Pressure reduction type air gap diffusion distillation device and use method thereof

Abstract

The invention belongs to the technical field of efficient decompression separation of solutions, and discloses a decompression type air gap diffusion distillation device and a use method thereof. On the basis of normal pressure type air gap diffusion distillation, a pressure reduction type operation environment is used, so that the flux of the device and the utilization efficiency of low-grade heat energy are improved. Wherein the influence of the reduced pressure environment on the improvement of the flux of the device mainly comprises the following three aspects: (1) on an evaporation level, under the reduced pressure condition, a solution to be treated has a lower boiling point, and the evaporation rate is higher at the same heating temperature; and (2) on the steam diffusion layer surface, under the pressure reduction condition, the solution steam has lower mass transfer resistance in the distillation kettle, and the diffusion coefficient of the solution steam is higher than that under normal pressure, so that the steam obtained by evaporation is timely diffused to a cold wall for condensation. And (3) on the condensing layer, most air in the equipment is pumped out by the vacuum pump, so that the influence of non-condensable steam on condensation is greatly weakened in a condensation link, and solution steam is fully condensed on a cold wall.

Description

Technical Field

[0001] The present invention relates to the technical field of efficient decompression separation of solutions, and in particular to a decompression type air gap diffusion distillation device and a use method thereof. Background Art

[0002] Distillation separation technology is a common thermal separation method, widely used in a variety of fields, including concentration, separation, purification, and seawater desalination. Its main advantage is that it eliminates the need for introducing solvents unrelated to the system components during the separation process, effectively avoiding the generation of new impurities. It also allows the use of low-grade heat as a heat source to drive the separation equipment.

[0003] Air gap diffusion distillation uses porous medium materials as evaporators, eliminating the membrane components in air gap membrane distillation, thereby avoiding the disadvantages of membrane wetting in air gap membrane distillation. However, since it operates at normal pressure, there is a problem of low evaporation flux of the device.

[0004] The present invention proposes "a reduced-pressure air gap diffusion distillation device and its use method". On the basis of normal-pressure air gap diffusion distillation, a reduced-pressure operating environment is used to improve the device throughput and the utilization efficiency of low-grade thermal energy. The reduced-pressure environment has the following three main effects on improving the device throughput: (1) At the evaporation level, under reduced-pressure conditions, the solution to be treated has a lower boiling point, and at the same heating temperature, its evaporation rate is higher. (2) At the steam diffusion level, under reduced-pressure conditions, the solution vapor has a lower mass transfer resistance in the distillation kettle, and its diffusion coefficient is higher than the diffusion coefficient under normal pressure, so that the evaporated vapor diffuses to the cold wall in time for condensation. (3) At the condensation level, since the vacuum pump extracts most of the air in the equipment, the influence of non-condensable steam on condensation is greatly weakened in the condensation link, so that the solution vapor is fully condensed on the cold wall. Summary of the Invention

[0005] To address existing technological needs, the present invention proposes a vacuum-type air-gap diffusion distillation apparatus and its use method to achieve efficient and low-cost solution separation. This distillation method combines the advantages of vacuum membrane distillation and porous medium air-gap diffusion distillation, avoiding the high membrane replacement costs of vacuum membrane distillation and the low evaporation flux of atmospheric pressure air-gap diffusion distillation apparatus, thereby more efficiently utilizing low-grade thermal energy.

[0006] In order to achieve the above object, the present invention is implemented by the following technical solutions: a vacuum air gap diffusion distillation device, comprising a vacuum distillation kettle 1, a condenser 2, a cooling water circulation pump 4, a condensate collection tank 5, a needle valve 6, a vacuum pump 7, a heating water tank 14, a feed water tank 18, a feed circulation pump 21 and a ball valve;

[0007] The cooling water circulation pump 4 is connected to the bottom of the vacuum distillation kettle 1 and the bottom of the condenser 2 through cooling water pipelines; the top of the vacuum distillation kettle 1 and the top of the condenser 2 are respectively connected back to the cooling water circulation pump 4 through cooling water pipelines; a ball valve is set on the cooling water pipeline to control opening and closing;

