WO2003084650A1

WO2003084650A1 - Cross-flow filtration installation

Info

Publication number: WO2003084650A1
Application number: PCT/CH2003/000195
Authority: WO
Inventors: Eduard Hartmann
Original assignee: Bucher-Guyer Ag
Priority date: 2002-04-10
Filing date: 2003-03-25
Publication date: 2003-10-16
Also published as: CN1646210A; EP1492614A1; PL370708A1; AU2003210115A1

Abstract

The invention relates to a cross-flow filtration installation comprising at least one filter element (1) to which a substance mixture from a product tank (2) can be supplied via a supply line (3). Rinsing water can also be supplied to the filter element (1) from a rinsing water tank (14). According to the invention, a supply line shut-off valve (28) is arranged in front of the entrance of the supply line (3) in the filter element (1), and a compressed air line (25) ends on the input side of the filter element (1) and can be blocked by means of a compressed air shut-off valve (26). The supply line shut-off valve (28) is embodied in such a way that it closes automatically in the event of a disturbance, while the compressed air shut-off valve (26) and other valves (9, 11; 12) are embodied in such a way that they automatically open. In the event of disturbances, for example as a result of a power failure, the residue in the filter element (1) is displaced by means of compressed air such that blockages are not created when the installation is not in operation. Operating disturbances caused by blockages of the filter element (1) are thus avoided.

Description

Cross-flow filtration plant

The invention relates to a cross-flow filtration system of the type mentioned in the preamble of claim 1.

Such cross-flow filtration systems are used advantageously when it comes to molecularly disperse or colloidally disperse substance mixtures, at most with proportions of solid or To filter suspended solids. Examples of such mixtures of substances are mixtures of substances which initially arise in the production of fruit and fruit juices. These mixtures of substances are then separated by filtration into clear fruit or fruit juice on the one hand and the essentially remaining turbid substances on the other. For example, activated carbon can also be added to the mixture of substances before the filtration in order to achieve certain effects. This activated carbon must then also be separated from the liquid with the cloudy substances.

A cross-flow filtration system of the type mentioned in the preamble of claim 1 is known from WO-Al-01/51186. A solution is shown here how blockages of the filtration module can be removed by fixed retentate portions. The problem with systems of this type is that the filter elements can become blocked, so that production has to be interrupted in order to first remove the blockages. Production interruptions are undesirable.

From EP-AI-0 669 159 a method for backwashing filtration modules is known. Since this is about filtration modules for water purification, there are no problems comparable to the production of fruit and fruit juices.

A membrane filter system is known from WO-A2-02 / 26363. It contains a device for fumigation. By gassing the mixture of substances to be filtered, the pressure difference between the inlet and outlet of the membrane filter module can be changed, so that it becomes zero, for example, which should improve the efficiency of the filtration system.

It is known from Swiss patent application 2242/01 to monitor the viscosity of the mixture of substances during the filtration process. This means that constipation does not occur at all. From WO-Al-00/03794 a filtration system is known in which, after the completion of a filtration cycle, rinse water can be fed in via a valve, which serves to displace highly viscous retentate residues from the filter unit. Such a flush can prevent clogging if it is initiated in good time. The initiation of the rinsing is not without problems, however, because the viscosity changes suddenly. Thus, despite the timely initiation of a rinse, the retentate can become blocked in the membrane tubes of the filtration module.

From Swiss patent application 0204/02 it is known to carry out the flushing in such a way that the sudden change in viscosity is prevented.

It is also known (WO-A2-01 / 15797) to operate the storage tank of such a system, the so-called batch tank, under pressure. The mixture of substances to be filtered is subject to a certain pressure, which is generated, for example, by compressed air. This has the advantage that the pump used to convey the mixture of substances has to produce less power.

Various configurations of cross-flow filtration systems are therefore known which enable safe operation. Basically, however, there is the problem that unpredictable malfunctions can also occur which lead to the interruption of operations. For example, there may be a power cut that causes the cross-flow filtration system to stop immediately. If the retentate has already reached a high viscosity during the course of the process, the standstill of the feed pump leads to the retentate standing still in the filter element. This can lead to blocking of the filter element, which makes it impossible to restart the delivery. The filter element must then be removed and cleaned by hand, but this is not always possible.

The invention has for its object to provide a cross-flow filtration system in which blockages of the filter element are avoided even in the event of unforeseeable events.

The stated object is achieved according to the invention by the features of claim 1. Advantageous further developments result from the dependent claims. An exemplary embodiment of the invention is explained in more detail below with reference to the drawing.

