JPH10302819A - Fuel cell generating set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure simplification, high efficiency, and cost reduction of a fuel cell generating set by combusting an anode exhaust gas containing unburned combustibles and a cathode exhaust gas containing oxygen and supplying a part of the cathode exhaust gas together with that exhaust gas to a carbonic- acid gas recycle line. SOLUTION: In a reformer 22, anode and cathode exhaust gases are combusted by a combustor 22b, that exhaust gases is mixed with air through a carbonic-acid gas recycle line 10 together with a part of a bypassed cathode exhaust gas through a heating chamber of a main body 22a, and is supplied to a cathode of a fuel cell 20. On the other hand, city gas and steam mixture gas supplied to the reformer of the main body 22a is reformed in hydrogen rich, is supplied to an anode, and generates the fuel cell 20. Further, exhaust heat of the excess cathode exhaust gas is utilized for a turbine compressor 28 and a turbine power generator 29 of air supplied to a cathode, and that turbine exhaust gas is utilized as a heat source of a steam generator 30 for a fuel gas material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell power generation system in which high-efficiency exhaust gas is introduced into a cathode to improve efficiency.

[0002]

2. Description of the Related Art Molten carbonate fuel cells have features not found in conventional power generators, such as high efficiency and low environmental impact, and have attracted attention as power generation systems following hydro, thermal and nuclear power. Currently, intensive research is underway.

FIG. 2 is a diagram showing an example of a power generation facility using a molten carbonate fuel cell using city gas as fuel. In the figure, a power generation facility is a reformer 22 for reforming a fuel gas (city gas) mixed with steam into an anode gas containing hydrogen.
And a fuel cell 20 that generates power from a cathode gas containing oxygen and an anode gas containing hydrogen.
The anode gas produced in the fuel cell 20 is supplied to the fuel cell 20 through the anode gas line 2, and the majority of the anode gas is consumed in the fuel cell 20 to become the anode exhaust gas. It is supplied to the combustion chamber.

[0004] In the reformer 22, combustible components (hydrogen, carbon monoxide, methane, etc.) in the anode exhaust gas are burned in a combustion chamber to generate a high-temperature combustion gas, which is used to heat the reforming chamber. The fuel gas is reformed by the reforming catalyst in the reforming chamber to produce anode gas. The anode gas exchanges heat with the fuel gas mixed with the steam flowing through the fuel gas line 1 by the fuel preheater 24, and after being cooled, is supplied to the anode of the fuel cell 20. The flue gas leaving the combustion chamber is cooled by an air preheater 26 in a flue gas line 7 and then cooled by a condenser 4.
4. Water is removed through the steam separator 46, pressurized by the low-temperature blower 34, combined with the air from the air line 8 and heated by the air preheater 26 to become a cathode gas. The combustion exhaust gas contains a large amount of carbon dioxide, and serves as a source of carbon dioxide necessary for the battery reaction.

The cathode gas enters a cathode circulation line 3 circulating through the cathode and reacts in the fuel cell 20 to produce a high-temperature cathode exhaust gas. Part of the cathode gas circulates back to the cathode circulation line 3 and part of the cathode gas is circulated. Exhaust gas line 5
After the power is recovered by a turbine compressor 28 that drives a compressor that compresses air in an exhaust heat utilization line 6, the remaining heat is recovered by a waste heat recovery steam generator 30. Energy is recovered and discharged out of the system. The steam generated by the exhaust heat recovery steam generator 30 enters the fuel gas line 1 through the steam line 9, mixes with the fuel gas, and is sent to the reformer 22.

[0006]

In such a fuel cell device, the condenser 44, the steam separator 4
6, the gas containing carbon dioxide gas was supplied to the circulation line 3. However, by supplying the high-moisture combustion exhaust gas from which water has not been removed recently to the cathode, the efficiency of the fuel cell can be improved. It is planned. In this case, the reformer 22
A carbon dioxide gas recycle line for directly supplying combustion exhaust gas to the cathode is provided.
Is supplied. However, since two circulation lines are provided for the cathode, simplification of the system has been desired. Further, when the combustion exhaust gas is directly supplied to the cathode as described above, the thermal energy that has conventionally been discharged from the condenser 44 is supplied to the cathode, and thus the cathode exhaust gas contains excess energy.

