JP2001076750A - High temperature fuel cell facility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase power generation efficiency of a power generating unit that uses a high temperature fuel cell. SOLUTION: Air supplied to a solid-oxide fuel cell SOFC11 is cooled by an air cooler 15 before being pressurized by an air compressor 13. This reduces the power of the air compressor 13 required for pressurization so as to generate electricity using surplus power of a gas turbine 12, resulting in increasing power generation efficiency of a high temperature power cell facility 10 as a whole. The air cooler 15 cools air by using coolant cooled by cold liquefied natural gas in an LNG carburetor 18. In a coolant heater 16, the coolant absorbs heat of effluent gas output from a regenerator 14. Since coolant can store cold of liquefied natural gas, air that the air compressor 13 inhales can be cooled stably even if the flow of the liquefied natural gas changes. Using a natural gas turbine 19, it is also possible to collect expameion energy of the natural gas vaporized in the LNG vaporizer 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-temperature fuel cell system for generating electricity by causing an electrochemical reaction between a fuel containing hydrogen or carbon and a reaction gas containing oxygen at a high temperature.

[0002]

2. Description of the Related Art Heretofore, fuel cells, which directly convert chemical energy of fuel into electrical energy without passing through mechanical energy, have been attracting attention for effective use of energy. Although various types of fuel cells are considered, a room-temperature fuel cell and a high-temperature fuel cell are particularly attracting attention. Room-temperature fuel cells are characterized in that they can operate at room temperature and do not become hot. However, there is a problem that an expensive platinum group metal catalyst must be used in order to increase the reaction rate and obtain a high current density. Therefore, a high-temperature fuel cell that can increase the chemical reaction rate by increasing the temperature and obtain a high current density has attracted attention.
As a high temperature fuel cell, a solid oxide fuel cell (SOF)
C), a molten carbonate fuel cell (MCFC), and a polymer electrolyte fuel cell (PEFC) which is not a high temperature but is not high in temperature as a low cost fuel cell.

FIG. 11 shows a basic configuration for generating power using a solid oxide fuel cell. SOFC1, which is a solid oxide fuel cell, has, for example, city gas (C
ITS GAS). Air is supplied as a reaction gas for oxidizing city gas as fuel. S
OFC1 generally supplies a large amount of pressurized air and
The reaction is proceeding while maintaining a high temperature around 00 ° C. For this reason, the exhaust gas from the SOFC 1 uses a gas turbine (GT).
2 is driven, and an air compressor (AC) 3 is operated by the power to compress the air supplied to the SOFC 1. Since the exhaust gas discharged from the gas turbine 2 is still at a considerably high temperature, the regenerator 4 outputs the SOFC 1 from the air compressor 3.
Exchanges heat with the air supplied to the furnace to reduce the temperature and discharge the air. The air sucked into the SOFC 1 exchanges heat with the exhaust gas to enter a preheated state in which the temperature further rises. SOFC1
Is generated as DC, which is converted into AC by an inverter and output.

[0004]

Generally, compressive fluid such as air has a larger compressive power as the temperature before compression becomes higher. In a solid oxide fuel cell power generation system as shown in FIG. 11, a large amount of pressurized air is generally required, and when operated at a high pressure, the power to be recovered by the gas turbine 2 increases and the efficiency increases. . However, when the pressure is increased, the compression power of the air compressor 3 increases, and the discharge temperature increases, so that the amount of heat that can be recovered by the regenerative heat exchanger 4 decreases. In order to further improve the power generation efficiency as a whole, it is necessary to add a new, for example, steam turbine cycle using the exhaust gas exiting the regenerative heat exchanger 4 as a heat source.

An object of the present invention is to provide a high-temperature fuel cell system which uses a high-temperature fuel cell which requires a large amount of pressurized air, and which can increase the overall power generation efficiency with a simple device configuration. It is to be.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a high-temperature fuel cell system for electrochemically oxidizing fuel in a high-temperature fuel cell and directly converting chemical energy of the fuel into electric energy. And a cooling device for cooling a reaction gas introduced into the compressor.

