JPH0623240A - Operation method of hollow fiber membrane filter - Google Patents

Abstract

PURPOSE:To restrain rise of differential pressure across the membrane when a filter device by which water incorporating suspended matters is filtered by using a hollow fiber membrane, is used for a long time and also to reduce a load of the equipment necessary for the operation and to curtail the operation cost. CONSTITUTION:In the filter device in which liquid to be treated incorporating the suspended matters is passed in a cross flow into a tube of the hollow fiber membrane of an internal pressure type hollow fiber membrane filter using the hollow fiber membrane with 0.3-6mm inside diameter and >=50cm length, a flow rate of water not to be transmitted is set so as to be <=400, preferably <=250, in Reynolds number in the hollow fiber tube.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to water treatment for the semiconductor industry,
Regarding the operation method of the hollow fiber membrane filter to obtain clear water by filtering the liquid containing suspension such as power plant water treatment, tap water pretreatment, wastewater treatment, etc. Provide a method of operation that is effective in extending the filter medium life and reducing the required power when treating liquid (usually "water" is the target) is passed through a hollow fiber membrane filter in a cross-flow manner to obtain treated water. It is a thing.

[0002]

2. Description of the Related Art A turbidity eliminator for removing turbidity from a liquid containing a suspension to obtain a clear liquid is used in many industrial fields, and its constitution is extremely diverse.

For example, in the condensate treatment of a nuclear power plant, a pre-coat type filter, a hollow fiber membrane filter, etc. It is used. The hollow fiber membrane filter targeted in the present invention is also used as one of the turbidity removing devices, and generally, the water to be treated containing the suspension is circulated in the tube of the membrane filter, It is used as a turbidity treatment device in which only water permeates to the outside of the tube by pressure and the suspension is blocked by the membrane.

By the way, in this internal pressure type membrane filter, the suspended matter, which is blocked during the filtration, is deposited on the surface of the filter medium (inner side surface of the hollow fiber membrane), and if the amount of this deposit is increased, the deposited layer is formed. Since the resistance of water passing through increases and the filtration pressure difference increases,
When the filtration pressure difference rises to a certain level, it is usual to remove deposits by washing such as backwashing and recover the pressure difference. In addition, depending on the quality and quantity of the deposit, the deposit cannot be easily removed by ordinary backwashing or the like, so it is necessary to dissolve it with a chemical or replace the film.

However, industrially, it is desired to extend the service life of the filter medium and reduce the amount of backwash waste liquid, and therefore, an operation method devised for the purpose of preventing the accumulation of suspended matter on the surface of the filter medium as much as possible has been conventionally practiced. . Specifically, in the internal pressure type membrane filter, the whole amount of the water to be treated, which has flowed into the membrane tube, is not permeated to the outside of the membrane tube (this is generally referred to as a total volume filtration method), but is allowed to flow. A so-called cross-flow filtration method is used in which a part of the water to be treated is permeated to the outside of the pipe and the rest is taken out as non-permeated water without permeating the membrane, and the non-permeated water is circulated to the inlet side of the membrane. In addition, a method is adopted in which the flow rate of the circulating water is increased as much as possible to increase the flow velocity of the water in the pipe, thereby utilizing the scavenging force of the inner surface of the pipe to reduce the amount of accumulation.

FIG. 4 shows the results of a membrane draining process of an equipment drain waste liquid containing iron oxide as a suspension in a nuclear power plant while circulating non-permeate water with an internal pressure type ultrafilter. In the case of a tube type filtration membrane having an inner diameter of 10 to 25 mmφ, the circulating water amount is 1 to 5 m ³ / hr and the circulating water flow velocity is 2
When operated at ˜4 m / sec, as can be seen from the figure, the smaller the amount of circulating water, that is, the slower the flow velocity in the pipe, the greater the decrease in permeate flow rate per hour, and the effect of the operating method for increasing the flow velocity in the pipe described above. Is confirmed.

[0007]

However, according to the study of the present inventors, the method of increasing the flow velocity in the pipe of the internal pressure type membrane filter is not necessarily an effective operation method in all the membrane filters. For example, it was found that a hollow fiber membrane filter having a small inner diameter and a large flow resistance in a pipe had no effect.

