JP2016087545A - Method for cleaning film distillation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily and reliably cleaning a film distillation apparatus, in particular, a hydrophobic porous membrane in a film distillation apparatus.SOLUTION: According to a method for cleaning a film distillation apparatus, first, washing water R of a room temperature or lower is flown into a raw water chamber 3 thereby washing away a liquid W to be treated remaining in the raw water chamber 3 (first cleaning process). Next, a hot cleaning chemical of 50 to 80°C is circulated in a condensation chamber 4 thereby cleaning the condensation room 4 side (second cleaning process). Subsequently, a cleaning chemical of a room temperature or lower is circulated in the raw water chamber 3 thereby cleaning adsorptive components (impurities) of the liquid W to be treated which are adsorbed onto a hydrophobic porous membrane 2 surface on the raw water chamber 3 side (third cleaning process).SELECTED DRAWING: Figure 6

Description

  The present invention relates to a method for cleaning a membrane distillation apparatus, and more particularly to a method for easily and reliably cleaning a hydrophobic porous wet membrane of a membrane distillation apparatus.

  In addition to seawater desalination, dehydration from solvents and oils, membrane distillation technology is energy-saving and space-saving for food processes such as concentrating sugars and broth such as fruit juice, sugar solution or honey. Expected as a technology. In particular, in recent years, interest in a vacuum membrane distillation apparatus has increased.

  This vacuum membrane distillation apparatus has a flow path (raw water chamber) for passing a liquid to be treated at about 60 ° C. to 80 ° C. on one side through a hydrophobic porous membrane (permeating only water vapor) that repels water. The structure in which the water vapor that has passed through the hydrophobic membrane is arranged in a condensing chamber that leads to the condensation section on the opposite side of the liquid to be treated to condense and obtain distilled water is a unit structure, and this unit structure is composed of a plurality of stages. It is arranged in series. As a result, the concentrated liquid concentrated in the first stage of the unit structure is further concentrated in the second stage arranged in series, and the processed liquid concentrated in the second stage is further concentrated in the third stage, In this way, it is concentrated one after another, and is collected after being concentrated to a desired concentration in the final stage. On the other hand, the condensing chamber condenses the water vapor that has passed through the hydrophobic membrane to obtain distilled water, and is therefore at a temperature that is several degrees lower than the liquid to be treated. In this condensing chamber, the water vapor is condensed into distilled water, which is collected separately from the concentrated liquid. As such a vacuum membrane distillation apparatus, techniques as shown in Patent Documents 1 and 2 are known, and a highly porous Teflon (registered trademark) resin film is widely used as the hydrophobic porous film. .

  FIG. 13 shows an example of the membrane distillation apparatus as described above. The membrane distillation apparatus 21 includes a hydrophobic porous membrane 22, and a raw water chamber 23 and a condensing chamber 24 are formed by being partitioned by the hydrophobic porous membrane 22. The raw water chamber 23 is an example of a raw water unit that introduces the liquid W to be treated, and the condensing chamber 24 is an example of a condensing unit that condenses the vapor S that has passed through the hydrophobic porous membrane 22.

  The hydrophobic porous membrane 22 is an example of means for selectively allowing only the vapor of the liquid W to be treated introduced into the raw water chamber 23 to pass through. As the hydrophobic porous membrane 22, a fluororesin porous membrane can be suitably used because of its excellent heat resistance. In this hydrophobic porous membrane 22, only the vapor S of the liquid W to be treated is permeated, hardly affected by the osmotic pressure and viscosity of the liquid W to be treated with respect to the amount of vapor passing through the membrane, and has high vapor permeability. Concentration of suspended components of the treatment liquid W can be performed efficiently.

  A raw water line 25 for introducing the liquid W to be treated is connected to the raw water chamber 23. On the other hand, a vacuum pump 26 is connected to the condensation chamber 24, and a cooling unit 27 is provided on the wall surface of the condensation chamber 24. Then, the raw water chamber 23 is decompressed by the vacuum pump 26 together with the condensing chamber 24 and is maintained in a decompressed state, and the cooling unit 27 is cooled by a cooling means (not shown) to a temperature to condense the vapor S in contact therewith. . Reference numeral 28 denotes a concentrate recovery line for recovering the concentrate W1 from the raw water chamber 23, and reference numeral 29 denotes a distilled water discharge line for recovering the distilled water W2 from the condensation chamber 24.

