JPS61156638A - Cooling-system controller for fuel cell power generation system - Google Patents

Abstract

PURPOSE:To facilitate operation of a fuel reformation system by improving the control of cell operation temperature by directly detecting the temperature of cooling water flowing near the inlet of a cell stack and controlling the pressure of steam in a steam separator so as to control the influence of the variation in the heating value in the stack on the temperature of cooling water. CONSTITUTION:The heat exchanger 7 of a cooling-system controller is installed parallel to a main line of cooling water. It is controlled by separating cooling water. while cooling water separated from steam in a steam separator 1 is fed to a cell stack 2 by means of a circulation pump 6, part of the cooling water is cooled by being fed through the exchanger 7 before passing through a three-way control valve 8. The control valve 8 is operated by using a thermometer 5 to measure the temperature of cooling water flowing near the inlet of the stack 2 and then using a PI computing element 10B to compute the difference between the measure temperature and set temperature (To). A flow-ratecontrolling valve 4 is installed near the outlet of a heat exchanger 3 attached to the upper portion of the separator 1. A pressure detector 9 is used to measure the internal pressure of the separator 1 and then the difference between the measured internal pressure and set pressure (Po) is obtained to operate the valve 4, thereby improving the control of cell operation temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a battery cooling system control device in a fuel cell power generation system.

[Technical background of the invention]

In a fuel cell power generation system, the battery cooling system is a subsystem that absorbs thermal energy generated within the battery stack from within the battery stack by passing cooling water through it, thereby maintaining a uniform battery operating temperature. The cooling water that has absorbed the heat in the battery stack becomes a two-phase flow of steam and water and is returned to the steam-water separator. The liquid phase portion is recirculated as cooling water, and the gas phase portion is used as steam for fuel reforming in the fuel supply system. In this way, the battery cooling system is a subsystem that not only cools the battery but also serves as a source of fuel reforming steam.

FIG. 2 shows the prior art. battery stack 2
The thermal energy generated within the fuel is in excess of the energy contained in the steam for reforming the fuel.
This causes an increase in the temperature of the cooling water, leading to a decrease in cooling capacity. Therefore, this surplus energy must be discharged outside the system. In this respect, in the conventional technology, the steam in the steam separator 1 is passed through the heat exchanger 3 to liquefy it, and the latent heat '1i at this time is taken away by the secondary cooling water, thereby accumulating energy in the system. In other words, the idea was to prevent the temperature of the cooling water from rising. Control system is temperature detector 5
The temperature of the cooling water at the inlet of the gas stack is detected, and based on this signal, the amount of steam extracted from the steam separator 1, that is, the amount of energy discharged outside the system, is adjusted.

[Problems with background technology]

In general, temperature and pressure have very different speeds in their dynamics. In such a system in which dynamics with different time constants are mixed, for example, even if an attempt is made to control a slow-moving element by manipulating a fast-moving element, the operator cannot expect significantly better controllability. Not only that, but it would also lead to unstable phenomena. In the case of conventional battery cooling systems, the steam flow rate extracted from the steam water separator is directly controlled by looking at the cooling water temperature, which has a slow response. This leads to fluctuations in the steam pressure inside the separator 1. Although the steam flow rate and steam pressure have a nonlinear relationship, they are equivalent, and both exhibit a much faster response than the cooling water temperature. Now, let's consider a case where the cooling water temperature rises above a given set value. The control system operates to adjust the cooling water temperature to a set value. When a rise in temperature is detected, the flow control valve 4 is operated to increase the steam flow rate. As a result, the steam inside the steam water separator 1 escapes, and the steam pressure quickly decreases. At this time, the energy discharged outside the system exceeds the equilibrium point, and the cooling water temperature tends to decrease, but since the temperature changes slowly, the steam pressure inside the steam separator 1 reaches an excessive point. The decline continues.

In order for the steam pressure to return to the equilibrium point, it is necessary to wait for a while for the cooling water temperature to return to the set value. The problem at this time is not only that the feedback effect on the cooling water temperature is slow, but also that the steam in the steam separator is the source of fuel reforming steam, so this drop in steam pressure directly affects the fuel. This affects the reforming system and even the battery system. In order to operate the fuel reforming system in a stable state, it is necessary that the steam pressure in the steam separator is kept constant.

