JPH08236132A - Fuel cell power generating system - Google Patents

Abstract

PURPOSE: To cool a reformed gas and an exhaust air so as to keep optimum temperature, working as safety protection when a heat exchanger for exhaust heat recovery using as a heat source of heating-cooling equipment stops and without being affected by heat load variation in an exhaust heat utilizing line in a fuel cell power generating system adopting cogeneration. CONSTITUTION: Heat exchangers 6, 10 for exhaust heat recovery for using as a heat source of exhaust heat utilizing equipment are installed in the front steps of a reformed gas cooling device 7 and an exhaust air cooling device 11 in a reformed gas supply line 3 and an exhaust air line 4. Bypass paths 6a, 10a for bypassing the whole amounts of reformed gas and exhaust air when the operation of the exhaust heat utilizing equipment is stopped and gas shut off valves 6b-6d, 10b-10d are arranged in the heat exchangers for exhaust heat recovery. Flow rate control valves 7a, 11a of cooling water and temperature controllers 7b, 11b are installed in the reformed gas cooling device and the exhaust air cooling device to cool the reformed gas and the exhaust air to a constant temperature, and to condense and separate steam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended to collect exhaust heat generated in a fuel cell power plant and use it for district cooling and heating.
The present invention relates to a fuel cell power generation system that employs a generation method.

[0002]

2. Description of the Related Art As is well known, in a fuel cell (phosphoric acid fuel cell) power generation system, a hydrogen-rich gas obtained by steam reforming a raw fuel such as natural gas and air are used as a reaction gas in the fuel cell. Power is generated by supplying it to the fuel electrode and air electrode. Further, in this case, excess steam introduced into the fuel reformer and steam generated on the air electrode side due to the electrode reaction in the fuel cell are condensed in the system of the power generation system to be separated into gas and liquid. The condensed water obtained in step 2 is used as cooling water for the fuel cell main body or steam again to be supplied to the reformer. In order to condense the reformed gas and water vapor contained in the exhaust air in the system, a reformed gas cooler,
In the current situation, exhaust gas coolers (heat exchangers) are used, and in many power plants, the exhaust heat of the coolers is directly discharged to the outside of the system via a cooling tower or the like.

On the other hand, recently, a co-generation system for recovering exhaust heat generated by power generation and utilizing it for cooling, heating, etc. to improve energy use efficiency has been developed and popularized, and even in a fuel cell power generation system. Attempts have been made to adopt the co-generation system in some areas. And specifically, the reformed gas supply line leading to the fuel electrode of the fuel cell, the reformed gas cooler inserted in the exhaust air line drawn from the air electrode, and the exhaust heat recovery heat in series with the exhaust air cooler. An exchanger is inserted and connected, and the exhaust heat recovered through the heat exchanger is used to operate a hot water-fired absorption type refrigerator or a hot water heater for cooling and heating.

In this case, the gas temperature of the reformed gas passing through the fuel reformer and the carbon monoxide shift converter is 150 to 160 ° C.,
The temperature of the exhaust air discharged from the fuel cell is about 190 ° C in the case of the phosphoric acid fuel cell (operating temperature is about 200 ° C). In either case, it is necessary to lower the temperature of the reformed gas and the exhaust air to about 80 ° C. in order to condense the steam contained in the reformed gas and the exhaust air in excess and separate the water vapor.

On the other hand, hot water of about 90 ° C. is required for operation of the hot water-fired absorption type refrigerator, which is a co-generation system device, and hot water of about 55 ° C. is required for operation of the hot water heater. Therefore, in the fuel cell power generation system adopting the above-mentioned co-generation system, the cooling of the high temperature reformed gas and the exhaust air is shared by the gas cooler and the heat exchanger for exhaust heat recovery connected in series therewith. The temperature of the gas is finally lowered to about 80 ° C. while the exhaust heat is recovered by the heat exchanger for recovery of exhaust heat to condense steam and separate water and water.

[0006]

By the way, as described above, the exhaust gas heat recovery heat exchanger is connected in series with the reformed gas cooler and the exhaust air cooler of the fuel cell power generation system to recover the exhaust heat. -The following problems occur in operation in the generation method. In other words, 1) During periods when the cooling and heating facilities are not used depending on the season such as spring and autumn, high temperature gas such as reformed gas and exhaust air may flow to the heat exchanger for exhaust heat recovery as the fuel cell power generation system operates. Regardless, the heat recovery heat exchanger remains stopped and the circulating water for heat recovery does not flow. For this reason, a large amount of scale (scale) is generated in the heat exchanger for exhaust heat recovery while stopped, deteriorating the heat exchange efficiency, or the heat exchanger is changed due to an increase in internal pressure due to boiling of cooling water. May cause troubles such as damage.