  In the membrane distillation apparatus 21 as described above, first, the liquid W to be treated is set to a predetermined temperature, for example, less than 100 ° C., preferably 40 to 90 ° C., particularly about 50 ° C. to 80 ° C. by a heat exchanger (not shown). The temperature is adjusted and supplied from the raw water line 25. Here, the inside of each vacuum membrane distillation apparatus 21 is depressurized by a single vacuum pump 26. For this reason, the liquid W to be treated is sucked into the raw water chamber 23 of the membrane distillation apparatus 21.

  In this case, since the condensing chamber 24 is maintained in a reduced pressure state, the condensing chamber 24 has not only a function of drawing the steam S but also a function of lowering the boiling point of the liquid W to be processed. Thereby, the vapor | steam S which arises from the to-be-processed liquid W becomes remarkable, and the vapor | steam amount which permeate | transmits the hydrophobic porous membrane 22 increases. As a result, the concentrate W1 is obtained in the raw water chamber 23. That is, since much steam S is condensed and removed from the liquid W to be processed and converted into the concentrated liquid W1, the liquid W to be processed in the raw water chamber 23 is efficiently concentrated. Accordingly, a large amount of concentrated liquid W1 is generated from the raw water chamber 23 and recovered from the concentrated liquid recovery line 28. On the other hand, the steam S touches the cooling unit 27 of the condensation chamber 24 and condenses, and water droplets L are generated. Thereby, in the cooling unit 27, the steam S is condensed and distilled water W <b> 2 is discharged from the distilled water discharge line 29.

JP 2011-173097 A JP 2013-212464 A

  In the membrane distillation apparatus as described above, the hydrophobic porous membrane 22 that partitions the raw water chamber 23 and the condensing chamber 24 through which the liquid W to be treated flows is indispensable to be hydrophobic. In the course of continuing, the dissolved component of the liquid W to be treated is adsorbed on the hydrophobic porous film 22 and becomes dirty, so that the hydrophobicity of the film decreases, that is, the hydrophobic film becomes hydrophilic and the liquid W to be treated is liquid. There is a problem in that distilled water is not obtained by passing through the pores of the hydrophobic porous membrane 22 as it is, the concentration factor of the concentrated solution W1 is reduced, and the recovery rate of the concentrated solution W1 is also reduced. In addition, when applied to a food process, for example, concentration of fruit juice, sugar liquid or honey liquid, it is necessary to clean the inside of the membrane distillation apparatus before the concentration operation.

  For these reasons, it is necessary to wash the hydrophobic porous membrane 22 of the membrane distillation apparatus. However, the inside of the pores of the hydrophobic porous membrane 22 cannot be sufficiently washed simply by circulating clean water. There is a possibility that the concentration rate is gradually lowered by long-term use. Therefore, a cleaning method capable of sufficiently cleaning both the raw water chamber 23 side and the condensing chamber 24 side of the hydrophobic porous membrane 22 of the membrane distillation apparatus has been demanded.

  The present invention has been made in view of the above-mentioned problems, and the liquid component to be treated is adsorbed on the hydrophobic porous membrane and the hydrophobicity is reduced, so that it does not repel water or is applied to a food process. It is an object of the present invention to provide a simple and reliable method for cleaning a hydrophobic porous membrane of a membrane distillation apparatus, particularly a membrane distillation apparatus, in the case of pre-cleaning.

  In order to solve the above problems, the present invention provides a raw water section and a condensation section partitioned by a hydrophobic porous membrane, a decompression means for maintaining the condensation section in a decompressed state, and a cooling means for cooling the condensation section. A membrane for introducing a heated liquid to be treated into the raw water portion and allowing the vapor of the liquid to be treated to permeate the hydrophobic porous membrane, thereby concentrating the liquid to be treated to produce a concentrated liquid. A cleaning method for a distillation apparatus, wherein a first cleaning step of flowing a wash water of 27 ° C. or less to the raw water portion to wash away a liquid to be treated remaining in the raw water portion, and a temperature of 50 to 80 ° C. to the condensing portion Cleaning of a membrane distillation apparatus comprising: a second cleaning step for circulating and cleaning a warm cleaning chemical solution; and a third cleaning step for circulating and cleaning a cleaning chemical solution of 27 ° C. or less in the raw water portion A method is provided (Invention 1).

