Air gap membrane distillation assembly and method for controlling such assembly

Abstract

The present invention relates to an air gap membrane distillation assembly (1) for supplying purified water, the air gap membrane distillation assembly (1) comprises an air gap membrane distiller (2) configured to produce purified water, a water supply unit (3), and a reservoir (4) connected to the air gap membrane distiller (2), the air gap membrane distiller (2) comprising an evaporation chamber (7), a condensation chamber (8), a membrane (9) having a pore size of 1000 nanometers or less separating the evaporation chamber (7) and the condensation chamber (8), a cooling chamber (30) disposed adjacent to the condensation chamber (8), and a film (31) separating the cooling chamber (30) and the condensation chamber (8) from each other. The air gap membrane distillation assembly (1) comprises pressure control means configured to maintain the pressure in the evaporation chamber (7) at 0.1 bar(e) or more and 1 bar(e) or less, and to control the pressure difference between the evaporation chamber (7) and the condensation chamber (8) to 1 bar or less.

Description

Technical Field

[0001] The present invention generally relates to an air-gap membrane distillation assembly configured to remove plastic / contaminants from water, i.e., to produce purified / clean water for industrial applications. More specifically, the present invention relates to an air-gap membrane distillation assembly capable of producing nano / ultra-purified water that does not contain particles larger than 10 nanometers. The air-gap membrane distillation assembly according to the present invention is based on a thermally driven process. That is, the raw water side is at a higher temperature than the purified water side, and the vapor pressure gradient between the raw water side and the purified water side is the driving force that causes the evaporation of the liquid and the movement of the vapor through the membrane from the raw water side to the purified water side. As a result, the vapor condenses back into a liquid on the purified water side.

[0002] The present invention particularly relates to an air-gap membrane distillation assembly for supplying purified water, and the air-gap membrane distillation assembly includes - an air-gap membrane distiller configured to produce purified water; - a water supply unit connected to the air-gap membrane distiller and configured to supply water to the air-gap membrane distiller; - a reservoir connected to the air-gap membrane distiller and configured for intermediate storage of the purified water. The air-gap membrane distiller includes an evaporation chamber, a condensation chamber, a membrane separating the evaporation chamber and the condensation chamber and having a pore size of 1000 nanometers or less, a cooling chamber disposed adjacent to the condensation chamber, and a film separating the cooling chamber and the condensation chamber from each other.

[0003] The present invention also relates to a method for controlling such an air-gap membrane distillation assembly.

[0004] The air-gap membrane distillation assembly is particularly useful in the semiconductor manufacturing industry, and semiconductor wafers along the production line pass through a plurality of cleaning steps using purified water.

Background Art

[0005] This invention is based on the fact that semiconductors are becoming increasingly miniaturized to meet the demands for faster, lower-cost, and more energy-efficient electronic devices. Therefore, in order to have wafers containing more semiconductors / structures, the semiconductors / structures on the silicon wafer become smaller, and the distances between them also decrease.

[0006] Therefore, in order to prevent semiconductor short circuits and failures, there is a growing demand for more efficient cleaning of wafers from even very small contaminants, and the water used must be ultra-purified water so as not to contaminate the wafer. Wafer cleaning consumes a large amount of ultra-purified water to obtain the required cleaning results, but the production of ultra-purified water is time-consuming, energy-intensive, and the effective life of the produced ultra-purified water is short, for example, less than 30 minutes. Furthermore, the transport of purified water in tanks or pipes generates contamination, i.e., contamination occurs due to the proliferation of existing contaminants and the addition of contaminants from the tank / pipe materials. Known air gap membrane distillation apparatuses cannot produce the required amount of purified water because the processing speed of conventional technology is too slow.

[0007] Known configurations such as direct contact membrane distillation maximize water throughput by creating a pressure difference on both sides of the membrane, or by increasing the temperature difference, in addition to the temperature difference between the evaporation chamber and the condensation chamber.

[0008] However, if the temperature difference between the evaporation chamber and the condensation chamber is high or increases, the system will be affected by temperature fluctuations within the evaporation and condensation chambers. Temperature fluctuations in the system are normal in such processes, especially with changes in the output / use of purified water. When there is a large output / use of purified water, it is necessary to add new raw water, which is at a much lower temperature than the optimal temperature in the evaporation chamber, and the temperature fluctuates while the raw water is being heated, and these temperature fluctuations are extremely difficult or impossible to predict. According to known configurations, the raw water is heated in the condensation chamber where large temperature changes occur. According to known configurations, the only way to ensure a precise temperature is to continue the water purification process, i.e., by forcibly interrupting the purification process. However, this results in a very inefficient and intermittent purification process, which has a significant negative impact on production lines that use purified water.

[0009] Temperature fluctuations have both direct technical drawbacks and the effect of increasing the pressure difference between the evaporation and condensation chambers, leading to uncontrollable fluctuations and resulting in insufficient water purification. In some cases, the vapor pressure gradient may be too low, and in other cases, water may be forced through.

[0010] Therefore, there is a need for equipment configured to efficiently generate large quantities of ultra-purified water at the point of use, i.e., near the cleaning station within a cleanroom. In addition to being used as a cleaning solution, purified water can be used as a solvent in various industrial applications.

[0011] (Purpose of the invention) The objective of the present invention is to overcome the shortcomings and problems of conventionally known air gap membrane distillation assemblies and to provide an improved air gap membrane distillation assembly.

[0012] A primary object of the present invention is to provide an improved air gap membrane distillation assembly of the type described above, which continuously provides the required amount of purified water and can be used in cleanrooms of semiconductor / wafer manufacturing plants. Another object of the present invention is to provide an air gap membrane distillation assembly that continuously provides purified water of the required purity. Another object of the present invention is to provide an air gap membrane distillation assembly with improved purity of purified water. Another object of the present invention is to provide an air gap membrane distillation assembly that reduces tap water consumption. [Overview of the project]

[0013] According to the present invention, at least the primary object is achieved by the aforementioned air gap membrane distillation assembly and method having the features described in the independent claims. Preferred embodiments of the present invention are further defined by the dependent claims.

[0014] According to a first aspect of the present invention, an air gap membrane distillation assembly of the aforementioned type is provided, characterized in that the air gap membrane distillation assembly includes pressure control means configured to maintain the pressure in the evaporation chamber at 0.1 bar(e) or more and 1 bar(e) or less, and to control the pressure difference between the evaporation chamber and the condensation chamber to 1 bar or less.

