JPS6180764A - 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 [Technical Field of the Invention] The present invention relates to a method of controlling a fuel cell power generation system, and more particularly to a method of controlling a fuel cell power generation system including a turbo compressor.

[Conventional technology]

Fuel cell power generation systems have advantages over conventional steam power generation, such as higher efficiency and better environmental protection.
In recent years, development has been actively underway with the aim of putting it into practical use. A fuel cell power generation system consists of a fuel cell body consisting of an air electrode, a fuel electrode, and an electrolyte layer.

Hydrocarbon fuels such as natural gas are reformed to produce fuel cells (
A reformer that supplies hydrogen gas as fuel.

It is equipped with a turbo compressor that supplies air to the fuel cell body and a reformer. The performance of the fuel cell itself shows a tendency to improve as the pressure of the reactant gas increases.

For this reason, the operating pressure of fuel, air, and each reaction gas is, for example, 4
The pressure is maintained at ~6 kg/ci. At this time, compressing the air requires a large amount of power.

This power is provided by a turbo-pressure turbine which introduces combustion exhaust gas from the reformer and surplus air from the air electrode of the fuel cell main body. In other words, this turbo compressor uses a turbine to recover system exhaust gas energy, and a coaxial compressor supplies the necessary compressed air, thereby recovering power within the system and improving system efficiency. .

Now, in such a fuel cell power generation system, a wide and quick load response control is required as a so-called power generation system. The amount of air supplied to the fuel cell main body and the reformer is, for example, 25 to 1o.

% variation control is required. On the other hand, the pressure of the air supplied to the fuel cell main body is determined from the viewpoint of maintaining the characteristics of the fuel cell main body, and in order to suppress the differential pressure with the fuel side pressure and prevent gas leakage between the two electrodes, that is, crossover phenomenon. Control is required to maintain a constant value even when the load fluctuates. That is, the turbo compressor basically requires variable air flow control using the air travel pressure.

As a specific conventional method, for example, JP-A-58-
There is a system disclosed in No. 12268, and the system is shown in FIG. In the figure, (1) is the air electrode (la
), a fuel cell main body consisting of a fuel electrode (lb), and an electrolyte layer (IC), (2) reforming hydrocarbon fuel such as natural gas and supplying rich hydrogen gas to the fuel cell main body (1) It is a reformer and consists of a burner section (2a) and a reaction section (2b). (3) is driven, for example, by both the exhaust gas from the reformer (2) and the surplus air at the outlet of the air electrode (1λ) of the fuel cell main body (1), and the air electrode (1a) of the fuel cell main body (1) is 2. A turbo-pressure machine consisting of a turbine (3a) that supplies the necessary compressed air to the burner section (2a) of the generator (2), and a compressor (3b) arranged coaxially with the turbine (3a). ((4) is an air supply pipe that supplies air compressed by the compressor (3b) of this turbo compressor (3) to the air electrode (la) of the fuel cell main body (1), (5)
) is a surplus air pipe that guides surplus air from the air 11 (la) of the fuel cell main body (1) to the turbine (3a) of the turbo compressor (3).

(6) is reformed! The combustion exhaust gas from 1 (2) is passed through the turbine (
Exhaust gas pipe leading to 3al, (7) is surplus air pipe (5)
and a system exhaust gas pipe that joins the exhaust gas pipe (6) and guides the excess air and combustion exhaust gas to the turbine (3a);
(8) is a fuel supply pipe that supplies hydrocarbon fuel such as natural gas to the reformer (2), and (9) is a fuel supply pipe that supplies hydrogen-rich gas reformed in the reformer (2) to the fuel cell body (1). fuel 1!1
Reformed fuel supply pipe that supplies i (lb).

(10) is a surplus fuel supply pipe that supplies surplus fuel from the fuel electrode (1b) of the fuel cell main body (1) to the burner part (2a) of the reformer (2), (11) is an air supply pipe (4 ), and (12) is an atmospheric vent pipe installed in this atmospheric vent pipe (11), which adjusts the pressure of the air supplied to the air 1fj (la) of the fuel cell body (1). A release valve, (13) is a pressure detector that detects the pressure inside the air supply pipe (4), and (14) is this pressure detector (
IJ of the atmosphere release valve (12) in response to a signal from
There is a pressure controller that performs iJ closing control, and these (1
2) and (14) control the discharge air pressure of the compressor (3b). (]5) is air supply piping (4)
installed in

(1B) is a flow rate detector that detects the flow rate in the air supply pipe (4); (17) is a flow rate control valve that adjusts the amount of air supplied to the air electrode (1a) of the fuel cell main body (1); This is a flow rate controller that controls the opening and closing of the flow rate regulating valve (15) in response to the signal from the flow rate detector (16).

