Ocean temperature difference energy water, electricity and hydrogen cogeneration system based on non-azeotropic working medium and membrane distillation

Abstract

The invention relates to the field of ocean energy utilization, in particular to an ocean temperature difference energy water, electricity and hydrogen cogeneration system based on a non-azeotropic working medium and membrane distillation. The system comprises a direct contact type membrane distillation module, a non-azeotropic working medium circulation module and a seawater hydrogen production module, the direct contact type membrane distillation module comprises a direct contact type membrane distillation assembly which is internally provided with a first hydrophobic breathable membrane and is divided into a feed liquid side and a fresh water side by the first hydrophobic breathable membrane, a hot seawater pump for conveying hot seawater to the feed liquid side, a fresh water tank circularly communicated with the fresh water side, and a heat exchanger positioned between the fresh water side and the fresh water tank; the seawater hydrogen production module comprises an electrolytic cell which is internally provided with a second hydrophobic breathable membrane and is divided into a seawater side and an alkali liquor side by the second hydrophobic breathable membrane, a seawater pump for conveying hot seawater to the seawater side, an oxygen separator and a hydrogen separator for separating oxygen from hydrogen, and a hydrogen treatment assembly. According to the invention, seawater is spontaneously evaporated into water vapor which is absorbed by alkali liquor, so that seawater desalination without electric energy consumption is realized, and hydrogen is prepared by using the alkali liquor.

Description

Technical Field

[0001] The present invention relates to the field of ocean energy utilization, and in particular to an ocean temperature difference energy, water-power and hydrogen cogeneration system based on non-azeotropic working fluid and membrane distillation. Background Art

[0002] When thermal methods such as multi-stage flash evaporation and multi-effect distillation are coupled with Ocean Thermal Energy Conversion (OTEC), additional energy is required to heat the seawater, and the equipment will be too large, which is not conducive to offshore applications. Reverse osmosis technology has the advantages of low equipment cost, compact device and small footprint, but it has high requirements for water quality and requires consumption of electricity for complex pretreatment.

[0003] Alkaline water electrolysis is the main way to produce hydrogen. In the process of alkaline water electrolysis, water is decomposed into hydrogen and oxygen, and hydrogen and oxygen will take away some saturated steam moisture. Therefore, the alkaline water electrolysis cycle will consume water, which will lead to excessive concentration of alkali solution, thereby reducing the efficiency of hydrogen production. Therefore, if the alkaline water electrolysis hydrogen production needs to operate stably, it is necessary to continuously add water to the cycle to ensure that the alkali solution is maintained within a certain concentration range and to ensure that the system is always within the optimal hydrogen production efficiency range.

[0004] Most existing offshore hydrogen production systems use indirect seawater hydrogen production technology, which involves first desalinating seawater to form high-purity fresh water and then producing hydrogen. However, the cost of desalination equipment is high and requires additional electricity consumption. Summary of the invention

[0005] The purpose of the present invention is to address the problems existing in the background technology and propose an ocean temperature difference energy hydropower hydrogen cogeneration system based on non-azeotropic working fluid and membrane distillation, so that seawater can evaporate spontaneously into water vapor and be absorbed by alkaline solution, thereby realizing seawater desalination without electricity consumption, and then using the alkaline solution to produce hydrogen.

