JPH0317353B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a 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 oil, coal, etc. as fuel, and are also environmentally friendly and have flexibility in terms of location. are doing. Therefore, in recent years, not only power supplies for special purposes such as space exploration, but also
Various uses are being considered for use as a power source for commercial power, and development efforts are being activated with the aim of putting it 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. Therefore, the operating pressure of each of the reaction gases is set to a value of about 4 to 6 kg/cm ² g, for example. At this time, compressing the air requires a large amount of power, amounting to about 20% of the energy generated by the battery. On the other hand, the reforming reaction for producing fuel gas for the battery is carried out at a high temperature of about 800° 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.

Under these circumstances, in recent fuel cell power generation systems, it has become common to use a turbo compressor as the air supply means. That is, the turbo compressor includes a turbine driven by excess 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 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 system efficiency by collecting and using the air to compress it.

Incidentally, such a fuel cell power generation system requires stable control during steady operation and wide and quick load response control as a so-called power generation system. Thus, the amount of air supplied to the fuel cell and reformer is e.g. 25-100%
Fluctuation control is required within the range of . On the other hand, the pressure of the air supplied to the fuel cell is adjusted during steady operation in order to maintain the characteristics of the 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. Therefore, control is required to maintain a constant value regardless of load fluctuations.

As a concrete 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, 1a, 1
b and 1c indicate the air electrode, fuel electrode, and electrolyte portion of the combustion cell 1, respectively. 2 is a reformer for converting hydrocarbon fuel into hydrogen-rich gas;
a and 2b indicate a burner section and a reaction section of the reformer 2. 3 is a turbo compressor, and 3a and 3b indicate a turbine portion and a compressor portion of this turbo compressor 3. 4, 5, and 6 are mechanisms for controlling the compressor discharge pressure, 4 is an atmosphere release valve for adjusting the pressure, 5 is a pressure transmitter, and 6 is a pressure controller. Reference numerals 7, 8, and 9 are flow rate adjustment mechanisms for adjusting the amount of air supplied to the fuel cell, 7 is a flow control valve, 8 is a flow transmitter, and 9 is a flow controller. 10 is an air supply pipe (compressor discharge pipe) that guides air from the compressor 3b to the fuel cell 1; 11 is an excess air pipe that guides exhaust air from the fuel cell air electrode 1a to the turbine 3a; and 12 is a reformer burner section 2a. The fuel exhaust gas pipe 13 is the surplus economy pipe 11 and the fuel exhaust gas pipe 12.
A system exhaust gas pipe 14 is a pipe that is open to the atmosphere after the gases are joined and before the gas is introduced into the turbine 3a. Further, 15, 16, and 17 are mechanisms for controlling the reaction air pressure of the fuel cell 1, 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 indicates a pressure controller. 18, 19, and 20 are mechanisms for controlling the reaction fuel gas pressure of the fuel cell 1, 18 is a pressure regulating valve, 19 is a differential pressure transmitter that detects the differential pressure between the reaction air pressure and the reaction fuel gas pressure, and 20 is a pressure controller. 21 is a fuel supply pipe to 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 for supplying surplus fuel from the fuel cell 1 to the reformer burner section 2a. It's plumbing. 24, 25, 26 are the reformer reaction section 2b
24 is a flow control valve, 25 is a flow transmitter, and 26 is a flow controller. Although omitted in the conventional example of JP-A-58-12268, the burner air supply pipe that branches from the air supply pipe 10 and supplies fuel to the reformer burner section 2a is shown in FIG. will be added.