The present invention has been made in view of the above-mentioned problems, and has a single circulation line provided for the cathode, and furthermore, the effective use of surplus energy contained in the cathode exhaust gas to improve the efficiency of the fuel cell device and improve the efficiency of the fuel cell system. The objective is to reduce costs.

[0008]

To achieve the above object, according to the first aspect of the present invention, a fuel cell comprising a cathode and an anode and generating electricity from a cathode gas containing oxygen and an anode gas containing hydrogen, and a fuel cell discharged from the anode are provided. A reformer that burns the anode exhaust gas and the cathode exhaust gas discharged from the cathode, reforms the fuel gas containing water vapor with the heat, and supplies the fuel gas to the anode as anode gas, and supplies the combustion exhaust gas from this reformer to the cathode A carbon dioxide gas recycling line, an air line for supplying air to the carbon dioxide gas recycling line, a cathode exhaust gas bypass line for bypassing a cathode exhaust gas supplied to the reformer and supplying the same to the carbon dioxide gas recycling line, An air branch line that branches from the line and supplies air to the reformer, and a cathode exhaust gas Water is heated by comprising a heat recovery steam generator to be mixed into the fuel gas to generate steam, a.

An anode exhaust gas containing unburned components and a cathode exhaust gas containing oxygen are burned in a combustor of the reformer, and the combustion waste gas is supplied to a carbon dioxide gas recycling line. Air is supplied from the air line 8 to the carbon dioxide gas recycling line, and becomes a cathode gas containing carbon dioxide and oxygen necessary for a battery reaction at the cathode, and is supplied to the cathode. Part of the cathode exhaust gas is supplied to the carbon dioxide gas recycling line through a cathode exhaust gas bypass line that bypasses a combustor of the reformer. Thereby, a circulation line is formed in the cathode. The temperature of the combustion gas of the reformer needs to be a predetermined temperature suitable for reforming the fuel gas.If the temperature is higher than the predetermined temperature, the air is supplied to the combustor from the air branch line to be cooled, If the temperature is low, the predetermined temperature can be set by reducing the bypass amount going to the cathode exhaust gas bypass line and increasing the flow rate of the hot cathode exhaust gas going to the combustor.

In a second aspect of the present invention, a cathode exhaust gas power generation line drives a turbine with the cathode exhaust gas to generate electric power and supplies the exhaust gas to the exhaust heat recovery steam generator.
A steam branch line that supplies a part of the steam generated by the exhaust heat recovery steam generator to a turbine of the cathode exhaust gas power generation line.

As a method of utilizing the surplus energy of the cathode exhaust gas, the surplus energy is used to generate power by a turbine-driven generator to recover the energy. Further, energy can be recovered by supplying the steam generated by the exhaust heat recovery steam generator to the turbine that drives the generator with the surplus energy.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of a fuel cell power generation device according to an embodiment of the present invention. In this figure, FIG.
Those having the same functions as those described above are denoted by the same reference numerals. The fuel cell power generator includes a reformer 22 that reforms a fuel gas containing steam into an anode gas containing hydrogen, and a fuel cell 2 that generates electricity from the anode gas and a cathode gas containing oxygen and carbon dioxide.
The reformer 22 includes a reformer main body 22a that generates a reformed gas (anode gas) and a catalytic combustor 22b that burns the gas using a catalyst to generate a combustion exhaust gas. The anode exhaust gas discharged from the fuel cell 20 is supplied to the catalytic combustor 22b by the anode exhaust gas line 4 and burns together with a part of the cathode exhaust gas. The reformer main body 22a includes a reforming chamber for converting city gas containing water vapor into a reforming gas by a catalyst, and a heating chamber for heating the reforming chamber with the combustion exhaust gas from the catalytic combustor 22b. A combustion exhaust gas containing carbon dioxide is supplied to the cathode by a carbon dioxide gas recycle line 10, and air containing oxygen is supplied by an air line 8.
These are mixed and supplied as a cathode gas.