  According to this invention (Invention 1), since the decrease in the concentration rate of the membrane distillation apparatus is caused by the decrease in the hydrophobicity due to particularly the contamination of the hydrophobic porous membrane, first, in the first washing step, Washing water at room temperature (27 ° C. or less) is circulated to wash away the liquid to be treated remaining in the raw water portion, and then in the second washing step, the inside of the pores of the hydrophobic porous membrane is washed with a warm washing chemical solution having a small surface tension. The adsorbed component (dirt) is dissolved and washed from the condensing part side, and then in the third washing step, a cleaning chemical solution at room temperature is passed through the raw water part and adsorbed on the hydrophobic porous membrane surface on the raw water part side. Wash the adsorbed components (dirt) of the liquid. At this time, the cleaning chemical solution is set to room temperature or lower to prevent a decrease in the surface tension of the liquid and to prevent the cleaning chemical solution from permeating through the pores of the hydrophobic porous membrane and entering the condensing part. Thereby, the inside of the pores of the hydrophobic porous membrane can be cleaned and the concentration rate of the membrane distillation apparatus can be recovered.

  In the said invention (invention 1), it has a warm water washing | cleaning process which distribute | circulates 50-80 degreeC warm washing | cleaning water to the said condensation part and wash | cleans the said warm washing | cleaning chemical | medical solution after a said 2nd washing | cleaning process. After the washing step, it is preferable to have a room temperature water washing step in which washing water of 27 ° C. or lower is passed through the raw water portion to wash away the cleaning chemical solution of 27 ° C. or lower (Invention 2).

  According to this invention (Invention 2), after washing the chemical solution with the washing water after washing with the chemical solution, the dirt removed from the hydrophobic porous membrane is prevented from reattaching to the pores of the hydrophobic porous membrane. And can be washed well.

  In the said invention (invention 1 or 2), it is preferable to have a water-repellent reproduction process after the said 3rd washing | cleaning process (invention 3).

  According to this invention (invention 3), the concentration performance of the membrane distillation apparatus can be greatly recovered by further improving the water repellency of the cleaned hydrophobic porous membrane.

  In the method for cleaning a membrane distillation apparatus of the present invention, since the decrease in the concentration rate of the membrane distillation apparatus is caused by the decrease in hydrophobicity due to especially the contamination of the hydrophobic porous membrane, first, the liquid to be treated remaining in the raw water portion Next, the adsorbed component (dirt) in the pores of the hydrophobic porous membrane is dissolved and washed from the condensing part side with a warm washing chemical solution with a small surface tension, and then a room temperature washing chemical solution is circulated in the raw water part. Treatment to be adsorbed on the surface of the hydrophobic porous membrane on the raw water part side while preventing the surface tension of the liquid from decreasing and preventing the cleaning chemical from permeating the pores of the hydrophobic porous membrane and entering the condensing part Wash the adsorbed components (dirt) of the liquid. Thereby, the inside of the pores of the hydrophobic porous membrane can be cleaned and the concentration performance of the membrane distillation apparatus can be recovered.

It is the schematic which shows the state at the time of concentration of the membrane distillation apparatus which can apply the washing | cleaning method of the membrane distillation apparatus by one Embodiment of this invention. It is the schematic which shows the state at the time of the washing | cleaning of the membrane distillation apparatus which can apply the washing | cleaning method of the membrane distillation apparatus of the embodiment. It is the schematic which shows the state of the hydrophobic porous membrane at the time of concentration in the washing | cleaning method of the membrane distillation apparatus of the embodiment. It is the schematic which shows the state of the hydrophobic porous membrane at the time of the pollution initial stage in the washing | cleaning method of the membrane distillation apparatus of the embodiment. It is the schematic which shows the state of the hydrophobic porous membrane at the time of the contamination progress in the washing | cleaning method of the membrane distillation apparatus of the embodiment. It is the schematic which shows the 1st washing | cleaning process in the washing | cleaning method of the film | membrane distillation apparatus of the embodiment. It is the schematic which shows the 2nd washing | cleaning process in the washing | cleaning method of the film | membrane distillation apparatus of the embodiment. It is the schematic which shows the warm water washing | cleaning process in the washing | cleaning method of the film | membrane distillation apparatus of the embodiment. It is the schematic which shows the 3rd washing | cleaning process in the washing | cleaning method of the film | membrane distillation apparatus of the embodiment. It is the schematic which shows the normal temperature water washing | cleaning process in the washing | cleaning method of the film | membrane distillation apparatus of the embodiment. It is the schematic which shows the water-repellent reproduction process after the 3rd washing | cleaning process in the washing | cleaning method of the film | membrane distillation apparatus of the embodiment. It is the schematic which shows the drying process of the hydrophobic porous membrane after washing | cleaning in the washing | cleaning method of the membrane distillation apparatus of the embodiment. It is the schematic which shows the typical example of a membrane distillation apparatus.

