EP1926545A1

EP1926545A1 - Method and device for microfiltering solid substance-containing liquids

Info

Publication number: EP1926545A1
Application number: EP06761289A
Authority: EP
Inventors: Roman Inderbitzin
Original assignee: PILATUS FILTER AG
Current assignee: PILATUS FILTER AG
Priority date: 2005-09-06
Filing date: 2006-08-18
Publication date: 2008-06-04
Also published as: WO2007028261A1

Abstract

The invention relates to a method and device for microfiltering solid substance-containing liquids, wherein a filtering performance decrease caused by a covering layer formation is diminished by the operation of a low excess-pressure filter on the input side and a filtering performance is increased by applying an underpressure on a filtrate side. The underpressure is produced by the use of a special filtering pump. Surprisingly, it is displayed that the covering layer formation is substantially delayed when a driving force, a pressure difference respectively, is primary produced by applying an excessive pressure on the filtrate side and non by the application thereof on the input side. In order to obtain a quasi-continuous operation with a permanent filtering performance by automatically cleaning the filter, the covering layer consisting of impurity particles is removed, when a threshold pressure is attained, by the combination of a short term backflushing and cleaning of the filter surface by a high-pressure nozzle.

Description

Process and apparatus for microfiltration of solids laden fluids

Field of the invention

The present invention relates to a method for microfiltration solids in asteter fluids with the features of the preamble of claim 1 and a device for microfiltration solids laden fluids having the features of the preamble of claim 10th

Background of the invention

In many industrial processes, wastewater streams are produced, which are loaded with ultrafine solid particles in suspended or colloidal form. Prior to discharge into public sewers or rivers, these effluents have to be treated in accordance with legal requirements in order to reach certain limit values. Frequently residual currents of other fluids accumulate, which otherwise have to be disposed of. A more ecological, and often more cost-effective, variant is the at least partial recirculation of process fluids, since in this case processing can not be carried out according to legal limit values but according to the internal requirements of the process.

In the recycling of process fluids in particular membrane methods have proven that can be optimally adapted to the specific requirements in terms of quality. Since these processes are carried out at moderate temperatures (in contrast, for example, for evaporation) and without the use of auxiliaries (in contrast, for example, to adsorption or precipitation processes). In many cases, they also allow the recovery of valuable raw materials from the process streams.

The membrane process for separating finely divided (suspended or colloidal) solids is the so-called microfiltration, in which porous membranes with pores in the order of a few microns to about 0.1 microns are used. In this case, the contaminated fluid (feed) under pressure (usually 0.5 to 5 bar) is pressed through the porous material, whereby solid particles which are larger than the pores of the filter material, similar to a sieve, are retained. The purified fluid is withdrawn on the back or filtrate side of the filter as a so-called filtrate.

Filtration performance, or filtrate flow, is generally accepted by the relationship

Filtrate flow = driving force / filter resistance (equation 1)

given as the driving force in the microfiltration exclusively the pressure difference between the inlet side and filtrate side of the filter acts. According to the state of the art, microfiltration systems are therefore operated such that an overpressure is generated with the aid of the feed pump for feeding the filter and the filtrate is passively discharged. The filter resistance is not a constant, but is continuously increased by the formation of a cover layer of dirt particles on the filter. In order to obtain a constant filtrate flow, the person skilled in the art compensates for this increase in resistance by increasing the inlet-side overpressure. Since for stability reasons, and also for reasons of economy, this pressure increase can not be continued arbitrarily, a filter must be periodically cleaned, that is, the cover layer must be removed from the filter. The person skilled in the art is aware of two principal process variants of microfiltration. In the so-called cross-flow operation, the membrane is tangentially overflowed, wherein the purified filtrate, which passes through the membrane, discharged on the back and a concentrate containing the retained solids, is pumped in the circulation. The overflow of the membrane, the formation of a cover layer is difficult, so that the decrease in power is delayed and cleaning only at longer intervals necessary. On the other hand, the concentrate must still be able to be pumped around easily, so that the concentration is limited and a liquid waste stream is obtained, which must be disposed of or further processed. Another disadvantage is the high energy requirement for the. Membrane overflow must be spent.

In so-called dead-end filtration, the membrane is directly flowed through by the medium to be filtered. All retained particles deposit on the membrane. It creates a cover layer more quickly and it is also more compact overall than in the cross-flow filtration. This cover layer of dirt particles must therefore be removed more frequently, which requires an interruption of the filtration and in many cases a considerable maintenance. The advantages of this mode of operation are the significantly lower energy requirement and the higher concentration or the higher yield of purified filtrate.

