JP2922059B2 - Operating method of hollow fiber membrane filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to water treatment for the semiconductor industry,
Regarding the operation method of the hollow fiber membrane filter for filtering the liquid containing suspended matter such as water treatment for power plants, pretreatment of clean water, wastewater treatment, and the like, to obtain clear water by turbidity. Provided is an effective operation method for extending the life of the filter medium and reducing the required power when obtaining the treated water by flowing the liquid to be treated (usually for "water") with a cross flow through the hollow fiber membrane filter. Things.

[0002]

2. Description of the Related Art A clarifier for removing a turbid substance from a liquid containing a suspension to obtain a clear liquid is used in many industrial fields, and the constitution thereof is extremely wide.

For example, in a condensate treatment at a nuclear power plant, a pre-coat type filter, a hollow fiber membrane filter and the like, and in a turbidity treatment of a pure water device such as a pretreatment of ultrapure water at a semiconductor factory, an agglomerated sedimentation filter and the like are used. Used. The hollow fiber membrane filter targeted in the present invention is also used as one of the clarifiers, and generally, the water to be treated containing the suspension is circulated in the tube of the membrane filter, and the It is used as a turbidity treatment device that allows only water to permeate the outside of the tube of the membrane by pressure and blocks suspended matter with the membrane.

[0004] In this internal pressure type membrane filter, the suspended matter that is blocked during filtration accumulates on the surface of the filter medium (the inner side surface of the hollow fiber membrane). As the resistance of passing water increases and the filtration differential pressure increases,
When the filtration pressure difference rises to a certain level, it is usual to remove deposits by washing such as back washing and recover the pressure difference. Further, depending on the quality and quantity of the deposit, the deposit is not easily removed by ordinary backwashing or the like, so that it is necessary to dissolve with a chemical or replace the film.

However, industrially, since it is desired to extend the life of the filter medium and to reduce the amount of backwash waste liquid, an operation method devised for the purpose of minimizing the accumulation of suspended matter on the surface of the filter medium has been conventionally performed. . Specifically, in the internal pressure type membrane filter, the entire amount of the water to be treated that has flowed into the membrane tube is allowed to flow in instead of permeating the outside of the membrane tube (this is generally referred to as a total filtration method). A part of the water to be treated is permeated to the outside of the tube, and the remainder is taken out as non-permeated water without permeating the membrane, using a so-called cross-flow filtration method, and circulating the non-permeated water to the inlet side of the membrane. In addition, a method is employed 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, so that the above-mentioned accumulation amount is reduced by using the scavenging force of the pipe inner surface.

FIG. 4 shows the results when the equipment drain waste liquid containing iron oxide as a suspension in a nuclear power plant is subjected to membrane filtration while circulating non-permeated 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 amount of circulating water is 1 to 5 m ³ / hr,
When operated at ４4 m / sec, as can be seen from the figure, as the amount of circulating water decreases, that is, as the flow velocity in the pipe decreases, the per-hour flow rate of the permeate decreases more. Is confirmed.

[0007]

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

The reason will be described below. Hollow fiber membrane filter with large flow resistance in the tube, for example, 0.3 to 2 mm in inner diameter
When a hollow fiber membrane filter is operated at an internal pressure type, the inside diameter of the hollow fiber membrane is small in this filter, so that the flow resistance in the pipe per unit length increases. For this reason, for example, 10 mmφ
3 m / sec possible with a membrane filter with a large inner diameter as described above
In a hollow fiber membrane filter that cannot be operated in a turbulent flow region of c or more and has a large flow resistance in a pipe, an operation is generally performed in which the water to be treated flows at a flow rate of about 1 m / sec. However, when the operation is performed under such conditions, a phenomenon that the amount of deposits at the inlet portion of the hollow fiber membrane becomes locally large appears, and as a result, the differential pressure rise of the entire membrane becomes faster. I will.

FIG. 3 is a diagram for explaining such a phenomenon in a model manner. In FIG. 3, reference numeral 21 denotes an inner diameter of 0.3 to 2 mm.
Assuming that a hollow fiber membrane having a diameter of 50 cm or more and being operated with an internal pressure cross-flow at a flow rate of about 1 m / sec in the pipe of the water to be treated, the flow resistance in the pipe is 0.5 kg / cm ² or more. For this reason, the pressure difference between the inlet end of the hollow fiber membrane and the outlet end is 0.5 kg / cm ^2.
As described above, the membrane permeation flow rate of water permeating from the inside of the membrane to the outside of the membrane differs accordingly. For example, the hollow fiber membrane 21 of FIG.
Assuming a membrane whose permeate flow rate is doubled with a pressure difference of 5 kg / cm ² , the membrane permeated water amount Qx is 2: 1 at the membrane inlet and membrane outlet. As a result, the amount of deposit on the film surface at the entrance increases. In membrane filtration, the relationship between filtration flow rate and differential pressure rise is (differential pressure rise) = (flow rate) ² ("Microfiltration""Basic and New Development of Separation Technology-Mechanical Separation Technology"; Japan Society of Chemical Engineering, Kanto Branch (1988 )), The pressure difference at the entrance of the hollow fiber membrane rises quickly, and the membrane surface is blocked by deposits. When the pressure difference rises due to the blockage, it means that the flow rate of the permeated water decreases in that part. Therefore, the flow rate of the permeated water, that is, the flow velocity of the other surface of the membrane surface is gradually increased as a whole.

