System for gradient utilization of waste heat of SOFC, and operation method therefor

Abstract

Disclosed in the present invention are a system for gradient utilization of waste heat of an SOFC, and an operation method therefor. The system comprises an SOFC, a tail-gas burner, a thermoelectric generator device, an air flow path, a fuel flow path, and a tail-gas waste heat flow path; the air flow path is used for pressurizing and preheating fresh air and then feeding same into the SOFC for electrochemical reaction with fuel; the fuel flow path is used for pressurizing and preheating the fuel and then feeding same into the SOFC for electrochemical reaction with oxygen ions in the air; and the tail-gas waste heat flow path is used for feeding residual hydrogen from an anode of the SOFC and residual air from a cathode of the SOFC into the tail-gas burner for burning, and then converting heat energy into electric energy, cooling residual tail gas to a safe temperature and then discharging same, enabling cooling water to flow through a tail-gas condensation device to heat same therein to a safe temperature, and then delivering the heated cooling water to a heat storage device through a pipe to supply heat to a user. In the present invention, energy in high-temperature tail-gas of an SOFC is recovered by means of a thermoelectric generator device, and is converted into system electric energy to be output, ensuring that the structure and needed installation space of a system do not need to be greatly changed.

Description

A SOFC waste heat cascade utilization system and a method for operating the same TECHNICAL FIELD

[0001] The present application belongs to the field of solid oxide fuel cells, and particularly relates to a SOFC waste heat cascade utilization system and a method for operating the same. BACKGROUND

[0002] As a kind of advanced fuel cell technology, solid oxide fuel cell (SOFC) can efficiently convert chemical energy in fuel into electrical energy at high temperature (500-1000 DEG C), and has the advantages of high power generation efficiency, environmental protection, strong fuel adaptability, no electrolyte corrosion danger and flexible capacity, and is considered as a new choice for efficient energy utilization.

[0003] The exhaust gas of a solid oxide fuel cell (SOFC) power generation system has a high temperature, and if directly discharged into the environment, a large amount of energy will be lost. In order to make full use of the high-temperature exhaust gas of the solid oxide fuel cell power generation system, many waste heat recovery methods and technical means have been proposed. However, for the solid oxide fuel cell power generation system, many application scenarios have limited installation space, and the traditional waste heat recovery devices and technologies often require a large equipment installation space, and therefore cannot adapt to such scenarios. The thermoelectric generator is a device for directly converting heat energy into electrical energy, and has the advantages of small size, flexible installation scale, full solid state and no moving parts, and is very suitable for the requirements of solid oxide fuel cell waste heat recovery.

[0004] The use of a thermoelectric generator (TEG) to recover energy from the exhaust gas of a solid oxide fuel cell (SOFC) can improve the system efficiency. However, part of the heat of the high-temperature exhaust gas of the solid oxide fuel cell is used to heat the air and fuel required for its own operation, and the other part is used to drive the thermoelectric generator, which makes the energy coupling effect of the solid oxide fuel cell waste heat recovery system strong. Moreover, the current thermoelectric generator has a low thermoelectric conversion efficiency, and more than 80% of the energy absorbed by the hot side of the thermoelectric generator is conducted to the cold side, which is taken away by the cooling medium of the cold side, and has a great impact on the working state of the SOFC itself. SUMMARY

[0005] The present application aims to overcome the defects of the prior art, and provides a SOFC waste heat cascade utilization system and a method for operating the same, which can efficiently utilize the energy of the high-temperature exhaust gas of the SOFC, recover the energy in the high-temperature exhaust gas of the SOFC by using a thermoelectric generator, convert it into system electrical energy output, and at the same time ensure that the system structure and required installation space do not need to be greatly changed.

[0006] A SOFC waste heat cascade utilization system, comprising a solid oxide fuel cell (hereinafter referred to as SOFC), a tail gas burner, and a thermoelectric generator; the system further comprises:

[0007] An air flow path for fresh air to enter the SOFC to react with fuel after being pressurized and preheated; comprising an air compression device, a cold side of the thermoelectric generator, an air preheating device inlet, and a SOFC cathode inlet connected in sequence;

[0008] A fuel flow path for fuel to enter the SOFC to react with oxygen ions in the air after being pressurized and preheated; comprising a fuel compression device, a fuel preheating device inlet, and a SOFC anode inlet connected in sequence;

[0009] A tail gas waste heat flow path: the remaining hydrogen from the SOFC anode and the remaining air from the cathode enter the tail gas burner to burn, heat the fuel at room temperature, convert thermal energy into electrical energy, and the remaining tail gas is cooled and discharged; the cooling water flows through the tail gas condensing device, is heated to a safe temperature therein, and is then transported to the heat storage device through a pipeline for user heating; comprising a tail gas burner, a fuel preheating device, a hot side of the thermoelectric generator, an air preheating device, and a tail gas condensing device connected in sequence;

[0010] The SOFC is used for the electrochemical reaction of fuel entering the anode and air entering the cathode to generate electricity; the cold side of the thermoelectric generator uses fresh air as a cold source and high-temperature tail gas from the tail gas burner as a heat source, a part of the heat source is partially converted into electrical energy by the thermoelectric effect, and the remaining heat source is used for the initial heating of fresh air; the tail gas burner is used for burning the remaining hydrogen from the SOFC anode and the remaining air from the cathode.