Summary of the invention

The object of the invention is to provide a method for the filtration of solids-loaded fluids, which operates robustly and continuously, and does not or only to a lesser extent have the disadvantages of the abovementioned methods. It should allow the most complete possible separation of liquid and solids and reduce personnel-intensive manipulation to a minimum. Another object of the invention is a To provide apparatus for the filtration of solids contaminated fluids, which does not have the disadvantages of the above-mentioned devices.

These objects are achieved by a method according to claim I and a device according to claim 10. In the filtration process, dead-end filtration is performed so that the reduction in filtrate performance is minimized by topcoat formation and automatic filter cleaning enables quasi-continuous operation with constant filtrate performance.

The decrease in the filtrate through cover layer formation is inventively reduced by the fact that the filter is operated at low pressure on the inlet side and the filtrate performance is increased by applying negative pressure on the filtrate side. The negative pressure is preferably generated by the use of a special filtrate pump. Surprisingly, it has been shown that the formation of the cover layer is greatly delayed if the driving force or the pressure difference is generated at least partially by the application of a negative pressure on the filtrate side, and not exclusively by applying an overpressure on the inlet side. Depending on the type and amount of solids contained in the feed or the tendency for topcoat formation, an optimum result is achieved when the differential pressure is generated to 25 to 60% by negative pressure on the filtrate side. In order to achieve a constant filtrate performance, the pressure in an inventive mode of operation must therefore be increased substantially more slowly than would be the case without known filtrate pump according to the prior art.

The results of a direct comparison in the microfiltration of a water contaminated with 2 ppm of fine particles in a constant filtrate flow, as shown in the following table, clearly show the effect of applying a negative pressure on the filtrate side: Differential pressure (bar)

Time with filtrate pump without filtrate pump

(Minutes)

10 0.07 0.15

20 0.1 0.35

30 0.13 0.95

40 0.16 1.85

2.4

60 0.27

80 0.4

1 10 0.7

125 1.55

2.5

If a differential pressure of more than 2.5 bar is reached, in this case the filtration must be interrupted and the filter must be cleaned. Without the use of the permeate pump, this is 2-3 times more necessary.

The negative pressure on the filtrate side is determined according to the present invention on the basis of preliminary experiments and the filtrate performance kept constant by continuously increasing the pressure on the inlet side and / or increasing the negative pressure on the filtrate side. Upon reaching a predetermined limit pressure, an automatic cleaning is performed. It consists in a combination of short-term backwashing to loosen the top layer and a cleaning of the filter surface by a high-pressure nozzle cleaning. Investigations with different test fluids have shown that this combination cleans the filter particularly efficiently and after the cleaning according to the invention the original filtrate performance is again achieved. In both cleaning steps is preferably pure filtrate used so that no additional fluid or chemicals are needed for the periodic cleaning. For the backwashing, the same pump can be used in a preferred embodiment by means of a device for reversing the flow, as for the generation of the negative pressure on the filtrate side.

Purification by backwashing is state of the art in microfiltration. An additional cleaning with high-pressure nozzles, however, is only possible from the outside and with reasonable effort in the conventional pipe membranes only at complete standstill of the system and disassembly of the filter. The inventive use of a conical filter with a large clear diameter allows automated periodic see cleaning using a corresponding cleaning process and a corresponding cleaning device and thus a quasi-continuous operation.

Brief description of the figures

FIG. 1 shows the structure of the filtration device.

Detailed description of preferred embodiments

A microporous filter I _1, preferably a hollow cylinder, which is sealingly installed in a housing 2 at the top and bottom and closed at a lower outlet end with a drain valve 3, from the upper end by means of a feed pump 4 via an open inlet valve 10 with the cleaning fluid from a reservoir 23 fed. The fluid is, for example, a process stream which is loaded with fine, colloidal or suspended solids. The feed pressure is adjusted via the inlet pressure regulator 5 so that the flow rate measured by the flow meter 6 remains approximately constant during a filtration cycle. The pressure difference between inlet side and filtrate side is in the inventive method between 0.05 and 10.0 bar, preferably between 0.1 and 2.5 bar. The filtrate collects after passing through the filter 1 in an outer space 7 and is sucked from there by means of a Filtratpumpe 8 with opened first and second filtrate valves 13 and 14 and closed second and first backwash valves 1 5 and 16, wherein a negative pressure on the filter back in the outer space 7 of the dense and pressure-stable housing 2 is formed. The negative pressure on the filtrate side can be adjusted via a filtrate pressure regulator 9 and accounts for between 20 and 90%, preferably between 25 and 60%, of the differential pressure in the methods according to the invention. In the embodiment of Figure 1, the filtrate is collected in an intermediate container 22. This is either emptied periodically, or the filtrate is removed via a derivative, not shown. As described below, the particle-enriched retentate or concentrate is conveyed batchwise via a drain line 25 when the drain valve 3 is open by a drain pump 11 into a concentrate container 12.

