JPH11169687A - Cleaning method of membrane separation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the sedimentation of a sludge or the deposition of scale in a system in a long operation stop period of a membrane separation device by discharging the sludge in a pipe line and a membrane module in the membrane separation device before a cleaning water is passed through the pipe line and cleaning the membrane module. SOLUTION: A blow pipe 16 is provided by being branched from a raw water introducing pipe line (downstream side of a pump 3) 13. At the time of the long period operation stop, the pump 3 is stopped to stop the feed to the membrane module 4 at first and a blow valve V1 is opened to discharge the sludge in the pipe lines 13, 15 and the membrane module 4 in the membrane separation device out of the system. After that, the blow valve V1 is closed, an injection valve V3 is opened and a stop valve V3 is closed to feed an industrial water as the cleaning water to the membrane module 4 through pipe lines 17, 16 and 13 and to let flow to a circulating vessel 2 from a pipe line 15. As a result, the remaining sludge in the pipe lines and membrane module is washed out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a membrane separation device, and more particularly to a method for cleaning a membrane separation device which is treating wastewater for a long period of time, during which the operation is stopped. The present invention relates to a method for preventing trouble such as blockage of pipes by preventing sludge deposition and scale generation in the pipes.

[0002]

2. Description of the Related Art In recent years, a membrane separation device has been widely used as a solid-liquid separation means in place of a precipitation tank in the coagulation / solid-liquid separation treatment of wastewater.

[0003] The operation of a membrane separator is stopped several times a year, about three days in a short case, and several months in a long time in the case of a periodic inspection or in connection with other auxiliary equipment. At the time of this operation stop, the operation of the apparatus is simply stopped without performing any processing, or the operation of the apparatus is stopped only by supplying industrial water to the raw water chamber side of the membrane module.

Japanese Patent Application Laid-Open No. 63-294904 discloses that a hollow fiber membrane is stored in degassed and sterilized water in order to prevent the hollow fiber membrane from being deteriorated by microorganisms during the operation stop period. A method is described.

[0005]

In a membrane separation apparatus which performs solid-liquid separation of a coagulation treatment liquid of wastewater, separated sludge always remains in a pipe or a membrane separation apparatus.
For this reason, if such a membrane separation device is stopped as it is, sludge is deposited on the lower part of the pipe and the membrane surface during the shutdown period, scale is deposited, and if the operation is stopped for as long as 5 to 10 days, When the operation is resumed, the flow rate decreases due to the sediment sludge and scale in the pipes, and it is not possible to obtain the expected water sampling amount. The occurrence of such troubles lowers the operation rate of the membrane separation device, impairs stable operation, and reduces the reliability of the device.

[0006] For example, a membrane separation apparatus for neutralizing coagulation treatment of sludge flue gas desulfurization wastewater of a thermal power plant with slaked lime and subjecting the coagulated water to membrane separation is operated at a raw water SS concentration of about 5%. However, SS in raw water has a high sedimentation property, and solidifies when deposited for a long period of time.
Is difficult to resuspend. For this reason, SS deposited on the lower part of the pipe during the operation period is not flushed by the raw water flow when the operation is restarted, and causes a pipe blockage. Further, in this membrane separation device, the water temperature during operation is about 30 ° C., but the water temperature decreases to 10 to 20 ° C. due to the stoppage of the operation, so that the solubility of Ca ions and sulfate ions in the system decreases and the scale ( Gypsum) is generated. The generated scale peels off from the pipe wall due to vibration or the like at the time of restart of operation, and is flown to the membrane module side, causing the inlet of the membrane module to be blocked.

[0007] Even if industrial water is supplied to the membrane module or the membrane is deposited in degassed or sterilized water as described in JP-A-63-294904, the sludge concentration is slightly diluted. However, since the sludge still remains in the pipe, the problems of sludge deposition and scale formation in the pipe cannot be solved.

The present applicant has previously proposed a method of restoring membrane performance during a long period of operation stoppage of a membrane separation apparatus by bringing a cleaning agent solution into contact with the membrane surface during a long period of operation stoppage. However, even if the membrane surface is kept in contact with the cleaning solution as described above, troubles in the piping of the membrane separation device and the inlet of the membrane module due to residual sludge are prevented. May not be possible.

