JPH0824054B2 - Fuel cell power plant and control method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a reformer for steam-reforming a raw material gas, for example, natural gas to produce hydrogen fuel gas, and a hydrogen fuel gas obtained from the reformer. The present invention relates to a fuel cell power generation plant that includes a fuel cell as a fuel and uses anode exhaust gas of the fuel cell as fuel for a reformer, and a control method thereof.

[Background of the Invention]

As a known example closest to the present invention, there is JP-A-57-212779.

Fuel cell power plants are currently undergoing various research and development improvements, but there are some system problems.
One of them is the problem of responsiveness when the plant load changes. That is, the response to the load change of the fuel cell main body is almost instantaneous, but the response of the reformer has a time delay, so that the temperature of the reformer decreases and the load decreases when the load increases, for example. There is a problem that the temperature of the reformer rises.

As one of measures against this, Japanese Patent Laid-Open No. 57-212779 mentioned above,
A method has been proposed in which auxiliary fuel is constantly supplied to the reformer and an anode exhaust gas discharge line is provided. In this method, the temperature of the reformer is controlled by adjusting the flow rate of the auxiliary fuel that is constantly supplied to the reformer in the region where the load change rate is small, and the anode exhaust gas is discharged when the load is suddenly reduced. The temperature of the reformer is controlled by letting it escape from the line.

However, in this method, the auxiliary fuel is always supplied to the reformer in addition to the anode exhaust gas, so the plant thermal efficiency is lower than when the auxiliary fuel is not used, and the anode exhaust gas is released to the outside when the plant load suddenly decreases. Because
There was a drawback that the thermal efficiency of the plant was lowered and an exhaust gas treatment device was required.

[Object of the Invention]

An object of the present invention is to change a load in a fuel cell power plant including a reformer that steam-reforms a raw material gas to generate a hydrogen fuel gas and a fuel cell that uses the hydrogen fuel gas obtained from the reformer as a fuel. It is an object of the present invention to provide a fuel cell power generation plant capable of improving the thermal efficiency of the plant and prolonging the life of the reformer catalyst while maintaining the rapid change of the plant load with respect to the demand, and a manufacturing method thereof.

[Outline of Invention]

In the conventional control method of the fuel cell power generation plant, the auxiliary fuel is always used and the anode exhaust gas is discarded to the outside, so that the thermal efficiency of the plant is lowered and the anode exhaust gas treatment device is required.

The present invention provides a system in which the anode exhaust gas is bypass-recirculated from the reformer combustion section inlet to the reformer fuel gas outlet or the reformer raw material gas inlet, or the anode exhaust gas is gasified from the reformer combustion section inlet. The amount of anode exhaust gas supplied to the reformer combustion unit by establishing a system that bypasses the combustor installed at the turbine inlet and detecting the temperature of the reformer combustion unit or reformer unit to control the anode exhaust gas bypass flow rate. It is possible to improve the thermal efficiency of the plant and extend the life of the reformer catalyst by adjusting the.

Example of Invention

 Embodiments of the present invention will be described below with reference to the drawings.

 FIG. 1 shows a first embodiment of the present invention.

The fuel cell power plant of the first embodiment includes a gas refining section 1, a reformer 4 having a reformer reforming section 2 and a reformer combustion section 3, an anode 5, an electrolyte 6 and a cathode 7. Fuel cell 8 having, gas / gas heat exchanger 9, and steam separator 10
, Compressors 11, 12, 13, turbine 14, and feed pump 15
And an exhaust heat recovery boiler 16 and the like.

In the gas refining section 1, as a raw material gas 17, about 10 to 12 kg / cm ²
A pressurized natural gas or the like is supplied to a. Since the sulfur content in the natural gas causes a decrease in the activity of the reforming catalyst, the raw gas 18 is sent to the reformer reforming section 2 after removing the sulfur content in the natural gas in the gas refining section 1. .