When the pressure measured by the inlet pressure regulator 5 on the inlet side reaches a predetermined upper limit value, the filtration process is interrupted, that is to say the inlet pump 4 is switched off and the inlet valve 10 is closed. The filtrate pump 8 continues to run for an adjustable period of time and the first and the second filtrate valves 13 and 14 remain open, so that the contents of the hollow cylinder 1 are filtered and the filtrate is pumped into the intermediate container 22. In this case, the filtrate 7 also partially deflates, which has been found to be positive in a practical experiment.

In a first cleaning step, after emptying the filter contents, a first and a second backwash valves 16 and 15 are opened, the first and second filtrate valves 13 and 14 are closed and the filtrate pump 8 is operated for a short time in the reverse direction, that is, the filtrate pump 8 switched on for an adjustable short time. The filtrate 8 presses a small amount of filtrate from the intermediate container 22 of the Outside of the filter cylinder 1 in its interior, whereby the cover layer is detached or at least loosened.

In a second cleaning step, the filtrate pump 8 is turned off, the backwash valves 15 and 16 are closed and the inner surface of the hollow cylinder 1 is freed from the cover layer by at least one spray jet of filtrate. The filtrate is conveyed from the intermediate container 22 with the high-pressure valve 17 open through a high-pressure line 26 to at least one cleaning nozzle 19, which is arranged in the interior of the hollow cylinder 1. In the embodiment of Figure 1, two nozzles 19 are shown, which are arranged offset by 180 ° on a cleaning arm 20 in the center of the filter body 1. The filtrate is sprayed from the nozzles 19 radially on the dirty inner surface of the filter and removes the previously loosened cover layer or the remains of the cover layer, which still adhere to the filter surface. The cleaning is carried out at a pressure of 10 to 30 bar, preferably 20 bar. As nozzles, all commercially available nozzle types can be used, whereby it must be ensured that the entire inner surface of the filter body is uniformly covered by the high-pressure jet. The fluid with the solids originating from the covering layer is pumped off into the concentrate container 12 during the cleaning processes with the pump 11 when the valve 3 is open. After switching off the high pressure pump 18 and closing the valves 17 and 3, the inlet valve 10 is opened again, and the feed pump 4 is turned on and started a new filtration cycle.

The cleaning arm is rotatable in a preferred embodiment by 360 ° and there are performed several complete rotations per cleaning cycle. In an advantageous embodiment, not shown in the figure, a plurality of high-pressure cleaning nozzles 19 are fastened to each other on a cleaning arm 20 rotatable by at least 360 °, which can be rotated by a drive 21 about its own longitudinal axis. If the cleaning arm is equipped with two rows of nozzles offset by 180 °, it is sufficient in accordance with a rotation of the cleaning arm 20 by at least 180 °. The cleaning arm according to a further preferred embodiment is also arranged axially displaceable, so that a single nozzle, which is arranged at a lower end region of the cleaning arm, sufficient to clean the entire inner surface of the filter.

The hollow cylindrical filter is conically shaped in a preferred embodiment with a height of 20 to 100 cm, preferably between 30 to 60 cm and has an upper diameter of 10 to 60 cm, preferably 15 to 40 cm, and a lower diameter of 4 to 25 cm, preferably from 5 to 15 cm, on. This form not only allows a particularly efficient cleaning by rotating high-pressure nozzles, but it has also proved to be particularly stable with respect to the alternating pressure load from inside and outside.

In the following, three application examples of methods and devices according to the invention are given:

Example 1 :

Feed: Test mixture with 2 ppm of silicate pigment of grain size 0.1 to 100 μm in water.

