A hybrid system of solid oxide fuel cell and proton exchange membrane fuel cell using ammonia as fuel

Abstract

The present invention provides a hybrid system of a solid oxide fuel cell and a proton exchange membrane fuel cell using ammonia as fuel. The present invention includes a solid oxide cell stack module (SOFC), a proton membrane fuel cell module (PEMFC), a reforming ammonia module, a control module, and an electricity module. The ammonia reforming module cracks ammonia into nitrogen and hydrogen, and supplies them to the solid oxide fuel cell module, and then the remaining hydrogen is supplied to the proton membrane fuel cell module. The process is regulated by the control module, and the electricity module consumes the generated electricity. The present invention can combine solid oxide cells with proton exchange membrane cells, maximize the advantages of the two fuel cells, and solve the carbon emission problem. The design scheme can more efficiently utilize the respective advantages of SOFC and PEMFC, make full use of the waste heat of SOFC to efficiently reform ammonia, improve the energy conversion efficiency of ammonia to hydrogen, and can utilize the high volume energy density of PEMFC to improve the comprehensive energy density of the power generation system.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a hybrid system of a solid oxide fuel cell and a proton exchange membrane fuel cell using ammonia as fuel. Background Art

[0002] A fuel cell is an energy conversion device controlled by electrochemical principles, that is, the working principle of a primary cell, which directly converts the chemical energy stored in the fuel and oxidant into electrical energy isothermally, so that its actual process is still a quiet redox reaction. Theoretically, the reason why fuel cells have received widespread attention in the international market is that they can even achieve a thermal efficiency of nearly 100% during operation. At present, various types of fuel cells that can be used in practice are limited by factors such as hydrogen transportation, storage and transportation energy consumption, and considering the energy consumption of the device or the entire system, so the total conversion efficiency of the general fuel cell system is mostly in the range of 40% to 60%. However, if the use of heat exhaust is considered, the total conversion efficiency can be more than 80% after different optimization treatments.

[0003] Solid oxide fuel cell: Solid oxide fuel cell, referred to as SOFC, is an all-solid-state chemical power generation device that directly converts chemical energy stored in fuel and oxidant into electrical energy in an efficient and environmentally friendly manner at high temperature. It is an energy conversion device with the highest theoretical power generation efficiency among several fuel cells currently available. SOFC uses an oxide with ion conductivity as the electrolyte, and is equipped with positive and negative electrodes on both sides of the electrolyte. The anode supplies fuel and the cathode supplies oxidant. The fuel and oxidant react electrochemically at high temperature and generate electricity quietly and efficiently. In this system, the reformed ammonia is decomposed into nitrogen and hydrogen, and the oxygen ions react with hydrogen through the ion-conductive electrolyte to generate water vapor, generating electricity and heat. The thermal energy can also be collected for fuel reforming and battery startup, but most of the thermal energy is wasted.

[0004] Proton exchange membrane fuel cell: Proton exchange membrane fuel cell, referred to as PEMFC, it is composed of cathode, anode and proton exchange membrane. Its power generation principle is similar to SOFC. Its power generation process does not involve the combustion of hydrogen and oxygen, so it is not limited by the Carnot cycle. It has a high energy conversion rate. The operating temperature of the proton exchange membrane fuel cell is much lower than that of the solid oxide fuel cell. The emissions are water and water vapor, which is basically zero pollution. The power generation unit is modular, highly reliable, easy to assemble and maintain, and has no mechanical vibration, low noise and low heat radiation. It is a clean and efficient green energy, so it is a fuel cell with good development prospects. Because there is no complex fuel processing system and it directly uses high-purity hydrogen, the volume and weight energy density of PEMFC are relatively high, currently reaching 4kw / l, but the fact that it can only use high-purity hydrogen is also a limitation of PEMFC development. Summary of the invention

[0005] According to the technical problems raised above, a hybrid system of solid oxide fuel cell (SOFC) and proton exchange membrane fuel cell (PEMFC) using ammonia as fuel is provided. For SOFC, due to the high operating temperature, a lot of heat will be generated during long-term operation. Currently, this part of heat is dissipated through air cooling, resulting in a large degree of energy waste, so the use of this part of heat becomes the key; in addition, for hydrogen fuel cells, the transportation cost of hydrogen is very high, and how to reduce the cost is also a very important topic. Therefore, this system can better make up for the defects of both SOFC and PEMFC batteries, and also combine the advantages of the two, thereby improving the overall efficiency of the system. The technical means adopted by the present invention are as follows:

[0006] A hybrid system of a solid oxide fuel cell and a proton exchange membrane fuel cell using ammonia as fuel comprises: an ammonia reforming module, a solid oxide fuel cell, an air supply module, a separation gas module, a control module, an electricity module and a proton exchange membrane fuel cell, wherein the ammonia reforming module is used to prepare gas for use by the anode of the solid oxide fuel cell, the air supply module is used to supply an oxidant for use by the cathode of the solid oxide fuel cell, the separation gas module is used to separate the gas that does not participate in the reaction at the anode of the solid oxide fuel cell, the control module comprises a first control module and a second control module, the first control module is used to control the gas flow rate flowing into the PEMFC, the second control module is used to control the current and voltage passed into the load of the SOFC and the PEMFC so that the current and voltage are stably passed into the load, and the electricity module is a load, which is used to consume the current generated by the SOFC and the PEMFC.

