WO2015135545A1

WO2015135545A1 - Apparatus and method for membrane filtration

Info

Publication number: WO2015135545A1
Application number: PCT/DK2014/050055
Authority: WO
Inventors: Swami Sundaram; Erling Skroder Hansen; Shanti BHUSHAN; Bruce David Blanchard
Original assignee: Gea Process Engineering A/S
Priority date: 2014-03-11
Filing date: 2014-03-11
Publication date: 2015-09-17

Abstract

The apparatus (1) for membrane filtration of a feed has a housing (2) with a feed inlet (3) and a feed outlet (4). At least two membrane elements (10, 20) are provided in extension of each other and each having an associated permeate tube (11,21), and an anti-telescoping device, ATD (12, 15, 22)at a respective end. Pressure regulating means (14, 24) is provided in connection with each permeate tube(11, 21), specifically in the form ofaback pressure valve (14, 24).

Description

Apparatus and method for membrane filtration

Field of the invention

The present invention relates to an apparatus for membrane filtration of a liquid feed, comprising at least one housing defining a longitudinal direction, a feed inlet, a feed outlet, at least one membrane element having a first end and a second end, and a permeate tube. The invention furthermore relates to a method for membrane filtration of a feed.

Background of the Invention

Filtration of a liquid or fluid feed is one way of separating particles of different size in the feed from each other.

In particular, membrane filtration systems that utilize technologies in- eluding microfiltration, ultrafiltration, nanofiltration or reverse osmosis have gained extended use over recent years. The operating principle of membrane filtration involves passing the feed across the filter membrane at positive pressure relative to the permeate side. A proportion of the material which is smaller than the membrane pore size passes through the membrane as per- meate, whereas the rest is retained on the feed side of the membrane as re- tentate.

Membrane filtration is utilized as a manufacturing step in many process lines in the food, dairy, pharmaceutical/biotechnology, chemical and starch and sweetener industries worldwide. The ability to produce very spe- cific separations at low or ambient temperatures with no phase change can, in many applications, make membrane filtration a much more cost-effective solution than more conventional methods such as rotary vacuum filtration or filter presses.

Examples of suitable fields of application include microfiltration (MF) and ultrafiltration (UF) of skim milk and whey. In such fields of application, the separation of casein from skim milk and fat from whey protein concentrate (WPC) are processes that require a firm control of the Trans-Membrane- Pressure (TMP). If the TMP is not controlled correctly, the permeability of the whey proteins is too low, and the final product will not be satisfactory.

Prior art apparatus and methods of membrane filtration are shown in for instance documents WO 2009/035700 A2, US 2007/0158256 A1 and DE 39 14 326 A1 .

Due to the need for accurate setting of the operating pressures, in particular the TMP, a single membrane element is traditionally placed in the housing, and the pressure gradient on the membrane is adapted to the spe- cific product parameters. However, this is costly and has a high utility consumption.

Summary of the invention

With this background, it is an object of the invention to provide mem- brane filtration in a more cost-effective manner, while retaining suitable operating conditions to obtain satisfactory product quality and composition.

In a first aspect, this and further objectives are achieved by an apparatus of the kind mentioned in the introduction, which is furthermore characterized in that at least two membrane elements are provided in extension of each other in said longitudinal direction, each membrane element having an associated permeate tube, and that pressure regulating means is provided in connection with each permeate tube.

By the combination of these features, an apparatus is devised that is more cost-effective as only one housing is provided to accommodate the at least two membrane elements. Hence, only one feed inlet and feed outlet need to be provided, and the resources required for auxiliary equipment such as supply and discharge lines etc are reduced correspondingly. By the provision of pressure regulating means connected to the permeate tube of the individual membrane element, the Trans-Membrane Pressure, TMP, may be controlled such that TMP is the same for each membrane element. In turn, this means that the level of permeability is the same in both or each of the membrane elements. Furthermore, providing pressure regulating means on both sides of the housing will allow an increased baseline pressure, which in turn provides for possibilities for better control of the concentrate flow.

The term TMP is a well-known parameter.

In one embodiment, at least one anti-telescoping device, ATD is pro- vided at at least one of the first and second ends of each membrane element. This is a well-known and reliable technical solution.