The present invention solves the above-mentioned conventional problems, and prevents sludge deposition and scale deposition in a system during a long-term shutdown period of a membrane separation apparatus for treating wastewater, thereby reducing the membrane separation apparatus. It is an object of the present invention to provide a method for cleaning a membrane separation device that improves the operation rate and reliability.

[0010]

The method for cleaning a membrane separation apparatus according to the present invention is a method for cleaning a membrane separation apparatus when shutting down a membrane separation apparatus for treating wastewater for a long period of time. After the sludge in the piping and the membrane module of the membrane separation device is discharged out of the system, the washing water is passed through the piping and the membrane module for washing.

In the present invention, the sludge in the piping and the membrane module is discharged to the outside of the system, and then the washing water is passed through the system for washing. Therefore, the amount of sludge remaining in the system is significantly reduced. Scale components in the system are also greatly reduced, preventing sludge deposition and scale formation during shutdown periods.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for cleaning a membrane separation apparatus according to the present invention will be described below with reference to the drawings.

FIG. 1 is a system diagram of an apparatus for performing coagulation and membrane separation of flue gas desulfurization effluent of a thermal power plant. Raw water (smoke flue gas desulfurization effluent) is used in a coagulation reaction tank 1 as a coagulant and a neutralizing agent. After the slaked lime is added and coagulated, the water is fed from the pipe 11 to the circulation tank 2 and introduced into the MF (microfiltration) membrane module 4 via the pipes 12 and 13 by the pump 3 to supply water SS
The membrane is separated under a condition of a concentration of about 1 to 10% by weight. The permeated water of the membrane module 4 is discharged as treated water from the pipe 14 to the outside of the system, and the concentrated water is returned to the circulation tank 2 from the pipe 15. The type of the membrane module 4 is not particularly limited, and various types of membrane modules such as a tubular type and a hollow fiber type can be adopted.

The raw water introduction pipe (pump 3) of the membrane module 4
(A downstream side) 13, a blow pipe 16 is provided in a branched manner, and the blow pipe 16 is connected to a pipe 17 for introducing industrial water. V ₁ was blow valve, V ₂ is the injection valve, V ₃ is opened and closed valves.

When the operation of the membrane separation device is stopped for a long time,
First, the pump 3 is stopped, after stopping the supply of water to the membrane module 4, the blow valve V ₁ is opened to discharge the sludge piping 13, 15 and the membrane module 4 of the membrane separator to the outside of the system.

Thereafter, the blow valve V ₁ is closed and the injection valve V ₂
The opening, the opening and closing valve V ₃ is closed, and passed through the industrial water to the membrane module 4 via piping 17,16,13 as wash water, by flowing from the pipe 15 to the circulation tank 2, in these pipes and membrane module The remaining sludge is washed away.

At this time, the flow rate of the industrial water is such that the sludge remaining in the piping and the membrane module is sufficiently discharged, and the scale-forming components in the piping and the membrane module are reduced to a concentration at which no scale is generated (general). It is desirable that the amount is sufficient to dilute (to about 1/2 or less than the saturated concentration of the scale component), and it depends on the piping design and the quality of the raw water. It is preferable to pass 2 to 20 times, particularly 5 to 10 times the amount of water with respect to the total volume of the entire piping and the volume of the raw water chamber of the membrane module.

The water passed through the membrane module 4 may be introduced into the circulation tank 2 as described above, or may be discharged outside the system and treated separately. As the cleaning water, city water or the like may be used in addition to industrial water. In any case, a sludge discharge section is provided so that the sludge in the system is sufficiently discharged, and an injection section and a discharge section of the cleaning water are provided so that the water in the piping and the membrane module can be sufficiently replaced with the cleaning water. Is preferably provided.

In the present invention, when the operation of the membrane separation device is stopped, the opening and closing of the blow valve and the injection valve from the stop of the pump can be automatically controlled.

Further, in the present invention, in order to easily and surely discharge the sludge from the blowpipe, wash out the residual sludge with the washing water, and dilute the scale components, the pipe design is devised to eliminate the liquid reservoir. It is preferable to adopt a device configuration in which washing water flows smoothly.

In accordance with the present invention, the membrane separation apparatus which has performed sludge discharge and washing water flow has no sludge deposition in the system when the operation is resumed after a long period of shutdown.
Since the scale component is also diluted, there is no problem of scale precipitation, so that stable and favorable operation can be performed without causing impediment of water flow.

