KR102392274B1 - Apparatus and Method for Cleaning Membrane - Google Patents

Abstract

The present invention relates to a membrane cleaning method and apparatus, and more particularly, to perform a membrane evaporation method by simultaneously introducing raw water having a Total Dissolved Solids (TDS) of 58,000 mg/L or more and bubbles, wherein the bubbles are represented by the following Equation 1 Calculation according to the contamination index (FI) of the membrane to determine the injection cycle of the bubbles, and at the same time desalination of seawater by membrane evaporation and cleaning the evaporation membrane, thereby preventing and delaying the adhesion of contaminants on the membrane surface, thereby prolonging the life of the separation membrane; It relates to a membrane cleaning method and apparatus that can be expected to improve the quality of treated water, maintain a stable production quantity and quality, and reduce the amount of chemicals used.
[Equation 1]
FI(%)=[(Q0-Qt)/Q0]×100
(Where, FI is the membrane fouling index, Q0 is the production quantity for the first hour after starting filtration, and Qt is the production quantity for the current hour)

Description

Membrane cleaning method and apparatus {Apparatus and Method for Cleaning Membrane}

The present invention relates to a membrane cleaning method and apparatus capable of cleaning the contamination of the evaporation membrane during a seawater desalination process using the membrane evaporation method.

Water is man's most important natural resource, covering about 75% of the Earth's surface. About 97% of the water on Earth is in the ocean, and about 2/3 of the remaining 3% is in polar ice caps or glaciers.

However, seawater existing in the sea is too salinity to be used as water for human life or industrial use.

Moreover, today, the amount of fresh water usable for human life is gradually decreasing due to the continuous increase in industrialization and environmental pollution.

Therefore, as a method for solving such a shortage and depletion of freshwater, a method for converting a large amount of seawater into fresh water as described above is being sought, and in order to implement this method, various desalination devices for seawater have been developed.

In general, seawater desalination methods are largely evaporation method (Distillation), reverse osmosis method (Reverse Osmosis), electric dialysis method using electric field (Electro-dialysis), freezing method using cold energy (Freezing Process), and membrane distillation method using hydrophobic membrane (membrane distillation) ) is there.

Among them, the membrane evaporation method is a water treatment method combining membrane filtration and evaporation, and is a process for separating water from raw water in a pure vapor state using a porous separation membrane having a hydrophobic surface (Korean Patent Application Laid-Open No. 2008-0082627) .

The raw water treated by membrane evaporation comes into contact with one side of the separation membrane, but because the raw water does not permeate into the pores of the separation membrane due to the surface tension generated due to the high hydrophobicity of the membrane surface, water does not pass through, and only the vapor passes through the separation membrane. do. The reason mass transfer occurs in the membrane evaporation process is because of the temperature difference formed between the raw water at a high temperature and the filtered water at a low temperature across the separation membrane. It becomes a driving force to move from raw water to treated water.

Membrane evaporation methods are direct contact membrane distillation (DCMD), air gap membrane distillation (AGMD), Sweep gas flow membrane evaporation (SGMD), vacuum membrane evaporation (Vacuum Membrane Distillation; VMD) can be divided into four methods.

Since membrane evaporation is not significantly affected by osmotic pressure, concentrated water (raw water with high salt concentration) of evaporation or reverse osmosis can be treated with a high recovery rate. There is this.

However, since membrane evaporation is also a process using a membrane, as filtration continues, membrane contamination inevitably occurs due to contaminants excluded from the membrane. When membrane contamination occurs, the amount of treated water decreases and the quality of treated water deteriorates, as well as membrane wetting, which has a limitation in that the operation of the membrane evaporation process must be stopped.

Accordingly, it is an object of the present inventors to provide a method and apparatus for cleaning a membrane that does not stop the operation of the membrane evaporation process and does not reduce the amount of treated water and the quality of the treated water due to membrane contamination.

The present invention performs a membrane evaporation method by simultaneously introducing raw water having a Total Dissolved Solids (TDS) of 58,000 mg/L or more and bubbles, wherein the bubbles are calculated according to the contamination index (FI) of the membrane of Equation 1 below, and the bubbles are sprayed An object of the present invention is to provide a method for cleaning a membrane for a membrane evaporation method, characterized in that the evaporation membrane is washed at the same time as seawater desalination by membrane evaporation method by determining a cycle.