The pressure regulating means may in principle comprise any suitable pressure regulating systems, for instance pressure regulation valves. In an embodiment, the pressure regulating means comprises a back pressure valve. This is a simple and mechanically reliable solution to obtain pressure regulation. As an alternative to the back pressure valve a pressure regulating control system may be connected to the pressure regulating means.

In principle, one ATD could be connected to each end of each membrane element, or one end of one, both or each membrane elements could be closed by an end plug. However, in a preferred embodiment, only one ATD is provided between neighbouring membrane elements. In a further development of this preferred embodiment, the ATD between neighbouring membrane elements is formed such that the permeate tubes associated with the respective membrane elements are not connected with each other. Although requiring a specially designed ATD, the overall installation costs are reduced by the provision of such an ATD which is common to neighbouring membrane elements, which in turn allows for an even further increased cost-efficiency of the apparatus.

The chosen number of membrane elements in one housing may de- pend on a number of factors such as capacity and space requirements. For instance, the number may be larger than two, preferably three or four; or alternatively exactly two.

In one embodiment, two housings are provided and connected to each other by a conduit, the feed inlet being connected to one housing and the feed outlet to the other housing. This increases the overall cost-efficiency of the apparatus.

In a further preferred embodiment, the membrane element comprises a spiral wound membrane, having a pore size of 0.005 μηι to 5 μηι. Due to their compact layout and relatively large amount of membrane area per element, spirals are good cost-effective solutions to high volume applications with minimal or no suspended solids, with the primary advantage being both low capital investment and energy costs. They are available for all types of filtration from microfiltration to reverse osmosis.

The spiral wound membranes used may be commercially available membranes. Preferably, they have a pore size typically of 0.01 μηι to 1 μηι.

The material of the membrane element could be any suitable mate- rial such as ceramic or steel. However, it is preferred to utilize a membrane element of a polymer material, preferably chosen from the group comprising polyvinylidene fluoride (PVDF), polysulfone (PS) or polyethersulfone (PES).

In a mechanically simple embodiment, the permeate tube of the respective membrane elements is provided with a permeate outlet at a respec- tive longitudinal end of the housing.

In a second aspect, a method for membrane filtration of a liquid feed is provided, the method comprising the steps of:

providing at least one longitudinally extending housing with a feed inlet and a feed outlet,

providing a first membrane element with a first end and a second end,

providing at least a second membrane element with a first end and a second end, in longitudinal extension of the first membrane element,

associating a permeate tube with each membrane element, and regulating the pressure in each permeate tube.

Optionally, the method may include the further step of providing an anti-telescoping device, ATD, at at least one of the first and second ends of each membrane element,

While it is presently preferred that the pressure is regulated by means of a back pressure valve in connection with each permeate tube, an alternative would be to control the step of regulating the pressure by a pressure regulating control system. Preferably, the step of providing an ATD includes providing only one ATD between neighbouring membrane elements.

Whereas the method of the invention is applicable within many fields of application, it is particularly advantageous that the feed is a whey product, preferably whey protein concentrate, WPC. In addition to fat removal from whey, the method is applicable to casein concentration in skim milk, for instance in the production of serum protein reduced micellar casein concentrate (MCC), and other processes requiring accurate control of the TMP.

Further embodiments and advantages will appear from the following description. Details relating to any one aspect of the invention may apply to the other aspects as well.

Brief description of the drawings

Fig. 1 is a schematic overview of an apparatus according to the in- vention in a first embodiment;

Fig. 2 is a schematic overview of an apparatus according to the invention in a second embodiment;

Fig. 3 is a schematic overview of an apparatus according to the invention in a third embodiment;

Fig. 4 is a schematic overview of an apparatus according to the invention in a fourth embodiment; and

Fig. 5 is a schematic overview of an apparatus according to the invention in a fifth embodiment. Detailed description of the invention and of preferred embodiments

In Fig. 1 , a first embodiment of an apparatus generally designated 1 is shown. The apparatus 1 is a membrane filtration apparatus for the filtration of a feed and comprises a housing 2 defining a longitudinal direction. At one longitudinal end of the housing 2, a feed inlet 3 is provided, and at the oppo- site end a feed outlet 4 is provided. The housing 2 is designed substantially as a pressure vessel, and further auxiliary equipment such as supply and discharge lines, socket pieces and connecting branches etc. may be present in a manner known per se.

