JP2011031245A - Membrane filtration system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow a membrane differential pressure to be more effectively reduced by carrying out a plurality times of short time washing. <P>SOLUTION: A membrane filtration system includes: a raw water tank 1 for temporarily storing raw water; a membrane module 2 for filtering the raw water; a raw water pump 3 for supplying the raw water in the raw water tank to the membrane module; a treatment water tank 4 for storing treatment water filtered by the membrane module; a compressor 5 for supplying pressurized air into the membrane module; a back washing water pump 6 for supplying the treated water to the membrane module as washing water; and a washing water tank 9 for introducing to store a part of the treated water stored in the treated water tank as washing water. In the membrane filtration system, a membrane module washing process combines ordinary physical washing with hot water washing a where water having temperature higher than that of ordinary washing water is reversely passed through at a periodic frequency and raw water rinsing where the raw water is supplied to the membrane module after the hot water washing. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a membrane filtration system suitable for water treatment of seawater such as fresh water such as surface water, groundwater, rainwater storage, industrial wastewater, sewage, and ballast water.

  Conventionally, in the field of water treatment, raw water (for example, fresh water such as surface water, groundwater, rainwater storage water, industrial wastewater, sewage such as sewage, seawater such as ballast water) is filtered and used for domestic water, industrial water, and agricultural water. As a method of obtaining, for example, a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane, or a reverse osmosis membrane is used.

  The membrane has a high separation performance with respect to solids such as microorganisms, algae, and clay in the raw water, and its application in the water treatment field is expanding. In recent years, it is common to use a hydrophilic material as the material of the membrane. Even when a hydrophobic material is used, it has been studied to improve the filtration performance by hydrophilizing the membrane surface with a sulfuric acid solution of potassium dichromate or the like (see, for example, Patent Document 1).

  However, when the raw water is continuously passed through the membrane, the solute in the raw water accumulates on the outer surface of the membrane or in the pores of the membrane, and the filtration resistance may increase and the filtration performance may deteriorate.

  Therefore, in such a membrane filtration system, physical cleaning with filtered treated water or compressed air is performed at a preset cycle or when the membrane shows a predetermined differential pressure increase, and the membrane outer surface or membrane pores Of the deposits inside, reversible ones are removed.

  On the other hand, deposits that are difficult to remove by such physical cleaning gradually accumulate on the outer surface of the membrane and in the membrane pores, so when the membrane differential pressure exceeds the preset upper limit value, membrane filtration treatment Is stopped and chemical cleaning is performed to remove deposits that could not be removed by physical cleaning.

  And even if chemical cleaning is performed, it is impossible to remove deposits such as the membrane surface and inside, and recovery of the membrane differential pressure is not recognized, or when the usage period of the membrane exceeds a certain period, The membrane is replaced when it is judged that it has reached the end of its life.

JP-A-5-23553

  In such a membrane filtration system, the membrane filtration process must be stopped each time chemical cleaning, filtration membrane replacement, or the like is performed. For this reason, it is necessary to reduce the frequency of chemical cleaning and filtration membrane replacement as much as possible, increase the operating rate of the membrane filtration system, and reduce the cost required for chemical cleaning and membrane replacement.

  The present invention has been made in consideration of such circumstances, and can increase the amount of treated water to increase the system operating rate, reduce the cost required for chemical cleaning and membrane replacement, and reduce the total running cost. The object is to provide a membrane filtration system.

  (1) A membrane filtration system according to the present invention is filtered by a raw water tank that temporarily stores raw water, a membrane module that filters raw water, a raw water pump that supplies raw water from the raw water tank to the membrane module, and a membrane module. Treated water tank for storing treated water, a compressor for supplying pressurized air into the membrane module, a backwash water pump for supplying treated water to the membrane module as washing water, and treated water stored in the treated water tank This is a membrane filtration system equipped with a washing water tank that introduces and stores a part of it as washing water. It is characterized by combining warm water cleaning for reverse water flow and raw water rinsing for supplying raw water to the membrane module after the hot water cleaning.

(2) The membrane filtration system according to the present embodiment is characterized in that in (1) above, the hot water cleaning is performed at the following times (2-1) to (2-5).
(2-1) When the recovery value of the membrane differential pressure by one physical cleaning becomes a constant value.
(2-2) When the recovery value of the membrane differential pressure after multiple physical cleanings reaches a certain value.
(2-3) When the increase in the membrane differential pressure has reached a certain value since the end of the previous physical cleaning.
(2-4) When the increase in membrane differential pressure has reached a certain value since the end of the previous hot water cleaning.
(2-5) When the preset pressure differential is reached.

