KR20020031686A - Apparatus and method of efficiency improvement for Fuel Cell generation of electric power sysytem - Google Patents

Abstract

PURPOSE: Provided are a device and a method for enhancing an efficiency of electric generating system in fuel cell. CONSTITUTION: The device comprises stack of fused carbonate fuel cell(105); stack of solid oxide fuel cell(107); inverter and load controller(108) for regulating electric power supplied to the fused carbonate fuel cell(105) and stack of solid oxide fuel cell(107); and hydraulic control valve(112,113) for controlling a hydraulic pressure. The method comprises cooling the stacks with gas supplied to anode and reducing a differential pressure of the anode and cathode.

Description

Apparatus and method of efficiency improvement for Fuel Cell generation of electric power sysytem}

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. The present invention relates to an apparatus and a method for improving the efficiency of a fuel cell power generation system using a inverter and a load controller connected to each stack and increasing the efficiency of the entire fuel cell power generation system.

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, an electrolyte is present in a molten state under operating conditions, so that a crossover may be generated in the stack during pressurization.

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 of this is to increase the efficiency of the entire fuel cell power generation system by installing an inverter and a load device in each stack to change the load on the stack to uniformly adjust the gas conditions of additional power generation used in the rear stage of the stack.

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 predetermined range due to the increase in the anode supply gas as well as the cooling effect of the stack by the anode supply gas. The purpose is to adjust the fuel utilization, stack outlet temperature, and output of the intermediate heater to correspond to the change in fuel utilization due to the initial operation of the fuel cell power generation system and the load variation by connecting a load unit.

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, 114: heat exchanger

104: reformer 105: molten carbonate fuel cell (MCFC)

106: anode and cathode heater

107: solid oxide fuel cell (SOFC) 108: inverter and load controller

109: catalytic combustion 110: high temperature blower

111: compressor and expander 112, 113: flow control valve

36, 37, 38, 39: current line 35: heater power supply line

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

A feature of the present invention for achieving the above object is, in a fuel cell power generation system, a molten carbonate fuel cell stack, a solid oxide fuel cell stack, a molten carbonate fuel cell stack and a solid oxide fuel cell stack operating at high temperature. Inverter and load controller to adjust the power, and includes a hydraulic control valve for adjusting the hydraulic pressure.

In addition, the inverter and the load controller controls the power supplied to the anode and the cathode heater to control the outlet temperature and power output of the molten carbonate fuel cell stack and the solid oxide fuel cell stack, and the hydraulic control valve of the cathode It consists of a valve for adjusting the hydraulic pressure and the valve for adjusting the hydraulic pressure of the fuel electrode, characterized in that for controlling the flow rate circulating.

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

The configuration is gas compressor 100, heat exchanger 101, 102, 103, 114, reformer 104, molten carbonate fuel cell 105, anode and cathode heater 106, solid oxide fuel cell 107, inverter And a load controller 108, a high temperature blower 110, a compressor and an expander 111, flow control valves 112 and 113, and the like.

Gas compressor 100 serves to increase the pressure of the supplied gas, heat exchanger (heat exchanger) (101, 102, 103, 104) is composed of a plurality of tubes so that the heat exchange between the hot fluid and cold fluid is hot Fluid cools cold fluids.

The reformer 104 functions to reform natural gas into hydrogen and carbon dioxide gas, and the high temperature blower 110 is installed to reuse the cathode gas and is used at a high temperature and has a smaller inlet / outlet pressure difference than the compressor. Compressor and expander 111 is a compressor is used to increase the pressure of the gas, the expander is a turbine is installed is a high-temperature and high-pressure gas to rotate the turbine to work and discharge to the low-temperature low-pressure gas. The flow regulating valves 112 and 113 are controlled by air pressure and regulate the flow rate at the pressure and temperature determined by the measurement.

On the other hand, the operation of the power generation system in conjunction with the molten carbonate fuel cell 105 stack and the solid oxide fuel cell stack 107 is described as follows.

When the natural gas 11 is transmitted, the gas is compressed in the gas compressor 100, and when the pressure is increased, the fuel gas 15 supplied through the reformer 104 after joining the steam 33 through the heat exchanger 101 is After being supplied to the molten carbonate fuel cell anode stack 105 and an electrochemical reaction occurs, the molten carbonate fuel cell anode stack 105 is supplied to the solid oxide fuel cell anode stack 107 via the anode and cathode heater 106.

After the reaction in the solid oxide fuel cell anode stack 107, the unreacted gas 18 is supplied from the outside through the heat exchanger 114 to heat the air 19 transferred to the compressor and the expander 111, and then again to the cathode. The catalyst is supplied to the catalytic combustor 109 along with the recycle 27 line and then catalytically burned, and then supplied to the cathode 23 of the molten carbonate fuel cell stack 105 through the high temperature blower 110, and the reacted air is a solid oxide fuel. The battery 25 is supplied to the cathode stack 107 and is discharged through the turbine 111 or supplied to the catalytic combustor 109 via the heat exchanger 114.

The electricity produced from the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107 is supplied to the inverter and the load controller 108 via a current line 36 (SOFC, 37: MCFC), and during initial operation and load. The adjustment of the anode and the cathode heater 106 at the time of change is made through the adjustment 35 of the amount of power controlling the power of the load and the heater in the inverter and the load controller 108. The circulation amount of the cathode flow rate is controlled through the flow rate control valve 112 and the heating source of the anode feed fuel is controlled through the flow rate control valve 113.

