Salt-containing wastewater hydrogen production system coupled with membrane evaporation and utilizing electrolysis waste heat

Abstract

The invention relates to the technical field of wastewater treatment, and discloses a salt-containing wastewater hydrogen production system coupled with membrane evaporation and utilizing electrolysis waste heat, which comprises an electrolysis hydrogen production unit, a membrane evaporation unit and a heat exchange unit, an electrolyte outlet of the electrolytic hydrogen production unit is communicated with an electrolyte inlet of the heat exchange unit, and electrolyte in the electrolytic hydrogen production unit enters the heat exchange unit and exchanges heat with salt-containing wastewater in the heat exchange unit; an electrolyte inlet of the electrolytic hydrogen production unit is communicated with an electrolyte outlet of the heat exchange unit, and cooled electrolyte flows back to the electrolytic hydrogen production unit; a salt-containing wastewater outlet of the heat exchange unit is communicated with an inlet of the membrane evaporation unit, the salt-containing wastewater after heat exchange enters the membrane evaporation unit to prepare water vapor, and the water vapor is cooled to obtain fresh water to provide a fresh water raw material for the electrolytic hydrogen production unit. By coupling electrolytic hydrogen production and membrane evaporation technologies, multiple targets of recycling electrolytic waste heat and salt-containing wastewater, wastewater treatment and hydrogen energy preparation are achieved, and a green circulating process with higher energy and resource utilization efficiency is formed.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a system for producing hydrogen from saline wastewater by coupling membrane evaporation and utilizing waste heat from electrolysis. Background Art

[0002] Saline wastewater contains high concentrations of soluble salts (such as sodium chloride, sodium sulfate, potassium chloride, etc.) and is widely used in many industries, including chemical, printing and dyeing, pharmaceutical, food processing, seawater desalination, oil and gas field exploitation and mining. These wastewaters usually have high electrical conductivity, which can easily lead to equipment corrosion. Discharge will cause environmental problems such as soil salinization and water pollution, seriously affecting the health of the ecosystem and causing waste of water resources. At present, the treatment technologies for saline wastewater mainly include evaporation concentration, reverse osmosis and biological treatment. However, these methods generally have the problems of high energy consumption and low efficiency, and the desalinated fresh water is difficult to fully utilize. How to efficiently treat and utilize saline wastewater has become a hot spot and difficulty in current research.

[0003] As a clean and efficient secondary energy source, hydrogen plays an important role in the global energy transition. Among them, water electrolysis hydrogen production technology has become the focus of research and application due to its simple process and high purity of hydrogen production. However, the demand for fresh water resources in the process of water electrolysis hydrogen production is large, especially in areas with water shortages. This bottleneck limits the promotion and application of the technology.

[0004] If saline wastewater can be used for electrolytic hydrogen production, it will not only effectively alleviate the high demand for freshwater resources in the electrolysis process, but also provide new technology for the treatment of saline wastewater.

[0005] In addition, the existing water electrolysis hydrogen production technology still has the following problems in practical application. On the one hand, the large amount of low-grade waste heat generated in the process of electrolysis hydrogen production is difficult to be efficiently recycled, resulting in low energy utilization efficiency; on the other hand, the high concentration of salts and impurities in the salty wastewater will cause equipment corrosion, increased energy consumption and side reactions, limiting its direct application in the existing electrolysis hydrogen production process.

[0006] Membrane evaporation technology is an efficient separation and concentration method that combines the advantages of traditional evaporation technology and membrane separation technology. It has been widely used in many industries and has the unique advantage of being driven by low-grade thermal energy. However, the source of low-grade thermal energy required for membrane evaporation technology is also a difficulty in current research.

[0007] Therefore, how to efficiently convert saline wastewater into fresh water suitable for hydrogen production is the core technical problem that needs to be solved at present. Summary of the invention The main purpose of the present invention is to provide a saline wastewater hydrogen production system that couples membrane evaporation and utilizes electrolysis waste heat, aiming to solve the problem of difficulty in converting saline wastewater into fresh water suitable for hydrogen production.