[0011] Further, the fuel of the system is selected from one of the following: hydrogen, natural gas, ammonia, and methane.

[0012] Further, the temperature of the tail gas at the outlet of the tail gas burner is 900-1200℃.

[0013] Further, the pressure of the fuel compression device is 1-5bar, and the pressure of the air compression device is 2-10bar.

[0014] Further, the air preheating device is used to preheat the air to 650-900℃.

[0015] Further, the tail gas condensing device is used to heat the cooling water to 60-80℃ by high-temperature tail gas for user heating, the first outlet of the tail gas condensing device is connected to the user heat storage device, and the tail gas outlet of the tail gas condensing device is connected to the outside for exhaust gas discharge.

[0016] Further, the tail gas condensing device is a tail gas heat exchanger.

[0017] The operation method of the SOFC waste heat cascade utilization system comprises the following steps:

[0018] The fuel from the fuel supply device enters the fuel compression device to be pressurized to 1-5 bar, and the compressed fuel enters the fuel preheating device to be preheated to 700-1000 DEG C and then enters the SOFC through the SOFC anode inlet;

[0019] At the same time, fresh air enters the air compression device to be pressurized to 2-10 bar, and the compressed air enters the cold side of the thermoelectric power generation device and the air preheating device in sequence, is preheated to a preset temperature in the air preheating device, and then enters the SOFC through the SOFC cathode inlet;

[0020] Part of the oxygen in the SOFC anode is reduced to oxygen ions by accepting electrons from an external load circuit in the SOFC cathode, and the oxygen ions reach the anode through each layer of the electrolyte to react with the fuel in an electrochemical reaction;

[0021] The hydrogen gas that is not reacted in the SOFC anode and the air remaining in the cathode enter the tail gas combustor to react in a combustion reaction, and tail gas at 900-1200 DEG C is discharged; then the tail gas heats normal-temperature fuel through the fuel preheating device, and then enters the hot side of the thermoelectric power generation device, and part of the heat energy is converted into electric energy under the action of the temperature difference between the air in the cold side of the thermoelectric power generation device, and then the normal-temperature air is heated through the air preheating device, and then enters the tail gas condensing device to be cooled to below 150 DEG C and discharged to the outside of the system;

[0022] The cooling water flows through the tail gas condensing device, is heated to a safe temperature in the tail gas condensing device, and is then delivered to the heat storage device through a pipeline for user heating.

[0023] Further, the safe temperature is 60-80 DEG C.

[0024] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0025] The SOFC waste heat recovery system of the present application recovers the high-temperature waste heat of the SOFC by using the thermoelectric power generation device, the system operation is reliable, the power generation efficiency and output performance of the system can be effectively improved, and energy saving and high-efficiency utilization of energy can be realized.

[0026] The thermoelectric power generation device works at a relatively high temperature, and the thermoelectric conversion efficiency is relatively high, so that more heat energy in the tail gas is converted into electric energy.

[0027] Meanwhile, the cold side of the thermoelectric generator uses fresh air as a cold source and high-temperature exhaust gas as a heat source, and under the action of the temperature difference between the high-temperature exhaust gas and the fresh air, the heat energy in the exhaust gas is partially converted into electric energy, and the remaining energy is used for the initial heating of the fresh air. BRIEF DESCRIPTION OF DRAWINGS

[0028] Fig. 1 is a schematic diagram of the SOFC waste heat cascade utilization system described in the present application.

[0029] In the figure: AC-air compression device, FC-fuel compression device, AP-air preheating device, FP-fuel preheating device, SOFC-solid oxide fuel cell, AB-exhaust gas burner, TEG-thermoelectric generator, WP-cooling water supply device, HEX-exhaust gas heat exchanger, 11: water pump. DETAILED DESCRIPTION

[0030] The technical solutions of the present application will be further described in detail below in combination with the drawings and specific examples, and the specific examples described are only used to explain and illustrate the present application, and do not limit the present application.

