Low-viscosity gas bubbling vacuum enhanced direct contact membrane distillation seawater desalination device

Abstract

The present invention provides a low-viscosity gas bubbling vacuum enhanced direct contact membrane distillation seawater desalination device, which relates to the technical field of seawater desalination. The seawater desalination device includes a membrane distillation device, a low-viscosity gas circulation loop, a seawater circulation loop and a fresh water circulation loop; the membrane distillation device includes: a hot seawater flow channel, a fresh water flow channel and a hydrophobic breathable membrane; the seawater circulation loop includes: a seawater heater, a seawater storage tank, a concentrated brine storage tank, a seawater circulation pump, a first heat exchanger and a second heat exchanger; the fresh water circulation loop includes: a fresh water circulation pump, a fresh water storage tank and a vacuum pump; the low-viscosity gas circulation loop includes: a gas compressor, a low-viscosity gas storage tank, and a gas blower. The present invention not only takes into account the continuous disturbance of the hot seawater turbulence by the low-viscosity gas during the bubbling process, but also enhances the driving ability of the low-viscosity gas to the transmembrane transport of steam under the action of the macroscopic pressure difference.

Description

Technical Field

[0001] The invention relates to the technical field of seawater desalination, and in particular to a low-viscosity gas bubbling vacuum enhanced direct contact membrane distillation seawater desalination device. Background Art

[0002] At present, many countries around the world are in urgent need of pure and clean drinking water. Water shortage has become a major environmental problem further affected by global warming. With the rapid growth of the world's population, seawater desalination is increasingly considered necessary and feasible. In order to further save energy and improve the quality of produced water, membrane distillation seawater desalination technology is increasingly valued.

[0003] Compressed air bubbling is a means of intensifying the mass transfer process of membrane distillation desalination. For example, in patents CN101874984A and CN200810052864.2, the addition of compressed air on the raw water side makes the flow turbulence of the raw water in the membrane module stronger, thereby reducing the concentration polarization and temperature polarization of the boundary layer, and playing a role in intensifying the mass transfer process.

[0004] However, the current transmembrane permeation rate of water vapor in membrane distillation desalination devices is still not high, and the efficiency of seawater desalination needs to be improved. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] In view of the shortcomings of the prior art, the present invention proposes a low-viscosity gas bubbling vacuum enhanced direct contact membrane distillation seawater desalination device, which solves the problem that the water vapor transmembrane permeation rate of the membrane distillation seawater desalination device needs to be improved.

[0007] (II) Technical solution

[0008] The present invention provides a low-viscosity gas bubbling vacuum enhanced direct contact membrane distillation seawater desalination device, the seawater desalination device comprising: a membrane distillation device, a low-viscosity gas circulation loop, a seawater circulation loop and a fresh water circulation loop;

[0009] The membrane distillation device comprises: a hot sea water flow channel, a fresh water flow channel and a hydrophobic breathable membrane; the hot sea water flow channel and the fresh water flow channel are arranged alternately side by side, and adjacent hot sea water flow channels and fresh water flow channels are separated by a hydrophobic breathable membrane;

[0010] The seawater circulation loop comprises: a seawater heater, a seawater storage tank, a concentrated brine storage tank, a seawater circulation pump, a first heat exchanger and a second heat exchanger;

[0011] The fresh water circulation loop comprises: a fresh water circulation pump, a fresh water storage tank and a vacuum pump;

[0012] The low-viscosity gas circulation loop includes: a gas compressor, a low-viscosity gas storage tank, and a gas blower;

[0013] The low-viscosity gas circulation loop is filled with low-viscosity gas, which is a non-condensable gas with relatively low dynamic viscosity.

[0014] Preferably, the low-viscosity gas is hydrogen.

[0015] Preferably, the fresh water storage tank is filled with gas and fresh water, with a gas-liquid volume ratio of 1% to 20%, and is in a closed state. After the vacuum pump extracts the air inside the fresh water storage tank, a certain vacuum degree is formed in the fresh water circulation loop.

[0016] Preferably, the vacuum degree in the fresh water circulation loop is 0-0.1 MPa.

[0017] Preferably, a flow control valve is provided after the seawater heater.

[0018] Preferably, a gas nozzle is provided at the low-viscosity gas inlet of the hot seawater flow channel.

