JPH0317352B2 - - Google Patents

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 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, 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 requires variable control within a range of, for example, 25 to 100%. On the other hand, the pressure of the air supplied to the fuel cell is adjusted even during load fluctuations in order to maintain the characteristics of the fuel cell and to suppress the differential pressure with the fuel side pressure to prevent gas leakage between the two electrodes, that is, the crossover phenomenon. Control to maintain a constant value is required.

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 pole 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 merge and before being 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 control 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 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, 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 pressure difference between the reaction air pressure and the compressor discharge pressure is maintained by the pressure regulating valve 15 so that the reaction air pressure is linked to the decrease in 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 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 amount of the atmosphere release valve 4 disappears, the fuel cell reaction increases in conjunction with the decrease in the compressor discharge pressure. This is an attempt to lower the gas pressure.

[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 sealing pressure problems with 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 the reactant gas pressure of the battery is changed when the load fluctuates,
A large pressure difference is created between the nitrogen gas pressure in the case 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.

The present invention was made with the aim of solving these problems all at once, and not only does not cause the turbine to run out of power in any operating range, but also minimizes wasted energy. The object of the present invention is to provide a load control method for a fuel cell power generation system that can quickly and accurately respond to a wide range of load fluctuations without worrying about the aforementioned deterioration of battery characteristics.

[Means for Solving the Problems] In order to achieve the above-mentioned objects, the present invention provides a fuel cell power generation system equipped with the above-mentioned atmosphere release valve, in which the exhaust gas piping is connected to the turbine of the turbo compressor. (For the idea of introducing an auxiliary combustion furnace, see, for example, Japanese Patent Publication No. 58-56231.
In addition, the turbine of the Darbo compressor is of a variable nozzle type, and the atmosphere release valve is kept fully closed or slightly opened during steady operation of the system. The combustion amount of the auxiliary combustion 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 combustion furnace and the turbine nozzle opening are controlled by feedback control based on a program. The present invention is characterized in that feedback control is performed to keep the compressor discharge pressure constant using the open valve.

[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, 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. In that case, in parallel, feedback control is performed to keep the compressor discharge pressure constant by the atmosphere release valve, and the 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 the reaction gas pressure and the differential pressure between the reaction gas pressure and the casing nitrogen gas pressure are always maintained constant. Can be done.

In addition, when the inlet pressure is constant, the power of the turbine is proportional to ^1/2 (inlet absolute temperature T) and the nozzle area S, so it is possible to control not only the combustion amount of the co-heating furnace but also the nozzle area when the load fluctuates. By doing so, the turbine power can be increased to a desired value while keeping the 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.

[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 their explanations will be omitted. Further, 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 a computing unit that puts the variable nozzle 3c under control of the pressure controller 37 only in abnormal situations. In other words, this computing unit 3
8 transmits a load command signal based on a program as described later to the variable nozzle 3c when the exhaust gas pressure detected by the pressure transmitter 36 is within a normal range; The nozzle opening degree is controlled by the signal. On the other hand, if the pressure of the exhaust gas deviates from the normal range and drops, for example, the load command signal is temporarily cut off, and the pressure controller 37 operates to open the nozzle so that the exhaust gas pressure returns to the normal range. It is now possible to control the degree of control.

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 atmospheric release valve 4 is kept fully closed or kept at a certain minute opening by the operation of the computing unit 35, and the pressure controller 6 actually functions. do not. 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 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 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.

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.
be under the control of Next, set values for the auxiliary furnace fuel flow rate and the combustion air flow rate are directly given to the flow rate controllers 30 and 33 as load commands to increase the turbing 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. It is designed to release into the atmosphere at the exit side.
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 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 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, 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 The program should be programmed so that there is no need to release part of the exhaust gas directly into the atmosphere. 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 opening degree of the atmosphere release valve 4 is gradually decreased from the current opening degree by the calculator 35. Either the valve is narrowed down to a fully closed position, or it is held at a very small opening. As described above, this operation is to minimize the energy loss of the system, and the air release valve 4 is throttled down by fine adjustment so as not to upset the control balance of the turbo compressor 3. During this time, the compressor discharge pressure is controlled to be constant 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 closed, the state returns to the state when the load is steady.

Figure 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 _t1 , the auxiliary furnace fuel flow rate _F1 responds to the load command. By increasing the feeder forward control operation, 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, since the system air flow rate _F4 is still maintained at the value before the load command, the compressor discharge pressure _P1 is about to increase. 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, the opening degree of the compressor outlet atmospheric release valve 4 is adjusted by the constant control operation of _P1 in this process.
F ₃ changes. 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 control by adjusting the amount of air discharged from the compressor outlet atmosphere release valve 4 to control by adjusting the combustion amount of the auxiliary combustion furnace 27. Can be switched. 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. In the process from t ₂ to t ₃ , the auxiliary furnace fuel flow rate F ₁ is increased through the constant control operation of P ₁ .
Control is performed to narrow down the search results.

In the above embodiment, a pressure transmitter pressure controller is provided on the inlet side of the turbine, and the nozzle opening degree of the turbine 3a is exceptionally separated from the load command only when the exhaust gas pressure changes to an unreasonable value. Although the case where the safety device is controlled has been described, the present invention also includes a case where such a safety device is omitted. In addition, although we have described an example in which the feedforward operation of the nozzle opening is started at the time (t) when the system air flow rate F ₄ starts to increase, it is also possible to start the same feedforward operation at the time of the load command (time t ₁ ). Also good. At this time, nozzle control is performed to suppress a 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 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) In addition, this method uses a variable nozzle type turbine, which not only controls the combustion of the auxiliary combustion furnace when the load fluctuates, but also changes the nozzle opening using feedforward control to actively load the turbine power. I try to change it according to changes.
Therefore, excellent response adjustment 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, if the inlet pressure _P2 is constant, the turbine power is proportional to (inlet absolute temperature T) ^1/2 and the nozzle area S. Therefore, when trying to deal with load fluctuations by changing only the turbine inlet temperature without changing the nozzle area, the combustion amount of the auxiliary combustion furnace 27 must be increased considerably, as shown by the imaginary line in Fig. 3. Therefore, the amount of air released from the atmosphere release valve 4
Unless F ₃ is increased sufficiently and the system air flow rate F ₄ is then changed to the target value, the load cannot be changed while leaving a margin A for the discharge air volume. In contrast, according to the present invention, when changing the system air flow rate F ₄ to the scale value,
At the same time, it is possible to increase the power of the turbine 3a by changing the nozzle area S using feed forward control. Therefore, the system air flow rate F4 can be started from a state where the air flow rate F3 discharged from the atmosphere release valve ₄ is relatively small. Also, at the first 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 saves time (t) required to raise the temperature of system exhaust gas. ₁ to t) and the time required to change the system air flow rate (t to _t2 ) can both be shortened, and rapid 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 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, 14...Atmospheric release piping.

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. In a fuel cell power generation system, the air release valve is provided on an air release pipe and is provided with an air release valve that adjusts the amount of air discharged to the atmosphere through the pipe, and the air release valve is fully closed or closed during steady operation of the system. The combustion amount of the auxiliary combustion furnace is controlled by feedback control that keeps the compressor discharge pressure constant when the combustion chamber is slightly opened, and when the system load fluctuates, the combustion control of the auxiliary combustion furnace and the turbine nozzle opening control are performed using feedback control based on a program. A load control method for a fuel cell power generation system, characterized in that the air release valve performs feedback control to maintain a constant compressor discharge pressure.