[0015] According to a second aspect of the present invention, a method is provided for controlling such an air gap membrane distillation assembly, the method being: - The step of providing a pressure of 0.1 bar(e) or more and 1 bar(e) or less in the evaporation chamber, - A step of controlling the pressure difference between the evaporation chamber and the condensation chamber to 1 bar or less, It is characterized by the following.

[0016] Therefore, the present invention is based on the insight that it is extremely important that water is not pushed / forced through the membrane from the evaporation chamber to the condensation chamber and that the evaporation pressure gradient is continuously at an optimal level in order to maximize continuous output. Accordingly, the inventors have found that the purification process is delicate and that an essential action to ensure the above requirements and provide an efficient purification process is to maintain a moderately low pressure level in the condensation chamber and to make the pressure difference between the condensation chamber and the evaporation chamber as small as possible, or even zero.

[0017] According to the present invention, the air gap membrane distiller includes a cooling chamber positioned adjacent to a condensing chamber, and the membrane distiller includes a film / foil separating the cooling chamber and the condensing chamber from each other. The adjacent position of the cooling chamber ensures proper and efficient cooling of the cooling chamber, and the separation by the film / foil ensures that the pressures in the cooling chamber and the condensing chamber are the same.

[0018] According to various embodiments of the present invention, the pressure control means for the air gap membrane condensation assembly comprises a pressure regulating device configured to control the water pressure at the inlet of the condensation chamber and the inlet of the cooling chamber. This efficiently achieves the pressure limiting of the present invention.

[0019] According to various embodiments of the present invention, the primary water supply piping includes a first buffer tank, the secondary water supply piping includes a second buffer tank, and the pressure regulating device of the pressure control means is configured to control the water pressure downstream of the first buffer tank and downstream of the second buffer tank, thereby controlling the water pressure at the inlet of the condensing chamber and the inlet of the cooling chamber. This ensures the water pressure at the inlet of the condensing chamber and the inlet of the cooling chamber, and the pressure limiting of the present invention is efficiently achieved.

[0020] According to various embodiments of the present invention, in order to control the water pressure at the inlet of the condensation chamber and the inlet of the cooling chamber, the pressure regulator includes a pressurized gas source, and the pressurized gas source is connected to the primary water supply pipe and the secondary water supply pipe. Thereby, the pressure limit of the present invention is effectively achieved.

[0021] According to various embodiments of the present invention, the primary water supply pipe includes a heater. Thereby, when the treated / purified water reaches the evaporation chamber, it is already at an appropriate / accurate temperature.

[0022] According to various embodiments of the present invention, the secondary water supply pipe includes a cooler. Thereby, the water used to cool the condensation chamber is already at an appropriate / accurate temperature when it reaches the cooling chamber.

[0023] Further advantages and features of the present invention will become apparent not only from the other dependent claims but also from the detailed description of the preferred embodiments described below.

Means for Solving the Problems

[0024] To fully understand the foregoing and other features and advantages of the present invention, it will become apparent from the detailed description of the preferred embodiments shown below in conjunction with the accompanying drawings.

Brief Description of the Drawings

[0025] [Figure 1] FIG. 1 is a schematic diagram of the main components of an air gap membrane distillation apparatus. [Figure 2] FIG. 2 is a schematic diagram of the reservoir of the air gap membrane distillation apparatus according to the first embodiment. [Figure 3] FIG. 3 is a schematic diagram of the reservoir of the air gap membrane distillation apparatus according to a modification of the first embodiment shown in FIG. 2. [Figure 4] FIG. 4 is a schematic diagram of the reservoir of the air gap membrane distillation apparatus according to the second embodiment. [Figure 5] FIG. 5 is a schematic diagram of the water supply unit of the air gap membrane distillation apparatus according to the first embodiment. [Figure 6] Figure 6 is a schematic diagram of the water supply unit of an air gap membrane distillation apparatus, which is a modified example of the first embodiment shown in Figure 5. [Figure 7] Figure 7 is a schematic diagram of the water supply unit of the air gap membrane distillation apparatus according to the second embodiment. [Figure 8] Figure 8 is a schematic diagram of the water supply unit of an air gap membrane distillation apparatus, which is a modified example of the second embodiment shown in Figure 7. [Figure 9] Figure 9 is a schematic exploded side view of an air gap membrane distillation apparatus according to a schematic embodiment. [Figure 10] Figure 10 shows a schematic side view of the air gap membrane distillation apparatus shown in Figure 9. [Figure 11] Figure 11 is a schematic side view of another schematic embodiment of an air gap membrane distiller. [Modes for carrying out the invention]

[0026] First, refer to Figure 1, which shows a schematic diagram of the main components of the air gap membrane distillation apparatus indicated by reference numeral 1.

[0027] The air gap membrane distillation assembly 1 comprises an air gap membrane distiller 2 configured to produce purified water, i.e., ultra-purified water; a water supply unit 3 connected to the air gap membrane distiller 2 and configured to supply the water to be treated to the air gap membrane distiller 2; a reservoir 4 connected to the air gap membrane distiller 2 and configured to receive purified water from the air gap membrane distiller 2; and a purified water dispensing device 5 connected to the reservoir 4. The reservoir 4 is configured for the intermediate / temporary storage of purified water.

[0028] The water supply unit 3 is connected to at least one raw water source 6, for example, a water pipe, i.e., tap water. The purified water dispensing device 5 may be a manually operated nozzle / handle or an automatically controlled nozzle.

[0029] The air gap membrane distillation apparatus 2 comprises a sealed evaporation chamber 7 and a sealed condensation chamber 8, which are separated from each other by a membrane 9. The condensation chamber 8 is also known as a gas chamber. According to various embodiments, the air gap membrane distillation apparatus 2 comprises multiple sets of evaporation chambers 7 and condensation chambers 8, such sets arranged parallel to each other. Preferably, each evaporation chamber 7 is integrated with two condensation chambers 8, and the condensation chambers 8 are arranged facing each other with respect to the evaporation chamber 7, i.e., one on each side of the evaporation chamber. The membrane 9 has a pore size of 1000 nanometers or less, preferably 750 nanometers or less, and more preferably 500 nanometers. The membrane 9 has a pore size of 100 nanometers or more. Smaller pore sizes generally allow for the supply of cleaner water, but at the same time, the production of purified water is slower. The pores must be small enough to prevent liquid penetration.