In the housing 2, a first membrane element 10 is positioned at the end of the housing 2 proximate to the feed inlet 3. In extension of the first membrane element 10, a second membrane element 20 is provided. The first and second membrane elements 10, 20 are each provided with an associated, respective permeate tube 1 1 , 21 .

In the embodiment shown, the first membrane element 10 is, at a first end, connected to an anti-telescoping device or ATD 15, and to an ATD 12 at an opposite, second end. The second membrane element 20 is, at its first end, connected to the same ATD 15 as the first membrane element 10. Furthermore, the second membrane element 20 is at its opposite, second end connected to another ATD 22.

The permeate tube 1 1 of the first membrane element 10 is at the second end thereof connected to a permeate outlet 13, which in turn is con- nected to a pressure regulating means, which in the embodiment shown is a back pressure valve 14. In the embodiment shown, the permeate outlet 13 is provided at a longitudinal end of the housing 2. The connection between the permeate tube 1 1 and the pressure regulating means could also be formed as a direct connection, other than via the permeate outlet 13.

The second membrane element 20 is provided with its own, individual pressure regulating means connected to the permeate tube 21 . In the embodiment shown, the pressure regulating means is a back pressure valve 24, and the connection between the permeate tube 21 and the pressure regulating means is provided via a permeate outlet 23.

Permeate discharged from the permeate outlets 13 and 23 is conducted to not-shown reception means in the form of containers or the like.

The back pressure valves 14, 24 constituting the pressure regulating means of the embodiment of Fig. 1 provide individual, accurate control of the Trans-Membrane Pressure, TMP, over each of the membrane elements 10, 20. The back pressure valves may for instance be spring loaded valves or another type of suitable valve providing the pressure regulation required.

In the embodiment shown in Fig. 1 , the two neighbouring membrane elements 10, 20 have a common ATD 15, in that only one ATD is provided between the facing first ends of the first and second membrane elements 10, 20. Furthermore, the ATD 15 between neighbouring membrane elements 10, 20 is in the embodiment shown in Fig. 1 formed such that the permeate tubes 1 1 , 21 associated with the respective membrane elements are not connected with each other. This provides for optimum cost-efficiency and accuracy of control of the TMP of the individual membrane elements 10 and 20.

The membrane elements 10 and 20 may comprise any commercially available membranes and in principle have any suitable dimensions, either identical or different. For instance, in the embodiment shown the membrane elements have identical lengths of 38 inches or approximately 96.5 cm, and a diameter of 6.3 or 7.9 inches, or approximately 16 or 20 cm, but a smaller diameter such as 3.8 inches or 9.7 cm is also conceivable. A typical range of values would be approximately between 15 and 100 inches. The dimensions are standard sizes of commercially available membrane elements. The housing 2 in the embodiment shown thus has a length which is large enough to accommodate the two membrane elements in extension of each other and to provide for other equipment such as feed inlet 3, feed outlet 3 etc., resulting in a length of approximately double the length of one membrane element, i.e. about 2 m in the embodiment shown. Correspondingly, the diameter of the housing 2, or cross-sectional dimensions, if the housing is provided with another overall shape than cylindrical, is chosen such that sufficient space for accommodating the membrane elements 10, 20 and allow feed to reach the outer surface of the membrane elements is provided. For instance, the diame- ter of the housing may be chosen to exceed 20 cm slightly.

In the shown preferred embodiment of Fig. 1 , each membrane element comprises a spiral wound membrane. The pore size may be any conceivable to fit the specific field of application of the apparatus 1 , typically mi- crofiltration or ultrafiltration, and have matching pore sizes of 0.005 μηι to 5 μηι. It is however preferred that the spiral wound membrane has a pore size of 0.01 μΓΠ to 1 μΓΠ.

Each membrane element comprises, in the preferred embodiment, a polymer material. Typical materials are chosen from the group comprising polyvinylidene fluoride (PVDF), polysulfone (PS) or polyethersulfone (PES).

In the following, second and third embodiments will be described with reference to Figs 2 and 3, respectively. Elements having the same or analo- gous function as in the first embodiment of Fig. 1 carry the same reference numerals. Only differences from the first embodiment will be described in detail.

The number of membrane elements in the housing may in principle be any conceivable number. In the embodiment shown in Figs 1 and 3, the number is two, but the number could also be larger than two, for instance three, as shown in the embodiment of Fig. 2, or four.