The method for cleaning a membrane separation apparatus according to the present invention is a method for operating a flue gas desulfurization effluent of a thermal power plant or the like for a long period of 2 days or more, especially 5 days or more. It is effective when stopping.

[0023]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1 The flue gas desulfurization effluent (pH 1.6, S
S950mg / L, Ca920mg / L, SO 4 350
(0 mg / L) when the coagulation / membrane separation device was shut down for a long time, the membrane separation device was washed according to the present invention.

The flue gas desulfurization effluent is fed to the coagulation reactor 1
Slaked lime is added as a flocculant and a neutralizing agent to adjust the pH to 6 to 7, and 30 mg / L of wellclean (manufactured by Kurita Industry Co., Ltd.) is added as a heavy metal collecting agent.

The coagulated water in the coagulation reaction tank 1 passes through a circulation tank 2 and is pumped by a pump 3 into a tubular MF membrane module (inner diameter 5.5 mm, pore diameter 0.2 μm, membrane area 0.036 m).
² ) It is introduced into 4 and subjected to membrane separation under the condition of an SS concentration of 5% by weight. The permeated water is discharged out of the system as treated water, and the concentrated water is circulated to the circulation tank 2.

The hit the stop of the operation of the membrane separation apparatus, after stopping the pump 3 was first drained sludge in the system the blow valve V ₁ is opened. Then, closing the blow valve V _1, the injection valve V ₂ opens, and passed through at 2L / min in the piping industrial water off valve V ₃ is closed and the membrane module. The flow rate of this industrial water is 4 L, which is about 10 times the total of the total internal volume of the distribution pipe (300 mL) and the volume of the raw water chamber of the membrane module (100 mL). The water after passing was introduced into the circulation tank 2.

The concentration of Ca ²⁺ , SO ₄ ²⁻ and the amount of scale generated in the pipe after stopping the membrane separator for 30 days after passing the water through the industrial water were examined. The results are shown in Table 1. In addition, the scale generation amount was determined by forming a part of a pipe with a detachable short tubular test piece, removing the test piece, and measuring the amount of adhered scale.

Table 1 also shows the Ca ²⁺ concentration and SO ₄ ²⁻ concentration of water in the pipe immediately after the operation of the apparatus was stopped.

Comparative Example 1 The operation of the membrane separation apparatus was stopped in the same manner as in Example 1 except that the operation was stopped without any treatment, without any treatment. ^{The 2+} concentration, SO ₄ ^2- concentration and the amount of scale generation were examined. The results are shown in Table 1.

Comparative Example 2 In Example 1, the same operation as in Example 1 was carried out except that the sludge was not discharged prior to the passage of the industrial water but the industrial water was directly passed in stopping the operation of the membrane separation apparatus. And after washing for 30 days, the concentration of Ca ²⁺
₄ ^2- Concentration and scale generation were examined, and the results are shown in Table 1.

[0032]

[Table 1]

From Table 1, it can be seen that according to the present invention, scale formation in the system during operation stoppage is prevented, and good operation can be restarted.

On the other hand, in Comparative Example 1 in which no processing is performed when the operation of the apparatus is stopped, a large amount of scale is generated. In Comparative Example 1, when the operation of the membrane separation device was restarted, a part of the scale was separated from the inner wall of the pipe due to the water flow and the vibration applied from outside the pipe at the time of restarting the operation,
The peeled scale clogged the orifice and the like, causing a water flow obstacle.

Further, in Comparative Example 2, although the industrial water is passed through, the sludge is not discharged prior to the flow of the industrial water, so that the SS in the pipe is smoothly pushed out by the industrial water. As a result, the amount of scale generated has increased due to the deposition of SS during the operation stop period.

[0036]

As described above in detail, according to the method for cleaning a membrane separation device of the present invention, sludge deposition and scale deposition in the system during a long-term shutdown period of a membrane separation device treating wastewater. Can be prevented, and the operation rate and reliability of the membrane separation device can be improved.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of a method for cleaning a membrane separation device of the present invention.

[Explanation of symbols]

 1 Coagulation reaction tank 2 Circulation tank 3 Pump 4 MF membrane module

Claims (1)

[Claims] 1. A method for cleaning a membrane separation device for treating a waste water when shutting down the membrane separation device for a long period of time, wherein sludge in piping and a membrane module of the membrane separation device is taken out of the system. A method for cleaning a membrane separation device, comprising washing the pipe and the membrane module with water for washing after discharging the water.