JPS6180762A - Load control method for fuel cell power generation system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a load control method for a fuel cell power generation system equipped with a turbo compressor.

[Conventional technology] Fuel cell power generation systems can achieve higher thermal efficiency than steam power generation systems that use petroleum, coal, etc. as fuel, are environmentally friendly, and have flexibility in terms of location. are doing. Therefore, in recent years, various uses are being considered not only as power sources for special purposes such as space exploration, but also as power sources for departmental use, and development is becoming more active with the aim of putting them into practical use.

A fuel cell power generation system consists of a fuel cell that has an electrolyte layer interposed between an air electrode and a hydrogen electrode, and a hydrocarbon fuel such as natural gas that is reformed to supply hydrogen gas as fuel to the hydrogen electrode. A reformer for supplying air, and an air supply means for supplying air to the air electrode and the reformer. The performance of the fuel cell tends to improve as the pressure of each reaction gas increases. For this reason, the operating pressure of each of the reaction gases is set to a value of about 1g, for example 4 to 6Kg/am. It accounts for about 20% of the energy.On the other hand, the reforming reaction to generate the fuel gas for the battery requires about 80% of the energy.
The process is carried out at a high temperature of 0° C., and high temperature exhaust gas is discharged from the reformer.

Therefore, if the power for compressing air can be obtained from the exhaust gas energy of the system, it will have a significant effect on improving the efficiency of the system.

Due to these circumstances, recent fuel cell power generation systems
It has become common to use a turbo compressor as the air supply means. That is, the turbo pressure 'IN machine is a turbine driven by surplus air at the air electrode outlet of the fuel cell and exhaust gas from the reformer.

The compressor is directly connected to the turbine and is energized by the turbine to supply the compressed air necessary for the fuel cell and the reformer.The turbine uses the energy contained in the exhaust gas, etc. The system aims to improve the efficiency of the system by collecting the air and using it for compressing air.

Incidentally, in such a fuel cell power generation system, wide and quick load response control is required as a so-called power generation system. Therefore, the amount of air supplied to the fuel cell and the reformer is required to be controlled in a range of, for example, 25 to 100%. On the other hand, the pressure of the air supplied to the fuel cell is adjusted to maintain the characteristics of the P4 fuel cell, and to suppress the differential pressure with the fuel side pressure and prevent gas leakage between the two electrodes, that is, the crossover phenomenon. Control is required to maintain the value at a constant value. ! As a specific example of this method, a conventional example proposed in Japanese Unexamined Patent Publication No. 12268/1982 is shown in FIG. In the figure, 1 is a fuel cell, and 1a, lb, and 1c are air electrodes of the fuel cell 1, respectively.

The fuel electrode and electrolyte parts are shown. 2 is a reformer for converting hydrocarbon fuel into hydrogen-rich gas, and 2a, 2
b indicates the eighth part and reaction part of the reformer 2, 3 is a turbo compressor, and 3a and 3b' indicate the turbine part and the combustor/sensor part of this turbo compressor 3. 4. 5 and 6 are mechanisms for controlling the compressor discharge pressure, 4 is an atmosphere release valve for reducing the pressure to 1AT1, 5 is a pressure transmitter, and 6 is a pressure controller. Reference numerals 7, 8, and 9 are flow rate adjustment mechanisms for supplying the amount of air to the fuel cell according to jA, 7 is a flow control valve, 8 is a flow transmitter, and 9 is a flow controller. 10 is an air supply pipe (Kombu I/tube discharge pipe) that guides the air from the compressor 3b to the fuel cell 1, 11 is an excess air pipe that leads the exhaust air from the fuel cell air electrode 1a to the turbine 3a, and 12 is a modified J 'j A combustion exhaust gas pipe from the nose burner part 2a, 13 is a system exhaust gas pipe between the time when the surplus air pipe 11 and the combustion exhaust canine pipe 12 are joined and before being introduced into the turbine 3a.
4 is a pipe open to the atmosphere. Further, 15, 16, and 17 are mechanisms for controlling the reaction air pressure of the fuel cell l, 15 is a pressure regulating valve, 16 is a differential pressure transmitter that detects the differential pressure between the compressor discharge pressure and the reaction air pressure, and 17 18.19.20 is a mechanism for controlling the reaction fuel gas pressure of the fuel cell 1, and 18 is the pressure jm! i dialect,
19 is a historical pressure transmitting base that detects the differential pressure between the reaction air pressure and the reaction/reaction fuel gas pressure.