The operation of the system described in such a conventional example will be explained. In the process of reducing the load on the fuel cell 1, the compressor discharge pressure also decreases as the amount of air supplied to the compressor 3b decreases. 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 atmosphere release valve 4, the reaction air pressure is linked to the decrease in the compressor discharge pressure, that is, the differential pressure between the reaction air pressure and the compressor discharge pressure is maintained by the pressure regulating valve 15. In addition, the pressure regulating valve 18 controls and adjusts the pressure difference 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 a crossover phenomenon from occurring. In other words, this system basically maintains a constant air pressure by adjusting the atmosphere release valve 4, but when the adjustment allowance for the atmosphere release valve 4 is eliminated, the fuel cell discharge pressure decreases and the fuel cell pressure decreases. 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 battery characteristics are not necessarily maintained for the following reason. In other words, fuel cells are 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. are kept equal, but
Because the buffer volume of nitrogen gas inside the housing is large,
It is difficult to change the enclosure nitrogen gas pressure to follow the rate of change in the reaction gas pressure. In other words, if you change the battery's reaction gas pressure when the load fluctuates,
A large pressure difference is created between the enclosure nitrogen gas pressure and
There is a problem in that the manifold seal is broken and nitrogen gas leaks into the reaction gas, or conversely, the reaction gas leaks into the casing, degrading the characteristics of the fuel cell.

In addition, the conventional technology shown in Figure 1 has no choice but to maintain the compressor discharge pressure at a constant value by constantly discharging high-pressure air from the atmosphere release valve in a certain load range, which reduces energy consumption. There is also the problem that there is a tendency for energy to be wasted, and that it is difficult to operate efficiently when the load fluctuates widely.

In addition, this system performs constant air pressure control by adjusting the air release around the rated load, and assumes that the turbine power is surplus to the compressor's required power, but in an actual system, the turbine power is equal to the compressor's required power. Therefore, it is expected that control using only the adjustment allowance of the atmosphere release valve will be difficult.
Turbine power shortage is particularly noticeable at partial loads.

However, as a system control method that can eliminate such inconveniences, in a fuel cell power generation system equipped with an atmosphere release valve as described above, a turbine is installed in the exhaust piping leading to the turbine of the turbo compressor. An auxiliary combustion furnace is installed to compensate for the lack of power (the concept of introducing an auxiliary furnace is known, for example, as shown in Japanese Patent Publication No. 58-56231), and the above-mentioned atmosphere is opened during steady operation of the system. When the valve is fully closed or slightly opened, the combustion amount of the auxiliary furnace is controlled by feedback control that keeps the compressor discharge pressure constant, and when the system load fluctuates, the combustion control of the auxiliary furnace and the turbine nozzle opening control are programmed. This method (hereinafter referred to as the "improved method") performs feedback control to maintain a constant compressor discharge pressure using the atmospheric release valve.
) can be considered.

However, this method maintains the turbine nozzle opening at least during steady operation.
The compressor discharge pressure, and thus the system back pressure, are maintained at a desired value solely by controlling the combustion amount of the auxiliary furnace. Therefore, even if the optimal value of the nozzle area fluctuates due to changes in various ambient conditions such as temperature and humidity during steady operation, the turbine power must be adjusted to the required value only by controlling the combustion amount of the auxiliary furnace. No. Therefore, as will be described later, there are some problems with efficiency during steady operation.

The present invention not only solves the problems of the system shown in FIG. 1, but also aims to reliably solve the problems of the improved system described above during steady operation. .

[Means for Solving the Problems] In order to achieve the above-mentioned objects, the present invention further improves the above-mentioned improvement method, and improves the turbine nozzle opening so that the system back pressure remains constant during steady operation. It is characterized by feedback control.

[Function] According to such a configuration, during steady operation, the atmosphere release valve is maintained in a fully closed or slightly open state,
By controlling combustion in the auxiliary combustion furnace, the compressor discharge pressure is controlled to be constant, and energy loss is minimized as long as the turbine power is not insufficient. On the other hand, when the system load fluctuates, at least the combustion control of the auxiliary combustion furnace is performed by feedforward control based on a preset program. And in that case, in parallel,
The air release valve performs feedback control to keep the compressor discharge pressure constant, and a temporary increase in the amount of air discharged from the compressor during a transient period is released to the atmosphere.

Moreover, if the system back pressure attempts to change due to changes in ambient conditions such as temperature during steady operation,
Feedback control adjusts the turbine nozzle opening to maintain the system backpressure at a constant value. Note that when the inlet pressure is constant, the power of the turbine is proportional to (inlet absolute temperature T) ^1/2 and the nozzle area S, so it is possible to control not only the combustion amount of the co-heater during steady operation, but also the nozzle area. If you do this,
Turbine power can be maintained at a required value while the turbine inlet temperature (exhaust gas temperature) is relatively suppressed.

