DD148859A3 - PROCESS FOR MEMBRANE FILTRATION AND DEVICE FOR THEIR IMPLEMENTATION - Google Patents

Abstract

The invention relates to the field of separation processes in which semipermeable membranes are used. The aim of the invention is a method and a device which ensure an effective and stable membrane filtration of real solutions by reducing the concentration polarization, preventing deposits and permanently removing existing or emerging particles. According to the invention, the feed stream before entering the membrane separation unit, preferably already in the suction nozzle of the pump, is mixed with a gas stream and passed through a suitable separation apparatus after passing through the membrane separation unit and depressurization to ambient pressure. Additional embodiments of the method consist in a partial relaxation of the feed stream prior to contact with the membranes, periodic short-term interruptions of the feed stream and the addition of surface-active substances. Possible fields of application are in membrane filtration with solutions, in particular for those in which particles are contained or arise. In a drawing, the apparatus for performing the method is shown.

Description

Membrane filtration process and apparatus for carrying it out

Field of application of the invention

The invention relates to the field of material separation by means of membranes, in particular ultrafiltration and reverse osmosis. Their use is useful when the concentration polarization reaches high levels, deposits on the membrane occur and when particles are contained in the solution or during membrane filtration arise.

Characteristic of the known technical solutions

It is known that the concentration polarization which inevitably occurs in membrane filtration can be reduced by increasing the flow rate of the solution flowing through the membrane. However, this is limited by stony pressure loss and correspondingly increasing energy expenditure. In addition, the formation of deposits can often not be prevented with certainty. ^ϊ;

It is also known that the substances deposited on the membranes can be removed by periodically carried out rinsing with selected detergents, so that the initial capacity of the system is reached again briefly. Flushing processes, however, reduce the technological

Lending costs for chemicals. Problems arise with regard to the use of the piI-trate obtained during the rinsing and the remaining rinsing agent solution after rinsing has ended. Finally, the operating effort increases. · ".. · '

Also known is the use of cleaning bodies for the elimination or prevention of deposits on the membrane. However, this process must be limited to tubular membrane devices, which in turn have other disadvantages.

Furthermore, it is known that deposits can be largely avoided by a thorough pretreatment. However, this pretreatment is usually very high and increases the overall cost of the process. It has become known, in some special cases, the assignment of such separation processes for membrane filtration, which allow the selective removal of existing and emerging particles from the membrane filtration circuit.

Specifically, this relates once the involvement of a gravity separator in the solution stream, the effectiveness of which is often too low and on the other the utilization of the residual pressure of the solution leaving the membrane separation unit to operate an ejector with subsequent flotation, but which ensures only the deposition of the particles which did not adhere to the separation unit (USP 3917526).

Object of the invention

The aim of the invention is to provide a method and the associated device, which enable a more effective and in the treatment of real solutions stable operation of the membrane filtration.

Explanation of the essence of the invention

The invention has for its object to provide a method for membrane filtration and the device for its implementation by which the concentration polarization re-

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duced, the formation of deposits prevented, existing deposits can be removed and existing or emerging particles can be removed from the solution.

According to the invention the object is achieved in that the Be schickungsstrom before entering the pump, but at the latest before entering the membrane separation unit, a gas stream is supplied and that the mixed with the gas feed stream is relaxed after leaving the membrane separation unit to ambient pressure.

The supply of the feed stream to the separation unit is carried out at elevated pressure, this partial absorption of the gas supplied, but for the most part, an adsorption on'die present in the solution or in the wake of solvent removal resulting particles. The gas which has not been adsorbed or absorbed and the gas bubbles which desorb again during the pressure drop along the flow path lead to the local separation of the boundary layer and thus to a reduction of the concentration polarization compared to the simple membrane filtration.

After leaving the separation unit, the solution stream is depressurized to ambient pressure, thereby again growing the volume of adhering to the particles of gas bubbles, so that they can be deducted in suitable downstream separation apparatuses as foam v / earth. Separation apparatuses which can be used are known flotation tanks, in particular their calming and foam stripping devices.

An improvement of the process is achieved by partially relieving the compressed feed stream with the gas before entering the membrane separation unit, since the particles thus contained are already surrounded by gas bubbles prior to contact with the membrane and thus are not deposited on the membrane can. The reason for this is that the surface tension of the liquid, pore radius, size of the air bubbles and operating pressure after the partial relaxation are in such a ratio that the air bubbles can not be sucked through the pores of the membrane.

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This pressure reduction takes place in part already by the pressure loss on the flow path to the separation unit without additional throttle valve. Another embodiment of the method is to periodically interrupt the feed stream for a short time. As a result, gas bubbles are formed on particles that have already been deposited on the membrane or have formed there, so that detachment from the membrane surface takes place. By then re-entering. Feed stream are washed away these particles surrounded by air bubbles.

In special cases, there is an extension of the method in the addition of surface-active substances to the solution. It comes in solutions with insufficient foam stability and unfavorable particle properties in embossing.

