flow rate of the fuel cell stack 3, a pump 13 and a relief valve 15 for controlling the cathode exhaust gas flow rate, and the anode exhaust gas flow rate. The flow rate of the cathode exhaust gas is controlled so as to match the combustion temperature assumed from the above, and the temperatures of the combustors C1 to Cn can be optimally controlled. Reference numeral 14 is an air supply passage for supplying combustion air.

The same parts in each embodiment are designated by the same reference numerals, and the duplicated description is omitted.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of a fuel cell system according to the present invention.

FIG. 2 is a schematic configuration diagram of a second embodiment of a fuel cell system according to the present invention.

FIG. 3 is a schematic configuration diagram of a third embodiment of a fuel cell system according to the present invention.

[Explanation of symbols]

1 reformer 2 CO remover 3 Fuel cell stack 4 Raw material supply passage 5 Evaporative fuel passage 6 reformed gas communication 7 Anode exhaust gas passage 8 Cathode exhaust gas passage 9 exhaust gas passage 10 Air supply passage 11 Air supply passage C1-Cn combustor V1-Vn evaporator FC1-FCn Fuel cock

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 8/04 H01M 8/04 P

Claims (9)

[Claims] 1. A fuel cell system including a reformer for producing a reformed gas containing hydrogen as a main component from a raw material containing a liquid fuel, and an evaporator for evaporating the raw material supplied to the reformer, A plurality of sets of combustors for supplying heating gas as a heat source to the evaporator are provided, and the plurality of evaporators and combustors are connected in series so that the exhaust heating gas from the evaporator is introduced to the downstream side combustor. A fuel cell system characterized by being connected to. 2. The fuel according to claim 1, wherein the raw material supply device for supplying the raw material to the plurality of evaporators is configured to selectively supply the raw material to the number of evaporators according to the load of the fuel cell. Battery system. 3. The fuel cell system according to claim 1, wherein the combustor is a catalytic combustor using a combustion catalyst. 4. The hydrocarbon component contained in the fuel cell anode exhaust gas as a combustible component and / or the oxygen contained in the fuel cell cathode exhaust gas as an oxidation aid is supplied to the combustor. Item 5. The fuel cell system according to any one of Items 3. 5. The plurality of combustors, the total combustion capacity,
The fuel cell system according to claim 4, wherein the fuel cell anode exhaust gas is set so that substantially all of the combustible components of the exhaust gas can be burned. 6. The combustion efficiency is set to be higher as the plurality of combustors are located on the downstream side.
7. The fuel cell system according to claim 5. 7. The first stage from the upstream side of the plurality of combustors is 0.1 to 0.1 when the total sum of the combustion capacities is 1.
0.3, 2nd stage is 0.2-0.4, 3rd stage is 0.3-
7. The fuel cell system according to claim 6, comprising three combustors each having a combustion capacity set within a range of 0.7. 8. The fuel cell according to claim 4, wherein the fuel cell anode exhaust gas flow rate supplied to the combustor is measured to control the oxygen amount supplied to the combustor. system. 9. The fuel cell system according to claim 1, wherein alcohol or low hydrocarbon such as gasoline is contained as a fuel component in the raw material.