[0019] Preferably, the gas nozzles are arranged side by side, with a parallel spacing ranging from 20 mm to 60 mm, and a nozzle diameter ranging from 2 mm to 8 mm.

[0020] Preferably, the type of the hydrophobic breathable membrane depends on the direct contact form of the membrane distillation device, including: a hydrophobic breathable flat membrane, a hydrophobic breathable hollow fiber membrane, and a hydrophobic breathable tubular membrane.

[0021] (III) Beneficial effects

[0022] The present invention provides a low-viscosity gas bubbling vacuum enhanced direct contact membrane distillation seawater desalination device. Compared with the prior art, it has the following beneficial effects:

[0023] In the present invention, the seawater desalination device effectively combines low-viscosity gas bubbling with vacuum enhancement to greatly increase the transmembrane permeation rate of water vapor; through the action of the vacuum pump, a low-pressure state is formed on the permeation side, and the mass transfer driving force at this time is dominated by the vapor pressure difference and the macroscopic pressure difference on both sides of the membrane;

[0024] Compared with air, low-viscosity gas can carry more water vapor through the hydrophobic breathable membrane into the permeation side, thereby increasing the transmembrane transport rate of water vapor. Although the vapor pressure difference and macroscopic pressure difference mentioned above have little effect on the permeation of water vapor through the hydrophobic breathable membrane, they can greatly increase the rate at which low-viscosity gas permeates the hydrophobic breathable membrane, thereby further greatly increasing the amount of water vapor that passes through the hydrophobic breathable membrane with the low-viscosity gas, thereby greatly increasing the efficiency of seawater desalination. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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 only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 This is a schematic diagram of the low-viscosity gas bubbling vacuum enhanced direct contact membrane distillation seawater desalination device in Example 1;

[0027] Among them, there are membrane distillation device 1; hydrophobic breathable membrane 2; hot sea water flow channel 3; fresh water flow channel 4; low viscosity gas 5; gas compressor 6; low viscosity gas storage box 7; gas fan 8; flow control valve 9; seawater heater 10; seawater storage box 11; concentrated brine storage box 12; seawater circulation pump 13; heat exchanger 14; desalination circulation pump 15; fresh water storage box 16; vacuum pump 17; gas nozzle 18; first flow meter Q1; second flow meter Q2; third flow meter Q3; fourth flow meter Q4; fifth flow meter Q5; first thermometer T1; second thermometer T2; third thermometer T3; fourth thermometer T4; fifth thermometer T5; sixth thermometer T6; first pressure gauge P1; second pressure gauge P2; third pressure gauge P3. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. 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.

[0029] The embodiment of the present application solves the problem that the water vapor transmembrane permeation rate of the membrane distillation seawater desalination device needs to be improved by providing a low-viscosity gas bubbling vacuum enhanced direct contact membrane distillation seawater desalination device.

[0030] The technical solution in the embodiment of the present application is to solve the above technical problems, and the overall idea is as follows:

[0031] After the seawater under atmospheric pressure is heated by the seawater heater, the high-temperature seawater is pumped into the hot seawater flow channel by the seawater circulation pump as the feed liquid, the low-viscosity gas in the low-viscosity gas storage tank is blown into the feed liquid through multiple gas nozzles, and the low-temperature fresh water with a certain vacuum degree is pumped into the fresh water flow channel by the fresh water circulation pump.

[0032] Due to the existence of total pressure and vapor pressure difference, part of water vapor and low-viscosity gas flows from the membrane surface of the feed liquid side to the membrane surface of the permeate side. When water vapor encounters low-temperature fresh water, it will condense, while low-viscosity gas flows upward and is discharged from the membrane distillation device. The fresh water tank isolated from the external atmosphere is filled with water and a small amount of air, which is kept at a certain vacuum degree by a vacuum pump, thereby creating a low-pressure state for the fresh water flow. The first heat exchanger and the second heat exchanger preheat the seawater with the concentrated brine and fresh water discharged from the membrane distillation device respectively, and the preheated seawater is reheated by the seawater heater before entering the membrane distillation device. At the same time, the circulating fresh water is cooled before entering the membrane distillation device, and the low-viscosity gas discharged from the membrane distillation device and attached to the surface is compressed to atmospheric pressure by the gas compressor and then cooled. The steam is separated from the low-viscosity gas and used as part of the water product. The necessary parameter monitoring instruments (thermometer, pressure gauge, flowmeter) are set to test the temperature, pressure and flow of each circuit at a certain position, and the data is also used for the flow control valve to maintain the set value of each parameter under given conditions.

