WO1985000297A1 - Process and device for the separation of substances by means of membranes - Google Patents

Abstract

Process and device for the separation of substances of fluid or gaseous multisubstances media by means of membranes (21) in a pressure container (20) with pretreatment and conduction of the medium to be treated in a circulation circuit. The medium to be treated mixed with a concentrate is circulated by a separate pump (23) with minimum energy and a large volume flow after the membrane prefiltration (3) and after charging with the operating pressure without pressure reduction by throttle inside the high pressure area. Thereby the operating pressure generator (11) can be adjusted to a volume flow which is just equal to the sum of the permeate volume flow plus the concentrate volume flow and which contains no fraction of the circulation circuit.

Description

Method and device for separating substances by means of membranes

Description

The invention relates to a process for the separation of liquids or gaseous multi-media by means of membranes, in which the medium to be treated is first subjected to a working pressure required for the separation and is then passed over the surface of the working membrane.

In the present case, such a process includes both filtration processes with small and smallest membrane pore sizes, in particular microfiltration with pore sizes in the range from 1.0 to 0.1 μm and ultrafiltration in the range from approximately 0.1 to 0.01 μm as well as the reverse Understood osmosis. The nutrient media in question can therefore be both cloudy, ie dispersions of solid particles in one liquid phase or a smoke as well as solutions or gas mixtures. The separation of viruses and pyrogens from liquid phases, the desalination of seawater and brackish water or the concentration of industrial wastewater containing radioactive salts are typical examples of the material separation processes of the type in question, which are hereinafter briefly referred to as "membrane processes".

The invention further relates to a device for carrying out such membrane processes using a working membrane element which is arranged in a pressure vessel, which has an inlet connection for the medium to be treated by means of a pressure generator, usually a displacement pump, a discharge connection for the permeate or filtrate and a concentrate connection at which the medium concentrated by the membrane treatment and retained in front of the membrane can escape.

The fine-pored membranes used to carry out these membrane processes or practically pore-free in the case of reverse osmosis are in some cases quite sensitive structures which, if no precautionary measures are taken, quickly show a significant reduction in flow. The best known and most effective measure for suppressing the flow performance drop of membranes of the type in question can be seen in the fact that the medium to be treated, which is used to achieve the separation effect on the membrane with an overpressure in the range from a few bar to a few 10 bar acted upon. is carried out with the greatest possible flow speed parallel to the surface of the working membrane over this membrane surface. This is realized in practice in such a way that the medium to be treated is subjected to the working pressure by a pressure generator, is pumped under this pressure into a pressure vessel in which the membrane element is arranged, and after which it overflows the surface of the membrane exits the pressure vessel via a throttle device. The medium, which is then usually referred to as concentrate or retentate, is returned to the pressure generator after the expansion, behind the throttling device, pressurized again and in turn returned to the pressure vessel and over the working membrane surface. Depending on the parameters given by the separation task to be solved, part of the retentate is usually branched off and withdrawn as a concentrate from this circuit.

Another precautionary measure to prevent the drop in the flow rate of the working membrane, which is taken in combination with the fluidic measure described above, is that the medium to be treated supplied to the working membrane is pretreated chemically and physically, in particular by flocculation and depth filtration. Treatment measures of this type, however, require additional operational measures and investments due to the additional chemical operations and to separate the liquid phase from the flocculation, which make the actual membrane process significantly more expensive. In addition, in order to maintain the cross flow over the working membrane surface, the pumps which apply the working pressure to the medium to be treated must be designed for a relatively large volume flow, since they must also promote the circulation flow in addition to the actual product flow. The pumps required for this, however, not only represent a considerable investment in the system, but also require an energy supply for operation, which is a significant factor in the running costs of such a system for membrane treatment of media that are to be subjected to material separation.

In view of this prior art, the invention lies The object of the present invention is to create a method and a device for separating liquids or gaseous multi-material media by means of membranes of the type mentioned at the outset, which enable such membrane processes to be carried out with a lower level of plant technology and which require operational outlay; in particular, means are to be found to reduce the working pressure generator and to reduce the pretreatment effort.

