KR20000066675A - Method and apparatus for controlling a feul cell power generation system - Google Patents

Abstract

PURPOSE: A control method and a control apparatus of a fuel battery energy system is provided to control properly a thermal energy of a fuel battery energy system by optimizing the reaction temperature of a battery stack. CONSTITUTION: A control method and a control apparatus of a fuel battery energy system comprise the steps of: detecting the variation of a thermal load of a steam system; performing an operation process for the varied capacity of the thermal load by a controller and producing a control setup value; controlling temperature and humidity of cooling water input to a battery stack by using the produced control setup value and providing the generated steam corresponding to the varied load to the steam system.

Description

Method and apparatus for controlling fuel cell power generation system

The present invention relates to a fuel cell power generation system for supplying thermal energy in the form of steam or hot water to the outside by means of an electrochemical reaction, and more specifically, water cooling by controlling the pressure and temperature of the cooling water flowing into the fuel cell body. The present invention relates to a control method and apparatus for a fuel cell power generation system in which the amount of cooling water in a liquid phase and a gaseous phase discharged to a system can be controlled and supplied to an amount of steam required for an external heat load device.

A fuel cell is a high-efficiency power generation system that converts chemical energy of a fuel directly into electrical energy.As a result of chemical reactions, heat is generated to generate electricity as a result of chemical reactions. It has

As the fuel cell generates heat during the electricity generation process, a cooling process is required to maintain an appropriate temperature (for example, a temperature range of 180 to 220 ° C. for a phosphate fuel cell) required for an electrochemical reaction. The heat generated in the process can be used as direct heating heat by connecting to the outside, or as a driving heat source for cooling heat by connecting to an absorbing air conditioner. Generally, the steam discharged from the gas-liquid separator connected to the hot water outlet side of the battery body has a high temperature of 160 to 180 ° C., and thus has higher utilization value than hot water of 45 to 65 ° C. discharged from the cooling water heat exchanger. It can be used as a high efficiency cooling and heating heat source by connecting to the outside.

In general, the water-cooled cooling method of a fuel cell is a method of recovering heat of a fuel cell main body (hereinafter, referred to as a "cell stack") in a pure liquid state without phase conversion by pressurized hot water, and heating and evaporating a liquid under a constant pressure. The latter is classified into a method of recovering heat by using latent heat simultaneously. The latter method of using evaporative heat can maintain the temperature inside the cell stack more uniformly, and the vaporized vapor can be used for reforming fuel gas. It is known to be advantageous.

Steam generated from a water-cooled cooling system using the heat of evaporation of a conventional fuel cell is supplied to a reformer for generating hydrogen gas from a hydrocarbon-based fuel or supplied to an absorption type cooler through a gas-liquid separator, thereby taking a simple form to be used as a heat source for cooling. have.

On the other hand, as a way to more efficiently use steam or hot water generated in a water-cooled fuel cell power generation system, Japanese Laid-Open Publication No. 5-114411 has a plurality of gas-liquid separators installed in a stack and flowed into the primary gas-liquid separator. The steam is used as an external load and all of the steam generated in the stack is fed to the reformer by supplying some hot water from the primary gas-liquid separator to the flash tank, the secondary gas-liquid separator, to supply the steam generated by the pressure drop to the reformer. A fuel cell power generation system is disclosed that can be used as an external heat source.

In addition, Japanese Patent Application Laid-open No. Hei 6-36786 controls the discharge of condensate generated from the absorption chiller connected to the gas-liquid separator and returned to the fuel cell water cooling system to maintain a constant pressure (or temperature) of the cooling water flowing into the stack. Absorption chiller connection system of a fuel cell is known to improve the freezing capacity of the absorption chiller by maintaining a constant pressure of the absorption chiller.

In a similar form to the absorption chiller connection system, JP-A-6-36786 calculates the coolant temperature or pressure of the fuel cell to maintain the required coolant temperature by using the temperature of the coolant output from the absorption heat pump as a load. After that, a control valve is installed between the gas-liquid separator and the heat pump so that the amount of steam can be controlled by adjusting the valve so that the performance coefficient of the absorption heat pump can be maintained high. Is shown.

In another type of conventional fuel cell pressure control system, a device is installed in a steam pipe supplied from an gas-liquid separator to an external load to control the amount of steam in the valve to compare the load-side pressure with the pressure of the gas-liquid separator so as to be set. It is known from Japanese Patent Application Laid-open No. Hei 5-275100.

