JP2006043670A - Cleaning method using hyperfine bubble - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for effectively cleaning the surface of a separation-functional membrane being an object to be cleaned without damaging base materials constituting the separation-functional membrane while dispensing with treatment of waste cleaning liquid. <P>SOLUTION: This method for physically cleaning the surface of the separation-functional membrane comprises the steps of: compressively dissolving a gas component in raw water; releasing the gas component-dissolved water in a low-pressure area in a moment to prepare bubble water containing countless, independent and minute bubbles of high density each having a highly negative charge on the surface; and exfoliating/removing the foreign matter accumulated on the surface of the separation-functional membrane by neutralizing an electric charge of the foreign matter by anions of minute bubbles. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

    The present invention can be effectively applied to a wide range of fields that require adhesion suppression to RO membranes, MF membranes, UF membranes, ion exchange membranes, ion exchange resins, and the like, and peeling recovery operation of adhered foreign substances.

Separation membrane cleaning methods suitable for water treatment include chemical cleaning and physical cleaning. For chemical cleaning, inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid and soda hypochlorite and organic acids such as oxalic acid and citric acid are used.
As physical cleaning, there are an escrabing method in which pressurized air is blown into the membrane surface, a water backwash method in which water is pushed backward from the back side of the membrane, and an air backwash method in which backwashing is performed with high-pressure air (0.6 MPa). These are often performed in parallel.

Usually, physical cleaning is performed every 20-60 minutes. In addition, chemical cleaning is carried out in 1 to 3 months, but chemicals and physical cleaning that removes a large amount of used chemicals as waste liquid and causes disposal become a problem. Except for the purpose of recovering and maintaining the membrane permeation performance, the deposit may not be completely recovered.
Nitto Denko Co., Ltd. Catalog applicable cleaning procedures.

    The influence of the accumulation degree of adhering foreign matter that can be tolerated differs depending on the membrane type to which each separation function is given, and the influence on the contact membrane surface differs depending on the dissolved state of the substance dissolved in the target liquid to be supplied. At the same time, there is a possibility that the solution in the vicinity of the membrane is affected by the charge state of the approaching membrane holding structure, and the adhesion and adsorption strength to the membrane surface changes in a complex manner and becomes difficult to separate.

The energy required to peel off such deposits is caused by physical changes such as supplying chemicals and adjusting the concentration to swell the deposits, etc. It has been considered that it is a regular method to enable the peeling operation from the film surface and the auxiliary structure material surface due to the above effects.

  However, the problem is that it is difficult to apply an effective drug, considering the drug composition that can swell the adhered foreign material for the purpose of peeling, the alteration of the material constituting the separation membrane, or the destruction of the surface functional structure. Has a strong affinity with the constituent materials of the separation membrane and involves considerations such as poor drug outflow detergency. In particular, the outflow and replacement operation of the drug that has permeated into the separation membrane after the chemical cleaning, and the disposal operation of the working cleaning liquid after the operation are problematic.

  Therefore, in order to compensate for the many difficulties of the methods that depend on the help of the addition effect of these chemical agents, the movement to find a separation operation that can be commonly applied to a wider range of separation membranes, In order to exert the separation effect common to a wide range of fields in consideration of the different complex bonding forces formed by, by penetrating into a very narrow gap and separating the bonding points connected by weaker bonds, If a method that can gradually expand the collapse point and avoid the influence on the surroundings by concentrating the coupling points in a small range gradually, it is judged as an ideal solution.