The only figure shows a schematic of a cross-flow filtration system.

In the figure, 1 denotes a filter element in which the desired liquid phase is separated from the mixture of substances. The design of the filter element 1 is not important. The invention is primarily used when the filter element 1 contains, for example, straight or wound tubular membranes or capillary tubes, since such filter elements 1 mostly process substance mixtures with high turbidities. If parts of the filter element 1 become blocked, this regularly leads to an interruption in operation with all its disadvantageous consequences.

The mixture of substances to be filtered is located in a product tank 2. From there it passes through a feed line 3 to the filter element 1. A feed pump 4 and a flow meter 5 are inserted into the feed line 3, the speed of the feed pump 4 through the flow meter 5 in the manner It can be controlled or regulated that either the delivery rate through the feed line 3 or the pressure in the feed line 3 at the input of the filter element 1 remains constant. This enables economical production in a known manner.

In the outlet of the product tank 2, which opens into the feed line 3, there is a tank shut-off valve 6, which can be actuated by a motor or pneumatically. On the secondary side of the filter element 1, a permeate line 7 is connected to it, through which the permeate separated off in the filter element 1, for example the clear fruit juice, can be removed.

On the other hand, a return line 8 leads from the filter element 1 to the product tank 2, in which the retentate is returned from the filter element 1 to the product tank 2. In this return line 8, a throttle valve 9 is inserted, which can also be actuated by a motor or pneumatically. This throttle valve 9 can be controlled by a retentate line pressure sensor 10, which detects the pressure at the retentate inlet of the filter element 1. A further retentate line pressure sensor 10 ′ can be arranged on the return line 8 directly behind the filter element 1. The one from the Pressure sensor 10 detectable pressure in the feed line 3 immediately before the filter element 1 is related to the delivery rate of the feed pump 4 and the state of the filter element 1. The higher the viscosity of the mixture of substances, the higher the flow resistance. An increase in viscosity can be caused, for example, by an increased proportion of solids or suspended matter in the mixture of substances. In

Depending on this penetration resistance, the throttle valve 9 can now be opened or closed more or less by motor or pneumatically. Before the return line 8 opens into the product tank 2 there is a return line shut-off valve 11 which is always open when the retentate leaving the filter element 1 is to be returned to the product tank 2.

The mixture of substances in the product tank 2 is conveyed to the filter element 1 with the aid of the feed pump 4 when the tank shut-off valve 6 is open. Permeate is separated from the mixture of substances in filter element 1. The retentate is returned to the product tank 2 through the return line 8 with the return line shut-off valve 11 open. As a result, the viscosity of the circulating mixture of substances increases in the course of the filtration process, because the proportion of solid or suspended substances in the mixture of substances increases the more permeate has been separated in filter element 1. At the same time, the filtration performance drops. When the viscosity of the mixture of substances has reached a certain level, the filtration must be stopped, and in good time so that the filter element 1 cannot become blocked. The circulating mixture of substances can therefore be removed from the circuit by opening an outlet valve 12 which is arranged behind the filter element 1.

If the filtration process is to be started, the mixture of substances to be filtered is first fed to the product tank 2 via a product line 13. The feed pump 4 then goes into operation. Initially, the mixture of substances contained in the product tank 2 is relatively low-viscosity. The feed pump 4 is controlled so that the delivery rate through the supply line 3 remains constant. Permeate is separated off in the filter element 1, so that the retentate leaving the filter element 1 has a higher viscosity. This retentate is returned to the product tank 2. Its amount is smaller because of the deposition of permeate in the filter element 1. To compensate, 13 additional substance mixture is fed through the product line. As the process progresses, the viscosity of the mixture of substances in the product tank 2 increases further and further. Leading then to the fact that when the feed pump 4 keeps the delivery rate through the feed line 3 constant, the pressure detectable with the retentate line pressure sensor 10 increases. Because this pressure must not exceed a certain limit value with regard to the load capacity of the filter element 1, the feed pump 4 is then regulated so that this limit value is not exceeded. The filtration performance then drops.

This then leads to a condition that the filtration capacity becomes too low for economical operation and is ultimately no longer safe. Then the filtration should be ended. However, the feed pump 4 of the filtration system must not be switched off because this would inevitably lead to a blockage. It is now necessary to displace the mixture of substances in the system. This is done in a known manner by rinsing. So that the product located on the secondary side of the filter element 1, the permeate, is not diluted by rinsing water, it is drained off before the rinsing process begins.

