JPH0817919B2 - Membrane evaporative concentrator and method of operating the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to an evaporative concentration apparatus for evaporating and concentrating a stock solution containing salts to obtain highly purified product water, and an operating method thereof, and particularly to a hydrophobic porous material. The present invention relates to a membrane evaporative concentrator using a membrane and a method of operating the same.

[Conventional technology]

Membrane evaporative concentrator uses a membrane having the property of passing gas but not liquid, that is, a hydrophobic porous membrane as an evaporating surface, for example, only water vapor generated from a stock solution containing salts passes through pores of the membrane, A concentrator for condensing pure water by condensing on a cooling wall, and the concentrator and its operating method are described in, for example,
As disclosed in Japanese Patent No. 61, a structure is provided in which a cooling wall is provided so as to face a film partition of an evaporation surface with a narrow space therebetween, and is composed of an evaporation chamber, a condensation chamber and a cooling chamber.

As shown in FIG. 7, a conventional membrane evaporative concentrator has an evaporation chamber 2 for containing a high temperature stock solution to be supplied, for example, a solution containing salts, and water vapor that passes through the membrane partition wall 6 from the evaporation chamber to produce water. The condensing chamber 25, which was collected as, had a structure separated by one hydrophobic porous membrane.

The evaporative concentrator 1 using the hydrophobic porous membrane having such a structure has a free evaporating surface, which facilitates downsizing of the device.
Moreover, even if the temperature difference between the stock solution and the heating source is small, steam can be generated, and waste heat or the like can be effectively used. Furthermore, since vapor can be generated from the undiluted solution at a low temperature and normal pressure, a synthetic resin that is relatively resistant to corrosion can be used as a structural material. As described above, the heat transfer tube type evaporative concentrator made of the conventional metal material has many advantages.

By the way, the biggest point of using a hydrophobic porous membrane in an evaporative concentrator is that only the water vapor generated from the stock solution passes through this membrane, the water vapor condenses on the cooling wall, and the produced water and the stock solution are completely formed. It can be isolated.

In the normal case, this membrane fulfills its function sufficiently, and by operating the membrane evaporative concentrator, highly purified product water can be obtained. However, in the hydrophobic porous membrane used in the membrane evaporative concentrator, the completeness of separation between the stock solution and the produced water may be destroyed due to the following reasons, and the stock solution may leak to the produced water side. One is that the hydrophobicity of the membrane itself is incomplete.

The mechanism for preventing the liquid from becoming hydrophobic, that is, the liquid leakage due to the hydrophobic porous structure, is that the critical surface tension of this film is sufficiently smaller than the surface tension of the liquid, and there is water pressure resistance due to the pore diameter of the film. It is maintained by operating below that. This, on the contrary, indicates that the hydrophobization of this membrane may be broken and the stock solution may be leaked due to a decrease in the surface tension of the system or a change in the operating pressure due to the incorporation of impurities into the stock solution. The second is derived from the structure of the membrane evaporation concentrator. The membrane evaporative concentrator is provided with a narrow space on the high temperature side for evaporating the stock solution and a low temperature side for cooling the steam, and there is a temperature difference of several tens of degrees Celsius. Therefore, the frame plate holding the film may be distorted and the undiluted solution may leak.

Next, the effect when the hydrophobic porous membrane of the membrane evaporator is destroyed and the stock solution leaks to the produced water side will be described. For example, when a membrane evaporative concentrator is used for concentrating plant waste liquid, a stock solution (salt solution) containing salts such as sodium sulfate (Na ₂ SO ₄ ) is evaporated to reduce Na ₂ SO ₄ to 20 to 30%. The product water that is concentrated in the highest possible concentration and that is collected in the condensing chamber should have a standard value for recovering the product water, such as Na ₂ SO ₄ concentration of 0.5 mg / l.
It is required as a water quality control target that the water has a high purity satisfying the requirement that the conductivity is 1 μS / cm or less. The quality of the produced water is required to have a hydrogen ion concentration (pH) of 6 to 8 as a management target. FIG. 8 shows the calculated relationship between the leak rate and the Na ₂ SO ₄ concentration of the produced water for each salt concentration of the stock solution. If the stock solution is a 20% Na ₂ SO ₄ solution, change the Na ₂ SO ₄ concentration of the product water to 0.5 m of the recovery standard value.
In order to make it below g / l, the leak rate of the undiluted solution to the produced water should be 2
Below the intersection of the solid line of 0% and the dotted line of the collection standard value, that is,
It can be seen that it must be suppressed to a very small amount of 0.00025% or less. On the contrary, even if the stock solution retains 99.99975% hydrophobicity in this membrane, the produced water will be contaminated.

