KR100405142B1 - Electric power system for Fuel Cell generation - Google Patents

Abstract

The present invention increases the fuel utilization of the entire stack by linking the molten carbonate fuel cell stack and the solid oxide fuel cell stack, which are high-temperature fuel cells, and using the load inverter / power controller commonly connected to each stack. It relates to a fuel cell power generation system that increases the efficiency of the.

According to the present invention, the anode / air cathode heater 106 is connected between the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107, and the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack ( A load inverter / power controller 108 is provided to adjust the load of 107 and the power of the anode / air cathode heater 106 to supply unreacted gas and air from the molten carbonate fuel cell stack 105 to the solid oxide fuel. While used as a feed fuel for the cell stack 107, the amount of air or waste heat source discharged from the solid oxide fuel field stack 107 is configured to be regulated through recirculation control means, thereby reducing additional supply heat and increasing fuel utilization. By increasing the efficiency of the entire fuel cell power generation system, and also when the fuel cell system is commercialized, the operation of the stack can increase the efficiency of the stack. The use of can solve the utilization changes associated fuel cell system can significantly reduce the environmental pollution.

Description

Fuel cell power generation system {Electric power system for Fuel Cell generation}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell power generation system, and in particular, a molten carbonate fuel cell stack, which is a high-temperature fuel cell, and a stack of a solid oxide fuel cell are linked to each other to form a fuel utilization rate of the entire stack. And increase the efficiency of the entire fuel cell power generation system by using a load inverter / power controller commonly connected to each stack.

In general, molten carbonate fuel cell power generation system can use various fuels such as natural gas and coal gas, and produce electricity by electrochemical reaction where fuel is directly converted into electricity at high temperature of 650 ℃ without combustion process. In the case of using a variety of fuels such as natural gas, coal gas, methanol and at a high temperature of 1000 ℃ it is possible to combine the power generation using high temperature and high pressure steam generated in the rear of the fuel cell. In addition, since there is no combustion process and direct generation from fuel to electricity, noise and air pollutant emissions are low, and it is attracting attention as a next generation power generation method.

In the conventional fuel cell power generation system, a fuel and air utilization rate is determined by a predetermined load in a fuel cell stack, and a system is constructed around a method of efficiently treating the remaining exhaust gas without reacting.

The molten carbonate fuel cell system is a high-temperature fuel cell power generation method. The performance varies depending on temperature, but the heat source of the feed fuel is heated to 580 ° C, and the solid oxide fuel cell system is heated to 900 ° C. Therefore, the overall efficiency of the high-temperature fuel cell power generation system is changed according to the temperature raising and arrangement method of the fuel in the system, and the conventional fuel cell linkage method increases the overall utilization rate by multi-stage fuel use by connecting the same type of fuel cells in series. Unreacted fuel in the fuel cell stack was recovered using a combustor to recover fuel and heat.

Molten carbonate fuel cells are used as sources of carbon dioxide in cathodes, and hot steam is used as fuel sources, reformers or heat recovery (HRSG) systems for anodes using combustion reaction heat. In addition, in the solid oxide fuel cell system, a high temperature exhaust gas of more than 1000 ° C. can be configured in conjunction with a gas turbine and a steam turbine, but there are problems such as emission of environmental pollutants and noise.

On the other hand, the prior patent (US6033794) uses a molten carbonate fuel cell and a solid oxide fuel cell composed of a flat plate by installing a fuel cell stack up to 400 ~ 1000 ℃ in one unit device, the prior patent (US5712055, US5518828, US5413878) , US4080487, JP4188567, employ a method of cooling the hot gas after the reaction before moving to the next stage through a series connection to the same type of fuel cell system.

In addition, in the preceding patent (JP60227363), the phosphate fuel cell stack and the molten carbonate fuel cell stack are configured in connection with the cathode, but the cathode line must be separated because carbon dioxide is not supplied to the cathode of the phosphate fuel cell and the high temperature fuel cell (MCFC) It is not possible to move to a low temperature fuel cell (PAFC), and another prior patent (US6033794) has been proposed to use a Ni alloy in order to operate the separator plate of the molten carbonate fuel cell by connecting the various fuel cells directly adjacent to each other, but economically It can be seen as a costly power generation system.

Prior patent (US5541014) is used with a gas turbine in conjunction with a molten carbonate fuel cell and a solid oxide fuel cell, but generates environmental pollutants due to the high temperature combustor, and the pressure condition of the solid oxide fuel cell stack and the molten carbonate fuel cell stack I'm driving differently. This is because, unlike a solid oxide fuel cell, in the case of a molten carbonate fuel cell, the electrolyte may exist in a molten state under operating conditions, and crossover may be generated in the stack when pressurized.