This object is achieved by the invention by a process for the separation of liquids or gaseous multi-media, in which the medium to be treated is subjected to a working pressure of a working pressure of a few to a few 10 bar and then passed over the surface of a working membrane, in that the medium subjected to the working pressure is circulated over the surface of the working membrane with only the unavoidable pressure drop due to the flow, so that the working pressure generator only needs to convey the volume flow that is required for the actual membrane process, i.e. only one volume flow of the medium to be treated needs to convey, which is equal to the sum of the volume flows of the concentrate and permeate, which are withdrawn from the system continuously or discontinuously. In other words, the volume flow of the mixture of concentrate and injected medium to be treated, which is circulated for the purpose of suppressing the blocking of the membrane and for suppressing the flow reduction of the membrane, is circulated in the high-pressure region in front of the working membrane and is returned without being relaxed. Although an additional pump is required for this circulation, simpler, cheaper and smaller pumps can be used for this purpose, which are characterized in particular by an extremely low energy requirement. With this additional pump, however, the required flow rate in the working pressure generator be reduced by at least a factor of 5 to 10. This, in turn, can in practice reduce the size and energy consumption of the pump used as a working pressure generator by an entire dimension. This circulation volume flow, which in practice is at least five to ten times the volume flow actually required for the membrane process and by which the working pressure generator is relieved according to the method according to the invention, is now circulated in the high-pressure region in front of the membrane according to the method according to the invention, namely without leaving this high-pressure area, so that the circulation pump required for this only has an energy requirement which has to compensate for the unavoidable pressure drop in the circuit due to the flow. However, the pressure to be applied for this is around 1 to 3 orders of magnitude lower than the pressure with which the working pressure generator acts on the medium to be treated. Overall, the additional investment costs caused by the additional circulation pump are therefore already far overcompensated by the investment costs saved for the working pressure generator, so that the entire considerable operating energy savings in the economic balance sheet are available unabated.

According to one embodiment of the invention, the membrane treatment process is carried out in such a way that the medium to be treated is prefiltered through at least one membrane before it reaches the surface of the working membrane. Such a membrane has an average pore size that is larger than the average pore size of the working membrane. As a result, the customary depth filtration and in particular the flocculation process can be saved with little energy and expense. In particular, according to a further embodiment of the invention, a membrane prefilter and a membrane postfilter are used in front of the actual working membrane. The mean pore size of the membrane prefilter is larger than the mean pore size of the membrane filter and is the average pore size of this membrane post-filter is again larger than the average pore size of the working membrane. If, for example, the working membrane is a membrane for carrying out the reverse osmosis, an ultrafiltration membrane is used as the post-filtration membrane and a microfiltration membrane is used as the prefilter membrane. Since in this embodiment of the invention the medium for the pre-filter membrane hardly needs to be subjected to any noteworthy pressure, whereas for the filtration through the post-filter membrane some pressure is already required in order to achieve a sufficiently high flow rate, according to a further embodiment of the invention the working pressure generator preferably switched between the pre-filter membrane and the post-filter membrane. This has the advantage that no unnecessary pressure drop is generated by connecting the pre-filter membrane in the high-pressure area of the system, ie after the working pressure generator, and that an additional separate pressure generator can be saved for the post-filter membrane.

The device for carrying out the method described above essentially consists of a working membrane element which is arranged in a pressure vessel, which in turn is preceded by a pressure generator in which the medium to be treated fed into the pressure vessel is subjected to the working pressure required for the membrane treatment. The working membrane element is preferably a spiral winding element, but can likewise be constructed in a different way, for example as a tubular filter element, labyrinth element or plate filter. The only decisive factor in this connection is that the working membrane element used in each case provides a sufficiently large surface area of the membrane which can be flowed over by the medium to be treated.