[0030] The water supply unit 3 supplies raw water to the evaporation chamber 7, that is, the evaporation chamber 7 is filled with hot water, for example, hot water between 80°C and 90°C. The water itself cannot pass through the membrane 9, but the vapor at the interface between the water and the membrane 9 passes through the membrane 9 and enters the condensation chamber 8, leaving contaminants / particles in the evaporation chamber 7. The temperature in the condensation chamber 8 is lower than the temperature in the evaporation chamber 7, that is, the evaporation chamber 8 is cooled, and the vapor that has passed through the membrane 9 accumulates / condenses as droplets in the condensation chamber 8. The condensation chamber 8 is equipped with a cooling surface 10 where more efficient vapor condensation occurs. The droplets accumulate and eventually flow to the bottom of the condensation chamber 8, from which purified water exits the air gap membrane distiller 2 and enters the reservoir 4.

[0031] The film 9 is manufactured from a thermally and chemically stable material, preferably a hydrophobic material, such as polytetrafluoroethylene (PTFE), polypropylene (PP), or polyvinylidene fluoride (PVDF).

[0032] The reservoir 4 includes at least one tank 11a for intermediate / temporary storage of purified water. For example, purified water used during wafer cleaning may be collected in the tank / drain 12 and reused in the water source 6. The tank / drain 12 may be equipped with appropriate filters to prevent contaminants / substances added to the water during the cleaning step from reaching the water source 6. The air gap membrane distillation assembly 1 may also include a pre-filter positioned between the water source 6 and the water supply unit 3.

[0033] Refer to Figure 2-4, which shows different schematic embodiments and variations of the reservoir 4 of the air gap membrane distillation assembly 1.

[0034] First, referring to Figure 2, a schematic diagram of the reservoir 4 of the air gap membrane distillation assembly 1 according to a first schematic embodiment is shown, which includes one tank 11a for the intermediate / temporary storage of purified water.

[0035] According to various embodiments, the first tank 11a comprises an intermediate pipe 13 connected to an air gap membrane distiller 2 and preferably having a controllable intermediate valve 14, and an outlet pipe 15 connected to a purified water distributor 5 and preferably having a controllable outlet valve 16. The first tank 11a is arranged so that purified water flows automatically toward the outlet pipe 15, which is connected to the tank at the bottom of the tank.

[0036] If the purified water in the first tank 11a is not completely utilized within the time limit, i.e., before the effective period of the purified water in the first tank 11a ends, the remaining contents of the first tank 11a are discharged / discarded before the first tank 11a is refilled. This discharge / discarding may be done manually by directing the dispenser 5 directly into the tank / drain 12. It should be noted that the first tank 11a does not need to be completely filled before the purified water from the first tank 11a is utilized. Preferably, the first tank 11a is filled to an extent / range corresponding to the required amount of purified water by the dispenser 5 during the time the purified water is considered clean / usable.

[0037] Next, we refer to Figure 3, which shows a schematic diagram of the reservoir 4 of the air gap membrane distillation assembly 1, a modified example of the first schematic embodiment shown in Figure 2.

[0038] According to various embodiments, the first tank 11a is equipped with a discharge / waste piping 17 having a controllable discharge valve 18, and the discharge piping 17 bypasses the distribution device 5. By using such a configuration, the discharge / waste of excess contents from the first tank 11a is performed automatically without the risk of contaminating the distribution device 5 with old / unusable water. The discharge piping 17 is preferably connected to a water source 6, either directly or via a tank / drain 12.

[0039] It is important that no residue remains in the tank, as any residue would contaminate the next batch of purified water if the first tank 11a is emptied. According to various embodiments, the membrane distillation assembly 1 comprises a pressurized gas source 19, preferably containing nitrogen gas or the like. The first tank 11a comprises a gas supply piping 20 connected to the gas source 19 and having a controllable gas valve 21. The pressurized gas from the gas source 19 is used to empty the first tank 11a via an outlet valve 16 and / or a discharge valve 18. The gas supply piping 20 is preferably connected to the first tank 11a via an intermediate pipe 13 and an adjacent or downstream intermediate pipe 13 of an intermediate valve 14.

[0040] Next, we refer to Figure 4, which shows a first schematic embodiment of the reservoir 4 of the air gap membrane distillation assembly 1.

[0041] The reservoir 4 includes at least two tanks 11a and 11b for the intermediate / temporary storage of purified water. The tanks 11a and 11b are connected in parallel to each other between the air gap membrane distillation apparatus 2 and the purified water dispensing apparatus 5. During the operation of the air gap membrane distillation assembly 1, the first tank 11a is filled with purified water from the membrane distillation apparatus 2, and the second tank 11b supplies purified water to the dispensing apparatus 5, and vice versa. This allows for the simultaneous and continuous production and utilization of purified water. Preferably, the first tank 11a is filled to a degree / range corresponding to the demand for purified water in the dispensing apparatus 5 at the same time as the second tank 11b, etc., is being filled.

[0042] According to various embodiments, each of the tanks 11a and 11b is connected to the air gap membrane distiller 2 and comprises an intermediate pipe 13 having a controllable intermediate valve 14, and an outlet pipe 15 connected to the purified water distributor 5 and having a controllable outlet valve 16. This allows the distribution tanks of the reservoir 4 to be filled and emptied individually. The tanks 11a and 11b are arranged so that purified water flows automatically toward the outlet pipe 15, which is connected to the lowest tank relative to the tanks.

[0043] If the purified water in the first tank 11a is not completely utilized within the time limit, i.e., before the effective period of the purified water in the first tank 11a ends and / or before the second tank 11b is filled, the remaining contents of the first tank 11a are discharged / discarded before the purified water in the second tank 11b is utilized. This discharge / discarding may be done manually by directing the dispensing device 5 directly into the tank / drain 12.

[0044] According to various embodiments, each of the tanks 11a and 11b is equipped with a discharge / waste pipe 17 having a controllable discharge valve 18, and the discharge pipe 17 bypasses the distributor 5. By using such a configuration, the discharge / waste of excess contents from one of the tanks 11a and 11b is performed automatically, and / or, at the same time, the purified water from the other tank 11a and 11b is utilized by the distributor 5. The discharge pipe 17 is preferably connected directly to the water source 6 or indirectly via a tank / drain 12.