[0007] Furthermore, it also includes a heat exchange module, the ammonia reforming module includes an ammonia supply mechanism and a reformer, one input end of the reformer is connected to the ammonia output end, and the other input end is connected to the heat exchange module, the output end of the reformer is connected to the anode of the solid oxide fuel cell, and one output end of the anode of the solid oxide fuel cell is connected to the input end of the heat exchange module, and the heat after the combustion of the remaining ammonia at the anode of the solid oxide fuel cell and the remaining air at the cathode is supplied to the air supply module through the heat exchange module.

[0008] Furthermore, it also includes a combustion module, which includes a burner, whose input end is connected to the output end of the separation gas module and the output end of the solid oxide fuel cell cathode, and whose output end is connected to the pipeline of the air supply module for heating the air entering the solid oxide fuel cell cathode.

[0009] Furthermore, the gas separation module includes a separator for separating hydrogen and ammonia, and the separator includes a pressure swing adsorption system or a metal palladium membrane purification system. The separated hydrogen then enters the PEMFC through the flow controller in the first control module to control the hydrogen flow, so as to achieve control of the output current.

[0010] Furthermore, the hydrogen separated by the gas separation module is also used to heat the oxygen at the cathode inlet of the proton exchange membrane fuel cell.

[0011] Furthermore, the current generated by the SOFC and PEMFC is regulated by the current and voltage controller in the second control module and then passed into the load to meet the current and voltage requirements of the load.

[0012] The ammonia reforming module of the present invention cracks ammonia into nitrogen and hydrogen, and supplies them to the solid oxide battery module, and then the remaining hydrogen is supplied to the proton membrane battery module. The process is regulated by the control module, and the electric module consumes the generated electricity. The present invention can combine the solid oxide battery with the proton exchange membrane battery, maximize the advantages of the two fuel cells, and solve the carbon emission problem. This design scheme can more efficiently utilize the respective advantages of SOFC and PEMFC, make full use of the waste heat of SOFC to efficiently reform ammonia, improve the energy conversion efficiency of ammonia to hydrogen, and can use the high volume energy density of PEMFC to improve the comprehensive energy density of the power generation system.

[0013] At the same time, the present invention uses the heat generated by the solid oxide fuel cell system for the reforming of ammonia, and can continue to pass the unreacted product hydrogen at the solid oxide fuel cell anode into the proton exchange membrane fuel cell, effectively making up for the insufficient power generation efficiency of a single battery. The power of the composite system can reach more than 60%, which is higher than the power of a single battery system. Combined with the high energy density of PEMFC, the available scenarios of the entire power generation system are improved, including the application fields of mobile scenarios such as vehicles and ships. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0015] Figure 1 This is a system structure diagram of the present invention.

[0016] The solid line in the figure is material flow and the dotted line is heat flow. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] The main components of a fuel cell can be seen as consisting of the following four parts according to the reaction principle: cathode, anode, external circuit and electrolyte. The anode and cathode in the fuel cell are respectively fed with the fuel gas and oxidant gas required by the system. During the reaction, according to the law of conservation of electrons, after the fuel gas passes to the anode, electrons are released on the anode, and then the electrons are conducted to the cathode through the external circuit, thereby combining with the oxygen passed into the cathode and generating ions. After the ions generated at the cathode, under the action of the electric field force, the electrolyte is used as a medium to migrate to the anode, and finally the ions react with the fuel gas, so that a loop is formed in the system and current is generated accordingly. In addition, since the fuel cell itself has an electrochemical reaction and the battery itself has a certain internal resistance, these factors will also cause the fuel cell system to generate a certain amount of heat. The cathode and anode of the fuel cell not only have the function of conducting electrons, they can also serve as catalysts for the redox reaction of the battery itself to increase the electrochemical reaction rate of the fuel and the oxidant. When the fuel entering the fuel cell is a hydrocarbon, its anode is required to have a higher catalytic activity. Porous structures are often used in the cathode and anode of fuel cells. This structural design is to facilitate the discharge of products and the introduction of reaction gases required by the system. The main function of the electrolyte is to separate the fuel gas and the oxidant gas and to transfer ions.