It can be said that the prior art shown in FIG. 2 does not take this point into consideration at all. Simply put, it takes a macro view of the battery cooling system and controls the thermal energy stored within the system. This is not a direct method of cooling water temperature control, and results in large fluctuations in the pressure inside the steam/water separator.Therefore, the problem with the conventional technology is the control of the battery stack cooling water temperature. In terms of performance, this can be said to be due to the stabilization of the steam pressure inside the steam separator.

[Purpose of the invention]

The present invention has been made to solve the above problems, and is a battery cooling system for a fuel cell power generation system that improves the stabilization of steam pressure in a steam separator and the control performance of the cooling water temperature at the inlet of a battery stack. The purpose is to provide a system control device.

[Summary of the invention]

The present invention is equipped with a heat exchanger for absorbing steam latent heat and a heat exchanger for regulating the temperature through direct passage of cooling water. The flow rate to be cooled is controlled by passing the signals from the stack inlet cooling water temperature detectors through arithmetic units.

[Embodiments of the invention]

Examples will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. The symbols in the figure correspond to those in FIG. 7 is a heat exchanger which is parallel to the main cooling water line and is controlled by separating the cooling water. The cooling water separated from steam by the steam separator 1 is drawn by a circulation pump 6 and sent to the battery stack 2. During this time, the cooling water is cooled by being divided into a heat exchanger 7 installed in parallel with the main line, and then merges at a three-way control valve 8. At this time, the temperature is adjusted by distributing the flow rates between the high temperature side and the low temperature side using the three-way control valve 8. The temperature of the battery stack inlet cooling water detected by 5 and 9 is the difference t- from the temperature set value 'ro.
This is calculated by the PI calculator 10B and used as an operation signal for the three-way control valve 8. The cooling water that has passed through the battery stack returns to the steam/water separator 1 again.

On the other hand, the heat exchanger 3 is installed in a line connecting a steam pipe attached to the upper part of the steam-water separator 1 to a cooling water pipe, and a flow rate control valve 4 is provided at the outlet of the heat exchanger.

Reference numeral 9 denotes a pressure detector, and the difference between the pressure inside the steam and water separator and the pressure setting value is calculated by a PI calculator 10A, and the result is used as an operation signal for the control valve 4. The operation of the device configured as described above will be explained as follows.

First, the cooling water at the inlet of the battery stack 2 is controlled by the control valve 8 to maintain it at a set temperature.

Furthermore, since the control valve 8 is a three-way valve and the flow rate is distributed between the high-temperature side and the low-temperature side, the total flow rate of cooling water to the circulation bonder 6 is constant, and there is no adverse effect on the pump such as cavitation. It is configured so that it can be avoided. On the other hand, regarding steam pressure control in the steam separator 1, PI control is performed by the heat exchanger 3 and the flow rate control valve 4 to maintain it at a set value.

Since the pressure response is fast, disturbances in the amount of heat generated within the battery stack first appear as vapor pressure and fluctuations. Therefore, suppressing this fluctuation also means performing cooling water temperature control in advance.

〔Effect of the invention〕

As explained above, according to the present invention, the temperature of the cooling water at the inlet of the battery stack is directly detected, and the influence of fluctuations in the amount of heat generated in the battery stack on the cooling water temperature can be quickly compensated for by controlling the steam pressure in the steam separator. Therefore, the control performance of battery operating temperature is further improved. Furthermore, since the steam pressure in the steam separator is controlled to a constant value, it is possible to facilitate the operation of the fuel reforming system.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of a battery cooling system control device for a fuel cell power generation system according to the present invention, and FIG. 2 is a schematic diagram of a conventional battery cooling system.

Claims (1)

[Claims] The thermal energy generated within the battery stack is cooled through cooling water and returned to the steam/water separator, and the steam in the steam/water separator is introduced into a heat exchanger to adjust the amount of liquefaction for recirculation. In the battery cooling system of the fuel cell power generation system, a second heat exchanger is installed in parallel to the cooling water line at the inlet of the battery stack, and the first heat exchanger for adjusting the amount of liquefaction is a steam separator. A battery cooling system control device for a fuel cell power generation system, characterized in that the second heat exchanger is controlled according to the temperature of cooling water at an inlet of the battery stack.