DK202330177A1 - Apparatus for membrane filtration - Google Patents

Abstract

The present invention relates to an apparatus and a method for crossflow membrane filtration which may be used for filtration processes requiring a controllable low Transmembrane Pressure (TMP) and at the same time a controllable high crossflow. This may be the case both for microfiltration and for ultrafiltration processes. Particularly, the apparatus is directed to use in preparation of food ingredients where fractionating is required. In particular, the invention relates to an apparatus for crossflow membrane filtration comprising a plurality of membrane modules (1), and a retentate circulation pump (13) continuously forcing fluid feed through the plurality of membrane modules (1), wherein each membrane module (1) comprises at least one membrane element (4), an inlet (2) for fluid feed, an outlet (3) for retentate, and an outlet (6) for permeate, each membrane module (1) or a group of membrane module(s) (1) comprise(s) pressure control means (9) such as a valve configured to control the pressure and/or flow at the outlet (6) for permeate from one or for a group of membrane modules (1), which apparatus comprises at least a first section comprising m1 membrane modules (1) where m1 ≥ 2, wherein the inlet (2) of each of the m1 membrane modules (1) of the first section are connected to a common inlet (30) for fluid feed, and the outlet (3) of each of the m1 membrane modules are connected to a common outlet (31) or to a common inlet (30) for a following section i.e. the m1 membrane modules of the first section are parallelly connected on the retentate side, and either the common inlet (30) or the common outlet (31) comprises a pressure or flow measuring means (12) configured to control the crossflow.

Description

DK 2023 30177 A1 1

Apparatus for membrane filtration

The present invention relates to an apparatus and a method for crossflow membrane filtration which may be used for filtration processes requiring a controllable low Transmembrane Pressure (TMP) and at the same time a controllable high crossflow. This may be the case both for microfiltration and for ultrafiltration processes. Particularly, the apparatus is directed to use in preparation of food ingredients where fractionating is required.

Background Art:

A membrane is a thin layer of semi-permeable material that separates substances when TMP is applied to the membrane. Membrane processes are increasingly used for removal of bacteria, microorganisms, particulates, and natural organic material, which can impart color, tastes, and odors to water and react with disinfectants to form disinfection byproducts. As advancements are made in membrane production and module design, capital and operating costs continue to decline. Often used membrane processes are microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO).

Microfiltration (MF) is loosely defined as a membrane separation process using membranes with a pore — size of approximately 0.03 to 10 microns (1 micron = 0.0001 millimeter), and a relatively low feed operating pressure of approximately 50 to 400 kPa (7 to 60 psi). Materials commonly removed by MF include sand, silt, clays, Giardia lamblia and Crypotosporidium cysts, algae, and some bacterial species. MF is also used as a pretreatment to RO or NF to reduce fouling potential.

Ultrafiltration (UF) is loosely defined as a membrane separation process using membranes with a pore size of approximately 0.002 to 0.1 microns, a MWCO of approximately 1,000 to 100,000 daltons, and an operating pressure of approximately 120 to 700 kPa (17 to 100 psi). UF will remove all microbiological species removed by MF (partial removal of bacteria), as well as some viruses (but not an absolute barrier to viruses) and humic materials.

The document WO 2015/135545 discloses an apparatus and a method for membrane filtration. The apparatus has a membrane housing (2) comprising a feed inlet (3) and a feed outlet (4), further, the membrane housing (2) comprises at least two membrane elements (10, 20) each element having an associated permeate tube and outlet (11, 21). WO 2015/135545 teaches how to increase flux of material by placing more than one membrane element in serial position relative to fluid feed flow, but as the permeate flows countercurrent compared to the fluid feed flow, the permeate will face an increasing pressure and increasing incoming flux when flowing towards the feed inlet (3). This feature causes a risk of a dead pocket appearing in the permeate tube closest to the central ATD (15), either during production or during cleaning, which is highly undesirable if the apparatus is used for separating food components such as whey or the like. Also, it is necessary to use a non-standard component in form of the ATD (15) blocking transport of permeate between the membrane elements, contrary to standard operation where the ATD allows transport of permeate through a central opening of the ATD.