Therefore, a rinse water tank 14 is provided, from which rinse water can be fed into the feed line 3 through a rinse line 15. In the course of the flush line 15, a flush line shut-off valve 16 is used. Between the rinse water tank 14 and the rinse line shut-off valve 16 there is another element, the task of which is to prevent significant amounts of the mixture of substances from flowing back from the feed line 3 to the rinse water tank 14 when the rinse line shut-off valve 16 is opened. During the transition from the filtration to the flushing process, the tank shut-off valve 6 is closed more or less simultaneously and the flushing line shut-off valve 16 is opened. The tank shut-off valve 6 and the flushing line shut-off valve 16 are actuated by a control unit 20, with which the filtration process can be controlled. When the flushing line shut-off valve 16 is opened more or less simultaneously and the tank shut-off valve 6 is closed, a mixture of substances from the product tank 2 could flow to the flushing water tank 14 as a result of a level difference H between the content in the product tank 2 and the content in the flushing water tank 14 Level difference H has a certain size, it must also be taken into account that the density in the product tank 2 is greater than that of the rinse water in the rinse water tank 14. This penetration of significant amounts of the substance mixture in the direction of the rinse water tank 14 is prevented by the element mentioned. There with known filtration systems, the rinsing line 15 is usually several meters long, the rinsing water tank 14 is spared from the ingress of substance mixture. The water contained in the rinse water tank 14 is therefore not contaminated.

This element preventing the mixture reflux is either a check valve 17 or a reflux throttle 17 ', as is known from the Swiss patent application 0204/02.

At the end of a previously described production cycle, there is 1 rinsing water in the filter element. The cross-flow filtration system can now be switched off. Maintenance work can then also be carried out.

Such a cross-flow filtration system can therefore be operated very safely and economically. In normal operation, blocking of the filter element 1 can be excluded with certainty. However, there is the problem that a malfunction leads to the system being shut down, as mentioned at the beginning, and above all a power failure can be the cause of the malfunction. However, other defects are also possible.

According to the invention it is therefore provided that a compressed air line 25 opens into the supply line 3 to the filter element 1 and can be shut off by a compressed air shut-off valve 26. By opening the compressed air shut-off valve 26, the retentate located in the filter element 1 is displaced from the filter element 1 by means of compressed air. So that the compressed air does not penetrate into the feed line 3 and the feed pump 4 and the flow meter 5 arranged therein, it is also necessary to arrange a feed line shut-off valve 28 in the vicinity of the filter element 1 in the feed line 3.

The outlet valve 12 known from the Swiss patent application 0204/02 is advantageously arranged directly behind the filter element 1, as shown in the figure.

So that in the event of a power interruption through which the control unit 20 is no longer functional, the retentate is immediately displaced from the filter element 1 before it can block, the compressed air shut-off valve 26 is designed according to the invention in such a way that it opens automatically when there is no control. At the same time, the supply line shut-off valve 28 is such that it closes automatically when there is no control. The throttle valve 9 and the return line shut-off valve 11 or the outlet valve 12 are also designed such that they open automatically when there is no control. If the throttle valve 9 and the return line shut-off valve 11 are of such a nature, the retentate displaced by means of compressed air from the filter element 1 is fed into the product tank 2, which is generally sensible. Alternatively, the outlet valve 12 can also be designed so that it opens automatically. The retentate displaced from the filter element 1 is then passed into a collecting trough 30, so that the maintenance personnel can later decide what should happen to this part of the retentate.

So if a fault occurs, be it due to a power failure or by operating an emergency stop switch, the compressed air shut-off valve 26 on the one hand and the return line shut-off valve 11 or the outlet valve 12 on the other hand open automatically, while the supply line shut-off valve 28 closes automatically , Without the need for an operation, it is thus achieved that the retentate located in the filter element 1 is instantly displaced from the filter element 1 by compressed air.

The aforementioned automatic opening and closing of the valves can be solved in various ways depending on the type of valve and the type of control and also depending on the type of fault. For example, opening or closing in the event of a fault is possible by spring force as well as by a pneumatic control.

The compressed air line 25 advantageously has a memory 32. This means that a sufficient amount of compressed air is available in the immediate vicinity of the cross-flow filtration system. In fact, there is often the problem that compressed air lines which are in operation do not have a large cross section and are relatively long. This memory 32 is advantageous in order to guarantee that the filter element 1 is blown out completely and quickly. The size of the store 32 depends on the conditions of the cross-flow filtration system, namely in particular on the dimensions of the filter element 1. Since the generation of compressed air is also ended in the event of a power failure, this store 32 can therefore be indispensable, depending on the conditions of the system to ensure sufficient security.