[0008] To achieve the above-mentioned purpose, the present invention provides a saline wastewater hydrogen production system that couples membrane evaporation and utilizes electrolysis waste heat, comprising an electrolysis hydrogen production unit, a membrane evaporation unit and a heat exchange unit; The electrolyte outlet of the electrolytic hydrogen production unit is used to communicate with the electrolyte inlet of the heat exchange unit, so that the heated electrolyte flowing out of the electrolytic hydrogen production unit enters the heat exchange unit and performs heat exchange cooling with the salt-containing wastewater entering the heat exchange unit; The electrolyte inlet of the electrolytic hydrogen production unit is communicated with the electrolyte outlet of the heat exchange unit so that the cooled electrolyte flows back to the electrolytic hydrogen production unit; The salt-containing wastewater outlet of the heat exchange unit is connected to the inlet of the membrane evaporation unit, so that the salt-containing wastewater heated after heat exchange enters the membrane evaporation unit to generate water vapor, and the fresh water obtained by cooling the water vapor provides fresh water raw material to the electrolytic hydrogen production unit.

[0009] Optionally, the electrolysis hydrogen production unit includes a battery stack, an electrolyte storage tank, a hydrogen gas-liquid separator and an oxygen gas-liquid separator; The electrolyte storage tank is used to provide electrolyte to the battery stack; The anode outlet of the stack is connected to the inlet of the oxygen gas-liquid separator; the cathode outlet of the stack is connected to the inlet of the hydrogen gas-liquid separator; The first liquid outlet of the oxygen gas-liquid separator and the second liquid outlet of the hydrogen gas-liquid separator are respectively connected to the electrolyte inlet of the heat exchange unit; The electrolyte outlet of the heat exchange unit is used to flow back to the inlet of the fuel cell stack.

[0010] Optionally, the membrane evaporation unit comprises a wastewater storage tank for containing saline wastewater, and the saline wastewater inlet of the heat exchange unit is connected to the outlet of the wastewater storage tank.

[0011] Optionally, the membrane evaporation unit also includes a membrane evaporation device and a fresh water storage tank; the salt-containing wastewater outlet of the heat exchange unit is connected to the upstream inlet of the membrane evaporation device; the upstream outlet of the membrane evaporation device is connected to the inlet of the wastewater storage tank; the downstream outlet of the membrane evaporation device is connected to the inlet of the fresh water storage tank; the outlet of the fresh water storage tank is connected to the downstream inlet of the membrane evaporation device, so that the salt-containing wastewater entering the heat exchange unit and heated up by heat exchange enters the membrane evaporation device from the upstream inlet of the membrane evaporation device, and the salt-containing wastewater entering the membrane evaporation unit uses its own sensible heat to evaporate and generate water vapor, and the water vapor passes through the membrane unit in the membrane evaporation device and is collected in the fresh water storage tank.

[0012] Optionally, the fresh water storage tank is connected to the hydrogen gas-liquid separator or the oxygen gas-liquid separator via a water replenishment pump.

[0013] Optionally, the electrolysis hydrogen production unit adopts any one of an alkaline electrolysis hydrogen production method, a proton exchange membrane electrolysis hydrogen production method and an anion exchange membrane electrolysis hydrogen production method.

[0014] Optionally, the functional element structure of the membrane evaporation unit is any one of a tubular structure, a plate structure, a spiral wound structure, and a hollow fiber structure.

[0015] Optionally, the membrane unit in the membrane evaporation unit adopts a hydrophilic membrane or a hydrophobic membrane.

[0016] Optionally, the membrane unit in the membrane evaporation unit is any one of a polyvinyl alcohol membrane, a molecular sieve membrane, a polytetrafluoroethylene membrane, a polyvinylidene fluoride membrane and a polypropylene membrane.

[0017] Optionally, the saline wastewater is any one of oilfield produced water, coal chemical coking wastewater, seawater and food industry wastewater.

[0018] In the technical solution of the present invention, the saline wastewater enters the low-temperature side solution inlet of the heat exchange unit, and the electrolyte inlet (i.e., the high-temperature side solution inlet) of the heat exchange unit is connected to the electrolyte outlet of the electrolytic hydrogen production unit, so that in the heat exchange unit, the saline wastewater is heated by the electrolyte heated during the electrolysis process, and the electrolyte is cooled by the saline wastewater; the electrolyte cooled in the heat exchange unit flows back to the electrolytic hydrogen production unit to continue to circulate the electrolytic hydrogen production reaction; and the saline wastewater heated in the heat exchange unit enters the membrane evaporation unit, and the water vapor generated after membrane evaporation is cooled to fresh water, which is used as the fresh water raw material of the subsequent electrolytic hydrogen production unit, and the saline wastewater concentrated after membrane evaporation is collected and continues to be circulated with reference to the above steps. Therefore, the system no longer needs to set up an additional electrolyte cooling device, and can also use the waste heat in the electrolyte cooling process to heat the saline wastewater, providing heat energy for the saline wastewater to evaporate in the membrane evaporation unit to produce water vapor, and the fresh water obtained after the water vapor prepared by the membrane evaporation unit is cooled can be cleverly used as a fresh water raw material for electrolytic hydrogen production. The clever recycling process of waste heat, wastewater and hydrogen production coupling is realized.