[0006] The technical solution of the present invention is an ocean temperature difference energy, hydropower and hydrogen cogeneration system based on non-azeotropic working fluid and membrane distillation, including a direct contact membrane distillation module, a non-azeotropic working fluid circulation module and a seawater hydrogen production module; the direct contact membrane distillation module includes a direct contact membrane distillation component with a built-in first hydrophobic breathable membrane and a feed liquid side and a fresh water side separated by the first hydrophobic breathable membrane, a hot seawater pump that transports hot seawater to the feed liquid side, a fresh water tank that is circulated and connected to the fresh water side, and a heat exchanger located between the fresh water side and the fresh water tank, part of the water on the feed liquid side evaporates into water vapor and enters the fresh water side through the first hydrophobic breathable membrane to condense into fresh water, and the heat exchanger is cooled to maintain the temperature required for condensation of water vapor in the direct contact membrane distillation component; the non-azeotropic working fluid circulation module includes a circulating working fluid The hot seawater flowing out from the feed liquid side is heat exchanged through the evaporator, and the saturated steam of the working medium generated is expanded in the turbine to do work, thereby driving the generator to generate electricity; the seawater hydrogen production module includes an electrolyzer with a built-in second hydrophobic breathable membrane and separated into a seawater side and an alkali solution side by the second hydrophobic breathable membrane, a seawater pump for conveying hot seawater to the seawater side, an oxygen separator and a hydrogen separator for separating oxygen and hydrogen generated by electrolysis of the alkali solution on the alkali solution side, and a hydrogen processing component for processing the hydrogen output by the hydrogen separator; there is a saturated steam pressure difference on both sides of the second hydrophobic breathable membrane, and the seawater on the seawater side evaporates spontaneously into water vapor, passes through the second hydrophobic breathable membrane and is absorbed by the alkali solution on the alkali solution side.

[0007] Preferably, the evaporator heats the working fluid flowing in the non-azeotropic working fluid circulation module and evaporates it into saturated working fluid steam. The saturated working fluid steam flows into the turbine to expand and do work, driving the generator to generate electricity. The exhaust steam after cooling and pressure reduction enters the condenser, exchanges heat with the cold seawater coming out of the heat exchanger, is condensed into liquid and flows to the working fluid pump for the next cycle.

[0008] Preferably, the cold seawater flowing out of the condenser exchanges heat on the alkali solution side through a pipeline to increase the saturated steam pressure difference on both sides of the second hydrophobic breathable membrane, and the hot seawater flowing out of the evaporator and the cold seawater after heat exchange on the alkali solution side of the electrolyzer are mixed and discharged.

[0009] Preferably, the direct contact membrane distillation module further comprises a cold seawater pump for delivering cold seawater to the heat exchanger.

[0010] Preferably, when the exhaust steam after cooling and pressure reduction enters the condenser, if the cold seawater from the heat exchanger is insufficient, the cold seawater is directly added to the condenser through the cold seawater pump according to demand.

[0011] Preferably, the remaining alkali liquid except the alkali liquid from which oxygen and hydrogen are separated by electrolysis is returned to the alkali liquid side of the electrolytic cell through an alkali liquid circulation pump to participate in the circulation again.

[0012] Preferably, the hydrogen processing assembly comprises a hydrogen cooler, a hydrogen dryer, a hydrogen compressor and a solid hydrogen storage tank which are connected in sequence, and the input end of the hydrogen cooler is connected to the output end of the hydrogen separator.

[0013] Compared with the prior art, the present invention has the following beneficial technical effects:

[0014] The present invention can make seawater evaporate spontaneously into water vapor and be absorbed by alkali solution, thus realizing seawater desalination without electricity consumption. The alkali solution is maintained within the required concentration range by continuously replenishing water, so that the alkaline water electrolysis hydrogen production process can operate stably, ensuring that the system is always within the optimal hydrogen production efficiency range, and then the alkali solution is used to produce hydrogen. In the entire hydropower hydrogen cogeneration system, in addition to hydrogen, fresh water and electricity can also be produced. This hydropower hydrogen cogeneration system does not require additional power supply and is particularly suitable for applications such as offshore and isolated islands. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of the system structure of an embodiment of the present invention;

[0016] Figure 2 A schematic diagram of the parallel connection of multiple sets of plate membrane distillation components that make up the seawater desalination module.

[0017] Figure numerals: 1. hot seawater pump; 2. direct contact membrane distillation component; 3. heat exchanger; 4. fresh water tank; 5. cold seawater pump; 6. evaporator; 7. turbine; 8. generator; 9. condenser; 10. working fluid pump; 11. seawater pump; 12. electrolyzer; 13. oxygen separator; 14. hydrogen separator; 15. alkali solution circulation pump; 16. hydrogen cooler; 17. hydrogen dryer; 18. hydrogen compressor; 19. solid hydrogen storage tank. DETAILED DESCRIPTION

[0018] like Figure 1 and Figure 2 As shown, the ocean temperature difference energy, hydropower and hydrogen cogeneration system based on non-azeotropic working fluid and membrane distillation proposed in this embodiment includes a direct contact membrane distillation module, a non-azeotropic working fluid circulation module and a seawater hydrogen production module. The direct contact membrane distillation module can desalinate seawater to produce fresh water, the non-azeotropic working fluid circulation module can be used for power generation, and the seawater hydrogen production module is used for hydrogen production.