[0045] According to the present invention, the air gap membrane distillation assembly 1 is configured to maintain the pressure in the evaporation chamber 7 between 0.1 bar(e) and 1 bar(e), and to control the pressure difference between the evaporation chamber 7 and the condensation chamber 8 to 1 bar or less. Therefore, water is not forced / pushed through the membrane 9, but is drawn in through the membrane by the vapor pressure gradient from the temperature difference between the evaporation chamber 7 and the condensation chamber 8. Note that 1 bar(e) means an overpressure of 1 bar.

[0046] According to various embodiments of the present invention, the pressure control means is configured to maintain the pressure in the evaporation chamber 7 at 0.6 bar(e) or less, and / or the pressure control means is configured to control the pressure difference between the evaporation chamber 7 and the condensation chamber 8 to 0.6 bar or less, preferably 0.3 bar or less. The process is preferably controlled to prevent any pressure difference from occurring between the evaporation chamber 7 and the condensation chamber 8.

[0047] According to various embodiments, the pressure control means includes sub-means configured to maintain / control the pressure of raw water supplied / flowed from the water supply unit 3 to the evaporation chamber 7, and sub-means configured to maintain / control the gas pressure in the condensation / gas chamber 8. The condensation / gas chamber preferably contains nitrogen gas or the like. The gas pressure in the condensation / gas chamber 8 may be maintained / controlled directly or indirectly, as described below. A control unit may be operably connected to the means for maintenance and control, thereby configured to maintain the pressure limits, or the system to adjust automatically.

[0048] Therefore, according to the present invention, the method comprises the steps of providing a pressure of 0.1 bar(e) or more and 1 bar(e) or less in the evaporation chamber 7, and controlling the pressure difference between the evaporation chamber 7 and the condensation chamber 8 to 1 bar or less. Preferably, the pressure in the evaporation chamber 7 is the reference, and the pressure in the condensation chamber 8 is adapted / adjusted.

[0049] Next, different schematic diagrams of the water supply unit 3 of the air gap membrane distillation assembly 1 are shown, with reference to Figures 5-8, which include different embodiments of the pressure control means. These modifications and embodiments have basic features common to each other, which will be described with reference to Figure 5.

[0050] According to various embodiments, the water supply unit 3 is connected to the evaporation chamber 7 of the air gap membrane distiller 2 and includes a primary water supply pipe indicated by reference numeral 22, the primary water supply pipe 22 including a heater 23 configured to raise the temperature of the water in the primary water supply pipe 22. Thus, the water supplied to the evaporation chamber 7 is preheated to an appropriate temperature before entering the evaporation chamber 7. This minimizes / eliminates temperature fluctuations within the evaporation chamber 7.

[0051] At the outlet (lower end) of the primary water supply pipe 22, the primary water supply pipe 22 is preferably equipped with appropriate sensors, such as temperature, pressure, and flow sensors, which allow monitoring of the characteristics / properties of the water flow into the evaporation chamber 7, i.e., downstream of the heater 23.

[0052] According to various embodiments of the water supply unit 3, the primary water supply piping 22 is connected to a heater 23 and includes a water supply piping 26 configured to be connected to a water source 6, the water supply piping 26 includes a controllable charge valve 27 for charging the primary water supply piping 22. According to various embodiments, the water supply unit 3 includes a primary return water piping 28 extending from the evaporation chamber 7 to the heater 23, to which unpurified water in the air gap membrane distiller 2, i.e., water that has not passed through the membrane 9, is returned / reused, which is advantageous because it already has a high temperature. Note that even if the returned / reused untreated water is conveniently diluted by adding new raw water via the charge valve 27, the returned / reused untreated water will become more contaminated with each input. Therefore, the primary water supply piping 22 may include a dump / discharge valve for discharging untreated water with a high degree of contamination.

[0053] Preferably, a sensor located at the downstream end of the primary water supply piping 22 is also used to control the charge valve 27 and / or heater 23. The primary water supply piping 22 preferably includes an air vent adjacent to the heater 23, which removes unwanted evaporated air from the water when the water is heated in the heater 23.

[0054] The water supply unit 3 is equipped with a pressure regulating / reducing valve 29 to prevent the pressure from becoming excessively high in the primary water supply piping 22. The pressure regulating valve 29 may be located between the water source 6 and the water supply unit 3, or within the water supply unit 3, which is not shown in the figure.

[0055] The flow rate in the primary water supply piping 22 is within the range of 1-5 liters / minute, and the production rate of purified water stored in the reservoir 4 is within the range of 1-4 liters / minute.

[0056] According to the present invention, as shown in Figure 1, the air gap membrane distiller 2 includes a sealed cooling chamber 30 positioned adjacent to the condensing chamber 8. The cooling chamber 30 is configured to have a cooling surface 10. The air gap membrane distiller 2 includes a film / partition / foil 31 separating the cooling chamber 30 and the condensing chamber 8 from each other, i.e., the cooling surface 10 is part of the film / partition 31. The cooling chamber 30 contains a liquid / water or gas.

[0057] According to various embodiments, the thickness of the film 31 is 0.08 mm or more and 0.25 mm or less, preferably 0.1 mm or more and 0.2 mm or less. This makes the film 31 resistant to deformation, easy to install, and keeps its insulating properties low. The cooling surface 10 is preferably as smooth as possible to allow purified water to flow downstream easily. Preferably, the film 31 is hydrophobic to allow purified water to flow downstream easily. The film 31 is preferably a hydrophobic material such as polyvinylidene fluoride (PVDF).

[0058] According to various embodiments, the feedwater unit 3 is connected to the cooling chamber 30 of the air gap membrane distiller 2 and includes a secondary feedwater pipe indicated by reference numeral 32, the secondary feedwater pipe 32 includes a cooler 33 configured to reduce the temperature of the water in the secondary feedwater pipe 32. The water in the cooling chamber 30 is at a suitable temperature to efficiently condense the vapor in the condensing chamber 8 into purified water.

[0059] The cooler 33 is preferably a thermoelectric heat pump, such as a Peltier element, which uses electrical energy to transfer heat from one side of the device to the other. The heater moves heat from the liquid / water in the secondary water supply piping 32 to the ambient air. According to another embodiment, such a thermoelectric heat pump may be directly connected to the cooling chamber 30.

[0060] At the outlet (lower end) of the secondary water supply piping 32, the secondary water supply piping 32 is preferably equipped with appropriate sensors for temperature, pressure, flow rate, etc., so that the characteristics / properties of the water flow downstream of the cooling chamber 30, i.e., the cooler 33 can be monitored.