[Problems to be Solved by the Invention]

As described above, the conventional membrane evaporative concentrator provided with only one stage of the hydrophobic porous membrane evaporates due to the severe conditions that destroy the hydrophobicity of the membrane or the defect of the structure of the membrane evaporative condenser. Since it is not easy to completely isolate the stock solution stored in the chamber with the hydrophobic porous membrane, there is a possibility that the stock solution may leak to the produced water side.If this stock solution leaks to the produced water side,
There is a problem that the purity of the produced water is reduced even with a small amount.

It is an object of the present invention to provide a membrane evaporative concentrator having a structure that enables recovery of high-purity generated water even if leakage of the stock solution occurs from the evaporation chamber side to the adjacent condensation chamber side, and a method of operating the same. To do.

[Means for solving the problem]

The object of the above-mentioned invention is to store a high temperature stock solution introduced from the outside, and to provide the stock solution as a membrane partition using a hydrophobic porous membrane on the evaporation surface as a membrane partition, and to be provided opposite to the membrane partition. In a film evaporation concentrator comprising a condensing chamber forming a narrow space with a cooling wall and a cooling chamber formed in the space provided via the cooling wall, the condensing chamber has one or more film shapes. Membrane Evaporative Concentration, characterized in that it has a plurality of liquid recovery chambers formed by being divided by the hydrophobic porous material facing the membrane partition wall, and each of the liquid recovery chambers has a liquid discharge pipe and an opening. By providing a container, and containing the high-temperature stock solution introduced from the outside, the evaporation surface of the stock solution using a hydrophobic porous membrane as the partition wall and the evaporation chamber as a membrane wall A condensing chamber forming a narrow space between the cooling wall provided, and In a method for operating a membrane evaporative concentrator comprising a cooling chamber formed in a space provided through a cooling wall, the condensation chamber is opposed to the membrane partition wall by one or more membrane-like hydrophobic porous materials. The following procedure, namely, (a) Evaporation is performed. The membrane evaporation concentrator is characterized in that it has a plurality of liquid recovery chambers divided and formed, and each of the liquid recovery chambers has a liquid discharge pipe and an opening. The steam generated from the hot stock solution in the room
A water quality measurement procedure for measuring the water quality of the liquid that is introduced into a plurality of liquid recovery chambers in the condensation chamber formed by being divided by the hydrophobic porous material and flows out from each liquid recovery chamber, (b) This water quality A method for operating a membrane evaporation concentrator, which is characterized in that, based on the measurement result, a liquid whose measured value satisfies a recovery standard value is collected as generated water, and the liquid which does not satisfy it is returned to a stock solution. It is achieved by

[Action]

Plural liquid recovery chambers were formed by disposing one or more membrane-like hydrophobic porous materials between the membrane partition wall of the evaporation chamber and the cooling wall of the cooling chamber, facing the membrane partition wall. In the membrane evaporation concentrator, when the high temperature stock solution leaks from the membrane partition wall of the evaporation chamber to the condensation chamber side, the leaked stock solution is extracted from the discharge pipe of the liquid recovery chamber adjacent to the membrane partition wall and returned to the stock solution.

On the other hand, the water vapor that has passed through the hydrophobic porous material and has reached the chamber adjacent to the cooling wall is condensed to produce water, which is withdrawn from the discharge pipe of the liquid recovery chamber and recovered as produced water.

When water is extracted from the discharge pipe of each liquid recovery chamber, air is sucked from the opening of each liquid recovery chamber, so that the water is discharged without decreasing the internal pressure of each liquid recovery chamber.

The operation method of this membrane evaporative concentrator is as follows: Water produced in a liquid recovery chamber other than the liquid recovery chamber adjacent to the cooling wall is a liquid discharge pipe with water whose purity of detected water conforms to the recovery criteria as generated water. Non-conforming water is collected from the liquid and returned to the stock solution through the liquid discharge pipe.

〔Example〕

Examples of the present invention will be described. The membrane partition of the hydrophobic porous membrane used on the evaporation surface of the evaporation chamber that stores high-temperature stock solution containing salts such as Na ₂ SO ₄ supplied from the outside and generates water vapor is According to the present invention, even if raw water leaks from the evaporation chamber side through the membrane partition wall to the condensation chamber side due to incompleteness or destruction of the property, the condensation is further caused by one or more hydrophobic porous materials, that is, hydrophobic materials. Of multiple liquid recovery chambers with permeable porous membrane, namely, leakage liquid recovery chamber and generated water recovery chamber
The leaked undiluted liquid is collected in the leaked liquid recovery chamber and returned to the undiluted liquid, and only the above generated in the evaporation chamber is condensed in the generated water recovery chamber, so the undiluted liquid leaked from the membrane partition of the evaporation chamber is mixed. Can be prevented, and highly purified product water can be stably obtained.