According to the present invention, the oxidizing reaction gas used for electrochemically oxidizing the fuel in the high-temperature fuel cell is cooled by the cooling device before being supplied under pressure by the compressor. To reduce the power of the compressor to pressurize to the pressure of
Overall power generation efficiency can be increased.

In the present invention, the cooling device exchanges heat with liquefied natural gas, and cools the reaction gas with a refrigerant capable of storing cold heat of the liquefied natural gas.

According to the present invention, it is possible to exchange heat between the liquefied natural gas and the refrigerant, store the cold heat of the liquefied natural gas in the refrigerant, and cool the reaction gas sucked into the compressor by the refrigerant. In addition, the overall power generation efficiency of the high-temperature fuel cell equipment can be improved by effectively utilizing the cold energy of the liquefied natural gas. Since the liquefied natural gas exchanges heat with the refrigerant, even if the amount of the liquefied natural gas vaporized fluctuates, the cold gas stored in the refrigerant can stably cool the reaction gas sucked into the compressor.

Further, the present invention is characterized in that a turbine capable of recovering power by raising the temperature of liquefied natural gas to a high temperature and expanding the liquefied natural gas using exhaust gas discharged from the high-temperature fuel cell as a heat source is provided.

According to the present invention, the liquefied natural gas that exchanges heat with the refrigerant is heated to a high temperature by the high-temperature exhaust gas discharged from the high-temperature fuel cell, expands the liquefied natural gas, and effectively powers the turbine. Can be recovered.

[0012]

FIG. 1 shows a schematic configuration of a high-temperature fuel cell system 10 as one embodiment of the present invention. About 950 from SOFC11 which is a solid oxide fuel cell
A high-temperature reaction gas of about ° C. is discharged as exhaust gas, and drives the gas turbine 12. The output shaft of the gas turbine 12 is connected to the rotation shaft of the air compressor 13.
Air, which is a reaction gas sucked into 11, is pressurized. The reaction gas may be any gas containing oxygen. Air compressor 13
The air pressurized by the SOFC 1 is heated by exchanging heat with the exhaust gas from the gas turbine 12 by the regenerator 14 and then heated.
1 is supplied. In SOFC11, city gas etc.
Fuels containing carbon and hydrogen are electrochemically oxidized to generate DC power. The configuration including the SOFC 11, the gas turbine 12, the air compressor 13, and the regenerator 14 is basically the same as the conventional solid oxide fuel cell shown in FIG.
DC output power from the SOFC 11 is converted from DC to AC by an inverter.

In the high-temperature fuel cell system 10 of the present embodiment,
The air taken into the air compressor 13 is cooled by the air cooler 15. Cooling heat for cooling is liquefied natural gas (hereinafter, referred to as liquefied natural gas).
"LNG"). The air cooler 15 exchanges heat with LNG, for example, −14.
A refrigerant cooled to 0 ° C. is supplied, and exchanges heat with air to cool the air to, for example, −130 ° C. When this air is pressurized by the air compressor 13, the temperature also rises, and is further heat-exchanged with the exhaust gas by the regenerator 14 to be preheated to, for example, about 490 ° C. and supplied to the SOFC 11.

The refrigerant that has exchanged heat with the air in the air cooler 15 exchanges heat with the exhaust gas of, for example, about 90 ° C. discharged from the regenerator 14 in the refrigerant heater 16.
Heat to 0 ° C. The refrigerant heated by the refrigerant heater 16 is pressurized by the refrigerant circulating pump 17 and is cooled by the LNG vaporizer 18.
And heat exchange with LNG to be cooled. The LNG vaporizer 18 raises the temperature of the liquefied natural gas to, for example, about 65 ° C.
It is vaporized at a pressure of Pa. Delivery pressure of natural gas is about 3M
Assuming that the pressure is Pa, the natural gas is further expanded by the natural gas turbine 19 by the amount of the differential pressure to recover the power. LNG is pressurized by the LNG pump 20,
It is supplied to the LNG vaporizer 18.