[0061] According to various embodiments of the water supply unit 3, the secondary water supply piping 32 includes a water supply piping 36 configured to connect to a water source 6 and to a cooler 33, and the water supply piping 36 includes a controllable charge valve 37 for charging the secondary water supply piping 32. According to various embodiments, the water supply unit 3 includes a secondary return water piping 38 extending from the cooling chamber 30 to the secondary water supply piping 32, to which the cooling water is returned / reused, which is advantageous as the temperature has already dropped and reduces water usage. Preferably, a sensor located at the downstream end of the secondary water supply piping 32 is also used to control the charge valve 37 and / or the cooler 33. The secondary water supply piping 32 preferably includes an air vent.

[0062] The primary water supply piping 22 and the secondary water supply piping 32 may be connected to the water source 6 in parallel to each other, either via individual pressure reducing / regulating valves or via the same pressure reducing / regulating valve 29.

[0063] According to various embodiments, the pressure control means of the air gap membrane distillation assembly 1 includes a pressure regulator configured to control the water pressure at the inlet of the condensing chamber 7 and the inlet of the cooling chamber 30. The film 31 between the cooling chamber 30 and the condensing chamber 8 is slightly flexible and transmits the pressure state in the cooling chamber 30 to the condensing chamber 8.

[0064] Figure 5 shows a first modification of the first embodiment of the water supply unit 3. The pressure regulating device includes a pressurized gas source 19, which is preferably identical to the pressurized gas source 19 with respect to the discharge of tanks 11a and 11b of the reservoir 4. According to various embodiments, the pressure level of the gas supplied from the pressurized gas source 19 is preferably monitored and controlled using a control unit 77 so that it remains more or less constant over time. The pressurized gas source 19 is connected to the primary water supply piping 22 and the secondary water supply piping 32, thereby having substantially the same pressure level state in both water supply pipes, and consequently having substantially the same pressure level state in the evaporation chamber 7 and the cooling chamber 30 / condensing chamber 8. Individual pressure tanks are positioned between the pressurized gas source 19 and the primary water supply piping 22 and the secondary water supply piping 32, respectively.

[0065] The primary water supply piping 22 and the secondary water supply piping 32 are arranged so that pressurized gas does not enter the evaporation chamber 7 and / or cooling chamber 30. The pressure limit of the present invention described above is guaranteed / maintained by monitoring and controlling the pressure level of the gas supplied by the pressurized gas source 19.

[0066] The pressure limit of the present invention also ensures that the pressurized gas does not dissolve in water. If the pressure in the evaporation chamber 7 is higher than the pressure limit of the present invention, there is a high and imminent risk of bubbles forming / appearing in or within the membrane 9, thereby making the process / purification inefficient or inhibited.

[0067] The pressurized gas source 19 is preferably connected to the primary water supply piping 22 downstream of the heater 23, and preferably connected to the secondary water supply piping 32 downstream of the cooler 33.

[0068] Next, we refer to Figure 6, which shows a second modified example of the first embodiment of the water supply unit 3. Only features and circumstances that deviate from the embodiment according to Figure 5 are described; the remaining features are the same.

[0069] According to various embodiments, the primary feedwater piping 22 comprises a first buffer tank 25. Preferably, the first buffer tank 25 is integrated with a heater 23, and they may be arranged in a continuous manner with respect to each other as separate components along the primary feedwater piping 22. In one example of a disclosed embodiment, the feedwater piping 26 is connected to the heater 23 by connecting to the first buffer tank 25 which comprises the heater 23, a controllable charge valve 27 is configured to charge the first buffer tank 25, and the primary return water piping 28 extends from the evaporation chamber 7 to the first buffer tank 25. Alternatively, in a schematic embodiment having a heater 23 located upstream of the first buffer tank 25 along the primary feedwater piping 22, the primary return water piping 28 is connected to the heater 23.

[0070] According to various embodiments, the secondary water supply piping 32 comprises a second buffer tank 35. Preferably, the second buffer tank 35 is integrated with a cooler 33, or they may be arranged continuously with each other as separate components along the secondary water supply piping 32. In one example of the disclosed embodiments, the water supply piping 26 is connected to the cooler 33 by connecting to the second buffer tank 35 which comprises the cooler 33, a controllable charge valve 37 is configured to charge the second buffer tank 35, and the secondary return water piping 38 extends from the cooling chamber 30 to the second buffer tank 35. Alternatively, in a schematic embodiment having a cooler 33 located upstream of the second buffer tank 35 along the secondary water supply piping 32, the secondary return water piping 38 is connected to the cooler 33.

[0071] According to various embodiments, the pressurized gas source 19 is connected to the primary water supply piping 22 and the secondary water supply piping 32, respectively, by being connected to the first buffer tank 25 and the second buffer tank 35, thereby controlling the water pressure downstream of the first buffer tank 25 and the second buffer tank 35.

[0072] According to various embodiments, each of the first buffer tank 25 and the second buffer tank 35 includes a water chamber 78, a gas chamber 79, and a flexible partition 80 separating the water chamber 78 and the gas chamber 79 from each other, and a pressurized gas source 19 is connected to the gas chamber 79. This prevents the pressurized gas from mixing with the water in each tank and from reaching the evaporation chamber 7 or the cooling chamber 30, i.e., it does not interfere with the process / purification.

[0073] Next, we refer to Figure 7, which shows a first modified example of the second embodiment of the water supply unit 3. Only features and circumstances that deviate from the embodiments according to Figures 5 and 6 are described; the remaining features are the same.

[0074] According to various embodiments, the pressure regulating device includes a first water regulator 24 configured to control the flow and pressure of water supplied from a primary water supply pipe 22 to an evaporation chamber 7, a second water regulator 34 configured to control the flow and pressure of water supplied from a secondary water supply pipe 32 to a cooling chamber 30, and a control unit 77 operably connected to the first water regulator 24 and the second water regulator 34. The first water regulator 24 is located downstream of the heater 23, and the second water regulator 34 is located downstream of the cooler 33.

[0075] The first water regulator 24 and the second water regulator 24 are each preferably composed of a pump. The pump is preferably automatically drawn in by gravity to suppress excessive pressure in the evaporation chamber 7 and the cooling chamber 30, respectively.

