JPH07230819A - Internally modified solid electrolyte fuel cell system having self-heat exchange type heat insulating prereformer - Google Patents

Abstract

PURPOSE:To provide internal modification performed on a fuel electrode simultaneously as fuel modification and power generation reaction by providing functions of modifying hydrocarbon of C2 or more in city gas, and controlling a methane reaction ratio easily. CONSTITUTION:Modifying gas and air flowing from a tube 15 through an air blower 8 and a heating air preheater 9 are supplied from a tube 23 to a solid electrolyte fuel cell 10 to generate power at 1000 deg.C, and temperature of fuel discharge gas getting into a combustor 11 also becomes about 1000 deg.C. Next, recycle gas of 1000 deg.C inside a tube 17 supplies heat to a reaction tube part 7b of a low temperature for heat absorption reaction to lower the temperature of the recycle gas itself to be low-temperature recycle gas of 500-800 deg.C, which is then supplied from a tube 22 through a recycle gas flow regulation valve 6 to an ejector 5. Hydrocarbon of C2 or more in city gas is thus modified in the reformer 7, thereby methane reformation reaction can be controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal reforming type solid electrolyte fuel system having a self-heat exchange type adiabatic prereformer.

[0002]

2. Description of the Related Art The spread of cogeneration, which supplies electric power and heat from a single system, is being promoted as one of the effective use technologies of city gas. Among them, fuel cells are excellent in environmental compatibility and high power generation. Positioned as an important technology with efficiency.

The solid oxide fuel cell (SOFC) has an operating temperature as high as 1000 ° C. as compared with other types of fuel cells. Therefore, it is possible to obtain a power generation efficiency of 60% or more by using a gas turbine and a steam turbine together. You can

However, the combination of these bottoming cycles is possible only in a large-scale facility such as a power plant,
Not suitable for fuel cells for on-site cogeneration. Therefore, in developing an SOFC for on-site cogeneration in the future, it is necessary to consider a system configuration that enables high-efficiency operation without the bottoming cycle, and also to consider the performance required for the battery.

The power generation efficiency of a fuel cell is the product of theoretical efficiency, voltage efficiency, fuel utilization efficiency, inverter efficiency, external extraction efficiency and the like. Theoretical efficiency, fuel utilization efficiency, and external extraction efficiency can be improved by fuel reforming because city gas is used as fuel. Generally, when a fuel cell is operated at a high temperature, the entropy loss increases, and the theoretical efficiency decreases. For example, the theoretical efficiency when using hydrogen as fuel is 71% at 1000 ° C.
Falls to. However, when methane is used as the fuel, the theoretical power generation efficiency can be improved to 88% by reforming by endothermic reaction between methane and water.

High efficiency is likely to be obtained by using the reformed gas as fuel in a low temperature operation type fuel cell such as a phosphoric acid type fuel cell, but in reality, it is an endothermic reaction at 800 ° C. which is required for fuel reforming.
Since it is necessary to burn a part of the fuel to obtain a high temperature heat source, the fuel utilization rate decreases and the efficiency does not rise as much as desired. In this respect, SOFC operates at 1000 ° C., so that sufficient heat necessary for reforming can be supplied by the waste heat of the battery, so that the fuel utilization efficiency increases and high efficiency operation becomes possible.

[0007]

Pre-reformers are used for fuel reforming. The solid electrolyte fuel cell pre-reformer that has been conventionally used consists of a reforming catalyst, a reaction tube that fills the catalyst, and a heating device that heats the reaction tube.The pre-reformer reacts the hydrocarbons contained in city gas with water vapor. It has a role of decomposing a part or all of hydrocarbons into hydrogen and carbon monoxide, and supplying a reaction product as a fuel for a fuel cell.

However, in such a conventional external heating reformer, it is difficult to control the reforming rate of methane contained in city gas, and in reality, almost all of the methane is reformed. There has been a problem that internal reforming cannot be performed in the solid oxide fuel cell, which lowers the efficiency of the cell.

The present invention has been made in view of the above points. Focusing on the fact that an SOFC is operated at a high temperature, self-heating that enables internal reforming in which fuel reforming and power generation reaction are simultaneously performed on the fuel electrode. An object of the present invention is to provide an internal reforming type solid electrolyte fuel cell system having an exchange type adiabatic pre-reformer.

[0010]

In order to solve the above problems, the present invention provides a solid electrolyte fuel cell, a self-heat exchange type adiabatic prereformer filled with a reforming catalyst, and a fuel electrode outlet gas of the fuel cell. A circulating fuel recycling line,
It is characterized by having a supply device for city gas and steam, reforming hydrocarbons of C2 or higher in city gas, and having a function of easily controlling the reaction rate of methane.