As described above, in the conventional fuel cell power generation system, the molten carbonate fuel cell and the solid oxide fuel cell stack are not directly connected, and the operating temperature range is 650 ° C and 1000 ° C, resulting in a large temperature difference and 350 ° C. to be.

In addition, the solid oxide fuel cell system has a high temperature exhaust gas of more than 1000 ℃ can be configured in conjunction with the gas turbine and steam turbine, but there are problems such as the emission of environmental pollutants and noise.

The present invention has been made to solve the problems described above, by directly connecting the molten carbonate fuel cell stack and the solid oxide fuel cell stack which is a high-temperature fuel cell power generation system to reduce the supply heat source used for fuel supply, The purpose is to provide a fuel cell power generation system that can increase the efficiency of the entire fuel cell power generation system by consistently adjusting the gas conditions of additional power generation used at the rear stage by varying the load on the stack by installing a load inverter / power controller in each stack. There is this.

In addition, by lowering fuel utilization during operation of the molten carbonate fuel cell stack, the differential pressure between the anode and the cathode is maintained within a certain range by increasing the anode supply gas as well as the cooling effect of the stack by the anode supply gas. To provide a fuel cell power generation system that can control fuel utilization, stack exit temperature, and output of intermediate heater to cope with the change of fuel utilization according to the initial operation and load fluctuation of fuel cell power generation system by connecting / power controller. In order to achieve the above object, the present invention relates to a gas compressor for compressing natural gas, a reformer for converting natural gas and steam through heat exchanger into hydrogen and carbon gas, and a fuel produced from the reformer. A pair of molten carbonates or a pair of solid oxide fuel cells that receive gas and generate electricity A fuel cell power generation system comprising a stack, a catalytic combustor for reburning unreacted gas after an electrochemical reaction in the fuel cell stack, and a compressor for supplying compressed air to the catalytic combustor, wherein the molten carbonate fuel cell stack and the solid A cathode / air heater is connected between an oxide fuel cell stack, and a load inverter / power controller is provided to adjust the load of the molten carbonate fuel cell stack and the solid oxide fuel cell stack and the power of the anode / air heater. The unreacted gas and air in the carbonate fuel cell stack are used as a feed fuel for the solid oxide fuel cell stack, and the amount of air or waste heat source discharged from the solid oxide fuel cell stack is controlled through a recycling control means. .

1 is an overall schematic diagram of a fuel cell power generation system.

FIG. 2 is a detailed view of the linkage stack and load controller of FIG.

3 is a graph comparing efficiency with capacity of a fuel cell power generation system.

Description of the main parts of the drawing

100: gas compressor

101, 102, 103: heat exchanger

104: reformer 105: molten carbonate fuel cell stack

106: anode / air cathode heater 107: solid oxide fuel cell stack 108: load inverter / power controller 109: catalytic burner 110: high temperature blower 111: compressor 112: air control valve 113: heat exchange valve

114 heat exchanger 115 turbine 36, 37, 38, 39 current line 35 heater power supply line

15, 16, 17: anode supply line 23, 24, 25: cathode supply line

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present invention, the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107 are configured in conjunction with the power generation system controlled by the load inverter / power controller 108 as shown in FIG. 1. At this time, both the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107 may be separately connected to the anode and the cathode.

The configuration includes gas compressor 100, heat exchanger 101, 102, 103, 114, reformer 104, molten carbonate fuel cell stack 105, anode / air cathode heater 106, solid oxide fuel cell stack 107 , A load inverter / power controller 108, a high temperature blower 110, a compressor 111, a recirculation control means, a turbine 115, and the like.

The gas compressor 100 serves to raise the pressure of the gas to be supplied. The heat exchanger (101, 102, 103, 114) is composed of a plurality of tubes to exchange heat between hot and cold water well. The reformer (104) is reformed (natural gas) by reforming the natural gas and hydrogen It is made of carbon dioxide. The anode / air heater 106 controls the outlet temperature and power output of the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107 during initial operation and load variation. 110 is a device that is installed to reuse the cathode gas, is a device used at high temperatures and smaller inlet and outlet pressure difference than the compressor. The compressor 111 is used to increase the pressure of the gas, the turbine 115 is a high-temperature, high-pressure gas to the turbine It works by turning and venting out with low-temperature, low-pressure gas. The recirculation control means is composed of an air control valve 112 for adjusting the amount of air to be recycled at the outlet of the solid oxide fuel cell stack 107 and a heat exchange valve 113 for adjusting the amount of waste heat source to be recycled.