[0019] Therefore, compared with the existing technical solutions, the present invention achieves multiple goals of waste heat and wastewater recycling, hydrogen energy production and fresh water co-production by coupling electrolytic hydrogen production and membrane evaporation technology, forming a green recycling process with higher energy and resource utilization efficiency and a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a main function flow chart of the process for producing hydrogen from saline wastewater by coupling membrane evaporation and utilizing waste heat from electrolysis in the present invention; Figure 2 This is a process flow chart of producing hydrogen from saline wastewater by coupling membrane evaporation and utilizing waste heat from electrolysis in the present invention; Figure 3 This is a schematic diagram of the film evaporation process in the present invention.

[0021] Description of Figure Numbers: 1-electrolysis hydrogen production unit, 2-heat exchange unit, 3-membrane evaporation unit, 11-control cabinet, 12-rectifier, 13-transformer, 14-oxygen gas-liquid separator, 15-hydrogen gas-liquid separator, 16-fuel cell, 17-first electrolyte circulation pump, 18-second electrolyte circulation pump, 19-electrolyte storage tank, 21-heat exchanger, 31-membrane evaporation device, 32-wastewater storage tank, 33-fresh water storage tank, 34-wastewater circulation pump, 35-water make-up pump, 36-fresh water circulation pump.

[0022] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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.

[0024] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0025] In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0026] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0028] See also Figures 1 to 3 To achieve the above-mentioned purpose, the present invention provides a saline wastewater hydrogen production system that couples membrane evaporation and utilizes electrolysis waste heat, including an electrolysis hydrogen production unit, a membrane evaporation unit and a heat exchange unit; The electrolyte outlet of the electrolytic hydrogen production unit is used to communicate with the electrolyte inlet of the heat exchange unit, so that the heated electrolyte flowing out of the electrolytic hydrogen production unit enters the heat exchange unit and performs heat exchange cooling with the salt-containing wastewater entering the heat exchange unit; The electrolyte inlet of the electrolytic hydrogen production unit is communicated with the electrolyte outlet of the heat exchange unit so that the cooled electrolyte flows back to the electrolytic hydrogen production unit; The salt-containing wastewater outlet of the heat exchange unit is connected to the inlet of the membrane evaporation unit, so that the salt-containing wastewater heated after heat exchange enters the membrane evaporation unit to generate water vapor, and the fresh water obtained by cooling the water vapor provides fresh water raw material to the electrolytic hydrogen production unit.

[0029] In the technical solution of the present invention, the saline wastewater enters the low-temperature side solution inlet of the heat exchange unit, and the electrolyte inlet (i.e., the high-temperature side solution inlet) of the heat exchange unit is connected to the electrolyte outlet of the electrolytic hydrogen production unit, so that in the heat exchange unit, the saline wastewater is heated by the electrolyte heated during the electrolysis process, and the electrolyte is cooled by the saline wastewater; the electrolyte cooled in the heat exchange unit flows back to the electrolytic hydrogen production unit to continue to circulate the electrolytic hydrogen production reaction; and the saline wastewater heated in the heat exchange unit enters the membrane evaporation unit, and the water vapor generated after membrane evaporation is cooled to fresh water, which is used as the fresh water raw material of the subsequent electrolytic hydrogen production unit, and the saline wastewater concentrated after membrane evaporation is collected and continues to be circulated with reference to the above steps. Therefore, the system no longer needs to set up an additional electrolyte cooling device, but uses the waste heat in the electrolyte cooling process to heat the saline wastewater, providing heat energy for the saline wastewater to evaporate in the membrane evaporation unit to produce water vapor, and the fresh water obtained after the water vapor prepared by the membrane evaporation unit is cooled can be cleverly used as fresh water raw material for electrolytic hydrogen production. The clever recycling process of waste heat, wastewater and hydrogen production coupling is realized.

