JPS6233506A - Membrane distillation apparatus - Google Patents

Abstract

PURPOSE:To enhance the heat efficiency of the titled apparatus and to prevent the deterioration of the diffusion efficiency of the membrane due to the clogging of a vapor space with the descending condensate by providing a heater at the central part of a heat-transfer tube and progressively increasing the cross-sectional area of an evaporation space formed between a membranous tube and the heat-transfer tube from the upper part to the lower part. CONSTITUTION:A tapered heat-transfer tube 2 is provided in the inside of a cylindrical outer tube 1, and the cross-sectional area of the vapor space 6 formed between a membranous tube 3 and the heat-transfer tube 2 is progressively increased from the upper part to the lower part. A rod-shaped heater 4 with the upper end supported and the free lower end is furnished at the central part of the heat-transfer tube 2. The membranous tube 3 is provided between the heater 4 and the heat-transfer tube 2, the inside of the membranous tube 3 is used as the raw liq. passage 7 and the outside is used as the vapor space 6. The raw liq. from a raw liq. introducing pipe 11 is heated by the heater 4 and only the vapor is passed through the membranous tube 3, diffused into the vapor space 6 and condensed on the surface of the heat-transfer tube 2. The condensate flows downward and the amt. of the condensate is progressively increased toward the lower part. However, the vapor space is not substantially decreased, since the cross-sectional area of the vapor space is increased toward the lower part.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a membrane distillation apparatus, and more specifically, to thermopervaporation, which performs distillation by promoting evaporation of a stock solution using heat.

<Prior art> As a method for separating and concentrating a solution, a high temperature liquid to be treated, that is, a raw liquid such as hot sea water, is passed through the primary side of a porous polymer membrane that allows liquid vapor to pass through but not the liquid itself. The vapor generated from the stock solution and passed through the porous membrane is cooled and condensed on the secondary side, thus concentrating the stock solution on the next side and obtaining a condensed liquid on the secondary side. ration is already known, and various devices for it have been proposed.

For example, in Japanese Patent Publication No. 49-45461, a large number of vertically extending membrane walls and a large number of heat transfer walls are provided parallel to each other with a space between them, and a gap between two adjacent membrane walls is disclosed. A high-temperature raw liquid passageway is provided between the two adjacent heat transfer walls, a cooling water passage is provided between two adjacent heat transfer walls, and a steam space is provided between the adjacent membrane wall and the heat transfer wall for use as a passage for generated steam and distilled water. A device is described that defines cooling water passages between the heat transfer wall and the side walls, respectively, and further defines cooling water passages at both ends of the device body.

<Problems to be Solved by the Invention> According to such conventional devices, the high-temperature stock solution is heated by a heat exchanger installed outside and then introduced into the device in parallel, so the thermal efficiency due to heat radiation during introduction is low. There was a problem that a decrease in the amount of water was inevitable.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a membrane distillation apparatus that prevents wasteful heat radiation without providing a heat retaining device and has good thermal efficiency.

<Means for Solving the Problems> The membrane distillation apparatus of the present invention includes an outer tube, a heat transfer tube provided inside the outer tube to form a passage for a cooling heat medium, and a heat transfer tube of the heat transfer tube. a heater provided in the center; a membrane tube made of a porous polymer membrane that does not allow the undiluted solution to pass through but allows the vapor of the undiluted solution to pass through, and that is provided between the surface of the heater and the heat transfer tube; A stock solution inlet pipe and a stock solution outlet pipe for passing the stock solution between the membrane tube and the stock solution flow path of the heater, and a cross-sectional area that increases from the top to the bottom are provided between the membrane tube and the heat transfer tube. It is characterized by having a gradually increasing evaporation space and a condensate outlet pipe for taking out the condensate generated in the evaporation space to the outside.

<Example> FIG. 1 shows a longitudinal cross-sectional view of an example of the present invention, and FIG. 2 shows a cross-sectional view thereof.

The outer tube 1 is cylindrical and has a cooling water tube 9 at its lower end.
However, a cooling water outlet 8 is provided at the upper end thereof, and
A heat transfer tube 2 is provided inside the outer tube 1 at a predetermined distance from the outer tube, and a cooling heat medium flow path 5 is formed between the outer tube and the outer tube. A rod-shaped heater 4 is provided at the center of the heat exchanger tube 2, the upper end of which is supported and the lower end of which is a free end. A membrane tube 3 is provided between the heater 4 and the heat transfer tube 2. The inner side partitioned by the membrane tube 3 becomes the stock solution flow path 7, and the outer side becomes the evaporation space 6. The heat exchanger tube 2 is tapered so that the cross-sectional area of the evaporation space 6 gradually increases from the top to the bottom. A stock solution inlet pipe 10 is provided at the upper end of the stock solution channel 7, and a stock solution outlet pipe 11 is provided at the lower end. Further, a condensate outlet pipe 12 is provided at the lower end of the evaporation space 6 .