[0033] Low-viscosity gas is used as the bubbling gas, and a certain vacuum negative pressure is created on the permeation side, so that the low-viscosity gas can not only optimize the flow state of the raw water, but also produce a water vapor carrying enhancement effect across the membrane flow, further improving the enhancement effect of the bubbling process.

[0034] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0035] Embodiment 1:

[0036] like Figure 1 As shown, the present invention provides a low-viscosity gas bubbling vacuum enhanced direct contact membrane distillation seawater desalination device, the seawater desalination device comprising: a membrane distillation (MD) device 1, a low-viscosity gas circulation loop, a seawater circulation loop and a fresh water circulation loop;

[0037] The membrane distillation device 1 comprises: a hot sea water flow channel 3, a fresh water flow channel 4 and a hydrophobic breathable membrane 2; the hot sea water flow channel 3 and the fresh water flow channel 4 are arranged alternately side by side, and adjacent hot sea water flow channels 3 and fresh water flow channels 4 are separated by the hydrophobic breathable membrane 2;

[0038] The seawater circulation loop comprises: a seawater heater 10, a seawater storage tank 11, a concentrated brine storage tank 12, a seawater circulation pump 13, a first heat exchanger 14a and a second heat exchanger 14b; the seawater circulation loop sequentially connects the seawater storage tank 11, the first heat exchanger 14a, the seawater circulation pump 13, the second heat exchanger 14b, the seawater heater 10, the hot seawater flow channel 3, the first heat exchanger 14a and the concentrated brine storage tank 12 through a pipeline;

[0039] Driven by the seawater circulation pump 13, the seawater is preheated by the first heat exchanger 14a, the second heat exchanger 14b and heated by the seawater heater 10 from the seawater storage tank 11, and then input into the hot seawater flow channel 3. The concentrated brine obtained by membrane distillation is heat-exchanged with the seawater just pumped out from the seawater storage tank 11 through the first heat exchanger 14a from the hot seawater flow channel 3, and then injected into the concentrated brine storage tank 12.

[0040] The fresh water circulation loop comprises: a fresh water circulation pump 15, a fresh water storage tank 16 and a vacuum pump 17; the fresh water circulation loop sequentially connects the fresh water storage tank 16, the fresh water flow channel 4, the fresh water circulation pump 15, the second heat exchanger 14b and the fresh water storage tank 16 through a pipeline to form a loop; the fresh water storage tank 16 is provided with a vacuum pump 17, and the vacuum pump 17 keeps the fresh water storage tank 16 at a certain vacuum degree to provide negative pressure for the fresh water flow channel 4;

[0041] The fresh water in the fresh water storage tank 16 flows into the fresh water flow channel 4 through a pipeline, and the fresh water in the fresh water flow channel 4 is pumped into the second heat exchanger 14b by the fresh water circulation pump 15, and after exchanging heat with seawater in the second heat exchanger 14b, flows back to the fresh water storage tank 16;

[0042] The low-viscosity gas circulation loop includes: a gas compressor 6, a low-viscosity gas storage tank 7, and a gas blower 8; the low-viscosity gas storage tank 7 is connected to the gas blower 8 and the hot sea water flow channel 3 in sequence through a pipeline, and the gas discharge pipe of the fresh water flow channel 4 is connected to the gas compressor 6. After the gas compressor 6 is connected to the gas discharge pipe of the hot sea water flow channel 3 through a pipeline, it is connected to the low-viscosity gas storage tank 7 to form a loop;

[0043] The low-viscosity gas circulation loop is filled with low-viscosity gas 5, and the low-viscosity gas 5 is a non-condensable gas with low dynamic viscosity;

[0044] The low-viscosity gas 5 is input into the hot sea water flow channel 3 from the low-viscosity gas storage tank 7 through the gas blower 8, a part of it passes through the hydrophobic breathable membrane 2 and enters the fresh water flow channel 4, and the rest remains in the hot sea water flow channel 3. The low-viscosity gas 5 discharged from the fresh water flow channel 4 is pressurized by the gas compressor 6 and merges with the low-viscosity gas 5 discharged from the hot sea water flow channel 3 and returns to the low-viscosity gas storage tank 7.