[0030] Therefore, compared with the existing technical solutions, the present invention achieves multiple goals of waste heat and wastewater recycling, hydrogen energy production and fresh water co-production by coupling electrolytic hydrogen production and membrane evaporation technology, forming a green recycling process with higher energy and resource utilization efficiency and a wide range of applications.

[0031] This study proposed an innovative coupling process, which uses the waste heat generated during the electrolytic hydrogen production process to drive membrane evaporation, efficiently converting saline wastewater into fresh water suitable for hydrogen production, while achieving waste heat recovery and fresh water resource utilization. This process not only solves the problem that saline wastewater cannot be directly used for hydrogen production in existing technologies, but also significantly improves the overall energy efficiency of the hydrogen production process, providing new ideas and technical support for the development and promotion of green hydrogen energy.

[0032] Specifically: The hydrogen production unit by electrolysis, the membrane evaporation unit and the heat exchange unit are coupled with each other. Through the heat exchange between the saline wastewater and the electrolyte, the electrolyte cooling of the hydrogen production unit is realized without the need to provide additional coolant. The heat recovered from the electrolyte by the saline wastewater is also used in the membrane evaporation process of the saline wastewater. There is no need to provide additional heat for the membrane evaporation process of the saline wastewater, and there is no additional energy consumption. Moreover, the fresh water prepared by the membrane evaporation process of the heated saline wastewater can also be used as the source of fresh water for hydrogen production by electrolysis, which solves the dependence on fresh water resources in the hydrogen production process.

[0033] Thus, the present invention couples the electrolytic hydrogen production unit, the membrane evaporation unit, and the heat exchange unit together, realizes the ingenious utilization of waste heat and waste water, and achieves a good combination of the three. In addition to the electric energy required for the electrolysis process itself, no other energy is required for the process of treating wastewater into fresh water, and fresh water is also prepared through saline wastewater. Therefore, compared with the original hydrogen production process, the system's additional saline wastewater treatment and fresh water preparation functions can almost achieve self-sufficiency in energy and fresh water to a certain extent.

[0034] Furthermore, the present invention also achieves the concentration of saline wastewater through the membrane evaporation unit.

[0035] Furthermore, hydrogen energy, as a clean and efficient secondary energy source, occupies an important position in the global energy transformation. The technology of producing hydrogen by electrolysis of water has been widely studied and applied because of its simple process and high purity of hydrogen production. However, the existing technology of producing hydrogen by electrolysis of water faces several problems that need to be solved urgently. On the one hand, a large amount of low-grade waste heat in the process of hydrogen production by electrolysis is difficult to recycle efficiently, resulting in low energy utilization efficiency; on the other hand, the electrolysis process has a large demand for fresh water resources, and the global shortage of fresh water resources is becoming increasingly serious. The technical solution of the present invention also happens to solve these two problems.

[0036] On the other hand, the treatment and resource utilization of saline wastewater in industrial and domestic discharge has also become a hot topic and difficulty. Traditional wastewater desalination and treatment technologies are energy-intensive and inefficient. The membrane evaporation technology in the present invention is a high-efficiency water treatment technology driven by low-grade thermal energy. It just utilizes the low-grade waste heat of the electrolyte to effectively recover the fresh water resources in the wastewater, while concentrating the salt and realizing the resource treatment of the wastewater.

[0037] The system proposed in the present invention is a process for coupling electrolysis and membrane evaporation to produce hydrogen for saline wastewater. By utilizing the waste heat generated in the process of electrolytic hydrogen production to drive the membrane evaporation unit to concentrate and desalinate the saline wastewater, it not only realizes the self-circulating supply of water for electrolysis, but also effectively improves the utilization efficiency of waste heat and the overall energy utilization rate of the system. The present invention organically combines membrane evaporation with the process of electrolytic hydrogen production to form a new technical path for the coordinated and efficient treatment of saline wastewater and the production of clean energy. It can be applied to a variety of high-salt wastewater scenarios such as oilfield produced water, coal chemical wastewater, and seawater, providing a technical solution that is both economical and environmentally friendly for resource processing and hydrogen energy preparation. At the same time, the present invention can achieve the co-production of hydrogen and fresh water by adjusting the voltage of the electrolyzer, and realize the efficient recovery of salt ions by controlling the concentration multiple of membrane evaporation, providing solid technical support for promoting the deep integration of clean energy and wastewater resource utilization.