In the embodiment of Fig. 2, three membrane elements 10, 20, 30 are provided in extension of each other in said longitudinal direction. The length of the housing 2 is adapted correspondingly (unless membrane ele- ments of a smaller length are provided).

A permeate tube 1 1 , 21 , 31 is associated to each membrane element 10, 20, 30. An ATD is provided at at least one of the first and second ends of each membrane element, such that the first membrane element 10 in the embodiment shown has two ATDs 12 and 15, the second membrane element 20 one ATD 22 at one end, and an ATD 25 which is common with neighbouring membrane element 30, which in turn is provided with an ATD 32 at its other end. Pressure regulating means 14, 24; 34 is provided in connection with each permeate tube. In the embodiments shown, the connection is carried out via permeate outlets 13, 23, 33 at a respective longitudinal end of the housing 2. The pressure regulating means comprises a back pressure valve 14, 24; 34.

In the embodiment of Fig. 3, two housings 2a, 2b are provided and connected to each other by a conduit 100. The feed inlet 3 is connected to one housing 2a and the feed outlet 4 to the other housing 2b. The configura- tion of membrane elements 10, 20 in housing 2a and membrane elements 30, 40 in housing 2b, corresponds in substance to the embodiment of Fig. 1 . Hence, membrane elements 30, 40 has a respective permeate tube 31 , 41 , a permeate outlet 33, 43, and pressure regulating means in the form of back pressure valve 34, 44. Membrane element 30 has an ATD 32 at one end, and at the other end an ATD 35 which is common with the other membrane element 40, which in turn has an ATD 42 in its other end. Slight variations are conceivable, however, just as the number of membrane elements in each housing may be other than the shown two.

In the alternative embodiment of Fig. 4, elements having the same or analogous function as in the embodiment of Fig. 1 are denoted by the same reference numerals. Only differences from the embodiment of Fig. 1 will be described in detail. In Fig. 4, it is seen that the membrane element 10 is provided as two contiguous membrane element parts 10a, 10b that are separated by a plug 45. The plug 45 prevents permeate flow between the membrane element parts 10a, 10b and as such has the same function as the ATD 15 of the embodiment of Fig. 1 .

In the further alternative embodiment of Fig. 5, two membrane filtration apparatus 1 , 101 are coupled in parallel. The apparatus 101 has substantially the same configuration as apparatus 1 , and parts having the same or analogous function carry the same reference numerals to which 100 has been added. In turn, apparatus 1 has substantially the same configuration as the apparatus 1 of the first embodiment shown in Fig. 1 . Only differences will be described in further detail. The two apparatus 1 , 101 have a common inlet system and a common outlet system. Furthermore, permeate outlets 13, 1 14 are connected to a common back pressure valve 14, and permeate outlets 23, 123 are connected to another, common back pressure valve 24.

When devising a plant including filtration systems incorporating apparatus according to the invention, it is advantageous to provide several loops, each with a common recirculation pump. Several housings may be placed in parallel, the number being possibly larger than the shown two, maybe even up to 15. In all of these housings, the same concentration, the same pressure and the same fouling will prevail. This arrangement will pose certain requirements to for instance the piping and a suitable velocity range. In those cases, a common permeate regulator for each permeate outlet in each loop will be possible.

In all of the above embodiments, the membrane filtration is carried out in substantially the same manner, according to the method of the invention as will be described in the following.

The method for membrane filtration of a feed thus comprises the steps of:

providing a longitudinally extending housing with a feed inlet and a feed outlet,

providing a first membrane element with a first end and a second end,

Optionally, an anti-telescoping device, ATD, is provided at at least one of the first and second ends of each membrane element,

The pressure is regulated by means of a back pressure valve in connection with each permeate tube.

The step of providing an ATD includes providing only one ATD be- tween neighbouring membrane elements.

As an alternative, not-shown embodiment, a pressure regulating control system could be connected to the pressure regulating means and the step of regulating the pressure could be carried out by control by a pressure regulating control system.

At regular intervals, for instance as a part of a cleaning regimen, the apparatus may be cleaned. This may be carried out as a Cleaning-ln-Place (CIP) procedure which is as such well-known in membrane filtration. In the apparatus according to the invention as described in the above, the flow of cleaning liquid, most often water, is controllable by the pressure regulating means as well. As the flow of cleaning liquid may be regulated, it is possible to reduce the total flow, which in turn may reduce the power consumption.