[Example] Hereinafter, an example of the present invention will be described 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 description thereof 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 compressor 3, and 28 indicates this auxiliary combustion furnace 2.
7 is a fuel supply pipe, 29 is a fuel flow control valve installed in this fuel supply pipe 28, and 30 is an auxiliary furnace fuel for detecting the fuel flow rate flowing through the fuel supply pipe 28 and adjusting the fuel flow control valve 29. It is a flow controller. The turbo compressor 3 is the first
Unlike the one shown in the figure, this is a so-called variable nozzle type in which a turbine 3a is equipped with a variable nozzle 3c. The variable nozzle 3c, for example, is
As shown in No. 103160, a valve body 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. 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. Further, 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, and 32 is the auxiliary combustion furnace installed in this air pipe 31. An air flow control valve 33 is an air flow controller for an auxiliary combustion furnace for detecting the air flow flowing through the air pipe 31 and adjusting the air flow control valve 32, and 34 is installed at the outlet of the compressor 3b of the turbo compressor 3. a pressure controller for providing control signals to an auxiliary furnace fuel amount controller 30 and an auxiliary furnace combustion air flow rate controller 33 in accordance with the compressor discharge pressure detected by the pressure detector 5;
35 is an arithmetic unit for adjusting the operation signal given from the pressure controller 6 to the atmosphere release valve 4 depending on whether the turbo compressor 3 is in steady operation or in excessive operation. Further, 36 is the system exhaust gas pipe 13
37 is a pressure controller, and 38 is an arithmetic unit that controls the signal supplied to the nozzle 3c. That is, during steady operation, this computing unit 38 puts the variable nozzle 3c under the control of the pressure controller 37, while at the time of load fluctuation, it basically supplies a pre-programmed load command signal to the nozzle 3c. It is configured. If the system back pressure detected by the pressure transmitter 36 at the time of load fluctuation deviates from a preset range of values, the load command signal is temporarily cut off, and the pressure controller 37 The nozzle power is controlled so that the system back pressure returns to a value within the predetermined range.

Next, the operation of this system will be explained.

During steady operation of the system, that is, during constant image operation of the turbo compressor 3, the atmospheric release valve 4 is kept fully closed or at a constant minute opening by the operation of the computing unit 35, and the pressure controller 6 is actually It doesn't work. The reason why the atmosphere release valve 4 is fully closed or kept at a small constant opening is to minimize energy loss during steady operation. At this time, since the system is in steady operation, all process quantities within the system are supposed to be maintained at constant values. In reality, process quantities such as temperature and pressure gradually change due to changes in the amount of heat.
As mentioned earlier, in response to such changes,
It is important to keep the compressor 3b discharge pressure and system back pressure constant at all times. 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 controllers 30 and 33 so that the pressure detected from the pressure detector 5 by the pressure controller 34 becomes a constant target value. To do this. That is, during steady operation of the system, feedback control is performed to keep the compressor discharge pressure constant by adjusting the combustion amount in the auxiliary combustion furnace.
Further, the system back pressure is controlled by adjusting the opening degree of the nozzle of the turbine 3a so that the pressure detected by the pressure detector 36 by the pressure controller 37 becomes a constant target value. That is,
During steady operation, feedback control is performed to keep the system back pressure constant by adjusting the nozzle opening.