2) When the reformed gas obtained in the fuel reforming system is supplied to the fuel cell to generate electricity, the composition (hydrogen gas concentration) of the reformed gas must be kept as constant as possible. However, as described above, when the reformed gas flowing through the reformed gas supply line is cooled to the condensing temperature by using the reformed gas cooler and the exhaust heat recovery heat exchanger together, the use of the exhaust heat utilization destination, In other words, the temperature of the reformed gas supplied to the fuel cell also changes depending on whether the exhaust heat utilization device is the hot water-fired absorption refrigerating machine or the hot water heater described above, and further due to the heat load fluctuation of cooling and heating. . Moreover, when the reformed gas temperature changes, the steam partial pressure, that is, the steam molar partial pressure also changes with the saturation temperature, resulting in a change in the hydrogen concentration of the fuel gas supplied to the fuel cell.

In this case, the pressure of the reformed gas is 6.5 kg / cm.
² G, with reference to the temperature of 80 ° C., waste heat utilization facility (cold, heating equipment) 70 ° C. cooling temperature of the gas by the heat load change,
Assuming that the temperature has changed to 90 ° C, a trial calculation shows that the hydrogen amount in the reformed gas increases by 2.3% at 70 ° C, and the hydrogen amount decreases by 3.3% at 90 ° C. On the other hand, the phosphoric acid fuel cell is
Generally, the hydrogen utilization rate is in the range of 75-80%.
Therefore, the temperature of the reformed gas supplied to the fuel cell is 80 ° C.
When the gas temperature rises, the amount of hydrogen becomes insufficient and the power generation characteristics of the fuel cell deteriorates.On the contrary, when the cooling temperature becomes low, an excessive amount of hydrogen is needed for the fuel cell. When it is input, it causes problems such as a decrease in power generation efficiency.

3) On the other hand, since the exhaust air discharged from the air electrode of the fuel cell contains about 10% of unreacted oxygen, the exhaust air in the fuel cell power generation system is used as it is to improve the efficiency. Instead of releasing it inside, the water vapor contained in the exhaust air is condensed and separated to increase the oxygen concentration, and then supplied to the burner of the fuel reformer and used as combustion air. However, in this case, it is desirable to keep the oxygen concentration of the exhaust air as constant as possible in order to stabilize the burnability (fuel / oxygen ratio) of the burner.

In this respect, as in the case of the reformed gas described in 2) above, when the high temperature exhaust air is cooled to the condensing temperature by using the exhaust air cooler and the exhaust heat recovery heat exchanger in combination, When the cooling temperature of the exhaust air changes due to heat load fluctuations such as cooling and heating on the heat utilization side, the oxygen concentration in the exhaust air also changes. Here, when the exhaust air pressure is 5.5 kg / cm ² G and the temperature is 80 ° C. as a reference, the oxygen concentration in the exhaust air is calculated on the assumption that the exhaust air temperature changes to 70 ° C. and 90 ° C. At 70 ° C, the oxygen concentration increases by 0.3%, and at 90 ° C, the oxygen concentration decreases by 0.42%. Therefore, when the exhaust air is used as the combustion air of the burner of the fuel reformer, if the oxygen concentration of the exhaust air after steam separation changes due to fluctuations in the heat load on the heat recovery side, the amount of fuel / fuel oxygen in the burner will change. The ratio deviates from the initially planned value and the actual value, and especially when the oxygen concentration in the exhaust air decreases, the burner will be incompletely burned and the temperature inside the reformer furnace will fluctuate, and the reforming reaction efficiency will also be adversely affected. It will be covered.

The present invention has been made in view of the above points, and a fuel cell power generation system adopting co-generalization for recovering exhaust heat generated in the system of a power generation system and utilizing it for district cooling, heating, etc. In order to solve the problems described in 1) to 3) above, the safety protection when the heat exchanger for exhaust heat recovery used as a heat source for cooling and heating equipment is stopped, and the heat of the exhaust heat utilization system. It is an object of the present invention to provide a fuel cell power generation system capable of maintaining a stable cooling temperature of reformed gas and exhaust air without being affected by load fluctuations.

