JPS6180765A - Control method for fuel cell power generation system - Google Patents

Abstract

PURPOSE:To make the air supply with good load responsiveness and no fluctuation possible, by keeping the discharge air pressure of the compressor of a turbo compressor constant under the feedback control by operating a by-pass valve, while keeping the combustion control of a sub-combustion furnace under the feed-forward control based on a program. CONSTITUTION:In case of the regular operation of a system, the combustion volume control of a combustion furnace (28) is kept constant under the feedback control of the constant discharge air pressure compressor (3b) of a turbo compressor, by opening an atmospheric open valve (12) to its fuel or small opening. In case of the load fluctuation of the system the discharge air pressure of the compressor (3b) of the turbo compressor is always kept constant by keeping the constant feedback control of the discharge air pressure of the compressor (3b) by operating the atmospheric open valve (12), while keeping the combustion control of a sub-combustion furnace under the feed-forward control based on a program.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Summary of the Invention] The present invention relates to a control method for a fuel cell power generation system, and particularly to a control method for 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.

A reformer that reforms hydrocarbon fuel such as natural gas and supplies hydrogen gas as fuel to the fuel cell body.

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
Pressure is maintained at ~6 kg/cg. At this time, compressing the air requires a large amount of power.

This power is provided by the turbine of the turbo compressor, which introduces the 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 team (,
? As a so-called power generation system, wide and quick load response control is required. The amount of air supplied to the fuel cell main body 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 main body is determined from the viewpoint of maintaining the characteristics of the fuel cell main body and by suppressing the differential pressure with the fuel side pressure to prevent gas leakage between the two electrodes.
In order to prevent the crossover phenomenon, control is required to maintain a constant value even when the load fluctuates. That is, the turbo compressor basically requires constant pressure variable air volume control.

Two specific conventional methods include, 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 (1 m
), 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 excess air at the outlet of the air electrode (1a) of the fuel cell main body (1), and the air electrode (1a) of the fuel cell main body (1) is A turbo compressor consisting of a turbine (3a) that supplies the necessary compressed air to the burner section (2a) of the compressor (2), and a compressor (3b) disposed coaxially with the turbine (3a).

(4) is the compressor (3) of this turbo compression i (3)
b) Air supply piping that supplies compressed air to the air i [1a) of the fuel cell main body (1), (5) turbo-compresses surplus air from the air electrode (1a) of the fuel cell main body (1) Excess air piping leading to the turbine (3a) of m(3).

(6) converts the combustion exhaust gas from the reformer (2) into the turbine (3).
(7) is a system exhaust gas pipe that merges the surplus air pipe (5) and the exhaust gas pipe (6) and leads the surplus 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 main body (1). Fuel electrode (1b
) Reformed fuel supply piping.

(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 11 (la) of the fuel cell main body (1). (13) is a pressure detector that detects the pressure inside the air supply pipe (4); (14) is this pressure detector (1);
It is a pressure controller that controls the opening and closing of the atmosphere release valve (12) in response to signals from L (12) to (3).
14) controls the discharge air pressure of the compressor (3b). (15) is installed in the air supply pipe (4).

(16) 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 electrode (1a) 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. This is a pressure controller that controls the opening and closing of the pressure regulating valve (21) in response to a signal from the detector (22), and these (21) to (23) control the reaction fuel gas pressure in the fuel cell main body (1). be done. (24) is a flow rate control valve installed in the fuel supply pipe (8), (25) is a flow rate detector that detects the flow rate in the fuel supply pipe (8), and (26) is this flow rate detector (25).
) is a flow controller that controls the opening and closing of the flow control valve (24) in response to signals from (24) to (2).
6) controls the flow rate of fuel supplied to the reformer (2). Although not shown, a burner air supply pipe is provided which branches from the air supply pipe (4) 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 main body (1),
As the supply air flow rate from the compressor (3b) decreases, the discharge air pressure of the compressor (3b) also decreases, but the reaction air pressure or the differential pressure between the reaction air pressure and the reaction fuel gas pressure is maintained by the following method. There is. 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 (1
In the range below the load range where the adjustment allowance of 2) disappears, the reaction air pressure is linked to the decrease in the discharge air pressure of the compressor (3b), that is, the discharge air pressure of the compressor (3b) is adjusted by the pressure control valve (18). The pressure difference between the reaction air pressure and 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. Arrange. 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. reactor. That is, this system basically maintains a steady pressure by adjusting the atmosphere release valve (12), but there is no adjustment allowance for the atmosphere release valve (12).
In this case, the pressure of the reactant gas in the fuel cell main body (1) is lowered in conjunction with the lowering of the discharge air pressure of the compressor (3bl!).