Referring to FIGS. 1 and 2, the operation of the power generation system in which the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107 are described as follows.

When the natural gas 11 is transmitted, it is compressed in the gas compressor 100 and sequentially combined with the steam 33 through the heat exchanger 103 through the heat exchangers 101 and 102 so that hydrogen and carbon gas are the main components of the reformer 104. To phosphorus feed gas. Thereafter, the fuel gas 15 is supplied to the molten carbonate fuel cell stack 105 and then supplied to the solid oxide fuel cell stack 107 through the anode / air cathode heater 106 after the electrochemical reaction takes place. The unreacted gas 18 reacted in the oxide fuel cell stack 107 is supplied to the catalytic combustor 109 through the heat exchanger 114, and the external air 19 is supplied to the compressor 111 and the heat exchanger 114. ) Is combined with the unreacted gas (18) in the catalytic combustion (109) and fed back to the molten carbonate fuel cell stack (105) through the high temperature blower (110). The air discharged from the solid oxide fuel cell stack 107 is recycled while passing through the heat control valve 113, the catalytic combustion 109, and the high temperature blower 110 by controlling the amount of the air from the air control valve 112. The waste heat source discharged from the solid oxide fuel cell stack 107 is adjusted in the heat exchange valve 113 to enter the heat exchanger 102, 103, and 101 to heat the water. Here, through the load inverter / power controller 108. The temperature and pressure of the outlet gas of the solid oxide fuel cell stack 107 are controlled by using the air control valve 112 and the heat exchange valve 113.

The electricity produced in the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107 is supplied to the load inverter / power controller 108 via a current line 36 (SOFC, 37: MCFC). Through the adjustment of the amount of power 35 that controls the power of the load and the heater in the load inverter / power controller 108, the control of the anode / air heater 106 is performed at the time of initial operation and at the load change.

FIG. 2 is a detailed diagram of a linkage configuration of a molten carbonate fuel cell stack 105 and a solid oxide fuel cell stack 107 and a load inverter / power controller in FIG. 1. ) And a line 35 for supplying power to the anode / air cathode heater 106 according to the initial operation and load variation based on the power produced by the control of the load inverter / power controller.

Table 1 shows the configuration and operation characteristics of each fuel cell.

type condition ion Operating temperature (℃) fuel apply Alkali Liquid OH ^- <120 H ₂ spaceship Solid polymer solid H ⁺ <120 H ₂ car Phosphate Liquid H ⁺ 150-220 H ₂ Combined cycle Molten carbonate Liquid CO ₃ ^2- 600-700 H ₂ CO Combined cycle Solid oxide solid O ^2- 1000 H ₂ CO Combined cycle

As shown in Table 1, the operating temperatures of the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107 among the fuel cells usable in the power generation system show a difference of about 300 ° C.

Due to the high operating temperature of the solid oxide fuel cell stack 107, it is difficult to manufacture the sealant and the high temperature separation plate, and the development of the manufacturing technology of the electrolyte (Ce and Bi) and the thin film fuel cell enables the medium temperature solid oxide fuel cell. As a result, the solid oxide fuel cell having a support structure in which the thickness of the electrolyte is adjusted to 30 μm or less can be lowered to 800 ° C.

Accordingly, the outlet temperature of the molten carbonate fuel cell stack 105 may be directly linked to the inlet temperature of the solid oxide fuel cell stack 107, that is, the electricity generated by the exothermic reaction by the direct linkage of fuel cell stacks having different operating temperatures. By a chemical reaction, the exhaust gas (about 700 ° C.) after the molten carbonate fuel cell stack 105 may be directly used as a supply gas of the solid oxide fuel cell stack 107.

In addition, in the case of the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107, natural gas, methanol, hydrogen, and the like may be directly used, and coal gasification gas may be directly used.

Table 2 shows the efficiency of the entire power generation system according to the combined configuration of the molten carbon fuel cell stack 105 and the solid oxide fuel cell stack 107 based on 125 MW.

Item Case 1 Case 2 Case 3 Absorbed Power (MW) ① 225.6 259.4 206.4 Delivered gross power (MW) ② 149.4 173.2 154.6 Aux. power consumption (MW) ③ 23.9 20.7 27.4 Delivered net power (MW) (②-③) 125.4 152.5 127.3 Gross Efficiency (%) (② / ①) × 100 66.2 66.7 74.9 Net Efficiency (%) ((②-③) / ①) × 100 55.6 58.8 61.7

In general, the efficiency is how much electricity is produced compared to the fuel supplied, which is called the gross efficiency, and the power supplied is the power when the fuel supplied is converted to work. Absorbed power gives an indication of the power of the heat of natural gas supplied.