20 is a pressure controller. 21 is the reforming reaction section 2b
22 is a reformed gas supply pipe to the fuel cell fuel electrode 1b, and 23 is a surplus fuel supply pipe that supplies surplus fuel from the fuel cell 1 to the reformer burner section 2a. 2
4.25.26 is a mechanism for adjusting the amount of fuel to the reformer reaction section 2b, 24 is a flow control valve, 25 is a flow transmitter, and 26 is a flow controller. In addition, this Unexamined Patent Application Publication No. 5
Although omitted in the conventional example of No. 8-12268, a burner air supply pipe that branches from the air supply pipe 10 and is supplied to the reformer burner section 2a for combustion is added to FIG.

The operation at the time of load fluctuation described in such a conventional example will be explained. In the process of reducing the load on the fuel cell 1, as the amount of air supplied to the blender 3b decreases, the compressor discharge pressure also decreases, or the reaction air pressure or the differential pressure between the reaction air pressure and the reaction fuel gas pressure decreases by the following method. We are trying to maintain it. First, in the range from the rated load to a certain load range, the compressor discharge pressure is kept constant by adjusting the throttle of the atmosphere release valve 4, and the reaction air pressure is maintained.

In the range below the load range where there is no adjustment allowance for the atmospheric release valve 4, the reaction air pressure is linked to the decrease in the compressor discharge pressure, that is, the pressure regulating valve 15 maintains the differential pressure of the reaction air pressure with respect to the compressor discharge pressure. Also, the pressure regulating valve 18 controls and adjusts the differential pressure between the reaction fuel gas pressure and the reaction air pressure to keep it constant. This makes it possible to stably supply air to the fuel cell, maintain the differential pressure between the reaction air and the reaction fuel gas, and prevent the occurrence of the Lycium 7 opa phenomenon. In other words, this system j± basically maintains the steady pressure by the jA node of the atmosphere release valve 4, but when the adjustment allowance for the atmosphere release valve 4 disappears, the fuel cell pressure decreases in conjunction with the decrease in the compressor discharge pressure. This is intended to lower the pressure of the reaction gas.

[Problems to be Solved by the Invention] However, such a conventional structure has a drawback that the battery characteristics are not always maintained for the following reasons. In other words, a fuel cell is usually installed in a case pressurized with nitrogen gas due to pressure-resistant seals of the manifolds for each reaction gas attached to the cell body, and the nitrogen gas pressure is approximately equal to the reaction gas pressure. However, since the buffer volume of the nitrogen gas in the raw material is large, it is difficult to change the enclosure nitrogen gas pressure to follow the rate of change of the reactant gas pressure. In short, change the reaction gas pressure of the battery when the load fluctuates g15. □□ka, 7. E
Ka,=ancka5. □ First, there is a problem that the manifold seal is broken and V element gas leaks into the reaction gas, or conversely, the reaction gas leaks into the casing, degrading the characteristics of the fuel cell.

In addition, as shown in Fig. 1, in the conventional Mizuko technology, in a certain load range, the compressor discharge EE must be maintained at a constant value by constantly discharging high-pressure air from the atmosphere release valve, so energy is reduced. There is a problem that it tends to be wasted and that it is difficult to operate with high efficiency when the load fluctuates widely.6 In addition, this type of pressure control is performed by adjusting the atmosphere release around the rated load. This assumes that the turbine power is surplus to the compressor's required power, but in actual systems, the turbine power may be equal to or even insufficient to the compressor's required power, so only the adjustment cost for the atmospheric release valve is calculated. It is expected that the control used last month will be difficult.