[0076] The control unit 77 is configured to control the first water regulator 24 so that the pressure in the evaporation chamber 7 is within the pressure limits of the present invention, and the control unit 77 is configured to monitor the pressure in the cooling chamber 30 and control the second water regulator 34 so that the pressure difference is within the pressure limits of the present invention, and preferably approaches zero. Controlling the first water regulator 24 and adapting / adjusting the second water regulator 34 as necessary is a continuous process. Thus, the first water regulator 24 may be called the master and the second water regulator 34 may be called the slave.

[0077] Next, we refer to Figure 8, which shows a second modification of the second embodiment of the water supply unit 3. Only features and circumstances that deviate from the embodiment according to Figure 7 are described; the remaining features are the same.

[0078] According to various embodiments, the primary feed piping 22 comprises a first buffer tank 25. Preferably, the first buffer tank 25 is integrated with a heater 23, or they may be arranged continuously with respect to each other as separate components along the primary feed piping 22. In one example of a disclosed embodiment, the feed piping 26 is connected to the heater 23 by connecting to the first buffer tank 25 which comprises the heater 23, a controllable charge valve 27 is configured to charge the first buffer tank 25, and the primary return water piping 28 extends from the evaporation chamber 7 to the first buffer tank 25. Alternatively, in a schematic embodiment having a heater 23 located upstream of the first buffer tank 25 along the primary feed piping 22, the primary return water piping 28 is connected to the heater 23.

[0079] According to various embodiments, the secondary water supply piping 32 comprises a second buffer tank 35. Preferably, the second buffer tank 35 is integrated with a cooler 33, or they may be arranged in a continuous manner as separate components along the secondary water supply piping 32. In one example of a disclosed embodiment, the water supply piping 26 is connected to the cooler 33 by connecting to the second buffer tank 35 which comprises the cooler 33, a controllable charge valve 37 is configured to charge the second buffer tank 35, and the secondary return water piping 38 extends from the cooling chamber 30 to the second buffer tank 35. Alternatively, in a schematic embodiment having a cooler 33 located upstream of the second buffer tank 35 along the secondary water supply piping 32, the secondary return water piping 38 is connected to the cooler 33.

[0080] According to various embodiments, the first water regulator 24 is located downstream of the heater 23 by being located downstream of the first buffer tank 25, and the second water regulator 34 is located downstream of the cooler 33 by being located downstream of the second buffer tank 35.

[0081] At least the reservoir 4 and the piping extending from the condensing chamber 8 to the distribution device 5 are preferably treated to have hydrophobic surfaces facing the purified water, thereby facilitating the flow of purified water.

[0082] Next, refer to Figure 9-10, which shows a schematic diagram of the air gap membrane distiller 2. The air gap membrane distiller 2 comprises a stack of different members / elements to supply the evaporation chamber 7, condensation chamber 8, and cooling chamber 30. However, the air gap membrane distiller 2 stack preferably comprises multiple combinations arranged parallel to each other. Preferably, the top and bottom of the stack are equipped with cooling chambers 30 to minimize heat dissipation to the ambient environment / cleanroom.

[0083] A membrane distiller 2 stack according to the disclosed schematic embodiment comprises a first end plate 39 preferably made of metal, an elastic first gasket 40, a membrane 9, a rigid first polymer frame 41, an elastic second gasket 42, a rigid second polymer frame 43, a film 31, an elastic third gasket 44, and a second end plate 45 preferably made of metal.

[0084] According to the disclosed embodiment, the first end plate 39 defines the evaporation chamber 7, and the second end plate 45 defines the cooling chamber 30, i.e., the end plates define the outer / adjacent chambers.

[0085] The membrane 9 is a multi-layer polymer membrane comprising a first layer 46 of nonwoven fabric having a pore size of 1000 nanometers or less, and a second layer 47 of spunpound laminated to the first layer 46, wherein the second layer 47 faces the condensation chamber 8, and the first layer 46 faces the evaporation chamber 7. According to various embodiments, the thickness of the membrane 9 is 0.1 mm or more and 0.4 mm or less, preferably 0.2 mm or more and 0.3 mm or less. Therefore, the first layer 46 of the membrane 9 is a filter layer. The first layer 46 of the membrane 9 preferably comprises a fluoropolymer such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF), and the second layer 47 of the membrane 9 preferably comprises a thermoreversible polymer such as polypropylene (PP).

[0086] The rigid polymer frames / carries 41, 43 preferably comprise a rigid fluoropolymer such as polyvinylidene fluoride (PVDF), and the elastic gaskets 40, 42, 44 preferably comprise an elastic fluoropolymer such as polytetrafluoroethylene (PTFE). The rigid polymer frames 41, 43 maintain their initial thickness in response to the membrane distiller 2 being installed / compressed. The elastic gaskets 40, 42, 44 acquire a thickness smaller than their initial thickness in response to the membrane distiller 2 being installed / compressed. The elastic gaskets are preferably compressed to 25% or more of their initial / unloaded thickness and 40% or less of their initial / unloaded thickness. Insufficient compression may result in leakage, while excessive compression may cause the gaskets to tighten too much, losing their sealing / elastic properties and potentially resulting in leakage. When the stack of air-gap membrane distiller 2 is installed / compressed, the first end plate 39 and the second end plate 45 are simultaneously tightened against each other as distance members with an appropriate length between the end plates to prevent overtightening. Therefore, the appropriate length of the distance member is equal to the sum of the final / compressed thickness of the gasket and the thickness of the polymer frame.

[0087] The first polymer frame 41 has a first surface 48, a second surface 49, and a central opening 50 extending between the first surface 48 and the second surface 49, and at least a portion of the condensation chamber 8 is formed by the central opening 50. The film 9 is welded to the first surface 48 of the first polymer frame 41, which covers the central opening 50, and the second layer 47 of the film 9 faces the first surface 48 of the first polymer frame 41. The film 9 may be connected to the first polymer frame 41 by other suitable methods such as adhesive, but welding (ultrasonic welding) is preferred. The second layer 47 of the film 9 facilitates the connection between the film 9 and the first polymer frame 41.

[0088] The second polymer frame 43 has a first surface 51, a second surface 52, and a central opening 53 extending between the first surface 51 and the second surface 52. The film 31 is welded to either the first surface 51 of the second polymer frame 43 that covers the central opening 53, or the second surface of the second polymer frame 43 that covers the central opening 53. The film 31 may be connected to the second polymer frame 43 by other suitable methods such as adhesive, but welding (ultrasonic welding) is preferred. When the film 31 is connected to the second surface 52 of the second polymer frame 43 (as shown in Figure 10), the central opening 53 is composed of at least a portion of the condensation chamber 8. When the film 31 is connected to the first surface 51 of the second polymer frame 43 (not shown in the figure), the central opening 53 is composed of at least a portion of the cooling chamber 30.