[0019] The direct contact membrane distillation module includes a direct contact membrane distillation component 2 with a built-in first hydrophobic breathable membrane and separated by the first hydrophobic breathable membrane into a feed liquid side and a fresh water side, a hot seawater pump 1 for conveying hot seawater to the feed liquid side, a fresh water tank 4 in circulation communication with the fresh water side, a heat exchanger 3 located between the fresh water side and the fresh water tank 4, and a cold seawater pump 5 for conveying cold seawater to the heat exchanger 3. Part of the water on the feed liquid side evaporates into water vapor and enters the fresh water side through the first hydrophobic breathable membrane to condense into fresh water, and the fresh water side uses circulating fresh water. The heat exchanger 3 cools and maintains the temperature required for the condensation of water vapor in the direct contact membrane distillation component 2, and the mass flow rate of the circulating fresh water remains constant. The first hydrophobic breathable membrane is a part of the plate membrane distillation component, and multiple sets of plate membrane distillation components connected in parallel constitute a seawater desalination module. The fresh water produced by membrane distillation is stored in the fresh water tank 4, which is one of the outputs of the ocean temperature difference energy, water, electricity and hydrogen cogeneration system.

[0020] The non-azeotropic working medium circulation module includes a working medium pump 10, an evaporator 6, a turbine 7 and a condenser 9 in a cyclic connection, and a generator 8 connected to the turbine 7. The hot seawater flowing out from the feed liquid side passes through the evaporator 6 for heat exchange. The evaporator 6 heats the working medium flowing in the non-azeotropic working medium circulation module and evaporates it into saturated steam of the working medium. The saturated steam of the working medium flows into the turbine 7 to expand and do work, driving the generator 8 to generate electricity. After the saturated steam of the working medium does work, it is cooled and depressurized. The exhaust steam after cooling and depressurization enters the condenser 9, exchanges heat with the cold seawater coming out of the heat exchanger 3, is condensed into liquid and flows to the working medium pump 10 for the next cycle, that is, the liquid working medium is transported to the evaporator 6 for heating and evaporation through the working medium pump 10, and the above process is continued to circulate, thereby realizing continuous power generation of the generator 8. When the exhaust steam after cooling and depressurization enters the condenser 9, if the cold seawater coming out of the heat exchanger 3 is insufficient, the cold seawater is directly added to the condenser 9 through the cold seawater pump 5 according to demand.

[0021] The seawater hydrogen production module includes an electrolytic cell 12 with a second hydrophobic breathable membrane built in and separated into a seawater side and an alkali solution side by the second hydrophobic breathable membrane, a seawater pump 11 for transporting hot seawater to the seawater side, an oxygen separator 13 and a hydrogen separator 14 for separating oxygen and hydrogen produced by electrolysis of the alkali solution in the alkali solution side, and a hydrogen processing component for processing the hydrogen output by the hydrogen separator 14. The second hydrophobic breathable membrane is part of a plate membrane distillation component, and a plurality of parallel connected plate membrane distillation components constitute a seawater desalination module. One side of the second hydrophobic breathable membrane is seawater, and the other side is a 35% KOH solution for electrolytic hydrogen production. Seawater flows in from the inlet on the seawater side of the second hydrophobic breathable membrane and flows out from the outlet. A seawater filter is provided at the inlet on the seawater side. During this period, the vapor pressure of the seawater is greater than the vapor pressure of the alkali solution, so that the water vapor generated by the seawater on the seawater side enters the alkali solution side from the hydrophobic breathable membrane. The cold seawater flowing out of the condenser 9 exchanges heat on the alkali liquid side through the pipeline, so that the temperature of the alkali liquid side is reduced, the saturated steam pressure difference on both sides of the second hydrophobic breathable membrane is increased, and the seawater desalination capacity is improved. The seawater on the seawater side evaporates spontaneously into water vapor, passes through the second hydrophobic breathable membrane and is absorbed by the alkali liquid on the alkali liquid side to ensure that the alkali liquid is maintained within the required concentration range.