On the other hand, steam 19 is generated in the exhaust heat recovery boiler 16 and supplied to the reformer reforming section 2.

In the reformer 4, the raw material gas 18 and the steam 19 undergo a reforming reaction by the heat supplied from the reformer reforming section 3 in the reformer reforming section 2, and the gas containing methane as a main component It is reformed into a gas composed mainly of hydrogen and carbon monoxide.

The fuel gas 20 containing reformed hydrogen and carbon monoxide as main components is supplied to the anode 5 of the fuel cell 8.

The fuel cell 8 is composed of a stack of fuel cells, and each fuel cell is composed of a positive electrode and an electrolyte disposed between the both electrodes.

The fuel gas 20 supplied to the anode 5 of the fuel cell 8 is
It reacts with the mixed gas 23 of the air 21 supplied from the compressor 13 and the reformer exhaust gas 22 supplied from the reformer reforming section 3 to generate a DC electric output by an electrochemical reaction. The direct current electric output is converted into alternating current by the inverter 24 to be a final output.

The anode exhaust gas 25 of the fuel cell 8 is heat-exchanged and cooled in the gas / gas heat exchanger 9, and is sent to the steam separator 10. The anode exhaust gas from which water in the gas has been separated by the steam separator 10 is pressurized by the compressor 11 and then heat-exchanged by the gas / gas heat exchanger 9 to be heated and sent to the reformer combustion section 3. To be

On the other hand, the cathode exhaust gas 26 of the fuel cell 8 is the turbine 14
Is sent to the cathode inlet of the fuel cell 8 and is recirculated. The cathode exhaust gas sent to the turbine 14 works in the turbine 14 to drive the compressor 13 and the generator 27 to generate an electric output.

Exhaust gas 28 from the turbine 14 is exhausted to the outside of the system after the heat is recovered by the exhaust heat recovery boiler 16 to generate steam.

Since the anode exhaust gas 25 sent to the reformer combustion section 3 contains unreacted combustion components such as hydrogen and carbon monoxide in the gas, it is catalytically burned by the air 29 supplied from the compressor 13, The heat is recovered in the reformer reforming section 2.

 The fuel cell plant control system will be described.

The fuel cell plant control device 39 inputs signals such as a plant load request signal 53, a fuel cell output 54, a turbine output 55, and a raw material gas flow rate signal 56 as inputs, and outputs control signals such as a fuel flow rate and a reforming steam flow rate. And control the plant. The fuel flow rate is controlled via the flow rate control valve 41, and the reforming steam flow rate is controlled by controlling the reforming steam flow rate adjusting valve 44 via the reforming steam flow rate controller 51. Further, the inverter 24 is controlled. In addition to this, in order to keep the temperature of the reformer 4 at a constant temperature according to the load demand, the reformer temperature controller 38
Can also be controlled.

 Further details will be described.

In response to the load request signal (for example, load increase) 53, the valve 41 changes (increases) the fuel flow rate to 20 and the battery inverter
A load increase signal is given to 24, and a reforming steam flow rate signal is given by a raw material gas flow rate measurement signal from a flow meter 48.
Further, the battery output 54 and the turbine output 55 from the inverter 24 are received to feed back the fuel flow rate. When the reformer temperature setting is, for example, a load decrease, a signal is given in advance in the temperature decreasing direction in anticipation of a temperature increase, and a feedback control is performed via the controller 38 so as to keep the temperature of the reformer constant. Perform word control.

The flow meter 45 detects the flow rate of the auxiliary fuel 52, and the flow meter 46
Performs the anode exhaust gas flow rate detection, the flow meter 47 performs the air flow rate detection, the flow meter 48 performs the source gas flow rate detection, and the flow meter 49 performs the reforming vapor flow rate detection.

The air flow rate controller 50 takes in the flow rates detected by the flow meters 45, 46, 47 and controls the opening degree of the air flow rate adjusting valve 43.