These (15) to (17) control the flow rate of air supplied to the air 1mC1a) of the fuel cell main body (1).

(18) is a pressure control valve installed in the surplus air pipe (5).

(19) is a differential pressure detector that detects the differential pressure between the discharge air pressure of the compressor (3b) and the reaction air pressure, and (20) is a pressure regulating valve that responds to the signal from this differential pressure detector (19). (18) A pressure controller that performs opening/closing control,
These (18) to (20) control the reaction air pressure in the fuel cell main body (1). (21) is a pressure control valve installed in the surplus fuel supply pipe (10), (22) is a differential pressure detector that detects the differential pressure between the reaction air pressure and the reaction fuel gas pressure, and (23) is this differential pressure. These (21) to (23) i are pressure controllers that control the opening and closing of the pressure regulating valve (21) in response to signals from the detector (22).
This controls the reaction fuel gas pressure in the fuel cell main body (1). (24) is installed in the fuel supply pipe (8).
(25) is a flow rate detector that detects the flow rate in the fuel supply pipe (8); (26) is a flow rate adjustment valve (24) that responds to the signal from the flow rate detector (25); These (24 flow controllers) and rollers control the opening and closing of
) to (2B) control the flow rate of fuel supplied to the reformer (2). 2. Although not shown, the air supply piping (
4) is provided with a burner air supply pipe that branches off from the reformer (2) and is supplied as combustion air to the burner section (2a) of the reformer (2).

Next, the operation of the conventional system configured as described above when the load fluctuates will be explained.

In the process of reducing the load on the fuel cell (fuel cell main body port), the discharge air pressure of the compressor (3b) also decreases as the supply air flow rate from the compressor (3b) decreases, but the reaction air pressure or reaction air pressure is reduced by the secondary method. The differential pressure with the reaction fuel gas pressure is maintained. First, in the range up to the load range consisting of the rated load, the discharge air pressure of the compressor (3b) is kept constant by adjusting the throttle of the atmosphere release valve (12) to maintain the reaction air pressure. Atmospheric release valve (12
), the reaction air pressure is linked to the decrease in the discharge air pressure of the compressor (3b), that is, the pressure control valve (18) is used to adjust the pressure of the discharge air of the compressor (3b). The pressure difference between the reaction air pressure is maintained, and the pressure regulating valve (21) controls the reaction fuel gas pressure so that the pressure difference between the reaction air pressure and the reaction air pressure is constant! Adjust by 1. As a result, air can be stably supplied to the air electrode (1a) of the fuel cell main body (1), and the differential pressure between the reaction air pressure and the reaction fuel gas pressure can be maintained to prevent crossover. . That is, this system basically maintains the air travel pressure by adjusting the atmosphere release valve (12), but when the adjustment amount of the atmosphere release valve (12) disappears, the discharge air pressure of the compressor (13b) decreases. In conjunction with this, the pressure of the reactant gas in the fuel cell body (1) is lowered.

However, such conventional systems have the disadvantage that the characteristics of the fuel cell are not necessarily maintained for the following reason. That is, the fuel cell main body (1) is usually installed in a casing pressurized with nitrogen gas due to sealing pressure problems of the manifolds for each reaction gas attached to the fuel cell main body (1), and the nitrogen gas pressure is The pressure is maintained almost equal to the reaction gas pressure, but because the nitrogen gas buffer volume inside the housing is large, it is difficult to change the nitrogen gas pressure inside the housing to follow the rate of change of the reaction gas pressure. . In other words, if the reactant gas pressure in the fuel cell main body (1) is changed during load fluctuations, a large pressure difference will be created between the reactant gas pressure in the fuel cell body (1) and the nitrogen gas pressure in the housing, and the manifold seal will be broken and nitrogen gas will be released into the reactant gas. Otherwise, the reactant gas may leak into the casing, degrading the characteristics of the fuel cell. moreover,
Air running pressure is controlled by adjusting the atmospheric release valve (12) near the rated load, and it is assumed that the turbine power is surplus to the compressor's required power, but in an actual system, the turbine power is not enough to meet the compressor's required power. On the other hand, it is the same or even insufficient, so it is difficult to control using the adjustment allowance of the atmosphere release valve (12).