  Hereinafter, an embodiment of a cleaning method for a membrane distillation apparatus of the present invention will be described in detail with reference to the accompanying drawings.

  FIGS. 1 and 2 are membrane distillation apparatuses to which the cleaning method of the present invention can be applied, and show the membrane distillation apparatus 1 when it is concentrated and washed, respectively. Basically, the membrane distillation apparatus shown in FIG. It exhibits the same structure and effect. The membrane distillation apparatus is configured to communicate with a plurality of stages, for example, 2 to 12 stages, preferably 3 to 10 stages in series until a desired concentration rate is achieved. However, in this embodiment, for convenience of explanation. The one-stage structure of the unit structure will be described.

  1 and 2, the membrane distillation apparatus 1 includes a raw water chamber 3 as a raw water portion serving as a flow path for the liquid W to be treated partitioned by a hydrophobic porous membrane 2, and a condensing chamber 4 as a water vapor condensing portion. Have A raw water line 5 for introducing the liquid W to be treated and a cleaning liquid supply line 6 are connected to the inflow side of the raw water chamber 3 by a raw water valve 7 and a cleaning liquid valve 8, while a concentrated liquid W1 is supplied to the discharge side. A concentrated liquid recovery line 9 and a cleaning liquid discharge line 10 to be recovered can be switched by a recovery valve 11 and a discharge valve 12. A discharge line 13 for distilled water W2 is connected to the discharge side of the condensing chamber 4 and a cleaning liquid supply line 14 is connected to the discharge side of the condensation chamber 4, and a cleaning liquid discharge line 15 is connected to the other side of the discharge side. . These lines can be switched by a distilled water discharge valve 16, a warm cleaning liquid supply valve 17, and a warm cleaning liquid discharge valve 18, respectively. A vacuum pump (not shown) is connected to the condensation chamber 4 and a cooling unit (not shown) is provided on the wall surface of the condensation chamber 4.

  As described above, in the membrane distillation apparatus 1, during the concentration shown in FIG. 1, the raw water valve 7 on the inflow side of the raw water chamber 3 is open, while the cleaning liquid valve 8 is closed, and the recovery valve 11 on the discharge side. Is opened, the discharge valve 12 is closed, and the liquid W to be treated can be supplied from the raw water line 5 to the raw water chamber 3 and the concentrated liquid W1 can be discharged from the concentrated liquid recovery line 9. Further, in the condensing chamber 4, the distilled water discharge valve 16 on the discharge side is open, while the warm cleaning liquid supply valve 17 is closed, and the warm cleaning liquid discharge valve 18 on the other side of the discharge side is closed, Distilled water W2 can be discharged from the discharge line 13.

  At the time of cleaning shown in FIG. 2, the raw water valve 7 on the inflow side of the raw water chamber 3 is closed, while the cleaning liquid valve 8 is opened, and the recovery valve 11 on the discharge side is opened, contrary to FIG. On the other hand, the discharge valve 12 is opened, and cleaning water R and cleaning chemical M2, which will be described later, can be supplied from the cleaning liquid supply line 6 to the raw water chamber 3 and discharged from the cleaning liquid discharge line 10. Further, in the condensing chamber 4, the distilled water discharge valve 16 on the discharge side is closed, while the warm cleaning liquid supply valve 17 is opened, and the warm cleaning liquid discharge valve 18 on the other side of the discharge side is opened, A warm cleaning chemical M1 and warm cleaning water H, which will be described later, are supplied from the cleaning liquid supply line 14 and can be discharged from the cleaning liquid discharge line 15.