Since the permeation pressure difference of the membrane is proportional to the flow rate, an increase in the permeation water flow rate of the membrane results in an increase in the membrane pressure difference, resulting in a faster increase in the pressure difference of the hollow fiber membrane filter. .

The present inventors have conducted further studies based on the above findings, and have changed the operation method for increasing the flow velocity in the pipe, which has been generally considered to be generally effective, in the membrane filter used in the internal pressure type. An object of the present invention is to provide a new 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 make it possible to reduce the size of various equipment such as valves, piping, pumps, etc., thereby realizing a great reduction in equipment costs and making it possible to use a pump having a small capacity. It is an object of the present invention to provide a method of operating a filter that can reduce power cost and processing cost.

Still another object of the present invention is to reduce the cleaning frequency and the like, so that the amount of chemicals used is small and the running cost is low. It is an object of the present invention to provide a method of operating a filter capable of reducing 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 as described in each of the claims.

One of the features of the present invention is that the inner diameter is, for example, 0.3.
~ 6mm, especially 0.7 ~ 2.0mm inner diameter, length 50
cm or more, generally a liquid to be treated containing a suspended substance is introduced into a tube of a hollow fiber membrane of a filter constructed using a hollow fiber membrane of 50 to 250 cm, and a part of the liquid to be treated is hollowed. An internal pressure type hollow fiber in which the treatment liquid is permeated to the outside of the fiber membrane to form a treatment liquid, and the remaining liquid to be treated is taken out of the end of the hollow fiber membrane as a non-permeate liquid without passing through the hollow fiber membrane. In the membrane filter, the flow rate of the non-permeate is adjusted so that the Reynolds number in the hollow fiber membrane tube is 400 or less, preferably 15 to 25.
0, and optimally set to 75 to 150, in the method of operating a hollow fiber membrane filter.

[0016] The hollow fiber membrane used in the present invention, microfiltration membrane, there may be mentioned an ultrafiltration membrane or the like 100 liters generally membrane permeate flow rate under a pressure of 1 kg / cm ² / Hr · m ² or more, especially 2
Feature of the present invention is effectively achieved when using a 50 l / hr · m ² or more of the high liquid film.

In the operating method of the present invention, the liquid to be treated containing the suspension is flowed in a cross-flow flow into the tube of the above-mentioned hollow fiber membrane filter, and the treatment liquid permeates outside the tube of the hollow fiber membrane by internal pressure. At the time of permeation, the permeate flow rate is 50 l / hr · m
^The operation may be performed at ² or more, preferably 60 to 80 l / hr · m ² .

The filter to which the method of the present invention can be applied may be any as long as it allows the liquid to be treated to flow through the hollow fiber membrane filter in a cross-flow manner. In general, a circulation type operation method in which the non-permeated liquid is circulated to the stock solution on the inlet side of the hollow fiber membrane filter is preferably employed.

In the filter constructed as described above, the flow resistance in the pipe can be effectively reduced by setting the non-permeate flow rate small under a certain set permeate flow rate. For example, circulating water (non-permeated water) flow rate 1 m / sec
c or less, the number of Reynolds nozzles of circulating water flowing in the pipe is 15 to
250, for example, by flowing the circulating water while maintaining the amount of the circulating water at substantially the same level as the flow rate of the permeated water, 0.3 to 2
The flow resistance in a 50 mm hollow fiber membrane is 0.2k.
g / cm ² or less.

Thus, the difference in the permeation flow rate between the inlet and the outlet of the hollow fiber membrane can be reduced, and the hollow fiber membrane can be operated from the inlet to the outlet at a substantially constant filtration flow rate 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 the flow rate due to the relation of (increase in differential pressure) = (flow velocity) ² , and therefore, the increase in the membrane differential pressure and the increase in the filter differential pressure Can be prevented.