The lack of turbine power is particularly noticeable at partial loads, and in order to compensate for this lack of turbine power, it is considered to install an auxiliary combustion furnace in the middle of the system exhaust gas piping2.
For example, there are several examples disclosed in Japanese Patent Publication No. 58-58231. For example, as disclosed in JP-A-59-18577, a bypass valve installed as a bypass in a combustion exhaust gas system is operated to open and close to adjust the amount of combustion exhaust gas released into the atmosphere, thereby controlling the amount of combustion exhaust gas supplied to the turbine. It is conceivable to control the discharge air pressure of the compressor of a turbo compressor by adjusting the be. In other words, since the combustion response of the auxiliary combustion furnace is generally slow, when the load fluctuates, the required air supply to the system cannot keep up and the bypass valve is fully closed, causing a temporary drop in the discharge air pressure of the turbo compressor's compressor. There was a drawback.

[Summary of the invention]

This invention was made in view of the drawbacks of the above-mentioned systems. During steady operation of the system, the combustion amount of the auxiliary combustion furnace is controlled by the discharge of the compressor of the turbo compressor with the bypass valve fully closed or slightly opened. Feedback control is used to keep the air pressure constant, and when the system load fluctuates, the combustion amount of the auxiliary combustion furnace is controlled by feedforward control based on a program, while the bypass valve is used to perform feedback control to keep the discharge air pressure of the turbo compressor's compressor constant. According to
It is an object of the present invention to provide a control method for a fuel cell power generation system that can always keep the discharge air pressure of a compressor of a turbo compressor constant.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described based on FIG. 2. In the figure, (3), (4), (7),
(13).

(151, (17) are the same as the configuration of the conventional system described above. (27) is the fuel cell main body (1) shown in FIG.
).

The reformer (2) and other related equipment are collectively shown in blocks. (28) is the system exhaust gas amount v(7
), the auxiliary combustion furnace (29) is installed to branch to the system exhaust gas pipe (7), and the turbo compressor (3
) bypass piping that bypasses the turbine (3a);
(30) is a bypass valve installed in this bypass pipe (29), which adjusts the amount of exhaust gas released into the atmosphere after passing through the auxiliary combustion furnace (28), and adjusts the amount of exhaust gas supplied to the turbine (3a); (31) ) is a fuel pipe that leads and supplies fuel from the round fuel supply pipe (8) to the auxiliary combustion furnace (28), (32
) is the flow control valve installed in this fuel pipe (31),
(33) is a flow controller that detects the flow rate of fuel flowing in the fuel pipe (31) and adjusts the flow control valve (32);
(34) is branched from the air supply pipe (4) to the auxiliary combustion furnace (2).
(35) is a flow control valve installed in this air pipe (34); (36) is a flow control valve (36) that detects the flow rate of air flowing in the air pipe (34);
35), the flow rate controller (37) is detected by the pressure detector (13)ttm.
3b) "Give control signals to the flow controller (33) and the flow controller (36) according to the discharge air pressure of the pressure controller, (38) detected by the pressure detector (13) of the compressor (3b)
A pressure controller (39) adjusts the opening degree of the bypass valve (30) according to the discharge air pressure of the turbo compressor (3). This is an arithmetic unit that adjusts m during operation and during transient operation.

Next, the operation will be explained. During steady operation of the system,
That is, during steady operation of the turbo compressor (3), the computing unit (
By the action of 39), the bypass valve (3o) is kept fully closed or kept at a certain minute opening.

The pressure controller (38) is practically non-functional. The purpose of keeping the bypass valve (30) fully closed or at a slightly constant opening is to minimize energy loss during steady operation. At this time, since the system is in steady operation, all process quantities in the system should be maintained at constant values, but the outside temperature during operation.

