JP2511038B2 - How to operate a hollow fiber membrane filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a method for operating a hollow fiber membrane filter used for microfiltration, ultrafiltration or reverse osmosis.

(Prior Art) Hollow fiber membranes have a minute ring-shaped cross-section, can take a large membrane area in a unit volume, and are excellent in pressure resistance, so they are widely used in various membrane separation devices. It is used.

By the way, in such a hollow fiber membrane, as the filtration time elapses, the fine particles to be treated are adhered and concentrated on the membrane surface to gradually reduce the filtration performance, or the fine particles captured and concentrated on the membrane surface are collected (from the treatment device). Will not be fully discharged. Therefore, in such a state, gas or liquid is permeated from the inside of the hollow fiber membrane to the outside, and a large number of bubbles are ejected from the outside of the hollow fiber membrane toward the hollow fiber membrane to blow the hollow fiber. BACKGROUND ART A so-called backwashing process is performed in which a liquid in a container accommodating a film is stirred and vibrated to remove fine particles adhering to the film surface.

FIG. 4 shows an example of a conventional experimental apparatus for performing filtration using a hollow fiber membrane filter while regenerating the membrane surface by such backwashing treatment.

In the figure, 1 indicates a hollow fiber membrane filter composed of a plurality of hollow fiber membranes. This hollow fiber membrane filter 1 is
It is fixed inside the hollow fiber membrane filter container 2.
A hollow plate 3 divides the inside of the hollow fiber membrane filter container 2 into two chambers, a stock solution chamber 4 and a filtrate chamber 5.

At the bottom of the stock solution chamber 4, a stock solution supply pipe 6 and a backwash treated water discharge pipe 7 are joined together near the connection part and connected. Hollow fiber membrane filter storage container 2 of undiluted solution supply pipe 6
The other end, which is not connected to, is branched and connected to the slurry supply pipe 8 and the clean water supply pipe 9. further,
The other end of the slurry supply pipe 8 is connected to the slurry tank 10, and the other end of the clean water supply pipe 9 is connected to the clean water tank 11.

An overflow pipe 12 is connected to the upper side surface of the stock solution chamber 4. This overflow pipe 12
The other end of the backwashing water discharge pipe 7 is open above the slurry tank 10.

In this experimental apparatus, the slurry tank 10 also serves as a container for preparing an experimental stock solution that is a suspension of fine particles having a predetermined concentration and a container for storing backwashing water discharged after the backwashing treatment, A stirrer 13 for stirring the suspension is provided.

The stock solution supply pipe 6 has a valve 14 and a pressure adjusting valve 15,
A valve 16 is provided in the backwash treated water discharge pipe 7, valves 17 and 18 and a slurry supply pump 19 are provided in the slurry supply pipe 8, and a valve 20 and a clean water supply pump 21 are provided in the clean water supply pipe 9. Each is provided. Further, the bypass pipe 22 and the valve 23 for adjusting the supply pressure are the clean water supply pipe 9
It is provided by branching from.

At the top of the filtrate chamber 5 of the hollow fiber membrane filter container 2,
One end of the filtrate discharge pipe 24 is connected, and the other end is opened above the clean water tank 11. The clean water tank 11 in this experimental device serves both as a container for storing the filtrate discharged during the filtration process and a storage container for the concentration adjusting water during the preparation of the experimental stock solution. In addition, a valve is installed on the filtrate discharge pipe 24.
25, a flow meter 26 and a thermometer 27 are provided.

In order to measure the filtration differential pressure (pressure loss) of the hollow fiber membrane filter, pressure gauges 28 and 29 and a differential pressure gauge 30 are installed in the stock solution supply pipe 6 and the filtrate discharge pipe 24, respectively. There is.

Further, in this experimental apparatus, in addition to the supply / drainage piping system (6, 7, 8, 9, 12, 22, 24) described above, an air supply piping system is provided. That is,
The air supply pipe 31 is connected from an air compressor 32 that supplies pressurized air, through a pressure adjusting valve 33 and an air filter 34, to a backwashing pressurized air supply pipe 35 and a backwashing air bubble jetting pipe 36. ing. A valve 37 and a flow meter 38 are provided in the pressurized air supply pipe 35 for the backwashing process, and the other end is connected to the top of the filtrate chamber 5 of the hollow fiber membrane filter storage container 2. This connection portion shares the opening with the filtrate discharge pipe 24. Similarly, a valve 39 and a flowmeter 40 are provided in the bubble jet pipe 36 for backwashing treatment, and the valve 39 and the flowmeter 40 are connected to the bottom of the stock solution chamber 4 of the hollow fiber membrane filter storage container 2, and this connection part is the stock solution. The opening is shared with the supply pipe 6 and the backwash treated water discharge pipe 7.