According to the present invention, when the original separation operation on the surface of the wet-type separation function membrane is continued and the characteristics of the original separation membrane function are contaminated due to the accumulation of foreign substances, the performance of the gas is reduced. Due to the adsorption effect exhibited by the ultrafine bubbles created by the explosion dispersion operation of the dissolved solution, a cleaning effect is obtained by adhering to and peeling off contaminants adhering to the membrane surface, and the cleaning waste liquid does not contain chemicals There is an advantage that there is no need for waste liquid treatment.
For this purpose, if a method of continuously creating and replenishing gas in water as ultrafine independent bubbles and applying it can be applied, high-density charge electrons are accumulated on the surface of such ultrafine closed cells. It is known to be negatively charged, and easily penetrates into narrow gaps, and in particular penetrates and adheres to the adhering surface (areas that are not wet are judged to be positively charged). It is expected to exert a peeling effect by completely wetting (changing under negative charge) while neutralizing with the reverse charge (minus) amount of the surface of the fine bubbles.
Specifically, when replenishing the fine bubble water to the dirty area, initially the fine bubble water does not flow out from the end of the contaminated area, but the liquid containing no bubbles flows out, but gradually grows. The liquid containing the large bubbles that have grown together flows out, and the particles gradually become smaller, and the original injected fine bubbles flow out, creating a situation that matches the reduction in the differential pressure that was generated. It has been confirmed that

  Accordingly, the higher the concentration of the supplied fine bubbles, the faster the recovery of the contaminated area is. However, depending on the degree of contamination, the same effect can be obtained by supplying a low concentration of bubble water for a long time. In order to avoid an increase in incidental facilities and an increase in power consumption related to the operation, the same effect has been recognized in the neutralization work taking time.

Many methods (such as ultrasonic vibration tuning method, high-pressure impact collision method, explosion dispersion method) are considered as methods for continuously generating such ultrafine bubble particles at a high concentration. Even if the method is used, it is assumed that the bubble particle diameter existing in the system increases the ratio of occupying a smaller particle diameter region, so that the effect of penetrating into a fine gap is improved.
Furthermore, the bubble is associated with the surface by neutralizing the surface charge of the bubble that has penetrated into the narrow space, and the bubble is expanded and ruptured, thereby producing a cleaning effect that generates a peeling force from the solid surface.
It is also possible to add a technique for reinforcing the peeling effect by combining the possibility of adjusting the bubble breaking strength by supplying an ultrasonic wave from the outside to a technique for generating another peeling effect.

  Furthermore, if the maintenance of the bubble particles can be controlled even in a hot water environment where the water temperature is increased, the work can be performed in an environment where the surface viscosity of the deposits is reduced to reduce the adsorption power or the peeling is likely to occur. Increasing the operation effect by selecting conditions is also an important selection condition.

Next, the present invention will be described in more detail with reference to examples.
A high-pressure pump that supplies raw water, for example, a multi-stage turbine pump, most preferably has an impact shearing function in which metal plates are alternately welded in a pipe connected to a pump capable of discharging 1.2 Mpa. Install a held shearer, press the gas to be dissolved before this shearer, supply the water and gas at the same time, contact each other in the shearer, and join this mixed water to the end of the pipe It is connected to the pressure tank, stays for a certain time as a bubble mixture, and is separated into completely saturated dissolved water and excess gas components after the passage, and the excess gas components are continuously passed through the work between the incidentals. Therefore, consideration is given to maintaining preferable operating conditions in which a constant pressurized state is always maintained and a stable bubble diameter is maintained.

Generally, the amount of air to saturate with water varies with the temperature of the liquid and the pressurizing conditions to be maintained, but if judged by volume ratio, a rough water volume of 1: 0.07 to 0.11 intruded gas. If the volume ratio is supplied as a guide, even if there is a change in the water temperature, a bubble water concentration with a fine bubble component weight concentration of approximately 180 to 220 ppm produced from a substantially constant supersaturation state will be supplied.
Thus, the pressure of the injected water is preferably kept at 0.6 Mpa or more, more preferably around 1 Mpa, most preferably kept at 1.2 Mpa or more, and the gas pressure pushed into these pressure waters is at least about 1 Mpa or more. It is expected that a stable gas from a pressure tank that maintains a high pressure will be injected.
The discharge / discharge pipe joined to the end of this pressure tank employs a specially structured valve consisting of the cross-sectional area of the discharge port, the valve seat and the valve body, so that the pressure water discharged from the valve seat through the discharge port Is discharged from the internal high-pressure part to the external low-pressure part instantaneously from the valve seat of almost the same area, causing the dissolved gas component to explode and boil according to the pressure difference. , Grow into fine bubbles and disperse.