[0008] The vacuum pump 7 is connected to the bottom of the condenser 2 and the top of the condensate collecting tank 5 through gas pipelines; the bottom of the vacuum distillation kettle 1 is connected to the top of the condensate collecting tank 5 through a gas pipeline; a needle valve 6 is provided on the gas pipeline to adjust the opening;

[0009] The bottom of the feed water tank 18 is connected to the top of the vacuum distillation kettle 1 through a hot liquid pipeline, a feed circulation pump 21, and a heating water tank 14 in sequence; the bottom of the vacuum distillation kettle 1 is connected to the top of the feed water tank 18 through a hot liquid pipeline;

[0010] The bottom of the condenser 2 and the bottom of the vacuum distillation kettle 1 are connected to the condensate collection tank 5 through condensate pipelines respectively;

[0011] The tops of the condenser 2, the vacuum distillation kettle 1, and the feed water tank 18 are connected in sequence through a gas pipeline; the gas pipeline between the vacuum distillation kettle 1 and the feed water tank 18 is connected to the external hot liquid pipeline at the top of the feed water tank 18 through a ball valve; the external hot liquid pipeline at the bottom of the feed water tank 18 is branched through a ball valve, one branch is connected to the external hot liquid pipeline at the top of the feed water tank 18 through a gas pipeline, and the other branch is connected to the atmosphere through a ball valve to lead out the hot liquid.

[0012] The vacuum distillation kettle 1 includes an upper flange 22, a cooling jacket 23, a lower flange 24, a sprayer 25, an inner cylinder 26, a porous medium 27, and an outlet weir plate 28. The upper and lower flanges 22 and 24 are respectively connected and fastened with gaskets at both ends of the vacuum distillation kettle 1 to ensure airtightness. The interior of the vacuum distillation kettle 1 is composed of the sprayer 25 and the upper air extraction port 34, the porous medium 27 and its supporting inner cylinder 26, the outlet weir plate 28, and the outlet pipe from top to bottom. The cooling jacket 23 is located on the inner side wall of the vacuum distillation kettle 1, and the two ends of the side wall of the cooling jacket 23 are respectively connected to the water outlet pipe 29 and the water inlet pipe 33.

[0013] The outlet pipe includes a lower air extraction port 31, a hot liquid outlet 30, and a condensate outlet 32, wherein the condensate outlet 32 ​​is located outside the hot liquid outlet 30;

[0014] The inlet of the sprayer 25 is connected to the hot liquid pipeline; when the vacuum-type air-gap diffusion distillation device is in operation, under the operation of the vacuum pump, the air in the vacuum distillation kettle 1 is extracted from the upper air pumping port 34 and the lower air pumping port 31, and the upper air pumping port 34 and the lower air pumping port 31 are connected to the air gap and the inner cylinder, and the air gap is located between the porous medium 27 and the cooling jacket 23. The upper air pumping port 34 is connected to the upper end of the condenser 2 through a gas pipeline, and the lower air pumping port 31 is connected to the upper end of the condensate collection tank 5 through a gas pipeline;

[0015] The hot liquid is evenly sprayed from the circular sprayer 25 above to the top of the porous medium 27 and flows out along the hot liquid outlet 30 of the lower flange 24. The outlet weir 28 isolates the hot liquid and condensate to prevent contamination.

[0016] The cold runner is arranged in the form of a cooling jacket. Cooling water flows in from the water inlet pipe 33 below the cooling jacket 23. The water inlet pipe 33 is connected to the outlet of the circulating pump 4 and flows out from the upper water outlet pipe 29 to cool the inner cold wall. The hot liquid vapor diffuses through the air gap and is condensed on the inner cold wall. The condensate flows down by gravity and flows out along the condensate outlet 32 ​​between the outlet weir plate 28 and the inner cold wall. The condensate outlet 32 ​​is connected to the condensate collection tank 5.

[0017] The decompression type air gap diffusion distillation device also includes a broken cavity 12; the vacuum pump 7 is connected to the broken cavity 12 through a gas pipeline through a needle valve and a ball valve; the bottom of the condensate collection tank 5 is connected to the top of the broken cavity 12 through a condensate pipeline through a ball valve; the side wall of the broken cavity 12 is connected to the air through a gas pipeline through a ball valve; the bottom of the broken cavity 12 is led out through a condensate pipeline through a ball valve.