The newly provided hydrophobic porous membrane can isolate a small amount of liquid mixed with the liquid droplets that have leaked into the leak liquid recovery chamber and the liquid droplets that have condensed vapor in this recovery chamber. Any material having a function of permeating only the generated water to the produced water recovery chamber may be used.

Since the amount of liquid retained in the leaked liquid recovery chamber is smaller and the concentration thereof is lower than that of the stock liquid stored in the evaporation chamber, this membrane is slightly hydrophobic as compared with the hydrophobic porous membrane used for the evaporation surface. It may be a low film, for example, a hydrophobic metal mesh used for a demister. In short, an appropriate hydrophobic porous material may be used in consideration of the degree of liquid leakage from the leaked liquid recovery chamber to the generated water recovery chamber.

Further, three or four hydrophobic porous membranes are installed in multiple stages, a liquid recovery chamber is provided between the respective membranes, and liquid retained in each liquid recovery chamber is drawn out from each liquid discharge pipe, The generated water is collected from the liquid recovery chamber closest to the cooling wall, and the liquid from other liquid recovery chambers detects the purity of the liquid and determines whether or not it meets the recovery standard value and collects it as the generated water. Or it can be returned to the stock solution. In this way, the hydrophobic porous membranes are installed in multiple stages, and the membrane evaporative concentrator has a structure in which the liquid is withdrawn from each liquid recovery chamber formed between the membrane partition wall and the cooling wall. Since the influence of the above case becomes smaller, the purity of the produced water to be recovered can be stabilized and improved. However, the membrane evaporative concentrator in which the membranes are installed in multiple stages and a plurality of liquid recovery chambers are formed between the membrane partition wall and the cooling wall is more effective than the conventional membrane evaporative concentrator having only one membrane. Since the number of sheets and the distance through which steam passes increase, it becomes a resistance against the passage of steam and the amount of produced water collected decreases. Therefore, the specifications of the membrane and the number of installed membranes are determined in consideration of the properties of the stock solution supplied to the evaporation chamber, the operating conditions, the degree of leakage from the evaporation chamber, the reference value for recovery of produced water, and the like.

The details of the embodiment will be described below with reference to FIGS. 1 to 6.

First Embodiment FIG. 1 shows a vertical sectional structure of a membrane evaporative concentrator 1 of the present invention. The membrane evaporative concentrator 1 includes an evaporation chamber 2 and a condensation chamber 25, which are two liquid recovery chambers formed by dividing one hydrophobic porous material 7, that is, a hydrophobic porous film, that is, a leakage liquid recovery chamber. 3, the generated water recovery chamber 4 and the cooling chamber 5 are configured. The evaporative chamber 2 and the leaked liquid recovery chamber 3 and the leaked liquid recovery chamber 3 and the generated water recovery chamber 4 are isolated by the hydrophobic porous membranes 6 and 7, and the generated water recovery chamber 4 and the cooling chamber are separated from each other. A cooling wall 8 made of a stainless steel plate or the like is isolated from each other. Further, the evaporation chamber 2 accommodates a high temperature stock solution containing salts and is provided with pipes 9 and 10 for supplying and discharging the stock solution. The leaked liquid recovery chamber 3 is provided with an opening 11 at the upper part for communicating with the outside and sucking air, and a liquid discharge pipe 12 at the lower part. The generated water recovery chamber 4 also has an opening 13 communicating with the outside at the upper part and a liquid discharge pipe 14 at the lower part. The cooling chamber 5 stores cooling water, and a pipe 15 for supplying and discharging cooling water and
16 is installed.

FIG. 2 is an overall configuration diagram of an evaporative concentration device configured to incorporate and operate the membrane evaporative concentrator 1 of the present invention. The evaporative concentrator is centered around the membrane evaporative concentrator 1, and a leakage system from the liquid discharge pipe of the leakage liquid recovery chamber 3 of the concentrator 1 and the circulation system 17 of the stock solution containing salts to be concentrated outside It is composed of a liquid recovery system 19 and a product water recovery system 20 from the liquid discharge pipe of the produced water recovery chamber 4. A heater 21 for heating the stock solution is provided in the circulation system of the stock solution to be concentrated.
And a pump 22 for circulating the stock solution is provided. The cooling water circulation system 18 is provided with a cooler 23 and a pump 24 for circulation. The leak liquid recovery system 19 is connected so as to return to the stock solution circulation system 17. Although not shown here, the purity of the recovered liquid in the leaked liquid recovery system 19 is monitored, and if the purity is within the control target value, it is connected to the produced water recovery system 20 and if the purity exceeds the control target value. A stock solution circulation system 17 can be connected.