In the filtration experimental device using the hollow fiber membrane filter configured in this way, the experimental stock solution to be filtered is prepared in the slurry tank 10, and this is mixed with the clean water filled in the clean water tank 11 in advance. To reach the desired concentration,
While controlling the valves 17, 18, 20, 15, 14 and the flow meter 26 and the pumps 19, 21, the solution is supplied to the stock solution chamber 4 of the hollow fiber membrane container 2 through the stock solution supply pipe 6. At this time, the valve 16 of the backwash treated water discharge pipe 7 is closed. When the undiluted solution permeates the hollow fiber membrane, the fine particles in the undiluted solution are captured on the membrane surface, and the filtrate from which the particles have been removed flows into the filtrate chamber 5, and the valve 25 is in the open state. Emitted from 24.

With the progress of the filtration process, the backwashing process performed when the filtration differential pressure increases due to the adhesion of fine particles to the membrane surface of the hollow fiber membrane,
The valve 25 is closed, pressurized air is supplied to the filtrate chamber 5 through the opening of the filtrate discharge pipe 24, and the filtrate is caused to flow backward, whereby the fine particles adhering to the outside of the hollow fiber membrane are peeled off. Further, pressurized air is supplied to the stock solution chamber 4 through the bubble jetting pipe 36 and jetted as bubbles to pulsate the hollow fiber membrane to wash out fine particles. The filtrate that has flowed back at this time is discharged to the outside of the hollow fiber membrane container through the overflow pipe 12 together with the stock solution.

After this, the valve 16 of the backwash treated water discharge pipe 7 provided at the bottom of the stock solution chamber 4 is opened to discharge the backwash treated water containing fine particles.

In the backwashing treatment of such a hollow fiber membrane filter,
When the gas or liquid introduced inside the hollow fiber membrane is permeated from the inside to the outside of the hollow fiber membrane, a certain pressure is applied inside the hollow fiber membrane, and the gas or liquid permeates due to the pressure difference between the inside and outside of the hollow fiber membrane. I am letting you. Then, by changing the pressure applied to the hollow fiber membrane, it is possible to adjust the permeation flow rate when the gas or liquid permeates the membrane. Further, it is known that such a permeation flow velocity has a great influence on the backwash effect, but so far, its influence has not been quantitatively grasped.

(Problems to be Solved by the Invention) By the way, it is difficult to remove all fine particles even if the backwashing treatment as described above is performed, and some fine particles are not removed, and the film surface is not removed. And remains in the pores of the membrane wall. The residual amount and location of the fine particles depend on the type of fine particles and the operating conditions of the hollow fiber membrane filter, but in any case, while the cycle of the filtration process and the backwash process is repeated, the residual fine particles are Is accumulating. Therefore,
The resistance of gas or liquid as it permeates the membrane increases progressively. As a result, when backwashing is performed by applying a constant pressure in the hollow fiber membrane in each cycle, the permeation flow rate of gas or liquid that permeates from the inside to the outside of the hollow fiber membrane during backwashing. However, as the processing progresses, it gradually decreases. Then, as a result of the decrease in the permeation flow rate, the backwash effect gradually decreases.

The present invention has been made in response to such conventional circumstances, and an object thereof is to provide a method for operating a hollow fiber membrane filter in which the backwashing effect is not deteriorated even when the filtration treatment and the backwashing treatment are repeatedly performed. And

[Structure of the Invention] (Means for Solving Problems) The inventors of the present invention conducted research by paying attention to the pressure and the permeation flow rate applied to the hollow fiber membrane during the backwashing treatment. It was found that the backwashing efficiency does not decrease when the backwashing is carried out at a constant flow rate by increasing the pressure applied to the hollow fiber membranes from the initial pressure every cycle.