(3) The membrane filtration system according to the present embodiment is characterized in that in (1) and (2) above, the reverse water flow is repeated a plurality of times.
(4) In the membrane filtration system according to the present embodiment, in the above (1) to (3), the time during which reverse water flow is measured by measuring the membrane differential pressure or flow rate during reverse water flow, and the slope of either value It is determined by the time when becomes constant.

  According to the present invention, a membrane can be obtained by combining normal physical cleaning (back pressure water method, reverse pressure air method, etc.) with warm water cleaning that reversely passes water at a higher temperature than normal cleaning water at a predetermined frequency. The differential pressure can be greatly reduced.

Hereinafter, an embodiment of a membrane filtration system of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram showing an embodiment of a membrane filtration system according to the present invention.
The membrane filtration system is a raw water tank 1 that temporarily stores raw water guided by a water pump (not shown), a raw water tank that filters raw water, for example, a hollow fiber membrane module 2, and the raw water from the raw water tank 1 is supplied to the membrane module. Raw water pump 3, treated water tank 4 for storing treated water filtered by the membrane module 2, a compressor 5 for supplying pressurized air into the membrane module 2, and treated water as washing water to the membrane module 2 A backwash water pump 6 and a wash water tank 9 for introducing and storing a part of the treated water stored in the treated water tank 4 as wash water are provided. Here, the washing water tank 9 includes a heater 10.

In FIG. 1, 7 _{1 to} 7 ₁₀ indicate pipes, and 8a to 8k, 8m, and 8n respectively indicate valves. Pipe 7 ₁ a pipe connecting the bottom portion of the lower side and the membrane module 2 in the raw water tank 1, the valve 8a, 8b is interposed. Pipe 7 ₂ in pipe connecting the upper part of the treatment water tank 4 and the top of the membrane module 2, the valve 8c, 8d is interposed. Pipe 7 ₃ by a pipe connected to the bottom of the membrane module 2, the valve 8e is interposed. Pipe 7 ₄ in pipe connected to the upper side of the membrane module 2, the valve 8f is interposed. Pipe 7 ₅ a pipe connected to the pipe 7 _4, the valve 8 is interposed. Pipe 7 ₆ in pipe connecting the bottom side of the compressor 5 and the membrane module 2, the valve 8h is interposed. Pipe 7 ₇ a pipe to be connected to the _second pipe 7 is branched from the pipe 7 ₆ connected to the compressor 5, the valve 8i is interposed. Pipe 7 ₈ a pipe connecting the bottom of the treating tank 4 and a pipe 7 _2, valve 8k is interposed. Pipe _7-9 in pipe connecting the lower portion of the lower side and the cleaning water tank 9 of the treating tank 4, valve 8m is interposed. Pipe 7 ₁₀ a pipe connecting the bottom of the treating tank 9 and the pipes 7 _8, valve 8n is interposed.

The operation of the membrane filtration system of FIG. 1 is as follows.
In the membrane filtration system, raw water is guided to the raw water tank 1 by a water pump (not shown). Then, raw water is introduced into the membrane module 2 by pressurization of the raw water pump 3, and the treated water that has permeated the membrane module 2 is stored in the treated water tank 4. Normal washing is carried out by the reverse pressure water step (1) and the raw water rinsing step (2) in the following procedure, which will be described using the normal filtration system of FIG. 2 is different from FIG. 1 in the area surrounded by the dotted line in FIG.

(1) Reverse pressure water process
The valves 8b, 8d, 8g, 8i, and 8n are closed, and the treated water in the treated water tank 4 is caused to flow back from the treated water side of the membrane module 2 by the backwash water pump 6 with the valves 8c, 8j, and 8k opened. raw water side of the pipe 7 ₃ of the lower part of the module 2, or discharged from the membrane module 2 the upper part of the raw water side of the pipe 7 _4. At this time, swinging the membrane module 2 from the raw water side of the pipe 7 ₆ of the membrane module 2 by flowing a pressurized air by a compressor 5.

(2) Raw water rinsing process
The valves 8a and 8b and the valve 8f above the membrane module 2 are opened, the raw water pump 3 is started, and the membrane module 2 is rinsed. At this time, the rinsing water may be circulated to the raw water tank 1. At this time, rinsing can be performed more effectively if the compressed air is allowed to flow from the compressor 5, but the compressed air may be stopped to reduce the power cost.

  In the filtration process in the membrane filtration system shown in FIG. 1, raw water is guided to the raw water tank 1 by a water pump not shown. Normal cleaning is performed in the same procedure as in FIG. And it wash | cleans with the warm water which adjusted the temperature of the washing water by the procedure of the following (3) and (4) with a certain frequency.