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 normally 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. Leakage: On the contrary, the reaction gas leaks into the casing and deteriorates the characteristics of the fuel cell. Furthermore, air travel pressure is controlled by adjusting the atmosphere 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 required for the compressor. Since the power is equal to or even insufficient for the power, control using the adjustment allowance of the atmosphere release valve (12) is difficult.

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 piping1.
For example, there is one disclosed in Japanese Patent Publication No. 58-56231. Also, for example, by bypassing the discharge air of the compressor of the turbo compressor disclosed in Japanese Patent Application Laid-open No. 18577/1982 using a bypass valve (corresponding to the atmosphere release valve (12)) and releasing it into the atmosphere outside the system. There is a method for controlling the discharge air pressure of the compressor of a turbo compressor, but in this case as well, it is difficult to create a printing section that utilizes the adjustment allowance of the bypass valve. Namely, 2 In this case, since the combustion response of the auxiliary combustion furnace is generally slow, the supply of necessary air to the system cannot keep up with the load fluctuations, and the bypass valve is fully closed.
There was a drawback that the discharge air pressure of the turbo compressor's compressor temporarily decreased.

[Summary of the invention]

This invention was made in view of the drawbacks of the above-mentioned systems, and during steady operation of the system, the combustion amount of the auxiliary furnace is controlled by the compressor of the turbo compressor with the atmosphere release valve fully closed or slightly opened. Feedback control is used to keep the discharge air pressure constant, and when the system load fluctuates, the combustion amount of the auxiliary combustion furnace is controlled by feedforward control based on the program, while feedback control is used to keep the discharge air pressure of the compressor of the turbo pressure wi machine constant using the atmosphere release valve. By doing φ
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)
, (1t) to (15L) (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 shown in one block. (28) is the system exhaust gas pipe (7) to compensate for the lack of turbine power of the turbo compressor (3).
), (29) is a fuel pipe that leads and supplies fuel from, for example, the fuel supply pipe (8) to this auxiliary combustion furnace (28), (301 is the fuel pipe of B (29)
), the flow control valve (31) is installed in the fuel pipe (
29) Detects the flow rate of fuel flowing through the flow rate control valve (30)
(32) is an air pipe branched from the air supply pipe (4) and connected to the auxiliary combustion furnace (28); (33) is a flow control valve installed in this air pipe (32); (34) is a flow controller that detects the flow rate of air flowing in the air pipe (32) and adjusts the flow rate control valve (33); (35) is the discharge of the compressor (3b) detected by the pressure detector (13); The flow controller (31) and the flow controller (
34) a pressure controller that provides a control signal for;
(36) is a computing unit that adjusts the operation signal given from the pressure controller (14) to the atmosphere release valve (12) depending on whether the turbo compressor (3) is in steady operation or transient operation. First, the operation will be explained. During steady operation of the system, that is, during steady operation of the turbo pressure 1'1 machine (3), the operation of the computing unit (36)
) is either fully closed or held at a certain minute opening.

The pressure controller (14) is practically non-functional. The reason why the atmosphere release valve (12) is kept fully open 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.

Due to changes in the suction conditions of the compressor (3b) due to changes in humidity, changes in system heat radiation, etc.

In reality, process variables such as temperature and pressure change gradually.

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 (35) so that the pressure detected by the pressure detector (13) becomes a constant target value.
) is controlled by the flow rate controller (31'), (34
). In other words, during steady disc rotation of the system, the combustion amount of the auxiliary combustion furnace (28) is equal to that of the compressor (3).
Feedback control of b) to keep the discharge air pressure constant is performed.

On the other hand, when the system load fluctuates, the following operations should be performed.

First, the atmospheric release valve (12) is placed under the control of the pressure controller (14) by operating the control circuit in the computing unit (36) immediately before a load command is issued. 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 (31) and (34) as load commands to increase the turbine power. As a result of (B), the discharge air pressure of the compressor (3b) tends to rise, but the pressure controller (14) adjusts the atmosphere release valve (12), that is, the atmosphere release piping. Constant control is achieved by adjusting the discharge air flow rate via (11). In this way, at the time of load command, the turbine power is increased by the feedforward operation of the combustion amount of the auxiliary combustion furnace (28), and as a result, a part of the increase in the discharge air flow rate of the compressor (3b) is transferred to the discharge air of the compressor (3b). The power-up of the turbo compressor (3) is planned while the pressure is kept constant and the air is discharged from the atmosphere release pipe (11) at the outlet of the compressor (3b) to the atmosphere via the atmosphere release valve (12). system air requirement is satisfied. Amount released from the atmosphere release valve (12).

That is, while the opening degree of the atmosphere release valve (12) is kept almost constant, the flow rate control valve (15) installed in the air supply piping (4) to the system is opened according to the amount required by the system, and the turbo is released. Air from the compressor (3b) of the compressor (3) is supplied to the system. At this time.