[0045] like Figure 1 As shown, a flow control valve 9 is arranged behind the seawater heater 10 , and the flow control valve 9 controls the rate at which seawater enters the hot seawater flow channel 3 .

[0046] like Figure 1 As shown, a gas nozzle 18 is provided at the low-viscosity gas inlet of the hot sea water flow channel 3 , and the low-viscosity gas 5 is injected into the hot sea water flow channel 3 through the gas nozzle 18 .

[0047] like Figure 1As shown, the gas nozzles 18 are arranged side by side, the parallel spacing ranges from 20 mm to 60 mm, and the nozzle diameter ranges from 2 mm to 8 mm.

[0048] The fresh water storage tank 16 is filled with gas and fresh water, with a gas-liquid volume ratio of 1% to 20%, and is in a closed state. The vacuum pump 17 extracts the air inside the fresh water storage tank 16 to form fresh water with a certain vacuum degree on the fresh water circulation side, and the vacuum degree is 0 to 0.1 MPa.

[0049] The low-pressure and low-viscosity gas 5 discharged from the fresh water flow channel 4 is pressurized to about 0.1 MPa by the gas compressor 6 .

[0050] The direct contact form of the membrane distillation device 1 is not limited to the flat plate type, and can also be other forms such as a tube type.

[0051] The type of the hydrophobic breathable membrane 2 depends on the direct contact form of the membrane distillation device 1, and can be a hydrophobic breathable flat membrane, a hydrophobic breathable hollow fiber membrane, a hydrophobic breathable tubular membrane, or other forms of membranes.

[0052] Various homemade and commercially available hydrophobic breathable membranes that meet the functional requirements of this application can be used in the present invention.

[0053] The devices in the three circulation loops of the present application are connected through pipelines, and the pipelines can be various flexible or rigid pressure-resistant pipes, with flexible materials being given priority.

[0054] like Figure 1 As shown, the seawater inlet pipe of the membrane distillation device 1 is provided with a first flowmeter Q1 for monitoring the seawater injection rate of the membrane distillation device 1; the seawater discharge pipe of the membrane distillation device 1 is provided with a second flowmeter Q2 for monitoring the seawater discharge rate of the membrane distillation device 1; the fresh water inlet pipe of the membrane distillation device 1 is provided with a third flowmeter Q3 for monitoring the fresh water injection rate of the membrane distillation device 1; the fresh water discharge pipe of the membrane distillation device 1 is provided with a fourth flowmeter Q4 for monitoring the fresh water discharge rate of the membrane distillation device 1; the low-viscosity gas inlet pipe of the membrane distillation device 1 is provided with a fifth flowmeter Q5 for monitoring the low-viscosity gas injection rate of the membrane distillation device 1.

[0055] like Figure 1 As shown, a first thermometer T1 is provided behind the seawater heater 10, a second thermometer T2 is provided at the seawater discharge pipe of the membrane distillation device 1, a third thermometer T3 is provided at the fresh water inlet pipe of the second heat exchanger 14b, a fourth thermometer T4 is provided at the fresh water outlet pipe of the second heat exchanger 14b, a fifth thermometer T5 is provided at the seawater inlet pipe of the second heat exchanger 14b, and a sixth thermometer T6 is provided at the seawater outlet pipe of the second heat exchanger 14b.

[0056] like Figure 1 As shown, the fresh water storage tank 16 is provided with a first pressure gauge P1, the membrane distillation device 1 is provided with a second pressure gauge P2, and the low-viscosity gas storage tank 7 is provided with a third pressure gauge P3.

[0057] Here’s how this application works:

[0058] After the seawater under atmospheric pressure is heated by the seawater heater 10, the high-temperature seawater is pumped into the hot seawater flow channel 3 by the seawater circulation pump 13 as the feed liquid, the low-viscosity gas 5 in the low-viscosity gas storage box 7 is blown into the feed liquid through multiple gas nozzles 18, and the low-temperature fresh water with a certain vacuum degree is pumped into the fresh water flow channel 4 by the fresh water circulation pump 15.