The city gas containing natural gas as a component is supplied by the fuel gas line 1, mixed with the steam from the steam line 9, preheated by the fuel preheater 24, and enters the reforming chamber of the reformer main body 22a. The anode gas generated from the reforming chamber is supplied to the anode of the fuel cell 20 after the fuel gas is heated by the fuel preheater 24 through the anode gas line 2. The cathode of the fuel cell 20 has a carbon dioxide recycle line 1
The cathode gas containing carbon dioxide gas and oxygen is supplied from the air line 8 and the air line 8 which joins the cathode gas. The fuel cell 20 is supplied with the anode gas and the cathode gas to generate power. An anode exhaust gas containing steam and unburned components is discharged by the reaction at the anode, and supplied to the catalytic combustor 22b through the anode exhaust gas line 4. A part of the cathode exhaust gas generated by the reaction at the cathode is supplied to the catalytic combustor 22b by the cathode exhaust gas line 5, and the remainder is supplied to the exhaust heat utilization line 6 and the cathode exhaust gas power generation line 12.

An anode exhaust gas and a cathode exhaust gas of the fuel cell 20 are supplied to the catalytic combustor 22b. Since the fuel utilization of the fuel cell is about 80%, 2%
About 0% fuel component is contained. Cathode exhaust gas contains oxygen necessary for combustion. Reformer body 22a
The combustion exhaust gas from the heating chamber contains carbon dioxide gas, which is necessary for the battery reaction at the cathode, and is supplied to the cathode by the carbon dioxide gas recycling line 10.

A part of the cathode exhaust gas is used as exhaust heat utilization line 6.
After driving the turbine of the turbine compressor 28, it is supplied to the exhaust heat recovery steam generator 30. In the exhaust heat recovery steam generator 30, feed water is converted into steam by the exhaust gas that drives the turbine of the turbine compressor 28, and supplied to the fuel gas line 1 through the steam line 9. Exhaust gas from the exhaust heat recovery steam generator 30 is condensed in the condenser 44, water is separated in the steam separator 46, and the separated water is sent to a pure water device (not shown). The exhaust heat recovery steam generator 30 receives a water supply necessary for steam generation from a pure device (not shown). The cathode exhaust gas leaving the steam separator 46 is released to the atmosphere.

A part of the cathode exhaust gas is further supplied to the cathode exhaust gas power generation line 12 to drive the turbine generator 29 to generate power, recover energy and supply the exhaust gas to the exhaust heat recovery steam generator 30. Exhaust heat recovery steam generator 3
No. 0 generates steam by the exhaust gas and the exhaust gas from the turbine compressor 28. A part of the generated steam is supplied to a turbine generator 29 by a steam branch line 9a branched from the steam line 9 to generate electric power.

The air compressed by the turbine compressor 28 is pressurized by the low-temperature blower 34 in the air line 8 and enters the carbon dioxide gas recycling line 10, where it is mixed with the combustion exhaust gas and supplied to the cathode. The carbon dioxide gas recycling line 10 is provided with a carbon dioxide gas circulation blower 38 and is driven by the electric motor M. The motor M is provided with a rotation controller 42, which controls the rotation of the motor M so that the temperature measured by the temperature measuring device 40 provided at the cathode inlet is a predetermined temperature, for example, 600 ° C to 650 ° C. A cathode exhaust gas bypass line 11 that enters the carbon dioxide gas recycling line 10 from the cathode exhaust gas line 5 on the inlet side of the catalytic combustor 22b is provided. Further, an air branch line 8a branched from the air line 8 is connected to a position closer to the catalytic combustor 22b than a position at which the cathode exhaust gas bypass line 11 is taken out.