The control operation of the pressure controller (14) performs adjustment 2 of the atmosphere release valve (12), that is, narrows down the amount of air released to the atmosphere, and the discharge air pressure of the compressor (3b) 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 air pressure of the compressor (3b) is transferred to the pressure controller (35), and the arithmetic unit (36) controls the air release valve (12). The opening degree is gradually narrowed down from the current opening degree until it is finally fully closed or kept at a very small opening degree. The purpose of this operation is to minimize the energy loss of the system, and the restriction of the atmosphere release valve (12) should be performed 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 constantly controlled by adjusting the combustion amount of the auxiliary combustion furnace (28) through the flow rate controller (31'l, (34)).

After the atmosphere release valve (2) is closed, the state returns to the state when the load is steady.

Figure 3 shows the change in the process amount when the system load fluctuates.When a load command is given at time T1, the fuel flow rate F1 of the auxiliary combustion furnace (28) is controlled by feedforward control according to the load command. As a result, the combustion exhaust gas from the auxiliary combustion furnace (28) is added to the system exhaust gas, the turbine power increases, and the turbo compressor (3
) rotation speed increases. At this time, since the air flow rate F4 to the system is still maintained at the value before the load command, the discharge air pressure P1 of the compressor (3b) is about to increase. In response to this, constant pressure control by the pressure controller (14) operates, and the excess air amount is released to the atmosphere.
By discharging the air to the atmosphere as 1 compressor (3b), the discharge air pressure P1 of compressor 1 (3b) is maintained constant. When the feedforward operation to the auxiliary combustion furnace (28) becomes stable, the air flow rate F4 to the system is increased to the target value based on the load command.

In this process, the discharge air pressure P1 of the compressor (3b)
Due to the constant control operation, the atmosphere release valve (12) is throttled down and the atmosphere release air flow rate F3 is reduced. The time when the air flow rate F4 to the system reaches the target value (time T2) is the first settling time for load fluctuations, and at this time, the control of the discharge air pressure Pl of the compressor (3b) is controlled by the atmosphere release valve (12).
) to control by adjusting the combustion amount of the auxiliary combustion furnace (28). After this, the atmosphere release valve (12) is gradually opened in response to a command from the second computing unit (36), and the time when the atmosphere release valve (12) is completely throttled down (time T31 is the second (final) settling time). In the process from time T2 to time T3, the compressor (3b
) through a constant control operation of the discharge air pressure P1 of the auxiliary combustion furnace (
28) Fuel for? Control is performed in the direction of narrowing down F1. In this way, when the system load fluctuates, the turbine power of the turbo compressor (3) is actively transferred to the auxiliary furnace (2).
8), and changes in the discharge air pressure of the compressor (3b) due to this operation are controlled by the atmospheric release valve (12).
), the discharge air pressure of the suppressor compressor (3b) is controlled at a constant level, so that a stable air supply with good load response and no pressure fluctuation can be provided to the system. In addition, since the atmosphere release valve (12) is fully closed or slightly opened during steady state, the compressor power of the turbo compressor (3) can be maintained at a minimum, thereby improving system efficiency. can.

〔Effect of the invention〕

As explained above, in this invention, during steady operation of the system, the combustion amount in the auxiliary combustion furnace is controlled by feedback control to keep the discharge air pressure of the turbo compressor constant with the atmosphere release valve fully closed or slightly opened. When the system load fluctuates, the combustion amount of the auxiliary furnace is controlled by feedforward control based on the program, while the atmosphere release valve performs feedback control to keep the discharge air pressure of the turbo compressor's combination constant. It is possible to obtain a control method for a fuel cell power generation system that can easily keep the discharge air pressure of a compressor 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, and (2) is the reformer. (3) is a turbo compressor, (3ml is a turbine,
(3b) is a compressor, (4) is an air supply pipe, (7
) is the system exhaust gas piping, (11) is the atmospheric release piping,
(12) is an atmosphere release valve, (14) is a pressure controller, and (15) is a flow rate control valve. (17) is the flow controller, (27) is the load,
(28) is an auxiliary combustion furnace, (30) is a flow control valve, (3
1) is a flow controller, (33) is a flow control valve, (
34) is a flow rate controller. (35) is a pressure controller, and (36) is a computing unit. Note that the same reference numerals 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. An auxiliary combustion furnace that makes up for the insufficient power of the turbine, an air release pipe that is branched from the air supply pipe that supplies the air compressed by the compressor of the turbo compressor to the fuel cell main body, and an air release pipe that is installed on this air release pipe. 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 combustion furnace is controlled with the atmosphere release 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 air release valve provides feedback to keep the discharge air pressure of the turbo compressor's compressor constant. A control method for a fuel cell power generation system, characterized by performing control.