The bubble particle size in the bubble water obtained by these operations is such that the greater the pressure difference between the indentation pump pressure during discharge operation (the pressure inside the tank and the pressure after the discharge explosion valve outlet (external pressure)), the more the explosion occurs. Determine the environment.
In the process in the middle of the cleaning operation system, the bubble diameter at the inlet is grown by the association of bubbles in the process of passing through the narrow gap on the membrane surface through the separation membrane to be cleaned. By passing through the pressure-adjusted throttle valve, there is a possibility that the fine particle size is subdivided due to the breakage of bubbles in the cavitation phenomenon.

Furthermore, it is assumed that the smaller the contact area between the valve seat and the valve and the shorter the contact time, the faster the discharged water speed and the smaller the particle size created by the scattered bubbles.
However, the most important bubble diameter is that the smaller the diameter when entering the gap of the separation bubble membrane in the first stage, the smaller the load pressure applied in the cross-sectional area direction of the separation membrane structure, and the mechanical deformation of the structure Less, changes in resistance to fluid flow are small, and air bubbles staying in the narrow space inside are expelled to promote hydrophilicity.

Therefore, the method for generating fine bubbles in the liquid flow system is not only the bubbles generated by the explosion method, but even if the bubble diameter deformed every time passing through the pressure pipe is greatly deformed, the function of these bubbles is It is judged that the value existing in the separation membrane structure to be processed is recognized by changing the strength.
In addition, it is not important to install these discharge valves as close as possible to the roasting mouth of the container in which the target separation membrane to be subjected to the separation cleaning operation is stored as much as possible.
If the operation of extending the discharged bubble water to a distance with a thin pipe is carried out, the bubbles will be associated with each other in the pipe, making it easier to grow into large bubbles, reducing the charge density of negative ions on the surface, It loses the special charge neutralization effect function expected of.

In order to avoid this problem, the piping distance to the original port of the discharge valve that has maintained the pressure is increased, and when the target film is cleaned, it is loaded as close to the containment vessel as possible to clean the target film. In operation, it can be said that the discharged bubble water can be loaded as close as possible to the containment vessel so that it can immediately contact the separation membrane to be cleaned quickly.
Operational conditions that are sufficiently common to adaptation of industrial water with salinity before and after river water can be obtained.

A number of methods have been applied as defensive measures to avoid obstacles due to the inflow of foreign objects into the narrow gaps of structures as a pretreatment for desalination operations, but inflow of coarse particles is inevitable in sand filtration. For the purpose of improving the accuracy of inhibition, MF membranes are applied, and coarse particles are avoided and avoided, but fine bacterial components (0.05 to 0.5 microns) pass through and have a finer separation diameter. Many events that accumulate on the surface and increase the number of problems appear due to increased reproduction, the adhesion energy of these fines is large, and it tends to be difficult to remove by alteration by chemicals.
Peeling conditions for such bacterial protein contaminants are required to have strong alkalinity. However, under effective concentration and temperature conditions, the material constituting the target separation membrane will also be affected, and the cleaning operation will inherently It has been confirmed that there is a possibility that it may be necessary to be prepared to have the harmful effect of losing its separation function.

Normally, when the reverse osmosis membrane device is operated for a long time, the pressure loss of the reverse osmosis membrane device tends to increase due to the contamination of the membrane module. A typical system using a separation membrane is shown in FIG.
This chemical cleaning is expected to dissolve and remove deposits contaminating the membrane module with chemicals, but the adhered foreign substances may not dissolve with various chemicals.
Fig. 2 shows the piping path when the RO membrane unit is cleaned with fine bubbles.
FIG. 3 shows a device arrangement diagram during the reverse osmosis operation loaded with the RO membrane.

Example 1
The primary sand filtration of river water was used. In the second stage, the cartridge was used as a safety filter to shield coarse particles, and this was adapted to the desalted water production process by low pressure operation reverse dialysis membrane dialysis.
The differential pressure during the operation after the elapse of 6 months reaches a critical deformation pressure of 0.08 Mpa / 1 element that induces damage to the internal structure presented by the membrane manufacturer. Since the pressure increased to .34 Mpa, the liquid flow operation was stopped, and an operation of peeling and flowing out obstacles due to adhered foreign matter accumulated on the separation membrane surface using fine bubble water was started.