The document WO 2003/055580 discloses a process for ultrafiltration using a spiral wound membrane filter. The document points to that the membrane elements of the apparatus disclosed in WO 2003/055580 may be operated at pressures significantly higher than the pressures known before publication of this document, the membrane elements may be operated at a pressure difference of 2 bar or more between

DK 2023 30177 A1 2 the entrance and the outlet of a membrane element having a length of approximately 1 meter (see page 6, lines 3-7). The high pressure is established by designing the filter in a way so that the passage between the spiral wound element and the housing is open for incoming fluid at the entrance of the membrane element and blocked or restricted at the outlet of the membrane element. Fig. 11 discloses an embodiment where 4 membrane elements are serially positioned inside a membrane housing, in this embodiment, the flow is also directed toward the inlet of the fluid feed thereby providing the risk of a dead pocket. The prior art documents do not teach how to overcome use of non-standard components and prevent possible dead- pockets in the permeate flow.

The document US10052590 B2 relates to a filtration device including separation membrane modules in — which a plurality of lines thereof are disposed in series, a chemical manufacturing apparatus utilizing the filtration device, and a method for operating a filtration device. A filtration device according to this document comprises a plurality of separation membrane modules each of which separates a liquid to be filtrated into a permeated liquid and a non-permeated liquid also known as retentate, which the filtration device comprises a series non-permeated/retentate liquid flow channel forming a series unit by connecting non-permeation/retentate sides of the plurality of separation membrane modules in series, the membrane modules may definitely not be connected parallelly on the non-permeation/retentate sides; and a parallel permeated liquid flow channel forming a parallel unit by connecting permeation sides of the plurality of separation membrane modules in parallel. The apparatus comprises a single pump, circulation pump (11), which pump both supply liquid to the filtration device and force liquid (feed or retentate) through the membrane modules. The membrane modules are not provided with pressure gauges at the retentate side, it is not the intention to control the pressure on the retentate side when controlling the TMP. According to this document, the pump 11 and the valve 141 sets the pressure on the retentate side of the membrane modules and the pressure set by the pump 11 may be determined by the production in the fermentor 1, the pressure in the permeate flow is then used to adapt and control the TMP. The retentate is not circulated in a loop through the membrane modules, instead the retentate is reintroduced into the fermentor 1 where it is part of a fermenting process.

The document WO2020120448 relates to an apparatus and a method for crossflow membrane filtration which may be used for filtration processes requiring a controllable low Transmembrane Pressure (TMP) and at the same time a controllable high crossflow. An apparatus comprises a plurality of n membrane modules (2,..., n) and a pump, where the membrane module (1) positioned immediately downstream of the pump is named the first membrane module (1a), each membrane module (1) comprises at least one membrane element (4), one inlet (2) for fluid feed and one outlet (3) for fluid feed, one outlet for permeate (6), and a back-pressure control means (9) such as a valve configured to control the pressure and/or the flow at the outlet for permeate (6), each membrane element (4) has a central opening (5) configured to collect permeate and direct the permeate to the outlet for permeate (6), which outlet for permeate (6) is positioned at the same end of the membrane module (1) as the outlet (3) for fluid feed providing concurrent flows in fluid feed and permeate in full length of each membrane module (1). The outlet (3) for fluid feed of the first membrane module (1a) is connected to the fluid inlet (2) of the second membrane module (1b), and if further membrane module(s) is/are present, the outlet (3) for fluid feed of a previous membrane module (n-1) is connected to the fluid inlet (2) of a following membrane module (n), and for the last membrane module (n), the outlet (3) for fluid feed is connected to the fluid inlet (2) for fluid feed of the first membrane module (1a). During operation, an amount of fluid feed is continuously pumped by a loop pump through a loop comprising a multiplicity of n membrane modules which modules are serially connected. The fluid feed and permeate flow concurrently through each of the n membrane module(s). As the loop pump is dedicated to control the pressure on the fluid feed side of the membrane and as the permeate pressure is controlled at the permeate outlet of each membrane module, this apparatus makes it possible to keep TMP within a desired range. Also, this invention secures concurrent flow directions for both retentate and permeate in all membrane elements using only standard equipment in the modules which prevents dead-pockets inside the membrane module. However, it has been shown that it is difficult to control the TMP in individual membrane modules in a system comprising such serially connected membrane modules. One reason for this problem is that individual membrane modules although of same type may have different pressure loss at a specific flow rate.

The purpose of the present invention is therefore to provide an apparatus and a method which make it possible to control the TMP to a higher degree than which is possible according to prior art when the TMP is very low and at the same time reduce the costs for an apparatus. — Definitions of words:

ATD — Anti Telescoping Device, prevents spiral wound membranes from extending in a longitudinal direction due to liquid flow through the membrane element.

TMP — Trans Membrane Pressure, pressure difference between feed and permeate. The TMP is calculated according to the formula: TMP = Pin Pou Pperm where pi, is the fluid feed/retentate pressure before or — attheinlet of a membrane module and pou is the fluid feed/retentate pressure after or at the outlet of a membrane module. pperm is the permeate pressure at the permeate outlet of the module.

