JPH04243538A - Method and device for controlling catalyst layer temperature of fuel reformer for fuel battery use - Google Patents

Abstract

PURPOSE:To provide a method and device for controlling the temp. of the catalyst layer of a fuel reformer for fuel battery use reducing the loss of heat and power, even if there is an excessive off-gas emission from the battery affording a heating source for heating the catalyst layer in a reaction pipe of a fuel reformer. CONSTITUTION:There is provided an off-gas emission system provided with a flow rate control value branched from an off-gas supply system for supplying an off-gas from a fuel battery to the burner of a fuel reformer, a flow rate control valve is controlled, so that the temp. of a catalyst layer in a reaction pipe becomes a predetermined value, so as to regulate the flow rate of the off-gas to be supplied to the burner, a ratio control is made of combustion air flow rate, so that an air/fuel ratio of the off-gas flow rate to the combustion air flow rate becomes a predetermined value and the off-gas is burned by the burner to control the temp. of the catalyst layer.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a fuel reformer that is incorporated into a fuel cell power generation device together with a fuel cell. The present invention relates to a catalyst layer temperature control method and apparatus for a fuel reformer for a fuel cell, which controls the temperature of the catalyst layer when steam reforming is performed by heating a reaction tube with off-gas discharged from the fuel reformer.

0002

2. Description of the Related Art A fuel reformer is combined with a fuel cell to construct a fuel cell power generation device. Here, the fuel reformer is
Raw fuel such as hydrocarbons such as natural gas or alcohols such as methanol is passed through a reaction tube containing a catalyst layer filled with a reforming catalyst, and the reaction tube is heated by a heat medium generated by combustion in a burner. It is heated and reformed into hydrogen-rich gas to produce reformed gas.

On the other hand, in a fuel cell, the above-mentioned reformed gas is supplied as a fuel and air is supplied as an oxidizing agent to cause a cell reaction and generate electricity. At this time, off-gas containing unused hydrogen that does not contribute to the cell reaction from the fuel electrode of the fuel cell is used as fuel to be burned in the burner of the fuel reformer.

As such a fuel cell power generation device, a system shown in FIG. 2 is known which is equipped with a fuel reformer for steam reforming raw fuel, for example, natural gas whose main component is methane or the like.

In FIG. 2, a fuel reformer 1 includes a reaction tube 4 containing a catalyst layer 3 filled with a reforming catalyst in a furnace vessel 2.
and a burner 5 at the top of the furnace vessel 2. The fuel cell 7 includes an electrolyte layer 8 that holds a phosphoric acid electrolyte, a fuel electrode 9 and an air electrode 10 that sandwich this, and a fuel chamber 11 and an air chamber 12 that supply reformed gas and air to these electrodes, respectively. It is equipped with

The desulfurizer 13 removes organic sulfur contained in natural gas raw fuel in the form of hydrogen sulfide. Further, the carbon monoxide shift converter 14 transforms carbon monoxide contained in the gas steam-reformed by the fuel reformer 1 to reduce its concentration.

The raw fuel supply system 15 includes a heat exchanger 16 and is connected to the desulfurizer 13, through which the raw fuel of natural gas flows.

[0008] The steam supply system 17 is connected to the raw fuel supply system 15 at the outlet of the destreamer 13, and steam to be added to the natural gas desulfurized in the destreamer 13 flows therethrough.

The reforming raw material gas supply system 18 is equipped with a heat exchanger 19 and is connected between the junction of the raw fuel supply system 15 and the steam supply system 17 at the outlet of the desulfurizer 13 and the reaction tube 4 of the fuel reformer 1. The reforming raw material gas consisting of desulfurized natural gas and steam flows through the inlet.

[0010] The reformed gas supply system 20 is connected to the carbon monoxide shift converter 1
4, connected to the outlet of the reaction tube 4 and the fuel chamber 11 of the fuel cell 7, subjected to steam reforming in the fuel reformer 1, and having a reduced carbon monoxide concentration in the carbon monoxide shift converter 14. Gas flows.