[0018] A method for using a reduced pressure air gap diffusion distillation device is divided into the following three steps:

[0019] Process 1: By adjusting the opening of the needle valve 6 and cooperating with the vacuum pump 7, the vacuum distillation kettle 1 is evacuated as a whole to maintain a low-pressure working environment in the vacuum distillation kettle 1;

[0020] Process 2: Cooling circulating water flows from bottom to top into the cooling jacket 23 in the vacuum distillation kettle 1 and the cooling pipe of the external condenser 2, absorbing heat to cool the cold wall of the vacuum distillation kettle 1 and the cooling pipe of the external condenser 2;

[0021] Process three: the feed solution to be separated is heated to a hot liquid by the heating water tank 14, first entering from the upper end of the vacuum distillation kettle 1, and then the hot liquid flows from the upper end sprayer 25 into the upper end of the hydrophilic porous medium 27 and seeps downward; finally, under the influence of the capillary force of the porous medium and the adsorption and transport action of the hydrophilic porous skeleton, the hot liquid gradually spreads evenly in the porous medium and diffuses to the interface between the hot runner and the air gap; at the "gas-liquid-solid" interface, the hot liquid vapor / gas molecules diffuse into the air gap in the form of surface free diffusion. Since the cooling wall surface of the vacuum distillation kettle 1 is affected by the heat absorption of the cooling water, the temperature is much lower than the average temperature in the air gap. Under the action of the saturated steam partial pressure difference, the hot liquid vapor / gas molecules in the air gap are condensed / absorbed on the surface of the condensation plate and flow downward along the condensation plate under the action of gravity to the condensate collection tank 5. The residual feed solution flows back from the lower end of the vacuum distillation kettle 1 to the feed water tank 18, and is mixed with the unevaporated feed solution to proceed to the next cycle;

[0022] Process 4: The hot liquid vapor that is not fully condensed in the vacuum distillation kettle 1 is drawn into the condenser 2 under the operation of the vacuum pump 7 for secondary condensation; the condensate in the condenser 2 and the condensate in the vacuum distillation kettle 1 flow into the condensate collection tank 5 by gravity, and can be obtained from the rupture cavity 12 by performing a rupture operation; the non-condensable gas in the condensate collection tank 5 is extracted by the vacuum pump 7.

[0023] The vacuum distillation kettle 1 is designed to be cylindrical in shape, and the porous medium inside it is selected according to the viscosity and type of the feed solution to be separated; the porous medium meets the following requirements: 1. It does not chemically react with the feed solution to be separated; 2. It does not undergo thermal deformation at the operating temperature; 3. It is a hydrophilic material with a contact angle of less than 90°.

[0024] The heating heat source of the heating water tank 14 is a low-grade heat source. The evaporation principle of the vacuum distillation kettle 1 is steam diffusion distillation driven by temperature difference under a reduced pressure environment. The heating temperature of the heating water tank 14 is lower than the boiling point of the liquid to be treated.

[0025] The vacuum pump 7 is selected with a corresponding pumping rate according to the scale of the device to ensure that a low-pressure environment is maintained for the entire device.

[0026] The feed solution to be separated is a saline solution, an acid solution and an alkaline solution that have been pre-treated and filtered.

[0027] The beneficial effects of the present invention are: on the basis of atmospheric pressure air gap diffusion distillation, a reduced pressure operating environment is used, thereby improving the device throughput and the utilization efficiency of low-grade thermal energy. The reduced pressure environment has the following three main effects on improving the device throughput: (1) At the evaporation level, under reduced pressure conditions, the solution to be treated has a lower boiling point, and at the same heating temperature, its evaporation rate is higher. (2) At the vapor diffusion level, under reduced pressure conditions, the solution vapor has a lower mass transfer resistance in the distillation kettle, and its diffusion coefficient is higher than the diffusion coefficient under atmospheric pressure, so that the evaporated vapor diffuses to the cold wall in time for condensation. (3) At the condensation level, since the vacuum pump extracts most of the air in the equipment, the effect of non-condensable steam on condensation is greatly weakened in the condensation link, so that the solution vapor is fully condensed on the cold wall. The device has a simple structure, easy operation, and low maintenance cost; it can separate inorganic or organic solutions including corrosive solutions; and it can use low-grade heat sources as heating sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the overall structural flow chart of the vacuum gas-gap diffusion distillation device;