Turbine power shortage is particularly noticeable at partial loads.The present invention was made with the aim of solving such problems all at once, and it does not cause turbine power shortage in any operating range. , we developed a load control method for a fuel cell power generation system that can minimize wasted energy use, and can respond quickly and accurately to a wide range of load fluctuations without worrying about the aforementioned deterioration of battery characteristics. This is what we are trying to provide.

[Means for Solving the Problems] In order to achieve the above objects, the present invention provides a fuel cell power generation system equipped with the above-mentioned atmosphere release valve, in which exhaust gas piping leading to the turbine of a turbo pressure IM machine is installed. An auxiliary combustion furnace is installed to compensate for the insufficient power of the turbine (the concept of introducing an auxiliary combustion furnace is known, for example, as shown in Japanese Patent Publication No. 58-56231), and the turbo compressor is The turbine is of a variable nozzle type, and roughly speaking, during steady operation of the system, the combustion amount of the auxiliary combustion furnace is controlled by feedback control to keep the compressor discharge pressure constant, with the atmosphere release valve fully closed or slightly opened. In addition, when the system load fluctuates, the combustion control of the auxiliary combustion furnace and the nozzle opening control of the turbine are performed by feedforward control based on a program, and the air release valve is used to perform feed/discharge control to keep the compressor discharge pressure constant. It is characterized by

[Function] According to such a configuration, during steady operation, the atmosphere release valve is maintained in a fully closed or slightly open state, and the compressor discharge pressure is controlled to be constant by combustion control of the auxiliary combustion furnace. Energy loss is minimized as long as the turbine power is not insufficient. On the other hand, when the load on the system fluctuates, the combustion control of the auxiliary combustion furnace and the nozzle opening control of the turbine are performed by feedforward control based on a preset program. And in that case,
In parallel, feedback control is performed to keep the compressor discharge pressure constant by the atmosphere release valve, and a temporary increase in the compressor discharge air amount during the transition period is released to the atmosphere. As a result of such control, the discharge pressure of the compressor is always maintained at a constant value, and 1. the reaction gas pressure and the differential pressure between the reaction gas pressure and the raw nitrogen gas pressure are always maintained constant. I can do it.

Note that, when the input pressure is constant, the power of the turbine is (inlet absolute temperature - r)2. Since it is proportional to the nozzle area S, it is not only possible to control the combustion amount of the auxiliary combustion furnace when the load fluctuates, but also to
If you also control the nozzle area.

Turbine power can be increased to a desired value while keeping turbine inlet temperature (exhaust gas temperature) relatively suppressed. Therefore, as will be described in detail later, it is possible not only to save fuel consumption when the load changes, but also to shorten the time required to change the load.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 2 and 3.

Note that parts that are the same as or correspond to those shown in FIG. 1 are given the same symbols and their explanations will be omitted. Furthermore, the load 39 shown in FIG. 2 is a collective representation of the fuel cell 1, reformer 2, and related equipment shown in FIG.

In FIG. 2, reference numeral 27 indicates an auxiliary combustion furnace installed in the middle of the system exhaust gas piping 13 to compensate for the lack of turbine power of the turbo-pressure engine 3, 28 indicates a fuel supply pipe for this auxiliary combustion furnace 27, and 29 indicates this fuel supply pipe 28. A fuel flow control valve 30 installed in the auxiliary combustion furnace is a fuel flow controller for detecting the fuel flow rate flowing through the fuel supply pipe 28 and adjusting the fuel flow control valve 29 . The turbo compressor 3 is
Unlike the one shown in FIG. 1, this is a so-called variable nozzle type in which a turbine 3a is equipped with a variable nozzle 3C.
The Ijf variable nozzle 3C is disclosed in, for example, Japanese Patent Application No. 1031/1986
As shown in No. 60, a valve body or the like is driven by an actuator such as a stepping motor operated by an electric signal, and the opening area of the nozzle can be changed by the movement of the valve body or the like. The auxiliary combustion furnace 27 burns the fuel sequentially supplied from the fuel supply pipe 28 and imparts thermal energy to the exhaust gas flowing through the system exhaust gas pipe 13. Moreover, 31 is an air pipe branched from the compressor discharge pipe 10 that guides the air discharged from the compressor 3b of the turbo compressor 3 and connected to the auxiliary combustion furnace 27.