Dead leg or dead pocket - are used to describe a piping or the like where flow has ceased creating pockets of stagnant fluid which pockets support microbial amplification in the fluid. This is highly undesirable in systems used to prepare foodstuff or food components or drinking water.

Cross flow — Linear flow along the membrane surface. Purpose is to minimize or control the dynamic layer on the membrane surface.

Pressure loss per membrane element or dP per membrane element or dP/element - is the driving force for the above-described crossflow. dP/element is the difference in pressure between pin, pressure of the fluid feed/retentate pressure before or at the inlet of a membrane module, and pout, pressure of the fluid — feed/retentate pressure after or at the outlet of a membrane module. dP/element = pin - Pout.

Membrane element or element - a membrane element is an element comprising or constituted of a membrane which membrane provides a barrier allowing permeate to pass through the membrane and preventing retentate from passing through. In the context of the present application the membrane element is normally a polymeric membrane such as a spiral wound membrane, where permeate flows from a peripheral position to a central opening of the membrane element, a hollow fiber membrane, a plate and frame membrane, or a tubular organic membrane.

Membrane module or module — assembly of one membrane housing including or comprising one or more membrane elements and supports such as ATDs and similar membrane housing interior, an inlet for fluid feed/retentate, an outlet for retentate and an outlet for permeate through which permeate separated

DK 2023 30177 A1 4 from the one or more membrane elements of the one membrane housing is removed. The outlet for retentate and the outlet for permeate is normally positioned at the same end of the housing, i.e. opposite the inlet for feed/retentate allowing for concurrent flow of retentate and permeate.

Membrane module segment or segment — assembly of two or more membrane modules in serial connection where serial connection means that a part of the fluid feed entering a first membrane module of the segment through an inlet for fluid feed exits the first membrane module through an outlet for fluid feed, whereafter at least a part of the fluid feed exiting the first membrane module enters an inlet for fluid feed of a second membrane module, etc. until last membrane module of the segment is reached. Segments according to this definition is not used in the apparatuses according to the present invention but is used — with prior art apparatuses. Segments are not used in the context of the present invention but is used in the context of the prior art apparatuses.

Section — parallel assembly either comprising two or more parallelly arranged segments as defined above according to prior art or comprising two or more parallelly arranged single membrane modules as in the context of the present invention, all segments or membrane modules of the parallel assembly are fed fluid feed through a common inlet or manifold.

Loop — assembly of one or more membrane modules which may constitute one or more sections through which retentate is forced by a circulation pump.

Summary of invention: — The present invention provides a possibility for building e.g. large compact apparatus for cross flow membrane filtration comprising membrane modules for filtration processes requiring even very low TMP.

The apparatus according to the present invention offers a high controllability for TMP while an apparatus according to the invention is also less expensive while maintaining a higher and more uniform quality due to improved control of pressure loss and TMP than similar large apparatus’ according to the prior art.

According to one aspect of the invention, the invention relates to an apparatus for crossflow membrane filtration comprising a plurality of membrane modules (1), and a retentate circulation pump (13) continuously forcing fluid feed through the plurality of membrane modules (1), wherein each membrane module (1) comprises at least one membrane element (4), an inlet (2) for fluid feed, an outlet (3) for retentate, and an outlet (6) for permeate, each membrane module (1) or a group of membrane module(s) — (1) comprise(s) pressure control means (9) such as a valve configured to control the pressure and/or flow at the outlet (6) for permeate from one or for a group of membrane modules (1), which apparatus comprises at least a first section comprising m1 membrane modules (1) where m1 2 2, wherein the inlet (2) of each of the m1 membrane modules (1) of the first section are connected to a common inlet (30) for fluid feed, and the outlet (3) of each of the m1 membrane modules are connected to a common outlet (31) orto a common inlet (30) for a following section i.e. the m1 membrane modules of the first section are parallelly connected on the retentate side, and either the common inlet (30) or the common outlet (31) comprises a pressure or flow measuring means (12) configured to control the crossflow.

The first section does not comprise membrane modules being serially connected on the retentate side i.e. each and all membrane modules of each section are connected to the common inlet 30 for that section. An apparatus according to the invention may comprise a series of sections where none of the sections comprise membrane modules being serially connected on the retentate side.

According to an embodiment of the invention, an apparatus may comprise two or more sections of parallelly connected membrane modules (1) each section (1%, 2M, ...., n'") where each section comprises at 5 least two membrane modules (1) being parallelly connected on the retentate side, and a common outlet (31) for retentate from a first or previous section is fluidly connected to the common inlet (30) of the second or following section of membrane modules.