The reformer temperature controller 38 takes in the temperature detected by the thermometer 32 of the reformer combustor 3 or takes in a feedforward control signal and controls the opening degree of the auxiliary fuel flow rate adjusting valve 42 and the bypass flow rate control valve 31. .

The reformer steam flow rate controller 51 receives the opening degree command control signal from the control device 39 and controls the opening degree of the reformer steam flow rate adjusting valve 44.

The general characteristics of the fuel cell power plant when the load changes will be described below.

When the load of the fuel cell power plant increases, the fuel cell plant control device 39 receives the load increase signal 53,
A signal for increasing the flow rate is input to the fuel gas flow rate adjusting valve 41, and the fuel gas flow rate increases. Since the load response of the fuel cell main body is extremely fast, the cell output increases, but the anode exhaust gas flow rate supplied to the reformer combustion section 3 does not immediately increase due to the control delay. Therefore, although the amount of heat required for reforming the raw material gas in the reformer reforming section 2 increases as the flow rate of the raw material gas increases, the amount of heat generated in the reformer combustion section 3 increases too much. However, the temperature of the reformer 4 decreases.

Further, when the load of the fuel cell power plant is reduced, the fuel cell control device 39 receives the signal 53 of increase / decrease and increase, and the fuel gas flow rate adjusting valve 41 receives the signal of narrowing the flow rate, and the fuel gas flow rate decreases. Since the load responsiveness of the fuel cell body is extremely fast as when the load increases, the cell output decreases, but the flow rate of the anode exhaust gas supplied to the reformer combustion section 3 has a time delay in control, and therefore it is not long afterwards. Does not decrease. Therefore, the reformer reforming unit 2 is reduced by reducing the flow rate of the raw material gas.
Although the amount of heat required for reforming the raw material gas is reduced, the amount of heat generated in the reformer combustion section 3 does not decrease so much, and the temperature of the reformer rises.

For the response delay of the control of the reformer 4 when the load of the fuel cell power plant changes as described above, when the load increases, the insufficient calorific value of the reformer combustion unit 3 is used as the auxiliary fuel.
It is solved by supplying 52.

On the other hand, when the load is reduced, the heat quantity of the reformer combustion section 3 is excessive.
Alternatively, it is necessary to partly discharge the anode exhaust gas to other than the reformer combustion section 3. When the reformer combustion section 3 is cooled, the amount of cooling heat is lost, which is not preferable in terms of plant thermal efficiency. In addition, the method of discharging the surplus anode exhaust gas to the outside of the system is not preferable in terms of plant thermal efficiency, and further, since the anode exhaust gas cannot be directly discharged to the atmosphere, a device for treating the anode exhaust gas is required, which is costly in terms of equipment and is not preferable. .

Therefore, it is required to treat the surplus anode exhaust gas in the plant system in terms of plant thermal efficiency and equipment cost.

As a method of treating the surplus anode exhaust gas in the plant system, there is a method of installing a surge tank at the inlet of the reformer combustion section 3 to absorb the surplus anode exhaust gas, but the pressure control of the anode is strict. However, since a surge tank having a large capacity is required, it is not suitable for a fuel cell power generation plant that requires compactness, and it requires a high facility cost.

In the embodiment of the present invention shown in FIG. 1, a system 30 for bypassing the anode exhaust gas 25 from the reformer combustion section 3 inlet to the reformer fuel gas outlet, and an anode exhaust gas bypass flow rate adjusting valve 31 are provided to perform reforming. The surplus of the anode exhaust gas supplied to the reactor combustion section 3 is recirculated to the fuel gas side to control the temperature of the reformer 4.

FIG. 2 shows the relationship between the plant load, each gas flow rate, and the reformer temperature when the plant load is reduced. The horizontal axis represents time, and the vertical axis represents load / flow rate and temperature. 33 is the plant load, 34 is the anode exhaust gas flow rate, 35 is the source gas flow rate, 36 is the anode exhaust gas bypass flow rate, and 37 is the reformer temperature. The control method when the plant load is reduced will be described below with reference to the system diagram of FIG.