32 is an air flow control valve for combustion in the auxiliary combustion furnace installed in the air pipe 31; 33 is an air flow controller for combustion in the auxiliary furnace for detecting the flow rate of air flowing through the air pipe 31 and adjusting the air flow control valve 32; 34 is for providing a control signal to the auxiliary furnace fuel flow controller 30 and the auxiliary furnace combustion air flow controller 33 in accordance with the compressor discharge pressure detected by the pressure detector 5 installed at the outlet of the compressor 3b of the turbo compressor 3. The pressure controller 35 converts the operation signal given from the pressure controller 6 to the atmosphere release valve 4 to the turbo pressure 1i! This is a computing unit for making adjustments depending on whether the machine 3 is in steady operation or in excessive flI operation. Further, 36 is a pressure transmitter that detects the exhaust gas pressure in the system exhaust gas pipe 13, 37 is a pressure controller,
Reference numeral 38 denotes a computing unit that puts the variable nozzle 3C under the control of the pressure controller 37 only in the event of an abnormality. That is, when the exhaust gas pressure detected by the pressure transmitter 36 is within a normal range, the calculator 38 sends a load command signal to the variable nozzle 3c based on a program as described below. This load command signal is used to control the nozzle opening.

On the other hand, if the pressure of the exhaust gas deviates from the normal range and, for example, decreases, the load command signal is temporarily cut off, and the pressure controller 37 works to return the exhaust gas pressure to the normal range. is designed to control the nozzle opening.

Next, the operation of this system will be explained.

During steady operation of the system, that is, during steady operation of the turbo compressor 3, the atmosphere release valve 4 is
is kept fully closed or kept at a constant minute opening, and the pressure controller 6 does not actually function.The atmosphere release valve 4 is kept fully closed or kept at a minute constant opening to minimize energy loss during steady operation. It's for a reason. At this time, the system
Since it is a steady operation, all process quantities in the system should be maintained at a constant value, but due to changes in compressor suction conditions due to changes in outside temperature and humidity during operation, and changes in system heat radiation, etc. During this process, process variables such as temperature and pressure gradually change.

Even with such changes, as described above, it is important to always keep the discharge pressure of the compressor 3b constant. At this time, the discharge pressure of the compressor 3b is controlled by controlling the combustion amount of the auxiliary combustion furnace 27 through the flow rate controller 30.33 so that the pressure detected from the pressure detector 5 by the pressure controller 34 becomes a constant target value. .

That is, during steady system operation, feedback control is performed to keep the compressor discharge pressure constant by adjusting the combustion amount in the auxiliary combustion furnace.

Next, the operation during load fluctuations will be described. First, by operating the control circuit in the computing unit 35 immediately before a load command, the atmospheric release valve 4 is placed under the control of the pressure controller 6.
Next, set values for the auxiliary furnace fuel flow rate and combustion air flow rate as load commands. Contact flow controller 30
．． 33 to increase the turbine power. As a result, the discharge pressure of the compressor 3b tends to rise;
Constant control is performed by adjusting the atmosphere release valve 4, that is, adjusting the amount of air released via the atmosphere release pipe 14. In this way, at the time of load command, the turbine power is increased by feedforward operation of the combustion amount of the auxiliary combustion furnace, and a part of the resulting reduction in the discharge air flow rate of the compressor 3b is used at the compressor outlet in order to keep the compressor discharge pressure constant. The air is discharged to the atmosphere on the side, and in this state the power amplifier of the turbo copressor 3 is measured to satisfy the system required air amount.