According to an embodiment of the invention, the retentate collected in a common outlet (31) of the last nt" section may be recirculated to the common inlet (30) of the first section. — According to an embodiment of the invention, one or each common outlet (31) for retentate may comprise a pressure or flow transmitter (12) measuring the pressure or flow at or through the common outlet (31) for retentate, normally the transmitter (12) is positioned downstream of the last connection to a retentate outlet (3) from a membrane module (1).

According to an embodiment of the invention, each membrane element (4) may comprise a central — opening (5) configured to collect permeat and direct the permeate to the outlet (6) for permeate, the outlet (6) for permeate is positioned at the same end of the membrane module (1) as the outlet (3) for retentate providing concurrent flows of the fluid feed and the permeat in full length of each membrane module (1).

According to an embodiment of the invention, the apparatus may comprise a feed pump (20) supplying — fluid feed to the circulating retentate flow either continuously or in batches.

According to an embodiment of the invention, the apparatus may comprise at least two sections, or at least three sections supplied by the retentate circulation pump (13), or the apparatus may comprise a n sections where 1<n<30,or 1<n<20,or1<n<10,orn>2,orn>3,orn<20orn<15orn< 10.

According to an embodiment of the invention, each section comprises m membrane modules where 5<m > <20, different sections of same apparatus may comprise same number of membrane modules i.e. Myst section = Msecond section = … = Mth section but two subsequent sections need not comprise the same number or dimension of membrane modules (1) i.e. optionally Mrist section # Msecond section # … % Minth section, OF €.8. Mrirst section 2 Msecond section 2 ++ 2 Mnth section.

That a membrane module is of a different “dimension” means that the membrane elements or modules is able to filtrate a different volume either because it has a smaller or larger diameter, a smaller or larger length, different internal components, etc..

According to an embodiment of the invention, the outlets (6) for permeate for a section of membrane modules (1) being parallelly connected on the retentate side may be connected to a common outlet (32) for permeate, and a plurality of common outlets (32) for permeate for 2-n sections may be connected to a — joined permeate outlet (33) for filtrated liquid.

According to an embodiment of the invention, an apparatus may further comprise an outlet for retentate (21) positioned downstream of the last or nth section and upstream of the retentate circulation pump (13).

According to any embodiment of the second aspect of the invention, the pressure at the inlet of the first membrane module may be in the area of 0.05-35 bar, e.g. at 0.1-25 bar or at 0.5-10 bar or at 2-4 bar, and/or the TMP may be in the area of 0.02-12 bar, e.g. 0.07-10 bar, or at 0.2-8 bar, or at 0.3-2 bar.

According to any embodiment of the second aspect of the invention, the base line pressure Pg, i.e. the pressure with which fluid feed is pumped into the loop, may be above 0.2 bar, or above 0.3 bar, or above 0.5 bar, or above 0,9 bar, or above 1,0 bar.

According to any embodiment of the second aspect of the invention, the booster pressure Ps may be above 0.1 bar per module in the loop or segment, i.e. Pg > n times 0.1 bar, or Ps may be above 0.2 bar, or above 0.3 bar, or above 0.4 bar, or above 0.5 bar, or above 0.6 bar, or above 0,9 bar, or above 1, 0 bar per module in the loop or segment. The preferred booster pressure will depend on the application i.e. for which separation process the method is used.

According to any embodiment of the second aspect of the invention, the permeate pressure of each module Pperm is smaller than or equal to the pressure at the outlet of the module Pour, i.e. Pperm < Pour, or e.g. Pperm < Pour + 0,5 bar.

According to any embodiment of the second aspect of the invention, the feed fluid may be a fluid in dairy industry or in dairy ingredients industry or in liquid food industry requiring accurate and same time control of TMP and cross flow, in particular the feed fluid can be feed for protein separation, fat separation, protein fractionation in dairy industry or dairy ingredients industry or liquid food industry, typically the fluid feed may be eo dairy industry and dairy ingredients industry cheese whey or eo dairy industry and dairy ingredients industry cheese whey WPC or e dairy industry and dairy ingredients industry skim milk or e dairy industry and dairy ingredients industry skim milk MPC or e dairy industry and dairy ingredients industry raw whole milk or e dairy industry and dairy ingredients industry whole milk or e dairy industry and dairy ingredients industry microfiltration permeates or eo liquid food industry vegetable (green) protein solutions or eo liquid food industry fish protein solutions or eo liquid food industry meat protein solutions or — e« liquid food industry microfiltration permeates.