That is, the present invention allows a stock solution containing fine particles to be treated to permeate from the outer side to the inner side of the membrane surface of the hollow fiber membrane to discharge the filtrate to the inner side of the hollow fiber membrane and fine particles on the outer surface of the hollow fiber membrane. A filtrate treatment step of capturing and concentrating, and a pressure of pressurized air is applied to the inside of the membrane surface of the hollow fiber membrane to allow the liquid to permeate from the inside to the outside of the membrane surface of the hollow fiber membrane, and the filtration treatment step causes the hollow In a method for operating a hollow fiber membrane filter, which comprises repeatedly performing a backwashing treatment step of removing fine particles trapped on the outer surface of the fiber membrane, adding to the inside of the membrane surface of the hollow fiber membrane during the backwashing treatment step. The pressure setting step of the pressurized air that sets the pressure of the pressurized air according to the filtration differential pressure during the filtration process, and the pressure of the pressurized air that applies the set pressurized air to the inner surface of the membrane surface of the hollow fiber membrane. And a pressurizing step. To have.

In the present invention, a pressure air pressure setting step of setting the pressure of the pressurized air applied to the inside of the membrane surface of the hollow fiber membrane during the backwash treatment step according to the filtration differential pressure during the filtration treatment, and this setting. Since a pressurizing step of applying pressurized air to the inner surface of the hollow fiber membrane is provided, the permeation flow rate of the liquid that permeates from the inner side to the outer side of the hollow fiber membrane in the backwash process. Can be maintained at a certain value or more, whereby the fine particles trapped on the membrane surface of the hollow fiber membrane in the filtered liquid can be removed to the same extent in each cycle to prevent a reduction in backwash efficiency. The effect that it can be obtained.

(Operation) In the method for operating the hollow fiber membrane filter of the present invention configured as described above, the fine particles captured on the membrane surface or in the pores of the membrane wall during the filtration treatment are effectively treated through each backwash treatment step. The fine particles can be removed, and the fine particles can be prevented from accumulating in the hollow fiber membrane to perform an efficient backwashing treatment.

Example An example of the present invention will be described below.

Filtration and backwashing were repeated as follows using the filtration experimental apparatus using the hollow fiber membrane filter shown in FIG.

That is, first, in the slurry tank 10, a suspension containing amorphous iron colloid and α-Fe ₂ O ₃ colloid in a ratio of 4: 1 was prepared, and the valve 20 was opened to clean the water previously filled in the clean water tank 11. An undiluted solution having an iron content of 10 ppm was mixed with water. Open this valve by opening valves 17, 18 and 14, 15 and adjusting pump 21.
A constant flow rate of 1 m ³ / hour · m ² is supplied to the stock solution chamber 4 of the hollow fiber membrane filter storage container 2 through the stock solution supply pipe 6. The stock solution is filtered by the hollow fiber membrane filter 1 and sent to the filtrate chamber 5, and the valve 25 is opened to be stored in the washing water tank 11 via the filtrate discharge pipe 24. The filtration differential pressure during this filtration process was measured with a differential pressure gauge 30 over time, and this filtration differential pressure was 0.3 kef / cm ² from the filtration differential pressure at the start of the filtration process (initial filtration differential pressure).
When the temperature rises, the above-mentioned valves are switched to complete the stock solution supply.

Then, the valve of the pipe 35 for supplying pressurized air leading to the filtrate chamber 5
37 is opened and pressurized air is supplied to apply pressure to the inside of the hollow fiber membrane filter 1 to perform the backwash process. At this time, the pressure of the air to be supplied is adjusted to 1 kgf / cm ² by adjusting the pressure adjusting valve 33 of the air supply pipe 31 in advance.

Next, the valve 41 of the overflow pipe 12 is opened to allow the filtrate in the filtrate chamber 5 to permeate from the inside of the hollow fiber membrane filter 1 to the outside, and then the valve 39 of the bubble jet pipe 36 for backwashing treatment is opened to open the stock solution chamber. Bubbles are jetted out into the hollow fiber membrane to pulsate the hollow fiber membrane. The air flow rate at this time was 0.04 Nm ³ / hour per unit cross-sectional area of the hollow fiber membrane filter container 2. When 20 to 30 minutes have passed after the bubbles were ejected, the valves 37 and 39 were closed, and the valve 16 of the backwash treated water discharge pipe 7 was opened to discharge the backwash water containing the concentrated fine particles into the slurry tank 10. . After the discharge, the valve 16 is closed, the valves 14, 15 and 25 are opened to supply the stock solution again into the hollow fiber membrane filter container 2, and when the stock solution comes out through the overflow pipe 12, the valve 41 is closed and the second Move to the cycle and start the filtration process again.

