JPH02284609A - Operation of ceramic filter - Google Patents

Abstract

PURPOSE:To sufficiently restore the capacity of the filter by backwashing at a low bulk velocity by allowing a fluid to flow in parallel with the filter only immediately after backwashing in the cross-flow filtration so that the wall- surface shearing stress is increased on the filter surface. CONSTITUTION:A liq. is filtered by the cross-flow ceramic filter 1, the filter is backwashed when the filtration differential pressure increases to restore the filtration performance, and filtration is repeated. The wall-surface shearing stress is increased on the filter surface only after backwashing by introducing a pressurized liq. into the circulating flow from another tank 18. Consequently, the capacity is sufficiently restored by the backwashing even at a low bulk velocity. Since the treatment is carried out only immediately after backwashing, the capacity of a pump and the diameter of the pipeline need not be increased, and even a cooler for removing the heat generated from the pump can be dispensed with. Accordingly, the filtration performance of the ceramic filter can be improved by the compact equipment.

Description

[Detailed Description of the Invention] [Purpose of the Invention (Industrial Application Field) The present invention is useful for removing or concentrating suspended solids in a liquid in the food industry, pharmaceutical industry, atomic crab industry, etc. This article relates to a method of operating a widely used ceramic filter.

(Conventional technology) Ceramic filters made of inorganic compounds such as alumina and silica have excellent strength, heat resistance, and corrosion resistance, and are therefore used in the food and pharmaceutical industries.

It is widely used in fields such as atomic crab industry.

Ceramic filters come in various shapes and operate in a variety of ways, but as the filtration time elapses, solids to be treated are trapped on the filter surface.

As a result, the filtration performance gradually decreases, and the resistance when passing through the filter increases, the filtration differential pressure rises, and the treatment flow rate decreases, making it impossible to obtain the desired treatment capacity. Therefore, it becomes necessary to clean the filter to restore processing performance.

Conventionally, filters are cleaned by washing or backwashing (flowing in the opposite direction to the filtration method) with permeate, clean water, or gas, but depending on the type of solids trapped or deposited on the filter surface, Since there are cases where treatment performance is not fully restored by this washing or backwashing alone, the chemical solution has been selected depending on the type of solid material.

An example of an operating method using a conventional ceramic filter will be explained with reference to the system diagram shown in FIG.

The liquid to be treated containing suspended solids in the liquid to be treated tank 3 is
The pump 4 connects liquid supply pipes 11, 13. The liquid is guided to the ceramic filter storage container 2 through the valve 6, flows through the flow path inside the tube of the ceramic filter 1, returns to the liquid to be treated tank 3 through the valve 7 and the circulation piping 14, and is circulated again along the same route.

In the ceramic filter 1 , so-called cross-flow filtration is performed in which a portion of the liquid to be treated passes through the filter in a direction perpendicular to the flow in the flow path inside the tube, and is discharged to the filtrate discharge pipe 15 .

When the liquid to be treated is circulated in this manner, the suspended solids in the liquid to be treated are gradually concentrated. By opening the valve 9, the concentrated liquid is discharged out of the system through the pipe 16. When the concentrated liquid is discharged, the liquid to be treated tank 3 is connected to the pipe 17. New liquid to be treated is supplied via valve 10.

In the above-mentioned cross-flow filtration, the flow direction of the filtrate passing through the filter and the flow direction of the liquid to be treated are different, so the deposition of solids on the filter surface is relatively unlikely to occur, but as the treatment progresses, Gradual deposition increases the resistance required for permeation, making it impossible to obtain the desired throughput. In such cases, cleaning or backwashing was performed using permeate, fresh water, gas, etc.

By the way, it has been found that the recovery of processing capacity is greatly influenced not only by the conditions of backwashing but also by the flow rate (bulk speed) of the circulating flow restarted after backwashing. FIG. 6 shows an example of the experimental results. This experiment was performed for circulating flow at four bulk velocities, with a backwash pressure of 5 kg/crl.
The permeation flux of the filtrate after backwashing was investigated when backwashing was performed under the same backwashing conditions of 41 (0.02 m3/distillate) of backwash water volume, but as shown in this figure, the same It can be seen that even under backwash conditions, the processing capacity recovers better when the bulk speed is higher.