[0038] Optionally, the electrolysis hydrogen production unit includes a battery stack, an electrolyte storage tank, a hydrogen gas-liquid separator and an oxygen gas-liquid separator; The electrolyte storage tank is used to provide electrolyte to the battery stack; The anode outlet of the stack is connected to the inlet of the oxygen gas-liquid separator; the cathode outlet of the stack is connected to the inlet of the hydrogen gas-liquid separator; The first liquid outlet of the oxygen gas-liquid separator and the second liquid outlet of the hydrogen gas-liquid separator are respectively connected to the electrolyte inlet of the heat exchange unit; specifically, the first liquid outlet of the oxygen gas-liquid separator and the second liquid outlet of the hydrogen gas-liquid separator are respectively connected to one end of a collecting pipe, and the other end of the collecting pipe is connected to the electrolyte inlet of the heat exchange unit.

[0039] The electrolyte outlet of the heat exchange unit is used to flow back to the inlet of the fuel cell stack.

[0040] It is easy to understand that the electrolytic hydrogen production unit also includes a transformer, a rectifier, a circulation pump, a connecting pipe and an instrument.

[0041] The electrolyte in the electrolytic hydrogen production unit is decomposed into one part of hydrogen and 1 / 2 part of oxygen in the fuel cell stack under the action of direct current; in addition, due to the existence of overpotential, the electrical energy not used to decompose fresh water into hydrogen and oxygen will be converted into heat for heating the electrolyte; the high-temperature electrolyte and the hydrogen produced by electrolysis enter the hydrogen gas-liquid separator under the action of a circulating pump, and the high-temperature electrolyte and the oxygen produced by electrolysis enter the oxygen gas-liquid separator under the action of a circulating pump; after hydrogen is separated by the hydrogen gas-liquid separator, it enters the subsequent hydrogen processing unit, and after oxygen is separated by the oxygen gas-liquid separator, it can be directly discharged or collected; the high-temperature electrolyte flowing out of the hydrogen gas-liquid separator and the oxygen gas-liquid separator flows out from the liquid phase outlet of the hydrogen gas-liquid separator and the oxygen gas-liquid separator respectively, and enters the heat exchange unit through the collecting pipe.

[0042] Specifically, the electrolyte outlet of the heat exchange unit is connected to the electrolyte storage tank and the electrolyte inlet of the stack through a pipeline. A valve is set at the outlet of the electrolyte storage tank. Before the electrolysis operation, the valve at the outlet of the electrolyte storage tank is opened to allow the electrolyte to flow into the electrolytic hydrogen production unit; during the electrolysis operation, the valve at the outlet of the electrolyte storage tank is closed to allow the electrolyte to enter the stack after being cooled by the heat exchange unit; Specifically, after heat exchange, the temperature of the electrolyte entering the electrolytic cell may be in the range of 50-80°C, and the temperature of the electrolyte flowing out of the electrolytic cell may be in the range of 80-130°C.

[0043] Optionally, the membrane evaporation unit comprises a wastewater storage tank for containing saline wastewater, and the saline wastewater inlet of the heat exchange unit is connected to the outlet of the wastewater storage tank.

[0044] Specifically, the heat exchange unit includes a heat exchanger, a connecting pipe and an instrument; the solution inlet on the high-temperature side of the heat exchanger, i.e., the electrolyte inlet, is connected to a collecting pipe connected to the outlet of the hydrogen gas-liquid separator and the outlet of the oxygen gas-liquid separator respectively; the solution outlet on the high-temperature side of the heat exchanger, i.e., the electrolyte outlet, is connected to the inlet of the fuel cell stack; the solution inlet on the low-temperature side of the heat exchanger, i.e., the saline wastewater inlet, is connected to the outlet of the wastewater storage tank; the solution outlet on the low-temperature side of the heat exchanger, i.e., the saline wastewater outlet, is connected to the upstream inlet of the membrane evaporation device; in the heat exchanger, the high-temperature electrolyte transfers heat to the low-temperature wastewater through heat exchange.