When the amount of air released from the atmosphere release valve 4 (opening degree of the atmosphere release valve) reaches the required value, the system air flow control valve 7 is opened according to the system requirement, and air from the turbo compressor enters the system. supplied to

At this time, the opening degree of the nozzle 3C of the turbine 3a is changed by feedforward control based on a preprogrammed load command to cope with changes in the exhaust gas flow area. That is, the exhaust gas flow rate W passing through the turbine 3a
is proportional to S-P/n, where S is the nozzle opening area, P is the nozzle inlet pressure, and T is the nozzle inlet absolute temperature. Therefore, the control pattern of the nozzle 3c may be such that the nozzle inlet pressure P fluctuates with changes in the system exhaust gas flow rate, the nozzle inlet absolute temperature T needs to be changed, or the upstream side of the turbine 3c In this case, the pressure controller 6 is programmed so that there is no need to release part of the exhaust gas directly to the atmosphere.
Through the control operation, the atmosphere release valve 4 is adjusted, that is, the amount of air released to the atmosphere is controlled, and the compressor discharge pressure is always maintained constant.

When the state change in response to the load command is completed and the system is stabilized, control of the discharge pressure is transferred to the pressure controller 34, and the arithmetic unit 35 gradually narrows down the opening degree of the atmosphere release valve 4 from the current opening degree. Finally, it is fully closed or kept at a very small opening. As mentioned earlier, this operation is to minimize the energy loss of the system, and the air release valve 4 is throttled by a fine JR adjustment so as not to upset the control balance of the turbo compressor 3.During this time, The compressor discharge pressure is controlled at a constant level by adjusting the combustion amount of the auxiliary combustion furnace through the flow rate controllers 30 and 33. After the atmosphere release valve 4 is throttled, the state returns to the state under steady load.

FIG. 3 shows the turbo pressure 1i! during load fluctuation according to this embodiment.
It represents the change in the process amount of m, and at time L1
When a load command is given to the auxiliary combustion furnace 27, the auxiliary combustion furnace combustion UtLWkF+ is increased by the feedforward control operation according to the load command, and the combustion exhaust gas from the auxiliary combustion furnace 27 is added to the system exhaust gas, increasing the turbine power, and the turbo compressor 3 Rotation speed increases. At this time, system air m, J
Since tF4 is still maintained at the value before the load command, the compressor discharge pressure P1 is about to increase by 1.

In response to this, constant pressure control by the pressure controller 6 operates to remove the excess air amount from the compressor and release the air amount F1 to the atmosphere.
The compressor discharge pressure P1 is maintained constant by discharging it to the atmosphere. When the feedforward operation for the auxiliary combustion furnace 27 becomes stable, the flow rate control valve 7 is opened to increase the system air flow rate F4 to the target value based on the load command, and the nozzle opening degree S of the turbine 3a of the turbo compressor 3 is increased. When it is increased by feedforward operation, during this process, the opening degree of the recompressor outlet atmosphere release valve 4 is adjusted by the constant control operation of Pl, and Fl changes.The time when eF4 reaches the target value (time L1) is the load change. At this point, the compressor discharge pressure P1 is controlled by the compressor outlet atmospheric release valve 4.
The combustion amount 5 of the auxiliary combustion furnace 27 is controlled by adjusting the amount of air discharged from the
Control will be switched to Section 11. After this, computing unit 3
5, the atmospheric release valve 4 is gradually opened, and the time when the atmospheric release valve 4 is completely closed (time mark) is the second time.
This is the next (final) settling point. In the process from ti to tl, control is performed in the direction of reducing the auxiliary furnace fuel flow rate F1 through a constant control operation of Pl.

In the above embodiment, a pressure transmitter and a pressure controller are provided on the inlet side of the turbine, and the nozzle opening of the turbine 3a is exceptionally separated from the load command only when the exhaust gas pressure changes to an unreasonable value. Although a case has been described in which the safety device is controlled by the driver, the present invention also includes a case in which such a safety device is omitted. In addition, although we have described an example in which the feedforward operation of the nozzle opening was started at the time point (1) when the system air flow 1#-F4 started to increase, the same operation could be started at the time of the load command (time 1+). However, nozzle control is performed to suppress the temporary increase in system back pressure due to increased combustion in the auxiliary furnace.