The second cycle filtration treatment is also performed under the same conditions as the first cycle filtration treatment, and then the second cycle backwash treatment is performed. In this way, the filtration process and the backwash process are repeated.

By the way, as described above, the filtration differential pressure at the start of the second cycle is higher than the filtration differential pressure at the start of the first cycle due to the fine particles remaining on the membrane surface and inside the pores of the hollow fiber membrane even after the backwashing treatment. . Therefore, assuming that the pressure of the pressurized air supplied from the pressurized air supply pipe 35 during the backwashing process in the second cycle is the same as in the first cycle, the inside of the membrane surface of the hollow fiber membrane during the backwashing process. The permeation flow velocity of the liquid permeating from the outside to the outside becomes lower than the permeation flow velocity in the first cycle. This applies for each cycle.

Therefore, in this embodiment, the pressure P of the pressurized air supplied from the pressurized air supply pipe 35 in each backwashing process is increased by the filtration differential pressure before each backwashing process.

That is, the value of the pressure P _n of the pressurized air in the nth cycle was temporarily set as in the following formula (I), and the filtration process and the backwash process were repeated.

P _n = P _o × D _n / D _o (I) (where D _o is the initial filtration differential pressure during the first cycle filtration treatment, P _o is the hollow fiber membrane during the first cycle backwash treatment) The applied pressure, D _n, represents the filtration differential pressure at the end of the backwash treatment in the (n−1) th cycle, that is, the initial filtration differential pressure during the filtration treatment in the nth cycle. FIG. 1 shows the filtration differential pressure after the filtration treatment step and after the backwash treatment in each cycle in which the backwash treatment step was repeated. Further, the backwash efficiency for each cycle is shown in FIG.

In these figures, the values marked with ○ are (I)
The filtration differential pressure and the backwashing efficiency were obtained by increasing the pressure P of the pressurized air according to the formula, and the values indicated by Δ are the same as those of the example for comparison with the present invention. , The pressure P of the pressurized air supplied into the filtrate chamber 4 at the time of backwashing is 1 k each time.
Backflushing was performed at a constant gf / cm ² , and the filtration differential pressure and backwashing efficiency were obtained in the same manner.

As is clear from these figures, when the pressure P of the pressurized air is increased according to the formula (I) according to this embodiment, the backwash efficiency remains 90% or more even after 20 cycles. However, good results were obtained in that the increase in the filtration differential pressure after backwashing in each cycle was also slight. On the other hand, when the pressure P of the pressurized air according to the comparative example is kept constant, the fine particles remaining on the membrane surface and the membrane pores of the hollow fiber membrane after each backwashing process are accumulated every cycle, and the backwashing is performed. During the treatment, the flow rate of the filtrate that permeates from the inside to the outside of the hollow fiber membrane gradually decreases.As the cycle progresses, the rate of increase in the filtration differential pressure after backwashing in each cycle increases and the backwashing also increases. Efficiency is decreasing.

That is, as the pressure P of the pressurized air, for example, as shown in the formula (I), a pressure corresponding to the filtration differential pressure in each cycle is used, so that from the inside to the outside of the membrane surface of the hollow fiber membrane during backwashing treatment. It is understood that by maintaining the permeation flow rate of the permeating liquid above a certain value, the fine particles captured on the membrane surface of the hollow fiber membrane after the filtration treatment are removed to the same extent in each cycle, and the backwash efficiency does not decrease. It

By the way, according to the results of the comparative example shown in FIG. 1 and FIG. 2, the backwashing efficiency is remarkably reduced from around 50 cycles, and there is no great difference from the results of this example from the start to the middle. I understand.

Therefore, an experiment was conducted on the relationship between the permeation flow rate during the filtration process and the permeation flow rate during the backwash process and the backwash efficiency, and the results shown in FIG. 3 were obtained. In the figure, the relationship between the backflow efficiency and the ratio of the permeation flow rates during the filtration process and the backwash process is shown.