In the present embodiment, the air is not directly cooled by the liquefied natural gas, but the refrigerant is circulated to accumulate cold heat and to supply the air. If, for example, a mixed alcohol having a composition of 55% of methanol and 45% of ethanol is used as the refrigerant, it can be cooled to about −140 ° C. to accumulate cold heat. By accumulating cold heat, it becomes possible to stably cool with a refrigerant regardless of fluctuations in the amount of liquefied natural gas used. At a natural gas supply base that uses liquefied natural gas as a raw material for city gas, for example, the amount of liquefied natural gas used also fluctuates as the demand for city gas fluctuates over time. Once the cold energy is transferred to the refrigerant and accumulated, the cold energy of the liquefied natural gas can be used stably and effectively. Conventionally, natural gas supply terminals that vaporize liquefied natural gas cannot be used effectively due to fluctuations in the amount of liquefied natural gas used. In the high-temperature fuel cell equipment of the embodiment, it can be stably and effectively used as cold energy for improving power generation efficiency.

In a conventional natural gas supply terminal, it is necessary to provide a large facility for exchanging heat with seawater or the like in order to obtain a heat source for vaporizing liquefied natural gas. If the high-temperature fuel cell equipment 10 of the present embodiment is provided, by supplying cold heat from liquefied natural gas, the liquefied natural gas itself is also heated and its temperature rises, so that external heat required for vaporization is unnecessary. . Further, as shown in FIG. 1, if a heat exchanger between the liquefied natural gas and the refrigerant is used for heating and vaporizing as the LNG vaporizer 18, it is possible to directly vaporize the natural gas and further vaporize the natural gas. It is also possible to drive the natural gas turbine 19 which is an expansion turbine. As a result, the expansion energy of natural gas can be effectively recovered as power, and the main body of the SOFC 11 and the SOFC 1
A gas turbine 12 for recovering the power of the exhaust gas from 1
And the natural gas turbine 19 can collect electric power and motive power in total, thereby increasing the overall power generation efficiency.

FIG. 2 shows a high-temperature fuel cell system 10 shown in FIG.
This shows a state rewritten according to a program for simulating the operation of the system. However, SO
A power turbine 21 is added in order to generate electric power by using surplus power obtained by extracting necessary power from the exhaust gas from the FC 11 by the air compressor 13. Also, in the refrigerant circulation path,
A refrigerant tank 22 is provided. The LNG pump 20 shown in FIG. 1 is a component that is required in any case to take out LNG from the LNG storage tank.
It is supplied in the state of being pressurized by the NG pump 20, and is excluded from the target of the simulation.

FIG. 3 shows an example of a result obtained by performing a simulation with the configuration of FIG. FIG. 3A shows operating conditions associated with the flow of a substance in each unit shown in FIG. c1 and c2 are for LNG, f1 is for city gas as fuel, r0 to r3 and r6 and r7 are for refrigerant, a1 to a5 are for air, and g1 to g5 are SOFC
Eleven exhaust gases are shown. FIG. 3 (b)
Indicates the energy at each part in FIG. w-ac indicates the required power of the air compressor 13 and is TURBINE POWER.
R indicates the output of the power turbine 21, w-rp2 indicates the required power of the refrigerant circulation pump 17, and SOFC POW
ER (DC) indicates the DC output power of the SOFC 11, and S
OFC EFF (DC% HHV) indicates the power generation efficiency of the SOFC 11 itself, WASTE HEAT indicates heat loss lost with exhaust gas, and NETPOWER (AC)
Indicates the overall AC output power, and NET POWER
REFF. (AC% HHV) indicates the overall power efficiency, HEAT LEAK indicates the heat leaking from the refrigerant tank 22, and LNG POWER indicates the natural gas turbine 1
9 shows the output obtained from 9. The DC output obtained from the SOFC 11 is converted into AC by an inverter having an efficiency of 94% and output. The converted output and the outputs of the gas turbine 12 and the natural gas turbine 19 are output to NET POWER (AC). Are summed up.

FIG. 4 shows a simulation result in the case of further improving the efficiency by changing the operating conditions in the configuration as shown in FIG. Under the conditions shown in FIG. 3, in the state of a2, the air is cooled to −111.4 ° C. by the air cooler 15.
In FIG. 4, the air is cooled to −136.1 ° C. in the state of a2. FIG. 5 shows the result obtained by the operation of FIG. It should be noted that the output of the power turbine 21 has increased to 933.7. The high-temperature fuel cell system 10 according to the present embodiment includes a supply-air cooling SOF using LNG cold heat.
It can be considered as a C combined cycle. L
The efficiency of the NG cold energy utilization system needs to be evaluated using exergy.

