KR101928203B1 - Exchange period elongation apparatus of ro membrane - Google Patents

Abstract

The present invention provides a system which minimizes the internal contamination of a reverse osmosis (RO) membrane by performing membrane cleaning at 10% of the initial pressure in order to determine the cleaning time when cleaning the RO membrane, and which manufactures and supplies a cleaning solution at low concentration in which an acidic solution has a pH of 4±0.2 and an alkaline solution has a pH of 10±0.2. In addition, an automatic valve is automated to be turned ON/OFF with logic for circulation of the cleaning solution during the membrane cleaning, thereby extending the life of the expensive RP membrane by 3 to 4.5 years and reducing the cost of acid and alkaline cleaning agent. Further, when chemicals are drained and flowed into a wastewater treatment plant, the load on a water treatment system is reduced.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a reverse osmosis membrane,

TECHNICAL FIELD The present invention relates to a technique of changing the cleaning technique of a reverse osmosis membrane using a membrane method in the field of water treatment, and thereby extending the life of the membrane. Currently, the reverse osmosis membrane used in water treatment in almost all fields will have a very large ripple effect. In addition, when the present invention is applied to an existing apparatus, it is considered to be a superior technology in terms of efficiency and economical efficiency due to cost reduction.

The permeation theory for the reverse osmosis process has been presented by S. Sourirajan as a preferential sorption-capillary flow mechanism model and a hydrogen bond model. This is the most well-known basic concept of membrane permeation theory, which assumes that the surface layer of the membrane, that is, the active layer with the separating function, has a microporous structure. The separation mechanism in the reverse osmosis process is determined by the phenomenon of membrane surface and the movement of fluid through the capillary. The size of the pores on the membrane surface, the number of pores, and the chemical properties of the surface layer are important components of the separation mechanism. If the chemical properties of the membrane surface layer in contact with the solution are selectively adsorptive or repellent to a particular solute, there will be a selectively adsorbed fluid layer on the surface of the membrane.

High molecular weight membranes with low dielectric constant such as cellulose acetate selectively remove water near the membrane by first selectively adsorbing water. Thus, when pressurized, only pure water comes out through the capillary of the membrane. Under certain separation conditions, a given membrane will have a critical pore size that represents optimal separation efficiency. This critical pore size is twice the thickness of the adsorbed pure layer. From the surface tension data, the thickness of the pure layer is estimated to be about 3.5 Å, or the thickness of a layer of water molecules.

There is also a theory of a hydrogen bonding model. As a concept of membrane permeation, there is a hydrogen bonding model which explains the selective permeability using a reverse osmosis membrane based on cellulose acetate as a basic model. Cellulose acetate Reverse osmosis membrane has its own carbonyl group, and Carbonyl group has hydrogen bond with water, ammonia and alcohol. The hydrogen-bonded solvent inside the pores of the membrane blocks the solute from entering and leaving. When the pressure is applied, the hydrogen-bonded solvent slowly passes through the membrane while continuing to bond with the surrounding carbonyl groups. This type of mass transfer is possible in membrane materials such as cellulose acetate, which have a structure that is organized in high units.

The RO membrane inevitably carries out cleaning work. The cleaning operation has various obstacles when operating the RO membrane. It is carried out in case of bioremediation (Bio-Fouling) accompanied by bacterial propagation and hardness related scaling occurs due to Particulate Fouling. In addition, membrane cleaning is required due to silica scale and oil & grease fouling. And sterilized with a biocide for prevention of biological fouling to prevent RO membrane. Cleaning and disinfection is carried out periodically 4 to 12 times a year. Membrane cleaning is generally performed when the initial RO membrane pressure is increased by 15%. Since it is generally easy to manage, the pressure change is set as a major factor. As shown in FIG. 1, as the number of times of cleaning is increased as the membrane cleaning is continued, the production amount is lower than the initial flow amount. In addition, the membrane cleaning cycle is often accelerated. Eventually, after a certain period of time, the film must be replaced.