As is clear from this figure,
It can be seen that excellent backwashing efficiency can be obtained by setting it to 1.0 or more, that is, by setting the permeation flow rate during the backwash treatment to be equal to or higher than the permeation flowrate during the filtration treatment. The permeation velocity ratio is 4.
It can also be seen that the backwash efficiency does not improve much even if the value is increased to 0 to 5.0.

Therefore, in this example, by performing the backwashing process of each cycle using the P value set by the formula (I), the above-mentioned permeation flow rate ratio was maintained at 1.0 or more during the progress of the process, and a good reverse Washing efficiency can be obtained.

[Effects of the Invention] As described above, according to the present invention, in the method for operating a hollow fiber membrane filter, the pressure of the pressurized air applied to the inside of the membrane surface of the hollow fiber membrane during the backwash treatment step is set during the filtration treatment. Since the pressure setting step of the pressurized air set according to the filtration differential pressure of and the step of pressurizing the pressurized air to add the set pressurized air to the inner surface of the hollow fiber membrane are provided, It is possible to maintain the permeation flow rate of the liquid that permeates from the inner side to the outer side of the membrane surface of the fiber membrane at a certain value or more for each backwash treatment step, which allows it to be captured on the membrane surface of the hollow fiber membrane after the filtration treatment. Effectively removes fine particles and prevents them from accumulating,
It is possible to extend the life of the hollow fiber membrane. Therefore, when the particles to be treated are radioactive substances, the number of maintenance inspections is reduced, and the chance of radiation exposure can be reduced.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the number of cycles and the filtration differential pressure after filtration and after backwashing in one embodiment of the present invention, and FIG. 2 shows the relationship between the number of cycles and backwashing efficiency at that time. The graph shown in FIG. 3 is a graph showing the relationship between the backwash efficiency and the ratio of the permeate flow rate during the backwash process and the permeate flow rate during the filtration process.
FIG. 4 is a system diagram of a filtration experiment device using a hollow fiber membrane filter used in Examples and Comparative Examples of the present invention. 1 ... Hollow fiber membrane filter 2 ... Hollow fiber membrane filter container 4 ... Stock solution chamber 5 ... Filtrate chamber 6 ... Stock solution supply pipe 7 ... Backwash treated water discharge pipe 10 ... Slurry tank 11 …… Clean water tank 12 …… Overflow pipe 24 …… Filtrate discharge pipe 28, 29 …… Pressure gauge 30 …… Differential pressure gauge 31 …… Air supply pipe 35 …… Backwash process Pressurized air supply pipe 36 …… Bubbling jet pipe for backwashing

Front Page Continuation (72) Inventor Fumio Tajima 1-1-1 Shibaura, Minato-ku, Tokyo Inside Toshiba Headquarters Office (56) Reference JP-A-61-197004 (JP, A)

Claims (2)

(57) [Claims] 1. A stock solution containing fine particles to be treated is permeated from the outer side to the inner side of the membrane surface of the hollow fiber membrane to discharge the filtrate into the hollow fiber membrane, and at the same time, the fine particles are formed on the outer surface of the hollow fiber membrane. A filtrate treatment step of capturing and concentrating, and a pressure of pressurized air is applied to the inside of the membrane surface of the hollow fiber membrane to allow the liquid to permeate from the inside to the outside of the membrane surface of the hollow fiber membrane, and the filtration treatment step causes the hollow In a method for operating a hollow fiber membrane filter, which comprises repeatedly performing a backwashing treatment step of removing fine particles trapped on the outer surface of the fiber membrane, adding to the inside of the membrane surface of the hollow fiber membrane during the backwashing treatment step. The pressure setting step of the pressurized air that sets the pressure of the pressurized air according to the filtration differential pressure during the filtration process, and the pressure of the pressurized air that applies the set pressurized air to the inner surface of the membrane surface of the hollow fiber membrane. A pressurizing step How to operate an empty fiber membrane filter. 2. The method according to claim 1, wherein a large number of bubbles are ejected from the outside of the hollow fiber membrane toward the hollow fiber membrane during the backwashing process to stir and vibrate the liquid around the hollow fiber membrane. A method for operating the described hollow fiber membrane filter.