In reality, process quantities such as temperature and pressure gradually change due to changes in the suction conditions of the compressor (3b) due to changes in humidity, changes in the amount of heat released by the system, etc. Even in response to such changes, it is important to always keep the discharge air pressure of the compressor (3b) constant. At this time, the discharge air pressure of the compressor (3b) is controlled by the pressure controller (37), which controls the combustion amount of the auxiliary combustion furnace (28) so that the pressure detected by the pressure detector (13) becomes a constant target value. This is done by controlling through (33) and (36). That is, during steady operation of the system, the combustion amount of the auxiliary combustion furnace (28) is feedback-controlled to keep the discharge air pressure of the compressor (3b) constant. On the other hand, when the system load fluctuates, the following operations are performed. First.

By operating the control circuit in the computing unit (39) immediately before the load command, the second bypass valve (30) is activated by the pressure controller (
38). Next, set values for the fuel flow rate and air flow rate to the auxiliary combustion furnace (28) are directly given to the flow rate controllers (33) and (36) as load commands to increase the turbine power. As a result, the discharge air pressure of the compressor (3b) tends to increase;
8) to adjust the bypass valve (30), i.e.
Constant control is performed by adjusting the flow rate 1e of the discharged exhaust gas passing through the bypass pipe (29) and adjusting the amount of exhaust gas supplied to the turbine (3a).

In this way, when the load is commanded, the turbine power is transferred to the auxiliary combustion furnace (
28) is increased by feedforward operation of the combustion amount, and a part of this increased amount of turbine power is transferred to the compressor (
3b) The turbine (
3a) Connect the front bypass pipe (29) or the bypass valve (3)
0) to the atmosphere, the turbo pressure faf
The power of ffl(3) is increased to satisfy the system air requirement. the amount released from the bypass valve (30);
That is, while the opening degree of the bypass valve (30) is kept almost constant, the flow control valve (15) installed in the air supply pipe (4) to the system is opened according to the amount required by the system, and the turbo compressor is (3) Air from compressor (3b) is supplied to the system.

At this time, the control i[I]v of the pressure controller (38)
By JJ's work, the bypass valve (30) is adjusted, that is, the amount of exhaust gas released into the atmosphere is narrowed down, and the compressor (30) is adjusted.
b) The discharge air pressure is always maintained constant. Once the state change in response to the load command is completed and the system has stabilized.

Next, control of the discharge air pressure of the compressor (3b) is transferred to the pressure controller (37) and also to the computing unit (39).

Therefore, the opening degree of the bypass valve (30) is gradually narrowed down from the current opening degree until it is finally fully closed or kept at a very small opening degree. This operation is aimed at minimizing energy loss in the system, and the bypass valve (30) is throttled down by fine adjustment so as not to upset the control balance of the turbo compressor (3) and the system. During this time, the discharge air pressure of the compressor (3b) is controlled by the flow controller (33).
, (36), constant control is performed by adjusting the combustion amount of the auxiliary combustion furnace (28).

After the bypass valve (30) is closed, the state returns to the state under steady load.

Figure 3 shows the change in the process amount when the system load fluctuates.When the load command is given at time T1, the fuel flow rate F1 of the auxiliary furnace (28) is fed forward according to the load command. Control! As the iDI operation increases, the combustion exhaust gas from the auxiliary combustion furnace (28) is added to the system exhaust gas, the turbine power increases, and the rotational speed of the turbo compressor (3) tends to increase. At this time, the air flow rate F2 to the system is still maintained at the value before the load command, so the increase in the output of the compressor (3b) due to the increase in the coupin power causes the output of the compressor (3b) to increase.
3b) is likely to appear in the form of an increase in the discharge air pressure.