Therefore, in order to continue more efficient operation over a long period of time in a ceramic filter, it is necessary to operate at a high bulk speed, that is, at a high circulating flow rate of the liquid to be treated.

(Problem to be Solved by the Invention) However, if the circulation flow rate of the liquid to be treated is increased in this way, the pump for circulating the liquid to be treated must have a high capacity, and the piping diameter of the circulation line must also be increased. Must. Furthermore, since the pump generates heat, cooling equipment is also required to remove the heat. Due to these factors, there is a problem that the device becomes large-scale.

The present invention has been made in view of the above circumstances, and its object is to provide a method of operating a ceramic filter that can sufficiently restore the throughput through backwashing even at low bulk speeds.

[Structure of the invention] (Means and effects for solving the problem) That is, the present invention filters the liquid to be treated, performs backwashing when the filtration differential pressure increases to restore the filtration performance, and then performs the filtration process again. In the operating method of a semi-crystal filter that repeats filtration processing, the semi-crystal filter increases the flow of fluid parallel to the filter surface using a method that increases the wall shear stress on the filter surface only immediately after backwashing. Regarding driving methods.

In the present invention, as a method of flowing fluid parallel to the filter surface in a manner that increases the wall shear stress on the filter surface, for example, pressurized liquid from another tank may be introduced into the circulating flow to temporarily cause the fluid to flow parallel to the filter surface. There are methods such as increasing the flow rate on the side of the liquid to be treated of the ceramic filter, or mixing gas into the circulating flow and flowing it through the flow path on the side of the liquid to be treated of the ceramic filter.

Since these treatments are performed only immediately after backwashing, there is no need to increase the pump capacity or pipe diameter, and there is no need for a cooling device to remove heat generated from the pump. Therefore, the filtration performance of the ceramic filter can be improved with compact equipment.

(Example) Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of the operating method of the present invention. Note that the same parts as those in FIG. 5 already explained are given the same reference numerals.]7.

In FIG. 1, a ceramic filter 1 is fixed in a storage container 2. As shown in FIG. A liquid supply pipe 13.11 has a valve 6 and a pump 4 on the inflow side of the storage container 2 and is connected to the liquid to be treated tank 3, and a valve 7 has a valve 7 on the outflow side of the storage container 2 to supply the liquid to be treated. A circulation pipe 14 connected to the tank 3 is connected to a side surface of the storage container 2, and a filtrate discharge pipe 15 equipped with a valve 8 is connected to the side surface of the storage container 2.

Further, a liquid pressurized injection tank 18 for the circulating flow is provided with a valve 19 between the ceramic filter of the liquid supply pipe 13 and the valve 6.
is connected.

Next, a method of operating the above device will be explained.

The liquid to be treated is circulated through a path including the liquid to be treated tank 3, the liquid supply pipe 11, the pump 4, the liquid supply pipe 13, the ceramic filter 1, the valve 7, and the circulation pipe 14. When the liquid to be treated passes through the ceramic filter 1 along this route, filtration is performed and the filtrate is discharged from the discharge pipe 15-.

If this operation is continued and suspended solids adhere to the surface of the ceramic filter on the liquid side to be treated, and the resistance to filtration increases,
The circulation flow is stopped by closing the valve 6, and the filtrate is allowed to flow back through the discharge pipe 15 and the valve 8, thereby performing backwashing.

After backwashing, the valve 6 is opened again to resume circulation of the liquid to be treated.

At this time, the pressurized liquid injection tank 18 is pressurized and the liquid stored in advance is injected into the circulating flow, and the bulk velocity in the flow path on the liquid-to-be-treated side of the ceramic filter is temporarily adjusted to a predetermined wall shear stress. increase as expected.

FIG. 2 shows the change in permeation flux of the filtrate after backwashing in this example. Shown here is a bulk speed of 5 m/s and 3 m/s for 30 seconds after backwashing.
/s. In addition, the backwash pressure is 6kg/
cnf, the amount of backwash water is 41 (0.02 m'/n(). As a comparative example, the results (dashed line) are shown when the bulk speed is not increased after backwashing.