The hydrogen recycling system 22 includes a reformed gas supply system 20 at the outlet of the carbon monoxide shift converter 14 and a raw fuel supply system 15.
A part of the reformed gas flows for hydrogenation to desulfurize the organic sulfur contained in the natural gas flowing through the raw fuel supply system 15 into hydrogen sulfide in the desulfurizer 13 .

The off-gas supply system 23 is connected to the fuel chamber 11 of the fuel cell 7 and the burner 5 of the fuel reformer 1.
An off-gas containing hydrogen that does not contribute to the battery reaction is discharged from the burner 5 and supplied to the burner 5 . In addition, air supply system 2
4 is equipped with a blower 25 and is connected to the air chamber 12, through which reaction air to be supplied to the air chamber 12 flows. Note that 26 is air chamber 1
This is an air exhaust system through which the exhaust air discharged from 2 flows.

The combustion air supply system 27 includes a blower 28 and is connected to the burner 5, through which combustion air to be sent to the burner 5 flows. Note that 29 is an exhaust gas system that discharges combustion gas from combustion in the burner 5 to the outside through the heat exchanger 19.

With such a configuration, the raw fuel supply system 15
The natural gas supplied through the hydrogen recycle system 22 is added with reformed gas supplied through the hydrogen recycle system 22, and after being preheated in the heat exchanger 16, it flows into the desulfurizer 13 and is desulfurized. The desulfurized natural gas is added with steam supplied through a steam supply system 17 and preheated in a heat exchanger 19, and then flows into the reaction tube 4 of the fuel reformer 1.

The reformed raw material gas consisting of natural gas and steam that has entered the reaction tube 4 flows through the catalyst layer 3 within the reaction tube 4 . Then, in the burner 5, the off-gas supplied via the off-gas supply system 23 is combusted by the combustion air supplied via the combustion air supply system 27 by the drive of the blower 28, and the reaction tube 4 is heated by the heat medium generated to catalyze the catalyst. The reforming raw material gas flowing through the layer 3 is steam-reformed into a gas containing hydrogen as a main component. Note that the combustion gas is exhausted to the outside via the exhaust gas system 29.

In the case of methane, the reaction at this time is expressed by the following formula. CH4 +H2 O → 2H2 +CO

001
7] The gas mainly composed of hydrogen sent out from the reaction tube 4 is sent to the carbon monoxide shift converter 13 via the reformed gas supply system 20, where carbon monoxide is converted together with excess water vapor and converted into monoxide. The reformed gas is reformed into a hydrogen-rich gas with a low carbon concentration.

The reaction at this time is represented by the following formula. CO + H2 O → H2 + CO

The reformed gas thus obtained is supplied to the fuel cell 7, and the fuel cell 7 causes a cell reaction with the air supplied through the air supply system 24 by driving the blower 25 to generate electricity. Note that exhaust air containing oxygen that does not contribute to the battery reaction is exhausted from the air chamber 12 to the outside via an air exhaust system 26.

By the way, the reformed gas supplied to the fuel cell 7 is determined based on the amount of power generated by the fuel cell 7, taking into consideration the isodistribution of the reformed gas to the fuel electrode 9 of the fuel cell 7 and the overall heat balance. The amount of reformed gas is approximately 20% larger than the corresponding amount of reformed gas. Therefore, the off-gas contains about 20% of this excess hydrogen, which is sent to the burner 5 of the fuel reformer 1 and burned, and the heat of combustion heats the reaction tube 4 to steam reform the natural gas. ing.

However, when generating electricity with a fuel cell, the amount of reformed gas supplied to the fuel cell is usually an excess amount of reformed gas greater than the above-mentioned 20% so that it can immediately follow load fluctuations, especially load increases. This is because if the amount of reformed gas is insufficient, the amount of off-gas supplied to the burner 5 of the fuel reformer 7 will be insufficient, resulting in insufficient combustion heat, and as a result, the reforming reaction will not occur sufficiently and the raw material This is because the fuel itself may be supplied to the fuel cell, causing a decrease in efficiency, or the gas may be distributed unevenly to the electrodes of the fuel cell, causing damage to the cell.