[0029] Figure 2 Schematic diagram of a vacuum distillation kettle; (a) is a partial cross-sectional view; (b) is an axonometric view;

[0030] In the figure: 1- vacuum distillation kettle, 2- condenser, 3- ball valve a, 4- cooling water circulation pump, 5- condensate collection tank, 6- needle valve, 7- vacuum pump, 8- ball valve b, 9- ball valve c, 10- ball valve d, 11- ball valve e, 12- broken cavity, 13- ball valve f, 14- heating water tank, 15- ball valve g, 16- ball valve h, 17- ball valve i, 18- feed water tank, 19- ball valve j, 20- ball valve k, 21- feed circulation pump, 22- upper flange, 23- cooling jacket, 24- lower flange, 25- sprayer, 26- inner cylinder, 27- porous medium, 28- outlet weir, 29- water outlet pipe, 30- hot liquid outlet, 31- lower air pumping port, 32- condensate outlet, 33- water inlet pipe, 34- upper air pumping port. DETAILED DESCRIPTION

[0031] The specific implementation process of the present invention is described in detail below in conjunction with the technical solution and the accompanying drawings.

[0032] A vacuum porous medium air gap diffusion distillation device comprises a vacuum distillation kettle 1, a condenser 2, a cooling water circulation pump 4, a condensate collection tank 5, a needle valve 6, a vacuum pump 7, a cavity 12, a heating water tank 14, a feed water tank 18, a feed circulation pump 21 and a plurality of ball valves.

[0033] The cooling water circulation pump 4 is connected to the bottom of the vacuum distillation kettle 1 and the bottom of the condenser 2 through cooling water pipelines respectively through ball valves a3 and c9; the top of the vacuum distillation kettle 1 and the top of the condenser 2 are respectively connected back to the cooling water circulation pump 4 through cooling water pipelines; the ball valves a3 and c9 control opening and closing;

[0034] The vacuum pump 7 is connected to the bottom of the condenser 2 and the top of the condensate collecting tank 5 through gas pipelines; the bottom of the vacuum distillation kettle 1 is connected to the top of the condensate collecting tank 5 through a gas pipeline; a needle valve 6 is provided on the gas pipeline to adjust the opening;

[0035] The bottom of the feed water tank 18 is connected to the top of the vacuum distillation kettle 1 through a hot liquid pipeline, a feed circulation pump 21, and a heating water tank 14 in sequence; the bottom of the vacuum distillation kettle 1 is connected to the top of the feed water tank 18 through a hot liquid pipeline;

[0036] The bottom of the condenser 2 and the bottom of the vacuum distillation kettle 1 are connected to the condensate collection tank 5 through condensate pipelines respectively;

[0037] The tops of the condenser 2, the vacuum distillation kettle 1, and the feed water tank 18 are connected in sequence via a gas pipeline. The gas pipeline between the vacuum distillation kettle 1 and the feed water tank 18 is connected to the external hot liquid pipeline at the top of the feed water tank 18 via a ball valve g15. Ball valves h16 and i17 are installed on the external hot liquid pipeline at the top of the feed water tank 18.

[0038] The external hot liquid pipeline at the bottom of the feed water tank 18 branches out after passing through the ball valve j19. One branch passes through the gas pipeline to the external hot liquid pipeline at the top of the feed water tank 18, and the other branch passes through the ball valve k20 to communicate with the atmosphere to lead out the hot liquid.

[0039] Preferably, the pressure-reducing air gap diffusion distillation device also includes a rupture cavity 12; the vacuum pump 7 is connected to the rupture cavity 12 through a gas pipeline through a needle valve 6 and a ball valve e11; the bottom of the condensate collection tank 5 is connected to the top of the rupture cavity 12 through a condensate pipeline through a ball valve d10; the side wall of the rupture cavity 12 is connected to the air through a gas pipeline through a ball valve b8; the bottom of the rupture cavity 12 is led out through a condensate pipeline through a ball valve f13.