[0045] In the heat exchanger, the high-temperature electrolyte transfers heat to the low-temperature saline wastewater through heat exchange; the high-temperature electrolyte is cooled to the required temperature of the fuel cell stack inlet; and the low-temperature saline wastewater is heated to the upstream inlet temperature of the membrane distillation.

[0046] Specifically, the temperature of the saline wastewater entering the membrane evaporation unit may be in the range of 60-100°C, and the temperature of the wastewater flowing out of the membrane evaporation unit may be in the range of 30-45°C.

[0047] In the present invention, the heat exchanger can be any one of a shell-and-tube heat exchanger, a plate heat exchanger and a plate-fin heat exchanger. The heat exchanger must be made of corrosion-resistant and excellent heat-conducting material, such as stainless steel or silicon carbide.

[0048] Optionally, the membrane evaporation unit also includes a membrane evaporation device and a fresh water storage tank; the salt-containing wastewater outlet of the heat exchange unit is connected to the upstream inlet of the membrane evaporation device; the upstream outlet of the membrane evaporation device is connected to the inlet of the wastewater storage tank; the downstream outlet of the membrane evaporation device is connected to the inlet of the fresh water storage tank; the outlet of the fresh water storage tank is connected to the downstream inlet of the membrane evaporation device, so that the salt-containing wastewater entering the heat exchange unit and heated up by heat exchange enters the membrane evaporation device from the upstream inlet of the membrane evaporation device, and the salt-containing wastewater entering the membrane evaporation unit uses its own sensible heat to evaporate and generate water vapor, and the water vapor passes through the membrane unit in the membrane evaporation device and is collected in the fresh water storage tank.

[0049] The membrane evaporation unit also includes a circulation pump, a pipe and an instrument; the saline wastewater heated by heat exchange enters the membrane evaporation device from the upstream inlet of the membrane evaporation device under the action of the circulation pump; the saline wastewater entering the membrane evaporation unit uses its own sensible heat to evaporate and generate water vapor; the generated water vapor passes through the hydrophobic porous membrane or the hydrophilic dense membrane, and is collected in a fresh water storage tank through circulation and cooled into fresh water; Specifically, the wastewater inlet of the wastewater storage tank in the membrane evaporation unit is a supply channel for saline wastewater; the outlet of the wastewater storage tank is connected to the low-temperature solution inlet of the heat exchanger, and the saline wastewater enters the heat exchanger through a circulation pump; the inlet of the wastewater storage tank is connected to the outlet upstream of the membrane evaporation device, and the concentrated saline wastewater after the membrane evaporation process will return to the wastewater storage tank; the inlet upstream of the membrane evaporation device is connected to the low-temperature solution outlet of the heat exchanger, and the saline wastewater heated by heat exchange in the heat exchanger will enter the membrane evaporation device for the membrane evaporation process; the inlet downstream of the membrane evaporation device is connected to the outlet of the fresh water storage tank, and the fresh water is in direct contact with water vapor in the membrane evaporation device to achieve the purpose of recovering water vapor; the outlet downstream of the membrane evaporation device is connected to the inlet of the fresh water storage tank, and the fresh water after recovering water vapor flows into the fresh water storage tank for storage; the second outlet of the fresh water storage tank is connected to the hydrogen gas-liquid separator or the oxygen gas-liquid separator to replenish fresh water raw materials for the electrolytic hydrogen production unit.

[0050] Optionally, the fresh water storage tank is connected to the hydrogen gas-liquid separator or the oxygen gas-liquid separator via a water replenishment pump. According to the water consumption requirement of the electrolyte storage tank, a water replenishment pump can be used to replenish fresh water into the hydrogen gas-liquid separator or the oxygen gas-liquid separator. Specifically, in the present invention, the fresh water storage tank replenishes fresh water into the hydrogen gas-liquid separator via a water replenishment pump.

[0051] Optionally, the electrolysis hydrogen production unit adopts any one of an alkaline electrolysis hydrogen production method, a proton exchange membrane electrolysis hydrogen production method and an anion exchange membrane electrolysis hydrogen production method.

[0052] Optionally, the functional element structure of the membrane evaporation unit is any one of a tubular structure, a plate structure, a spiral wound structure, and a hollow fiber structure.

[0053] Optionally, the membrane unit in the membrane evaporation unit adopts a hydrophilic membrane or a hydrophobic membrane.