The contamination of the membrane is influenced by the contamination of the outside in the early stage, the pressure is increased, and the contamination source penetrates into the inside of the membrane and the pressure is increased sharply. Generally, when the initial pressure is 15%, the contamination is often penetrated into the inside of the membrane, thereby shortening the lifetime of the membrane.

The present invention seeks to prevent membrane contamination from penetrating into the membrane by conducting membrane cleaning at 10%, rather than at a 15% increase in pressure (FIG. 2). In this case, even if the concentrations of nitric acid and caustic soda, which are chemicals consumed in cleaning, are lowered, it is possible to effectively remove the contamination source. When the acid and alkali are used at a low concentration, even when the effluent water flows into the wastewater treatment plant, it does not cause a great load on the water treatment. In addition, there is an advantage of reducing the drug cost.

The following will examine the differentiation from the present invention with reference to the previously registered patent. An industrial water purification apparatus disclosed in Japanese Patent Application Laid-Open No. 10-2008-0082331 is an industrial water purification apparatus that receives raw water and purifies it and uses it as water for use. It is located at the lower part of the storage tank side and receives the detection signal of the lower limit sensor indicating the replenishment state of the water. By the operation of the given timer, the solenoid valve on the discharge line side of the reverse osmosis membrane is opened for a predetermined time to separate the waste water in the reverse osmosis membrane So that the efficiency of purifying the filter can be increased, and the life of the filter can be greatly extended, so frequent replacement is not required.

In the case of the above-mentioned patent, when the storage tank is full after producing the treated water for a predetermined time, the system is stopped and the water present in the membrane is drained. However, if the water can not be supplied for a long period of time after the drainage, the membrane can not guarantee the efficiency of the dry bottom treatment.

The reverse osmotic pressure water purification system and its control method disclosed in Japanese Patent Application Laid-Open No. 10-0089-1040000 is a method of recycling concentrated water. Conventionally, water is separated into purified water and concentrated water through a pretreatment filter and an activated carbon adsorption filter. In order to solve the problem that the water is stored in the purified water pressure storage tank and the concentrated water is discharged, the waste water is wasted and the lifetime of the pretreatment filter and the activated carbon adsorption filter is required. In order to solve this problem, A water quality sensor capable of sensing a substance on the influent water of the concentrated water storage tank is installed in the front end, that is, in the activated carbon adsorption filter, and the concentrated water is drained when the concentration is more than the set concentration and the concentrated water is recycled below the set temperature, The life of the filter and the activated carbon adsorption filter is prolonged, and resource reuse and cost reduction are effective.

In the case of the above patent, the concentrated water is devised as a system for recycling or draining water according to a desired water quality. However, when the concentrated water is recycled, the reverse osmosis device has a disadvantage that the membrane is damaged due to more load.

In the present invention, it is aimed to maximize the effect by effectively performing film cleaning at the time of film contamination. To do this, we focus on the pressure change, and if the initial pressure is increased by 10%, the membrane is cleaned. In this case, a method for minimizing the use of acid and alkaline components should be sought.

In the present invention, when the initial pressure of the RO membrane is about 10 bar, when the membrane cleaning is carried out at 11.5 to 12.0 bar as compared with the initial pressure, the acid solution pH 2 or less and the alkaline solution pH 12 or more are each conducted for 30 minutes. In this case, the problem is that as the membrane cleaning is performed, the treatment efficiency of the membrane tends to decrease. The initial production flow rate is reduced and the membrane cleaning cycle is also shortened and the membrane must eventually be replaced. The main reason for the replacement is that the contaminants inside the membrane are not removed through membrane cleaning. When the membrane is cleaned at a pressure of 11 bar, it is possible to remove contaminants from the surface of the membrane and maintain the membrane in the initial state before the internal contamination. Appropriate control logic is also needed to reach these results.

The technical problem of the present invention as described above is achieved by the following means.