The reason will be described below. A hollow fiber membrane filter with a large flow resistance in the pipe, for example, an inner diameter of 0.3 to 2 mmφ
When a hollow fiber membrane filter of a certain degree is operated by an internal pressure system, the flow resistance in the pipe per unit length becomes large because the inner diameter of the hollow fiber membrane is small in this filter. Therefore, for example, 10 mmφ
3m / se which is possible with the above membrane filter with large inner diameter
In a turbulent flow region of c or more, the hollow fiber membrane filter having a large flow resistance in the pipe cannot generally be operated, and the treated water is generally operated to flow at a flow rate of about 1 m / sec. However, when operating under such conditions, a phenomenon in which the amount of deposits locally increases at the inlet of the hollow fiber membrane appears, and as a result of this, the differential pressure rise over the entire membrane also becomes faster. I will end up.

FIG. 3 is a diagram for explaining such a phenomenon as a model, and 21 in the figure is an inner diameter of 0.3 to 2 mm.
If a hollow fiber membrane with a diameter of φ and a length of 50 cm or more is used, and the operation is performed by securing the in-pipe flow velocity of the water to be treated at about 1 m / sec with an internal pressure type cross flow flow, the in-pipe flow resistance is 0.5 kg / cm ² or more. Therefore, the pressure difference between the inlet and outlet of the hollow fiber membrane is 0.5 kg / cm ^2.
As described above, the permeation flow velocity of water permeating from the inner side to the outer side of the membrane is different accordingly. For example, the hollow fiber membrane 21 of FIG.
Assuming that the membrane has a double permeate flow rate with a pressure difference of 5 kg / cm ² , the membrane permeated water amount Qx is 2: 1 at the membrane inlet and the membrane outlet. As a result, the amount of deposits on the film surface at the inlet increases accordingly. In the membrane filtration, the relationship between the filtration flow rate and the increase in differential pressure is (increase in differential pressure) = (flow rate) ² ("precision filtration""Basic and new development of separation technology-mechanical separation technology-"; Chemical Engineering Association Kanto Branch (1988) )), The differential pressure at the inlet of the hollow fiber membrane rises quickly and the membrane surface is clogged with deposits. The increase in the differential pressure due to the blockage means that the permeated water flow rate at that part decreases. Since it will be compensated for, the permeated water flow rate of the other surface, that is, the flow velocity, is gradually increased in proportion to the whole.

Since the permeation pressure difference across the membrane is proportional to the flow velocity, an increase in the permeation flow velocity through the membrane results in an increase in the membrane pressure difference, resulting in a faster rise in the pressure difference in the hollow fiber membrane filter. .

The present inventors have conducted further research based on the above findings, and changed the operation method to increase the flow velocity in the tube, which was generally considered to be effective in the membrane filter used in the internal pressure system, to perform filtration. It is an object of the present invention to provide a novel operation method effective for extending the life of a vessel and reducing the frequency of cleaning such as backwashing.

Another object of the present invention is to enable miniaturization of various equipment such as valves, pipes, and pumps, thereby significantly reducing equipment cost and enabling the use of a pump having a small capacity. It is an object of the present invention to provide a method of operating a filter, which has low power costs and low processing costs.

Still another object of the present invention is to reduce the running cost because the amount of chemicals used is small due to the above-mentioned reduction of the cleaning frequency, and the burden of equipment for the waste liquid treatment of the wash water and the waste water treatment. It is an object of the present invention to provide a method of operating a filter that can reduce the amount.

[0014]

In order to achieve the above object, the present inventor has completed the invention of a method for operating a hollow fiber membrane filter described in each of the claims.

One of the features of the present invention is, for example, an inner diameter of 0.3.
~ 6 mm, especially 0.7-2.0 mm inner diameter, length 50
cm or more, generally 50 to 250 cm, the liquid to be treated containing the suspension is allowed to flow into the hollow fiber membrane tube of the filter constituted by the hollow fiber membrane, and a part of the liquid to be treated is hollow. An internal pressure type hollow fiber that is made to permeate to the outside of the tube of the fiber membrane to form a treatment liquid, and the rest of the liquid to be treated is taken out from the tube end of the hollow fiber membrane as a non-permeation liquid without permeating the hollow fiber membrane. In the membrane filter, the Reynolds number in the hollow fiber membrane tube is 400 or less, preferably 15 to 25
There is a method of operating a hollow fiber membrane filter characterized in that it is set to 0, and optimally 75 to 150.

Examples of the hollow fiber membrane used in the present invention include microfiltration membranes and ultrafiltration membranes. Generally, 100 liters of the membrane permeated water flow rate under a pressure of 1 kg / cm ^2. / Hr · m ² or more, especially 2
The features of the present invention are effectively exhibited when a highly water-permeable membrane of 50 liter / hr · m ² or more is used.