According to the invention, a device for carrying out the method consists of a preferably arranged in the suction line of the pump Gasansaugstutzen with flow control or a-Schnüffelventil on the pump or a supply for compressed gas in the discharge nozzle of the pump, a throttle body, e.g. a throttle valve in front of the separation unit, one of the separation unit downstream known separation apparatus and a controlled by time relay additional off and on switch for the pump motor.

During operation of the pump, this simultaneously sucks in solution and gas in a controllable ratio, mixes both intensively and brings the mixture to the pressure prevailing in the pressure port. The frictional losses and the throttle valve in front of the membrane separation unit provide for a partial relaxation of the feed stream. The separation unit downstream expansion device ensures the pressure build-up in the separation unit and after leaving the separation unit, the relaxation of the solution to ambient pressure. The separation valve connected downstream of the expansion valve allows the floating of the particles surrounded by air bubbles and their removal from the solution with the foam.

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embodiments

The invention will be explained below with reference to embodiments with reference to the accompanying drawings, which show the apparatus for carrying out the method. Show it:

Fig. 1: the device with time relay for periodic

Turn off; Fig. 2: the device with a second gas intake with solenoid valve.

A well-known application of membrane filtration is the treatment of oily wastewater from metalworking, which in addition to emulsified oil contain large amounts of impurities such as grinding dust, .Sand, graphite, dirt, metal shavings. Therefore, the concentration polarization, the deposits on the membranes and the decrease in the filtration performance with increasing concentration are particularly serious.

According to the method according to the invention, the waste water is sucked from the reservoir 1 of the pump 2 according to the first embodiment. The air is mixed in the pump 2 intensively with the feed stream 1 and compressed together with this on the pressure prevailing in the pressure line 5 before the membrane separation unit 7 pressure on the gas intake manifold with the control valve 3. In this case, according to the equilibrium conditions, an adsorption of air to the surface of the particles and larger, already coagulated oil droplets predominantly takes place. When the pressure reduction 6 is passed, a partial expansion of the air-mixed and compressed feed stream takes place before entry into the membrane separation unit 7 surrounded by gas bubbles, so that their deposition on the membranes is impossible. In the membrane separation unit 7, the oil-free filtrate 8 is removed from the wastewater. After passing through the membrane separation unit, the discharge of the feed stream to the pressure reduction 6 and the introduction into the calming and Schaumabstreifkammer 10 takes place.

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When relaxing, the volume of the air bubbles increases again, so that the particles associated with them quickly float and can be withdrawn as a strong oil-containing foam 11. Due to the constant removal of the originally colloidally distributed ingredients of the spent emulsion, the process works continuously. The timing relay 12 in the power supply of the pump motor 13 ensures short-term interruptions of the power supply at predetermined intervals. Due to the almost abrupt drop in the operating pressure to the ambient pressure, particles deposited or formed on the membrane are removed from the membrane by the corresponding gas bubbles and removed from the separation inlet when the feed stream is reinserted.

Of course, the same positive effects occur when using the process with other effluents or product solutions. By using germ-free inert gases instead of air, the method can also be used in the food industry or the pharmaceutical industry.

In a second embodiment, a modification of the apparatus for carrying out the method is carried out in such a way that a second Gasansaugstutzen 14 is incorporated into the suction line of the pump 2, which is closed by a solenoid valve 15 and that a time relay 16 for periodically short-term opening of the solenoid valve 15th is used while the time relay 12 is omitted in the power supply of the pump motor 13. During the brief opening of the solenoid valve 15, the amount of gas sucked in is so great that the liquid column breaks off in the pump suction line and is sucked in again only after closing the solenoid valve 15 '. There is thus also an interruption of the feed stream 1, without unfavorable load conditions occur in the pump by frequent switching on and off.

Claims (5)

20 845 2 - * ~ Invention claim. 1.' Method for Menibranfiltration with addition of a gas to the feed stream before and relaxation of the feed stream after the membrane separation unit and passage of a separation apparatus, characterized in that the relaxation takes place before the introduction of the feed stream in preferably operating under ambient pressure separating apparatus and separated by means of the separation apparatus foam and as Product is derived. 2. The method according to item 1, characterized in that the feed stream is mixed with surfactants. 3. The method according to the items 1 and 2, characterized in that the feed stream is partially relaxed before entering the membrane separation unit. 4. Apparatus for carrying out the method according to points 1-3, consisting of a reservoir, a Pumpensaugleit with gas inlet and control valve, a pump, a pressure line, a membrane separation unit, a separation apparatus and a return line from the separation apparatus to the reservoir, characterized characterized in that the separation apparatus is designed as a calming and foam stripping chamber (10), preferably under ambient pressure, which has a foam outlet (11) to the outside, while the connection of the return line (17) from the separation apparatus to the reservoir (.1) in the clear water zone the separation apparatus is provided and in the pressure line (5) in front of the membrane separation unit (7) a pressure reduction (6) and after the membrane separation unit immediately before the separation apparatus (10) a further pressure reduction (.9) is arranged. , 5. Device according to points 1 and 4, characterized in that an additional, by solenoid valve (.15) closable Gasansaugstutzen (14) in the suction line of the pump (2) is arranged, wherein a solenoid valve (15) by a timing relay (16 ) opens. Hienu_s & _Seiten Zeichnuncien