The pressure vessel, in which the working membrane element is arranged, has an inlet connection for the pressurized medium to be treated, a drain connection for the permeate if reverse osmosis is carried out, or for the filtrate if ultrafiltration is carried out, and a concentrate connection to which the medium concentrated by the membrane treatment and retained on the pressure side in front of the membrane from the Exit the pressure vessel and can be removed from the membrane treatment system. This membrane treatment arrangement which is customary in this respect is characterized according to the invention by a pump, preferably a turbine centrifugal pump, which is arranged in the pressure vessel in which the working membrane element is also accommodated and whose suction nozzle on the pressure side behind the working membrane element with the concentrate drain and its pressure nozzle with the pressure-side inlet space, inlet area or inlet channel is connected in front of the working membrane element, and by a branch line which connects the suction line of the pump between the concentrate outlet and the suction port of the pump with the concentrate connection of the pressure vessel. The pump arranged in this way in the pressure area of the system within the pressure vessel of the working membrane element thus acts as a circulation pump for the medium to be treated on the pressure side in front of the membrane. That for cross rinsing the pressure side surface of the. Working membrane circulated and medium to be treated which has already been concentrated by circulating is therefore not decompressed over its entire circulating circuit, so that the circulating pump only needs to impress the circulating medium with the energy or the pressure which inevitably has to be accepted on the circulating flow path to be traversed.

Since the circulating pump switched and arranged in this way has only an extremely low energy requirement, this pump is preferably equipped with a turbine drive according to a further embodiment of the invention, the turbine of which is fed via an associated turbine nozzle directly behind the inlet connection of the pressure vessel with that fed into the pressure vessel by the working pressure generator medium to be treated is applied. Depending on the construction and mode of operation of the system, the turbine pressure drop for the medium fed can be in the order of 0.2 to 8 MPa.

The concentrate drain or an additional electric motor can serve as additional drive energy sources for the circulation pump installed in the pressure vessel. If the concentrate outlet is used, it is guided in a separate turbine chamber onto a separate turbine impeller. If an electric motor is provided in addition or alone, it is preferably, but of course not necessarily, arranged outside the pressure vessel. The power transmission from. The electric motor for the circulating pump is then preferably, but again also not mandatory, via a coupling which is free of lead-through, for example a magnetic coupling, in order to prevent any technical problems which may occur which may occur when a dynamic seal is formed on a pressure vessel. Regardless of the problem of the seal, however, both an electrical auxiliary drive and an additional turbine drive, which can be driven both by external liquid or gaseous pressurized fluids and by utilizing the pressure concentrate discharge, are via a torque limiter, preferably a magnetic coupling, to the turbine which is acted upon by the medium to be treated which is fed in coupled.

A particular advantage of the device according to the invention can also be seen in the fact that the working filter unit and the circulating unit can be manufactured and sold as an integrated compact module in the pressure vessel. This significantly simplifies the assembly and maintenance of such systems for material separation using membranes.

The invention is explained in more detail below on the basis of exemplary embodiments in conjunction with the drawings. Show it:

Figure 1 shows the block diagram of a system for performing the method according to the invention.

. Figure 2 in axial section and in partial representation the head of the pressure vessel of a device according to the invention.

3 shows, in axial section and in partial representation, the schematic structure of a foot region of a pressure vessel of the device according to the invention; and

Fig. 4 is a partial view of the type shown in Fig. 2 in the formation with two turbine wheels.

1 shows the schematic block diagram of a system for carrying out the method according to the invention. The individual components of this system shown are provided with ISO codes which have the following meaning:

H 1 two-way ball valve overflow pipe

F 2 prefilter

H 2 three-way ball valve

X 2 air vent valve

V 2 drain valve

TPI 3 th ermomanometer

P-M-R 4 pressure booster unit

R 5 check valve

F 6 post-filter pulsation damper

PI-H 6 manometer test tube F-TM-M 7 membrane filter turbo module E. engine

PI 7 flow indicator PI 8 manometer

TPE 9 temperature and pressure switch

H 10 Two-way ball valve throttling

FI 11 flowmeter

Q E 12 conductivity measuring cell

PI 1 3 flow meter

S 14 control unit

Specifically, the medium to be treated passes through an inlet line 1 and an actuator 2 provided with an overflow stop to a prefilter 3, which is a combination filter comprising a poured, wound or sintered activated carbon filter 4 and a microfiltration membrane 5. The pre-filter 3 can be backwashed and cleaned via a drain valve 6 and can be aerated on the filtrate side via an aeration valve 7. In addition, the filtrate leaving the pre-filter 3 can be provided with an additive, for example with a marking substance, a reactant or a process additive, via an auxiliary feed line 8 and a three-way ball valve 9. The proper functioning of the filter 3 is monitored with a downstream manometer 10.