In the field of application described, the feed is a whey product, pref- erably whey protein concentrate, WPC. The method of the invention is however applicable within many fields of application. Other than a whey product, preferably whey protein concentrate, WPC, involving fat removal from whey, the method is applicable to casein concentration in skim milk, for instance in the production of serum protein reduced micellar casein concentrate (MCC), and other processes where a very firm control of the TMP is required.

The invention should not be regarded as being limited to the embodiments shown and described in the above, but various modifications and variations are conceivable without departing from the scope of the appended claims.

Claims

P A T E N T C L A I M S

1 . An apparatus (1 ) for membrane filtration of a liquid feed, comprising at least one housing (2; 2a, 2b) defining a longitudinal direction, a feed inlet (3), a feed outlet (4), at least one membrane element (10, 20; 30; 40) having a first end and a second end, and a permeate tube (1 1 , 21 ; 31 ; 41 ), characterized in that at least two membrane elements (10, 20; 30; 40) are provided in extension of each other in said longitudinal direction, each membrane element having an associated permeate tube (1 1 , 21 ; 31 ; 41 ), and that pressure regulating means (14, 24; 34; 44) is provided in connection with each permeate tube.

2. An apparatus according to claim 1 , wherein at least one anti- telescoping device, ATD (12, 15, 22; 25, 32; 35, 42) is provided at at least one of the first and second ends of each membrane element,

3. An apparatus according to claim 1 or 2, wherein the pressure regulating means comprises a back pressure valve (14, 24; 34; 44).

4. An apparatus according to claim 2 or 3, wherein only one ATD (15; 25; 35) is provided between neighbouring membrane elements (10, 20; 30; 40).

5. An apparatus according to claim 4, wherein the ATD (15; 25; 35) between neighbouring membrane elements is formed such that the permeate tubes (1 1 , 21 ; 31 ; 41 ) associated with the respective membrane elements are not connected with each other.

6. An apparatus according to claim 1 , wherein a pressure regulating control system is connected to the pressure regulating means.

7. An apparatus according to any one of the preceding claims, wherein the number of membrane elements (10, 20; 30; 40) is larger than two.

8. An apparatus according to claim 7, wherein the number of membrane elements (10, 20, 30; 40) is three or four.

9. An apparatus according to any one of claims 1 to 6, wherein the number of membrane elements (10, 20) is two.

10. An apparatus according to any one of the preceding claims, wherein two housings (2a, 2b) are provided and connected to each other by a conduit (100), the feed inlet (3) being connected to one housing (2a) and the feed outlet (4) to the other housing (2b).

1 1 . An apparatus according to any one of the preceding claims, wherein the membrane element comprises a spiral wound membrane, having a pore size of 0.005 μηι to 5 μηι.

12. An apparatus according to claim 1 1 , wherein the spiral wound membrane has a pore size of 0.01 μηι to 1 μηι.

13. An apparatus according to any one of the preceding claims, wherein the membrane element of a polymer material, preferably chosen from the group comprising polyvinylidene fluoride (PVDF), polysulfone (PS) or polyethersulfone (PES).

14. An apparatus according to any one of the preceding claims, wherein the permeate tube (1 1 , 21 ; 31 ; 41 ) of the respective membrane ele- ments (10, 20; 30; 40) is provided with a permeate outlet (13, 23; 33; 43) at a respective longitudinal end of the housing (2; 2a, 2b).

15. A method for membrane filtration of a liquid feed, comprising the steps of:

providing a first membrane element with a first end and a second end,

16. The method of claim 15, wherein an anti-telescoping device, ATD, is provided at at least one of the first and second ends of each membrane element,

17. The method of claim 15 or 16, wherein the pressure is regulated by means of a back pressure valve in connection with each permeate tube.

18. The method of claim 16 or 17, wherein the step of providing an ATD includes providing only one ATD between neighbouring membrane elements.

19. The method of claim 15, wherein the step of regulating the pressure is controlled by a pressure regulating control system.

20. The method of any one of claims 15 to 19, wherein the feed is a whey product, preferably whey protein concentrate, WPC.

21 . The method of any one of claims 15 to 19, wherein the feed is skim milk and wherein casein is separated from the skim milk.