The operation of the concentrator of FIG. 2 incorporating the membrane evaporative concentrator 1 shown in FIG. 1 will be described. A stock solution containing salts is put into a circulation system 17, heated by a heater 21 to a predetermined temperature, and circulated in the system by using a pump 22. On the other hand, in the cooling water circulation system 18, while cooling the cooling water by the cooler 23 to a predetermined temperature, the pump 24 is operated to circulate in the system. The stock solution supplied to the evaporation chamber 2 of the film evaporation concentrator 1 is
Water vapor is generated corresponding to the composition and temperature of the stock solution, and only the water vapor passes through the pores of the membrane partition wall and enters the leak liquid recovery chamber 3. Here, the liquid droplets in the leaked liquid recovery chamber 3 and the liquid leaked from the evaporation chamber 2 side are discharged from a pipe provided at the bottom of the leaked liquid recovery chamber 3. However, the water vapor in the leak liquid recovery chamber 3 further passes through the pores of the next hydrophobic porous membrane 7, reaches the produced water recovery chamber 4, is cooled by the cooling wall 8 and is condensed. It becomes generated water, and the generated water recovery chamber 4
It is discharged from the pipe installed at the bottom of the. The membrane evaporation concentrator 1 has the above-described structure and operation, and the produced water obtained from the produced water recovery chamber 4 has high purity.

Second Example An example for carrying out the present invention will be described below. The test apparatus has the same structure as that shown in FIG. The membrane evaporative concentrator 1 is composed of 6 and 7 Teflon porous membranes having a membrane area of 150 cm ^2.
The cooling wall 8 was a stainless steel plate. The stock solution used was a 20% Na ₂ SO ₄ solution as a salt solution, which was heated to 60 ° C. by a heater 21 and circulated by a pump 22 so that the evaporation chamber 2
Supplied within. On the other hand, the cooling water was cooled to 10 ° C. by the cooler 23, circulated by the pump 24, supplied to the cooling chamber 5 of the membrane evaporation concentrator 1, and circulated. FIG. 3 and FIG. 4 show changes over time in the purity (here, represented by conductivity) of the liquid recovered in the leaked liquid recovery chamber 3 and the produced water recovery chamber 4 and the outflow rate of the liquid, respectively. Even if the conductivity of the liquid recovered from the leaked liquid recovery chamber 3 is 150 to 200 μS / cm and the purity is lowered, the conductivity of the liquid recovered from the generated water recovery chamber 4 is 1.2 to 2.0 μS / cm.
cm, and the produced water with high purity could be collected. The outflow rate of the recovered liquid from the produced water recovery chamber 4 was about 80% of the outflow speed of the entire recovered liquid. Further, in order to reuse the produced water as condensate, the conductivity is reduced to 1 μS / cm or less by ion exchange treatment or nitrogen gas purging treatment.

Next, as a comparative example, as shown in FIG. 7, a conventional membrane evaporative concentrator provided with only one stage of the hydrophobic porous membrane 6 was operated in the same manner as the above-mentioned embodiment of the membrane evaporative condenser of the present invention. Assuming that a similar leak occurs from the hydrophobic porous membrane 6 on the evaporation surface under the conditions, the generated water recovered in one condensation chamber of the conventional membrane evaporation concentrator is the same as the leakage liquid recovery chamber of the present invention. Since the total amount of liquid collected in the two chambers, the produced water recovery chamber, is the same, the outflow rate of the produced water recovered by the conventional membrane evaporation concentrator is approximately 45 kg / m ² d.
However, the purity of the produced water is about 40 μS / cm, which means that the produced water is contaminated. The conductivity is about 20 to 30 times higher than that of the present invention.