[0012]

In order to achieve the above object, according to the present invention, a fuel cell power generation system is constructed as follows. 1) In the reformed gas supply line to the fuel cell, which is provided with a reformed gas cooler for condensing excess steam in the reformed gas in combination with a steam separator, the reformed gas cooler is used. A heat exchanger with a cooling temperature control function, and a heat exchanger for exhaust heat recovery that serves as a heat source for exhaust heat utilization equipment such as cooling and heating in the preceding stage, and is modified when the exhaust heat recovery heat exchanger is not in use. A bypass passage is provided to allow the quality gas to bypass the heat exchanger and flow to the reformed gas cooler in the subsequent stage.

2) In the exhaust air line drawn from the fuel cell, which is provided with an exhaust air cooler for condensing excess water vapor in the exhaust air in combination with a steam separator, the exhaust air cooler is cooled. A heat exchanger with a temperature control function, and a heat exchanger for exhaust heat recovery, which serves as a heat source for waste heat utilization equipment such as cooling and heating, and exhaust air when the heat exchanger for exhaust heat recovery is not in use. A bypass path is provided for bypassing the heat exchanger and flowing to the exhaust air cooler in the subsequent stage.

3) In the above paragraphs 1) and 2), a gas flow path switching valve is provided between the heat exchanger for exhaust heat recovery and its bypass passage.

[0015]

In the above structure, when operating the exhaust heat utilization equipment (cooling, heating equipment), the valve of the bypass path is closed,
After passing the high-temperature reformed gas and exhaust air through the exhaust heat recovery heat exchanger to recover the exhaust heat, the cooling temperature is adjusted by the reformed gas cooler or exhaust air cooler on the subsequent stage. The temperature is lowered to the predetermined condensing temperature (80 ° C) by the reforming gas,
Excess water vapor contained in the exhaust air is separated into steam and water.
When the heat load of the exhaust heat utilization equipment fluctuates in this operating state, the refrigerant (cooling water) flowing to the cooler is changed based on the temperatures of the reformed gas and the exhaust air detected at the outlet end of the cooler on the subsequent stage. The condensing temperature of the reformed gas and exhaust air is kept almost constant by controlling the flow rate.

On the other hand, when the operation of the equipment for utilizing exhaust heat is stopped, the inlet and outlet valves of the heat exchanger for exhaust heat recovery are closed and the valve of the bypass passage is opened so that the high temperature reformed gas and exhaust air can be discharged. To bypass the exhaust heat recovery heat exchanger to directly flow to the reformed gas cooler and exhaust air cooling on the latter stage side, and control the refrigerant flow rate with these coolers to control the reformed gas and exhaust air to a predetermined level. Cool to condensation temperature.

Thus, heat recovery at a required temperature can be performed through the exhaust heat recovery heat exchanger without being influenced by the type of the exhaust heat utilization device, its utilization temperature, and the heat load fluctuation of the exhaust heat utilization device. While performing, the reformed gas and the exhaust air can be cooled to an appropriate temperature required in the process of the fuel cell by the cooling temperature control in the cooler on the latter stage side to separate the steam from the steam.

Further, by providing a bypass passage in the exhaust heat recovery heat exchanger and stopping the gas flow to the exhaust heat recovery heat exchanger to bypass the bypass passage when the exhaust heat utilization equipment is stopped, the scale ( Problems such as generation of water stains and damage due to boiling water in the heat exchanger can be prevented.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plant system diagram of a fuel cell power generation system, in which 1 is a fuel cell, 2 is a fuel reformer, and 3 is a fuel reformer.
Is the reformed gas steam-reformed by the fuel reformer 2 in the fuel cell 1
The reformed gas supply line 4 for supplying the fuel electrode 1a of the fuel cell 1a to the exhaust electrode 1b of the fuel cell 1
A heat exchanger 5, an exhaust heat recovery heat exchanger 6, a reformed gas cooler 7, and a steam separator 8 are sequentially connected to the reformed gas supply line 3 from the fuel reformer 2 side. In the exhaust air line 4, a heat exchanger 9, an exhaust heat recovery heat exchanger 10, an exhaust air cooler 11, and a steam separator 1 are arranged in this order from the fuel cell 1 side.
2 is connected. Although not shown, hot water-fired absorption type refrigerators, hot water heaters, etc. are connected to the secondary sides of the heat exchangers 6 and 10 for recovering exhaust heat as waste heat utilization equipment.