[0022] However, as mentioned above, the off-gas generated by the cell reaction that is carried out when an excessive amount of reformed gas is supplied becomes excess fuel and is supplied to the burner. Since the temperature of the catalyst layer is excessively increased due to the heat of combustion, the amount of combustion air is made surplus to cool the heat medium, and the heat of combustion is lowered to control the temperature of the catalyst layer to a predetermined value. The temperature of this catalyst layer is controlled as follows.

In FIG. 2, the temperature at the reformed gas outlet of the catalyst layer 3 in the reaction tube 4 is detected by a temperature detector 30, and the detected temperature reaches a predetermined value appropriate for the reforming reaction of the catalyst layer 3. The number of rotations of the blower 28 is controlled to control the amount of combustion air so that the temperature of the catalyst layer is controlled to a predetermined value.

[0024]

[Problem to be Solved by the Invention] As mentioned above, in order to be able to immediately follow the load fluctuations of the fuel cell, the excess off-gas that is discharged due to the supply of an excessive amount of reformed gas to the fuel cell is transferred to the fuel reformer. When burning with a burner, in order to maintain the temperature of the catalyst layer in the reaction tube at a predetermined value, the heating medium generated by combustion is cooled using the amount of excess combustion air.In addition to increasing the blower driving power, the excess combustion This has the disadvantage that combustion heat is dissipated to the outside by air, resulting in large power and heat losses.

An object of the present invention is to provide a fuel reformer for a fuel cell, which is capable of controlling the temperature of the catalyst layer of the fuel reformer while reducing power and heat loss even when excessive off-gas is discharged from the fuel cell. An object of the present invention is to provide a catalyst layer temperature control method and apparatus thereof.

[0026]

[Means for Solving the Problems] In order to solve the above problems, according to the present invention, a reaction system containing a catalyst bed filled with a reforming catalyst is supplied with hydrocarbon-based or alcohol-based raw fuel. a burner for combusting off-gas containing unused hydrogen discharged from the fuel cell and supplied via an off-gas supply system with combustion air supplied via a combustion air supply system including a blower; In a control method for controlling the temperature of a catalyst layer in a fuel reformer in which the raw fuel is reformed into a hydrogen-rich gas by heating the reaction tube with a heat transfer medium generated in a fuel cell and supplied to a fuel cell, The temperature of the catalyst layer is detected by a temperature detector, and the off-gas supply system is controlled by controlling the flow control valve installed in the off-gas exhaust system, which branches off from the off-gas supply system and sends off-gas to the outside so that the detected temperature reaches a predetermined temperature. The air-fuel ratio between the off-gas flow rate detected by the off-gas flow rate detector installed in the off-gas supply system and the combustion air amount detected by the air flow rate detector installed in the combustion air supply system reaches a predetermined value. The amount of combustion air sent from the blower shall be controlled so that

[0027] Furthermore, in the catalyst layer temperature control device for a fuel reformer for a fuel cell that controls the temperature of the catalyst layer in the fuel reformer, a temperature detector for detecting the temperature inside the reaction tube;
an off-gas exhaust system that branches off from the off-gas supply system and sends off-gas to the outside; a flow control valve provided in the off-gas exhaust system that controls the flow rate of off-gas flowing into the off-gas supply system; and detection of the catalyst layer by the temperature detector. A control means for controlling a flow rate control valve based on the deviation between the temperature and a target value of a predetermined temperature of the catalyst layer; an off-gas flow rate detector provided in the off-gas supply system for detecting the flow rate of off-gas; and an off-gas flow rate detector provided in the combustion air supply system for detecting the flow rate of off-gas , an air flow detector for detecting combustion air flow;
It shall be equipped with a ratio control means for controlling the combustion air flow rate sent from the blower so that the air-fuel ratio between the off-gas flow rate detected by the off-gas flow rate detector and the air flow rate detector and the combustion air flow rate becomes a predetermined value. .

[0028]

[Operation] As described above, off-gas containing unused hydrogen is discharged from the fuel cell in excess of the amount corresponding to the amount of electric power generated by the fuel cell. Therefore, the temperature of the catalyst layer in the reaction tube is detected by a temperature detector, and the flow control valve installed in the off-gas exhaust system branched from the off-gas supply system is controlled based on the deviation between this detected temperature and the target value of the predetermined temperature of the catalyst layer. By controlling the flow rate of off-gas flowing through the off-gas supply system, the temperature of the catalyst layer is kept at a predetermined value.