(1) a reverse osmosis membrane inflow line (1) into which water is introduced; A high-pressure pump (4) installed on the inflow line (1) for supplying inflow water to the RO system; A low pressure sensor 2 provided at the front end of the high pressure pump 4 and a high pressure sensor 3 provided at the rear end of the high pressure pump 4; Stage reverse osmosis membrane (5) through the high-pressure pump (4), and the treated water is treated by the first-stage reverse osmosis membrane (5) The water moves to the treated water line 9, the concentrated water moves to the concentrated water line 6 and passes through the two-stage reverse osmosis membrane 7, and the treated water processed in the two- The concentrated water is moved to the circulation line 12 by the circulating water automatic valve 10 and discharged to the drainage line 13 by the drainage valve 11 in the case of concentrated water drainage A reverse osmosis membrane processor; An alkaline solution tank 16 for supplying an alkaline solution having a pH of 10 ± 0.2 and a sterilizing tank 17 for supplying an alkaline solution having a pH of 10 ± 0.2, And the treated water treated in the respective reverse osmosis membranes is supplied to the acidic solution tank 15, the alkaline solution tank 16 and the bactericide tank 17 by the membrane washing water inflow line 14, The reverse osmosis membrane treatment unit supplies the membrane cleaning liquid to the reverse osmosis membrane treatment unit through the cleaning liquid input lines 18, 19 and 20 and the washing liquid passing through the first stage reverse osmosis membrane 5 and the second stage reverse osmosis membrane 7 passes through the washing liquid recovery line 21 And a plurality of tanks,
Pressure sensor (3) detects a period of 10% of the initial pressure at the time of membrane cleaning, and the membrane washing liquid is circulated by an automatic valve in the order of acid, alkali and sterilizing agent by a PLC program A replacement cycle extension device for the membrane.

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Through the present invention, the expensive RO membrane can be extended from 3 to 4.5 years, resulting in cost saving of acid and alkali detergent. In addition, when these chemicals are drained and flowed into the wastewater treatment plant, there is an advantage of reducing the load on the water treatment system.

Fig. 1 shows changes in the number of production and the cleaning cycle according to the number of times of cleaning according to the present invention.
Figure 2 shows the external and internal contamination of the RO membrane of the present invention.
Figure 3 shows the RO system and membrane cleaning system of the present invention.
Figure 4 is a comparison of membrane cleaning in a typical membrane cleaning and 10% pressure increase in an embodiment of the present invention.

The reverse osmosis membrane and the membrane cleaning system according to the present invention are shown in FIG. 3, and the configuration and description of the reactor are as follows.

The water is introduced through the reverse osmosis membrane inflow line 1 and the low pressure sensor 2 and the high pressure sensor 3 are installed at the front and rear of the high pressure pump 4, respectively. The introduced constant is transferred to the treated water line 9 via the first stage reverse osmosis membrane 5 of the RO system (or reverse osmosis membrane processing unit) through the high-pressure pump 4 and the concentrated water is transferred to the concentrated water line 6 And passes through the second stage reverse osmosis membrane (7). The process number is also moved through the process number line 8.

In the case of the concentrated water, it is moved to the circulation line 12 by the circulating water automatic valve 10, and is discharged to the drainage line 13 by the drain valve 11 in the case of concentrated water drainage.
In the present invention, a membrane cleaning unit is included for membrane cleaning. In the present invention, it is preferable that the high pressure sensor 3 senses a period of 10% of the initial pressure at the time of film cleaning using the superficial portion, and the film cleaning is performed by the PLC program. Hereinafter, the membrane washing process using the submerged membrane will be described in more detail.