In such a fuel cell power generation system, as is well known, after the raw fuel (natural gas) is steam-reformed by the fuel reformer 2, the reformed gas supply line 3 is used to further reform the high-temperature fuel containing excess steam. After the quality gas is cooled and separated into water and water, it is supplied to the fuel electrode 1a of the fuel cell 1 and the electrode reaction with the air supplied to the air electrode 1b through the blower 13 generates electricity. The off gas emitted from the fuel electrode 1a of the fuel cell 1 is supplied to the burner 2a of the fuel reformer 2 as fuel.
On the other hand, the high-temperature exhaust air discharged from the air electrode 1b is cooled in the exhaust air line 4 and separated into water and steam, and then supplied to the burner 2a of the fuel reformer 2 as combustion air. Furthermore, the heat recovered on the secondary side of the heat exchangers 6 and 10 for recovering exhaust heat is supplied to the exhaust heat utilization equipment (cooling and heating equipment) for exhaust heat utilization.

On the other hand, the heat exchangers 6 and 10 for exhaust heat recovery
In contrast, according to the present invention, the bypass passages 6a and 10a bypassing the heat exchanger are connected in parallel, and the bypass passages 6a and 10a and the exhaust heat recovery heat exchangers 6 and 10 have inlets and outlets. Gas shutoff valve 6 on each side
b, 6c, 6d and 10b, 10c, 10d are provided. Further, the reformed gas cooler 7 and the exhaust air cooler 11 are provided with flow rate control valves 7a and 11a in the cooling water (refrigerant) supply line on the secondary side, and the gas temperature is connected to the outlet side of the cooler. The flow rate of the cooling water is controlled based on the signals from the regulators 7b and 11b so that the temperatures of the gas reforming gas and the exhaust air supplied to the steam separators 8 and 12 are maintained at a predetermined temperature (about 80 ° C.). To control the temperature. In addition to the illustrated example, the cooler 7,
There is also a method in which a bypass passage is provided on the primary side of 11 and the reforming gas and exhaust air are controlled to a predetermined temperature by adjusting the flow rate of the gas flowing through the bypass passage while keeping the cooling water amount constant.

When the exhaust heat utilization equipment is operated to recover the exhaust heat, the gas cutoff valve 6b connected to the bypass passages 6a, 10a of the exhaust heat recovery heat exchangers 6, 10 described above,
After 10b is closed and high-temperature reformed gas and exhaust air are passed through the heat exchangers 6 and 10 for exhaust heat recovery to recover heat, the reformed gas cooler 7 and the exhaust air cooler 11 in the latter stage are used. It is cooled to a predetermined temperature (80 ° C.) by controlling the cooling temperature to condense excess steam, and further steam-water separators 8 and 12 separate the steam. Even if a heat load fluctuation occurs on the side of the exhaust heat utilization equipment, the flow rate of the cooling water of the reformed gas cooler 7 and the exhaust air cooler 11 is controlled accordingly to control the reformed gas and the exhaust air. Keep the condensing temperature constant.

On the other hand, the operation of the waste heat utilization equipment is stopped (in spring,
When the cooling and heating operations are stopped in the season such as autumn, the gas cutoff valves 6c, 6d, 10c, 10d on the inlet and outlet sides of the exhaust heat recovery heat exchangers 6, 10 are closed and the bypass line 6a is closed. , 10a to open the gas shutoff valves 6b and 10b to allow the entire amount of the reformed gas and exhaust air to flow to the reformed gas cooler 7 and the exhaust air cooler 11 on the subsequent stage via the bypass paths 6a and 10a. Here, temperature control is performed to cool to a predetermined gas temperature.

In the illustrated embodiment, the reformed gas supply line 3 and the exhaust air line 4 have exhaust heat recovery heat exchangers 6, 6.
Although 10 is installed and exhaust heat is recovered at two places, it is also possible to recover exhaust heat only at either one.

