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Title:
HIGH EFFICIENCY MEMBRANE FILTRATION
Document Type and Number:
WIPO Patent Application WO/2012/175804
Kind Code:
A1
Abstract:
In the membrane filtration according to the invention the liquid flow not permeating the filter membrane is connected to the liquid flow from a pressurized liquid source. Both the liquid flow permeating the filter membrane and the liquid flow not permeating the filter membrane are maintained with the liquid flow coming from a pressurized liquid source.

Inventors:
AULANKO ESKO (FI)
Application Number:
PCT/FI2012/050638
Publication Date:
December 27, 2012
Filing Date:
June 19, 2012
Export Citation:
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Assignee:
EMP INNOVATIONS OY (FI)
AULANKO ESKO (FI)
International Classes:
B01D61/00; B01D29/90; B01D63/00; C02F1/44
Domestic Patent References:
WO2002055182A12002-07-18
Foreign References:
US7695614B22010-04-13
US20090314695A12009-12-24
US4983301A1991-01-08
GB2383001A2003-06-18
US20090218274A12009-09-03
US20050230311A12005-10-20
Other References:
See also references of EP 2723477A4
Attorney, Agent or Firm:
SALOMAKI OY (Hyvinkää, FI)
Download PDF:
Claims:
CLAIMS

1. Method for arranging liquid circulation in membrane filtration, in which method a liquid flow is conducted from a pres- surized liquid source to a filter membrane, characterized in that at least a part of the liquid flow not permeating the filter membrane is connected to .the liquid flow from a pressurized liquid source. 2. Method according to claim 1, characterized in that the membrane filtration is cross-flow membrane filtration.

3. Method according to claim 1 or 2, characterized in that the liquid flow not permeating the filter membrane is connected to the liquid flow from a pressurized liquid source.

4. Method according to any of the preceding claims, characterized in that both the liquid flow permeating the filter membrane and the liquid flow not permeating the filter membrane are maintained with a liquid flow coming from a pressurized liquid source.

5. Method according to claim 4, characterized in that both the liquid flow permeating the filter membrane and the liquid flow not permeating the filter membrane are maintained from a pressurized liquid source into the liquid circulation with a liquid flow being fed in with one or more nozzles.

6. Method according to any of the preceding claims, character- ized in that the volume and/or pressure of the liquid flow being fed in from a pressurized liquid source, or at least a change in one of these, is controlled cyclically and/or on the basis of at least one of the following: the pressure in the liquid flow not permeating the filter membrane, the magnitude of the liquid flow permeating the filter membrane, the magnitude of the liquid flow not permeating the filter membrane, the content of one or more substances in the liquid flow not permeating the filter membrane, the content of one or more substances in the liquid flow permeating the filter membrane, and in that on the basis of the set control criterion, the liquid of the flow of the liquid circulation not permeating the filter membrane is at least partly replaced with liquid from a pressurized liquid source.

7. Method according to any of the preceding claims, characterized in that the pressure of the liquid flow not permeating the filter membrane is decreased periodically to be so low that the flow direction of the liquid flow permeating the filter membrane changes.

8. Method according to claim 7, characterized in that the pressure of the liquid flow not permeating the filter membrane is maintained to be greater than the pressure of the liquid flow that has permeated the filter membrane.

9. Membrane filter apparatus, comprising at least one filter membrane, a first liquid space and a second liquid space on opposite sides of the aforementioned filtration membrane, a pressure difference arranged over the aforementioned filtration membrane, in the first liquid space a liquid flow in the direction of the aforementioned filtration membrane, a liquid flow from the first liquid space into the second liquid space resulting from the pressure difference, and the feeding of liquid into the first liquid space from a pressurized liquid source, characterized in that the membrane filter apparatus comprises a flow path for conducting at least a part of the aforementioned liquid flow in the direction of the filtration membrane back with the liquid flow from a pressurized liquid source .

10. Apparatus according to claim 9, characterized in that the liquid flow not permeating the filter membrane and bypassing the filter membrane is conducted to unite with the liquid flow from a pressurized liquid source.

11. Apparatus according to claim 9 or 10, characterized in that both the liquid flow permeating the filter membrane and the liquid flow bypassing the filter membrane are arranged by the aid of a liquid flow coming from a pressurized liquid source.

12. Apparatus according to claim 11, characterized in that both the liquid flow permeating the filter membrane and the liquid flow bypassing the filter membrane are arranged by the aid of a liquid flow supplied from a pressurized liquid source via one or more nozzles.

13. Membrane filter device (101), which comprises a membrane filter unit (1) comprising an inlet connection (102) for con- ducting aqueous solution into the membrane filter unit (1), a first outlet connection (103) for conducting permeate from the membrane filter unit (1), and a second outlet connection (104) for conducting concentrate from the membrane filter unit (1), and which water treatment device (101) comprises a flow chan- nel (105) leading to the inlet connection (102), characterized in that the second outlet connection (104) is led into the flow channel (105), and in that in the flow channel (105) is an actuator (222), such as a pump, propeller or nozzle (2), maintaining the flow from the second outlet connection (104) towards the inlet connection (102), and in that in the flow channel is a nozzle (2) for feeding the high-pressure water to be treated into the flow channel (105) .

14. Membrane filter device (101), which comprises a membrane filter unit (1) comprising an inlet connection (102) for conducting aqueous solution into the membrane filter unit (1), a first outlet connection (103) for conducting permeate from the membrane filter unit (1), and a second outlet connection (104) for conducting concentrate from the membrane filter unit (1), and which water treatment device (101) comprises a flow channel (105) leading to the inlet connection (102), characterized in that the second outlet connection (104) is led into the flow channel (105), and in that in the flow channel (105) is at least one nozzle (2) for feeding the water to be treated into the flow channel {105), and in that at least one nozzle (2) is arranged to feed water to be treated towards the infeed connection (102) .

15. Membrane filter device according to claim 13 or 14, characterized in that one nozzle (2) alone or a number of nozzles together feeding into a flow channel (105) are exclusively a drive means for . the flow occurring in the flow channel from the direction of the second outlet connection (104) towards the infeed connection (102).

16. Membrane filter device according to claim 13, 14 or 15, characterized in that the nozzle (2) is directed to feed the high-pressure water to be treated in the direction of the flow channel (105) .

17. Membrane filter device according to claim 13, 14 or 15, characterized in that there is more than one nozzle and the nozzles (2) are directed obliquely from the wall (W) of the flow channel (105) into the flow channel differing in the direction of the flow channel (105) .

18. Membrane filter device according to claim 17, character— ized in that the nozzles (2) are directed over the center line of the flow channel (105) .

Description:
HIGH EFFICIENCY MEMBRANE FILTRATION

The object of the invention is membrane filtration, more particularly the invention relates to a method and a manner, with which membrane filtration is delivered, both to a membrane filtration hardware platform and to apparatuses using membrane filtration. One object of the invention is reverse osmosis filtration or inverted filtration separation. Membrane filters are very widely used in industry and elsewhere for water purification as well as for other purposes. Membrane filtration technology is also a developing field, in which new techniques and opportunities for different applications and uses are emerging.

The operation of a membrane filter, which can also called a membrane separator, can be described in a simplified manner as ollows : The permeable membrane to be used, which possesses certain properties, allows a permeate, e.g. water, to pass through it and retains other materials. In practice, the separation in membrane filters is not perfect, in which case the result of the separation is the permeate that passed through the membrane and the concentrate, or corresponding, obtained from the material to be filtered. Often the permeate is the intended product, e.g. when purifying water, but membrane separation can be used for concentrating the sought material, e.g. when recovering process chemicals or when concentrating solutions . A generally used membrane filtration method for liquids is so- called cross flow filtering. Cross flow filtering is in use in many different types of membrane filtering methods, e.g. in reverse osmosis filtration, nanofiltration, ultrafiltration and microfiltration . In cross flow filtering the material to be purified is brought to flow in the direction of the surface of the filtering membrane in which case, although some of the material filters through the membrane, the material to be purified rinses the surface of the membrane and in this way keeps the membrane permeable while preventing clogging or a large local concentration on the surface of the membrane. The driving force in membrane filtration is a pressure difference across the membrane. Energy is also needed, apart from over- coming the resistance caused by the membrane, for moving and conducting the liquids in the different phases of the process as well as for raising the pressure of the liquid to the operating pressure needed. Membrane filter devices and their components are generally available for various purposes. Membrane filter plants and devices are fabricated from commercially available components and are based on generally known techniques , For example reverse osmosis filters are commercially available for various applications and suitably also for the treatment of various solutions and for the separation of many types of substances, and, inter alia, filters for salt removal can be optimized and also the salt content ratio of the water to be treated can be selected .

The aim of this invention is to develop membrane filtration and to achieve inexpensive, reliable, safe and well functioning membrane filtration solutions. More- particularly the invention aims for reverse osmosis filtration solutions, nano- filtration solutions, ultrafiltration solutions and microfil- tration solutions and especially the type of solutions that are suitable for use in the reverse osmosis enrichment or reverse osmosis purification of aqueous solutions. The features characteristic to the invention are presented in the claims, in which also the embodiments of the invention that are believed to be advantageous are disclosed.

An important advantage to be achieved with the invention is a high coefficient of efficiency for membrane filtration. In particular the favorable, at least momentary, avoidance of pressure losses to be achieved with an implementation of the invention assists in reaching a high coefficient of effi- ciency. Also other advantages can be achieved with the invention.

Preferably the invention is embodied as a method with which a liquid circulation is arranged in membrane filtration. In a preferred embodiment of the method, a pressurized liquid flow is conducted from a pressurized source, e.g. from a pressure container, pressurized network or pump, to a filter membrane, and at least a part of the liquid flow not permeating the fil- ter membrane is connected to the liquid flow from a pressurized liquid source. An advantageous solution is also to connect the liquid flow not permeating the filter membrane fully to a liquid flow from a pressurized liquid source. With this procedure the concentrated liquid is returned to be refil- tered. Benefit is gained from the method in two ways: firstly, the yield can be improved; and secondly, the liquid coming for refiltering is pre-pressurized, in which case costs are not incurred in this respect by raising the pressure. Preferably both the liquid flow permeating the filter membrane and the liquid flow not permeating the filter membrane can be maintained, with the liquid flow coming from a pressurized liquid source. By suitably shaping and dimensioning the liquid flow infeed and the liquid circulation, very- low energy consumption in maintaining the liquid flow can be achieved. In addition, the apparatus is simple. With the invention, both large and small plants can be implemented energy-efficiently without pressure exchangers or corresponding energy recovery devices being needed. With the solution also a rather high yield can be achieved, which is important e.g. in water purification, in which pretreatment and/or the untreated water has a significant proportion in the total costs.

From time to time it is advantageous to rinse the pressurized side of filter membranes better than the cross flow itself rinses. This can be done by replacing the concentrated liquid with less concentrated liquid obtainable from the pressure source. At the same time, if the pressure is reduced sufficiently, with a small counterpressure over the membrane - with osmotic pressure when reverse osmosis membranes are in question - even a fine structure of a membrane can be easily rinsed. The invention is also embodied as types of alternative embodiments wherein the pressure of the liquid flow not permeating the filter membrane is controlled to decrease periodically to be so low that the flow direction of the liquid flow permeating the filter membrane changes. Preferably the pressure of the liquid flow not permeating the filter membrane, i.e. of the concentrate, is however maintained to be greater than the pressure of the liquid flow that has permeated the filter membrane, i.e. of the permeate. Thus sediment, or some other impurity to be separated, which should be filtered out, can get into the concentrate circulation from this type of back-flush or from the rinsing of the cross-flow or otherwise. It is, in fact, advantageous to add a filter or other suitable device, e.g. a cyclone separator, for separating the sediment. In some embodiments of the invention, the volume or pressure, or both, of the liquid flow from a pressurized liquid source, or a change in one of these, is controlled cyclically and/or oh the basis of at · least one of the following: the pressure in the liquid flow not permeating the filter membrane, the magni- tude of the liquid flow permeating the filter membrane, the magnitude of the liquid flow permeating the filter membrane, the content of one or more substances in the liquid flow not permeating the filter membrane, the content of one or more substances in the liquid flow permeating the filter membrane.

On the basis of the set control criterion, the liquid of the flow of the liquid circulation not permeating the filter membrane is at least partly replaced with liquid from a pressurized liquid source. The control criterion can be linked to the control of a change in the volume or in the pressure of the liquid flow, or in either of these, or it can be separate from these. One way of embodying the invention is membrane filtration apparatuses . One preferred membrane filter apparatus implementing the invention comprises at least one filter membrane, a first liquid space and a second liquid space on opposite sides of the filtration membrane, a pressure difference arranged over the filtration membrane, in the first liquid space a liquid flow in the direction of the aforementioned filtration membrane, a liquid flow through the filter membrane from the first liquid space into the second liquid space resulting from the pressure difference, and the infeed of liquid into the first liquid space from a pressurized liquid source and a flow path for conducting together at least some of the aforementioned liquid flow in the direction of the filtration membrane with the liquid flow from a pressurized liquid source. The liquid flow not permeating the filter membrane and bypassing the filter membrane can be conducted in its entirety to unite with the liquid flow from a pressurized liquid source. Particularly advantageous is a device solution wherein both the liquid flow permeating the filter membrane and the liquid flow bypassing the filter membrane are arranged by the aid of a liquid flow coming from a pressurized liquid source.

A preferred activation of a liquid flow of a membrane filter apparatus with a liquid flow coming from a pressurized liquid source is fabricated by the aid of a shaped, e.g. conical or funnel-shaped, nozzle in the flow channel. The spraying aperture of a conical or funnel-shaped nozzle is typically round. The flow channel can also be shaped for optimizing the coefficient of efficiency. The nozzle feeds liquid in the desired direction and by the aid of the rapid flow of the infed liquid also the liquid in the flow channel is brought to move.

Preferably the nozzle feeding liquid into the flow channel is shaped to only slightly affect the flow with its shape, in which case the effect of the nozzle on the flow is essentially what is brought about by the liquid flow it feeds in. One aspect of the invention is the connecting of the flow to be achieved from a nozzle disposed in the liquid circulation of membrane filtration to be a drive source for the liquid circulation and at the same time also the use of the nozzle to bring an amount of liquid to be filtered in the membrane filtration and for replacing the amount of liquid otherwise to be possibly removed. A requirement in this case is a sufficiently high flow speed and correspondingly a fairly small output aperture of the nozzle.

A nozzle aperture that is other than round is also possible, and even advantageous, within the scope of the invention. For example, a slot-shaped aperture of the nozzle shortens the connection distance of the flow coming from the nozzle into the flow of the flow channel and enables at least in some cases a shorter flow channel.

A slot-shaped nozzle is easy to fabricate from a pipe extending into the flow channel, said pipe having in its side a slot giving the direction of the flow. This type of pipe can be flattened or even shaped to aim for a particularly small flow resistance. The slot giving the direction of the flow does not necessarily need to be straight, e.g. a ring-shaped · nozzle slot can be made by fitting the actual flow channel inside a pipe part feeding in new liquid, preferably coaxially. In this type of solution, in which a possibly partly laminar flow of a ring-shaped nozzle from the edges of the flow channel pipe meets a turbulent flow in the flow channel, mixing is effective and occurs in a fairly short distance.

One aspect of the invention is embodied as the using of a number of nozzles for driving the flow in the flow channel. The flow can also be driven intentionally to be turbulent, at least in the transverse direction to the main flow. It is good to make the flow channel as one that expands at the point of, or in the proximity of, the nozzles. When using a number of nozzles to drive the flow in the flow channel, all the nozzles can be in line with each other in the longitudi- nal direction of the flow channel. Alternatively, the effect of the nozzles can also be phased such that the nozzles are at different points of the length of the flow channel. By means of the invention a membrane filter device suited as a water treatment device can be conveniently implemented from commercially available components and with simple jointing techniques, which membrane filter device comprises a membrane filter unit comprising an inlet connection for conducting aqueous solution into the membrane filter unit, a first outlet connection for conducting permeate from the membrane filter unit and a second outlet connection for conducting concentrate from the membrane filter unit, and which membrane filter device comprises a flow channel leading to the inlet connection, into which a second outlet connection is led, and in the flow channel is an actuator, e.g. a pump, a propeller or a nozzle, maintaining the flow from the second outlet connection towards the inlet connection; in the flow channel is a suitable nozzle for feeding into the flow channel the high-pressure wate to be treated. A preferred device solution is one in which the nozzle feeding water to be treated into the flow channel is directed to feed the water to be treated towards the infeed connection. A preferred implementation of a membrane filter device is one in which one or more nozzles together feeding into a flow channel are exclusively a drive means for the flow occurring in the flow channel from the direction of the second outlet connection towards the infeed connection.

The invention is particularly advantageous in water purifica- tion applications, e.g. in desalination, in making process water, boiler water or plant water, in preparing irrigation water or drinking water, and even for the purification of waste water. The invention is also suited to the enrichment of dissolved substances, e.g. in the food industry or in the min- ing industry.

In the invention, the solution not permeating the filter membrane is recirculated at essentially the same pressure back to the filter membrane. In practice in this recycling there are a certain amount of pressure losses, but these pressure losses are relatively small compared to the pressure difference that is needed in the membrane filtration itself. Especially in reverse osmosis filtration, the pressure difference over the membrane is considerable.

The invention is preferably applied to the cross flow filtering principle generally in use. The invention has a number of embodiments, which are not fully convergent with each other, e.g. the method of the invention to be implemented is not very dependent on the device environment and the apparatus of the invention to be implemented includes, or at least might include, parts that are not necessary for implementing the method. The embodiments of the invention and the ways of embodying it can differ from each other.

It is characteristic to one aspect of the invention to recycle the solution not permeating the membrane to the membrane for filtering again essentially at the operating pressure of the membrane. It is characteristic to a second aspect of the invention to arrange a liquid channel in which the solution not permeating the membrane that has flowed past the membrane is transferred for refiltering by the membrane. In practice, in the cross flow of the membrane filter and in the flow channels connecting to it there is a certain pressure loss, which, however, is small compared to the operating pressure of . the membrane, particularly when reverse osmosis membranes are in question. Despite this pressure loss, the pressure of the non- permeating side of the membrane can be regarded, within the scope of the pressure losses, to be essentially constant.

An important aspect of the invention is to apply membrane filtration, particularly membrane filtration or membrane separa- tion based on reverse osmosis, for water purification or desalination . Cross flow filtering is in use in many different types of membrane filtering methods, e.g. in reverse osmosis filtration, nanofiltration, ultrafiltration and microfiltration . In the invention cross flow filtering is applied such that the con- centrate is returned under pressure back to be fed in for filtering again and simultaneously more material, the same amount that exited as permeate, is fed into the pressurized flow.

The invention can also be embodied otherwise than what is de- fined in the claims. In addition to the embodiments of the invention defined by the claims, other embodiments of the invention are described or presented in the preceding and in the following . The invention is also suited to the concentration of liquids, in which case instead of the quality or quantity of the permeate, or other factor of the production of the permeate, primarily determining the process, or the device optimization, of the membrane separation, the devices and the control of the process are configured to be best from the viewpoint of the quality and production of the concentrate. It is possible, for example, to aim for sufficiently concentrated solutions or only for a certain rather precisely set solution concentration. The process costs can also be optimized in relation to yield.

The primary conceived use of the invention is the application of it in reverse osmosis separation. Many effects or technical solutions are very similar in other membrane separation tech- niques. Within the scope of applicability, the inventive solutions can therefore be extended to be used in other membrane separation procedures also, although the description and explanations of the technical solutions are presented here in this context most often in a reverse osmosis device environ- men .

In the following the calculation relating to the reverse osmosis phenomenon and to the application of the invention, as well as the optimization according to the invention of the functions, will be briefly presented as bases for application of the invention and for understanding its application. Symbols are used in the presentation as follows: The use of units given in square brackets can vary, e.g. % can be marked as a percentage or as a broader relative proportion. p = driving pressure [Pa] [bar]

posm = osmotic pressure [Pa] [bar]

Pmioss = pressure loss of membrane element [Pa] [bar]

Ppioss = pressure loss of piping [Pa] [bar]

k = permeability coefficient of membrane [m 3 /(s Pa)] (depends on membrane and is heavily temperature-dependent)

Q p = volume flow rate of permeate [m 3 /s]

Qf = volume flow rate of feed flow [m 3 /s]

Qc = volume flow rate of concentrate [m 3 /s]

Qin = volume flow rate fed into system [m 3 /s]

Cin = salt concentration of untreated water [%]

Cmin = concentration entering membrane element [%]

Cniout = concentration leaving membrane element [%]

c m = average concentration of membrane element [%]

Cc = salt concentration of concentrate [%]

R s = recovery ratio of system (= yield) [%]

R m = recovery ratio of membrane element [%]

PRO = power consumed by reverse osmosis [W]

Pmioss = power loss of membrane element [W]

ERO = specific energy needed by reverse osmosis [J/m 3 ]

E F = specific energy of feed flow [J/m 3 ]

E S = specific energy of whole system [J/m 3 ]

Π.ΗΡΡ = coefficient of efficiency of high-pressure pump (including motors)

ricp = coefficient of efficiency of circulating pump for feed flow including motors

Reverse osmosis follows the equation:

Qp - k (p - Posm ) (1) In order for reverse osmosis to occur, the pressure (driving pressure) must be greater than the osmotic pressure, otherwise the flow will change direction and change into osmosis. The operating pressure (driving pressure) required can be resolved from the equation (1) : For example, the 0 sm of a salt solution = approx. 8 bar / Cin%, i.e. the posm of a 1% salt solution = approx. 8 bar and the posm of seawater with a 3.5% salt content = approx. 28 bar (rough value) . It must be noted that the concentration increases from the upstream end to the downstream end of the membrane element, and the concentration right on the surface of the membrane■ is greater than the average concentration of the solution flowing through. The task of the turbulent feed flow is to rinse the surface of the membrane as efficiently as possible.

The average concentration in the membrane element is:

Cm ~ ( Cmo t + Cmin)/ / Cmout = C m n/ (1~ Rm) (3)

In other words, the minimum pressure needed forms via that. In order for the flow rate to be positive, there must be a sufficient margin for that minimum pressure. The maximum driving pressure is determined via the maximum permeate flow permitted for the membrane element. It can also be said that the maximum pressure is determined via the maximum pressure permitted for membrane element.

The power needed by reverse osmosis = pressure*volume rate:

PRO » PQ In a cyclical solution, for which the invention is particularly suited, there is a closed feed flow circulation - i.e. a certain type of feedback of the concentrate for refiltering together with new infeed, only the liquid of the volume flow of the permeate is pressurized. (Qf = Q p ) .

From this it follows that:

PRO = pQp = pk(p - p OS m ) = Q P 2 /k + Q p p OS n, (4)

Specific energy needed by reverse osmosis:

ERO = PRO/Q P = p = Qp/k + posm (5) In other words, the energy minimum of reverse osmosis is at the lowest possible pressure (absolute minimum when p = p 0 sm) .

Since the yield is, however, directly proportional to the pressure exceeding the osmotic pressure, and since the qual- ity of the permeate improves as the pressure increases, in the energy dimensioning a compromise must always be made in relation to equipment costs, permeate quality and energy costs. In addition to the energy to be consumed in reverse osmosis itself, energy is also needed in the system for moving the permeate, the concentrate and the infeed solution and for overcoming the losses. Pressure rise per cycle

Feed flow needed:

Qf = Q P /R m (6) This is resisted by the losses of the membrane and of the piping.

Required power Pf = (Pmloss + Pploss) *Qf = (pmloss + Pploss) *Qp/Rm ( 7 )

Specific energy of feed flow Ef = Pf/Qp = (Pmloss + Pploss) /Rm (8)

When taking the coefficients of efficiency of the pumps into account, the following is obtained for the specific energy of the whole system:

Es = ρ/ ΗΡΡ + (Pmloss + Pploss) / (RmHCp) = Qp/(kn. H pp) + Posm/η,ΗΡΡ +

(Pmloss + Pploss) / (Rmncp) (9)

The energy according to the equation (9) is instantaneous energy. In closed circulation the concentration increases during the whole cycle, in which- case either the pressure increases or the permeate flow decreases during the cycle.

When keeping either one constant, the other changes linearly.

The average specific energy of the system can therefore be calculated by using the average pressure during the cycle in the equation (9) (when driving with constant flow rate) or the average flow rate (when driving with constant pressure) .

E s = (Pstart + Pstop) / (2η Η Ρρ) +(Pmloss + Pploss )/ ( jnHcp ) (10)

If both change, the average energy must be integrated point by point .

The basic principle of operation of a membrane filter unit to be used in the invention is per se known in the art, and a number of different filter membranes as well as of different membrane filter units are commercially available. Filter membranes and membrane filter units are commercially available for many types of applications and operating conditions.

One aspect of the invention is to arrange two or more membrane filtration steps consecutively. The filtration in each phase can be performed with a cycle or with a batch process or with a continuous process. In practice, applicable solutions are of the type in which after a cyclic filtration step follows a filtration step of either cyclical or a continuous filtration. Arrangements of consecutive filtration steps do not need to be similar to each other, and the filters used in them can be different to each other. Preferred solutions are of the type in which at least the final filtration step is based on a continuous process. The invention is also applied such that in a multistep filtration apparatus is one or more filtration phases according to prior art and one or more filtration phases functioning according to the invention.

In the following the invention will be described in more detail by the aid of one example of its embodiment with refer- ence to the attached simplified drawings, wherein presents as a diagram a simplified apparatus applicable to the invention,

presents an application of the invention,

presents as a diagram an apparatus applicable to the invention,

presents a modification of the apparatus of Fig. 3a,

Fig. 4b

present a second application of the invention, and presents a two-phase solution applicable to the invention,

presents a second two-phase solution applicable to the invention,

presents yet another two-phase solution applicable to the invention,

presents yet another two-phase solution applicable to the invention,

presents a side view of yet another preferred flow channel for the structural principle of the nozzle driving the liquid circulation, Fig. 6b presents the solution of Fig. 6a as viewed from the end of the flow channel, and

Fig. 7 presents a flow channel solution comprising a number of nozzles.

Fig. 1 diagrammatically presents a simplified apparatus applicable to the invention. The water treatment device 101 comprises a membrane filter unit 1, with piping connections, and a flow channel 105, into which connects a nozzle 2 feed- ing under pressure water to be purified. The membrane filter unit 1 is, in practice, a vessel that holds pressure, inside which vessel a filter membrane, e.g. a reverse osmosis filter membrane, is arranged. The membrane filter unit 1 comprises an inlet connection 102 for conducting aqueous solution into the membrane filter unit 1, a first outlet connection 103 for conducting permeate from the membrane filter unit 1 and a second outlet connection 104 for conducting concentrate from the membrane filter unit 1. The connections 102, 103 and 104 can be regarded as being single ones in the membrane filter unit, to which are connected with a pipe, or the connections 102, 103, 104 can also be regarded as comprising pipes with which they are connected to other parts of the water treatment apparatus. The second outlet connection of the water treatment device 101 is connected to a flow channel leading to the inlet connection 102 of the water treatment device 101, in which case the concentrate is able to circulate back. In the flow channel 105 is a nozzle 2, with which new water to be treated is fed into the flow channel. The nozzle 2 feeds new water to be treated at quite a high speed towards the infeed connection 102. The volume flow rate of the water volume supplied by the nozzle is of the same magnitude as what filters through the membrane and finally exits from the first outlet connection 103. This fast flow of the nozzle arranges a cross flow on the surface of the membrane. At the same time the nozzle simultaneously transmits into the liquid space leading to the membrane the pressure needed for the filtering function of the membrane. In many cases one nozzle is sufficient, but e.g. in very large systems, comprising a number of membrane filter units connected to each other, it can be advantageous to use a number of nozzles as the source of the flow of the flow channel or possibly even of a number of flow channels .

It is easiest to make the operation of this type of water treatment device cyclical such that with the apparatus there is alternately filtration and alternately the concentrated concentrate is removed. A rinsing connection 106, 106', comprising a valve 107, 107', is in the membrane filter unit 1 or in a branch from the second outlet connection 104, via which rinsing connection the concentrated concentrate is removed .

Fig. 2 contains an example of an application. A system of the type of Fig. 2 is suited e.g. to producing the household water of an apartment or holiday home, or to some other small- scale water purification. The basis for an apparatus accord- ing to the figure is a relatively low salt content of the untreated water, in which case the untreated water can be e.g. mains water, well water, fresh surface water, brackish water - at least when it has a lower salt- content - or even sea water.

By the aid of the nozzle 2 in the flow channel, the pre- treated/prefiltered untreated water is driven into the membrane filter unit, i.e. into the membrane element 1, in which is a reverse osmosis membrane. The outlet coupling for the concentrate of the membrane element 1 is connected back to the inlet connection of the membrane element via the flow channel. The nozzle in the flow channel functions as a drive means for the flow of the membrane element and, via it, also the liquid pathway leading to the membrane element is pres- surized to the pressure necessary for the operation of the membrane element. In the system of Fig. 2, the incoming untreated water is taken either from some pressurized mains water network 6, in which the water pressure is typically 3...6 bar, or from a low-pressure/unpressurized untreated water source, e.g. a well, a lake, a river or fcfte 3@c When taking untreated water from a low-pressure or unpressurized untreated water source, often a pump 5 is needed for transferring the untreated water and driving it to prefiltering. If the untreated water is available pressurized, then the pump 5 is not needed. If the untreated water is not very saline, it is very sufficient for the pump 5 to raise the pressure to approx. 6 bar. The operation of the pump 5 or of the valve 6 is controlled with the control 14 in order to supply or not to supply untreated water .

The untreated water is conducted through a prefilter 4. The prefilter or prefilters is/are selected according to the properties of the untreated water and possibly according to other bases. There can be a number of filters. When making household water for domestic use, or corresponding, the prefilter 4 typically comprises a sediment filter (e.g. 5 m) and an active carbon filter.

The alternation of the filtering stages and rinsing stages of the membrane filter unit 1 can be controlled e.g. based on data about the volume of water passing through the system. By disposing a flow meter 3 in the line in which untreated water, or water prefiltered from it, is conducted towards the nozzle 2, the data needed for the control is obtained. Pref- erably the data is an electrical signal. The data obtained from the flow meter about the speed of the flow and/or the volume of water that has flowed through is delivered to the control unit 14, with which the pumps and valves of the system are controlled. The volume of water that has flowed through is also monitored over a longer time span, in which case data is obtained about when filters or other parts should be serviced or replaced. The flow meter can be disposed in the water circulation before or after the prefilter or also, if a pressure pump 15 is a part of the apparatus, in connection with the pressure pump. The prefiltered water is conducted into the circulation of the water to be purified by the membrane filter unit 1 via a nozzle 2. Trie nozzle is di- mensioned, disposed and shaped such that the kinetic energy of the water flowing through it brings about a sufficient water circulation in the closed circulation of the water to be purified. Before the nozzle 2 the pressure of the water to be purified and to be fed into the circulation can be raised with a pressure pump 15. Pure water permeates the membrane of the membrane filter unit 1 by means of reverse osmosis, which pure water is conducted into the tank 9. Since water is not able to exit the closed circulation via any way other than through the membrane, the inlet flow rate of the water is equal to the drainage of pure water. Permeation of the membrane depends on the properties of the membrane, the salt content of the water, the temperature and the pressure acting over the membrane, which must be greater than the osmotic pressure of the water to be purified in order for permeation to occur. The salt content on the dirty side of the membrane increases and the purpose of the water circulation rinsing the surface of the membrane is to transport excess salt concentration away from the surface of the -membrane so that reverse osmosis will continue. The salt content of- water in closed circulation rises ' as the process continues. Water that is saltier than the incoming water that has passed through the dirty water side of the membrane filter unit 1 is removed from the membrane filter unit 1 and controlled with the valve 7 either to continue its circulation or to discharge into the sewer 8. The purified water is collected in the tank 9, from where it is conducted to the point of usage via the pump 10 and the valve 11. The pump 10 can be controlled e.g. via the position of the valve 11 or via the pressure of the discharge pipe of the pump 10. If necessary, or if desired, water puri- fied by the membrane filter unit 1 can be further filtered, in which case an after-filter 12 must be included in the system. An active carbon filter is typically used as an after- filter. In the tank 9 are devices 13 measuring the surface height of the water, which devices notify the control after the surface of the water has dropped below a certain limit or risen above a certain limit. The water surface height data is used to control the volume of the production of purified wa- ter . After the salt content has risen sufficiently, the position of the valve 7 is changed such that the water in circulation exits into the sewer 8. Since the pressure in the circulation then drops, the nozzle 2 is then able to pass a larger amount of water and the water in circulation changes quickly. After the water has changed sufficiently, the valve 7 is turned such that the discharge channel to the sewer closes and the channel to the water circulation opens. The pressure in the system increases, reverse osmosis starts again, and the water circulation continues. It must be noted that after the pressure of the membrane has dropped to below the osmotic pressure in the rinsing, osmosis starts, transferring purified water back through the membrane. This significantly enhances the cleaning of the membrane. In order for this to be able to occur, care must be taken that the back-flow from the purified water side is possible, and that water is available for this, even though the amount needed is not large. It is possible, for example, to monitor that the outlet pipe coming from the membrane filter unit 1 is always below water in the tank 9.

With the device a yield of a certain magnitude, e.g. 80...90%, is aimed for. The yield refers to the ratio of the purified water and the water used. With a yield of 90%, for example, 90% of the volume of the untreated water taken ends up in use as purified water and 10% as concentrate in the sewer. The desired yield depends on the quality of the untreated water, the cost of the untreated water, the pressure available, the properties of the membrane element, the energy costs, et cetera, and it is set in advance to be what is de- sired.

At its simplest, the control ensures the desired yield by using a flow meter 3. Since the volume V 0 of the closed water circulation of the device is known, the water volume used for rinsing is measured to be roughly the same magnitude as that volume V 0 . During the purification process the water volume Vi fed into the device is measured. The control calculates the ratio Vi/(Vo+Vi) and when the desired value is achieved starts the rinsing.

When controlling on the basis of the water requirement, the control 14 starts the pump 5 or opens the valve 6, and if the system comprises a pressure pump 15 it also starts the pressure pump 15, when the surface height of the tank 9 is at the set bottom limit and, correspondingly, stops the pumps and closes the valve when the top limit for surface height is reached. The control manages the control of the valve 7. When the apparatus is standing unused for long periods, the control can at regular intervals perform an extra rinsing circulation .

Fig. 3a diagrammatically presents one apparatus applicable to the invention. Simply put, the basic structure can be regarded as being similar to the apparatus of Fig. 1 - the operation, however, differs from the apparatus of Fig. 1. The arrangement of Fig. 3 can be applied to many devices, e.g. for the purification of mains water in small so-called "kitchen sink" devices, or in other devices in which a low purchase price is especially important. Likewise the apparatus is suited as a second-step purification device, e.g. for purifying once-purified water to make it even purer. The process of the apparatus of Fig. 3 is continuous, in which case it does not need valve controls, but instead purification occurs with constant adjustments.

The water treatment device 199 comprises a membrane filter unit 1, with piping connections, and a flow channel 105, into which connects a nozzle 2 feeding under pressure water to be purified. The membrane filter unit 1 is in practice a vessel that holds pressure, inside which vessel a filter membrane, e.g. a reverse osmosis filter membrane, is arranged. The membrane filter unit 1 comprises an inlet connection 102 for conducting aqueous solution into the membrane filter unit 1, a first outlet connection 103 for conducting permeate from the membrane filter unit 1 and a second outlet connection 104 for conducting concentrate from the membrane filter unit 1. The connections 102, 103 and 104 can be regarded as being branch couplings on the membrane filter unit, to which pipes are interfaced, or the connections 102, 103, 104 can also be regarded as comprising pipes with which other parts of the water treatment apparatus are interfaced. A second outlet connection of the water treatment device 101 is connected to the flow channel leading to the inlet connection 102 of the water treatment device 199, in which case the concentrate is able to recycle back. In the flow channel 105 is a nozzle 2, with- which new water to be treated is fed under pressure into the flow channel. The nozzle 2 feeds new water to be treated at quite a high speed towards the infeed connection 102. The volume flow rate of the water volume supplied by the nozzle is to some extent greater than what filters through the membrane and finally exits from the first outlet connection 103. This fast flow of the nozzle is arranged on the surface of the membrane. If necessary, there can be a number of nozzles, especially if a number of parallel membrane filter units are made in the apparatus.

The operation of this type of water treatment device is continuous . The water volume being supplied is the amount of permeate leaving plus the amount of concentrate that is al- lowed to leak from the recirculation branch via the outlet connection 198. In the outlet connection 198 the flow is limited e.g. with constriction such that the pressure in the recirculation branch starting from the branch coupling 104 does not drop too much. The outlet connection limiting the flow is suitably e.g. a needle valve or other device, with which the magnitude of the flow can be set. In the apparatus of Fig. 3a, feed flow is supplied with a nozzle towards the membrane unit, for which feed flow the incoming volume flow rate is Qin, the pressure p, and the power Qin*p. The concentrate is recirculated and there is a controlled leak in the recirculation pipe. The concentrate leak is constricted so that the desired yield R, e.g. 90%, is achieved. In this case the permeate flow rate is Qp = R*Qin and the concentrate flow rate leaking out Qc = (l-R)*Qin. The device is continuous-action and runs at the desired recovery ratio, which in this way can therefore be quite high. Thus, if R = 90%, the dissipated energy leaving with the concentrate is only approx. 10% and the apparatus can be run continuously at maximum pressure.

If the salt content, or the content of some other substance, of the incoming water is relatively low, the difference between minimum pressure and maximum pressure is not great, in the region of 5...10%, in which case the losses are only in the region of 15...20% greater compared to a device that is optimized for minimum energy consumption. In this type of device the energy consumption results from pressure losses, in which case the consumption of energy is not necessarily a significant extra cost, at least not if the apparatus is ac- tivated with the pressure of the mains water network. The over 90% yield that is achievable in practice is appreciably better than that of many commercial "kitchen sink" ' devices, which are able to utilize less than one-half of the untreated water they use. The simple composition and operation of the apparatus are an excellent advantage.

Fig. 3b presents an apparatus modified from the apparatus of Fig. 3a. The idea behind the apparatus 197 of Fig. 3b is to achieve a simple and easy-to-operate "kitchen sink device" for household or corresponding use. The operation of the device is controlled by the water inlet valve 195. In the water inlet pipe 194 is a rinsing tank 196 between the water inlet valve 195 and the nozzle 2. The rinsing tank fills and emp- ties at a lower pressure than that at which the filter membrane in the membrane filter unit 1 permeates, or permeates significantly. Preferably the rinsing tank 196 is fabricated from a flexible rubber bag or corresponding, which fills and expands at a very low pressure, e.g. below 0.5 bar, which pressure is also greatly below the pressure of the infeeding water main. In this way the rinsing tank 196 fills when the valve 195 is opened, and the membrane filter apparatus 197 starts to operate in the manner of the apparatus of Fig. 3a. When the valve 195 is closed, the pressure in the apparatus starts to decline and soon permeate stops coming from the outlet connection 103. When the pressure decreases, the recirculated flow continues for some time, being compelled by the rinsing tank 196 and leaking via the choke 198. At the same time also the back flush pushes the impurities adhering to the membrane back into the concentrate flow, in which case the membrane saturates itself with permeate. Instead of a separate rinsing tank, the flexings of parts of the system, e.g. of pipings, filters or other tanks, can be used for the same function.

Figs. 4a and 4a diagrammatically present a water treatment device 101 applicable to the invention, which device comprises a number ' of membrane filter units 1, with* piping con- nections, and a flow channel 105 into which connects a nozzle 2 feeding under pressure water to be purified. In this embodiment, a number of membrane filter units 1, each of which comprises a vessel that holds pressure, arranged inside which vessel is a filter membrane, e.g. a reverse osmosis filter membrane, are arranged to receive a water infeed into a common flow channel 105 or alternatively into common flow channels .

' The concentrate from the second outlet connections 104 is conducted into the common flow channel 105 by means of the piping 204 and the concentrate is conducted from the common flow channel 105, into which concentrate the still untreated aqueous solution being fed in with the nozzle 2 mixes, for distributing with the piping 202 to the inlet connections 102 of the membrane filter units 1. The first outlet connections 103 of the membrane filter units 1, which outlet connections are for conducting permeate from the membrane filter unit 1, are connected together with outlet piping 203. A separate actuator 222, such as a pump or propeller, can be in the flow channel 105, or the flow is maintained with the directed high-pressure water infeed of the nozzle 2 into the flow channel 105.

The connections 102, 103 and 104 can be regarded as being branch couplings on the membrane filter unit, to which pipes are interfaced, or the connections 102, 103, 104 can also be regarded as comprising pipes with which interfaces to the other pipings 202, 203, 204 of the water treatment apparatus are made .

The operating pressure of the water treatment device 101 is delivered by a pressure pump 215, with which water is sup- plied into the flow channel leading to the inlet connection 102 via the nozzle 2. The volume flow rate of the water volume supplied by the nozzle 2 is of the same magnitude as what filters through the membrane and finally exits from the first outlet connection into the outlet pipe 203. In many cases one nozzle is sufficient, but e.g. in very large systems, comprising a number of membrane filter units connected to each other, it can be advantageous to use a number of nozzles as the source of the flow of the flow channel or possibly even of a number of flow channels.

It is easiest to make the operation of the water treatment device cyclical such that with the apparatus there is alternately filtration and alternately the concentrated concentrate is removed. A discharge valve 207, via which the con- centrated concentrate is removed, is connected to the flow channel 105 or to the pipings 202, 204 connected to it. Figs. 5a, 5b, 5c, 5d diagrammatically present membrane separation/membrane filter systems by way of example, wherein two membrane filter units 501, 502 are connected in series. The circuit of membrane filter units has different solutions, depending on the operating method selected. The first pump 503 supplies the filter unit 501 of the first filtration phase, or in some cases a whole chain of filter units connected in series. The second pump 504 is supplying the filter unit 502 of the second filtration phase. In larger plants each filtration phase can comprise a number of filter units in parallel and the necessary number of pumps for supplying the liquid, either such that the water infeeds of the parallel filter units are in connection with each other or such that each filtration unit of the filtration step in question has its own pump supplying only this filtration unit.

In the solution of Fig. 5a, the filtration of the first phase is arranged to be cyclical and the second phase is implemented as continuous. In the first purification phase the pump 503 supplies the water to be purified via the nozzle 507 into the flow channel 506 bringing about a flow towards the filter unit 501, from where the permeate is conducted into the storage tank 505 and the concentrate is conducted back into the flow channel. This circulation is maintained, in which case the concentrate of course becomes more concentrated, until on the basis of the selected control criterion the concentrate is replaced completely, or almost completely, for a new batch of water to be purified. The changeover occurs with the valve device 512, which is controlled to dis- charge the concentrate into the sewer, on the dashed line pointing downwards, instead of the concentrate being conducted to circulate back to the filter unit 501. At the same time the liquid pathway, from where the water to be purified is conducted past the pump 503 to the space of the concen- trate being removed, is opened with the valve device 512. When the concentrate has been replaced the valve device 512 is controlled to close the supply of water coming via it to be purified and to conduct the concentrate back into the flow channel. In the second purification phase the pump 504 pumps the permeate of the first phase from the tank 505 onwards for purification in the second phase. Pressure comes into the flow channel 508 via the infeeding nozzle 509 as well as the maintenance of the flow. A rather pure permeate, arrow pointing to the right, is obtained from the second filter unit 502. The concentrate of the second phase is circulated partly back into the flow channel 508 and partly via the choke valve 511 for purification of the first phase. The pressure ratios can easily be set to be such that the concentrate of the second phase to be circulated via the choke valve 511 can be fed in upstream of the pump 503. In the solution according to Fig. 5a it is possible to alternatively omit the tank 505 and the pump 504 and to connect the permeate output of the first filter unit 501 to directly feed permeate to the second phase via the nozzle 509, in which case also the second phase follows the cyclical operation of the first phase. This type of alternative, of course, requires a pump 503 and configuration- of the pressure conditions.

In the solution of Fig. 5b the filtrations of both the first and the second phase are arranged to be cyclical. In the first purification phase the pump 503 supplies the water to be purified via the nozzle 507 into the flow channel 506 bringing about a flow towards the filter unit 501, from where the permeate is conducted into the storage tank 505 and the concentrate is conducted back into the flow channel. The concentrate in the first phase is replaced with new water to be purified cyclically in the same manner as in the apparatus of Fig. 5a. In the second purification phase the pump 504 pumps the permeate of the first phase from the tank 505 onwards for purification in the second phase. Also the second phase is controlled to operate cyclically. Pressure comes into the flow channel 508 via the infeeding nozzle 509 as well as the maintenance of the flow. A rather pure permeate, arrow pointing to the right, is obtained from the second filter unit 502. The concentrate of the second phase is circulated back into the flow channel 508. In the second purification phase of Fig. 5b, the circulation supplied by the pump 504 is maintained, until on the basis of the selected control criterion the concentrate of the second phase is replaced completely, or almost completely, for a new batch of the permeate of the first phase. The changeover occurs with the valve device 513, which is controlled to discharge the concentrate of the second phase upstream of the pump 503 of the first phase, instead of the concentrate being conducted to circulated back to the filter unit 502. At the same time the liquid pathway from where the permeate of the first phase is conducted past the pump 504 to the space of the concentrate being removed is opened with the valve device 513.

In the solution of Fig. 5c the filtrations of both the first and the second phase are implemented as continuous and each phase is activated with its own pumps. In the first purification phase the pump 503 supplies the water to be purified via the nozzle 507 into the flow channel 506 bringing about a flow towards the filter unit 501, from where the permeate is conducted into the storage tank 505 and the concentrate is partly conducted back into the flow channel and partly to the sewer via the choke valve 510. In the second purification phase the pump 504 pumps the permeate of the first phase from the tank 505 onwards for purification in the second phase. Pressure comes into the flow channel 508 via the infeeding nozzle 509 as well as the maintenance of the flow. A rather pure permeate, arrow pointing to the right, is obtained from the second filter unit 502. The concentrate of the second phase is circulated partly back into the flow channel 508 and partly via the choke valve 511 for purification of the first phase . In the solution of Fig. 5d the filtrations of both the first and the second phase are implemented as continuous and with a pump jointly activating both phases. The solution of Fig. 5d is reminiscent of the solution of Fig. 5c, with the differ- ence that the permeate output of the first filter unit 501 is configured to directly feed permeate to the second phase via the nozzle 509 Figs . 6a and 6b present a preferred construction principle of a nozzle driving a liquid circulation of a membrane filter device. A nozzle 62 is disposed inside the flow channel 61, in the side of which nozzle is a slot 63 opening in the direction of the flow channel. In Fig. 6a, the direction of the liquid flow coming into the flow channel from the nozzle as well as the direction of the liquid flow of the flow channel is for reference purposes indicated by means of arrows. Owing to turbulence and to the fact that the spray coming from the nozzle tries to open, the directions of the flows presented by the arrows are not at all exact.

In the flow channel solution presented in Fig. 7, a plurality of nozzles, at least two nozzles, preferably 3 or more nozzles, feed liquid into the flow channel from a pressure source. At their simplest the nozzles 2 are borings from the more highl pressurized liquid space through the wall W of the flow channel, said borings extending into the flow channel 105. One alternative implementation for the solution of Fig. 7 is such that pipe-shaped nozzles protruding from the inner wall of the flow channel are disposed in these types of borings. Preferably the nozzles according to Fig. 7, or the nozzles of a solution varying from the basic idea of it, are directed obliquely in the direction of the flow channel, and even more preferably over the center line of the flow chan- nel. By feeding new liquid over the center line of the flow channel the connection distance of the infeed flow with the receiving flow can be lengthened. It is good to make the flow channel as one that expands at the point of, or in the proximity of, the nozzles. All the nozzles can be in line with each other in the longitudinal direction of the flow channel. The effect of the nozzles can also be phased such that the nozzles are at different points of the length of the flow channel . It is obvious to the person skilled in the art that the invention is not limited to the examples described above, but that it may be varied within ; the scope of the claims pre- sented below as well as of the description and the drawing presented.