Filter Multilayer steel wire mesh laminate, finest machine width 1 μm

Filter area: 0.339 m ²

Filtrate flow: 4500 liters / h (constant)

Frequency of cleaning cycles 120-130 minutes Retentate amount per cleaning cycle 40 liters Filtrate yield> 99.5%

Example 2:

Feed: process water from a wire erosion plant (solids loading 5 ppm)

Filter Multilayer steel wire mesh laminate, finest mesh size 5 μm

Filter area: 0.137 m ²

Filtrate flow: 3000 liters / h (constant)

Example 3:

Inlet: lightly contaminated tap water

Filter ceramic filter with a nominal pore size of 0.1 μm

Filter area: 0.137 m ²

Filtrate flow: 400 liters / h (constant)

Frequency of cleaning cycles 180-200 minutes amount of retentate per cleaning cycle 12 liters filtrate yield> 99%

In a further preferred embodiment, two or more filter units operated in parallel are switched so that the periodic cleaning never takes place simultaneously, so that the filtration can be operated without interruption.

Suitable materials of the hollow cylindrical filter are all sufficiently pressure-resistant microfiltration membranes in question. Preferred materials are stainless steel or ceramic. special Materials which have a finer pore on the inside of the hollow cylinder are suitable since, in the case of such filters, the cover layer is inferiorly anchored and therefore can be cleaned particularly efficiently. Surface filters of the preferred type can consist of several layers of metal mesh of different fineness or of sintered metals with a finer inner layer or of ceramic shaped bodies with a coating of finer ceramic. If necessary, these materials can be additionally protected on the outside with a metal grid against deformation by negative pressure.

In experiments with various industrial residual streams, for example process water from grinding, emery, water jet cutting and erosion plants, waste water from the paint and ceramics industry, fruit and vegetable juices, food and hydraulic oils, etc., the recovery rate of purified fluid was typically over 98.5 %, often over 99%.

List of reference numbers

1 filter

2 housings

3 drain valve 4 feed pump

5 inlet pressure regulator

6 flow meters

7 outdoor space

8 filtrate pump 9 outlet pressure regulator

10 Inlet valve π Drain pump

12 concentrate containers

13 First filtrate valve 14 Second filtrate valve

15 Second backwash valve

16 First backwash valve

17 high pressure valve

18 high-pressure pump 19 cleaning nozzles

20 cleaning arm

21 drive

22 intermediate container

23 storage tank 24 supply line

25 drain line

26 high pressure line

Claims

claims

A process for the microfiltration of solids-laden fluids in which a contaminated raw fluid is fed to an inlet side of a filter (1), and the purified filtrate is discharged from a filtrate side of the filter, characterized in that the

Pressure difference as a driving force of microfiltration is at least partially generated by the application of a negative pressure on the filtrate side.

2. The method according to claim 1, characterized in that the fluid to be cleaned is acted upon on the inlet side of the filter under pressure.

3. The method according to claim 1 or 2, characterized in that the pressure difference between inlet side and filtrate side between 0.05 and 10.0 bar, preferably between 0.1 and 2.5 bar, wherein the negative pressure on the filtrate side between 20 and 90%, preferably between 25 and 60% the differential pressure.

4. The method according to any one of the preceding claims, characterized in that the filtrate is withdrawn under reduced pressure with a Filtratpumpe (8).

5. The method according to any one of claims 1 to 5, characterized in that the method comprises a dead-end filtration.

6. The method according to any one of claims 1 to 5, characterized in that after reaching a Crenzdruckes the inlet is turned off and backwashed in a first cleaning step and then in a second cleaning step, the inlet-side surface is freed with a fluid under high pressure from a cover layer , 7. The method according to claim 6, characterized in that backwashing and high-pressure cleaning with filtrate take place.

8. The method according to claim 6 or 7, characterized in that the backwashing takes place via a device for reversing the flow with the filtrate pump (8).

9 The method according to any one of claims 1 to 8, characterized in that two or more filtration units are operated in parallel and the periodic cleaning of these units is carried out sequentially, so that the filtration is interrupted at any time.

Device for microfiltration of solids-laden fluids comprising a filter (1) with an inlet side and a filtrate side, characterized in that a filtrate pump (8) can be brought into operative connection with the filtrate side, so that a negative pressure can be applied to the filtrate side.

1 1 Apparatus according to claim 10, characterized in that the filter (1) is a microporous hollow cylinder with a conical shape.

12 Apparatus according to claim 1 1, characterized in that the hollow cylinder made of stainless steel or ceramic

13. Device according to one of claims 1 1 or 12, characterized in that in the interior of the hollow cylinder at least one cleaning nozzle (19) on a cleaning arm (20) is arranged.

14 Apparatus according to claim IS, characterized in that the cleaning arm (20) is rotationally movable and / or axially movable driven. Device according to one of claims 10 or 14, characterized in that the filtrate pump (8) via a device for flow reversal for the backwashing of the filter (1) can be used.