[0089] The elastic first gasket 40 has a first surface 54, a second surface 55, and a central opening 56 extending between the first surface 54 and the second surface 55, and at least a portion of the evaporation chamber 7 is formed by the central opening 56. An inlet 57, which is part of the primary water supply piping 22, extends to the central opening 56 at the bottom of the first gasket 40, and a portion of the primary return water piping 28 extends from the central opening 56 at the bottom of the first gasket 40.

[0090] The elastic second gasket 42 has a first surface 59, a second surface 60, and a central opening 61 extending between the first surface 59 and the second surface 60, and at least a portion of the condensation chamber 8 is formed by the central opening 61. An outlet 62, which is part of the intermediate piping 13, extends from the central opening 61 at the bottom of the second gasket 42. The second gasket 42 may also be provided with a vent 63 to suppress pressure rise within the condensation chamber 8.

[0091] The elastic third gasket 44 has a first surface 64, a second surface 65, and a central opening 66 extending between the first surface 64 and the second surface 65, and at least a portion of the cooling chamber 30 is formed by the central opening 66. The inlet 67 of the secondary water supply piping 32, which is part of the primary water supply piping 22, extends to the central opening 66 at the top of the third gasket 44, and the outlet 68, which is part of the secondary return water piping 38, extends from the central opening 66 at the part of the third gasket 44.

[0092] Next, we refer to Figure 11, which shows another schematic diagram of the schematic air gap membrane distiller 2. Only the additions / differences from the schematic embodiment in Figures 9-10 will be described.

[0093] According to various embodiments, the air gap membrane distiller 2 includes a primary feed manifold 69 located below the first gasket 40, extending between the first surface 54 and the second surface 55 of the first gasket 40, with an inlet 57 extending from the primary feed manifold 69 to the central opening 56 of the first gasket 40. The primary feed manifold 69 is part of the primary feed piping 22 and extends from the first gasket 40 to the outside of the air gap membrane distiller 2, for example, to the outer surface 70 of the first end plate 39, through an intermediate element. The primary feed manifold 69 may penetrate the entire air gap membrane distiller 2, i.e., from the outer surface 70 of the first end plate 39 to the outer surface 71 of the second end plate 45. All evaporation chambers 7 are preferably connected to the same primary feed manifold 69.

[0094] According to various embodiments, the air gap membrane distiller 2 includes a primary return water manifold 72 extending between the first surface 54 and the second surface 55 of the first gasket 40, above the first gasket 40, and the outlet 58 extending from the central opening 56 of the first gasket 40 to the primary return water manifold 72. The primary return water manifold 72 is part of the primary return water piping 28 and extends from the first gasket 40 to the outside of the air gap membrane distiller 2, for example, through an intermediate element to the outer surface 70 of the first end plate 39. The primary return water manifold 72 may penetrate the entire air gap membrane distiller 2, i.e., from the outer surface 70 of the first end plate 39 to the outer surface 71 of the second end plate 45. All evaporation chambers 7 are preferably connected to the same primary return water manifold 72.

[0095] According to various embodiments, the air gap membrane distiller 2 includes a purified water manifold 73 located below the second gasket 42, extending between the first surface 59 and the second surface 60 of the second gasket 42, with the outlet 62 extending from the central opening 61 of the second gasket 42 to the purified water manifold 73. The purified water manifold 73 is part of the intermediate piping 13 and extends from the second gasket 42 to the outer surface of the air gap membrane distiller 2, for example, through an intermediate element to the outer surface 70 of the first end plate 39. The purified water manifold 73 may penetrate the entire membrane distiller 2, i.e., from the outer surface 70 of the first end plate 39 to the outer surface 71 of the second end plate 45. All condensing chambers 8 are preferably connected to the same purified water manifold 73.

[0096] According to various embodiments, the air gap membrane distiller 2 includes a vent manifold 74 extending between the first surface 59 and the second surface 60 of the second gasket 42, above the second gasket 42, and a vent 63 extending from the central opening 61 of the second gasket 42 to the vent manifold 74. The vent manifold 74 extends from the second gasket 42 to the outside of the air gap membrane distiller 2, for example, through the outer surface 70 of the first end plate 39 via an intermediate element. The vent manifold 74 may penetrate the entire air gap membrane distiller 2, i.e., from the outer surface 70 of the first end plate 39 to the outer surface 71 of the second end plate 45. All condensing chambers 8 are preferably connected to the same vent manifold 74. The vent manifold 74 may be used to adjust the pressure level within the condensing chambers 8.

[0097] According to various embodiments, the air gap membrane distiller 2 includes a secondary feed manifold 75 extending between the first surface 64 and the second surface 65 of the third gasket 44, above the third gasket 44, with an inlet 67 extending from the central opening 66 of the third gasket 44 to the secondary feed manifold 75. The secondary feed manifold 75 is part of the secondary feed piping 32 and extends from the third gasket 44 to the outside of the membrane distiller 2, for example, through an intermediate element to the outer surface 71 of the second end plate 45. The secondary feed manifold 75 may penetrate the entire air gap membrane distiller 2, i.e., from the outer surface 70 of the first end plate 39 to the outer surface 71 of the second end plate 45. All cooling chambers 30 are preferably connected to the same secondary feed manifold 75.

[0098] According to various embodiments, the air gap membrane distiller 2 includes a secondary return water manifold 76 located below the third gasket 44, extending between the first surface 64 and the second surface 65 of the third gasket 44, and the outlet 68 extends from the central opening 66 of the third gasket 44 to the secondary return water manifold 76. The secondary return water manifold 76 is part of the secondary return water piping 38 and extends from the third gasket 44 to the outside of the air gap membrane distiller 2, for example to the second end plate 45, through an intermediate element. The secondary return water manifold 76 may penetrate the entire air gap membrane distiller 2, i.e., from the outer surface 70 of the first end plate 39 to the outer surface 71 of the second end plate 45. All cooling chambers 30 are preferably connected to the secondary return water manifold 76.