  A method for cleaning the membrane distillation apparatus 1 as described above will be described below.

  First, as shown in FIG. 3, in the concentration (distillation) process of the liquid W to be processed in a state where the hydrophobic porous membrane 2 is clean, the liquid W to be processed is heated to a predetermined temperature, for example, 100 ° C. by a heat exchanger (not shown). The temperature is adjusted to be less than, preferably 40 to 90 ° C., particularly about 60 to 80 ° C., and flows through the raw water chamber 3 to become the concentrated solution W1. At this time, since the hydrophobic porous membrane 2 repels the liquid W to be treated, the liquid / gas interface is outside the pores, and no liquid component enters the pores, but the water vapor S permeates into the condensation chamber 4. .

  Next, when the component C for hydrophilizing the hydrophobic porous membrane 2 is contained in the liquid W to be treated, as the distillation operation proceeds, the hydrophilizing component C first becomes hydrophobic porous as shown in FIG. Adsorption on the membrane surface of the membrane 2 starts to reduce hydrophobicity, the liquid / gas interface is located inside the pores, and the liquid W to be processed gradually enters the pores of the hydrophobic porous membrane 2 Start to do.

  As shown in FIG. 5, when the hydrophilizing component C comes into contact with and adsorbs on the inner surface of the pores of the hydrophobic porous membrane 2, the inside of the pores is hydrophilized, so that the hydrophobic porous membrane 2 repels water. As a result, the liquid / gas interface disappears and the liquid W to be treated penetrates into the pores of the hydrophobic porous membrane 2, and as a result, moisture caused by the liquid W to be treated permeates into the condensation chamber 4. become. Until this state is reached, the water quality of the distilled water W2 gradually deteriorates. On the other hand, since the sugar content (for example, Brix value (one of the indicators of sugar content)) and conductivity of the distilled water W2 start to increase, the distillation operation is performed when the water quality of the distilled water W2 starts to decrease below a predetermined level. Stop and clean inside the distillation unit. This washing is performed according to the following procedure.

  That is, as shown in FIG. 6, first, a cleaning water R of room temperature or lower, specifically 27 ° C. or lower, preferably pure water is flowed into the raw water chamber 3 to wash away the liquid W to be treated remaining in the raw water chamber 3 (first One washing step). Here, by using the cleaning water R at room temperature or lower, the evaporation of the cleaning water R is suppressed, and the intrusion of moisture into the condensing chamber 4 is prevented.

  Next, the 50 to 80 degreeC warm washing | cleaning chemical | medical solution M1 is distribute | circulated to the condensation chamber 4, and the condensation chamber 4 side is wash | cleaned (2nd washing process). Examples of the warm cleaning chemical solution M1 include alkali components such as sodium hydroxide and potassium hydroxide and mixed solutions thereof, or sodium hypochlorite and sodium perchlorate as chlorine components in these alkaline solutions. Can be used. The alkali concentration in the warm cleaning chemical M1 is, for example, about 3 mg / L to 50 g / L, preferably about 30 mg / L to 30 g / L, based on the mass of a strong alkali salt such as sodium hydroxide or potassium hydroxide. . The concentration of the chlorine reagent is about 3 mg / L to 50 g / L, preferably about 30 mg / L to 30 g / L. Furthermore, depending on the adsorbed component of the liquid W to be treated, an acidic agent such as hydrochloric acid, sulfuric acid, nitric acid, or an acidic solution of a mixture thereof can be used as the warm cleaning chemical solution M1. The concentration of the acidic solution is, for example, about 3 mg / L to 50 g / L, preferably about 30 mg / L to 30 g / L, based on the mass of a strong acid such as hydrochloric acid, sulfuric acid, or nitric acid.

  Needless to say, acid and alkali are not mixed. Therefore, when it is desired to wash with both chemical solutions, after washing with the warm washing chemical solution M1 using an alkali solution or a combination of alkali and chlorine, the alkali or alkali and chlorine are once washed away with pure water or ultrapure water. Wash with warm wash chemical M1 with acidic solution. Or, conversely, after washing with the warm cleaning chemical solution M1 using an acidic solution, the acid is once washed away with pure water or ultrapure water, and then washed with the warm cleaning chemical solution M1 using an alkali solution or a combination of alkali and chlorine. Conditions such as types and combinations of cleaning components, order, number of times of cleaning, required time, and the like can be optimized from the components in the liquid to be processed and the degree of contamination.

