JP2685905B2 - How to operate a ceramic filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is widely used for removing or concentrating suspended solids in a liquid in the fields of food industry, pharmaceutical industry, nuclear industry and the like. The present invention relates to a method of operating a ceramic filter used.

(Prior Art) Ceramic filters composed of inorganic compounds such as alumina and silica have excellent strength, heat resistance, and touch resistance, and are therefore widely used in fields such as food industry, pharmaceutical industry, and nuclear industry. ing.

There are various shapes of ceramic filters, and there are various operating methods, but the solid matter to be treated is uniformly trapped and deposited on the filter surface with the lapse of filtration time, and the filtration performance gradually deteriorates. Since the resistance when passing through the filter increases, the filtration differential pressure increases and the processing flow rate decreases,
A predetermined processing capacity cannot be obtained. Therefore, it is necessary to wash the filter to recover the processing performance.

Conventionally, the filter is washed with permeated liquid, clear water, or gas by washing or backwashing (flowing in the opposite direction to the filtration treatment method).

An example of the operation method using the conventional ceramic filter will be described with reference to the system diagram of FIG.

The liquid to be treated containing suspended solids in the liquid to be treated tank 3 is introduced into the ceramic filter container 2 by the pump 4 through the liquid supply pipes 11, 13 and the valve 6, and the ceramic filter 1
Through the valve 7 and the circulation pipe 14 and returns to the liquid tank 3 to be treated again, and circulates again in the same path. In the ceramic filter 1, so-called cross-flow filtration is performed in which a part of the liquid to be treated passes through the filter in the direction perpendicular to the flow in the flow path inside the pipe, and the filtrate is discharged to the filtrate discharge pipe 15.

When the liquid to be treated circulates in this way, suspended solids in the liquid to be treated are gradually concentrated. The concentrated liquid is discharged to the outside of the system through the pipe 16 by opening the valve 9. When the concentrated liquid is discharged, a new liquid to be processed is supplied to the liquid to be processed tank 3 through the pipe 17 and the valve 10.

In the above-mentioned cross-flow filtration, since the flow direction of the filtrate passing through the filter by filtration and the flow direction of the liquid to be treated are at right angles, the advantage that the deposition of solid matter on the filter surface is suppressed by the shearing force And as a result, the backwash interval is long.

In contrast to this cross-flow method, there is a so-called once-through filtration process in which the valve 7 is closed and all the liquid to be processed supplied to the filter is transmitted through the filter and filtered. According to this method, there is an advantage that the device becomes compact.

By the way, when operating not only a ceramic filter but also a backwash regeneration type filter, the time to switch from the filtration process to the backwash process is specified by the filtration differential pressure in the constant flow rate filtration process and by the filtration speed in the constant pressure filtration process. There are many.
The constant flow rate filtration process will be described below as an example.

The filtration differential pressure is generally determined in consideration of conditions such as the pressure resistance of the filter and the allowable pressure of the system in which the filter is installed.

The magnitude of this filtration differential pressure can theoretically be expressed by the following equation.

Here, t: time [s] ΔP: filtration differential pressure [kg / cm ² ] ΔPo: filtration differential pressure at t = 0 (initial filtration differential pressure) [kg / cm ² ] αm: specific resistance of the filter cake [M / kg] C: Concentration at inlet [kg / m ³ ] μ: Viscosity of filtrate [kg / m · s] q: Linear velocity on membrane surface [m / s] gc: Unit conversion coefficient 9.8 [kg ・ m / s ² · Kg].

From the formula (I), the filtration differential pressure is the specific resistance (α
m) and the amount of suspended solids trapped on the membrane surface (C × q × t)
And the linear velocity (q) on the film surface. Therefore, the method of defining the time to switch to the backwash process by the filtration pressure difference is considered to be rational in the normal filtration process.