When the plant load 33 is changed as shown in FIG. 2, the anode exhaust gas bypass flow rate adjusting valve 31 of FIG. 1 is closed and the anode exhaust gas bypass end 36 is 0 during normal operation of A to B. As the load is reduced from B to D, the fuel gas is reduced to meet the load change demand.
On the other hand, since the change of the anode exhaust gas flow rate 34 has a time delay as shown in FIG. 2, the reformer is supplied with more anode exhaust gas than the required amount of anode exhaust gas, and the temperature of the reformer is increased.
37 rises as shown in FIG. The temperature of the reformer is detected by the thermometer 32 shown in FIG. 1, and the temperature controller 38 shifts to the anode exhaust gas bypass flow rate adjusting valve 31 in a direction to make the deviation zero by the deviation from the reformer set temperature. A signal is given, and the unbalanced portion between the anode exhaust gas flow rate required in the reformer combustion section 3 and the anode exhaust gas flow rate supplied to the reformer combustion section 3 is re-routed to the fuel gas 20 line through the bypass system 30. Circulate. When the anode exhaust gas is bypassed and recirculated, the engine is operated up to the target load D shown in FIG. 2, and when E reaches a certain time after D,
The amount of anode exhaust gas under plant load is matched, and the anode exhaust gas bypass flow rate becomes zero.

Also, the load suddenly decreases and the set temperature of the reformer and the thermometer 32
After the deviation is detected, a signal is given to the anode exhaust gas bypass flow rate adjustment valve 31, and if a delay in the reformer temperature control is considered, the anode exhaust gas bypass flow rate adjustment valve 31 is sent to the plant control device 39 from the plant control device 39. The signal may be given in advance to control the feed forward.

FIG. 3 shows the relationship between the plant load, each gas flow rate, and the reformer temperature when the feedforward control is performed when the plant load suddenly decreases. A signal is sent from the plant controller to open the anode exhaust gas bypass flow control valve at the same time when the plant load starts to decrease, and the anode exhaust gas bypass flow rate is sent.
Flow 36 at a preset flow rate according to the load change rate. At the same time, the raw material gas flow rate 35 is also reduced prior to the plant load.

The relationship between the temperature difference of the reformer and the bypass amount / bypass valve opening will be described.

For a large load change, the anode exhaust gas bypass amount is preset according to the load change speed (for example, 100% → 25% in 5 minutes) to determine the opening degree of the bypass valve 31. Further, for a small load change, the temperature of the reformer is detected and the opening degree of the bypass valve 31 is controlled. In this case, perform linearly.

FIG. 4 shows the relationship between the temperature deviation and the valve opening. In this figure, the auxiliary fuel control valve 42 and the anode exhaust gas bypass flow control valve 31 are used as control target valves. The solid line shows a general control example, and the dotted line shows a control example in which the temperature is around the reformer set temperature. When the actual measured temperature is higher than the reformer set temperature (that is, when the temperature deviation is positive), the opening of the valve 42 is set to zero, that is, the valve 31 is closed linearly according to the deviation amount. Control. On the other hand, when the deviation is negative, the valve 31 is closed to stop the operation of the bypass passage, and instead, the opening of the valve 41 is linearly controlled in an inversely proportional direction.

 FIG. 5 shows a second embodiment of the present invention.

The basic concept of the control system when the load of the fuel cell power plant changes is similar to that of the first embodiment, but the anode exhaust gas bypass destination is the raw material gas inlet of the reformer. That is, it is bypassed via the bypass line 30 and the valve 31.

 FIG. 6 shows a third embodiment of the present invention.

In this embodiment, the anode exhaust gas bypass destination is the combustor 40 installed at the inlet of the turbine 14. Since the bypass gas of the anode exhaust gas is not recirculated to the fuel gas side, the controllability is further improved as compared with the first and second embodiments.