[0011]

The internal reforming method has the following actions in addition to the fuel reforming utilization described above. (1) The reformer heating device is not required and the entire system becomes compact. (2) The battery can be cooled by the reforming reaction. (3) The reforming rate is 100% because the reforming is performed at a high temperature. In particular, due to the cooling effect of the battery, the power generation efficiency is improved by reducing the electric power for the blower that feeds the cooling air, and the waste heat recovery efficiency is improved by reducing the cooling air amount.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a schematic structure of an internal reforming type solid electrolyte fuel cell system having a self-heat exchange type adiabatic pre-reformer of the present invention.

The biggest problem in performing internal reforming is
Carbon deposition due to thermal decomposition of C ₂ or higher hydrocarbons at high temperature. Therefore, we installed a pre-reformer that selectively removes C _{2 and} higher components from city gas.

The features of this system are as follows. (1) The pre-reformer is a self-heat exchange type adiabatic type, and the reforming rate is controlled by the adiabatic reaction temperature. (2) Recycle fuel at the cell outlet to save steam and improve fuel utilization. (3) Add steam for reaction from the outside to raise the steam ratio to about 2.5 and prevent carbon deposition.

The reforming rate of methane in the 13A gas is determined by the inlet temperature of the adiabatic reactor, and the inlet temperature can be controlled by the steam temperature and the recycle gas temperature / gas amount.

In FIG. 1, 1 is a desulfurization device, 2 is a fuel flow control device, 3 is a water pump, 4 is a water vaporization device, 5 is an ejector, 6 is a recycle gas flow control valve, and 7 is a self-heat exchange type adiabatic pre-reformer. , 8 is an air blower, 9 is an air preheater, 10 is a solid oxide fuel cell, 11 is a combustor, 1
2 is a waste heat recovery machine.

Next, the operation of such a system will be described. Mainly composed of methane supplied from the outside, C ₂ ~
City gas containing hydrocarbons of about C ₅ enters through the pipe 13,
After the sulfur component is removed by the desulfurization device 1, the fuel flow rate control device 2 sends the fuel gas at a predetermined flow rate from the pipe 16 to the ejector 5. The water enters the water pump 3 through the pipe 14, and is sent to the water vaporizer 4 with a predetermined flow rate, and becomes heated steam at 175 ° C. Due to the ejector effect in which the heated steam and the jet of city gas serve as a driving source, a recycled gas containing steam, carbon dioxide, carbon monoxide, hydrogen, etc., which circulates a part of the fuel exhaust gas, as main components to the ejector 5 from the pipe 17. The gas is sucked and mixed, and is supplied as a mixed gas from the pipe 18 to the adiabatic prereformer 7 of the heat exchange type, where the mixed gas is subjected to a steam reforming reaction (numbers 1 to 3) on the catalyst packed in the adiabatic prereformer. ) And is converted into reformed gas.

[0019]

[Equation 1]

[0020]

[Equation 2]

[0021]

[Equation 3] When any of the above-mentioned reforming reactions changes from the left side to the right side, it is an endothermic reaction, and therefore generally tends to occur preferentially when the reaction temperature is high. On the other hand, when the temperature is low, the equations 2 and 3 are reversible reactions, and conversely the reaction easily occurs from the right side to the left side.
Therefore, in the adiabatic pre-reformer 7, C _n H _m (hydrocarbons of C ₂ or more) in the mixed gas is decomposed into CO (carbon monoxide) and H ₂ (hydrogen) by an endothermic reaction according to the equation 1. It will lower the temperature. If the gas temperature is lowered to an appropriate temperature by the decomposition reaction of hydrocarbons having C ₂ or more (Equation 1), the reforming reaction of methane contained in city gas (reaction from the left side to the right side of Equation 2) will not proceed. Although the self-heat-exchange type adiabatic pre-reformer 7 exchanges heat once, but the gas after the exchange enters the reactor again, it has an isenthalpic change. Therefore, the methane reforming rate of the self-heat-exchange type adiabatic pre-reformer 7 is It can be controlled by the amount of sensible heat determined by the composition, temperature, and flow rate of various incoming gases.

A method of controlling the inlet temperature of the self-heat exchange type adiabatic pre-reformer 7 will be described below.

The reformed gas and the air flowing from the pipe 15 through the blower 8 and the air preheater 9 for raising the temperature are fed into the pipe 23.
Is supplied to the solid oxide fuel cell 10 from 1000 ° C.
Will generate electricity. Since the operation is performed at 1000 degrees, the temperature of the fuel exhaust gas entering the combustor 11 is also about 1000 degrees. A part of the fuel exhaust gas of the fuel cell 10 is circulated and reused as recycled gas from the pipes 20 and 22, but the remaining fuel exhaust gas and exhaust air are supplied to the combustor 11 through the pipes 20 and 23, respectively, and after combustion, The combustion heat is recovered by the water vaporizer 4, the air preheater 9 and the like and then released to the outside of the system.