However, the water cooling system control method of all the conventional fuel cells is not a method of actively controlling the amount of steam or hot water generated from the cell stack, but is simply set to a specific pressure and temperature value and the coolant flows into the stack. The main point is to increase the efficiency of using a certain amount of steam or hot water generated by the present invention. Therefore, it is pointed out that when the load is changed, it cannot adequately respond to the change in the load.

Accordingly, the present invention is to solve the above-mentioned problems in the water-cooling system of the conventional fuel cell, and to solve the above problems, the cooling water flowing into the cell stack in the fuel cell power generation system composed of a fuel cell body, a reformer and an external heat load device. The present invention provides a method and apparatus for controlling a fuel cell power generation system in which the amount of liquid and gaseous cooling water discharged to a water cooling system is controlled and supplied to the amount of steam required for an external heat load device by controlling pressure and temperature. The purpose is to.

That is, according to the present invention, an increase or a decrease in the amount of steam required for the changed external heat load is supplied to the external heat load of the water cooling system by causing the cooling water temperature and the pressure of the stack inlet to be reset in conjunction with the external heat load change of the water cooling system. The purpose is to ensure stable operation of the external heat load device.

1 is a schematic structural diagram of a fuel cell power generation system including a control device according to the present invention;

Figure 2 is a graph showing a heating curve and steam generation process inside the cell stack of the fuel cell power generation system according to the present invention.

3 is a flowchart of a control method of a fuel cell power generation system according to the present invention;

((Description of the code for the main part of the drawing))

1. Battery Body 2. Gas-liquid Separator

3. Cooling heat exchanger 4. Steam system

5. Reformer 6. Coolant Temperature Control

6a. Mixing Valve 7. Coolant Pressure Control

7a. Coolant Pump 8. Stack Reaction Temperature Control

8b. Stack Temperature Control Valve 11.Controller

12. Load detector

The control method and apparatus of the fuel cell power generation system of the present invention provide a means capable of adjusting the temperature and pressure of the cooling water flowing therein on a cooling water inlet conduit connected to the battery stack inlet, and changes the heat load of the thermal load device of the cooling system. By providing a means to detect the temperature and pressure of the coolant flowing into the battery stack by applying a control signal to the temperature and pressure regulating means installed in the stack inlet in accordance with the change of the detected heat load to reset the temperature of the cooling system from the battery stack It is a technical feature that the steam discharged to the furnace can be adjusted to the amount of steam required by the current heat load device.

In other words, the present invention can be said to be a method of operating a fuel cell power generation system that actively controls the amount of evaporation required by an external heat source and a reformer by controlling the pressure and temperature of the stack inlet cooling water, and a device suitable for performing such an operation method. .

In general, in a fuel cell power generation system, the heat of cooling consists of vapor discharge from a gas-liquid separator and cooling by heat exchange with cooling water in a cooling heat exchanger installed at the outlet of the gas-liquid separator. Therefore, in the present invention, the temperature and pressure of the cooling water at the inlet of the stack are controlled to eventually control the amount of steam supplied to the load by selectively controlling the two cooling heats and controlling the evaporation temperature. Will mean.

On the other hand, the stack inlet temperature of the cooling water serves as a variable for determining the amount of heat released to the steam and the amount of heat released to the cooling heat exchanger under a given pressure. In more detail, the high cooling water inlet temperature means less heat is emitted from the cooling heat exchanger, and in order to discharge the same heat, a large amount of heat must be released through the steam. This is because a higher stack inlet coolant temperature reduces the amount of heat that is heated to the liquid state inside the stack and increases the heat used for evaporation.

On the contrary, the low temperature of the cooling water inlet means that most of the heat is recovered from the cooling heat exchanger. Since the cooling water is supercooled, a large amount of heat is used to heat the cooling water in a liquid state in the stack, thereby reducing the amount of heat of evaporation.

Thus, it is possible to control the amount of evaporation under a given pressure by adjusting the stack inlet coolant temperature.

In addition, the evaporation temperature of the cooling water inside the stack is dependent on the pressure. If the pressure is high at a given temperature, evaporation occurs at high temperature. On the contrary, if the pressure is low, evaporation occurs at low temperature. By controlling the amount of heat recovery in the liquid state and the amount of heat recovery by evaporation can be adjusted to adjust the amount of evaporation.

At this time, when the evaporation temperature is lowered due to the pressure drop, the temperature of the steam decreases a lot, but the amount of steam increases, so that the heat of the entire steam increases. Particularly, if the pressure control is performed in the fuel cell power generation system, even if the heat generation amount in the stack is not sufficient in the fuel cell low load electric state, the reformer can generate enough low-temperature steam without using the preheating electric heater as an auxiliary power source. There is an advantage that can be supplied.