(Problems to be Solved by the Invention) However, when a liquid that is extremely easy to filter, that is, a liquid whose filter cake has a very small specific resistance (α _m ), is subjected to a filtration treatment, the filtration pressure difference does not increase, although However, when a large amount of suspended solids is captured and the process is switched to backwashing, the suspended solids captured will fill the liquid passage on the liquid side of the ceramic filter or the filter storage container, and the concentrated liquid will be discharged. However, there is a risk that it will become difficult to perform regeneration by backwashing. Therefore, in order to prevent the above-mentioned situation in the filtration process of such a liquid, the time of the backwash process may be regulated by the filtration amount or the filtration operation time other than the filtration differential pressure. However, the rationale for the value was not always clear.

On the other hand, when a liquid that is very difficult to filter, that is, a liquid with a very high specific resistance of the filter cake, is filtered, even though the suspended solids captured on the membrane surface are very small, the filtration pressure difference Rises and reaches the specified value for backwashing process.Therefore, if the time to switch to the backwashing process from the filtration process is specified by the filtration differential pressure, the switching frequency becomes very large, and There is a problem that there is no. Furthermore, when the suspended solids captured on the membrane surface do not form a filter cake, only the suspended solids in the vicinity of the micropores on the membrane surface are removed during the backwash treatment, and other suspended solids are removed. There is also a problem that a sufficient backwashing effect cannot be obtained because the remaining amount remains.

The present invention has been made in view of the above circumstances, and an object thereof is to allow a backwash regeneration type ceramic filter to continue to operate efficiently and stably for a long period of time, and to efficiently perform a filtration process and a backwash process. It is to provide a method of operating a ceramic filter.

[Structure of the Invention] (Means and Actions for Solving the Problems) A method of operating a ceramic filter according to the present invention comprises subjecting a liquid to be treated to filtration treatment, and performing backwashing when the filtration differential pressure increases or the filtration speed decreases. The method of operating a ceramic filter in which filtration performance is recovered by performing filtration treatment again by repeating filtration treatment is characterized in that the filtration speed is changed according to the properties of the fine particles contained in the liquid to be treated, that is, If the increase rate of the filtration differential pressure per unit mass of the solid content captured by the filter or the rate of decrease of the filtration rate is large, in the case of so-called difficult filtration, decrease the filtration rate, and conversely per unit mass of the solid content captured by the filter. In the case of so-called easy filterability in which the increase rate of filtration or the decrease rate of filtration rate is small, the feature is to increase the filtration rate.

Further, more specifically explaining the operating method of the present invention described above, for example, when the amount of solids captured by the filter in the filtration treatment step is 5 to 100 g / m ² The filtration rate may be controlled so that it rises within a range of 1 kg / cm ^{2 or} less than the initial differential pressure, and the amount of solids captured by the filter in the filtration treatment step is 5 to 10
Backwashing should be done at 0 g / m ² . This will be described below.

Mixing amorphous iron colloid and α-Fe ₂ O ₃ by using the ceramic filter device shown in the system diagram of Fig. 5 so that the filtration resistivity becomes about 10 ¹² , 10 ¹³ and 10 ¹⁴ m / kg, respectively. The suspension (content is 0.1 to 100 ppm as iron) adjusted to a constant flow rate (0.1 to ¹ m ³ / h / m ² ) at a constant flow rate (0.1 to ¹ m ³ / h / m ² ) of the suspended solids captured by the filter before backwashing. Quantity as a parameter,
Repeated experiments of filtration and backwash were performed.

The results are shown in FIGS. 1, 2 and 3. Figure 1 shows the relationship between the trapped solids content per unit filtration area and the rise of the filtration differential pressure with the filtration rate as a parameter for suspensions with filtration specific resistances of about 10 ¹² , 10 ¹³ , and 10 ¹⁴ m / kg, respectively. It shows the results of the examination.

(A) figure is about 10 ¹² filtration specific resistance, (b) figure is 10 ¹³ , (c)
The figure is a suspension of 10 ¹⁴ , in which the horizontal axis represents the amount of trapped solids per unit filtration area (g / m ² ), and the vertical axis represents (filtration differential pressure-initial filtration differential pressure) (Kg / m ² ). Is.