On the other hand, the anode and cathode heater 106 is an inverter and load changer 108 to adjust the outlet temperature and power output of the molten carbonate fuel cell stack 105 and the solid oxide fuel cell stack 107 stack during the initial operation and load fluctuations. It works by).

FIG. 2 is a detailed diagram of an integrated structure of the molten carbonate fuel cell 105 stack and the solid oxide fuel cell stack 107 and an inverter and a load controller in FIG. 1. ) And a line 35 for supplying power to the anode and the cathode heater according to the initial operation and the load change based on the power produced by the inverter and the load 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 105 and the solid oxide fuel cell 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 107, it is difficult to manufacture the sealant and the high temperature separation plate, and the development of electrolyte (Ce and Bi-based) and thin film fuel cell technology enables the medium temperature solid oxide fuel cell. 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.

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

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

Table 2 shows the overall efficiency of the 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 is a two-stage stack of molten carbonate fuel cell 105, Case 2 is a two-stage stack of solid oxide fuel cell 107, Case 3 is a stack of molten carbonate fuel cell 105 and solid oxide The stack of the fuel cell 107 is composed of 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 105 at a low fuel utilization rate. The differential pressure of the cathode and the anode can be reduced.

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 linked, shows the highest efficiency, and Case 1 has only the molten carbonate fuel cell 105 stack. The amount of additional power generation is relatively smaller than that of Case 2, and 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 is high (259.4MW) and the overall efficiency is 58.8%.

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

3 is an efficiency comparison graph 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 an increase in power and heat inside the fuel cell stack, and a stack of molten carbonate fuel cells 105 is connected. The efficiency of the solid oxide fuel cell 107 linked stack (SO-SOFC) is greater than that of MC-MCFC because additional power generation, such as a turbine, is possible due to the 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 linked to each other in a power generation system, the loads of the two fuel cell stacks are controlled by one inverter and the load controller 108. Gas temperature and pressure conditions at the rear end of the stack, which is a stack, may be changed according to load changes, and the temperature and pressure of the stack may be controlled during initial operation and load change of the stack.

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 molten carbonate fuel cell 105, which is the first of the two fuel cell stacks, and is calculated based on 80% utilization depending on the fuel supplied to the solid oxide fuel cell 107. .

As shown in Table 3, the temperature at the rear end of the stack of the solid oxide fuel cell 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 lowering the utilization rate of the molten carbonate fuel cell 105 stack. There is an effect that can protect the electrolyte in the melting point state by increasing the relative differential pressure of.

Meanwhile, the unreacted fuel and air from the molten carbonate fuel cell 105 are supplied to the solid oxide fuel cell 107 stack, and the heat of the electrochemical reaction generated from the molten carbonate fuel cell 105 stack is transferred to the solid oxide fuel cell 107. By using the stack as a fuel supply heat source, higher efficiency is achieved than a two-stage stack consisting of each fuel cell.

The associated two-stage stack not only provides high fuel utilization due to two-stage oxidation of the fuel, but also the fuel amount in the molten carbonate fuel cell 105 stack is excessively supplied to increase the pressure of the anode in the stack, thereby protecting the differential pressure and stacking of the stack using the anode gas. There is a cooling effect, and the temperature and pressure of the stack outlet gas can be controlled using the hydraulic control valves 112 and 113 which control the amount of air and fuel supply through the inverter and the load controller 108 in common. The temperature and pressure of the gas are adjusted to make the downstream flue gas suitable for additional power generation.

The inverter and load 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 that the fuel utilization rate and performance at the maximum output of the associated stack are controlled. Environmentally friendly power generation with high efficiency and no environmental pollutants such as SO _{X and} NO _X generated during combustion under the optimal operating conditions of the entire fuel cell power generation system under any operating conditions such as fuel utilization required for protecting the degraded stack. That's the way.

As described above, the molten carbonate fuel cell stack and the solid oxide fuel cell stack 105 and 107 are connected in series to form a power generation system, and a single inverter and load controller 108 having a common temperature and pressure condition of the associated power generation system is used. To control the anode and cathode heaters to increase the efficiency of the power generation system and to the anode of the molten carbonate fuel cell stack under high pressure. Excess fuel can be supplied 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)

In a fuel cell power generation system, A molten carbonate fuel cell stack operating at a high temperature, a solid oxide fuel cell stack, an inverter and a load controller for controlling power to the molten carbonate fuel cell and a solid oxide fuel cell stack, and a hydraulic control valve for regulating hydraulic pressure An efficiency improving apparatus of a fuel cell power generation system, characterized in that. The method of claim 1, The inverter and the load controller controls the power supplied to the anode and the cathode heater, the fuel characterized in that for controlling the outlet temperature and power output of the molten carbonate fuel cell stack and the solid oxide fuel cell stack in accordance with the change in load Efficiency improvement device of battery power generation system. The method of claim 1, The hydraulic control valve comprises a valve for adjusting the hydraulic pressure of the air electrode and the valve for adjusting the hydraulic pressure of the anode, the efficiency of the fuel cell power generation system, characterized in that for controlling the pressure temperature by controlling the flow rate circulating. In a fuel cell power generation system, When cooling is required for a long time operation, the fuel cell power generation system is characterized in that the flow rate input to the anode of the molten carbonate fuel cell stack is excessively supplied to cool the stack with unused fuel, and the differential pressure between the anode and the cathode is reduced. How to improve efficiency.