A temperature measuring device 4 is provided on the output side of the catalytic combustor 22b.
1 is provided to measure the temperature of the combustion exhaust gas supplied to the heating chamber. This temperature needs to be a predetermined temperature suitable for reforming the fuel gas in the reforming chamber, and the predetermined temperature is, for example, 780 ° C to 800 ° C. When the temperature is lower than the predetermined temperature, the amount of bypass is reduced by the flow control valve 48 provided in the cathode exhaust gas bypass line 11, and a large amount of high-temperature cathode exhaust gas is supplied to the catalytic combustor 22b. Higher. When the temperature is higher than the predetermined temperature, the flow rate of the air is increased by the flow control valve 49 provided in the air branch line 8a to lower the temperature of the combustion exhaust gas. The anode has a line for directly supplying fuel gas (city gas) (not shown).
When the temperature of the combustion exhaust gas is extremely low, the supply amount of the anode exhaust gas to the catalytic combustor 22b is increased to increase the amount of gas to be burned, thereby increasing the temperature of the combustion exhaust gas.

When the load on the fuel cell is substantially constant, the bypass amount of the cathode exhaust gas bypass line 11 is constant according to the load. Therefore, the flow control valve 48 may be a fixed orifice corresponding to the load. Although the flow control valve 48 is expensive due to its high-temperature specification, the use of an orifice can significantly reduce the cost.

[0020]

As is apparent from the above description, the present invention integrates a cathode circulation line and a carbon dioxide gas recycling line necessary for a fuel cell system which achieves high efficiency by introducing high-moisture exhaust gas to the cathode. However, by integrating the high-temperature cathode blower into the carbon dioxide gas circulation blower, it was possible to reduce the number of high-temperature specification blowers and achieve cost reduction. Further, by generating power using the surplus energy of the cathode exhaust gas, it is possible to promote higher efficiency of the power generation system. By taking such measures, it is possible to provide a power generation system that can compete with competing gas turbine combined systems, and it is possible to introduce a fuel cell power generation system into the market in terms of efficiency and cost.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a fuel cell power generation device according to an embodiment of the present invention.

FIG. 2 is an overall configuration diagram of a conventional fuel cell power generator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel gas line 2 Anode gas line 4 Anode exhaust gas line 5 Cathode exhaust gas line 6 Exhaust heat utilization line 8 Air line 8a Air branch line 9 Steam line 9a Steam branch line 10 Carbon dioxide gas recycling line 11 Cathode exhaust gas bypass line 12 Cathode exhaust gas power generation line Reference Signs List 20 fuel cell 22 reformer 22a reformer main body 22b catalytic combustor 24 fuel preheater 28 turbine compressor 29 turbine generator 30 exhaust heat recovery steam generator 34 low temperature blower 38 carbon dioxide circulating blower 40, 41 temperature measuring device 42 Rotation controller 44 Condenser 46 Steam separator 48, 49 Flow control valve

Claims (2)

[Claims] 1. A fuel cell comprising a cathode and an anode, which generates electricity from a cathode gas containing oxygen and an anode gas containing hydrogen, and an anode exhaust gas discharged from the anode and a cathode exhaust gas discharged from the cathode are burned. A reformer for reforming a fuel gas containing water vapor and supplying it as an anode gas to an anode; a carbon dioxide gas recycling line for supplying combustion exhaust gas from the reformer to a cathode; and air for supplying air to the carbon dioxide gas recycling line Line, a cathode exhaust gas bypass line that bypasses the cathode exhaust gas supplied to the reformer and supplies the carbon dioxide gas recycling line, an air branch line that branches from the air line and supplies air to the reformer, Heat supply water is heated by the cathode exhaust gas to generate steam, which is mixed with fuel gas to generate exhaust heat recovery steam And a fuel cell power generator. 2. A cathode exhaust gas power generation line for driving a turbine by the cathode exhaust gas to generate electric power and supplying the exhaust gas to the exhaust heat recovery steam generator, and a part of the steam generated by the exhaust heat recovery steam generator. The fuel cell power generator according to claim 1, further comprising: a steam branch line for supplying a turbine of the cathode exhaust gas power generation line.