[0059] Due to the existence of total pressure and vapor pressure difference, a part of water vapor and low-viscosity gas 5 flows from the membrane surface on the feed liquid side to the membrane surface on the permeate side. When water vapor encounters low-temperature fresh water, it will condense, while the low-viscosity gas 5 flows upward and is discharged from the membrane distillation device 1. The fresh water tank 16 isolated from the external atmosphere is filled with water and a small amount of air. The air is kept at a certain vacuum degree by the vacuum pump 17, thereby creating a low-pressure state for the fresh water flow. The first heat exchanger 14a and the second heat exchanger 14b respectively use the concentrated brine and fresh water discharged from the membrane distillation device 1 to preheat the seawater. The preheated seawater is then heated by the seawater heater 10 and enters the membrane distillation device 1. At the same time, the circulating fresh water is cooled before entering the membrane distillation device 1. The low-viscosity gas discharged from the membrane distillation device 1 and attached with steam on the surface is compressed to atmospheric pressure by the gas compressor 6 and then cooled. The steam is separated from the low-viscosity gas and used as part of the water product. Set up necessary parameter monitoring instruments (thermometers T1-T6, pressure gauges P1-P3, flow meters Q1-Q5) to test Figure 1 The temperature, pressure and flow rate of each circuit at a certain location are shown, and the data are also used by the flow control valve 9 to maintain the set value of each parameter under given conditions.

[0060] Embodiment 2:

[0061] On the basis of Example 1, the low-viscosity gas 5 is hydrogen, and is compared with nitrogen, air, oxygen as the bubbling gas and no bubbling gas, respectively, to obtain Table 1.

[0062] Table 1. Relationship between permeation flux and bubbling gas

[0063]

[0064] It can be seen from Table 1 that, when the feed liquid side velocity, feed liquid side temperature, feed liquid side pressure, permeate side velocity, permeate side temperature and permeate side pressure are the same, the lower the dynamic viscosity of the bubbling gas, the greater the permeate flux of the membrane distillation device. That is, low-viscosity gas can carry more water vapor through the hydrophobic gas permeable membrane into the permeate side, greatly improving the transmembrane transport rate of water vapor.

[0065] In addition, by comparing the cases without bubbling gas and with bubbling gas in Table 1, we can see that:

[0066] When hydrogen with low dynamic viscosity is used as the bubbling gas and a certain vacuum degree is provided on the permeation side, the permeation flux of the membrane distillation device is much greater than the permeation flux without bubbling gas, with an increase of 108%.

[0067] Even if the bubbling gas used is oxygen (the dynamic viscosity of oxygen is higher than that of air), under the condition of providing a certain vacuum degree on the permeation side, the permeation flux of the membrane distillation device greatly exceeds the permeation flux without bubbling gas, with an increase of 44%.

[0068] However, when no vacuum is provided on the permeate side, that is, the pressure on the permeate side is 101325Pa, there is no macroscopic pressure difference between the feed liquid side and the permeate side. Even if hydrogen is used as the bubbling gas, the permeate flux of the membrane distillation device only increases by 4% compared with the permeate flux without bubbling gas. Compared with the previous 108% flux increase, the difference is significant.

[0069] In summary, only when the bubbling gas is low-viscosity gas 5 and negative pressure is provided on the permeate side, can the permeate flux of the membrane distillation device be greatly improved. The principle is:

[0070] Compared with air, the low-viscosity gas 5 can carry more water vapor through the hydrophobic breathable membrane to enter the permeation side, thereby increasing the transmembrane transport rate of water vapor; and the negative pressure provided by the permeation side causes a pressure difference between the feed liquid side and the permeation side. Although the pressure difference has little effect on the permeation of water vapor through the hydrophobic breathable membrane, it can greatly increase the rate at which the low-viscosity gas permeates the hydrophobic breathable membrane, thereby further increasing the amount of water vapor that permeates the hydrophobic breathable membrane with the low-viscosity gas, thereby greatly increasing the efficiency of seawater desalination.