〔The invention's effect〕

As described above, according to the present invention, in the fuel cell power plant, while maintaining the rapid followability of the plant load change to the load change request, the plant thermal efficiency is improved, the life of the reformer catalyst is extended, and It is possible to reduce the number of processing devices for discharge to the outside of the anode exhaust gas system.

[Brief description of drawings]

1, 5 and 6 are system diagrams of a fuel cell power plant according to an embodiment of the present invention. 2 and 3 are diagrams showing the characteristics of the fuel cell power plant when the load changes. FIG. 4 is a relationship diagram between temperature deviation and valve opening. 1 ... Gas refining section, 2 ... Reformer reforming section, 3 ... Reformer combustion section, 4 ... Reformer, 5 ... Anode, 6 ... Electrolyte,
7 ... Cathode, 8 ... Fuel cell.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Naruhisa Sugita, 502 Jinritsucho, Tsuchiura-shi, Ibaraki Hiritsu Manufacturing Co., Ltd. Mechanical Research Laboratory (72) Inventor, Shoji Takahashi 4-6, Kanda Surugadai, Chiyoda-ku, Tokyo Inside Hitachi (56) Reference JP-A-53-81923 (JP, A) JP-A-58-133782 (JP, A) JP-A-59-68181 (JP, A)

Claims (2)

[Claims] 1. A reformer for steam-reforming raw water gas to produce hydrogen fuel gas, a fuel cell in which the produced hydrogen fuel gas is supplied as fuel to an anode, and an anode exhaust gas of the fuel cell. A system for reusing as a fuel for a reformer, a bypass pipe for branching the anode exhaust gas reused through the system upstream of the reformer to join with the raw material gas or the hydrogen fuel gas, and the bypass pipe A bypass valve for controlling the flow rate of the anode exhaust gas passing through the pipe; an auxiliary fuel supply system for assisting the fuel of the reformer; an auxiliary fuel valve provided in the auxiliary fuel supply system for adjusting the amount of auxiliary fuel; The detection means for detecting the temperature of the combustion part of the quality control device is compared with the temperature detected by the detection means and the reformer set temperature. When the detected temperature> the reformer set temperature, the auxiliary fuel valve is closed. The bypass valve Temperature control according to the temperature deviation, and when the detected temperature <reformer setting temperature, the bypass valve is closed and the auxiliary fuel valve opening degree is controlled according to the temperature deviation. Characteristic fuel cell power plant. 2. A reformer for steam-reforming a raw material gas to produce hydrogen fuel gas, a fuel cell in which the produced hydrogen fuel gas is supplied to an anode as a fuel, and an anode exhaust gas of the fuel cell. A system for reusing as a fuel for a reformer, and a bypass pipe for diverging a part of the anode exhaust gas recycled through the system into a bypass branch upstream of the reformer to join with the raw material gas or the hydrogen fuel gas. A bypass valve for controlling the flow rate of anode exhaust gas passing through the bypass pipe; an auxiliary fuel supply system for assisting the fuel of the reformer; and an auxiliary fuel valve provided in the auxiliary fuel supply system for adjusting the amount of auxiliary fuel. In the fuel cell power plant comprising a detection means for detecting the combustion section temperature of the reformer, the detection temperature by the detection means and the reformer set temperature are compared,
When the detected temperature is higher than the reformer set temperature, the auxiliary fuel valve is closed to shut off the auxiliary fuel, and the larger the temperature deviation is, the larger the bypass valve opening is to increase the bypass amount of the anode exhaust gas. If the detected temperature is less than the reformer setting temperature, the bypass valve is closed to shut off the bypass of the anode exhaust gas, and the auxiliary fuel valve opening is increased as the temperature deviation increases to increase the auxiliary fuel amount. A method of controlling a fuel cell power plant, comprising: