TECHNICAL FIELn

The inven icr. relates t: z. device fcr separation cf solid, liquid cr dissolved constituents present in a liquid, the separation device comprising a stack of a plurality of plates and membranes arranged between the plates .

Together with the membranes, recesses arranged in the plates form separation cells, which comprise at least one inlet for supply of untreated liquid to one side of the membrane, one outlet for discharge of the liquid, the reject, which does not pass through the membrane, or. the same side of the membrane, and one outlet for discharge of tne liquid, the permeate, which passes through the membrane, on the opposite side of the membrane .

BACKGROUND ART

Devices for membrane separation built up of a plurality of stacked plates with intermediate membranes are known, inter alia, from Swedish patent application 8704422-6, which describes filtering, and from Swedish patent application 8002233-6, which describes a device fcr membrane distilla¬ tion.

In the following description, the term "membrane" relates to membranes for different forms of membrane separation as well as to impermeable films intended to separate different media, for example a plastic film on one side of which a coolant is flushed to condense out a distillate during membrane distillation.

Sealing to prevent leakage cf untreated liquid - reject and permeate cr distillate - from the cells is usually achieved by means cf O-rings cr some other form of loose gasket . The gasket is fixed by placing it in grooves arranged in the

plate. These grooves weaken the plate mechanically and necessitate the use of a thicker plate.

In many applications, for example for cleaning of process water for the electronics or pharmaceutical industry, the use of loose seals such as O-rings entails a non-tolerable risk of contamination. Loose seals may give off particles or other undesirable substances and, in addition, these seals as well as the grooves arranged for fixing the seals constitute an excellent site for deposits and/or growth of microorganisms.

From British patent specification GB 2,150,851, it is known to apply a bead-like film onto the membrane, which film by polymerization cr vulcanization is bonded to the membrane. Further, the sealing provided by the applied bead-like film may be supplemented by elevations arranged on the filter plates, which elevations, when the filter plates are stacked together with the applied film, seal around spaces included in the separation cells, to prevent leakage from these spaces. Sealing according to GB 2,150,851 requires an accurate and expensive preparation of the membranes before they provide a seal when being assembled into a stack together with the plates. Insufficient accuracy during the application of the sealing film or during the assembly of the stack entails leakage from the separation cells and, what is worse, undesired passage of liquid between the spaces included in the separation cells.

The present invention aims at designing a filter plate which, during the assembly of a plurality of plates with intermediate membranes into a stack, brings about a seal which is simple and reliable in operation and which prevents treated liquid from being contaminated by untreated liquid or by the reject. Another object of the invention is to achieve, by the design of the plate, a seal without loose gaskets or a sealing film arranged on the membrane com¬ prising only elevations arranged on the plate and inter-

mediate smooth membranes, and to avoid time-consuming and expensive preparatory work while at the same time facilitating the assembly work.

SUMMAPY OF THE I I VEMT IO"

A device according to the invention for treatment of liquid, for example a device for membrane separation by filtering or distillation, comprises at least two plates arranged in a stack and membranes provided between the plates. Recesses provided in the plates in the form of depressions, channels or holes, form, together with the membrane arranged between the plates, spaces included in a separation cell. The separation cell comprises at least:

- one inlet fcr supply cf liquid to one side of the membrane,

- one outlet for discharge of liquid, the reject, which does not pass through the membrane, on the same side of the membrane as the inlet, and

- one outlet for discharge of the liquid, the permeate, which does pass through the membrane, on the other side of the membrane .

According to the invention, the plates are arranged with elevations around recesses provided in the plates . The elevations are adapted to press a smooth film, filter cloth or membrane, arranged between the plates, against the surface of the opposite plate so that the elevations solely in cooperation with the smooth membrane prevent the leakage of liquid between the spaces or out between the plates .

A device for membrane separation according to the invention may comprise both plates with elevations and smooth plates without such elevations. The plates are then stacked in a sequence such that sealing is still accomplished around all the spaces included in the device.

The sealing is accomplished either by the elevation as such, which is locally deformed to make tight contact with the opposite plate, or by the intermediate membrane being arranged to be squeezed and seal.

The plates are arranged with elevations around all the recesses provided in the plates, the elevations in co¬ operation with the intermediate smooth membranes then achieving a separate sealing around each space included in the separation cell, such that between each recess at least two elevations are adapted, in cooperation with membranes arranged between the plates, to prevent leakage between the spaces included in the separation cell.

In one embodiment of the invention, plates are arranged with elevations on both sides, around recesses provided in the plates, and smooth plates alternately arranged in a stack to form, together with membranes arranged between the plates, a device for membrane separation.

The invention may, for example, be applied to a filtering device for separation of particles or droplets present in a liquid, for example a cleaning plant for industrial process water.

Another application of a device according to the invention is in a device for membrane distillation for separation of constituents dissolved in a liquid, for example for desali¬ nation of saliferous water.

In a preferred embodiment of the invention, plates are arranged in a device for membrane distillation in which alternately smooth plates and plates with elevations on both sides are arranged in a stack with membranes and impermeable plastic films arranged between the plates. The plates comprise recesses in the form of depressions, channels or holes for supply of hot, untreated liquid and discharge of reject, for supply and discharge of coolant and for dis-

charge of the distillate obtained. The plates are stacked according to the following stacking sequence:

- a plate provided with elevations on both sides and com- prising recesses for flushing the membrane with hot un¬ treated liquid,

- a smooth membrane which is not wetted by the liquid but lets through evaporated liquid, - a smooth plate comprising recesses arranged as condensing chambers and outlets for distillate,

- an impermeable plastic film arranged as condensa¬ tion surface,

- a plate provided with elevations on both sides and com- prising recesseε for flushing the condensation surface with coolant,

- a smooth, impermeable plastic film arranged as condensa¬ tion surface,

- a smooth plate comprising condensing chambers and outlets for distillate,

- a smooth membrane, ana

- a plate provided with elevations on both sides and com¬ prising recesses for flushing the membrane with hot, un¬ treated liquid.

Elevations according to the invention stiffen and strengthen the plates, whereby plates formed according to the invention may be made considerably thinner than conventional plates and, consequently, more compact separation plates may be built.

In addition, the invention makes possible a better uti¬ lization of the plates. Plates according to the invention may be formed in a more optimum way, starting from func- tional criteria, since the invention essentially eliminates the limitations when forming grooves and channels which are associated with, for example, the geometry of the O-ring, or

the weakenings of the plate which result from the necessity to provide grooves for gaskets.

A device with plates formed according to the invention offers effective solutions for the treatment of liquids by membrane separation since the thin and functionally opti¬ mized plates provide a possibility of building compact sepa¬ ration units. At the same time, both the design and the assembly work are simplified since the seal is arranged essentially integrated into the plate or, alternatively, into the plate and the intermediate membrane . This also means that the risks of particles or other undesired sub¬ stances being given off to the cleaned liquid are substan¬ tially eliminated. The simplified design also means that deposits and growth sites for microorganisms can be essentially avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in greater detail by desc¬ ribing a few embodiments with reference to the accompanying figures. Figure 1 shows filter plates according to the invention included in a device for membrane separation.. Figure 2 shows part of two filter plates which are provided with sealing elevations according to the invention. Figure 3 shows plates according to the invention arranged for mem¬ brane distillation, and Figure 4 shows a preferred embodi¬ ment of a device for membrane distillation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 shows a stack of consecutively arranged filter plates 10 included in a device for membrane separation. Each one of the plates 10 is arranged with recesses 11 in the form of depressions, channels or holes, which together with membranes 13, arranged between the plates 10, form separation cells. The separation cells comprise at least one inlet 14a for supply of liquid to one side of the

membrane, an outlet 14b for discharge of liquid, the permeate, which passes through the membrane, and another outlet 14r fcr liαuid, ~. ^~ rejt z*- wh ch dees not pass through the membrane. At least some cf the piates 10 are provided with eievaticπ; 12. Togetner with the membranes 13 arranged between the plates 10, the elevations 12 are adapted to seal between the inlet 14a and the outlets 14b and 14c, such that uncleaned liquid or reject is not mixed with permeate, and to seal such that liquid does not leak out from the separation device.

Figure 2 shows part of two filter plates 10 and membranes 13 arranged therebetween. According to the invention the fil¬ ter plates 10 are provided with elevations 12. When arranging the plates in a stack of plates 10, the elevations 12 are adapted to press against the surface of the opposite plate 10 and, at least together with the intermediate membrane 13, to seal to prevent- liquid from passing in an undesired manner between the spaces 14a, 14b and 14c which, as shown in Figure 1, are formed by the recesses 11 and the membranes 13, and to prevent liquid from leaking out of the separation device.

Figure 3 shows filter plates 101, 102, 103 arranged to form part of a plant for membrane distillation. The filter plates 101, 102, 103 are provided with elevations 120 accor¬ ding to the invention. As is shown, the elevations 120 may be arranged on all the plates 101, 102, 103 or on certain plates only.

A device for memorane distillation comprises a number of consecutively arranged plates 101, 102, 103, at least one membrane 130, v; _ch is r.o wetted by the liquid to be treated but lets through evaporated liquid, and at least one impermeable film which is adapted to constitute tion surface 15C for the clean distillate.

One type of plate, A, 101 is provided with holes and recesses which form channels 141 for the supply of hot liquid to the membrane 130. This causes at least part of the evaporated liquid to pass through the membrane 130 into a condensing chamber 142 which is arranged in another type of plate, B, 102. In the condensing chamber 142 a conden¬ sation surface 150 is arranged for condensing out the clean distillate which is then discharged from the condensing chamber 142. The condensation surface 150 consists of an impermeable plastic film which on the opposite side is flushed with a coolant, which is adapted to be supplied through the recesses 143 in the third type of plate, C, 103.

In the membrane distillation plant shown in Figure 3 a filter plate of type B, 102, is provided with recesses which form a condensing chamber 142 with the membrane 130 on that side which abuts on a plate of type A, 101, and with the condensation surface 150 on that side which abuts on a plate of type C, 103. The membrane distillation device in Figure 3 is arranged with a stacking sequence of plates and membranes, impermeable films and separating membranes according to the following:

plate type A 101, membrane 130, plate type B 102, plastic film 150, plate type C 103, plastic film 150, plate type B 102, membrane 130, plate type A 101, membrane 130, etc.

Elevations 120 arranged on at least some of the plates seal, at least together with the intermediate membrane 130 or plastic film 150, so that no liquid leaks out between the

spaces in the plant in an undesired manner, or leak outs of the plant .

The plant described above may be modified in a great number of ways while utilizing the filter plate 10 provided with elevations according to the present invention. Among other things, the plate 102 of type B, which constitutes the condensing chamber 142, may be exchanged for a fabric or other open structure which is arranged between the conden- sation surface 150 and the membrane 130.

In a preferred embodiment, plates included in a membrane distillation device are arranged according to Figure 4. Smooth plates of type B, 2C1, are arranged as condensing chamber 242, one siαe of which is covered with an imper¬ meable plastic film, which constitutes the condensation surface 250, the opposite side being covered with a membrane 230 which is not wetted by the liquid to be treated but which lets through evaporated liquid. Plates of type A, 202, provided with elevations 222, according to the invention, and recesses 241 are arranged making contact with the impermeable plastic film 250 and the membrane 230 to flush these, 250, 230, with coolant and hot, untreated liquid, respectively. The stacking sequence in a membrane distillation device according to the embodiment mentioned is as follows :

- a plate of type A 202 arranged for supply of hot, untreated liquid, - a membrane 230,

- a plate of type B 201 arranged as condensing chamber 242,

- an impermeable plastic film 250, arranged as condensation surface,

- a plate of type A 202 arranged for supply of coolant, - an impermeable plastic film 250,

- a plate of type B 201,

- a membrane 230,

- a plate of type A 202 arranged for supply of hot, untreated liquid, and so on.

A membrane filtering plant according to the above may, for example, be arranged for filtering of industrial process water whereas a membrane distillation plant may be used for desalination of saliferous water, for example to satisfy the very extensive requirements within the electronics and pharmaceutical industries.