For reasons of clarity, control lines leading from the control unit 20 to the compressed air shutoff valve 26 and to the supply line shutoff valve 28 are not shown. The compressed air in the accumulator 32 advantageously has a pressure of at least 3 bar. The upper limit for the pressure is given by the load limit for the filter element 1 or its membrane tubes.

If no powerful compressed air system is available, another compressed gas can be used instead of the compressed air, for example nitrogen, which can be removed from a high pressure bottle 34. The reservoir 32 is then supplied with compressed gas from this high-pressure bottle 34, which can be done automatically by means of a pressure reducing valve 35 without the supply of external energy.

The person skilled in the art is surprised that the solution described here, of being able to displace the retentate from the filter element 1 by means of compressed air, actually works, because he knows that the displace- ment of the retentate by means of rinsing water can be problematic, as described at the beginning of the commentary on Al-00/03794 has been mentioned. This is because there may well be a partial blockage of the filter element 1. This has to do with the fact that the filter element 1 generally consists of a larger number of parallel membrane tubes. If rinse water is now suddenly conveyed, which displaces the more viscous mixture of substances from the filter element 1, it can happen that the more viscous mixture of substances remains in individual membrane tubes of the filter element 1, while it is displaced from other membrane tubes by the rinse water. At that point in time, the fewest solids are found in the membrane tube, which has the lowest filtration capacity due to the tolerances of such membrane tubes. This membrane tube is consequently flushed out of the rinse water first. So that the rinse water can flow through this membrane tube unhindered, with the result that the differential pressure drops over the length of the membrane tubes, which can then lead to the fact that the remaining differential pressure is no longer sufficient to flush other membrane tubes loaded with more solids.

So it is surprising that the membrane tubes can be freed from the retentate using compressed air, as detailed tests have shown. The surprising effect of compressed air is likely to be related to its compressibility. Even when using compressed air for flushing, the membrane tube that is least loaded with solids is flushed out first. As soon as the membrane tube in question is free, the flow rate of the compressed air through this membrane tube will increase sharply and although clearly above the flow rate that is generated with rinse water, because the flow rate of the rinse water is determined by the delivery rate of the feed pump 4 and thus limited. Due to the higher flow velocity of the compressed air, the pressure drop across the membrane tube that was cleared first increases. This has the consequence that a higher differential pressure is available to clear the remaining membrane tubes.

Claims

claims

1. cross-flow filtration system with at least one filter element (1), the substance mixture from a product tank (2) through a supply line (3) can be supplied, a tank shut-off valve (6) between the product tank (2) and the supply line (3) and in which rinsing water can be fed into the supply line (3) from a rinsing water tank (14) via a rinsing line (15) and a rinsing line shut-off valve (16), characterized in that

- That before the inlet of the supply line (3) in the filter element (1) a supply line shut-off valve (28) is arranged and that on the input side of the filter element (1) opens a compressed air line (25) which can be shut off by a compressed air shut-off valve (26) is

- That the supply line shut-off valve (28) is such that it closes automatically in the event of a fault,

- That the compressed air shut-off valve (26) and the throttle valve (9) are such that they open automatically in the event of a fault, and

- That the return line shut-off valve (11) or an outlet valve (12) arranged behind the filter element (1) is such that it opens automatically in the event of a fault.

2. Cross-flow filtration system according to claim 1, characterized in that a memory (32) is arranged in the compressed air line (25).

3. cross-flow filtration system according to claim 2, characterized in that the memory (32) can be charged to a pressure of at least 3 bar.

4. cross-flow filtration system according to one of claims 1 to 3, characterized in that the return line shut-off valve (11) is such that it opens automatically in the event of a fault, whereby the retentate displaced from the filter element (1) by means of compressed air into the product tank (2) is demandable.

5. cross-flow filtration system according to one of claims 1 to 4, characterized in that the outlet valve (12) is such that it opens automatically in the event of a fault, whereby the retentate displaced by means of compressed air from the filter element (1) into a collecting trough (30 ) is eligible.

6. cross-flow filtration system according to one of claims 1 to 5, characterized in that the memory (32) via a pressure reducing valve (35) from a high pressure bottle (34) can be supplied with compressed gas.