[0054] Optionally, the membrane unit in the membrane evaporation unit is any one of a polyvinyl alcohol membrane, a molecular sieve membrane, a polytetrafluoroethylene membrane, a polyvinylidene fluoride membrane and a polypropylene membrane.

[0055] Optionally, the saline wastewater is any one of oilfield produced water, coal chemical coking wastewater, seawater and food industry wastewater. The seawater can be seawater directly obtained from the ocean, or high-concentration saline wastewater, i.e., concentrated seawater, generated in the process of converting seawater into fresh water by a seawater desalination plant.

[0056] Figure 2 The process flow chart of hydrogen production from saline wastewater by coupling membrane evaporation and utilizing electrolysis waste heat in the present invention can be seen from the figure: before electrolysis and membrane evaporation are coupled to produce hydrogen, the first electrolyte circulation pump 17 and the second electrolyte circulation pump 18 are turned on to transport the electrolyte in the electrolyte storage tank 19 to the electrolysis hydrogen production unit; after the electrolyte transportation is completed, the rectifier 12 is turned on by operating the control cabinet 11 to power the stack 16. The electrolyte is decomposed into hydrogen and oxygen by the direct current in the stack 16. Hydrogen is separated from the electrolyte by the hydrogen gas-liquid separator 15, and oxygen is separated from the electrolyte by the oxygen gas-liquid separator 14. The separated electrolyte enters the heat exchanger 21 through the collecting pipe for heat exchange. After the high-temperature electrolyte enters the high-temperature side of the heat exchanger 21, the heat is transferred to the saline wastewater transported from the wastewater storage tank 32 to the low-temperature side of the heat exchanger through the wastewater circulation pump 34 through heat exchange, thereby reducing the temperature of the electrolyte and increasing the temperature of the saline wastewater. After the temperature rises, the salty wastewater enters the membrane evaporation device 31 for membrane evaporation treatment to evaporate water vapor. In the membrane evaporation device 31, the water vapor is transported from the fresh water storage tank 33 to the fresh water downstream of the membrane evaporation device 31 through the fresh water circulation pump 36, and is recovered and stored in the fresh water storage tank 33. The remaining high-salt wastewater in the membrane evaporation device 31 will circulate back to the wastewater storage tank 32 to continue to participate in the heat exchange and membrane evaporation process. The fresh water in the fresh water storage tank 33 will be transported to the hydrogen gas-liquid separator 15 or the oxygen gas-liquid separator 14 in the electrolytic hydrogen production unit through the water replenishment pump 35. Through this system, the waste heat generated by the electrolyte during the electrolysis process can be recycled, and the temperature of the salty wastewater can be effectively increased through the heat exchanger 21, providing a heat source for the membrane evaporation process, while maintaining the temperature of the electrolyte to meet the hydrogen production requirements.

[0057] Figure 3This is a schematic diagram of the membrane evaporation process in the present invention. As can be seen from the figure, in the membrane evaporation device, low-temperature fresh water and high-temperature saline wastewater are separated by a hydrophobic porous membrane, and both the cold-side and hot-side solutions are in direct contact with the hydrophobic porous membrane. Since the saturated vapor pressure of the high-temperature side solution is greater than the saturated vapor pressure of the low-temperature side solution, water vapor evaporates from the hot liquid surface interface of the high-temperature side, and then enters the cold liquid surface interface of the low-temperature side through the membrane pores to condense, completing the mass transfer process.

[0058] In the description of this specification, the description with reference to the terms "an embodiment", "another embodiment", "other embodiments", or "first embodiment to Xth embodiment" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, method steps or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0059] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or system. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or system including the element.

[0060] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0061] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A system for producing hydrogen from saline wastewater by coupling membrane evaporation and utilizing waste heat from electrolysis, characterized in that: It includes an electrolytic hydrogen production unit, a membrane evaporation unit and a heat exchange unit; The electrolyte outlet of the electrolytic hydrogen production unit is used to communicate with the electrolyte inlet of the heat exchange unit, so that the heated electrolyte flowing out of the electrolytic hydrogen production unit enters the heat exchange unit and performs heat exchange cooling with the salt-containing wastewater entering the heat exchange unit; The electrolyte inlet of the electrolytic hydrogen production unit is communicated with the electrolyte outlet of the heat exchange unit so that the cooled electrolyte flows back to the electrolytic hydrogen production unit; The salt-containing wastewater outlet of the heat exchange unit is connected to the inlet of the membrane evaporation unit, so that the salt-containing wastewater heated after heat exchange enters the membrane evaporation unit to generate water vapor, and the fresh water obtained by cooling the water vapor provides fresh water raw material to the electrolytic hydrogen production unit.