On the other hand, the recycle gas at 1000 ° C. in the tube 17 is used as the heat exchanger section 7a of the self-heat exchange type adiabatic pre-reformer.
The temperature of the recycle gas itself is lowered by supplying heat to the low temperature reaction tube portion 7b for the endothermic reaction, and the temperature of the recycle gas itself becomes low temperature recycle gas of 500 to 800 degrees Celsius. It is supplied to the ejector 5 via 6. The recycled gas flow control valve 6 is preferably a valve having a large opening area such as a butterfly valve or a gate valve. In the present invention, the recycle gas flow rate control valve 6 is adjusted to adjust the flow rate of the recycle gas to control the sensible heat supplied to the self-heat exchange type adiabatic pre-reformer 7.

FIG. 2 is a diagram for explaining an operation example of the self-heat exchange type adiabatic pre-reformer.

The heat transfer flow rate is adjusted by changing the heat transfer area of the self-heat exchange type adiabatic pre-reformer 7, and the temperature of 1
40% of fuel exhaust gas with a utilization rate of 85% at 000 ° C is pipe 17
The recycled gas is recycled to the reformer 7, and the recycled gas is cooled to 500 to 900 ° C. in the heat exchange section 7 a, and then the city gas of 15 ° C. that enters from the pipe 22 through the ejector 5 and the steam ratio of 2.5. 175 ° C. heated steam (entered from the tube 15) whose flow rate is adjusted so that Reaction tube portion 7b entering from the tube 18 at this time
The temperature of the mixed gas at the inlet is 340 ° C to 580 ° C.

This temperature is sufficiently lower than 640 ° C., which is the temperature of the mixed gas when no heat exchange is performed, and it can be seen that the present invention has the effect of lowering the temperature at the catalyst layer inlet. Further, if the temperature of the low-temperature recycled gas flowing through the pipe 22 is lowered to 600 ° C. by heat exchange, the temperature of the mixed gas at the inlet of the reaction tube portion 7b is lowered to about 400 ° C. at which carbonization precipitation due to thermal decomposition of hydrocarbons can be almost ignored. You can Moreover, since this pre-reformer is an adiabatic type, even if the temperature of the mixed gas is lowered by heat exchange, the reaction tube portion 7b
Since the outlet temperature is constant at 473 ° C., the reforming rate of methane in city gas is also constant. Therefore, under the above-mentioned conditions, the reforming rate of methane is 0%, and the reforming of only hydrocarbons of C ₂ or more can be selectively performed.

[0028]

EFFECTS OF THE INVENTION By adopting this self-heat exchange type adiabatic pre-reformer, the power generation efficiency is about 3% as compared with the external reforming system in which methane is completely reformed by the pre-reformer.
Can be improved. In addition, the present invention adopts a method of controlling the reaction rate by controlling the inlet temperature of the reactor and advancing the reaction by the sensible heat of the reaction product and terminating the reaction in an equilibrium state. It is possible to obtain stable control characteristics over a long period of time without being affected by changes in the fuel cell, and even when performing feedback control of the reforming rate, gas composition analysis etc. is unnecessary and the catalyst layer outlet temperature is controlled. Since it suffices to do so, the control can be performed at a low cost.

Further, since the recycled gas is once heat-exchanged to lower the temperature and then supplied to the recycled gas flow rate control valve 6 and the ejector 5, the heat resistance required for these is also moderate, which is cheaper and longer. It is possible to use one with a long life, and it is also possible to use a high temperature blower instead of the ejector.

Also for the catalyst, if the inlet temperature is lowered to about 400, deterioration due to carbon deposition can be prevented, and the temperature distribution in the flow direction of the catalyst layer also becomes small, so that activity deterioration is less likely to occur and a longer life can be expected. And so on.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an internal reforming type solid electrolyte fuel cell system having a self-heat exchange type adiabatic prereformer of the present invention.

FIG. 2 is a diagram illustrating an operation example of a self-heat exchange type adiabatic pre-reformer.

[Explanation of symbols]

 1 Desulfurization Device 2 Fuel Flow Control Device 3 Water Pump 4 Water Vaporizer 5 Ejector 6 Recycle Gas Flow Control Valve 7 Self-heat Exchange Adiabatic Prereformer 7a Heat Exchanger Part 7b Reaction Tube Part 8 Air Blower 9 Air Preheater 10 Solid Electrolyte Type fuel cell 11 Combustor 12 Waste heat recovery machine 13 City gas pipe 14 Water pipe 15 Heating steam pipe 16 Fuel gas pipe 17 Recycle gas pipe 18 Mixed gas pipe 19 Reformed gas pipe 20 Fuel exhaust pipe 21 Exhaust air pipe 22 Low temperature recycled gas Tube 23 air tube

Claims (1)

[Claims] 1. A solid electrolyte fuel cell, a self-heat exchange type adiabatic pre-reformer filled with a reforming catalyst, and a fuel recycling line for recirculating the fuel electrode outlet gas of the fuel cell.
A self-heat exchange type adiabatic pre-reformer equipped with a supply device for city gas and steam, reforming hydrocarbons of C ₂ or higher in city gas, and having a function of easily controlling the reaction rate of methane Internal reforming type solid oxide fuel cell system having the following.