  The reverse osmosis membrane desalination equipment to be washed is a low-pressure operation type 8 inch element x 4 element / vessel unit, the operation pressure is 0.8 Mpa, and the permeate product water recovery rate is around 75%. The river water supply was 5,800 l / h, the permeated desalted water was 4,000 l / hr, and the brine water was 1,800 l / hr (30 l / min). As the flow rate increased, the amount of permeated water decreased to 3,400 l / hr (15% down), and the differential pressure increased to 0.34 Mpa.

This can be said that the accumulation of contaminants on the membrane surface has counteracted the low-pressure membrane characteristics due to the decrease in the removal effect of the accumulated salt content due to surface charge.
Therefore, if it is judged that the adhesion of the accumulated foreign matter is a result of being attracted by the charge direction and the charge amount on the surface of the functional film, it is assumed that neutralization peeling is performed with the reverse charge amount stored on the surface of the fine bubbles. Is done.
The device for generating fine bubbles is a multi-stage turbine pump of 1.5 kW, an ultimate pressure of 0.85 Mpa of generated water amount of around 58 l / min, and the pressure air for generating fine bubbles is supplied at 1.0 Mpa × 6.2 L / min Then, both of them were impact-mixed, ejected from the discharge explosion valve (30A), and supplied and supplied from a branch pipe installed near the discharge valve of the 8-inch element.

  The amount of liquid pushed in from the explosion start valve is 56 l / min, and the cross-sectional flow rate of the 8-inch element is 0.17 cm / min, which is a low supply rate (0.12-0.19 cm / min during the desalting operation). However, after about 60 minutes of feeding at a feeding speed close to a sufficient feeding condition, the feeding resistance drops to 0.0032 Mpa / element, and the total of the four pieces reaches 0.004 Mpa. Declined.

  This means that if the cleaning operation of the element is not a chemical operation, it is not possible to perform the peeling operation of the adhered matter, and it is judged that the foreign matter is selectively adsorbed and adhered to different surfaces in the charge direction. It is explained that the problem can be avoided by supplying the bubble water with the reverse charge.

The contamination of the above elements is mainly due to bacterial contamination due to organic contamination, and chemical cleaning is not effective, such as protein denaturation and shrinkage, and on the contrary, the adhesion force is strengthened, but dare to clean with chemicals At first, 1 L sulfuric acid solution of acid was diluted and flowed by 1 L, but the differential pressure did not decrease, and it did not decrease even when 1 N sodium hydroxide was supplied.
Furthermore, after supplying these chemicals, 100 times the amount of clean water was passed, but the pH indicated by the wash water was high, the residual amount of alkali components adhering to the membrane surface was large, and a greater amount of wash water was required. Was showing.

Salt separation membrane test equipment flow using reverse osmosis membrane Reverse osmosis membrane unit cleaning line using microbubble water

Explanation of symbols

1: Raw water 2: Transfer pump 3: Pre-stage filtration equipment 4, Filtrated water storage tank 5: High pressure pump 6: Desalination membrane separation unit 7: Desalination water tank 8: Fine bubble generator 9: High pressure transfer pump 10: Compressor
11: Heating / circulation tank 12: Explosion separation valve

Claims (7)