In the operating method of the present invention, the liquid to be treated containing the suspension is passed through the tube of the hollow fiber membrane filter in a cross-flow flow, and the treatment liquid is permeated to the outside of the hollow fiber membrane tube by the internal pressure. Permeate flow rate is 50 liters / hr · m
^It is preferable to operate so as to be ² or more, preferably 60 to 80 liter / hr · m ² .

The filter to which the method of the present invention can be applied may be any filter as long as it allows a liquid to be treated to flow through a hollow fiber membrane filter in a cross-flow flow. It is also possible to discharge the non-permeated liquid to the raw material liquid on the inlet side of the water hollow fiber membrane filter, but an operation method of circulating type is preferably adopted.

In the filter having the above structure, the flow resistance in the pipe can be effectively reduced by setting the non-permeate flow rate to be small under a certain set permeate flow rate. For example, circulating water (non-permeated water) flow velocity 1 m / se
The number of Reynolds of circulating water flowing in the pipe is 15 to 10
When the flow rate of the circulating water is set to 250, for example, the circulating water is maintained at about the same amount as the permeated water flow rate, and the circulating water is flowed to 0.3 to 2
mmφ, 50 cm hollow fiber membrane flow resistance in the tube is 0.2 k
It can be g / cm ² or less.

As a result, the difference in the permeation flow velocity between the inlet and the outlet of the hollow fiber membrane can be made small, and the hollow fiber membrane can be operated from the inlet to the outlet at a substantially constant filtration flow velocity and filtration differential pressure. Since it becomes possible, in the operating method of the present invention, it is not necessary to compensate for the accelerated decrease in flow rate due to the relationship of (increase in differential pressure) = (velocity) ^2. Therefore, increase in transmembrane pressure, and thus increase in differential pressure of the filter. Can be prevented.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be further described below based on the embodiments shown in the drawings. FIG. 1 is a system flow diagram showing an example of the schematic constitution of a filtration apparatus to which the method of the present invention is applied.
In the figure, reference numeral 1 is a raw water tank, which temporarily stores raw water containing suspended matter (industrial water of Tsukuba Industrial Park in the embodiment) via an inlet valve 2.

The raw water stored in the raw water tank 1 is passed through a pipe 3 through a water pump 4 and inlet valves 5 and 5,
In this example, two series of ultrafiltration membrane (UF) hollow fiber modules 6 and 6 are flowed in a cross-flow manner, and the permeated water of the membrane is discharged from the outlet valve 7.
It is designed to be sent to the treated water tank 8 via.
Note that FIG. 1 schematically shows the UF hollow fiber module.

Reference numerals 9 and 9 are outlet flow rate control valves for controlling the flow rate of non-permeated water of the UF hollow fiber modules 6 and 6.
The non-permeated water is returned to the raw water tank through the outlet flow rate control valves 9, 9 and the circulation pipe 10.

Reference numeral 11 is a circulation shutoff valve, and 12 is a blow valve, which is opened / closed together with the above-mentioned opening / closing switching operation of each valve, and when the UF hollow fiber module 6 is backwashed and washed,
It is provided so that the backwash water is discharged to the outside of the system via the blow valve 12.

In the present invention, in the filtration device having the above-mentioned structure, the Reynolds number of the non-permeated water flowing in the hollow fiber membrane tube is 400 or less, preferably the non-permeated water flow rate is adjusted by the outlet flow rate control valve 9. The characteristic is that it is set to 15 to 250.

Test Example 1 The following test was conducted to confirm the effect of the present invention.

In the filtration device having the above structure, an acrylonitrile (PAN) hollow fiber membrane having an inner diameter of 0.5 mmφ and a length of 1 m is used in the UF hollow fiber module 6 (fraction molecular weight 5000).
2050 of 0) were bundled and a hollow fiber membrane module housed in a 3 ^B PVC pipe was used, and non-permeated water was circulated in the raw water tank 1 under the following conditions to compare the transmembrane pressure rise.

Permeate flow rate of hollow fiber membrane: 530 liters / hr · m ² (pressure 1 kg / cm ² ) Raw water (water to be treated): Industrial water of Tsukuba Industrial Park Permeate flow rate: 0.4 m ³ / hr ( Constant) Reynolds number in circulating water pipe (based on module outlet): 86, 238,
389, 800 (circulation water flow rate: m ^{3 /} hr) (0.4) (1.1)
(1.8) (3.7) Water passage time: Backwashing once every 5 minutes and 1500 hours or more of the test results are shown in the chart of FIG.