At this time, the air-fuel ratio between the off-gas flow rate detected by the off-gas flow rate detector provided in the off-gas supply system and the combustion air flow rate detected by the air flow rate detector provided in the combustion air supply system is set to a predetermined value. The amount of combustion air sent from the blower is controlled so that the off-gas is combusted in the burner at a predetermined air-fuel ratio.

Note that off-gas other than the off-gas flowing through the off-gas supply system whose flow rate is controlled by the flow rate control valve is supplied to the outside through the off-gas exhaust system and can be used as an effective heat source.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below based on the drawings. FIG. 1 is a system diagram of a fuel cell power generation apparatus equipped with a catalyst layer temperature control device of a fuel reformer for fuel cells according to an embodiment of the present invention. In FIG. 2, parts that are the same as those in the conventional example shown in FIG. The differences in FIG. 1 from the conventional example are as follows.

An off-gas exhaust system 34 is provided which branches off from the off-gas supply system 23 and supplies the off-gas to a heat recovery device 33, such as a hot water boiler or a heat exchanger for heating other fluids, which recovers the combustion heat of the off-gas. , this off-gas exhaust system 34 is provided with a flow rate control valve 35 . The temperature regulator 36 receives a signal of the temperature detected by the temperature detector 30 of the catalyst layer 3, and controls the flow rate control valve 35 based on the deviation between this detected temperature and a target value of a predetermined temperature of the catalyst layer.

The off-gas flow rate detector 40 is provided in the off-gas supply system 23 and detects the off-gas flow rate flowing through the off-gas supply system 23. The air flow rate detector 37 is provided in the combustion air supply system 27 and detects the flow rate of combustion air flowing into the combustion air supply system 27. The air-fuel ratio setter 38 sets the air-fuel ratio between the off-gas flow rate and the combustion air flow rate to a predetermined value. The ratio adjuster 39 receives a signal of the off-gas flow rate detected by the off-gas flow rate detector 40 and a signal of the combustion air flow rate detected by the air flow rate detector 37, and the ratio controller 38
The rotation speed of the blower 28 is controlled to control the combustion air flow rate so that the air-fuel ratio is set to the set air-fuel ratio.

With this configuration, the temperature detector 30 detects the temperature of the catalyst layer 3 in the reaction tube 4, and the signal of this detected temperature is input to the temperature controller 36, and the detected temperature and the catalyst layer 3 are inputted into the temperature controller 36.
The flow rate control valve 35 is controlled by the temperature regulator 36 based on the deviation of the predetermined temperature from the target value, and the off-gas flow rate that makes the temperature of the catalyst layer 3 reach the predetermined temperature flows into the off-gas supply system 23. Note that off-gas other than the off-gas flowing through the off-gas supply system 23 flows through the flow rate control valve 35 and is transferred to the heat recovery device 33.
The heat is recovered by combustion of the off-gas.

At this time, the air-fuel ratio between the flow rate of off-gas flowing through the off-gas supply system 23 and the flow rate of combustion air flowing through the combustion air supply system 27 is controlled to a predetermined value as described below. That is, the air-fuel ratio setter 3 is controlled by the ratio controller 39 into which the signal of the off-gas flow rate detected by the off-gas flow rate detector 40 and the signal of the combustion air flow rate detected by the air flow rate detector 37 are input.
The rotational speed of the blower 28 is controlled to control the combustion air flow rate so as to achieve the air-fuel ratio set in step 7. Therefore, the controlled off-gas flowing through the off-gas supply system 23 is combusted in the burner 5 at a predetermined air-fuel ratio.

In this example, temperature control of the catalyst layer when steam reforming hydrocarbon raw fuel is explained, but the same applies to temperature control of the catalyst layer when steam reforming alcohol raw fuel. Effect can be obtained.