Case 1 consists of a molten carbonate fuel cell stack 105 in two stages, Case 2 consists of a solid oxide fuel cell stack 107 in two stages, and Case 3 is a molten carbonate fuel cell stack 105 and a solid oxide. The fuel cell stack 107 is configured in two stages.

Natural gas is supplied to all three systems at 5 Kg / s, the fuel utilization of the first stack is 40% and the fuel utilization of the second stack is 80%, which is 80% utilization of each stack alone. .

A fuel utilization rate of 80% means that 20% of the fuel supplied has not reacted. Therefore, it is possible to cool the anode with the unreacted fuel by operating the molten carbonate fuel cell stack 105 at a low fuel utilization rate. During operation of the power generation system, the amount of fuel is lower than the amount of air, so the pressure is low. It is possible to reduce the pressure difference between the cathode and the anode.

As shown in Table 2, Case 3, in which the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107 are directly connected, shows the highest efficiency. The amount of electricity generated is relatively smaller than that of Case 2, while Case 2 has the largest amount of electricity produced (152.5MW), but it is operated at high temperature, so the amount of power required for preheating (259.4MW) is high, resulting in an overall efficiency of 58.8%.

The reason why the efficiency of case 3 is high is that the exhaust gas of the molten carbonate fuel cell stack 105 is transferred to the solid oxide fuel cell stack 107 by a power generation system in which the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107 are connected. This is because the amount of power required for fuel supply is the smallest using exhaust gas as it is, and at the same time, there is additional generation amount such as a turbine by the exhaust gas of the solid oxide fuel cell stack 107.

3 is a graph comparing efficiency according to the capacity of a fuel cell power generation system. As the capacity increases, the efficiency of the entire power generation system is increased due to the increase in power and heat in the fuel cell stack, and the molten carbonate fuel cell connection stick (MC-MCFC). The efficiency of the solid oxide fuel cell stack (SO-SOFC) is higher than that due to the additional power generation, such as turbines, under high temperature stack exit gas conditions.

In the present invention, when the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107 are configured in a power generation system, the loads of two fuel cell stacks are controlled by one load inverter / power controller 108. The gas temperature and pressure conditions of the second stack behind the solid oxide fuel cell stack 107 may be changed according to the load change, and the temperature and pressure of the stack may be controlled during the initial operation of the stack and the load variation.

Load change Power (kW) (MCFC | SOFC) Outlet temperature (℃) Gross Efficiency (Net) 50 mA / ㎠ 145.56 985.4 71.7 55.8 37.48 | 108.08 75 mA / ㎠ 148.62 963.6 72.8 56.6 44.05 | 104.81 100 mA / ㎠ 150.85 947.7 73.8 58.3 52.86 | 97.99 125 mA / ㎠ 152.78 931.3 74.8 60.0 61.67 | 91.10 150 mA / ㎠ 154.62 914.3 75.9 61.7 70.48 | 84.14

Table 3 is calculated based on the 100kW fuel cell power generation system and supplied 0.005kg / s of natural gas. The load variation given in Table 3 is the load variation applied to the first molten carbonate fuel cell stack 105 of the two fuel cell stacks and is calculated based on 80% utilization depending on the fuel supplied to the solid oxide fuel cell stack 107. .

As shown in Table 3, the temperature of the rear end of the solid oxide fuel cell stack 107, which is the rear end of the associated stack, can be adjusted according to the load change, that is, the outlet temperature decreases as the load increases. In case of using such a stack, it is possible to control the temperature of the stack outlet and the output of the heater according to the load variation, and to set the operating conditions for optimal system efficiency.

In addition, the two fuel cell systems maintain a higher pressure of the cathode than the anode by using air instead of oxygen as a reducing agent in the cathode in addition to the common anode gas, and lower the utilization rate of the molten carbonate fuel cell stack 105. There is an effect that can protect the electrolyte in the melting point state by increasing the relative differential pressure of.

On the other hand, the unreacted fuel and air from the molten carbonate fuel cell stack 105 is supplied to the solid oxide fuel cell stack 107 to transfer the heat of electrochemical reaction generated from the molten carbonate fuel cell stack 105 to the solid oxide fuel cell stack ( By using it as a fuel supply heat source in 107, higher efficiency is achieved than a two-stage stack consisting of each fuel cell.