[Effects of the Invention] Since the present invention has the above configuration, the following effects can be obtained.

(a) First, since the auxiliary combustion furnace is provided in the middle of the exhaust gas piping, the turbine does not run out of power in any load operating range.

(b) Since the compressor discharge pressure can be maintained at a constant value at all times, the differential pressure between the pressure of the reactant gas in the manifold of the fuel cell and the pressure of nitrogen gas in the housing can be maintained constant. This makes it possible to avoid deterioration of battery characteristics due to gas leakage as described above.

(C) Also, when the load is constant, the atmosphere release valve can be kept fully open or slightly open, so it is possible to minimize wasted energy and achieve high efficiency. I can drive.

(d) Moreover, in this method, the turbine is of a variable nozzle type, and in addition to controlling the combustion of the auxiliary combustion furnace when the load fluctuates, the nozzle opening is changed by feedforward control to actively adapt the turbine power to load fluctuations. I am trying to change it accordingly. Therefore, excellent responsiveness can be expected, and it becomes possible to quickly change the load on the fuel cell, in other words, the system flow rate.

This will be explained in detail based on the above embodiment as follows. First, assuming that the inlet pressure P1 is constant, the turbine power is proportional to the absolute inlet temperature TY and the nozzle area S. Therefore, we tried to deal with load fluctuations by changing only the turbine inlet temperature without changing the nozzle area. In this case, as shown by the imaginary line in FIG. 3, the amount of combustion in the auxiliary combustion furnace 27 is increased considerably to increase the amount of air discharged from the atmosphere release valve 4, F1, and then the system air flow is increased. Unless Fit F 4 is changed to the target value, it will not be possible to change the load while leaving margin A for the discharge air volume.
In contrast, according to the present invention, the system airflow it
When F4 is changed to the target value, the nozzle area S can be changed almost simultaneously by feedforward control to measure the power amplifier of the turbine 3a. Even if you start changing the system airflow tF4 from a low state, the first
At the next settling time t2, the discharge flow rate margin A can be easily secured. Therefore, compared to a system without a variable nozzle function, it is possible to reduce the amount of combustion in the auxiliary combustion furnace during load fluctuations, which not only saves fuel but also
The time required to raise the temperature of the system exhaust gas (1+~t
), and the time required to change the system air flow rate (1-11) can both be shortened,
Quick and accurate load control can be performed.

[Brief explanation of the drawing]

FIG. 1 is a system explanatory diagram showing a conventional example, FIG. 2 is a system explanatory diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing process behavior in the same embodiment. l... fist fuel cell 1a... air electrode 1b meeting, fuel electrode 2 working... reformer 3, fist, turbo compressor 3a1, turbine 3b --- compressor 3c11◆1 nozzle 4... chamber open to atmosphere valve

Claims (1)

[Claims] a fuel cell; a reformer for reforming hydrocarbon fuel to supply hydrogen gas to the fuel cell; a turbo compressor that operates a compressor using a variable nozzle turbine driven by both the exhaust gas of the reformer and supplies compressed air necessary for the fuel cell and the reformer from the compressor; An auxiliary combustion furnace is placed on the exhaust gas piping leading to the turbine to compensate for the insufficient power of the turbine, and an auxiliary combustion furnace is installed on the atmosphere release piping branched from the compressor discharge piping of the turbo compressor to adjust the amount of air discharged to the atmosphere through the piping. In a fuel cell power generation system equipped with an atmosphere release valve, during steady operation of the system, the combustion amount of the auxiliary furnace is controlled by feedback control with the compressor discharge pressure constant, with the atmosphere release valve fully closed or slightly opened. Further, when the system load fluctuates, the combustion control of the auxiliary furnace and the nozzle opening control of the turbine are performed by feedforward control based on a program, and the air release valve performs feedback control to keep the compressor discharge pressure constant. Load control method for fuel cell power generation system.