[0031] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0032] As shown in Fig. 1, a SOFC waste heat cascade utilization system includes a solid oxide fuel cell SOFC, an exhaust gas burner AB, a thermoelectric generator TEG, an air compression device AC, an exhaust gas heat exchanger HEX and a fuel supply unit. The exhaust gas burner AB, the fuel preheating device FP, the hot side of the thermoelectric generator TEG, the air preheating device AP and the exhaust gas heat exchanger HEX are connected in series to realize the cascade utilization and cooling of high-temperature exhaust gas.

[0033] The SOFC can generate electricity and has a SOFC anode, a SOFC cathode and an electrolyte, and the air and anode fuel of the SOFC cathode undergoes an electrochemical reaction inside the solid oxide fuel cell to convert the chemical energy of the fuel into electric energy;

[0034] The SOFC anode inlet is connected to the fuel preheating device FP to receive preheated fuel; the SOFC cathode and anode are connected to a DC-AC converter; the SOFC cathode inlet is connected to the air preheating device AP to receive preheated air; the SOFC anode and cathode outlets are both connected to the exhaust burner AB to deliver high-temperature air at 700-1000°C to the exhaust burner AB.

[0035] The DC-AC converter is connected to the SOFC cathode and anode to generate AC power output.

[0036] The exhaust burner AB inlet is connected to the SOFC anode and cathode outlets, and the exhaust burner AB outlet is connected to the fuel preheating device FP by a pipeline to provide high-temperature exhaust gas at 900-1200°C to the fuel preheating device FP.

[0037] The fuel preheating device FP inlet is connected to the fuel compression device FC outlet and the exhaust burner AB outlet, respectively, to heat the fuel from the fuel compression device FC to 700-1000°C by the high-temperature exhaust gas from the exhaust burner AB. The fuel preheating device FP outlet is connected to the TEG hot side and the SOFC anode inlet, respectively, and the TEG hot side outlet is connected to the air preheating device AP inlet. The TEG hot side is used to receive exhaust gas energy from the fuel preheating device and convert part of the thermal energy into electrical energy.

[0038] The fuel compression device FC inlet is connected to an external fuel supply device, and the fuel in the fuel supply device is selected from hydrogen, natural gas, ammonia, methane, etc. The fuel compression device FC outlet is connected to the fuel compression device FC, which is used to compress the fuel to 1-5 bar.

[0039] The air compression device AC inlet is connected to ambient air, and its outlet is connected to the TEG cold side to pressurize the air to 2-10 bar.

[0040] The air preheating device AP inlet is connected to the TEG cold side and the TEG hot side, respectively, and its outlet is connected to the SOFC cathode inlet and the exhaust heat exchanger HEX, respectively. The air preheating device AP is used to preheat the air to 650-900°C.

[0041] The inlet of the exhaust heat exchanger HEX is connected to the outlet of the air preheating device AP and the cooling water from the water pump 11 respectively, the first outlet of the exhaust heat exchanger HEX is connected to the user heat storage device for heating the cooling water to 60-80℃ and then supplying heat to the user, and the exhaust outlet of the exhaust heat exchanger HEX is connected to the outside for discharging the exhaust gas from the air preheating device AP.

[0042] The working process of the SOFC waste heat cascade utilization system is as follows:

[0043] The fuel at ambient temperature and state is compressed to 1-5bar in the fuel compression device FC, and then enters the fuel preheating device FP, where the fuel is heated to 700-1000℃ and enters the SOFC through the SOFC anode inlet to participate in the electrochemical reaction;

[0044] At the same time, the air is first pressurized to 2-10bar in the air compression device AC at ambient temperature and pressure, and then enters the cold side of the thermoelectric generator TEG and the air preheating device AP in sequence, absorbs heat from the TEG conduction in the thermoelectric generator TEG, and is heated to 650-900℃ in the air preheating device AP before entering the SOFC cathode inlet; part of the oxygen in the heated air is reduced to oxygen ions by accepting electrons from the external load circuit at the SOFC cathode, and the oxygen ions pass through the electrolyte layers to the anode to react with the fuel electrochemically;

[0045] The unreacted hydrogen gas at the SOFC anode and the remaining air at the cathode enter the exhaust burner AB to undergo a combustion reaction, and then the high-temperature exhaust gas is discharged through the exhaust burner outlet, with a temperature as high as 900-1200℃; the discharged high-temperature exhaust gas heats the normal-temperature fuel in the fuel preheating device FP, and then enters the hot side of the TEG, where part of the heat energy is converted into electrical energy under the temperature difference formed by the air at the cold side of the TEG, and then the normal-temperature air is heated in the air preheating device AP before entering the exhaust heat exchanger HEX and being cooled to below 150℃ before being discharged to the outside of the system;

[0046] The cooling water is heated to a safe temperature (i.e. 60-80℃) in the exhaust heat exchanger and then delivered to the heat storage device through a pipeline for user heating.