[0071] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0072] 1. In the embodiment of the present invention, the seawater desalination device effectively combines low-viscosity gas bubbling with vacuum enhancement to greatly improve the transmembrane permeation rate of water vapor; through the action of the vacuum pump, a low-pressure state is formed on the permeation side, and the mass transfer driving force at this time is dominated by the vapor pressure difference and the macroscopic pressure difference on both sides of the membrane;

[0073] Compared with air, low-viscosity gas can carry more water vapor through the hydrophobic breathable membrane into the permeation side, which increases the transmembrane transport rate of water vapor. Although the vapor pressure difference and macroscopic pressure difference mentioned above have little effect on the permeation of water vapor through the hydrophobic breathable membrane, they can greatly increase the rate at which low-viscosity gas permeates the hydrophobic breathable membrane, thereby further increasing the amount of water vapor that permeates the hydrophobic breathable membrane with the low-viscosity gas, greatly increasing the efficiency of seawater desalination.

[0074] 2. In the embodiment of the present invention, the introduction of low-viscosity gas will significantly increase the turbulence of the hot seawater, reduce the thermal boundary layer on both sides of the membrane, and effectively weaken the temperature polarization phenomenon; the increase in flux causes the surfaces on both sides of the membrane to absorb or release more heat, thereby improving the evaporation efficiency of the process.

[0075] 3. In the embodiment of the present invention, the presence of the first heat exchanger and the second heat exchanger can fully recover the residual heat of the discharged brine and fresh water, preheat the seawater, greatly improve the effective heat consumption of the whole process, and save energy; the brine produced in the membrane distillation process is stored in the brine storage tank, and the brine can be further recycled to increase resource utilization; low-viscosity gas can be recycled in the whole process, and no unnecessary waste of resources will be caused.

[0076] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device 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 device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-viscosity gas bubbling vacuum enhanced direct contact membrane distillation seawater desalination device, characterized in that: The seawater desalination device comprises: a membrane distillation device (1), a low-viscosity gas circulation loop, a seawater circulation loop and a fresh water circulation loop; The membrane distillation device (1) comprises: a hot sea water flow channel (3), a fresh water flow channel (4) and a hydrophobic breathable membrane (2); the hot sea water flow channel (3) and the fresh water flow channel (4) are arranged alternately side by side, and adjacent hot sea water flow channels (3) and fresh water flow channels (4) are separated by the hydrophobic breathable membrane (2); The seawater circulation loop comprises: a seawater heater (10), a seawater storage tank (11), a concentrated brine storage tank (12), a seawater circulation pump (13), a first heat exchanger (14a) and a second heat exchanger (14b); The fresh water circulation loop comprises: a fresh water circulation pump (15), a fresh water storage tank (16) and a vacuum pump (17); The low-viscosity gas circulation loop comprises: a gas compressor (6), a low-viscosity gas storage tank (7), and a gas blower (8); The low-viscosity gas storage tank (7) is connected to the gas blower (8) and the hot seawater flow channel (3) in sequence through a pipeline; the gas discharge pipe of the fresh water flow channel (4) is connected to the gas compressor (6); the gas compressor (6) is connected to the low-viscosity gas storage tank (7) after merging with the gas discharge pipe of the hot seawater flow channel (3) through a pipeline, thereby forming a loop; The low-viscosity gas circulation loop is filled with low-viscosity gas (5), and the low-viscosity gas (5) is a non-condensable gas with relatively low dynamic viscosity; the low-viscosity gas (5) is hydrogen.

2. The seawater desalination device according to claim 1, characterized in that: The fresh water storage tank (16) is filled with gas and fresh water, with a gas-liquid volume ratio of 1% to 20%, and is in a closed state. The vacuum pump (17) extracts the air inside the fresh water storage tank (16) to form a vacuum in the fresh water circulation loop.

3. The seawater desalination device according to claim 2, characterized in that: The vacuum degree in the fresh water circulation loop is 0-0.1 MPa.

4. The seawater desalination device according to claim 1, characterized in that: A flow control valve (9) is arranged behind the seawater heater (10).

5. The seawater desalination device according to claim 1, characterized in that: A gas nozzle (18) is provided at the low-viscosity gas inlet of the hot seawater flow channel (3).

6. The seawater desalination device according to claim 5, characterized in that: The gas nozzles (18) are arranged side by side, with a parallel spacing ranging from 20 mm to 60 mm, and a nozzle diameter ranging from 2 mm to 8 mm.

7. The seawater desalination device according to any one of claims 1 to 6, characterized in that: The type of the hydrophobic breathable membrane (2) depends on the direct contact form of the membrane distillation device (1), including: a hydrophobic breathable flat membrane, a hydrophobic breathable hollow fiber membrane, and a hydrophobic breathable tubular membrane.

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