FIG. 6 shows the results of the exergy evaluation for the present embodiment. The evaluation temperature is 15 ° C. SOFC
Assuming that the chemical exergy of the fuel supplied to 11 is 100, the exergy loss and exhaust gas loss occurring in each device and the output that can be recovered are shown by numerical values. LNG of liquefied natural gas is 4.5 cryogenic exergy by charge air cooling
The air supplied to the SOFC 11 is supplied from the cold exergy. On the other hand, from the exhaust gas of the gas turbine 12,
A hot exergy of 0.5 is provided to the high pressure natural gas. The total efficiency of the DC output from the SOFC 11 and the shaft end output of the gas turbine 12 is 81% based on the chemical exergy of the fuel. The total efficiency of the AC output of the SOFC 11 and the output of the power generation end of the gas turbine 12 is 71 based on the higher heating value.
%.

In a high-efficiency combined cycle (ACC) currently used in advanced thermal power plants, the power generation end efficiency is 52% at a turbine inlet reaction gas temperature of 1500 ° C. In ACC, the exergy losses associated with combustion and boiler heat transfer are 25% and 6.2%. On the other hand, in the present embodiment, the exergy loss corresponding to combustion is 15.2%, and the exergy loss corresponding to heat transfer is 2.2%, which is a loss from the regenerator 14, which is greatly reduced. You.

FIG. 7 shows a modified configuration for performing a simulation on the high-temperature fuel cell equipment using the conventional SOFC 1 shown in FIG. 8A shows a state along the flow of the substance corresponding to the configuration of FIG. 7, and FIG. 8B shows a state along the flow of energy. FIG. 1 and FIG.
1 are denoted by the same reference numerals, and FIG.
The power turbine 21 is added in the same manner as described above. The output of the conventional SOFC 1 using the SOFC 1 and the output of the SOFC combined cycle of the LNG supply / cooling system of the present embodiment will be compared. Although the output of the SOFC 1 does not change even in the conventional method, the total efficiency of the fuel for chemical exergy is 68.5%. When air supply cooling is performed as in the present embodiment, the output of the gas turbine 12 is improved by as much as 85%. The greatest reason for this output improvement is that exergy loss due to heat transfer in the regenerator 14 is suppressed and exhaust heat recovery is enhanced. That is, the thermal exergy of the exhaust gas at the outlet of the regenerator 14 is extremely small at 1.4 in the supply air cooling system, but is as large as 11.1 in the conventional system.

The power generation by the SOFC combined cycle of this embodiment is noted as a distributed power source. At present, there are 24 liquefied natural gas satellite stations in Japan, and the cold energy is not used at all. If the power generation system of the present embodiment is put into practical use, it is expected that the utilization of cold energy of liquefied natural gas will be promoted not only in large-scale liquefied natural gas bases but also in small-scale satellite bases.

FIG. 9 shows a configuration for simulation of a high-temperature fuel cell system 30 according to another embodiment of the present invention. The simulation result of the embodiment of FIG. 9 is shown in FIG.
FIG. 10 shows a state along the flow of the substance as 0 (a).
(B) shows a state along the flow of energy. In the present embodiment, a natural gas turbine 19 for recovering expansion energy of natural gas as shown in FIG. 3 is not used. Even if the expansion energy of the natural gas is not recovered, the cooling energy of the liquefied natural gas is recovered, and the overall power generation efficiency can be improved by about 10% as compared with the conventional method.

In each of the embodiments described above, the high temperature fuel cell equipment 1 is effectively used by effectively utilizing the cold heat of the liquefied natural gas.
At 0, 30, efficient power generation can be performed. 1998
The amount of liquefied natural gas received in Japan in the fiscal year is about 4800
10,000 tons, of which about 33 million tons are used as fuel for power generation. LNG cryogenic power generation using liquefied natural gas cryogenic power has been constructed in 1979, and 14 units are currently operating at 12 power and gas company LNG receiving terminals. These facilities use about 8.5 million tons of liquefied natural gas annually using seawater as a heat source.
The total power generation output is about 73000 kW.