[0040] The vacuum distillation kettle 1 includes an upper flange 22, a cooling jacket 23, a lower flange 24, a sprayer 25, an inner cylinder 26, a porous medium 27, and an outlet weir 28. The upper and lower flanges 22 and 24 are respectively connected and fastened with gaskets at both ends of the vacuum distillation kettle 1 to ensure airtightness. The interior of the vacuum distillation kettle 1 is composed of the sprayer 25 and the upper air extraction port 34, the porous medium 27 and its supporting inner cylinder 26, the outlet weir 28, and the outlet pipe from top to bottom. The cooling jacket 23 is located on the inner side wall of the vacuum distillation kettle 1 and is respectively connected to the water outlet pipe 29 and the water inlet pipe 33.

[0041] The outlet pipe includes a lower air extraction port 31, a hot liquid outlet 30, and a condensate outlet 32, wherein the condensate outlet 32 ​​is located outside the hot liquid outlet 30;

[0042] The inlet of the sprayer 25 is connected to the hot liquid pipeline; when the vacuum-type air-gap diffusion distillation device is in operation, under the operation of the vacuum pump, the air in the vacuum distillation kettle 1 is extracted from the upper air pumping port 34 and the lower air pumping port 31, and the upper air pumping port 34 and the lower air pumping port 31 are connected to the air gap and the inner cylinder, and the air gap is located between the porous medium 27 and the cooling jacket 23. The upper air pumping port 34 is connected to the upper end of the condenser 2 through a gas pipeline, and the lower air pumping port 31 is connected to the upper end of the condensate collection tank 5 through a gas pipeline;

[0043] The hot liquid is evenly sprayed from the circular sprayer 25 above to the top of the porous medium 27 and flows out along the hot liquid outlet 30 of the lower flange 24. The outlet weir 28 isolates the hot liquid and condensate to prevent contamination.

[0044] The cold runner is arranged in the form of a cooling jacket. Cooling water flows in from the water inlet pipe 33 below the cooling jacket 23. The water inlet pipe 33 is connected to the outlet of the circulating pump 4 and flows out from the upper water outlet pipe 29 to cool the inner cold wall. The hot liquid vapor diffuses through the air gap and is condensed on the inner cold wall. The condensate flows down by gravity and flows out along the condensate outlet 32 ​​between the outlet weir plate 28 and the inner cold wall. The condensate outlet 32 ​​is connected to the condensate collection tank 5.

[0045] During operation, cooling water, driven by cooling water circulation pump 4, flows from bottom to top into the cold wall flow channel of vacuum distillation kettle 1 and the cooling pipes within condenser 2. Under the operation of vacuum pump 7, the operating pressure of vacuum distillation kettle 1 is maintained by adjusting the opening of needle valve 6. After the liquid to be processed is added to feed water tank 18 through ball valves h16 and i17, the hot liquid flows to heating water tank 14 under the operation of feed circulation pump 21 for heating to a specified temperature. After heating, the hot liquid flows into vacuum distillation kettle 1, where it undergoes the physical processes of evaporation and condensation. After evaporation and separation, the residual hot liquid flows back to feed water tank 18, where it mixes with the unevaporated hot liquid and undergoes the next cycle of evaporation. The hot liquid vapor that has not condensed within vacuum distillation kettle 1 is drawn into condenser 2 under the operation of vacuum pump 7 for secondary condensation. The condensate within condenser 2 and vacuum distillation kettle 1 flows by gravity into condensate collection tank 5 and can be obtained through the rupture cavity 12 by a rupture operation.

[0046] The vacuum distillation kettle 1 is designed to be cylindrical due to the reduced pressure environment. The porous medium inside it can also be selected according to the viscosity and type of the solution to be treated. It must meet the following requirements: (1) not chemically react with the solution to be treated. (2) not thermally deform at the operating temperature. (3) be a hydrophilic material with a contact angle of less than 90°.