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 atmosphere release valve 4 is controlled by the pressure controller 6.
At the same time, by operating the control circuit in the computing unit 38, the feedback control of the nozzle opening by the pressure controller 37 is stopped in principle, and a load command signal is transmitted to the nozzle 3c by the turbine 3a. Try to get it. next,
As load commands, set values for the auxiliary furnace fuel flow rate and combustion air flow rate are directly transmitted to the flow rate controllers 30, 3.
3 to increase turbine power. As a result, the discharge pressure of the compressor 3b tends to rise, but the discharge pressure of the compressor 3b is controlled by the pressure controller 6 by adjusting the atmosphere release valve 4, that is, adjusting the amount of air released via the atmosphere release pipe 14. constant control is performed. In this way, at the time of load command, the durbin power is increased by the feedforward operation of the combustion amount of the auxiliary furnace, and a part of the increase in the discharge air flow rate of the compressor 3b is transferred to the compressor in order to keep the compressor discharge pressure constant. The air is discharged to the atmosphere on the exit side, and in this state the power of the turbo compressor 3 is increased 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 a certain level, the system air flow control valve 7 is opened according to the system demand, 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 the change in the exhaust gas flow rate. That is, the exhaust gas flow rate W passing through the turbine 3a is proportional to S·P/√, where S is the nozzle opening area, P is the nozzle inlet pressure, and T is the nozzle inlet absolute temperature. Therefore, in principle, the control pattern of the nozzle 3c requires that the nozzle inlet pressure, that is, the system back pressure _P2 , fluctuate with changes in the system exhaust gas flow rate, or that the nozzle inlet absolute temperature T needs to be changed. or the turbine 3c
The program is designed to avoid the need to release part of the upstream exhaust gas directly into the atmosphere. However, due to various condition changes such as a time delay in temperature change, the system back pressure may deviate from a preset range of values when the nozzle opening is changed by a load command. In this case, the computing unit 3
8, the control based on the load command is temporarily interrupted, the nozzle opening degree is corrected under control by the pressure controller 37, and the system back pressure _P2 is operated to return to a value within a certain range. That is, the nozzle opening degree is controlled by the load command while confirming that the system back pressure is maintained within a certain range. At this time, the pressure controller 6 adjusts the atmosphere release valve 4, that is, controls the amount of air released to the atmosphere, so that 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 pressure controller 3
7 restarts the constant feedback control of the system back pressure P ₂ , and then the computing unit 35 gradually narrows down the opening degree of the atmosphere release valve 4 from the current opening degree and finally closes it completely, or It is maintained at a certain opening. This operation is to minimize the energy loss of the system as mentioned earlier, and the throttling of the atmosphere release valve 4 is performed by the turbo compressor 3.
This is done by making fine adjustments so as not to upset the control balance. During this time, the compressor discharge pressure is controlled to a constant value by adjusting the combustion amount of the auxiliary furnace through the flow rate controllers 30 and 33, and the system back pressure _P2 is controlled to a constant value by adjusting the nozzle opening degree by the pressure controller 37. . Atmospheric release valve 4
After narrowing down the load, it returns to the state under steady load.

Incidentally, Fig. 3 shows the change in the process amount of the turbo compressor when the load fluctuates according to this embodiment. When a load command is given at time t ₁ , the auxiliary furnace fuel flow rate F ₁ changes to the load command. By increasing the feed forward control operation accordingly, the combustion exhaust gas from the auxiliary combustion furnace 27 is added to the system exhaust gas, the turbine power increases, and the rotation speed of the turbo compressor 3 increases. At this time, the system air flow rate F ₄
is still maintained at the value before the load command, so the compressor discharge pressure _P1 is about to rise. In contrast, pressure constant control by the pressure controller 6 operates to release the excess air amount to the atmosphere as the compressor discharge air release amount _F3 , thereby maintaining the compressor discharge pressure _P1 constant. When the feed forward operation for the auxiliary combustion furnace 27 becomes stable, the flow 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 of the turbine 3a of the turbo compressor 3 is opened. When the degree S is increased by the feedforward operation, in this process, the opening degree of the compressor outlet atmosphere release valve 4 is adjusted by the constant control operation of _P1 , and _F3 changes. The time when F ₄ reaches the target value (time t ₂ ) is the first settling point for load fluctuations, and at this point, the control of the compressor discharge pressure P ₁ changes from the control by adjusting the air discharge amount from the compressor outlet atmospheric release valve 4. The control is switched to control by adjusting the combustion amount of the auxiliary combustion furnace 27, and the feedback control for maintaining the system back pressure _P2 constant by the pressure controller 37 is restarted. Thereafter, a gradual closing operation of the atmosphere release valve 4 is performed in response to a command from the computing unit 35, and the time when the atmosphere release valve 4 is completely throttled down (time _t3 ) becomes the second (final) settling time. t ₂
In the process from to _t3 , control is performed in the direction of reducing the auxiliary furnace fuel flow rate _F1 through the constant control operation of _P1 .