Third Embodiment Next, a modified example of the present invention will be described. Although FIG. 1 shows the case where a flat membrane hydrophobic porous membrane is used, this configuration can be applied to a concentrator using a tubular membrane. 5 and 6 show the construction of the present invention using a tubular membrane. FIG. 5 shows a sectional structure when the cooling chamber 5 is installed in the central part and the evaporation chamber 2 is installed in the outer peripheral part, and FIG. 6 shows the evaporation chamber 2 installed in the central part and the cooling chamber 5 is installed in the outer peripheral part. The cross-sectional structure when is installed is shown. Two tubular hydrophobic porous membranes are provided to form four chambers. The chamber adjacent to the evaporation chamber 2 is the produced water recovery chamber 3, and the chamber adjacent to the cooling chamber 5 is the produced water recovery chamber 4. . The structure shown in FIGS. 5 and 6 may be taken as one unit, and a large number of these units may be combined together.

〔The invention's effect〕

According to the configuration of the present invention, even if the stock solution leaks from the membrane partition wall of the evaporation chamber to the condensation chamber side, the leaked stock solution is formed by dividing the condensation chamber with one or more hydrophobic porous materials. Of the multiple liquid recovery chambers, the liquid is recovered in the liquid recovery chamber adjacent to the evaporation chamber, and the liquid from the liquid recovery chambers other than the liquid recovery chamber adjacent to the cooling chamber that collects the generated water is based on the purity as the recovery standard. Since those that are not compatible are returned to the stock solution and those that are compatible are collected as product water, the product solution does not mix with the product water, and product water with high purity can be stably obtained.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing the structure of a membrane evaporative concentrator according to the present invention, FIG. 2 is an overall configuration diagram of an evaporative concentration apparatus incorporating the membrane evaporative concentrator according to the present invention, and FIG. It is a figure which shows the time-dependent change of the electrical conductivity of the effluent of the membrane evaporation concentrator by this invention, and FIG. 4 is a figure which shows the time-dependent change of the outflow rate of the effluent of the membrane evaporation concentrator by this invention. FIG. 6 is a vertical sectional view showing the structure of a membrane evaporative concentrator in which a tubular membrane is arranged around the cooling chamber, and FIG. 6 shows the structure of a membrane evaporative concentrator in which a tubular membrane is arranged around the evaporation chamber. FIG. 7 is a vertical cross-sectional view, FIG. 7 is a vertical cross-sectional view showing the structure of a conventional membrane evaporative concentrator, and FIG. 8 is a calculation result diagram showing the relationship between the undiluted solution leak rate and the purity of the produced water for each undiluted solution concentration. Is. 1 ... Membrane evaporative concentrator, 2 ... Evaporation chamber, 3,4 ... Liquid recovery chamber, 5 ... Cooling chamber, 6 ... Membrane partition, 7 ... Hydrophobic porous material, 8 ... Cooling wall, 11,13 …… Opening part, 12,14 …… Liquid discharge pipe.

Claims (3)

[Claims] 1. A high temperature stock solution introduced from the outside is stored,
An evaporation chamber that forms a membrane partition using a hydrophobic porous membrane on the evaporation surface of the stock solution, a condensation chamber that forms a narrow space between a cooling wall provided facing the membrane partition, and the cooling wall In a membrane evaporative concentrator comprising a cooling chamber formed in a space provided through the condensing chamber, the condensing chamber is formed by one or more membrane-like hydrophobic porous materials divided relative to the membrane partition wall. A membrane evaporation concentrator, comprising a plurality of liquid recovery chambers, and each of the liquid recovery chambers having a liquid discharge pipe and an opening. 2. The membrane evaporative concentrator according to claim 1, wherein the hydrophobic porous material is one of a hydrophobic porous membrane and a metal net having hydrophobicity. 3. A high temperature stock solution introduced from the outside is stored,
An evaporation chamber that forms a membrane partition using a hydrophobic porous membrane on the evaporation surface of the stock solution, a condensation chamber that forms a narrow space between a cooling wall provided facing the membrane partition, and the cooling wall In a method of operating a membrane evaporative concentrator, which comprises a cooling chamber formed in a space provided through a condensing chamber, the condensing chamber is divided by one or more membrane-like hydrophobic porous materials relative to the membrane partition wall. The membrane evaporation concentrator, which is characterized in that it has a plurality of formed liquid recovery chambers, and each of the liquid recovery chambers has a liquid discharge pipe and an opening, The steam generated from the stock solution of
A water quality measurement procedure for measuring the water quality of the liquid that is introduced into a plurality of liquid recovery chambers in the condensation chamber formed by being divided by the hydrophobic porous material and flows out from each liquid recovery chamber, (b) This water quality A method for operating a membrane evaporative concentrator, which comprises: collecting a liquid whose measured value satisfies a recovery reference value as generated water based on the measurement result, and returning the unsatisfied liquid to a stock solution.