  In this second cleaning step, by using the warm cleaning chemical solution M1 instead of the cleaning chemical solution below the room temperature, it is easy to dissolve the adsorbing component (dirt) caused by the liquid W to be treated, and the surface tension of the warm cleaning chemical solution M1 is increased. The hot cleaning chemical M1 can be flowed from the condensing chamber 4 to the raw water chamber 3 through the pores by lowering and facilitating entry into the pores of the hydrophobic porous membrane 2. By flowing the warm cleaning chemical solution M1 from the condensing chamber 4 to the raw water chamber 3 in this way, the warm cleaning chemical solution M1 flows from the region on the condensing chamber 4 side with a small amount of adsorbed components (dirt) to the raw water chamber 3 with a large amount of adsorbed components (dirt). It will flow to the area | region of the side, and there exists an effect that the condensation chamber 4 which is an area | region which obtains distilled water can be kept clean.

  When the adsorbed component (dirt) in the pores of the hydrophobic porous membrane 2 is washed away by the second washing step in this manner, the warm washing chemical solution M1 is washed with warm washing water at 50 to 80 ° C. as shown in FIG. (Warm pure water) It is preferable to change to H and wash away the chemical solution in the pores toward the raw water chamber 3 (warm water washing step). In this warm water washing process, by using the warm washing water H instead of the washing water below room temperature, the surface tension of the warm washing water H is lowered so as to penetrate into the pores of the hydrophobic porous membrane 2. It is possible to make it easier to remove the warm washing chemical solution M1.

  Subsequently, as shown in FIG. 9, a liquid to be treated adsorbed on the surface of the hydrophobic porous membrane 2 on the raw water chamber 3 side by flowing a cleaning chemical solution M2 at room temperature or lower, specifically 27 ° C. or lower, into the raw water chamber 3. The adsorbed component (dirt) of W is washed (third washing step). Here, the same cleaning chemical liquid M1 as the warm cleaning chemical liquid M1 can be used. Here, by setting the cleaning chemical liquid M2 to room temperature or lower, it is possible to prevent the surface tension of the cleaning chemical liquid M2 from being lowered, and to prevent the cleaning chemical liquid M2 from entering the side of the condensation chamber 4 that has been cleaned.

  Then, as shown in FIG. 10, it is preferable to wash the cleaning chemical solution M2 remaining in the raw water chamber 3 by flowing a cleaning water R, preferably pure water, of room temperature or lower, specifically 27 ° C. or lower, into the raw water chamber 3. Normal temperature water washing process). Here, by using the cleaning water R at room temperature or lower, evaporation of the cleaning water R can be suppressed, and moisture can be prevented from entering the condensing chamber 4.

  When the adsorption component (dirt) of the liquid W to be treated adsorbed on the surface of the hydrophobic porous membrane 2 on the raw water chamber 3 side, inside the pores, and on the condensation chamber 4 side is washed away as shown in FIG. In order to impart water repellency to the cleaned hydrophobic porous membrane, for example, an alcohol A such as ethyl alcohol, methyl alcohol, isopropyl alcohol or the like is passed through, and the water inside the pores of the hydrophobic porous membrane Is replaced with alcohols A (water repellency reproduction step). The alcohol A is passed through, for example, the raw water chamber 3 side, preferably the condensing chamber 4 side, and more preferably both.

  Finally, when water in the pores of the hydrophobic porous membrane 2 is replaced with alcohols A and alcohols are allowed to flow down from the raw water chamber 3 and the condensing chamber 4, the raw water chamber 3 and the condensing chamber 4 as shown in FIG. Is reduced in pressure with a vacuum pump (not shown), and the hydrophobic porous membrane 2 is dried to reproduce the water repellency.

  Although the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the combination of opening and closing of the valves is not required to mix the liquid W to be treated, the distilled water W2, and the cleaning chemicals M1 and M2, and can be changed as appropriate.

  The following specific examples further illustrate the present invention.