In the present invention, the coolant pressure control at the inlet of the stack is controlled through the rotation speed control of the pump which is changed in proportion to the frequency variable by the inverter. Such a control method controls the pressure through a conventional damper or valve. The pressure drop is lower compared to the system, which minimizes the use of additional energy.

In the present invention, the temperature control of the coolant at the inlet of the stack divides the hot water output line output from the gas-liquid separator into two branches so that one line is directed to the cooling water heat exchanger and the other line is directly introduced into the mixing valve. This is done by adjusting the flow rate of the line.

The reason for bifurcating the hot water output line from the gas-liquid separator in two ways is to shorten the heat transfer time by ensuring that as much flow rate as possible is supplied to the cell stack.

In the present invention, temperature control of the inlet temperature stack is performed through flow control through an automatic valve mounted at the outlet of the stack, and the flow rate of the coolant flowing into the stack is independent of the stack inlet coolant temperature and pressure. By controlling the supply, the internal temperature of the stack is kept constant within the temperature range appropriate for the electrochemical reaction of the fuel cell.

The fuel cell power generation system configuration and control method of the present invention will be described in detail with reference to FIG. 1 as follows.

First, FIG. 1 is a schematic structural diagram of a phosphoric acid fuel cell power generation system according to the present invention. As shown in the drawing, the fuel cell power generation system of the present invention includes a battery stack 1 including a fuel electrode and an air electrode, and a battery stack 1. Cooling water storage tank (Hot water tank) and gas-liquid separator 2 (hereinafter referred to as "gas-liquid separator") installed on the cooling water output side of the cooling water exchanger is installed on the hydrothermal output line separated through the gas-liquid separator (2) A hydrocarbon-based system (4) as a load device connected to a water cooler (3), a steam output line separated from the gas-liquid separator (2), and a steam line branched from the steam output line, It is composed of a reformer (5) for reforming the fuel to supply hydrogen to the fuel electrode of the cell stack (1) and the cooling water passing through the cooling heat exchanger (3) is configured to flow into the cell stack (1), Structure is a common kite It corresponds to the basic configuration of the fuel cell is provided in common in a cell power system.

Next, based on the basic structure of the fuel cell power generation system looks at the novel components applied to carry out the method of the present invention.

First, the control device of the fuel cell power generation system of the present invention is a stack inlet coolant temperature for controlling the inlet coolant temperature of the battery stack 1 on the coolant pipe circulated to the cell stack 1 via the cooling heat exchanger 3. A control unit 6 and a stack inlet coolant pressure control unit 7 are respectively provided, and a stack reaction temperature control unit 8 is installed on the coolant output line of the battery stack 1 to maintain a constant reaction temperature of the battery stack. One side of the gas-liquid separator 2 is equipped with a stack preheating temperature control unit 9 as a preheating system for initial driving of a fuel cell, and corresponds to the amount of steam discharged from the gas-liquid separator 2 through a steam output line. The water level control unit 10 is provided to automatically replenish the cooling water so as to replenish the cooling water so that the level of the gas-liquid separator 2 is always kept constant.

In the apparatus of the present invention, a controller 11 is provided to input and output a control signal to each of the controllers 6-10 so that automatic control is performed. On the output side of the steam use system 4, a change in heat load is provided. A load detector 12 for detecting is mounted.

In FIG. 1, the solid line connecting each component is a process line as a fluid conduit through which cooling water and steam flow, and the dotted line is a signal transmission line connected between each control unit 6-10 and the controller 11.

In the figure, reference numeral 13 denotes a water level detector for detecting the water level of the gas-liquid separator 2 and applying the detected value to the water level controller 10, and 14 is a water supply tank for supplying supplementary cooling water to the water level controller.

The stack inlet coolant temperature control unit 6 is installed on the mixing valve 6a, the temperature controller 6b for controlling the opening degree of the mixing valve, and the output line of the mixing valve to measure the temperature of the cooling water and measure the measured temperature. It consists of a temperature detector (6c) for applying a value to the temperature controller (6b), wherein the mixing valve (6a) is a cooling water passing through the cooling heat exchanger (3) and the hot water output line of the gas-liquid separator (2) The hot water flowing in through the branch line branched from is commonly introduced, the mixing ratio of the cooling water flowing through these two lines is controlled by the temperature controller 6b.

Next, the stack inlet coolant pressure control unit 7 is a coolant pump 7a, a coolant flowing into the pressure controller 7b and a battery stack 1 for applying a rotation speed control signal to the coolant pump via the inverter 7c. It consists of the pressure detector 7d which detects the pressure of this.