[0047] The heating heat source of the heating water tank 14 can be a low-grade heat source. Since the evaporation principle of the equipment is steam diffusion distillation driven by temperature difference under a reduced pressure environment, the heating temperature does not need to reach the boiling point of the liquid to be treated. Using a low-grade heat source that meets the operating conditions can meet the equipment operation requirements.

[0048] The vacuum pump 7 can be selected according to the scale of the device to select a vacuum pump with a corresponding pumping rate. It should be noted that the evaporation driving force of the device is still driven by temperature difference, so the vacuum pump mainly plays the role of maintaining a low-pressure environment for the device.

[0049] The solution to be separated can be filtered saline wastewater, acid solution, or alkali solution. The material selection of the equipment pipeline should be adjusted accordingly according to the composition and type of the solution to be separated.

[0050] The distillation method can be divided into the following three steps

[0051] Process 1: The device is evacuated by adjusting the opening of the needle valve 6 and cooperating with the vacuum pump 7 to maintain the reduced pressure working environment in the reduced pressure distillation kettle 1.

[0052] Process 2: Cooling circulating water flows from bottom to top into the cooling jacket 23 in the vacuum distillation kettle 1 and the cooling pipe of the external condenser 2, absorbing heat and cooling the cold wall in the vacuum distillation kettle 1 and the cooling pipe of the external condenser 2 to a lower temperature.

[0053] Process 3: The feed solution to be separated is heated to a hot liquid in the heating water tank 14. It first enters the vacuum distillation kettle 1 from the top, then flows from the top into the hydrophilic porous medium and seeps downward. Finally, under the influence of capillary forces in the porous medium and the adsorption and transport effects of the hydrophilic porous framework, the hot liquid gradually spreads evenly within the porous medium and diffuses to the interface between the hot runner and the air gap. At the "gas-liquid-solid" interface, the hot liquid vapor / gas molecules diffuse freely across the porous medium gas-liquid interface into the air gap. Because the cooling wall absorbs heat from the cooling water, its temperature is far lower than the average temperature within the air gap. Due to the saturated vapor partial pressure difference, the hot liquid vapor / gas molecules within the air gap condense / absorb on the condensation plate surface. Under the influence of gravity, a gradually thickening condensate film flows downward along the condensation plate into the condensate collection tank 5. The residual feed solution flows back from the bottom of the vacuum distillation kettle 1 to the feed water tank 18, where it mixes with the unevaporated feed solution and proceeds to the next cycle.

[0054] Process 4: The hot material vapor that is not fully condensed in the vacuum distillation kettle 1 is drawn into the condenser 2 by the vacuum pump 6 for secondary condensation of the high-temperature hot material vapor. The non-condensable gas is extracted by the vacuum pump 7 through the condensate collection tank 5.

[0055] First, close ball valves B8, D11, F13, G15, H16, I17, J19, and K20. Open ball valves A3, C9, and D10. Turn on vacuum pump 7 and adjust the opening of needle valve 6 to bring vacuum still 1 to the desired operating pressure. Turn on cooling water circulation pump 4 to allow cooling water to flow into cooling jacket 23 and condenser 2 within vacuum still 1. Connect the pipeline at feed tank ball valve I17 to the feed solution to be treated. Open ball valves H16 and I17 to allow the pressure differential to allow the treated solution to be added to feed tank 18. Once feeding is complete, close ball valve I17 and open ball valve G15. Turn on feed circulation pump 21. Once the treated solution fills heating tank 14, turn on the heating device within heating tank 14.

[0056] When sampling and testing the feed water tank, first open ball valve j19. The hot liquid will flow to the bottom of ball valve j19 due to gravity. After opening for 5 seconds, close ball valve j19, close ball valve g15 and ball valve h16, open ball valve i17 to break the air, and then open ball valve k20 to complete the feed side sampling work. When sampling and testing the condensate, first close ball valve d10 and ball valve d11, open ball valve b8 to break the air, and then open ball valve f13 to complete the condensate sampling work.

[0057] The above-described embodiments merely express the implementation methods of the present invention, but should not be understood as limiting the scope of the patent of the present invention. It should be pointed out that for those skilled in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A vacuum-type air-gap diffusion distillation apparatus, characterized in that: The vacuum type air gap diffusion distillation device comprises a vacuum distillation kettle (1), a condenser (2), a cooling water circulation pump (4), a condensate collecting tank (5), a needle valve (6), a vacuum pump (7), a heating water tank (14), a feed water tank (18), a feed circulation pump (21) and a ball valve; The cooling water circulation pump (4) is connected to the bottom of the vacuum distillation kettle (1) and the bottom of the condenser (2) respectively through cooling water pipelines; the top of the vacuum distillation kettle (1) and the top of the condenser (2) are respectively connected back to the cooling water circulation pump (4) through cooling water pipelines; a ball valve is provided on the cooling water pipeline to control opening and closing; The vacuum pump (7) is connected to the bottom of the condenser (2) and the top of the condensate collecting tank (5) through gas pipelines; the bottom of the vacuum distillation kettle (1) is connected to the top of the condensate collecting tank (5) through a gas pipeline; a needle valve (6) is provided on the gas pipeline to adjust the opening; The bottom of the feed water tank (18) is connected to the top of the vacuum distillation kettle (1) through a hot liquid pipeline, a feed circulation pump (21), and a heating water tank (14); the bottom of the vacuum distillation kettle (1) is connected to the top of the feed water tank (18) through a hot liquid pipeline; The bottom of the condenser (2) and the bottom of the vacuum distillation kettle (1) are respectively connected to the condensate collecting tank (5) through condensate pipelines; The tops of the condenser (2), the vacuum distillation kettle (1) and the feed water tank (18) are connected in sequence through a gas pipeline; the gas pipeline between the vacuum distillation kettle (1) and the feed water tank (18) is connected to the external hot liquid pipeline at the top of the feed water tank (18) through a ball valve; the external hot liquid pipeline at the bottom of the feed water tank (18) branches through the ball valve, one branch passes through the gas pipeline to the external hot liquid pipeline at the top of the feed water tank (18), and the other branch passes through the ball valve to communicate with the atmosphere to lead out the hot liquid.

2. The vacuum type air gap diffusion distillation apparatus according to claim 1, characterized in that: The vacuum distillation kettle (1) comprises an upper flange (22), a cooling jacket (23), a lower flange (24), a sprayer (25), an inner cylinder (26), a porous medium (27) and an outlet weir plate (28); the two ends of the vacuum distillation kettle (1) are respectively connected and fastened by the upper flange (22) and the lower flange (24) and a gasket to ensure air tightness; the interior of the vacuum distillation kettle (1) is respectively composed of a sprayer (25) and an upper air extraction port (34), a porous medium (27) and its supporting inner cylinder (26), an outlet weir plate (28) and an outlet pipe from top to bottom; the cooling jacket (23) is located on the inner side wall of the vacuum distillation kettle (1), and the two ends of the side wall of the cooling jacket (23) are respectively connected to a water outlet pipe (29) and a water inlet pipe (33); The outlet pipe comprises a lower air extraction port (31), a hot liquid outlet (30), and a condensate outlet (32), wherein the condensate outlet (32) is located outside the hot liquid outlet (30); The inlet of the sprayer (25) is connected to the hot liquid pipeline; when the reduced pressure air gap diffusion distillation device is in operation, under the operation of the vacuum pump, the air in the reduced pressure distillation kettle (1) is extracted from the upper air pumping port (34) and the lower air pumping port (31), the upper air pumping port (34) and the lower air pumping port (31) are in communication with the air gap and the inner cylinder, the air gap is located between the porous medium (27) and the cooling jacket (23), the upper air pumping port (34) is connected to the upper end of the condenser (2) through the gas pipeline, and the lower air pumping port (31) is connected to the upper end of the condensate collecting tank (5) through the gas pipeline; The hot liquid is evenly sprayed from the circular sprayer (25) above to the top of the porous medium (27) and flows out along the hot liquid outlet (30) of the lower flange (24). The outlet weir (28) isolates the hot liquid and condensate to prevent contamination. The cold runner is arranged in the form of a cooling jacket. Cooling water flows in from the water inlet pipe (33) below the cooling jacket (23). The water inlet pipe (33) is connected to the outlet of the circulation pump (4) and flows out from the water outlet pipe (29) above to cool the inner cold wall. The hot liquid vapor diffuses through the air gap and is condensed on the inner cold wall. The condensate flows down by gravity and flows out along the condensate outlet (32) between the outlet weir plate (28) and the inner cold wall. The condensate outlet (32) is connected to the condensate collection tank (5).