<Example 1>
The soup stock was concentrated by the membrane distillation apparatus 1 shown in FIGS. The obtained distilled water W2 had an electrical conductivity of 0.7 to 0.8 mS / m and was able to concentrate the soup stock. When the concentration was continued as it was, when 300 hours or more passed, the electrical conductivity of the distilled water W2 gradually increased to 0.9 to 1 mS / m. Therefore, the soup stock was stopped and washed by the method shown in FIGS. As the cleaning liquid conditions, pure water was used as the cleaning water R and warm cleaning water H, and a 0.1% sodium hydroxide solution was used as the cleaning chemicals M1 and M2. The temperature of the cleaning water R and the cleaning chemical liquid M2 was set to 20 ° C., and the temperature of the warm cleaning water H and the cleaning chemical liquid M1 was set to 60 ° C.

  After washing, the broth was concentrated again to obtain distilled water having an electric conductivity of 0.7 to 0.8 mS / m. The quality of distilled water after washing was good, and the distillation time until rewashing was the same as in the initial stage, so that the inside of the membrane could be washed sufficiently and the concentration performance was recovered.

<Comparative Example 1>
The same soup stock as in Example 1 was concentrated by the membrane distillation apparatus shown in FIGS. The obtained distilled water W2 had an electrical conductivity of 0.7 to 0.8 mS / m and was able to concentrate the soup stock. When the concentration was continued as it was, the electrical conductivity of distilled water W2 gradually increased to 0.9 to 1 mS / m when 300 hours or more had elapsed. Therefore, the stock broth concentration was stopped, and the remaining stock broth was washed out by passing pure water through the raw water chamber 3 in the manner of washing the reverse osmosis membrane module. Then, a 0.1% sodium hydroxide solution is stored in the raw water chamber 3 as a cleaning chemical solution and immersed for 2 hours at room temperature, and then pure water is passed through the raw water chamber 3 and the condensing chamber 4 to add 0.1% sodium hydroxide. % Solution was washed away.

  After washing, the stock broth was concentrated again to obtain distilled water having an electric conductivity of 0.8 to 0.9 mS / m. However, when the concentration exceeded 30 hours after the concentration, the electric conductivity of distilled water was 1 mS / m. It was higher than m, and it was judged that the recovery of the concentration performance was not sufficient.

  According to the method for cleaning a membrane distillation apparatus of the present invention, the concentration performance of the membrane distillation apparatus can be recovered by cleaning the pores of the hydrophobic porous membrane of the membrane distillation apparatus. And can be made more suitable as a concentration technique for food processing solutions.

DESCRIPTION OF SYMBOLS 1 ... Membrane distillation apparatus 2 ... Hydrophobic porous membrane 3 ... Raw water chamber (raw water part)
4 ... Condensing chamber (condensing part)
W ... Liquid to be treated W1 ... Concentrated liquid W2 ... Distilled water R ... Washing water M1 ... Warm cleaning chemical solution M2 ... Cleaning chemical solution H ... Warm cleaning water (warm pure water)
A ... Alcohol S ... Steam

Claims (3)

Raw water section and condensation section partitioned by a hydrophobic porous membrane;
Pressure reducing means for maintaining the condensing part in a reduced pressure state;
Cooling means for cooling the condensing part,
A membrane distillation apparatus for introducing a heated liquid to be treated into the raw water portion and allowing the vapor of the liquid to be treated to permeate the hydrophobic porous membrane, thereby concentrating the liquid to be treated to produce a concentrated liquid. A cleaning method,
A first washing step in which washing water of 27 ° C. or less is circulated in the raw water portion to wash away the liquid to be treated remaining in the raw water portion;
A second cleaning step of circulating and cleaning a hot cleaning chemical solution of 50 to 80 ° C. in the condensing part;
And a third cleaning step in which a cleaning chemical solution of 27 ° C. or lower is circulated in the raw water section to clean the membrane distillation apparatus.   After the second cleaning step, there is a warm water cleaning step in which 50-80 ° C. warm cleaning water is circulated through the condensing unit to wash away the warm cleaning chemical solution, and after the third cleaning step, the raw water unit 2. The method for cleaning a membrane distillation apparatus according to claim 1, further comprising a room-temperature water cleaning step in which cleaning water of 27 ° C. or lower is circulated to wash away the cleaning chemical solution of 27 ° C. or lower.   The method for cleaning a membrane distillation apparatus according to claim 1, further comprising a water repellency reproduction step after the third cleaning step.