In addition, the stack reaction temperature control unit 8 includes a reaction temperature detector 8a for detecting the internal temperature of the battery stack 1 and a stack temperature control valve 8b provided on the cooling water output line of the battery stack 1. ) And a reaction temperature controller 8c which applies a control signal for adjusting the opening degree of the control valve so that the temperature inside the battery stack 1 is always maintained in a temperature range suitable for the reaction.

On the other hand, the stack preheat temperature control unit 9 is the temperature detector (9a) for measuring the temperature inside the gas-liquid separator (2) and the temperature of the battery stack at the start of the fuel cell is the minimum operating operating range (for example about 100-130 ℃ It consists of an electric heater 9b and a preheating temperature controller 9c which heats the gas-liquid separator 2 to preheat).

Next, the water level controller 10 supplies tap water stored in the water supply tank 14 through the coolant line (process line) when the current level of the gas-liquid separator 2 detected by the water level detector 13 is lower than the set water level. It consists of a water supply pump (10a), a level controller (9b) for applying a drive control signal to the feed water pump and a water purifier (10c) for filtration of the cooling water supplied from the feed water pump (10a).

In addition, the controller 11 has a microprocessor built therein to process a signal input to the input / output port 11a through each control unit 6-10 to output a control signal to each control unit.

Referring to the operation process or the control method of the fuel cell power generation system of the present invention having such a structure in detail as follows.

First, when the load of the steam using system 4 is constant, the control will be performed so that the cooling water temperature difference of the stack entrance and exit can be maintained at a constant value so that the temperature inside the battery stack 1 is kept uniform. In other words, when there is no load change, the stack inlet coolant temperature control unit 6 and the pressure control unit 7 are controlled while maintaining the initial set value. Without changing the pressure and temperature, only control is performed to keep the reaction temperature within the stack within an appropriate range.

Next, when the load detection value input to the controller 11 through the load detector 12 is changed from the original value, it is calculated by the controller 11 and controlled by the coolant temperature controller 6 and the coolant pressure controller 7. The signal is output so that the pressure and temperature of the coolant flowing into the battery stack 1 change in response to the changed load.

That is, when the external heat load fluctuates, the flow rate of the steam supplied to the outside is controlled in proportion to the load variation by causing the temperature of the coolant flowing into the battery stack 1 to change within a given range in conjunction with the load. The temperature of the coolant flowing into the battery stack 1 is achieved by adjusting the mixing valve 6a of the coolant temperature control unit 6, and the relatively low temperature hot water that is cooled by passing through the cooling heat exchanger 3. Temperature control of the cooling water is performed by the mixing ratio between the hot water bypassed through the branch hydrothermal line without cooling.

On the other hand, in the present invention, in parallel with the control to control the amount of steam through the cooling water temperature control as described above when the load amount changes, the amount of steam through the cooling water pressure control can be changed in conjunction with the change in the heat load, the specific The control method is as follows.

First, when there is no change in the external load or when operating the system at a constant pressure irrespective of the electrical load, the control is performed to maintain a constant value regardless of the disturbance, and when a change in the external heat load occurs, the controller 11 The pressure controller 7b operates in response to the control signal to drive the coolant pump 7a. As a result, the pressure of the coolant flowing into the battery stack 1 is changed, whereby the evaporation temperature of the coolant passing through the stack is increased. The amount of vapor generated from the cell stack, which is changed from the initial set point, changes.

The heat recovery process through heating and evaporation of cooling water occurring in the battery stack 1 when the fuel cell power generation system of the present invention is operated will be described with reference to FIG. 2.

FIG. 2 is a graph showing a heating curve and steam generation process in a stack of a fuel cell power generation system according to the present invention. When there is no change in heat load, heat recovery by cooling water in the stack is liquid heating and evaporation as shown in curve A. The evaporation temperature is determined by the saturation pressure and the evaporation temperature is constant if the pressure is constant.

On the other hand, when the heat load increases, when the temperature of the stack inlet is raised as in curve B, the amount of heat used for heating the liquid decreases compared to the curve A, and the amount of heat used for evaporation increases, so that the heat can be supplied to the outside without changing the pressure. The amount of steam that can be increased. The rise of the stack inlet coolant temperature as the load increases is lower than the saturated steam temperature corresponding to the saturation pressure and is supplied to the stack inlet in a supercooled state than the saturation temperature because it must be pressurized by the pump 7a in the liquid state. . It is cooled by the cooling heat exchanger (3).