[0022] The remaining alkali liquid except the alkali liquid from which oxygen and hydrogen are separated by electrolysis is returned to the alkali liquid side of the electrolytic cell 12 through the alkali liquid circulation pump 15 to participate in the circulation again.

[0023] The hydrogen processing assembly includes a hydrogen cooler 16, a hydrogen dryer 17, a hydrogen compressor 18 and a solid hydrogen storage tank 19 which are connected in sequence, and the input end of the hydrogen cooler 16 is connected to the output end of the hydrogen separator 14. The hydrogen output from the hydrogen separator 14 is cooled, dried, compressed and stored in sequence through the hydrogen cooler 16, the hydrogen dryer 17, the hydrogen compressor 18 and the solid hydrogen storage tank 19.

[0024] The hot seawater flowing out of the evaporator 6 and the cold seawater after heat exchange on the alkali side of the electrolytic cell 12 are mixed and discharged directly to the ocean surface. There are many benefits to discharging deep seawater to the surface. The deep seawater is rich in nutrients, cold and pure, which can promote the growth of marine organisms such as oysters, lobsters, large algae and microalgae, and improve the economic benefits of aquaculture. In addition, discharging seawater below normal temperature to the surface can also help reduce the surface temperature of the ocean and help mitigate the greenhouse effect.

[0025] This system has the following advantages:

[0026] 1. This system is suitable for ocean temperature difference energy. The pumping work of cold seawater pumped up by ocean temperature difference energy generation accounts for the vast majority of the total pumping work. This system does not directly discharge the cold seawater, but further utilizes its temperature difference, which is more energy-efficient.

[0027] 2. In the seawater hydrogen production module, the concentration difference between the seawater side and the alkali liquid side will generate a driving force. The seawater side is hot seawater extracted from the seawater surface, and the alkali liquid side exchanges heat with cold seawater after power generation. The temperature difference between the seawater side and the alkali liquid side will generate a second driving force. These two driving forces will cause the seawater in the seawater side to spontaneously evaporate into water vapor and pass through the second hydrophobic breathable membrane into the alkali liquid side.

[0028] 3. The existing membrane distillation technology does not consider how to condense water vapor on the alkali liquid side, because condensation requires heat release, which requires a continuous supply of cold to take it away. The heat exchange between the cold seawater and the alkali liquid side of this system not only provides a pressure difference, but also takes away the heat of the condensed water vapor on the alkali liquid side, ensuring the stable operation of the system.

[0029] This embodiment can make seawater evaporate spontaneously into water vapor and be absorbed by alkali solution, thus realizing seawater desalination without electricity consumption, with low cost, and by continuously replenishing water to ensure that the alkali solution is maintained within the required concentration range, so that the alkaline water electrolysis hydrogen production process can operate stably, ensuring that the system is always within the optimal hydrogen production efficiency range, and then using the alkali solution to produce hydrogen, and the hydrogen is cooled, dried, compressed and stored in turn. In the entire hydropower hydrogen cogeneration system, in addition to hydrogen, fresh water and electricity can also be produced. This hydropower hydrogen cogeneration system does not require additional power supply and is particularly suitable for applications such as offshore and isolated islands.