The filtration differential pressure changes substantially according to the above formula (I).
However, since the ceramic filter used in this experiment is of the tubular internal pressure type, the internal surface area of the pipe, that is, the filtration area, decreases with the lapse of time of the filtration process due to the cake layer formed by the solid content trapped on the interior surface of the pipe. Therefore, if the constant flow rate filtration process is continued, the linear velocity on the membrane surface is substantially increased, and the increase rate of the filtration differential pressure is increased.

FIG. 2 is a graph showing the backwashing efficiency obtained from the mass balance. Similar to the case of FIG. 1, the filtration resistivity 10 ¹² , 10 ¹³ ,
10 ¹⁴ suspensions were investigated. 1 from this figure
If the amount of suspended solids captured by one filtration treatment is greater than 100 g / m ^{2, the} backwash efficiency will be significantly reduced.
It can be seen that the backwash efficiency is slightly reduced even when it is smaller than / m ² . Further, FIG. 3 shows the rate of increase in the filtration pressure difference immediately after backwashing when filtration and backwashing were repeated 20 to 100 times. From this figure, it can be seen that the smaller the amount of suspended solids captured by one filtration process, the greater the rate of increase in the filtration differential pressure immediately after backwashing.

From the results of FIG. 2 and FIG. 3, the backwash timing was such that the amount of suspended solids captured by one filtration treatment was 5 g / m ^{2 to} 100.
It can be seen that it is appropriate to set it in the range of g / m ² .

On the other hand, there is an appropriate range for the rise width of the filtration differential pressure in one filtration treatment, to suppress clogging of the micropores and to obtain a sufficient backwash effect under common-sense backwash conditions. Another experiment has shown that the rise width of the filtration differential pressure in one filtration treatment must be within 1 kg / cm ² .

By the way, the relationship between the amount of trapped solids per unit filtration area and the rise of the filtration differential pressure is as shown in FIG. 1, and the amount of trapped solids per unit filtration area is 5 to 100g which is appropriate for the backwash timing. The increase of the filtration differential pressure in the range of / m ² varies depending on the filtration resistivity and the filtration rate of the suspended solids.
A readily filterable suspension with a filtration specific resistance of 10 ¹² m / kg was filtered at a filtration rate of 1 m ^2.
When the filtration treatment is carried out at / h · m ² , the amount of trapped solids per unit filtration area is 80 g / m ² , and the filtration differential pressure rise is 0.5 kg / cm ² . On the other hand, when a difficult-to-filter suspension with a filtration resistivity of 10 ¹⁴ m / kg is filtered at a filtration rate of 1 m ³ / h · cm ² , even if the filtration differential pressure rises by 1 kg / cm ² , it will be captured. The solid content is only 3 g / m ² , which is not within the proper range.

Therefore, to continue long-term stable filtration and backwash flame filtration of the suspension of the filtration resistivity 10 ¹⁴ m / kg in the case of the filtration rate 0.5m ³ / h · m ^2, filtered difference Pressure rise is 0.7-1kg / cm
² (captured solid content 5 to 7 g / m ² ) and filtration rate 0.1 m ³ / h / m ² increase of filtration differential pressure is 0.15 to 1 kg / cm ² (captured solid content 5
~ 30g / m ² ).

Accordingly, performs backwash within amount of suspended solids of 5g / m ² ~100g / m ² to capture in a single filtration, and trapping of suspended solids last when within this range By adjusting the filtration speed so that it rises within the range of 1 kg / cm ² within the filtration differential pressure immediately after backwashing, the filtration process and backwashing can be continued stably for a long period of time, resulting in efficient operation. It becomes possible to do.

(Example) Hereinafter, an example of the present invention will be described.