As is clear from the figure, when the bulk speed is 1 m/s, the processing capacity cannot be fully recovered even after backwashing, but by increasing the bulk speed by pressurizing injection for only 30 seconds after backwashing. , it can be seen that the patient recovers well.

Next, FIG. 3 shows another embodiment of the operating method of the present invention using a system diagram. This embodiment uses a ceramic filter 1 instead of the liquid injection tank 18 of the embodiment shown in FIG.
- a gas-liquid mixer 20 is installed between the valve 6 and the valve 6;
The air supply pipe 22 is connected through the air supply pipe 1.

In this example, the same filtration process as in the previous example was performed,
When suspended solids adhere to the surface of the ceramic filter on the liquid-to-be-treated side and the filtration resistance increases, backwashing is performed in the same way, but when the circulation of the liquid to be treated is restarted after backwashing, the air supply Air is introduced through the pipe 22, and mixed with the liquid to be treated in the gas-liquid mixer 20 at the entrance of the ceramic filter 1-. By doing so, the wall shear stress on the surface of the ceramic filter on the liquid-to-be-treated side increases.

FIG. 4 shows the change in permeation flux of the filtrate after backwashing in the above example. The system shown here was operated at a bulk speed of 1 m/s, and 3 times and 6 times as much air by volume was blown into the circulating liquid flow equivalent to the bulk speed of 1 m/s for 30 seconds after backwashing. These are the experimental results for the case.

The backwash conditions are the same as in the previous example, backwash pressure 6 kg.
/c&, the amount of backwash water is 41 (0.02 m3/rr?).

The wall shear stress when the amount of air blown into the circulating flow equivalent to a bulk velocity of 1 m/s is 3 times the bulk velocity of 3 m/s.
/s, and the wall shear stress when the air volume is 6 times greater is equivalent to that when the bulk velocity is 5 m/s. As can be seen from these results, blowing air into the circulating flow also increases the wall shear stress and restores the filtration capacity.

[Effects of the Invention] As explained below, according to the present invention, the wall shear stress on the surface of the treated liquid side of the ceramic filter can be temporarily reduced immediately after backwashing without increasing the circulation flow rate during operation. The processing ability of the ceramic filter can be restored by processing it to increase its size. Therefore, there is no need to increase the size of piping or pumps that are required to increase the circulation flow rate, and there is no need for cooling equipment.
The system can be made more compact.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing the operating method of an embodiment of the present invention, Fig. 2 is a diagram showing the recovery status of processing capacity after backwashing of the embodiment shown in Fig. A system diagram showing the operating method of another embodiment, Fig. 4 is a diagram showing the recovery status of processing capacity after backwashing of the embodiment shown in Fig. 3, and Fig. 5 shows the operating method of the conventional ceramic filter. The system diagram, FIG. 6, is a diagram showing the state of recovery of processing capacity after backwashing by the operating method shown in FIG. 5. 15...Filtrate discharge piping 18...Liquid pressurized injection tank 20...Gas-liquid mixer 22...Air supply piping Agent Patent attorney (8733) Yoshiaki Inomata (and 1 others)
Name) 1...Ceramic filter 2...Ceramic filter storage container 3...To be treated liquid tank 4...Pump

Claims (3)

[Claims] (1) In a method of operating a semi-conductor filter in which the liquid to be treated is filtered, and when the filtration differential pressure increases, backwashing is performed to restore the filtration performance, and the filtration process is repeated again.
A method of operating a ceramic filter characterized by flowing fluid parallel to the filter surface in such a manner as to increase wall shear stress on the filter surface only immediately after backwashing. (2) The method of operating a ceramic filter according to claim 1, wherein the wall shear stress on the filter surface is increased by applying a large amount of pressurized circulating flow. (3) The method of operating a ceramic filter according to claim 1, wherein the wall shear stress on the filter surface is increased by blowing gas into the circulating flow.