If the amount of steam in the given pressure and the allowed temperature range is not sufficient, the amount of steam can be increased by changing the pressure by driving the pump 7a as shown in curve C so that the evaporation temperature according to the pressure is changed. In this case, the temperature of the steam decreases slightly, but the amount of steam increases at a given amount of heat, so that the total amount of heat contained in the steam increases, and even at low loads, it is possible to supply enough steam to the reformer in question.

3 is a flowchart illustrating a method of operating the fuel cell power generation system of the present invention as described above.

Cooling system operation of the fuel cell power generation system according to the present invention is performed by automatic control through a microprocessor of the controller in conjunction with the entire fuel cell operation system. That is, in the present invention, the coolant inlet pressure and temperature of the battery stack, the reaction temperature and the heat load change amount of the stack are measured as temperature or pressure change, and the controller performs calculations to calculate a control set value linked to the load change, and calculates the calculated value. By controlling the mixing valve to control the coolant inlet temperature and the coolant pump by controlling the coolant inlet pressure.

As described above, the present invention is controlled so that the reaction temperature of the battery stack is always maintained in the optimum temperature range, while the stack inlet coolant temperature and pressure are changed in response to the change in the heat load of the cooling system. By changing the amount of steam produced in conjunction with the system, it is expected that the steam using system using heat energy of the fuel cell power generation system as a heat source can be continuously and stably operated regardless of the heat load.

Claims (7)

In a water-cooled fuel cell power generation system consisting of a battery stack, a gas-liquid separator, a cooling heat exchanger, a steam use system, and a controller, detecting a heat load change of a steam use system, and performing a calculation based on a detection value of the heat load change amount in a controller. Calculating a control set point linked to the change, and controlling the temperature and pressure of the coolant flowing into the battery stack by the calculated control set point so that the amount of steam generated corresponding to the changed load can be supplied to the steam using system. Control method of a fuel cell power generation system comprising the step. The method of claim 1, wherein the temperature control of the cooling water flowing into the battery stack branches the hot water discharge pipe of the gas-liquid separator so that one pipe is directly connected to the mixing valve, and the other pipe is connected to the mixing valve through the cooling heat exchanger. The control method of the fuel cell power generation system, characterized in that made by controlling the mixing ratio of the flow rate flowing through these two pipelines. The method of claim 1, wherein the pressure control of the coolant flowing into the battery stack is performed by controlling the rotation speed of a coolant pump installed on an inlet coolant pipe of the battery stack. In a fuel cell power generation system comprising a battery stack (1), a gas-liquid separator (2), a cooling heat exchanger (3), a steam using system (4), and a cooling heat exchanger (3), the cooling heat exchanger (3) is The stack inlet coolant temperature control unit 6 and the stack inlet coolant pressure control unit 7 for controlling the inlet coolant temperature of the battery stack 1 are respectively installed on the coolant pipe circulated to the cell stack 1. On the cooling water output line of 1), a stack reaction temperature control unit 8 is installed to maintain a constant reaction temperature of the battery stack, and automatic control is performed by inputting and outputting control signals to the control units 6-8. A controller (11) is provided, and a load detector (12) for detecting a change in heat load is mounted on an output side of the steam use system (4). 5. The stack inlet coolant temperature control unit (6) is installed on the mixing valve (6a), the temperature controller (6b) for controlling the opening degree of the mixing valve, and the output line of the mixing valve to adjust the temperature of the cooling water. It consists of a temperature detector (6c) for measuring and applying the measured temperature value to the temperature controller (6b), the cooling valve and the gas-liquid separator (2) passed through the cooling heat exchanger (3) to the mixing valve (6a) The control apparatus of a fuel cell power generation system, characterized in that the hot water flowing through the branch line branched from the hot water output line of the common flow. 5. The stack inlet coolant pressure control unit (7) is a coolant pump (7a), a pressure controller (7b) and a cell stack (1) for applying a rotational speed control signal to the coolant pump via an inverter (7c). And a pressure detector (7d) for detecting the pressure of the cooling water flowing into the fuel cell power generation system. The stack reaction temperature control unit (8) according to claim 4, wherein the stack reaction temperature control unit (8) includes a reaction temperature detector (8a) for detecting an internal temperature of the battery stack (1), and a stack temperature provided on the cooling water output line of the battery stack (1). The control valve (8b) and a control signal for controlling the opening degree of the control valve by applying a control temperature controller (8c) so that the temperature inside the battery stack 1 is always maintained in a temperature range suitable for the reaction Control device of fuel cell power generation system.