[0021]

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

The raw water stored in the raw water tank 1 is passed through a pipe 3 through a water supply pump 4 and inlet valves 5, 5.
In this example, two series of ultrafiltration membrane (UF) hollow fiber modules 6 and 6 are passed in a cross-flow manner, and the permeated water is passed through an outlet valve 7.
Through the processing water tank 8.
FIG. 1 schematically shows a UF hollow fiber module.

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

Reference numeral 11 denotes a circulation shut-off valve, and reference numeral 12 denotes a blow valve. The opening and closing of the UF hollow fiber module 6 are switched when the above-mentioned valves are opened and closed.
The backwash water is provided to drain out of the system via the blow valve 12.

In the present invention, in the filtering apparatus having the above-mentioned structure, the Reynolds number of the non-permeated water flowing through the hollow fiber membrane tube is adjusted to 400 or less, preferably by adjusting the non-permeated water flow rate by the outlet flow control valve 9. The feature is that the setting is made to be 15 to 250.

Test Example 1 The following tests were performed to confirm the effects of the present invention.

In the filtration device having the above structure, the UF hollow fiber module 6 is provided with a hollow fiber membrane made of acrylonitrile (PAN) having an inner diameter of 0.5 mmφ and a length of 1 m (fraction molecular weight 5000).
0) 2050 present by bundling, 3 ^B using a hollow fiber membrane module housed in PVC pipe, by circulating non permeate into the raw water tank 1 under the following conditions, a comparison was made transmembrane pressure difference rises.

Flow rate of the permeated liquid of the hollow fiber membrane: 530 liter / hr · m ² (pressure 1 kg / cm ² ) Raw water (water to be treated): Industrial water of Tsukuba Industrial Park Permeated water flow rate: 0.4 m ³ / hr ( Constant) Reynolds number of circulating water in pipe (based on module outlet): 86, 238,
389, 800 (flow rate of circulating water: m ^{3 /} hr) (0.4) (1.1)
(1.8) (3.7) Water flow time: The results of conducting a test for more than 1500 hours after backwashing once every 5 minutes 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), the greater the increase in the transmembrane pressure, which is greater than the conventionally considered operation at a Reynolds number of 800 or more. 400 or less, preferably 25
It was confirmed that when the value was 0 or less, the rise in the transmembrane pressure during long-time operation could be reduced.

[0030]

As described above, according to the present invention, in the membrane filter used in the internal pressure type, the circulation flow rate is increased by increasing the flow rate in the pipe, which is generally considered to be generally effective, to about 10 times the flow rate of the permeated water. The present invention can provide a novel operation method in which the amount of circulating water is maintained at substantially the same level as the flow rate of permeated water, thereby extending the life of the hollow fiber membrane filter and cleaning such as back washing. There is an effect that the frequency can be reduced.

Further, according to the present invention, since the amount of circulating water is 1/5 to 1/10 of that of the prior art, it is possible to reduce the size of various equipment such as valves, pipes, pumps and the like. And the use of a small-capacity pump enables low power costs and low processing costs.

Further, according to the present invention, the number of times of washing can be reduced as compared with the prior art, so that the amount of chemicals used is reduced, and the burden on the treatment equipment for washing wastewater and the amount of wastewater treatment can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a table showing the relationship between the number of Ray nozzles in a pipe and the degree of differential pressure rise per unit time when water to be treated containing suspended matter is caused to flow in a cross flow through an internal pressure type hollow fiber membrane filter;

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

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

[Explanation of symbols]

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

Claims (4)

(57) [Claims] 1. A liquid to be treated containing a suspension is introduced into a tube of a hollow fiber membrane having a filtration function, and a part of the liquid to be treated is permeated outside the tube of the hollow fiber membrane to form a treatment liquid. Along with the internal pressure type hollow fiber membrane filter configured to take out the remainder of the liquid to be treated from the tube end of the hollow fiber membrane as a non-permeate liquid without passing through the hollow fiber membrane, the flow rate of the non-permeate liquid is as follows: A method for operating a hollow fiber membrane filter, wherein the Reynolds number in a hollow fiber membrane tube is set to be 400 or less. 2. The method according to claim 1, wherein the hollow fiber membrane of the filter has a membrane permeate flow rate of 1 kg / cm ^{2 and} a pressure of 1 kg / cm ^2.
A method for operating a hollow fiber membrane filter, wherein the membrane has a membrane of 00 liter / hr · m ² or more. 3. The method for operating a hollow fiber membrane filter according to claim 1, wherein the operation is performed such that the flow rate of the permeated liquid is 50 liter / hr · m ² or more. 4. In any of claims 1 to 3, hollow, characterized in that the non-permeate of the hollow fiber membrane filter, is recycled to the inlet side <br/> original liquid of the hollow fiber membrane filter Operation method of the thread membrane filter.