The associated two-stage stack is not only high fuel utilization due to two-stage oxidation of the fuel, but also an excessive amount of fuel is supplied to the molten carbonate fuel cell stack 105 to increase the pressure of the anode in the stack, thereby protecting the gap between the stack and the anode gas. There is a cooling effect, and the temperature and pressure of the stack outlet gas can be controlled using the air control valve 112 and the heat exchange valve 113 which control the air amount and the waste heat source through the load inverter / power controller 108 in common. To regulate the temperature and pressure of the gas so that it is suitable for additional power generation.

The load inverter / power controller 108 selects and adjusts an appropriate load amount for the molten carbonate fuel cell stack 105 and the solid compound fuel cell stack 107 even during initial operation and load variation, so as to maximize the fuel utilization rate at the maximum output of the associated stack, It does not have any operating conditions SO _X, NO _X, such as environmental pollution arising from the development of the combustion process, high efficiency, optimum operating conditions for the entire fuel cell power generation system in such fuel usage required for degraded stack protection, environmentally friendly It's a way of development.

As described above, the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107 are connected in series to form a power generation system, and one load inverter / power controller having a common temperature and pressure condition of the associated power generation system is used. A fuel cell stack (108) is used to control the anode / air cathode heater (106) to form a tail gas composition of the solid oxide fuel cell stack (107), and an associated stack configuration to increase the efficiency of the power generation system and to melt molten carbonate fuel cell stack under high pressure conditions. Excessive fuel is supplied to the anode of 105 to achieve differential pressure protection and cooling of the stack using fuel gas.

In addition, embodiments according to the present invention is not limited to the above, and those skilled in the art will be able to carry out various modifications and changes to the present invention within the obvious scope, such modifications, And changes are intended to fall within the technical scope of the present invention.

As described above, the present invention constitutes a power generation system in which a molten carbonate fuel cell and a solid oxide fuel cell are connected to each other, thereby reducing additional supply calories and increasing fuel utilization to increase the efficiency of the entire fuel cell power generation system. When produced, the produced coal gas produces electricity through the stack for linkage, and the high temperature and high pressure flue gas may generate additional power through a gas turbine and a heat recovery system.

In addition, when the fuel cell power generation system is commercialized, it is possible to solve the change in the utilization rate of the stack due to the initial start-up and the load variation in the operation method of the stack, and to reduce the environmental pollution by using the linked fuel cell power generation system. .

Claims (4)

A reformer 104 compressed by the gas compressor 100 and passing through the heat exchangers 101, 102, 103 to form hydrogen and carbon gas into natural gas joined with the steam 23, and the fuel gas 15 generated by the reformer 104. Molten carbonate fuel cell stack 105, a solid oxide fuel cell stack 107, which generate electricity through an electrochemical reaction, and an unreacted gas after the electrochemical reaction of the solid oxide fuel cell stack 107. In the fuel cell power generation system including a catalytic combustion unit 109 for receiving and re-burning) and a compressor 111 for supplying compressed air to the catalytic combustion unit 109, A fuel electrode / air electrode for supplying an electrochemical reaction gas from the molten carbonate fuel cell stack 105 to the solid oxide fuel cell stack 107 between the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107. The heater 106 is connected to the anode / air heater 106 to control the load of the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107 and the power of the anode / air cathode heater 106. An inverter / power controller 108 is connected to use unreacted gas and air of the molten carbonate fuel cell stack 105 as a feed fuel for the solid oxide fuel cell stack 107, while the solid oxide fuel display A fuel cell power generation system, characterized in that the amount of air discharged from the stack 107 or the waste heat source is controlled by recirculation control means to control the temperature and pressure of the gas at the stack outlet. The method of claim 1, wherein the load inverter / power controller 108, By controlling the electric power supplied to the anode / air electrode heater 106, controlling the outlet temperature and the power production amount of the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107 in accordance with the change of load amount A fuel cell power generation system characterized by the above. According to claim 1, wherein the recirculation control means, It consists of an air control valve 112 for regulating the amount of air to be recycled at the outlet of the solid oxide fuel cell stack 107 through the load inverter / power controller 108 and a heat exchange valve 113 for regulating the waste heat source to be recycled. A fuel cell power generation system characterized by the above. The method of claim 1, When cooling is required by a long time operation, the fuel cell power generation system, characterized in that to reduce the differential pressure between the poles by supplying an excessive amount of fuel to the molten carbonate fuel cell stack 105 to increase the pressure of the anode.