[0037]

As is clear from the above description, according to the present invention, gas is supplied from the fuel cell to the burner of the fuel reformer via the off-gas supply system so that the temperature of the catalyst layer in the reaction tube becomes a predetermined value. The off-gas flow rate is controlled by a flow control valve provided in the off-gas exhaust system, and the combustion air flow rate is controlled so that the air-fuel ratio between the controlled off-gas flow rate flowing into the off-gas supply system and the combustion air flow rate is a predetermined value. As a result, the temperature of the catalyst layer in the reaction tube is controlled to a predetermined value by the combustion heat generated by the combustion of off-gas in the burner, which is controlled at a predetermined air-fuel ratio, so there is no need to supply excess combustion air to the burner. Therefore, heat loss and power loss of the blower are reduced, and the off-gas other than the off-gas that does not flow to the off-gas supply system flows to the off-gas discharge system, which has the effect that this off-gas can be used effectively.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a fuel cell power generation device equipped with a catalyst layer temperature control device of a fuel reformer for fuel cells according to an embodiment of the present invention.

[Figure 2] System diagram of a fuel cell power generation device equipped with a conventional catalyst layer temperature control device of a fuel reformer for fuel cells

[Explanation of symbols]

1 Fuel cell reformer 3 Catalyst layer 4 Reaction tube 5 Burner 7 Fuel cell 23 Off-gas supply system 27 Combustion air supply system 28 Blower 30 Temperature detector 34 Off-gas exhaust system 35 Flow control valve 36 Temperature controller 37 Air flow rate detector 38 Air-fuel ratio setting device 39 Ratio adjuster 40 Off gas flow rate detector

Claims (2)

[Claims] Claim 1: A reaction tube containing a catalyst layer filled with a reforming catalyst to which hydrocarbon-based or alcohol-based raw fuel is supplied; and a burner that burns the off-gas containing hydrogen with combustion air supplied through a combustion air supply system equipped with a blower, and heats the reaction tube with the heat medium generated by combustion in the burner to produce the raw fuel. In a method of controlling the temperature of a catalyst layer in a fuel reformer that reformes hydrogen-rich gas and supplies it to a fuel cell, the temperature of the catalyst layer in a reaction tube is detected by a temperature detector, and this detected temperature is set to a predetermined temperature. The off-gas flow rate flowing through the off-gas supply system is controlled by controlling the flow rate control valve installed in the off-gas exhaust system that branches from the off-gas supply system and sends off-gas to the outside, and the off-gas flow rate detection system installed in the off-gas supply system It is characterized by controlling the amount of combustion air sent from the blower so that the air-fuel ratio between the off-gas flow rate detected by the combustion air flow rate detector and the combustion air amount detected by the air flow rate detector installed in the combustion air supply system becomes a predetermined value. A method for controlling the temperature of a catalyst layer in a fuel reformer for a fuel cell. Claim 2: A reaction tube containing a catalyst layer filled with a reforming catalyst to which hydrocarbon-based or alcohol-based raw fuel is supplied, and a reaction tube that is discharged from the fuel cell and supplied via an off-gas supply system. and a burner that burns the off-gas containing hydrogen with combustion air supplied through a combustion air supply system equipped with a blower, and heats the reaction tube with the heat medium generated by combustion in the burner to convert the raw fuel. A control device that controls the temperature of the catalyst layer in a fuel reformer that reformes hydrogen-rich gas and supplies it to a fuel cell includes a temperature detector that detects the temperature inside the reaction tube, and a temperature sensor that branches off from the off-gas supply system and connects the external an off-gas exhaust system that sends off-gas to the off-gas exhaust system; a flow rate control valve that is installed in the off-gas exhaust system to control the flow rate of off-gas flowing to the off-gas supply system; a control means for controlling a flow rate control valve based on the deviation from a target value; an off-gas flow rate detector provided in the off-gas supply system to detect the flow rate of off-gas; and an air-flow detector provided in the combustion air supply system to detect the flow rate of combustion air. a flow rate detector, a ratio control means for controlling the flow rate of combustion air supplied from the blower so that the air-fuel ratio between the off-gas flow rate detected by the off-gas flow rate detector and the air flow rate detector and the combustion air flow rate becomes a predetermined value; A catalyst layer temperature control device for a fuel reformer for a fuel cell, comprising: