Rolled membrane distillation equipment and membrane distillation system using the same

Abstract

A roll-type membrane distillation device and a membrane distillation system using the same. The roll-type membrane distillation device is formed by a hydrophobic membrane M and a condensing membrane C coupled in a roll shape, and is provided with a heating channel, a raw water channel and an evaporation channel, as well as a raw water inlet, a concentrated water outlet, a heating channel inlet, a condensing water outlet and an evaporation channel outlet; wherein the hydrophobic membrane M is a microporous flat membrane made of a hydrophobic material, and is used to provide an evaporation surface for the raw water; the heating channel is formed by being surrounded by the condensing membrane C, and is respectively adjacent to the raw water channel and the evaporation channel, and is used to input a heat source from the heating channel inlet to heat the raw water; the raw water channel is located between the condensing membrane C and the hydrophobic membrane M; and the evaporation channel is surrounded by two hydrophobic membranes. The present invention can solve the problem of high heat loss in the current roll-type membrane distillation, and can effectively control the problems of membrane wetting, concentration polarization and temperature polarization of the membrane distillation equipment.

Description

Technical Field

[0001] The invention relates to the technical fields of wastewater treatment, material separation and concentration, and resource recovery, and in particular to a roll-type membrane distillation device and a membrane distillation system using the same. Background Art

[0002] In recent years, the state has attached more and more importance to the discharge of sewage and energy conservation and emission reduction of enterprises, and has also made strict regulations on sewage discharge standards. More and more enterprises have also begun to improve their processes for energy conservation and emission reduction, and carry out primary treatment of the sewage to be discharged. Therefore, various water treatment and energy conservation and emission reduction technologies have received high attention and become a research hotspot. Among them, membrane distillation technology is an advanced technology that has received high attention. Compared with reverse osmosis and traditional evaporators, the most significant feature of membrane distillation is that it can operate stably at low pressure and low temperature, can use low-quality heat and waste heat for heating, has a high desalination rate, and has a low tendency of membrane pollution. Membrane distillation is an evaporation process in which heat transfer and mass transfer occur simultaneously. Concentration polarization and temperature polarization phenomena will also occur at the same time, thus affecting the flux and retention rate of membrane distillation. At present, the membrane distillation equipment on the market mainly includes flat plate type, roll type and hollow fiber type. Among them, only the plate type can be applied in small-scale engineering because it is easy to achieve multiple effects, while the roll type and hollow fiber type are limited due to high heat loss. Moreover, although the current roll-type membrane distillation equipment has increased the membrane area per unit volume, the membrane distillation process is still mainly vacuum membrane distillation and gas-sweep membrane distillation. In the process of realizing multiple effects, the long pipe path and complex heat loss are relatively high, resulting in high operating costs. Several roll-type membrane distillation design schemes are also disclosed in the prior art, but in the actual engineering process, the effect of reducing heat loss has not been reflected. In the application of current membrane distillation equipment, membrane wetting, concentration polarization and temperature polarization are still the key factors affecting its wide application and engineering. Summary of the invention

[0003] In view of this, the main purpose of the present invention is to provide a roll membrane distillation device and a membrane distillation system using the same, in order to at least partially solve at least one of the above-mentioned technical problems.

[0004] In order to achieve the above-mentioned object, as one aspect of the present invention, a spiral membrane distillation device is proposed, wherein the spiral membrane distillation device is formed by coupling a hydrophobic membrane M and a condensing membrane C in a spiral shape, and the spiral membrane distillation device is provided with a heating channel, a raw water channel and an evaporation channel, and is provided with a raw water inlet, a concentrated water outlet, a heating channel inlet, a condensed water outlet and an evaporation channel outlet; wherein:

[0005] The hydrophobic membrane M is a microporous flat membrane made of a hydrophobic material and is used to provide an evaporation surface for the raw water;

[0006] Condensation film C, used to condense the heat source flowing through the heating channel;

[0007] A heating channel, formed by being surrounded by the condensation film C and adjacent to the raw water channel and the evaporation channel respectively, for inputting a heat source from an inlet of the heating channel to heat the raw water to be treated in the raw water channel, and discharging the condensed heat source from a condensation water outlet;

[0008] A raw water channel, located between the condensation membrane C and the hydrophobic membrane M, is used to input raw water from the raw water inlet and discharge the concentrated raw water after heating and evaporation from the concentrated water outlet;

[0009] The evaporation channel is surrounded by the two hydrophobic membranes and is used to receive the steam generated by the evaporation of the raw water and discharge it from the outlet of the evaporation channel.

[0010] As another aspect of the present invention, a membrane distillation system is also proposed, characterized in that it comprises:

[0011] A spiral wound membrane distillation apparatus as described above;

[0012] A condensed water collection tank, which is installed outside the spiral membrane distillation assembly, is connected to the heating channel and the last stage evaporation channel in the spiral membrane distillation device, and is connected to the vacuum system;

[0013] The vacuum system is used to reduce the pressure in the evaporation channel of the roll membrane distillation equipment to increase the pressure difference on both sides of the hydrophobic membrane M. It is also used to guide the direction of the evaporation steam and pump the condensed water to the condensed water collection tank, so that the evaporation steam generated by each effect roll membrane distillation equipment enters the next effect roll membrane distillation equipment under the guidance of the vacuum system to heat the raw water.

[0014] Based on the above technical solution, it can be seen that the spiral membrane distillation equipment of the present invention has the following beneficial effects:

[0015] (1) The vertical connection of each effect membrane assembly from top to bottom greatly shortens the connection pipe, thereby reducing heat loss; the raw water flows through the raw water channel of each effect membrane assembly from top to bottom, and the flushing effect of the raw water effectively controls the membrane wetting, concentration polarization and temperature polarization;

[0016] (2) The equipment can be connected to an external self-cleaning device, and the intervals between cleaning the equipment can be controlled by PLC, which can effectively extend the membrane wetting time.

[0017] (3) Increasing the evaporation area of ​​membrane distillation can be achieved by increasing the diameter of the membrane module or by connecting multiple multi-effect spiral membrane distillation modules in parallel. When this distillation equipment is used, the membrane area per unit volume can be increased by more than 5 times compared with the plate membrane distillation equipment, thereby reducing the investment cost of membrane distillation;

[0018] (4) It can not only be used for concentrating high-salt wastewater, such as reverse osmosis / high-pressure reverse osmosis concentrated water, but also for concentrating waste acid (sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid), waste alkali and other materials;

[0019] (5) This equipment can be coupled with solar energy, factory waste heat, and waste heat generated by air compressors and refrigerators to reduce operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1A It is a longitudinal cross-sectional view of the rolled single-effect membrane distillation device of the present invention;

[0021] Figure 1B It is a transverse cross-sectional view of the rolled single-effect membrane distillation device of the present invention;

[0022] Figure 2 It is a structural schematic diagram of the roll-type multi-effect membrane distillation device of the present invention, in which a plurality of roll-type single-effect membrane distillation devices are connected in series;

[0023] Figure 3 It is a schematic diagram of the parallel connection of the spiral multi-effect membrane distillation equipment of the present invention to increase the evaporation area;

[0024] Figure 4 It is a schematic diagram of the connection of the batch five-effect spiral membrane distillation equipment of the present invention for concentrating the concentrated water of reverse osmosis;

[0025] Figure 5 It is a schematic diagram of the connection of the continuous five-effect spiral membrane distillation equipment of the present invention for the process of concentrating ferric chloride acid wastewater;

[0026] In the above drawings, the meanings of the reference numerals are as follows:

[0027] 1. Raw water inlet, 2. Water outlet, 3. Heating channel inlet, 4. Condensate outlet, 5. Evaporation channel outlet, M, hydrophobic membrane, C, condensation membrane, 6. Raw water channel, 7. Heating channel, 8. Evaporation channel, 9. Raw water storage tank, 10. Condensate collection tank, 11. Condenser, 12. Delivery pump, 13. Vacuum system. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0029] The present invention provides a roll-type membrane distillation device and a membrane distillation system using the same, which solves the problems of high heat loss and high operating cost in the current roll-type membrane distillation process, and can also effectively control the influence of membrane wetting, concentration polarization and temperature polarization.

[0030] Specifically, the spiral membrane distillation device of the present invention is formed by coupling a hydrophobic membrane M and a condensing membrane C in a spiral shape, and the spiral membrane distillation device is provided with a heating channel, a raw water channel and an evaporation channel, and is provided with a raw water inlet, a concentrated water outlet, a heating channel inlet, a condensed water outlet and an evaporation channel outlet; wherein:

[0031] The hydrophobic membrane M is a microporous flat membrane made of a hydrophobic material and is used to provide an evaporation surface for the raw water;

[0032] Condensation film C, used to condense the heat source flowing through the heating channel;

[0033] A heating channel, formed by being surrounded by the condensation film C and adjacent to the raw water channel and the evaporation channel respectively, for inputting a heat source from an inlet of the heating channel to heat the raw water to be treated in the raw water channel, and discharging the condensed heat source from a condensation water outlet;

[0034] A raw water channel, located between the condensation membrane C and the hydrophobic membrane M, is used to input raw water from the raw water inlet and discharge the concentrated raw water after heating and evaporation from the concentrated water outlet;

[0035] The evaporation channel is surrounded by the two hydrophobic membranes and is used to receive the steam generated by the evaporation of the raw water and discharge it from the outlet of the evaporation channel.

[0036] Wherein, the hydrophobic membrane M is a flat membrane with or without a support;

[0037] Preferably, the hydrophobic membrane M has a thickness of 30 to 500 microns and a pore size of 0.05 to 3 microns;

[0038] Preferably, the hydrophobic membrane M is made of PTFE, PVDF, PP, PE, organic / organic or organic / inorganic alloy material;

[0039] Preferably, the condensation film C is a flat non-porous film;

[0040] Preferably, the thickness of the condensation film C is 50 to 500 microns;

[0041] Preferably, the condensation film C is made of PTFE, PVDF, PP, PE, organic / organic or organic / inorganic alloy material.

[0042] The hydrophobic film M and the condensation film C are arranged in a stacked manner, and the hydrophobic film M and the condensation film C are separated by a mesh spacer with a thickness of 0.1 to 1 mm;

[0043] Preferably, the mesh spacer is woven or non-woven;

[0044] Preferably, the mesh spacer is made of PTFE, PVDF, PP, PE, organic / organic or organic / inorganic alloy material;

[0045] Preferably, the mesh size of the mesh spacer is 0.2 to 10 mm.

[0046] Wherein, the hydrophobic membrane M and the condensing membrane C are rolled into a cylindrical shape and vertically placed in the rolled membrane distillation equipment;

[0047] Preferably, the spiral membrane distillation equipment has a diameter of 10 to 100 cm and a height of 20 to 100 cm.

[0048] Among them, a plurality of single-effect roll-type membrane distillation devices are connected in series vertically from top to bottom to form a multi-effect roll-type membrane distillation device.

[0049] Wherein, in the multi-effect rolled membrane distillation equipment, the evaporation channel of the previous effect and the heating channel of the next effect are vertically connected; the raw water channel of the previous effect and the raw water channel of the next effect are connected.

[0050] Wherein, the operating temperature of the multi-effect spiral membrane distillation equipment is 40-100°C;

[0051] Preferably, the first effect is heated by a heat source of 70 to 150°C during operation, or by various waste heats, such as low-quality steam, or waste heat generated by the operation of air compressors and refrigeration equipment, or flue gas waste heat, cooling water process waste heat, or by coupling with solar energy equipment for heating.

[0052] The present invention also discloses a membrane distillation system, characterized in that it comprises:

[0053] A spiral wound membrane distillation apparatus as described above;

[0054] A condensed water collection tank, which is installed outside the spiral membrane distillation assembly, is connected to the heating channel and the last stage evaporation channel in the spiral membrane distillation device, and is connected to the vacuum system;

[0055] The vacuum system is used to reduce the pressure in the evaporation channel of the roll membrane distillation equipment to increase the pressure difference on both sides of the hydrophobic membrane M. It is also used to guide the direction of the evaporation steam and pump the condensed water to the condensed water collection tank, so that the evaporation steam generated by each effect roll membrane distillation equipment enters the next effect roll membrane distillation equipment under the guidance of the vacuum system to heat the raw water.

[0056] The membrane distillation system further comprises a self-cleaning device with integrated air-water flushing, which is connected to the raw water inlet and concentrated water outlet of the roll-type membrane distillation equipment and is controlled by a controller to regularly clean the hydrophobic membrane M.

[0057] The vacuum system generates a vacuum degree of 5-900 mbar.

[0058] As a preferred embodiment, the present invention further discloses a roll-type multi-effect membrane distillation device, which comprises:

[0059] A plurality of single-effect membrane distillation modules, each of which is provided with a raw water inlet, a concentrated water outlet, a heating channel inlet, a condensed water outlet and an evaporation channel outlet;

[0060] A hydrophobic membrane, which is installed in the membrane distillation module in a winding manner;

[0061] A condensing membrane, which is installed in the membrane distillation module in a winding manner;

[0062] A heating channel (condensation water channel), the heating channel is formed by a condensation film and is arranged in a winding manner in the membrane distillation module, and is adjacent to the raw water channel and the evaporation channel respectively;

[0063] A raw water channel, which is formed by a condensation membrane and a hydrophobic membrane and is disposed in the membrane distillation module in a winding manner and is adjacent to the evaporation channel and the heating channel respectively;

[0064] An evaporation channel, the evaporation channel is formed by a hydrophobic membrane and a condensation membrane and is arranged in a winding manner in the membrane distillation component and is adjacent to the raw water channel and the heating channel respectively;

[0065] The condensed water collection tank is installed outside the membrane distillation equipment, connected with the heating channel and the last stage evaporation channel in the membrane distillation equipment; and connected with the vacuum pump.

[0066] The water inlet is used to supply raw water to the membrane distillation component, the concentrate water outlet is used to discharge concentrated raw water (concentrated water) from the membrane distillation component, the membrane distillation component is used to evaporate the raw water under heating to generate steam, the heating channel inlet is used to supply the heat source to the membrane distillation component, the condensed water outlet is used to discharge the condensed heat source, the hydrophobic membrane is used for the evaporation steam generated by the raw water to enter the evaporation channel through the hydrophobic membrane, the condensation membrane is used to condense the heat source, the heating channel is used for the heat source to heat the raw water, the raw water channel is used for the raw water to receive the thermal enthalpy of the heat source and generate evaporation steam, the evaporation channel is used to collect the evaporation steam generated by the raw water for the next effect of heating the raw water, and the condensation water collection tank is used to collect condensed water generated by the steam.

[0067] The membrane assembly has a diameter of 10 to 100 cm and a height of 20 to 100 cm. The hydrophobic membrane is a flat membrane with or without a support, with a thickness of 30 to 500 microns and a pore size of 0.05 to 3 microns. The hydrophobic membrane is made of PTFE, PVDF, PP, PE, organic / organic or organic / inorganic alloy materials.

[0068] The condensation membrane is a flat non-porous membrane with a thickness of 50 to 500 microns. The condensation membrane is made of PTFE, PVDF, PP, PE, organic / organic or organic / inorganic alloy material.

[0069] The mesh spacer is woven or non-woven, and the mesh spacer is made of PTFE, PVDF, PP, PE, organic / organic or organic / inorganic alloy material, and the mesh size is 0.2 to 10 mm.

[0070] The hydrophobic membrane M and the condensation membrane C are arranged in a CM stacked arrangement, and the membranes are separated by a mesh liner of 0.1 to 5 mm. The hydrophobic membrane, the condensation membrane and the liner are rolled together into a cylindrical shape and placed vertically in the membrane distillation assembly. A membrane distillation assembly is a single-effect membrane distillation, and multiple single-effect membrane distillation assemblies are connected in series vertically from top to bottom to form a multi-effect membrane distillation device. The amount of raw water processed can be increased by connecting the multi-effect membrane distillation equipment in parallel. The upper effect evaporation channel and the lower effect heating channel are vertically connected; the upper effect raw water channel and the lower effect raw water channel are connected. The condensate outlet and the vacuum system are connected via a condensate collection tank.

[0071] In the above scheme, the operating temperature of the multi-effect membrane distillation equipment is 40-90℃. When working, the first effect heating can use a heat source of 70-150℃, such as low-quality steam, or various waste heat, such as hot water, flue gas, hot oil, etc. When working, the raw water enters the membrane distillation equipment from the raw water inlet of the first effect membrane distillation component at the top of the multi-effect membrane distillation equipment, flows through each effect membrane distillation component from top to bottom, and flows out from the concentrated water outlet of the last effect membrane distillation component. The flow rate can be adjusted by the valve of the last effect concentrated water outlet. In the first effect membrane distillation component, the raw water is heated by the heat source in the heating channel, and the generated steam enters the evaporation channel through the hydrophobic membrane, and enters the heating channel of the next effect membrane distillation component under the guidance of the vacuum system to heat the raw water; the heating source and the raw water exchange heat enthalpy and then condense and flow out from the condensed water outlet under the guidance of the vacuum system and enter the condensed water collection tank. The vacuum system is used to reduce the pressure of the evaporation channel to increase the pressure difference on both sides of the hydrophobic membrane to increase the membrane flux, and is also used to guide the direction of the evaporation steam and pump the condensed water to the condensed water collection tank. The vacuum degree of the vacuum system is 5-900mbar.

[0072] In order to make the technical solutions and advantages of the present invention more clear, the present invention is further described below with reference to the accompanying drawings and in combination with embodiments.

[0073] Example 1

[0074] like Figure 1A Shown is a longitudinal section of a single-effect spiral membrane distillation module of the present invention; Figure 1BThe figure shows a cross section of a single-effect spiral membrane distillation module; the spiral membrane distillation module is provided with a raw water inlet 1 and outlet 2, a heating channel inlet 3, a condensed water outlet 4 and an evaporation channel outlet 5; the module contains a hydrophobic membrane M and a condensation membrane C, which are stacked with CM and rolled into a shaft separated by a spacer and placed in a membrane shell to form a raw water channel 6, a heating channel 7 and an evaporation channel 8. Figure 2 As shown, multiple single-effect spiral membrane distillation modules are connected in series from top to bottom and connected to the raw water storage tank 9, the condensed water collection tank 10, the condenser 11, the delivery pump 12 and the vacuum system 13 to form a multi-effect spiral membrane distillation device. The raw water outlet of the previous effect is connected to the raw water inlet of the next effect, and the evaporation channel outlet of the previous effect is connected to the heating channel inlet of the next effect. The membrane area can be increased by increasing the diameter of the membrane module, or multiple multi-effect spiral membrane distillation modules can be connected in parallel to increase the membrane area, such as Figure 3 As shown. The delivery pump is used to deliver raw water.

[0075] Example 2

[0076] like Figure 4 As shown, a batch five-effect spiral membrane distillation device concentrates reverse osmosis concentrated water from TDS100,000ppm to TDS200,000ppm, and the high-temperature flue gas and hot water of the thermal power plant provide heat sources for it. The heat source enters the spiral multi-effect membrane distillation device from the heating channel of the first-effect membrane assembly, exchanges heat enthalpy with the reverse osmosis concentrated water entering the membrane distillation device from the top first effect, and then is condensed and flows out of the system. While the reverse osmosis concentrated water is heated, steam is generated under the control of vacuum degree and passes through the hydrophobic membrane to enter the evaporation channel; the evaporation steam enters the heating channel of the second effect under the guidance of the vacuum pump to heat the reverse osmosis concentrated water from the first effect; the heating steam of the second effect exchanges heat enthalpy with the reverse osmosis concentrated water and is condensed, and flows out from the condensation water outlet under the guidance of the vacuum system into the condensation water collection tank as water production; while the reverse osmosis concentrated water of the second effect is heated, steam is generated under the control of vacuum degree and passes through the hydrophobic membrane to enter the evaporation channel to provide a heating source for the third effect. Similarly, the concentrated reverse osmosis concentrated water flows out from the concentrated water outlet of the fifth-effect membrane distillation module and enters the reverse osmosis concentrated water balance tank for re-concentration; the steam generated by the fifth effect enters the external condenser from the evaporation channel under the guidance of the vacuum system, is condensed by external cold water, and then flows into the condensed water collection tank as produced water. Finally, the reverse osmosis concentrated water TDS can be concentrated to 220,000ppm. The equipment is connected to an external self-cleaning device, which can control the interval of equipment cleaning through PLC, and the water after cleaning the equipment is returned to the reverse osmosis concentrated water balance tank.

[0077] Example 3

[0078] like Figure 5As shown, a continuous five-effect spiral membrane distillation device is used to concentrate ferric chloride acid wastewater. The initial ferric chloride concentration is about 18%, and 100°C low-quality steam provides a heat source. The ferric chloride acid wastewater is pretreated to remove suspended matter and particulate matter before entering the membrane distillation device. The low-quality steam directly enters the roll membrane distillation equipment from the entrance of the heating channel of the first effect, exchanges heat enthalpy with the ferric chloride acid wastewater entering the membrane distillation equipment from the top first effect, and then is condensed and flows out from the condensation water outlet under the guidance of the vacuum system to enter the condensation water collection tank; while the ferric chloride acid wastewater is heated, steam is generated under the control of the vacuum degree, and passes through the hydrophobic membrane to enter the evaporation channel; under the guidance of the vacuum system, the evaporation steam enters the heating channel of the second effect to heat the ferric chloride acid wastewater from the first effect; the heating steam of the second effect exchanges heat enthalpy with the ferric chloride acid wastewater and is condensed, and flows out from the condensation water outlet under the guidance of the vacuum system to enter the condensation water collection tank to produce water; while the ferric chloride acid wastewater of the second effect is heated, steam is generated under the control of the vacuum degree, and passes through the hydrophobic membrane to enter the evaporation channel to provide a heating source for the third effect. By analogy, the concentrated ferric chloride acid wastewater flows out from the concentrated water outlet of the fifth-effect membrane distillation module through the lift pump and enters the second five-effect spiral membrane distillation device for further concentration. After 5 five-effect spiral membrane distillation devices in series, the concentration of ferric chloride can be concentrated to more than 40%. The equipment is connected to an external self-cleaning device, which can control the interval of equipment cleaning through PLC, and the water after cleaning the equipment is returned to the reverse osmosis concentrated water balance pipe.

[0079] Due to the use of the spiral membrane distillation of the present invention, the heat utilization rate in the above-described concentration process can reach 5 effects.

[0080] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A membrane distillation system, characterized in that: The invention comprises a spiral membrane distillation device, wherein the spiral membrane distillation device is formed by coupling a hydrophobic membrane M and a condensing membrane C in a spiral shape, and the spiral membrane distillation device is provided with a heating channel, a raw water channel and an evaporation channel, and is provided with a raw water inlet, a concentrated water outlet, a heating channel inlet, a condensed water outlet and an evaporation channel outlet; wherein: The hydrophobic membrane M is a microporous flat membrane made of a hydrophobic material and is used to provide an evaporation surface for the raw water; Condensation film C, used to condense the heat source flowing through the heating channel; A heating channel, formed by being surrounded by the condensation film C and adjacent to the raw water channel and the evaporation channel respectively, for inputting a heat source from an inlet of the heating channel to heat the raw water to be treated in the raw water channel, and discharging the condensed heat source from a condensation water outlet; A raw water channel, located between the condensation membrane C and the hydrophobic membrane M, is used to input raw water from the raw water inlet and discharge the concentrated raw water after heating and evaporation from the concentrated water outlet; The evaporation channel is surrounded by two hydrophobic membranes M and is used to receive the steam generated by the evaporation of the raw water and discharge it from the evaporation channel outlet; The hydrophobic membrane M and the condensing membrane C are rolled into a cylindrical shape and placed vertically in the rolled membrane distillation device; A plurality of the spiral membrane distillation devices are connected in series vertically from top to bottom to form a multi-effect spiral membrane distillation device; In the multi-effect spiral membrane distillation device, the evaporation channel of the previous effect is vertically connected to the heating channel of the next effect; the raw water channel of the previous effect is connected to the raw water channel of the next effect; The membrane distillation system also includes a self-cleaning device with integrated air-water flushing, which is connected to the raw water inlet and concentrated water outlet of the roll-type membrane distillation equipment and is controlled by a controller to regularly clean the hydrophobic membrane M.

2. The membrane distillation system according to claim 1, characterized in that: The hydrophobic membrane M is a flat membrane with or without a support; The hydrophobic membrane M has a thickness of 30 to 500 microns and a pore size of 0.05 to 3 microns; The material of the hydrophobic membrane M is PTFE, PVDF, PP, PE, organic alloy material or inorganic alloy material; The condensation film C is a flat non-porous film; The thickness of the condensation film C is 50-500 microns; The condensation film C is made of PTFE, PVDF, PP, PE, an organic alloy material or an inorganic alloy material.

3. The membrane distillation system according to claim 1, characterized in that: The hydrophobic film M and the condensation film C are arranged in a stacked manner, and the hydrophobic film M and the condensation film C are separated by a mesh spacer with a thickness of 0.1 to 1 mm; The mesh spacer is woven or non-woven; The mesh liner is made of PTFE, PVDF, PP, PE, an organic alloy material or an inorganic alloy material; The mesh size of the mesh spacer is 0.2-10 mm.

4. The membrane distillation system according to claim 1, characterized in that: The spiral membrane distillation equipment has a diameter of 10 to 100 cm and a height of 20 to 100 cm.

5. The membrane distillation system according to claim 1, characterized in that: The operating temperature of the multi-effect spiral membrane distillation equipment is 40-100°C; When working, the first effect adopts 70~150℃ heat source heating; Heat sources include: low-quality steam, or waste heat generated by the operation of air compressors and refrigeration equipment, or flue gas waste heat, cooling water process waste heat, or heating coupled with solar energy equipment.

6. The membrane distillation system according to claim 1, characterized in that: include: A condensed water collection tank, which is installed outside the spiral membrane distillation device, connected to the heating channel and the last stage evaporation channel in the spiral membrane distillation device, and connected to the vacuum system; The vacuum system is used to reduce the pressure in the evaporation channel of the roll membrane distillation equipment to increase the pressure difference on both sides of the hydrophobic membrane M. It is also used to guide the direction of the evaporation steam and pump the condensed water to the condensed water collection tank, so that the evaporation steam generated by each effect roll membrane distillation equipment enters the next effect roll membrane distillation equipment under the guidance of the vacuum system to heat the raw water.

7. The membrane distillation system according to claim 6, characterized in that: The vacuum system generates a vacuum degree of 5-900 mbar.

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