The pre-filter 3 is followed by a pressure generator 11, which in the exemplary embodiment shown here is designed as a centrifugal pump driven by an electric motor 12 with a downstream check valve 13.

After the check valve 13, a post-filter 14 is connected, which consists of an outer flexible and flexible hose 15 and an inner elastic membrane filter hose 16. While the membrane filter 5 of the pre-filter 3 has an average pore size of 0.45 μm, the elastic membrane filter tube 16 of the post-filter 14 has an average pore size of 0.1 μm. While working membrane poisons such as free chlorine, ozone or oxygen in the pre-filter on the activated carbon and in the membrane pre-filter all particles up to 0.45 μm, e.g. partly radioactive substances, colloidal suspensions, organic residues and partly bacteria, are retained all bacteria in particular are retained on the post-filter 14. The elastic design of the secondary filter 14 also serves to dampen pulsation and noise, in particular when the pressure generator 11 is a piston displacement pump.

The post-filter 14 is monitored with the aid of a manometer 17 and a sampling tap 18.

The actual membrane treatment, in the exemplary embodiment described here, is reverse osmosis, in assembly 19, referred to here briefly as "turbo module", which is essentially constructed from a pressure vessel 20, a working membrane element 21, a concentrate circulation line 22 and a circulation pump 23.

Even if a membrane for the reverse osmosis, a so-called RO membrane, is used for the membrane element 21 in the exemplary embodiment described here, the working membrane can of course also be an ultrafiltration membrane or a microfiltration membrane. It is only necessary to ensure that the membrane 16 of the secondary filter 14 has an average pore size which is larger than the average pore size of the membrane of the membrane element 21, and that the average pore size of the membrane 5 of the pre-filter 3 in turn has a larger pore size than that Membrane 16 of the night filters 14.

The circulation pump 23 is designed in the manner described in more detail below as a turbine centrifugal pump which is equipped with an auxiliary electric motor 24.

The filtrate circuit line 22 is equipped with a flow monitor

25 monitors.

The permeate or filtrate is passed through a permeate drain line

Removed 26, in which a flow monitor 27 is turned on. The quality of the permeate is monitored by means of a conductivity sensor 28.

The concentrate removed continuously via a concentrate discharge line 29 and monitored by means of a manometer 30 and a flow monitor 31 is continuously withdrawn from the concentrate flow circulated in the turbo module 19 via a two-way valve 32, the setting of which determines the withdrawal ratio of concentrate to permeate.

The electrical control and energy supply of the entire system takes place via a central control and regulating unit 33.

FIG. 2 shows a schematic representation of the head of the turbo module 19 shown in FIG. 1 with the cut membrane element 21 and the circulation pump 23. The circulation pump 23 is designed as a turbo centrifugal pump and essentially consists of the pump impeller 34, the turbine impeller 35, which can be acted upon by the turbine nozzle 36, and the auxiliary electric motor 24, which is coupled to the shaft of the turbine impeller 35 via a magnetic coupling 37. The electric auxiliary motor 24 is located outside the pressure vessel 20, but it is. connected to it by means of a mounting plate 38 to form an integral structural unit and by a cover 39 protected from mechanical influences.

The pressure vessel 20 has an inlet connection 40 for the medium to be treated with pressure by means of the pressure generator, an outlet connection 41 for the permeate (FIG. 3) and a concentrate connection 42 (FIG. 2), on which the membrane treatment concentrated and pressure side medium retained in front of the membrane can be drawn off continuously in a branch stream.

The suction port 43 of the circulation pump 23 is connected via the concentrate circulation line 22, which is also the suction line for the pump 23, to the concentrate outlet space 44 on the pressure side behind the working membrane element 21, while the pressure port 45 of the circulation pump 23 is connected to the inlet space 46 in front of the working membrane element 21. 2, the concentrate flow is indicated by the flow arrow K, while the flow of the medium to be treated is indicated by the flow arrow E.

2, the suction line 22 of the circulation pump 23 is connected to the concentrate connection 42 via a branch line 47.

The inlet connection 40 is connected to the turbine nozzle 36 via a connecting line 48. The medium to be treated flowing through the inlet pipe 40 via the connecting line 48 through the turbine nozzle 36 to the turbine impeller 35 passes through the turbine outlet 49 into the pressure-side inlet space 46 in front of the working membrane element 21 and is from there in the usual way over the membrane surface of the working membrane element, here Spiral winding module, directed, mixed with the concentrate circulated by the circulation pump 23. In Fig. 4, also in axial section and in partial representation, the head of a turbo module is shown, which differs from the turbo module head shown in Fig. 2 in that an electric motor is not provided as auxiliary drive energy as in the embodiment shown in Fig. 2 , but a second drive turbine, the turbine wheel 50 is acted upon by a turbine nozzle 51 with the high pressure concentrate under operating pressure from the concentrate branch line 47. The concentrate running off the turbine wheel 50 is led as a low-pressure concentrate via a low-pressure concentrate line 52 to a separate concentrate connection, where it is removed from the system as a concentrate stream.

As explained in detail in connection with the exemplary embodiment shown in FIG. 2, the concentrate auxiliary turbine described in the exemplary embodiment shown in FIG. 4 is also connected to the shaft of the main turbine 23 via a magnetic coupling 37.

In a multi-week operation with a pilot plant of the type shown in FIG. 1 using the turbo module shown in FIGS. 2 and 3, the removal of radioactive substances from an aqueous solution at an operating pressure of 30 bar, a salt concentration of 40,000 ppm in Concentrate and a permeate flow of 30%, based on the concentrate flow, with a salt retention capacity of over 99% in the entire reverse osmosis range, ie in the scope of the system shown in FIG. 1, achieved an electrical energy requirement of only 0.4 kWh. Such a value cannot be achieved with conventional systems.

Claims

Patent claims 1. A method for the separation of liquid or gaseous multi-media by means of membranes, in which the medium to be treated is initially subjected to a working pressure required for the separation and then passed over the surface of the working membrane, characterized in that the medium subjected to the working pressure with only the unavoidable pressure drop in the circuit is circulated over the surface of the working membrane. 2. The method according to claim 1, characterized in that the medium to be treated before it is on the surface reaches the working membrane, is pre-filtered through at least one membrane. 3. The method according to claim 2, characterized in that the medium to be treated, before it reaches the surface of the working membrane, is subjected to a membrane pre-filtration and a membrane post-filtration, the exposure to the working pressure taking place between the pre-filtration and the post-filtration. 4. Apparatus for carrying out the method according to claim 1 with a working membrane element which is arranged in a pressure vessel which has an inlet connection for the medium to be treated by means of a pressure generator to be treated, an outlet connection for the permeate or filtrate and a concentrate connection to which the the membrane treatment can escape concentrated medium retained in front of the membrane, characterized by a pump (23) which is arranged in the pressure vessel (20), the suction nozzle (43) with the concentrate outlet (44) on the pressure side behind the working membrane element (21) and the pressure nozzle (45) is connected to the inlet (46) in front of the working membrane element (21), and by a branch line (47) which connects the suction line (22) of the pump (23) to the concentrate connection (42). 5. The device according to claim 4, characterized in that the pump (23) is a centrifugal pump (34) with a turbine drive (35). 6. The device according to claim 5, characterized in that the inlet connection (40) is connected to the turbine nozzle (36) and siσh the turbine outlet (49) opens to the inlet (46) in front of the working membrane element (21). 7. The device according to claim 6, characterized in that the pump (23) has an additional auxiliary drive (24; 50) which is coupled to the turbine shaft via a torque limiter (27). 8. The device according to claim 7, characterized in that the auxiliary drive is an electric motor (24) and / or an additional turbine (50, the turbine nozzle (51) of which can be connected to the concentrate branch line (47). 9. The device according to claim 4, dadurσh g e k e n n z e i σ h n e t that between the pressure generator (11) and the inlet inlet (40) a membrane filter (14,16) is connected, the pores of which have a larger diameter than the pores of the working membrane (21). 10. The device according to claim 4, characterized in that the pressure generator (11) has a membrane filter (3, 5) is pre-formed, the pores of which have a larger diameter than the pores of the working membrane (21) and the pores of an optionally further downstream and intermediate Membrane filter (14, 16). 11. The device according to claim 10, characterized in that the membrane prefilter (5) is preceded by an activated carbon filter (4).