The porous membrane constituting the membrane tube 3 needs to have no affinity for high-temperature stock solutions; for example, if the stock solution is an aqueous solution, it must be hydrophobic; furthermore, it must not allow the stock solution to pass through; , it is necessary that the vapor has the property of being permeable. Furthermore, since the stock solution is heated, heat resistance is also required. Therefore, when the stock solution is an aqueous solution, a porous membrane made of a fluororesin such as polytetrafluoroethylene (polytetrafluoroethylene) is particularly preferred since it has both heat resistance and hydrophobicity. However, even if the porous membrane is made of a hydrophilic resin such as polysulfone or cellulose resin, the surface of the porous membrane may be coated with a water-repellent resin such as a fluororesin or silicone resin to provide a hydrophobic porous membrane surface. In some cases, these resin films can also be used.

The heat transfer tube 2 is desirably a thin-walled tube made of a material with high heat conductivity, such as metal, but may be made of plastic as long as it is a heat transfer body that has a higher heat transfer rate than the heat transfer rate due to vapor diffusion.

The membrane tube 3 is formed by supporting a porous membrane on a support tube. In this case, it is sufficient that the support tube is permeable to liquid vapor, for example made of polyamide.

A woven or nonwoven tube made of fluororesin or the like, or a porous tube made of ceramic is preferably used.

As a modified embodiment of the present invention, a circulation device or a stirring device may be provided to bring the stock solution into contact with the membrane tube 3 efficiently.

Further, a spacer may be provided between the membrane tube 13 and the heat exchanger tube 2, etc.

In the device of the present invention, the undiluted solution held in the membrane tube is heated by the heater, and while the undiluted solution is blocked by the membrane tube, only the vapor passes through, the vapor diffuses in the vapor space, and is cooled on the surface of the heat transfer tube. , the steam condenses and is led out of the device via a condensate outlet pipe.

At that time, condensate is generated on the entire surface of the heat transfer tube and flows downward, but since the cross-sectional area of the evaporation space gradually increases as it goes downward, even if the amount of condensate increases as it goes downward, Since the evaporation space is not blocked by the flowing condensate and the evaporation space is not substantially reduced, the diffusion efficiency by the membrane tube is not reduced. Further, the solute in the stock solution is blocked together with the liquid by the membrane tube and concentrated within the membrane tube. Therefore, for example, when seawater is used as the stock solution, the salts contained in the seawater are blocked by the membrane tube, and only water vapor passes through the membrane, so the seawater is concentrated in the membrane tube and distilled water can be obtained on the condensate side. can. It goes without saying that the present invention can be applied to the separation and concentration of solutions containing organic substances as well as aqueous solutions containing inorganic salts such as seawater.

<Effects of the Invention> According to the present invention, the solution is separated and concentrated by heating the stock solution and passing the vapor through a membrane, so unlike the conventional reverse osmosis method, there is no need to pressurize the stock solution to a high pressure. Moreover, it has extremely good solute blocking performance. Moreover,
Since the heat transfer tube is immersed in the center of the stock solution flow path, there is no need for a heat insulation device and there is almost no heat loss.

Further, according to the present invention, since the cross-sectional area of the evaporation space gradually increases from the top to the bottom, the evaporation space does not substantially decrease even if the condensate drops downward. The evaporation space is not blocked by the liquid and the diffusion efficiency of the membrane is not reduced.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view showing an embodiment of the present invention, and FIG. 2 is a cross-sectional view thereof. ■... Outer tube 2... Heat transfer tube 3... Membrane tube 4... Heater 5... Cooling heat medium channel 6... Evaporation space 7... Stock solution channel Patent applicant Nitto Electric Industry Co., Ltd. Agent Patent Attorney Nishi 1) New Procedure Nent Device (Method) November 5, 1985, 1985 Patent Application No. 173847 2, Title of Invention Membrane Distillation Device 3, Person making the amendment Relationship to the incident Patent applicant address: 1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Name
(396) Nitto Electric Industry Co., Ltd. Representative: Kamai 3rd Department 4, Agent address: 15-13 Usagano-cho, Kita-ku, Osaka City Add the column name "3. Detailed description of the invention."

Claims (1)

[Claims] An outer tube, a heat transfer tube provided inside the outer tube to form a passage for the cooling heat medium, and a heater provided in the center of the heat transfer tube to form a passage for the undiluted solution without allowing the undiluted solution to pass through. A membrane tube made of a polymer porous membrane that allows vapor to pass through, and is provided between the surface of the heater and the heat transfer tube, and a membrane tube for passing the raw solution through the raw solution flow path between the membrane tube and the heater. an evaporation space provided between the undiluted solution inlet pipe and the undiluted solution outlet pipe, the membrane tube and the heat transfer tube and whose cross-sectional area gradually increases from the top to the bottom, and the condensate produced in the evaporation space. A membrane distillation device with a condensate outlet pipe for taking out the condensate to the outside.