2. The system for producing hydrogen from saline wastewater by coupling membrane evaporation and utilizing waste heat from electrolysis according to claim 1, characterized in that: The electrolytic hydrogen production unit comprises a battery stack, an electrolyte storage tank, a hydrogen gas-liquid separator and an oxygen gas-liquid separator; The electrolyte storage tank is used to provide electrolyte to the battery stack; The anode outlet of the stack is connected to the inlet of the oxygen gas-liquid separator; the cathode outlet of the stack is connected to the inlet of the hydrogen gas-liquid separator; The first liquid outlet of the oxygen gas-liquid separator and the second liquid outlet of the hydrogen gas-liquid separator are respectively connected to the electrolyte inlet of the heat exchange unit; The electrolyte outlet of the heat exchange unit is used to flow back to the inlet of the fuel cell stack.

3. The system for producing hydrogen from saline wastewater by coupling membrane evaporation and utilizing waste heat from electrolysis according to claim 2, characterized in that: The membrane evaporation unit comprises a wastewater storage tank for containing saline wastewater, and the saline wastewater inlet of the heat exchange unit is communicated with the outlet of the wastewater storage tank.

4. The system for producing hydrogen from saline wastewater by coupling membrane evaporation and utilizing waste heat from electrolysis according to claim 3, characterized in that: The membrane evaporation unit also includes a membrane evaporation device and a fresh water storage tank; the salt-containing wastewater outlet of the heat exchange unit is connected to the upstream inlet of the membrane evaporation device; the upstream outlet of the membrane evaporation device is connected to the inlet of the wastewater storage tank; the downstream outlet of the membrane evaporation device is connected to the inlet of the fresh water storage tank; the outlet of the fresh water storage tank is connected to the downstream inlet of the membrane evaporation device, so that the salt-containing wastewater entering the heat exchange unit and heated by heat exchange enters the membrane evaporation device from the upstream inlet of the membrane evaporation device, and the salt-containing wastewater entering the membrane evaporation unit uses its own sensible heat to evaporate and generate water vapor, and the water vapor passes through the membrane unit in the membrane evaporation device and is collected in the fresh water storage tank.

5. The system for producing hydrogen from saline wastewater by coupling membrane evaporation and utilizing waste heat from electrolysis according to claim 4, characterized in that: The fresh water storage tank is connected to the hydrogen gas-liquid separator or the oxygen gas-liquid separator through a water replenishment pump.

6. The system for producing hydrogen from saline wastewater by coupling membrane evaporation and utilizing waste heat from electrolysis according to claim 1, characterized in that: The electrolytic hydrogen production unit adopts any one of an alkaline electrolytic hydrogen production method, a proton exchange membrane electrolytic hydrogen production method and an anion exchange membrane electrolytic hydrogen production method.

7. The system for producing hydrogen from saline wastewater by coupling membrane evaporation and utilizing waste heat from electrolysis according to claim 1, characterized in that: The functional element structure of the membrane evaporation unit is any one of a tubular structure, a plate structure, a spiral wound structure, and a hollow fiber structure.

8. The system for producing hydrogen from saline wastewater by coupling membrane evaporation and utilizing waste heat from electrolysis according to claim 1, characterized in that: The membrane unit in the membrane evaporation unit adopts a hydrophilic membrane or a hydrophobic membrane.

9. The system for producing hydrogen from saline wastewater by coupling membrane evaporation and utilizing waste heat from electrolysis according to any one of claims 1 to 8, characterized in that: The membrane unit in the membrane evaporation unit is any one of a polyvinyl alcohol membrane, a molecular sieve membrane, a polytetrafluoroethylene membrane, a polyvinylidene fluoride membrane and a polypropylene membrane.

10. The system for producing hydrogen from saline wastewater by coupling membrane evaporation and utilizing waste heat from electrolysis according to any one of claims 1 to 8, characterized in that: The saline wastewater is any one of oilfield produced water, coal chemical coking wastewater, seawater and food industry wastewater.

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