[0030] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited thereto, and various changes can be made within the knowledge scope of technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. Ocean temperature difference energy, hydropower and hydrogen cogeneration system based on non-azeotropic working fluid and membrane distillation, characterized in that: include: A direct contact membrane distillation module, comprising a direct contact membrane distillation component (2) having a first hydrophobic breathable membrane built therein and a feed liquid side and a fresh water side separated by the first hydrophobic breathable membrane, a hot seawater pump (1) for conveying hot seawater to the feed liquid side, a fresh water tank (4) in circulation communication with the fresh water side, and a heat exchanger (3) located between the fresh water side and the fresh water tank (4), wherein part of the water on the feed liquid side evaporates into water vapor and enters the fresh water side through the first hydrophobic breathable membrane and condenses into fresh water; A non-azeotropic working medium circulation module comprises a working medium pump (10), an evaporator (6), a turbine (7) and a condenser (9) which are circulated and connected, and a generator (8) connected to the turbine (7); hot seawater flowing out from the feed liquid side is heat exchanged through the evaporator (6), and the generated working medium saturated steam expands in the turbine (7) to do work, thereby driving the generator (8) to generate electricity; A seawater hydrogen production module comprises an electrolytic cell (12) having a second hydrophobic breathable membrane built therein and separated into a seawater side and an alkaline solution side by the second hydrophobic breathable membrane, a seawater pump (11) for conveying hot seawater to the seawater side, an oxygen separator (13) and a hydrogen separator (14) for separating oxygen and hydrogen generated by electrolysis of alkaline solution on the alkaline solution side, and a hydrogen processing component for processing hydrogen output by the hydrogen separator (14); a saturated vapor pressure difference exists on both sides of the second hydrophobic breathable membrane, and the seawater on the seawater side evaporates spontaneously into water vapor, passes through the second hydrophobic breathable membrane and is absorbed by the alkaline solution on the alkaline solution side.

2. The ocean temperature difference energy, water, electricity and hydrogen cogeneration system based on non-azeotropic working fluid and membrane distillation according to claim 1 is characterized in that: The evaporator (6) heats the working fluid flowing in the non-azeotropic working fluid circulation module and evaporates it into working fluid saturated steam. The working fluid saturated steam flows into the turbine (7) to expand and perform work, thereby driving the generator (8) to generate electricity. The exhaust steam after being cooled and reduced in pressure enters the condenser (9), exchanges heat with the cold seawater from the heat exchanger (3), is condensed into liquid, and flows to the working fluid pump (10) for the next cycle.

3. The ocean temperature difference energy, water, electricity and hydrogen cogeneration system based on non-azeotropic working fluid and membrane distillation according to claim 2 is characterized in that: The cold seawater flowing out of the condenser (9) exchanges heat on the alkali liquid side through a pipeline, thereby increasing the saturated steam pressure difference on both sides of the second hydrophobic breathable membrane. The hot seawater flowing out of the evaporator (6) and the cold seawater after heat exchange on the alkali liquid side of the electrolytic cell (12) are mixed and then discharged.

4. The ocean temperature difference energy, water, electricity and hydrogen cogeneration system based on non-azeotropic working fluid and membrane distillation according to claim 1 is characterized in that: The direct contact membrane distillation module also includes a cold seawater pump (5) for conveying cold seawater to the heat exchanger (3).

5. The ocean temperature difference energy, water, electricity and hydrogen cogeneration system based on non-azeotropic working fluid and membrane distillation according to claim 4 is characterized in that: When the exhaust steam after cooling and pressure reduction enters the condenser (9), if the cold seawater from the heat exchanger (3) is insufficient, the cold seawater is directly supplied to the condenser (9) through the cold seawater pump (5) according to demand.

6. The ocean temperature difference energy, water, electricity and hydrogen cogeneration system based on non-azeotropic working fluid and membrane distillation according to claim 1 is characterized in that: The remaining alkali liquid except the alkali liquid from which oxygen and hydrogen are separated by electrolysis is returned to the alkali liquid side of the electrolytic cell (12) through the alkali liquid circulation pump (15) to participate in the circulation again.

7. The ocean temperature difference energy, water, electricity and hydrogen cogeneration system based on non-azeotropic working fluid and membrane distillation according to claim 1 is characterized in that: The hydrogen processing component comprises a hydrogen cooler (16), a hydrogen dryer (17), a hydrogen compressor (18) and a solid hydrogen storage tank (19) which are connected in sequence, and the input end of the hydrogen cooler (16) is connected to the output end of the hydrogen separator (14).

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