[0025]

As described above, according to the present invention, the reformed gas cooler and the exhaust gas are recovered so that the exhaust heat is recovered from the reformed gas supply line and the exhaust air line in the plant system of the fuel cell power generation system. In an air cooler with an exhaust heat recovery heat exchanger, the exhaust heat recovery heat exchanger is installed in front of the reformed gas cooler and exhaust air cooler, and then the exhaust heat recovery heat exchanger is installed. By providing a bypass passage bypassing the air conditioner and a gas flow path switching valve, the reformed gas cooler and the exhaust air cooler on the rear stage side are configured to have a cooling temperature adjusting function. Play.

1) When stopping the operation of the exhaust heat utilization equipment such as an air conditioner and a heater using the exhaust heat recovery heat exchanger as a heat source,
The entire amount of high-temperature reformed gas and exhaust air bypasses the heat exchanger for exhaust heat recovery and flows through the bypass passage, so that the heat exchanger for exhaust heat recovery that is stopped is scale (scale) and heat exchange. Can be safely protected from damage due to boiling water in the vessel. 2) The reformed gas cooler in the subsequent stage, without being influenced by the type of exhaust heat utilization equipment that uses the heat exchanger for exhaust heat recovery as a heat source, the operating temperature, and the heat load fluctuations on the exhaust heat utilization equipment side, By controlling the cooling temperature in the exhaust air cooler, the gas temperature on the outlet side can be lowered to an appropriate predetermined temperature to condense and separate the reformed gas and steam excessively contained in the exhaust air.

In the reformed gas supply system, by keeping the temperature of the reformed gas supplied to the fuel cell constant, it is possible to suppress the fluctuation of the hydrogen concentration of the reformed gas due to the change of the gas temperature. As a result, it is possible to operate the fuel cell stably with high power generation efficiency while avoiding deterioration of fuel cell characteristics due to lack of hydrogen and avoiding excessive hydrogen injection. Even when the exhaust air is separated into steam and used as combustion air by supplying it to the burner of the fuel reformer, the cooling temperature of the exhaust air is kept constant to suppress the fluctuation of oxygen concentration in the exhaust air. Fuel at
It is possible to obtain an effect that a stable oxygen content ratio can be secured.

[Brief description of drawings]

FIG. 1 is a plant system diagram of a fuel cell power generation system according to an embodiment of the present invention.

[Explanation of symbols]

 1 Fuel Cell 2 Fuel Reformer 2a Burner 3 Reformed Gas Supply Line 4 Exhaust Air Line 6 Exhaust Heat Recovery Heat Exchanger 6a Bypass Path 6b, 6c, 6d Gas Cutoff Valve 7 Reformed Gas Cooler 8, 12 Steam Separator 10 Heat exchanger for exhaust heat recovery 10a Bypass passages 10b, 10c, 10d Gas cutoff valve 11 Exhaust air cooler

Claims (3)

[Claims] 1. A fuel cell power generation system for generating electric power by supplying hydrogen-rich reformed gas reformed through a fuel reforming device and air to a fuel electrode and an air electrode of a fuel cell. In a reformed gas supply line equipped with a reformed gas cooler for condensing excess steam in the reformed gas in combination with a steam separator, the reformed gas cooler is equipped with a cooling temperature control function. A heat exchanger for an exhaust heat recovery, which serves as a heat exchanger and a heat source for exhaust heat utilization equipment such as cooling and heating, and a reformed gas when the exhaust heat recovery heat exchanger is not in use A fuel cell power generation system, characterized in that a bypass path is provided for bypassing the gas and flowing to the reformed gas cooler in the subsequent stage. 2. A fuel cell power generation system for supplying power to a fuel electrode and an air electrode of a fuel cell by supplying hydrogen-rich reformed gas reformed through a fuel reforming device and air, which is drawn from the fuel cell. In the exhaust air line equipped with an exhaust air cooler for condensing excess water vapor in the exhaust air in combination with a steam separator, the exhaust air cooler is a heat exchanger with a cooling temperature control function, In addition, a heat exchanger for exhaust heat recovery, which is a heat source for exhaust heat utilization equipment such as cooling and heating, and exhaust air bypasses the heat exchanger when the heat exchanger for exhaust heat recovery is not in use The fuel cell power generation system is characterized in that a bypass passage is provided to allow the exhaust air cooler to flow. 3. The fuel cell power generation system according to claim 1 or 2, wherein a gas flow path switching valve is provided between the exhaust heat recovery heat exchanger and the bypass path thereof. Battery power generation system.