As can be seen from these results, the larger the Reynolds number (the larger the amount of circulating water) is, the larger the increase in the transmembrane pressure is, which is higher than the conventional Reynolds number of 800 or more. 400 or less, preferably 25
It was confirmed that when the temperature was 0 or less, the increase in transmembrane pressure when operating for a long time could be reduced.

[0030]

As described above, according to the present invention, in the membrane filter used in the internal pressure system, the flow velocity in the pipe, which has been generally considered to be conventionally effective, is increased to make the circulating water amount about 10 times the permeated water amount and perform the circulation operation. The method of the present invention can provide a novel operation method in which the circulating water amount is maintained at about the same level as the permeated water flow rate, which is completely different from the method of performing the above. This has the effect of reducing the frequency.

Further, according to the present invention, since the circulating water amount is 1/5 to 1/10 of that of the conventional one, various equipments such as valves, pipes and pumps can be miniaturized, whereby the equipment cost can be reduced. There is also an effect that the power cost can be reduced because the pump having a small capacity can be used and the processing cost can be reduced.

Further, according to the present invention, since the number of times of cleaning can be reduced as compared with the conventional method, the amount of chemicals used can be reduced, and the burden on the treatment facility for cleaning wastewater and the amount of wastewater treatment can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a schematic configuration of a filtration device to which the present invention is applied as a system flow diagram,

FIG. 2 is a chart showing the relationship between the number of Reynolds in the pipe and the degree of increase in differential pressure per unit time when the water to be treated containing the suspension is cross-flowed through the internal pressure type hollow fiber membrane filter.

FIG. 3 is a model view showing a distribution state of permeated water flow rate when the water to be treated is flown by a conventional method of flowing the water to be treated through the hollow fiber membrane at a high flow rate;

FIG. 4 is a diagram showing the relationship between the magnitude of the circulation flow velocity and the increase in differential pressure when the water to be treated is passed through the tubular membrane filter.

[Explanation of symbols]

1 ... Raw water tank, 3 ... Water supply pipe, 4 ... Water pump, 5 ... Inlet valve, 6 ... UF hollow fiber module, 7 ... Outlet valve, 8 ... Treated water Tank, 9 ...
Circulation flow control valve.

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[Procedure amendment]

[Submission date] July 12, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 4

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

As the hollow fiber membrane used in [correction contents present invention, microfiltration membrane, there may be mentioned an ultrafiltration membrane or the like, typically membrane permeate flow rate under a pressure of 1 kg / cm ² 100 Membrane of liter / hr · m ² or more, especially 250 liter /
The features of the present invention are effectively exhibited when a highly liquid- permeable membrane having an hr · m ² or more is used.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Details of correction] The filter to which the method of the present invention can be applied may be any filter as long as it allows the liquid to be treated to flow through the hollow fiber membrane filter in a cross-flow flow. Although it can be discharged to the outside, an operation method in which a non-permeate is circulated to the stock solution on the inlet side of the hollow fiber membrane filter is usually used preferably.

Claims (4)

[Claims] 1. A liquid to be treated containing a suspension is flowed into a hollow fiber membrane tube having a filtration function, and a part of the liquid to be treated is permeated to the outside of the hollow fiber membrane tube to form a treatment liquid. Along with the internal pressure type hollow fiber membrane filter, the remaining portion of the liquid to be treated is taken out from the pipe end of the hollow fiber membrane as a non-permeable liquid without permeating the hollow fiber membrane, and the flow rate of the non-permeable liquid is A method for operating a hollow fiber membrane filter, wherein the Reynolds number in the hollow fiber membrane tube is set to 400 or less. 2. The hollow fiber membrane according to claim 1, wherein the hollow fiber membrane has a membrane permeate flow rate of 1 kg / cm ²
A method for operating a hollow fiber membrane filter, which is a membrane having a volume of at least 00 liter / hr · m ² . 3. The method for operating a hollow fiber membrane filter according to claim 1 or 2, which is operated so that the permeated liquid flow rate is 50 liters / hr · m ² or more. 4. The hollow fiber membrane filter according to claim 1, wherein the non-permeate of the hollow fiber membrane filter is circulated to the raw water on the inlet side of the hollow fiber membrane filter. how to drive.