[0019] According to the above summary, the characteristics of fuel cells are: the chemical energy of fuel and oxidant is directly converted into electrical energy through electrochemical reaction without going through the heat engine process, so it is not limited by the Carnot cycle in the whole system reaction, so its energy conversion efficiency is very high. In addition, since the electrochemical process of the fuel cell itself will generate a certain amount of heat, and usually contains no or only a small amount of moving parts such as fans. Therefore, compared with traditional generator sets, its operation is more reliable, less maintenance, and less noise. All these factors make fuel cells recognized as a promising and optimal energy power device.

[0020] like Figure 1As shown, an embodiment of the present invention discloses a hybrid system of a solid oxide fuel cell and a proton exchange membrane fuel cell using ammonia as fuel, comprising: an ammonia reforming module, a solid oxide fuel cell, an air supply module, a separation gas module, a control module, an electricity module and a proton exchange membrane fuel cell, wherein the ammonia reforming module is used to prepare gas for use at the anode of the solid oxide fuel cell, and the air supply module is used to supply an oxidant for use at the cathode of the solid oxide fuel cell. Specifically, the air supply device passes air into the cathode of the battery through heat exchange to provide oxygen to the fuel cell system, and the separation gas module is used to separate the gas that does not participate in the reaction at the anode of the solid oxide fuel cell, and the separated high-purity hydrogen is transported to the anode of the proton exchange membrane fuel cell after cooling, and the proton exchange membrane fuel cell is used to consume the remaining gas and oxidant of the solid oxide fuel cell to generate electricity, thereby maximizing the utilization of heat and hydrogen. The control module includes a first control module and a second control module. The first control module is specifically a flow controller, which is used to control the gas flow flowing into the PEMFC. The second control module is specifically a current and voltage controller, which is used to control the current and voltage of the SOFC and PEMFC passing through the load so that the current and voltage can be stably passed through the load. The power consumption module is a load, which is used to consume the current generated by the SOFC and PEMFC.

[0021] Ammonia is a zero-carbon fuel and an excellent hydrogen carrier, with a hydrogen content of more than 17%, far exceeding liquid hydrogen. The transportation and storage costs of ammonia are much lower than those of hydrogen. Ammonia reforming produces hydrogen to supply fuel to the SOFC anode, avoiding the additional high costs of transporting and storing hydrogen. After ammonia passes through the reformer, a high-concentration mixture of hydrogen and nitrogen is produced, which is connected to the anode of the solid oxide fuel cell through a pipeline. The present invention combines the high power generation efficiency of solid oxide fuel cells, and the waste heat generated can be used for ammonia reforming to improve the overall power generation efficiency of the system. The advantage of the high energy density of low-temperature proton exchange membrane fuel cells is used to obtain a power generation system with high electrical conversion efficiency and high energy density. At the same time, combined with the advantages of the high energy density of low-temperature proton exchange membrane fuel cells, the two different types of fuel cells are given full play to their respective advantages.

[0022] In a solid oxide fuel cell, the hydrogen produced by ammonia reforming is not fully utilized, and the waste heat generated when the fuel cell generates electricity is used for ammonia reforming. To this end, a heat exchange module is also included, and the ammonia reforming module includes an ammonia supply mechanism and a reformer. One input end of the reformer is connected to the ammonia output end, and the other input end is connected to the heat exchange module. The output end of the reformer is connected to the anode of the solid oxide fuel cell, and one output end of the anode of the solid oxide fuel cell is connected to the input end of the heat exchange module. The heat exchange module is used to supply the heat after the remaining ammonia at the anode of the solid oxide fuel cell and the remaining air at the cathode is burned to the air supply module. The heat required for ammonia reforming comes from the heat generated by the high-temperature solid oxide fuel cell, which improves the overall power generation efficiency of the system. The heat exchange equipment supplies the heat after the remaining ammonia at the anode of the solid oxide fuel cell is burned with the remaining air at the cathode to the air supply module to increase the temperature of the air, thereby preventing low-temperature air from directly entering the reforming module.

[0023] It also includes a combustion module, the combustion module includes a burner, the input end of the burner is connected to the output end of the separation gas module and the output end of the solid oxide fuel cell cathode, the output end of the burner is connected to the pipeline of the air supply module, and is used to heat the air entering the solid oxide fuel cell cathode. The separation gas module includes a separator for separating hydrogen and ammonia, and the separator includes a pressure swing adsorption system (PSA) or a metal palladium membrane purification system. Based on this, the high-purity hydrogen obtained can be directly used in the proton exchange membrane fuel cell through cooling treatment, thereby improving the power generation efficiency of the system. The combustion module mixes and burns the trace ammonia remaining in the anode of the solid oxide fuel cell with the remaining air at the cathode.