On the other hand, at the same time as the load command, the compressor (3b)
Since the control system that performs constant control of the discharge air pressure PI by adjusting the opening degree of the bypass valve (30), that is, by adjusting the amount of exhaust gas discharged into the atmosphere, the discharged exhaust gas flow rate F
3 occurs, and the discharge air pressure P1 of the compressor (3b)
be kept constant. When the discharge exhaust gas flow rate F3 becomes stable, the air flow rate F2 to the system is increased to the target value based on the load command. During this process, the compressor (
By the constant control operation of the discharge air pressure P1 in 3b), the bypass valve (30) is throttled and the discharged exhaust gas flow rate F3 is reduced. The time when the air flow rate F2 to the system reaches the target value (time T2) is the first settling point for load fluctuation, and at this point the discharge air pressure P1 of the compressor (3b) is reached.
The control is switched from control by adjusting the amount of exhaust gas released from the bypass valve (30) to control by adjusting the combustion amount of the auxiliary combustion furnace (28). Thereafter, the bypass valve (30) is opened/closed according to a command from the computing unit (39), and the bypass valve (30) is opened and closed.
30) is completely narrowed down (time T3) becomes the second (final) settling time. (Flow rate of discharged exhaust gas F in Figure 3)
3 shows the case where the bypass valve (30) is fully closed) In the process from time T2 to time T3, the compressor (3b)
The auxiliary combustion furnace (2
8) is controlled in the direction of narrowing down the fuel flow rate F1. In this way, when the system load fluctuates, the turbine power of the turbo compressor (3) is actively manipulated by the combustion amount of the auxiliary combustion furnace (28), and the compressor (3b)
By controlling the bypass valve (30), fluctuations in the discharge air pressure of the compressor (3b) are suppressed and the discharge air pressure of the compressor (3b) is controlled at a constant level, so that a stable air supply with good load responsiveness and no pressure fluctuations can be achieved. It can be done to the system. Also, during steady state, bypass valve (30) 1
1! Since it is fully closed or slightly opened, the compressor power of the turbo compressor (3) can be kept to a minimum.

Thereby, system efficiency can be improved.

〔Effect of the invention〕

As explained above, during steady operation of the system, the combustion amount of the auxiliary combustion furnace is controlled by feedback control to keep the discharge air pressure of the compressor of the turbo compressor constant, with the bypass valve fully closed or slightly opened. When the load fluctuates, the combustion amount of the auxiliary furnace is controlled by feedforward control based on the program, while the bypass valve performs feedback control to keep the discharge air pressure of the turbo compressor compressor constant. It is possible to obtain a control method for a fuel cell power generation system that can easily keep the discharge air pressure constant at all times.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing a control method for a conventional fuel cell power generation system, FIG. 2 is a system diagram showing a control method for a fuel cell power generation system according to an embodiment of the present invention, and FIG. 3 is a system diagram showing a control method for a fuel cell power generation system according to an embodiment of the present invention. FIG. 2 is a characteristic diagram showing changes in process amount during fluctuations. In the figure, (1) is the fuel cell main body, (2) is the reformer,
(3) is a turbo compressor, (3a) is a turbine p
('') is the compressor, (4) is the air supply pipe, (7)
is the system exhaust gas piping, (13) is the pressure detector,
(15) is a flow control valve, (171 is a flow controller, (27) is a load, (28) is an auxiliary combustion furnace, (29) is a bypass pipe, (3
0) is a bypass valve, (32) is a flow control valve, (
33) is a flow controller, (35) is a flow control valve, (36) is a flow controller, (37) is a pressure controller, (38) is a pressure controller,
(39) is an arithmetic unit. Note that the same line numbers in the two figures indicate the same or equivalent parts.

Claims (1)

[Claims] A fuel cell main body, a reformer that supplies reformed fuel to the fuel cell main body, and a combustion exhaust gas from the reformer, or surplus air from the air electrode of the fuel cell main body, and a reformer that supplies reformed fuel to the fuel cell main body. A turbo compressor consisting of a turbine and a compressor that is driven by both combustion exhaust gas and supplies the compressed air necessary for the fuel cell main body and the reformer, and the system installed in the exhaust gas piping leading to the turbine of this turbo compressor. In a fuel cell power generation system comprising an auxiliary combustion furnace to compensate for insufficient power of the turbine, a bypass pipe installed branching off from the system exhaust gas pipe and bypassing the turbine of the turbo compressor, and a bypass valve installed in the bypass pipe. During steady operation of the system, the combustion amount of the auxiliary combustion furnace is controlled by feedback control to keep the discharge air pressure of the compressor of the turbo compressor constant with the bypass valve fully closed or slightly opened, and when the system load fluctuates. The control method for a fuel cell power generation system is characterized in that the combustion amount of the auxiliary combustion furnace is controlled by feedforward control based on a program, while the bypass valve performs feedback control to keep the discharge air pressure of the compressor of the turbo compressor constant. .