Claims

1. A SOFC waste heat cascade utilization system, characterized in that, The system comprises a solid oxide fuel cell (SOFC), an exhaust burner (AB), and a thermoelectric generator (TEG); the system further comprises: an air flow path for fresh air to enter the SOFC to react with fuel in an electrochemical reaction after being pressurized and preheated; the air flow path comprises, in sequence, an air compressor (AC), a cold side of the thermoelectric generator (TEG), an air preheater (AP) inlet, and a SOFC cathode inlet; a fuel flow path for fuel to enter the SOFC to react with oxygen ions in air in an electrochemical reaction after being pressurized and preheated; the fuel flow path comprises, in sequence, a fuel compressor (FC), a fuel preheater (FP) inlet, and a SOFC anode inlet; an exhaust waste heat flow path: remaining hydrogen from the SOFC anode and remaining air from the SOFC cathode enter the exhaust burner (AB) to be combusted, heating fuel at room temperature and converting thermal energy into electrical energy, and the remaining exhaust is cooled and discharged; cooling water flows through an exhaust condenser, is heated to a safe temperature in the exhaust condenser, and is then delivered to a heat storage device through a pipeline for heating users; the exhaust waste heat flow path comprises, in sequence, the exhaust burner (AB), the fuel preheater (FP), a hot side of the thermoelectric generator (TEG), the air preheater (AP), and the exhaust condenser; the SOFC is used for the electrochemical reaction of fuel entering the anode and air entering the cathode to generate electricity; the cold side of the thermoelectric generator (TEG) uses fresh air as a cold source and high-temperature exhaust from the exhaust burner as a heat source, a portion of the heat source is converted into electrical energy by the thermoelectric generator (TEG) under the action of a temperature difference, and the remaining heat source is used for the initial heating of fresh air; the exhaust burner (AB) is used for combusting remaining hydrogen from the SOFC anode and remaining air from the SOFC cathode.

2. The SOFC waste heat cascade utilization system according to claim 1, characterized in that, The fuel of the system is selected from one of the following: hydrogen, natural gas, ammonia, and methane.

3. The SOFC waste heat cascade utilization system of claim 1, wherein, The exhaust temperature at the outlet of the exhaust burner (AB) is 900-1200℃.

4. The SOFC waste heat cascade utilization system of claim 1, wherein, The pressure of the fuel compressor (FC) is 1-5 bar, and the pressure of the air compressor (AC) is 2-10 bar.

5. The SOFC waste heat cascade utilization system of claim 1, wherein, The air preheater (AP) is used for preheating air to 650-900℃.

6. The SOFC waste heat cascade utilization system of claim 1, wherein, The exhaust condenser is used for heating cooling water to 60-80℃ by high-temperature exhaust for heating users, a first outlet of the exhaust condenser is connected to a user heat storage device, and an exhaust outlet of the exhaust condenser is connected to the outside for discharging exhaust.

7. The SOFC waste heat cascade utilization system of claim 1, wherein, The exhaust condenser is an exhaust heat exchanger (HEX).

8. A method for operating the SOFC waste heat cascade utilization system according to any one of claims 1-7, comprising: fuel from a fuel supply device is pressurized to 1-5 bar by the fuel compressor (FC), and the compressed fuel is preheated to 700-1000℃ by the fuel preheater (FP) before entering the SOFC through the SOFC anode inlet; At the same time, fresh air enters air compression device (AC) to be pressurized to 2-10 bar, and the compressed air enters the cold side of the thermoelectric generator (TEG) and the air preheating device (AP) in turn, and after being preheated to a preset temperature in the air preheating device (AP), enters the SOFC through the SOFC cathode inlet; Part of the oxygen from the SOFC anode is reduced to oxygen ions by receiving electrons from an external load circuit in the SOFC cathode, and the oxygen ions reach the anode through the electrolyte layers to react electrochemically with the fuel; The hydrogen gas that is not reacted in the SOFC anode and the air remaining in the cathode enter the exhaust burner (AB) to undergo a combustion reaction, and exhaust gas at 900-1200℃ is discharged; the exhaust gas then passes through the fuel preheating device (FP) to heat the normal-temperature fuel, and then enters the hot side of the thermoelectric generator (TEG), where part of the heat energy is converted into electrical energy under the action of the temperature difference between the hot side and the cold side of the thermoelectric generator (TEG), and then the normal-temperature air is heated by the air preheating device (AP) before entering the exhaust condensing device to be cooled to below 150℃ and discharged to the outside of the system; The cooling water flows through the exhaust condensing device, is heated to a safe temperature in the exhaust condensing device, and is then transported to the heat storage device through a pipeline for user heating.

9. The method of operating of claim 8, wherein, The safe temperature is 60-80℃.

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