[0024] The remaining solid oxide fuel cell anode tail gas will contain a trace amount of ammonia. The hydrogen separated by SOFC has a higher temperature. This heat is used to slightly heat the oxygen at the PEMFC cathode inlet, thereby preventing air with too low a temperature from directly entering the anode.

[0025] The specific process of the present invention is as follows: first, ammonia is reformed and cracked into nitrogen and hydrogen. By using zero-carbon ammonia, the goal of carbon neutrality is achieved, and the technical and cost problems caused by the storage and transportation of hydrogen are avoided. The hydrogen and nitrogen mixed gas obtained by ammonia reforming, as the fuel gas of the solid oxide fuel cell, first enters the anode of the solid oxide fuel cell, and the preheated air enters the cathode as an oxidant. The hydrogen and oxygen in the air are not in direct contact inside the battery, but undergo an electrochemical reaction through the electrolyte membrane, thereby emitting heat and producing electrical energy. The heat generated is used for ammonia reforming and decomposition. The hydrogen in the solid oxide fuel cell does not react completely, and there will be a trace amount of uncracked ammonia in the anode tail gas, so the anode residual gas is divided into two parts by a separator, one part of which is high-purity hydrogen, and the rest enters the proton exchange membrane fuel cell module after cooling for PEMFC power generation; the other part is a mixture of nitrogen and trace ammonia, which generates heat by burning with the remaining oxygen at the cathode in the combustion module, and this part of the heat is used to heat the fresh air of the air supply module.

[0026] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A hybrid system of a solid oxide fuel cell and a proton exchange membrane fuel cell using ammonia as fuel, characterized in that: include: An ammonia reforming module, a solid oxide fuel cell, an air supply module, a separation gas module, a control module, an electricity module and a proton exchange membrane fuel cell, wherein the ammonia reforming module is used to prepare gas for use by the anode of the solid oxide fuel cell, the air supply module is used to supply an oxidant for use by the cathode of the solid oxide fuel cell, the separation gas module is used to separate the gas that does not participate in the reaction at the anode of the solid oxide fuel cell, the control module includes a first control module and a second control module, the first control module is used to control the gas flow rate flowing into the proton exchange membrane fuel cell, the second control module is used to control the current and voltage of the solid oxide fuel cell and the proton exchange membrane fuel cell passed into the load so that the current and voltage are stably passed into the load, and the electricity module is a load, which is used to consume the current generated by the solid oxide fuel cell and the proton exchange membrane fuel cell; It also includes a heat exchange module, the ammonia reforming module includes an ammonia supply mechanism and a reformer, one input end of the reformer is connected to the ammonia output end, and the other input end is connected to the heat exchange module, the output end of the reformer is connected to the anode of the solid oxide fuel cell, and one output end of the anode of the solid oxide fuel cell is connected to the input end of the heat exchange module, and the heat after the combustion of the remaining ammonia of the anode of the solid oxide fuel cell and the remaining air of the cathode is supplied to the air supply module through the heat exchange module; The hydrogen separated by the gas separation module is also used to heat the oxygen at the cathode inlet of the proton exchange membrane fuel cell; The combustion module also includes a burner, the input end of the burner is connected to the output end of the separation gas module and the output end of the solid oxide fuel cell cathode, and the output end of the burner is connected to the pipeline of the air supply module for heating the air entering the solid oxide fuel cell cathode. The gas separation module includes a separator for separating hydrogen and ammonia, and the separator includes a pressure swing adsorption system or a metal palladium membrane purification system. The separated hydrogen is then controlled by a flow controller in the first control module to control the hydrogen flow, and then enters the proton exchange membrane fuel cell to achieve control of the output current; The current generated by the solid oxide fuel cell and the proton exchange membrane fuel cell is regulated by the current and voltage controller in the second control module and then passed to the load to meet the current and voltage requirements of the load; The specific process is as follows: first, ammonia is reformed and cracked into nitrogen and hydrogen. The hydrogen and nitrogen mixed gas obtained by ammonia reforming is used as the fuel gas of the solid oxide fuel cell and first enters the anode of the solid oxide fuel cell. At the same time, the preheated air enters the cathode as an oxidant. The hydrogen and oxygen in the air do not have direct contact inside the battery, and an electrochemical reaction occurs through the electrolyte membrane, thereby generating heat and producing electricity. The generated heat is used for the decomposition of ammonia reforming; The hydrogen in the solid oxide fuel cell is not completely reacted, and there will be a trace amount of un-cracked ammonia in the anode tail gas. The remaining gas at the anode is divided into two parts by a separator, one part is high-purity hydrogen, and the rest enters the proton exchange membrane fuel cell module after cooling for PEMFC power generation; the other part is a mixture of nitrogen and trace ammonia, which burns with the remaining oxygen at the cathode in the combustion module to generate heat, and this heat is used to heat the fresh air of the air supply module.

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