(3) Reverse pressure water process
The treated water in the washing water tank 9 whose temperature was adjusted by the heater 10 with the valves 8b, 8d, 8g, 8i, 8j closed and the valves 8c, 8k, 8n opened, was treated with the reverse water washing pump 6 in the treated water of the membrane module 2. Supply from the side. The back flow, time, frequency, temperature, corrected pre-wash differential pressure converted to 25 ° C., post-wash differential pressure and recovery differential pressure converted to 25 ° C. are as shown in Table 1 below. It is. However, Table 1 also shows the conditions in the case of reverse pressure water when hot water is not used.

  According to Table 1, the recovery differential pressure is 8 kPa and 11 kPa in the case of the cleaning method using the reverse pressure water, but the recovery differential pressure is 25 kPa and the membrane differential pressure is greatly reduced in the case of the cleaning method using the reverse warm water of the present invention. It turns out that you can.

(4) Raw water rinsing process
The valves 8a and 8b and the valve 8f above the membrane module 2 are opened, the raw water pump 3 is started, and the membrane module 2 is rinsed. At this time, the rinsing water may be circulated to the raw water tank 1. At this time, rinsing can be performed more effectively if the compressed air is allowed to flow from the compressor 5, but the compressed air may be stopped to reduce the power cost.

  According to the embodiment, in the membrane filtration system including the raw water tank 1, the membrane module 2, the raw water pump 3, the treated water tank 4, the compressor 5, the backwash water pump 6, and the wash water tank 9, Membrane differential pressure is greatly reduced by combining normal physical cleaning (back pressure water method) with warm water cleaning that reversely passes water at a higher temperature (40 ° C) than normal cleaning water at regular intervals. Can do.

In addition, although the said embodiment described the case of 1 time of warm water washing | cleaning, you may perform not only this but warm water washing | cleaning in multiple times. Table 2 below compares the case where the number of times of warm water cleaning is 2 (Example 1) and 6 times (Example 2) with the case where the number of times of warm water cleaning is 1 time. In the case of Example 1, the recovery differential pressure in the case of one hot water cleaning was 4 kPa, whereas in the second hot water cleaning, the recovery differential pressure was 7 kPa. In the case of Example 2, the recovery differential pressure in the case of one hot water cleaning was 3 kPa, whereas in the six hot water cleanings, the recovery differential pressure was 15 kPa. As shown in Table 2 below, it has been clarified that the recovery differential pressure can be increased by performing the hot water cleaning a plurality of times as compared with the case of performing the hot water cleaning once.

  Moreover, although the case where the warm water washing | cleaning which reversely passes water was combined with normal physical washing | cleaning was described in the said embodiment, it does not restrict to this. The time for reverse water flow may be determined by measuring the membrane differential pressure or flow rate during reverse water flow, and the time during which the slope of either value becomes constant. 3 and 4 are characteristic diagrams showing the relationship between the hot water washing time and the membrane differential pressure during reverse water flow, respectively, and the materials of the hollow fibers used in the membrane module are different. In FIG. 3, it is clear that the membrane differential pressure becomes substantially constant from the line (a) when the hot water cleaning time is about 3 minutes and from the line (b) from about 4 minutes. Further, in FIG. 4, it is clear that the membrane differential pressure becomes substantially constant from the line (a) when the hot water washing time is about 2 minutes and from the line (b) from about 1 minute.

  5 and 6 are characteristic diagrams showing the relationship between the hot water cleaning time and the cleaning flow rate during reverse water flow, respectively, and the materials of the hollow fibers used in the membrane module are different. FIG. 5 shows the data of the membrane module similar to FIG. 3, and FIG. 6 shows the data of the membrane module similar to FIG. In FIG. 5, it is clear that the cleaning flow rate is substantially constant from the line (a) when the hot water cleaning time is about 3 minutes and from the line (b) from about 4 minutes. Further, in FIG. 6, it is clear that the cleaning flow rate is substantially constant from the line (a) from about 2 minutes of hot water cleaning time and from the line (b) from about 1 minute of hot water cleaning time.

Furthermore, in the above embodiment, warm water cleaning may be performed in the following cases.
(1) As shown in FIG. 7, when the recovery value (ΔP) of the film differential pressure by one physical cleaning becomes a constant value.
(2) As shown in FIG. 8, when the sum of the recovery values (ΔP) of the film differential pressure by a plurality of physical cleanings, that is, (ΔP1 + ΔP2 +... + ΔPn) becomes a constant value.
(3) As shown in FIG. 9, when the increase value (ΔP) of the membrane differential pressure becomes a constant value after the end of the previous physical cleaning.
(4) As shown in FIG. 10, when the increase value (ΔP) of the membrane differential pressure becomes a constant value after the end of the previous warm water cleaning.
(5) As shown in FIG. 11, the time when the preset film differential pressure is reached.