RO treatment water is introduced into the acidic solution tank 15, the alkaline solution tank 16, and the bactericide tank 17 in order to make the initial cleaning liquid. At this time, water is supplied to the membrane washing water inflow line 14, and water is supplied to the acidic solution tank 15, the alkaline solution tank 16, and the bactericide tank 17, respectively, which are membrane cleaning tanks. These tanks respectively supply the membrane cleaning liquid to the RO system through the cleaning liquid input lines 18, 19 and 20 by a pump. In this case, the pH of the acidic solution is 4 ± 0.2 and the pH of the alkaline solution is 10 ± 0.2. The order of supply is the acid solution first, the alkaline solution the next, and finally the bactericide solution.

The cleaning liquid that has passed through the first stage reverse osmosis membrane 5 and the second stage reverse osmosis membrane 7 flows into each membrane cleaning tank through the cleaning liquid recovery line 21.

Hereinafter, the present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention.

[Example]

[Example 1] A membrane was washed at 10%

In order to present concrete data of the present invention, the membrane washing is compared with the case of 15% and 10% in the general method. In 15% of cases, the membrane was washed 5 times for 1 year and 5 times for 10%. Figure 4 is a comparison of membrane cleaning with a typical membrane wash and 10% pressure increase. Generally, when the membrane was cleaned at 15%, the treated water was decreased with the increase of the membrane washing period, and the initial 5 ton / hr was reduced to 5 ton / hr after 5 times of membrane washing. However, when the membrane was washed at 10%, the initial amount of 5ton / hr was 4.9ton / hr after 5 times of membrane washing. As a result, it was confirmed that it is effective to perform film cleaning at 10% of the initial cleaning pressure at 15% of the initial cleaning pressure.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. It can be understood that

[Description of Symbols]

1: reverse osmosis membrane inflow line 2: low pressure sensor

3: high pressure sensor 4: high pressure pump

5: 1 stage reverse osmosis membrane 6: 1 stage concentrated water line

7: 2-stage reverse osmosis membrane 8: treated water line

9: Treated water line 10: Circulating water automatic valve

11: drain valve 12: circulation line

13: Drain line 14: Membrane rinse water inflow line

15: acidic solution tank 16: alkaline solution tank

17: Disinfectant tank 18: Cleaning liquid input line

19: Alkaline cleaning liquid input line 20: Disinfectant input line

21: cleaning liquid recovery line

Claims (3)

A reverse osmosis membrane inflow line 1 into which water is introduced; A high-pressure pump (4) installed on the inflow line (1) for supplying inflow water to the RO system; A low pressure sensor 2 provided at the front end of the high pressure pump 4 and a high pressure sensor 3 provided at the rear end of the high pressure pump 4; Stage reverse osmosis membrane (5) through the high-pressure pump (4), and the treated water is treated by the first-stage reverse osmosis membrane (5) The water moves to the treated water line 9, the concentrated water moves to the concentrated water line 6 and passes through the two-stage reverse osmosis membrane 7, and the treated water processed in the two- The concentrated water is moved to the circulation line 12 by the circulating water automatic valve 10 and discharged to the drainage line 13 by the drainage valve 11 in the case of concentrated water drainage A reverse osmosis membrane processor; An alkaline solution tank 16 for supplying an alkaline solution having a pH of 10 ± 0.2 and a sterilizing tank 17 for supplying an alkaline solution having a pH of 10 ± 0.2, And the treated water treated in the respective reverse osmosis membranes is supplied to the acidic solution tank 15, the alkaline solution tank 16 and the bactericide tank 17 by the membrane washing water inflow line 14, The reverse osmosis membrane treatment unit supplies the membrane cleaning liquid to the reverse osmosis membrane treatment unit through the cleaning liquid input lines 18, 19 and 20 and the washing liquid passing through the first stage reverse osmosis membrane 5 and the second stage reverse osmosis membrane 7 passes through the washing liquid recovery line 21 And a plurality of tanks,
Pressure sensor (3) detects a period of 10% of the initial pressure at the time of membrane cleaning, and the membrane washing liquid is circulated by an automatic valve in the order of acid, alkali and sterilizing agent by a PLC program A replacement cycle extension device for the membrane.
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