However, LNG cryogenic power generation is
In the 0s, construction has been stopped for economic reasons such as stable energy prices and rising construction costs. In particular, the adoption of a high-efficiency combined cycle (ACC) raises the vaporization pressure of liquefied natural gas and lowers the output that can be recovered, which is also a major factor. By applying the present invention, a next-generation high-efficiency power generation system can be realized by combining a fuel cell operating at a high temperature and a gas turbine.

[0027]

As described above, according to the present invention, a reaction gas containing oxygen, such as air supplied to a high-temperature fuel cell, is cooled by a cooling device at the compressor inlet side. The power of the exhaust gas from the high-temperature fuel cell is effective for preheating the reaction gas supplied to the high-temperature fuel cell, etc. And even with a simple configuration that does not use a steam turbine cycle or the like, the overall power generation efficiency can be increased.

Further, according to the present invention, the overall power generation efficiency of the high-temperature fuel cell equipment can be enhanced by utilizing the cold heat of the liquefied natural gas. Liquefied natural gas is heated and its temperature rises by supplying cold heat to the high-temperature fuel cell equipment. The liquefied natural gas whose temperature has risen requires less heat for vaporization, and the vaporizer required for use as natural gas can be downsized. In addition, since the reaction gas sucked into the compressor is cooled by the refrigerant that has exchanged heat with the liquefied natural gas, the cooling heat from the liquefied natural gas can be stored in the refrigerant, and the flow rate of the liquefied natural gas fluctuates. Even in this case, the reaction gas can be stably cooled.

Further, according to the present invention, when exchanging cold heat from liquefied natural gas with a refrigerant to heat and vaporize the liquefied natural gas, the expansion turbine is driven by the vaporized natural gas to convert the natural gas. The expansion energy is also recovered as power, and the energy of the natural gas is effectively used as the power generation output of the high-temperature fuel cell equipment, so that the overall power generation efficiency can be improved.

[Brief description of the drawings]

FIG. 1 shows a high-temperature fuel cell system 10 according to an embodiment of the present invention.
FIG. 3 is a process flow chart showing a schematic configuration of the first embodiment.

FIG. 2 is a diagram showing a configuration in which the high-temperature fuel cell equipment 10 of FIG. 1 is modified for simulation.

FIG. 3 is a table showing one simulation result for the configuration of FIG. 2;

FIG. 4 is a table showing another simulation result for the configuration of FIG. 2;

5 is a table showing evaluation results of exergy based on the simulation of FIG. 4.

FIG. 6 is a diagram illustrating an evaluation result of FIG. 5;

7 is a diagram showing a configuration in which the conventional high temperature fuel cell system shown in FIG. 11 is modified for simulation.

FIG. 8 is a table showing a simulation result of the configuration of FIG. 7;

FIG. 9 is a high-temperature fuel cell system 3 according to another embodiment of the present invention.
FIG. 9 is a diagram illustrating a configuration for simulation of 0.

FIG. 10 is a table showing simulation results of the embodiment in FIG. 9;

FIG. 11 is a block diagram showing a process flow of a conventional high-temperature fuel cell.

[Explanation of symbols]

 10, 30 High-temperature fuel cell equipment 11 SOFC 12 Gas turbine 13 Air compressor 14 Regenerator 15 Air cooler 16 Refrigerant heater 17 Refrigerant circulation pump 18 LNG vaporizer 19 Natural gas turbine 21 Power turbine

Claims (3)

[Claims] 1. A high-temperature fuel cell system for electrochemically oxidizing fuel in a high-temperature fuel cell and directly converting chemical energy of the fuel into electric energy, and a compressor for supplying a reaction gas for oxidation under pressure. And a cooling device for cooling a reaction gas introduced into the compressor. 2. The high-temperature high-temperature apparatus according to claim 1, wherein the cooling device exchanges heat with the liquefied natural gas and cools the reaction gas by a refrigerant capable of storing cold heat of the liquefied natural gas. Fuel cell equipment. 3. A turbine capable of recovering power by raising and expanding liquefied natural gas to a high temperature using exhaust gas discharged from the high-temperature fuel cell as a heat source. High temperature fuel cell equipment as described.