[Equation 1]

FI(%)=[(Q0-Qt)/Q0]×100

(Where, FI is the membrane fouling index, Q0 is the production quantity for the first hour after starting filtration, and Qt is the production quantity for the current hour)

In addition, the present invention is a raw water tank and raw water pipe for supplying raw water; membrane evaporation module for filtering raw water; a bubble generator and a bubble injection pipe for supplying bubbles; a cooling water tank and cooling water pipe for supplying cooling water; and a control unit for calculating the membrane contamination index of the membrane and determining a bubble injection period according to the calculated membrane contamination index, wherein the control unit determines the membrane contamination index using Equation 1 It is another object to provide an apparatus for cleaning a film for a film evaporation method.

The membrane cleaning method and apparatus according to the present invention has the advantage that it is possible to perform the membrane cleaning process at the same time as the seawater desalination process.

In addition, the membrane cleaning method and apparatus according to the present invention cause vibration and form shear force on the surface of the separation membrane while air bubbles move along the surface of the separation membrane, and some of them disappear in water to cause cavitation and prevent the adhesion of contaminants or Alternatively, there is an advantage that it can be delayed.

Due to the above advantages, it is possible to expect effects such as extending the life of the separation membrane, improving the quality of treated water, maintaining a stable production quantity and water quality, and reducing the amount of chemicals used.

1 shows a conceptual diagram of a membrane cleaning apparatus according to an embodiment of the present invention,
2 is a diagram illustrating a model prediction control signal processing method for determining a bubble injection method according to an embodiment of the present invention;
Figure 3 shows the change in the capacity of the production water per hour in the case of not injecting the bubbles and the raw water at the same time according to an embodiment of the present invention.

The present invention relates to a method and apparatus for cleaning a membrane for a membrane evaporation method capable of cleaning the contamination of the evaporation membrane during a seawater desalination process using the membrane evaporation method.

Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor should properly understand the concept of the term in order to best describe his invention. Based on the principle that it can be defined, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

Therefore, the embodiments described in this specification and the configurations shown in the drawings are only the most preferred embodiment of the present invention, and do not represent all of the technical spirit of the present invention, so at the time of the present application, they can be replaced It should be understood that various equivalents and modifications may exist.

In the membrane cleaning method for membrane evaporation according to the present invention, the membrane evaporation method is performed by simultaneously introducing raw water having a Total Dissolved Solids (TDS) of 58,000 mg/L or more and bubbles, wherein the bubbles are the contamination index (FI) of the membrane of Equation 1 ) to determine the injection cycle of the bubbles, and the evaporation membrane is washed at the same time as seawater desalination by membrane evaporation method.

When the seawater desalination process is performed, the membrane evaporation method is performed for raw water that has been subjected to desalination processes (RO, MSF, MED), etc. In the desalination process, most of the particulate matter and organic matter is removed. However, since the salt concentration is 1.4 to 2.5 times more concentrated than the influent before the desalination process (RO, MSF, MED), scale mainly due to calcium sulfate or the like is generated, resulting in contamination of the evaporation film.

In the membrane fouling path due to scale, calcium sulfate reaches a supersaturated state, and crystal nuclei are generated on the membrane surface due to concentration polarization (a phenomenon in which the salt concentration increases on the membrane surface), and the crystal nuclei grow and cover the membrane surface, resulting in a filtration area It is predicted to reduce the filtration rate and to form a separate filtration resistance by forming a cake layer by generating crystal nuclei in the solution and the crystal nuclei grow sufficiently and settle to the surface of the film.

Therefore, the present invention is characterized in preventing or delaying membrane contamination by injecting air bubbles together with raw water having a high salt concentration in order to simultaneously block the two membrane contamination pathways.

In this case, the air bubbles are included in the air, and the air containing these bubbles is preferably introduced at the same pressure as the raw water inlet pressure introduced into the membrane evaporation module, specifically in the range of 1.5 to 2.5 bar. When the inlet pressure of the bubble-containing air exceeds the raw water inlet pressure range, the raw water directly passes through the evaporation membrane and it may be difficult to perform the role as a separation membrane. In addition, it is preferable that the bubble has a diameter of 0.2 to 0.4 mm.

Contamination of the membrane used in the membrane evaporation method according to the present invention, the membrane surface is cleaned by the bubbles introduced together with the raw water, the bubbles are contained in the air is injected into the membrane evaporation module. The bubble injection method is determined according to the membrane contamination stage set based on the decrease in the quantity of produced water.

In general, since the membrane evaporation method operates the process in a constant flow method unlike the existing pressure-driven membrane process (MF/UF/NF/RO), it is impossible to operate while changing the temperature of the raw water in real time. Therefore, it is reasonable to judge the degree of membrane contamination based on the amount of decrease in production.

The membrane fouling step is divided by the membrane fouling index using Equation 1 below.