[0099] (Possible modifications of the present invention) The present invention is not limited to the embodiments described above and shown in the drawings, which are merely illustrative. This patented invention is intended to encompass all modifications and variations of the preferred embodiments described herein, and therefore the present invention is defined by the language of the appended claims, and the apparatus may be modified in all conceivable ways in the configuration of the appended claims.

[0100] It should also be noted that all information relating to terms such as above, below, superior, and inferior should be interpreted / understood in relation to the apparatus arranged according to the drawings. The drawings should be arranged so that the reference numerals can be read correctly. Therefore, these terms indicate relative relationships in the embodiments shown, and these relationships may change if the apparatus according to the present invention is provided in other configurations / designs.

[0101] It should also be noted that even if it is not explicitly stated that features from one embodiment can be combined with features from another embodiment, if such combinations are possible, they should be considered obvious.

Claims

1. The air gap membrane distillation assembly (1) for supplying purified water is - An air gap membrane distillation apparatus (2) configured to produce purified water, - A water supply unit (3) is connected to the air gap membrane distiller (2) and configured to supply water to the air gap membrane distiller (2), - A reservoir (4) connected to the air gap membrane distillation apparatus (2) and configured for the intermediate storage of purified water, Equipped with, The air gap membrane distillation apparatus (2) is, - Evaporation chamber (7), - Condensing chamber (8), - Separating the evaporation chamber (7) and the condensation chamber (8) from each other is a membrane (9) having a pore size of 1000 nanometers or less, - A cooling chamber (30) is arranged adjacent to the condensing chamber (8), - A film (31) separates the cooling chamber (30) and the condensing chamber (8) from each other, Equipped with, The air gap membrane distillation assembly (1) is characterized by comprising pressure control means configured to maintain the pressure in the evaporation chamber (7) at 0.1 bar(e) or more and 1 bar(e) or less, and to control the pressure difference between the evaporation chamber (7) and the condensation chamber (8) to 1 bar or less. Air gap membrane distillation assembly (1).

2. The pressure control means is configured to maintain the pressure in the evaporation chamber (7) at 0.6 bar(e) or less. The air gap membrane distillation assembly (1) according to claim 1.

3. The pressure control means is configured to control the pressure difference between the evaporation chamber (7) and the condensation chamber (8) to 0.6 bar or less, preferably 0.3 bar or less. The air gap membrane distillation assembly (1) according to claim 1 or 2.

4. The water supply unit (3) is equipped with a water inlet configured to be connected to a water source (6), The water supply unit (3) is - A primary water supply pipe (22) extending between the water intake port and the evaporation chamber (7), - A secondary water supply pipe (32) extending between the water intake port and the cooling chamber (30), Equipped with, The air gap membrane distillation assembly (1) according to any one of claims 1 to 3.

5. The pressure control means of the air gap membrane distillation assembly (1) includes a pressure adjustment device configured to control the water pressure at the inlet of the condensing chamber (7) and the inlet of the cooling chamber (30). The air gap membrane distillation assembly (1) according to any one of claims 1 to 4.

6. The primary water supply piping (22) includes a first buffer tank (25), The secondary water supply piping (32) includes a second buffer tank (35), The pressure regulating device of the pressure control means is configured to control the water pressure downstream of the first buffer tank (25) and downstream of the second buffer tank (35). The air gap membrane distillation assembly (1) according to claim 5.

7. The pressure regulating device includes a pressurized gas source (19), The pressurized gas source is connected to the primary water supply piping (22) and the secondary water supply piping (32). The air gap membrane distillation assembly (1) according to claim 5 or 6.

8. The pressurized gas source (19) of the pressure regulating device is connected to the first buffer tank (25) of the primary water supply piping (22) and the second buffer tank (35) of the secondary water supply piping (32). The air gap membrane distillation assembly (1) according to claim 7.

9. Each of the first buffer tank (25) and the second buffer tank (35) is, - Water chamber (78), - Gas chamber (79), - A flexible partition (80) separates the water chamber (78) and the gas chamber (79) from each other. Equipped with, The pressurized gas source (19) is connected to the gas chamber (79). The air gap membrane distillation assembly (1) according to claim 8.

10. The aforementioned pressure regulating device is - A first water regulator (24) configured to control the flow and pressure of the water supplied from the primary water supply pipe (22) to the evaporation chamber (7), - A second water regulator (34) configured to control the flow and pressure of the water supplied from the secondary water supply pipe (32) to the cooling chamber (30), - A control unit (77) operably connected to the first water regulator (24) and the second water regulator (34), Equipped with, The air gap membrane distillation assembly (1) according to claim 5.

11. The primary water supply piping (22) is equipped with a heater (23). The air gap membrane distillation assembly (1) according to any one of claims 4 to 10.

12. The water supply unit (3) is - A primary return water pipe (28) extends from the evaporation chamber (7) to the buffer tank (25), The air gap membrane distillation assembly (1) according to claim 6.

13. The secondary water supply piping (32) includes a cooler (33). The air gap membrane distillation assembly (1) according to any one of claims 4 to 12.

14. The water supply unit (3) is - A secondary return water pipe (38) extends from the cooling chamber (30) to the buffer tank (35), The air gap membrane distillation assembly (1) according to claim 6.

15. The air gap membrane distillation assembly (1) includes a purified water distributor (5) connected to the reservoir (4). The air gap membrane distillation assembly (1) according to any one of claims 1 to 14.

16. A method for controlling an air gap membrane distillation assembly (1) configured to supply purified water, The air gap membrane distillation assembly (1) is - An air gap membrane distillation apparatus (2) configured to produce purified water, - A water supply unit (3) is connected to the air gap membrane distiller (2) and configured to supply water to the air gap membrane distiller (2), - A reservoir (4) connected to the air gap membrane distillation apparatus (2) and configured for the intermediate storage of purified water, Equipped with, - The air gap membrane distillation apparatus (2) is, - Evaporation chamber (7), - Condensing chamber (8), - Separating the evaporation chamber (7) and the condensation chamber (8) from each other is a membrane (9) having a pore size of 1000 nanometers or less, - A cooling chamber (30) is arranged adjacent to the condensing chamber (8), - A film (31) separates the cooling chamber (30) and the condensing chamber (8) from each other, Equipped with, The aforementioned method, - The step of providing a pressure of 0.1 bar(e) or more and 1 bar(e) or less in the evaporation chamber (7), - A step of controlling the pressure difference between the evaporation chamber (7) and the condensation chamber (8) to be 1 bar or less, Characterized by, method.

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