  Improve the shear contact efficiency through the impact shear plate installed in the piping connecting both components with the pressure function pump that supplies the raw water and the function that compresses and pushes the gas, and continuously or intermittently gas components to the raw water In order to promote compression and dissolution of coarse dispersed bubbles in water, a buffer zone is provided to increase the amount of gas component dissolved, and the excessively supplied gas volume component is out of the tank. Dissolved components are combined with a specially constructed valve body and an extended connecting piping member in the pressurized piping system connected to the tank end, and the dissolved gas components are spread and dispersed by a combination that opens the pressurized system to the low pressure region at once. The surface of these generated bubbles has a high negative charge amount and is a bubbling water containing a myriad of independent fine bubbles at high density, and accumulated on the surface of the separation functional membrane by the reverse charge (minus ions) of the fine bubbles. Disability To neutralize the charge of the object, to restore the original function by peeling eliminated, the physical cleaning method of the separation functional membrane surface to eliminate inhibitory foreign matter out of the system.   By using a discharge valve that has a structure in which the cross-sectional area of the gap formed by the valve seat and valve body of the discharge port is approximately equal, it is possible to perform separation cleaning by separating the saturated water of gas components for generating bubbles from a distance. Washing characterized by exerting the desired delamination cleaning effect by applying active fine bubbles immediately after generation by adapting the valve body structure that can be pressurized and maintained attached to the required place Method   Separation operation that leads to the pressure vessel when replenishing the gas solution prepared by the method described in claim 1 that facilitates the generation of bubbles into a pressure vessel loaded with an object for surface cleaning. For the direction of the water flow supplied for the purpose of the above, from the reverse direction close to the reverse discharge port of the above-mentioned loading container, supply the bubbly water for the purpose of peeling and cleaning, and from the direction with less adhering contaminants on the membrane surface A cleaning method in which a higher cleaning effect can be expected for a liquid feeding operation in a conventional supply direction (forward direction) by supplying the flow in a rich direction (reverse direction). Pressurized sewage that enables generation of fine bubbles in which gas is dissolved is connected to the branched sub piping facility through a special valve to the main piping facility of the supply liquid of the main operation for separation operation. The liquid volume ratio of the mixture of the two at the connecting portion is intended to allow both liquids to be mixed uniformly while changing the ratio of the auxiliary water flow rate including air bubbles from 1: 0.1 to 20. Select the optimal mixing promotion equipment, and supply the mixed liquid in which the injected bubbles are uniformly dispersed in the pipe to improve the surface cleaning effect of the separation membrane to be treated. Is obtained.
However, the mixing ratio of this side stream and the main stream can be changed over time.Further, depending on the type of separation membrane used, the operation for stopping the injection of the side stream can be selected intermittently. A cleaning method characterized in that the separation function is improved by combining a management operation combined with a change in the operation pressure of the liquid supply piping and adding a vibration action of the adaptive separation membrane surface.   When supplying the bubbly water prepared by the operation described in claim 1 to the cleaning operation described in claims 3 and 4, the supply water temperature is set such that the contaminant is covered with a contaminated film caused by the growth of microorganisms. If it is judged, the water pressure is controlled so that the temperature of the biofouling film starts to be deformed and contracted from around 35 degrees Celsius to around 60 degrees Celsius, and the discharge water is supplied to the discharge valve. A cleaning method characterized by weakening the adhesive force due to alteration of the material and enhancing the effect of peeling and cleaning the attached organic matter. By changing the component of the gas component that is forcibly dissolved under the pressure described in claim 1, the acidity, the bursting speed, and the bursting strength of the pressurized water are changed, so that the saturated and dissolved pressure water is obtained. Through the first pressure holding valve, it is provided at the inlet end of the pressure vessel where the separation membrane to be cleaned is installed or at the end of the reverse final outlet. While an adjustment valve is installed to maintain the operating pressure of the membrane to be loaded at a low pressure close to atmospheric pressure, in this claim, a pressure adjustable valve is installed at this end, and the outlet of the pressure breaker valve The pressure system is maintained by the operation of a valve installed at the discharge destination at the end of the container in which the functional membrane to be cleaned is installed, and the pressurization is in the range of 0.5 to 4.5 kg / cm ² of gage pressure. By controlling the pressure, the degree of expansion of the bubble diameter at the end outlet of the pressure vessel is controlled. By controlling the bubble diameter particles controlled so as to be smaller than the narrow gap path of the separation functional membrane to be cleaned, the flow resistance can be reduced by suppressing the expansion of the fine aperture that occurs when passing through the narrow gap. A cleaning method characterized by reducing and improving the effect of removing adhered foreign substances.   By dividing the pressure regulating function valve installed at the end of the pressure vessel group loaded with the separation membrane to be cleaned according to claim 6 into a plurality, a plurality of bubbles are formed, By independently adjusting the pressure valve installed up to the final discharge port, the surface of the separation membrane in a plurality of connected pressure vessels is adjusted by adjusting the diameter of the expanded bubble via the adjustment valve. A cleaning method characterized by efficiently exhibiting a cleaning effect.

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