Note that the control mode at the time of load fluctuation is, of course, not limited to that of the embodiment described above, and various modifications can be made without departing from the spirit of the present invention.

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

(a) First, since an auxiliary combustion furnace is provided in the middle of the exhaust gas piping, there is no possibility of power shortage of the turbine in any load operation range.

(b) Since the compressor discharge pressure can always be kept at a constant value, 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 kept 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 closed or slightly open, so it is possible to minimize wasted energy and improve efficiency. Able to drive high.

(d) Furthermore, in this system, during steady operation, the system back pressure is maintained constant by adjusting the turbine nozzle opening using feedback control, which may lead to the aforementioned crossover phenomenon. Of course, it is possible to reliably eliminate the inconvenience of unstable combustion in the reformer due to pressure fluctuations, and it is also possible to reduce the amount of combustion in the auxiliary furnace for economical operation. Excellent effects can be obtained.

This will be explained in detail based on the above embodiments as follows. In other words, when the flow rate adjustment valve 7, the atmosphere release valve 4, etc. that control the system air flow rate are set at a constant opening degree and steady operation is being performed, the ambient conditions change and, for example, the atmospheric temperature rises. shall be. As a result, the amount of heat dissipated from the system decreases, and the exhaust gas increases accordingly, increasing the turbine inlet temperature. Then, the turbine power increases, the operating speed of the turbo compressor 3 increases, the compressor discharge pressure and air volume increase, and the system back pressure _P2 also begins to increase. At this time,
Energy can be controlled only by reducing the combustion amount in the auxiliary combustion furnace, but it is even more effective to control the system back pressure to a constant level by changing the nozzle opening in the direction of opening. Economical driving becomes possible. That is,
Assuming that the inlet pressure P ₂ is constant, the turbine power is:
(Inlet absolute temperature T) is proportional to the nozzle area S.
Therefore, if you try to deal with fluctuations in the process amount by changing only the turbine inlet temperature without changing the nozzle area, it may not be possible to sufficiently narrow down the combustion amount in the auxiliary combustion furnace 27, but the nozzle opening If S is controlled at the same time, it becomes possible to further reduce the amount of combustion in the auxiliary combustion furnace 27 while ensuring the required turbine power, and it is possible to save energy.

[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 system explanatory diagram showing an embodiment of the present invention.
The figure is a diagram showing the behavior of the process in the same example. 1... Fuel cell, 1a... Air electrode, 1b... Fuel electrode, 2... Reformer, 3... Turbo compressor, 3a
...Turbine, 3b...Compressor, 3c...
Nozzle, 4... Atmospheric release valve, 10... Compressor discharge piping, 13... System exhaust gas piping, 14
...Piping open to the atmosphere.

Claims (1)

[Claims] 1 a fuel cell, a reformer for reforming hydrocarbon fuel and supplying hydrogen gas to the fuel cell;
A compressor is operated using a variable nozzle turbine driven by both the exhaust gas of the reformer or the excess air at the outlet of the air electrode of the fuel cell and the exhaust gas of the reformer. A turbo compressor that supplies the compressed air necessary for the reformer, an auxiliary combustion furnace that is placed on the exhaust gas piping leading to the turbine of this turbo compressor and makes up for the lack of power in the turbine, and a combustion furnace that branches off from the compressor discharge piping of the turbo compressor. and an atmosphere release valve that is installed on the air release piping and adjusts the amount of air discharged to the atmosphere through the pipe, and during steady operation of the system, the atmosphere release valve is fully closed or slightly opened. The combustion amount of the auxiliary combustion furnace is controlled by feedback control with constant compressor discharge pressure.
In addition, the control method for the fuel cell power generation system is such that when the system load fluctuates, the combustion control of the auxiliary furnace is performed by feed forward control based on a program, and the air release valve is used to perform feedback control to keep the compressor discharge pressure constant. A control method for a fuel cell power generation system, further comprising: performing feedback control on the nozzle opening of the turbine so that the system back pressure becomes constant during steady operation.