[Equation 1]

FI(%)=[(Q0-Qt)/Q0]×100

(Where FI is the membrane fouling index, Q0 is the production quantity for the first hour after starting filtration, and Qt is the production quantity for the current hour).

Specifically, when the contamination index (FI) of the membrane is less than 5%, the air bubbles are intermittently injected, but the injection is performed for 1 minute and then stopped for 9 minutes; If the contamination index (FI) of the membrane is 5% or more to less than 10%, air bubbles are intermittently injected, but the injection is performed for 1 minute and stops for 4 minutes; If the contamination index (FI) of the membrane is 10% or more and less than 15%, the air bubbles are intermittently injected, but the injection is performed for 1 minute and then stopped for 1 minute; When the contamination index (FI) of the membrane is 15% or more, air bubbles are continuously injected.

The characteristics of the membrane cleaning apparatus for a film evaporation method according to the present invention can be understood by the embodiments described in detail with reference to the accompanying drawings.

Referring to FIG. 1 , a membrane cleaning apparatus for a membrane evaporation method according to the present invention relates to a device capable of cleaning the contamination of the evaporation membrane while performing a seawater desalination process.

Specifically, the raw water tank (2) and raw water pipe (7) for supplying raw water; a membrane evaporation module 17 for filtering raw water; a bubble generator 8 and a bubble injection pipe 9 for supplying bubbles; a cooling water tank 23 and a cooling water pipe 18 for supplying cooling water; and a control unit 30 for calculating the membrane contamination index of the membrane, and determining a bubble injection period according to the calculated membrane contamination index.

In addition, it consists of flowmeters 6, 13, 16, 21, operating pressure, pressure gauges 5, 10, 12, 15, 20, and thermometers 4, 11, 14, 19 for measuring the temperature of raw water and cooling water. .

2 illustrates a model prediction control signal processing method for determining a bubble injection method according to an embodiment of the present invention.

The model prediction control signal processing method of FIG. 2 is performed by the control unit. The control unit includes: a calculation unit for calculating the membrane contamination index using the flow rate, and determining the first membrane contamination step according to the calculated membrane contamination index; a comparison determination unit that compares the first membrane fouling step with the membrane fouling step of the previous cycle to determine a second membrane fouling step; and a processing unit for controlling the bubble generator according to the secondary membrane contamination step.

The calculator may calculate the first membrane contamination step according to the membrane contamination index calculated by Equation 1 above. The membrane fouling step may be a graded step according to an index.

Specifically, if the contamination index (FI) of the membrane is less than 5%, the membrane contamination step is determined as step 1, and if the contamination index (FI) of the membrane is 5% or more to less than 10%, the membrane contamination step is determined as step 2, If the contamination index (FI) of the membrane is 10% or more and less than 15%, the membrane contamination step is determined as 3 steps, and if the contamination index (FI) of the membrane is 15% or more, the membrane contamination step is determined as 4 steps.

The comparison determination unit determines the first membrane fouling step as the second membrane fouling step when the difference between the first membrane fouling step calculated by the calculating unit and the membrane fouling step of the previous cycle is less than three steps. Here, the secondary membrane contamination step may be a finally determined membrane contamination step.

In addition, the algorithm for calculating the model prediction control for determining the bubble injection method is as follows.

First, the production flow rate for the current hour is measured.

Next, using the calculated production flow rate, the membrane contamination index is calculated using Equation 1 above.

Next, the membrane fouling level is primarily determined using the calculated membrane fouling index.

Next, check whether the previous membrane contamination stage was stage 1 or stage 2.

Next, if the previous membrane fouling step is not step 1, the firstly determined membrane fouling step is applied.

Next, if the previous membrane fouling step is step 1, compare the firstly determined membrane fouling step with the membrane fouling step for the previous hour.

Next, if the difference between the membrane contamination stages is less than 3, the membrane contamination stage is determined by applying the firstly determined membrane contamination index, and if the difference is 3 or more, the membrane contamination stage is determined by resetting the membrane contamination index to 4.

Finally, membrane cleaning is performed by varying the bubble injection method according to the determined membrane contamination step.

Figure 3 shows the change in the capacity of the production water per hour in the case of not injecting the bubbles and the raw water at the same time according to an embodiment of the present invention. In the case of injecting air bubbles, while maintaining almost the same capacity for 20 hours, it was confirmed that there was no change in capacity for 10 hours in the case of not injecting air bubbles.

This is the result confirming that the bubble strengthens the shear force of the membrane surface to prevent concentration polarization, and prevents or delays the sedimentation of crystal grains in the solution to the membrane surface, thereby alleviating membrane contamination.