Furthermore, in the above-described embodiment, as shown in FIG. 12, physical cleaning is performed a plurality of times to reduce the membrane differential pressure to ΔP1, ΔP2, ΔP3, and ΔPk, and the final membrane differential pressure is a constant membrane differential pressure ( P ₁ ). In addition, as shown in FIG. 13, physical cleaning is performed a plurality of times to reduce the membrane differential pressure to ΔP1, ΔP2, ΔP3, and ΔPk, and the final membrane differential pressure becomes a constant membrane differential pressure (P ₁ ). However, it may be adjusted to be slightly inclined.

  In addition to the above, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine the component covering different embodiment suitably.

An explanatory view of a membrane filtration system concerning one embodiment of the present invention is shown. It is a figure for demonstrating an example of the physical washing | cleaning in the membrane filtration system which concerns on this invention. It is a characteristic view which shows the relationship between the warm water washing | cleaning time by this invention, and the film | membrane differential pressure at the time of reverse water flow. It is a characteristic view which shows the relationship between the warm water washing | cleaning time by this invention, and the film | membrane differential pressure at the time of reverse water flow. It is a characteristic view which shows the relationship between the hot water washing | cleaning time by this invention, and the washing | cleaning flow volume at the time of reverse water flow. It is a characteristic view which shows the relationship between the hot water washing | cleaning time by this invention, and the washing | cleaning flow volume at the time of reverse water flow. In the membrane filtration system of this invention, it is a characteristic view which shows the relationship between the elapsed time at the time of performing one physical cleaning, and a membrane differential pressure | voltage. In the membrane filtration system of this invention, it is a characteristic view which shows the relationship between the elapsed time at the time of performing physical cleaning of multiple times, and a membrane differential pressure | voltage. In the membrane filtration system of this invention, it is a characteristic view which shows the relationship between the elapsed time and membrane differential pressure in case the raise value of membrane differential pressure becomes a constant value after completion | finish of the last physical washing | cleaning. In the membrane filtration system of this invention, it is a characteristic view which shows the relationship between the elapsed time and membrane differential pressure in case the raise value of membrane differential pressure becomes a constant value after completion | finish of the last warm water washing | cleaning. In the membrane filtration system of this invention, it is a characteristic view which shows the relationship between the elapsed time and membrane differential pressure when it becomes a preset membrane differential pressure. In the membrane filtration system of this invention, it is a characteristic view which shows the relationship between the elapsed time at the time of performing physical cleaning of multiple times, and a membrane differential pressure | voltage. In the membrane filtration system of this invention, it is a characteristic view which shows the relationship between the elapsed time at the time of performing physical cleaning of multiple times, and a membrane differential pressure | voltage.

1 ... raw water tank, 2 ... raw water pump, 3 ... membrane module, 4 ... treatment water tank, 5 ... compressor, 6 ... backwash water _pump, 7 1-7 _{10 ...} pipe, 8a~8k, 8m, 8n ... valve, 9 ... washing water tank, 10 ... heater.

Claims (8)

A raw water tank for temporarily storing raw water, a membrane module for filtering raw water, a raw water pump for supplying raw water from the raw water tank to the membrane module, a treated water tank for storing treated water filtered by the membrane module, and a membrane module Compressor that supplies pressurized air inside, backwash water pump that supplies treated water to the membrane module as washing water, and washing that introduces and stores a part of the treated water stored in the treatment water tank as washing water A membrane filtration system with a water tank,
In the washing process of the membrane module, warm water washing in which water having a temperature higher than that of ordinary washing water is reversely passed to normal physical washing at a predetermined frequency, and raw water rinsing for supplying raw water to the membrane module after the washing with warm water. A membrane filtration system characterized by combining with   The membrane filtration system according to claim 1, wherein the warm water cleaning is performed when a recovery value of the membrane differential pressure by a single physical cleaning becomes a constant value.   The membrane filtration system according to claim 1, wherein the warm water cleaning is performed when a recovery value of the membrane differential pressure by a plurality of physical cleanings reaches a constant value.   2. The membrane filtration system according to claim 1, wherein the warm water cleaning is performed when an increase value of the membrane differential pressure becomes a constant value after the end of the previous physical cleaning.   2. The membrane filtration system according to claim 1, wherein the warm water cleaning is performed when an increase value of the membrane differential pressure becomes a constant value after the end of the previous warm water cleaning.   2. The membrane filtration system according to claim 1, wherein the hot water cleaning is performed when a preset membrane differential pressure is reached.   The membrane filtration system according to any one of claims 1 to 6, wherein reverse water flow is repeated a plurality of times.   The membrane according to any one of claims 1 to 7, wherein the reverse water flow time is determined by a time during which a slope of any value becomes constant by measuring a differential pressure or a flow rate during reverse water flow. Filtration system.

Images