3. The vacuum type air gap diffusion distillation apparatus according to claim 1, characterized in that: The decompression type air gap diffusion distillation device further comprises a rupture cavity (12); a vacuum pump (7) is connected to the rupture cavity (12) via a gas pipeline through a needle valve and a ball valve; the bottom of the condensate collection tank (5) is connected to the top of the rupture cavity (12) via a condensate pipeline through a ball valve; the side wall of the rupture cavity (12) is communicated with the air via a gas pipeline through a ball valve; and the bottom of the rupture cavity (12) is led out via a condensate pipeline through a ball valve.

4. A method for using the vacuum-type air-gap diffusion distillation device according to any one of claims 1 to 3, characterized in that: It is divided into the following three processes; Process 1: vacuuming the entire vacuum distillation kettle (1) by adjusting the opening of the needle valve (6) and cooperating with the vacuum pump (7) to maintain a low-pressure working environment in the vacuum distillation kettle (1); Process 2: Cooling circulating water flows from bottom to top into the cooling jacket (23) in the vacuum distillation kettle (1) and the cooling pipe of the external condenser (2), absorbing heat to cool the inner cold wall of the vacuum distillation kettle (1) and the cooling pipe of the external condenser (2); Process 3: The feed solution to be separated is heated to hot liquid by the heating water tank (14), first entering from the upper end of the vacuum distillation kettle (1), and then the hot liquid flows from the upper end of the sprayer (25) into the upper end of the hydrophilic porous medium (27), and seeps downward; finally, under the influence of the capillary force of the porous medium and the adsorption and transport action of the hydrophilic porous skeleton, the hot liquid gradually spreads evenly in the porous medium and diffuses to the interface between the hot runner and the air gap; at the "gas-liquid-solid" interface, the hot liquid vapor / gas molecules are free on the surface. The liquid vapor / gas molecules in the air gap are condensed / absorbed on the surface of the condensing plate under the action of the saturated steam partial pressure difference and flow downward along the condensing plate to the condensate collecting tank (5) under the action of gravity. The residual feed solution flows back from the lower end of the vacuum distillation kettle (1) to the feed water tank (18), and is mixed with the unevaporated feed solution to proceed to the next cycle. Process 4: The hot liquid vapor that is not fully condensed in the vacuum distillation kettle (1) is drawn into the condenser (2) under the operation of the vacuum pump (7) for secondary condensation; the condensate in the condenser (2) and the condensate in the vacuum distillation kettle (1) flow into the condensate collection tank (5) by gravity, and can be obtained from the rupture cavity (12) by performing a rupture operation; the non-condensable gas in the condensate collection tank (5) is extracted through the vacuum pump (7).

5. The method of use according to claim 4, characterized in that: The vacuum distillation kettle (1) is designed to be cylindrical in shape, and the porous medium inside it is selected according to the viscosity and type of the feed solution to be separated; the porous medium meets the following requirements: (1) does not chemically react with the feed solution to be separated; (2) does not undergo thermal deformation at the operating temperature; and (3) is a hydrophilic material with a contact angle of less than 90°.

6. The method of use according to claim 4, characterized in that: The heating source of the heating water tank (14) is a low-grade heat source, the evaporation principle of the vacuum distillation kettle (1) is steam diffusion distillation driven by temperature difference under a reduced pressure environment, and the heating temperature of the heating water tank (14) is lower than the boiling point of the liquid to be treated.

7. The method of use according to claim 4, characterized in that: The vacuum pump (7) is selected to have a corresponding pumping rate according to the scale of the device, so as to ensure that a low-pressure environment of the entire device is maintained.

8. The method of use according to claim 4, characterized in that: The feed solution to be separated is a saline solution, an acid solution and an alkaline solution that have been pre-treated and filtered.

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