1: Heater 2: Raw water tank 3: Raw water circulation pump
4, 11, 14, 19: thermometer
5, 10, 12, 15, 20: pressure gauge
6, 13, 16, 21: flow meter
7: Raw water piping 8: Bubble generator 9: Bubble injection piping
17: membrane evaporation module 18: cooling water pipe 22: cooling water circulation pump
23: coolant tank 24: cooler
30: control unit

Claims (9)

The membrane evaporation method is performed by simultaneously introducing raw water with TDS (Total Dissolved Solids) of 58,000 mg/L or more and air bubbles,
The bubbles are calculated according to the contamination index (FI) of the membrane of Equation 1 below, and the injection cycle of the bubbles is determined, and the evaporation membrane is washed simultaneously with desalination of seawater by membrane evaporation method,
The bubble has a diameter of 0.2 to 0.4 mm, and is contained in air and is injected at a pressure of 1.5 to 2.5 bar.
[Equation 1]
FI(%)=[(Q0-Qt)/Q0]×100
(Where, FI is the membrane fouling index, Q0 is the production quantity for the first hour after starting filtration, and Qt is the production quantity for the current hour)
The method according to claim 1, wherein when the contamination index (FI) of the membrane is less than 5%, the air bubbles are injected intermittently, 1 minute injection and 9 minutes stop;
If the contamination index (FI) of the membrane is 5% or more and less than 10%, the air bubbles are intermittently injected, but the injection is performed for 1 minute and stops for 4 minutes;
If the contamination index (FI) of the membrane is 10% or more to less than 15%, the air bubbles are injected intermittently for 1 minute and stop for 1 minute,
When the contamination index (FI) of the membrane is 15% or more, the cleaning method of a membrane for a membrane evaporation method, characterized in that the air bubbles are continuously injected.
delete Raw water tank and raw water pipe supplying raw water;
membrane evaporation module for filtering raw water;
a bubble generator and a bubble injection pipe for supplying bubbles;
a cooling water tank and cooling water pipe for supplying cooling water; and
Comprising a control unit for calculating the membrane contamination index of the membrane, and determining the injection period of the bubbles according to the calculated membrane contamination index,
The control unit determines the membrane contamination index using Equation 1 below,
The bubble has a diameter of 0.2 to 0.4 mm, and is contained in air and is injected at a pressure of 1.5 to 2.5 bar.
[Equation 1]
FI(%)=[(Q0-Qt)/Q0]×100
(Where FI is the membrane fouling index, Q0 is the production quantity for the first hour after starting filtration, and Qt is the production quantity for the current hour).
The method according to claim 4, wherein the control unit intermittently injects air bubbles when the contamination index (FI) of the membrane is less than 5%, but injects for 1 minute and stops for 9 minutes;
If the contamination index (FI) of the membrane is 5% or more and less than 10%, the air bubbles are intermittently injected, but the injection is performed for 1 minute and stops for 4 minutes;
If the contamination index (FI) of the membrane is 10% or more to less than 15%, the air bubbles are injected intermittently for 1 minute and stop for 1 minute,
When the contamination index (FI) of the membrane is 15% or more, the membrane cleaning apparatus for a membrane evaporation method, characterized in that the air bubbles are continuously injected.
The method according to claim 4, The raw water TDS (Total Dissolved Solids) of 58,000 mg / L or more, characterized in that the membrane cleaning apparatus for the membrane evaporation method.
delete The method according to claim 4, wherein the control unit calculates the membrane contamination index using the flow rate, the calculation unit for determining the first membrane contamination step according to the calculated membrane contamination index;
a comparison determination unit that compares the first membrane fouling step with the membrane fouling step of the previous cycle to determine the second membrane fouling step; and
A membrane cleaning apparatus for membrane evaporation, characterized in that it comprises a processing unit for controlling the bubble generator according to the secondary membrane contamination step.
The method according to claim 8, wherein the calculation unit determines the membrane contamination step as the first step if the contamination index (FI) of the membrane is less than 5%,
If the contamination index (FI) of the membrane is 5% or more to less than 10%, it is determined that the membrane contamination step is 2 steps,
If the contamination index (FI) of the membrane is 10% or more to less than 15%, it is determined that the membrane contamination step is 3 steps,
If the contamination index (FI) of the membrane is 15% or more, the membrane contamination step is determined as 4 steps,
When the difference between the first membrane contamination step calculated by the calculation unit and the membrane contamination step of the previous cycle is less than three steps, the comparison determining unit determines the first membrane contamination step as the second membrane contamination step. A device for cleaning forensic membranes.

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