Using the ceramic filter device shown in FIG. 5, filtration and backwash were repeatedly performed by the once-through method as follows. That is, in FIG. 5, the valve 7 is closed, and the liquid to be treated in the liquid to be treated tank 3 is guided by the pump 4 to the ceramic filter storage container 2 through the liquid supply pipes 11 and 13 and the valve 6, and the filtration treatment is performed here. Then, the processing liquid is piped through the valve 8.
Flush to 15. According to this method, first, a suspension (iron content of 10 ppm) containing easily filterable α-F _e2 O ₃ (filtration specific resistance: 10 ¹² m / kg) as a solid content was filtered at a filtration rate of 1 m ³ / h · m ² The filtration treatment was repeated and backwashing was repeated when the filtration pressure difference increased by 0.5 kg / cm ² . In this case, the amount of solids captured by one filtration process was 80 g / m ² .

Next, non-filterable amorphous iron colloid (filtration specific resistance: 5 ×
Suspension containing 10 ¹⁴ m / kg) as solid content (iron content 10pp
m) is filtered at a filtration rate of 0.1 m ³ / h / m ² to obtain a filtration differential pressure of 1 kg / c.
Backwashing was repeated when m ^{2 was} raised. In this case, the amount of solid matter captured by one filtration treatment was 7 g / m ² .

On the other hand, for comparison with the invention, a suspension (iron content 10 ppm) containing a non-filterable amorphous iron colloid (filtration specific resistance: 5 × 10 ¹⁴ m / kg) as a solid content was filtered at a filtration rate of 1 m ³ The filtration treatment was repeated at / h · m ² , and backwashing was repeated when the filtration pressure difference increased by 1 kg / cm ² . In this case, the amount of solids captured by one filtration process was 0.7 g / m ² .

FIG. 4 shows the filtration differential pressure after the filtration treatment and after the backwash in each cycle of the example and the comparative example. As is clear from this figure, in the examples in which the filtration rate was controlled so that the amount of suspended solids captured by one filtration treatment was within the range of 5 to 100 g / m ² , stable filtration treatment was performed. However, in the comparative example in which the suspended solid content was 0.7 g / m ² in one filtration treatment, the backwashing frequency was high and a sufficient backwashing effect was obtained with each backwashing. Since it could not be obtained, as the treatment progressed, the increase in the filtration differential pressure became so great that the operation became impossible.

[Effects of the Invention] As described above, according to the operating method of the present invention, it is possible to perform stable filtration and backwash regardless of the properties of the liquid to be treated, such as difficulty in filtration and easy filtration. Therefore, it is possible to extend the life of the ceramic filter.

[Brief description of the drawings]

FIGS. 1, 2 and 3 are views showing the operation of the present invention, and FIG. 1 shows trapping per unit filtration area when a suspension having various filtration specific resistances is filtered at various filtration speeds. Fig. 2 is a graph showing the relationship between the solid content and the rise in filtration differential pressure, Fig. 2 is a graph showing the effect of backwashing, and Fig. 3 is a graph showing the amount of solids captured in one filtration treatment and the filtration pressure difference immediately after backwashing. It is a graph which shows a rate of increase. FIG. 4 is a graph showing the effect in the embodiment of the present invention, and FIG. 5 is a system diagram showing a ceramic filter device. 1 ... Ceramic filter 2 ... Ceramic filter container 3 ... Liquid tank for treatment 4 ... Pump 13 ... Supply pipe 15 ... Filtration and discharge pipe

Claims (3)

(57) [Claims] Claim: What is claimed is: 1. A method for operating a ceramic filter, wherein a liquid to be treated is subjected to a filtration treatment, the filtration performance is restored when the filtration differential pressure rises or the filtration speed decreases, and the filtration treatment is repeated. When the rate of increase in the filtration differential pressure per unit mass of the solid content or the rate of decrease in the filtration rate is large, the filtration rate is decreased. Conversely, when the rate of the increase or decrease is small, the filtration is performed. A method for operating a ceramic filter characterized by increasing the speed. 2. When the amount of solids captured by the filter in the filtration process is 5 to 100 g / m ² , the filtration pressure difference is within 1 kg / cm ² from the initial pressure difference after the previous backwashing. The method for operating a ceramic filter according to claim 1, wherein the filtration rate is adjusted so as to increase. 3. The method of operating a ceramic filter according to claim 1, wherein backwashing is performed when the amount of solids captured by the filter in the filtration step is 5 to 100 g / m ² .