List of figures:

Figures 1A and 1B shows two embodiment of prior art membrane module;

Figure 2 shows an embodiment of a prior art apparatus comprising a segment of four serially connected membrane modules and a circulation loop for retentate;

Figure 3 shows an embodiment of an apparatus according to the invention comprising a plurality of membrane modules.

Figure 4 shows a second embodiment of an apparatus according to the invention comprising a plurality of membrane modules.

Figure 5 shows a third embodiment of an apparatus according to the invention comprising a plurality of membrane modules.

Figure 6 shows a fourth embodiment of an apparatus according to the invention comprising a plurality of membrane modules.

Figure 7 shows a fifth embodiment of an apparatus according to the invention comprising a plurality of membrane modules.

Figures 8A, 8B and 8C illustrate three different embodiments of a common inlet.

Throughout the application identical or similar elements of different embodiments are given the same reference numbers.

Detailed description of invention:

Two embodiments of a single membrane module 1 according to prior art are shown in fig. 1A and 1B. The embodiment of a membrane module shown in fig. 1A is without a second inlet for liquid whereas the embodiment of a membrane module shown in fig. 1B has a second inlet for liquid. Each membrane module 1 may comprise one or two membrane elements 4, possibly up to 4 or up to 6 membrane elements during a microfiltration operation or an ultrafiltration operation.

Each membrane module 1 has one inlet 2 for fluid feed leading fluid feed to an inlet distribution chamber 2a and an outlet distribution chamber 3a wherefrom fluid feed is lead through one outlet 3 for fluid feed, one outlet for permeate 6 and a back-pressure control means 9 configured to control the pressure at the outlet for permeate 6. Each membrane module 1 may comprise a pressure transmitter 10 which may be used to control the pressure at the permeate outlet 6, e.g. providing an automatic control procedure maintaining a constant pressure at the outlet or maintaining a constant TMP in the membrane module. — Also, the feed-side of the membrane module 1 may be provided with a pressure transmitter 12 either at the inlet distribution chamber 2a or at the outlet distribution chamber 3a for more precise control of the

TMP, the presence of the pressure transmitter 12 increases the likeliness of being able to maintain a constant TMP in a membrane module.

Each membrane element 4 has a central tube or opening 5 configured to collect permeate and direct the permeate to the outlet for permeate 6, during operation permeate flows into the central opening 5 over the full length of the opening 5, the opening 5 is closed at the end facing the inlet distribution chamber 2a to prevent unfiltered retentate to enter the opening 5. A central opening 5 is e.g. provided when using a spiral wound membrane as membrane element 4. The outlet for permeate 6 is positioned at the same end of the membrane module 1 as the outlet 3 for fluid feed providing concurrent flow of fluid feed and permeate in the complete length of the membrane element 4 and the membrane module.

As illustrated in fig. 1B, a single membrane module 1 may comprise a second inlet 24, the second inlet 24 may be used to add washing liquid e.g. water or diafiltration buffer to the membrane module 1. The second inlet 24 may lead liquid into the inlet distribution chamber 2a or into the conduit ending at the fluid inlet 2.

DK 2023 30177 A1 8

A membrane module 1 comprising a second inlet 24 may comprise flow control means 25 e.g. in form of a valve controlling the flow through the second inlet 24. Also, a membrane module 1 comprising a second inlet 24 may optionally comprise a flow transmitter 26 which may allow for automatic control of the flow to the membrane module 1. Although a membrane module 1 comprises a second inlet 24, liquid may not enter into the membrane module 1 through this second inlet 24 during operation. The flow of liquid through the second inlet 24 may be continuous or temporary or not take place at all during some operations.

In general, prior art membrane modules as disclosed in figs. 1A and 1B may be used in the context of the present invention. — Fig. 2 disclose an apparatus according to prior art comprising a segment with four serially connected membrane modules 1a, 1b, 1c, 1d. The outlet 3 for fluid feed or retentate of the first membrane module 1a is connected to the fluid inlet 2 of the second membrane module 1b, the outlet 3 for fluid feed of the second membrane module 1b is connected to the fluid inlet of the third membrane module 1c, etc., illustrating how the outlet 3 for fluid feed of a previous membrane module (n-1) is connected to the fluid inlet 2 of a following membrane module (n), and for the last membrane module (n), in fig. 2 this is the fourth membrane module 1d, the outlet 3 for fluid feed is connected to the inlet 2 for fluid feed of the first membrane module 1a via a circulation pump 13. The apparatus comprises a storage unit 19 for fluid feed which storage unit 19 may be constituted of one or more tanks or containers providing a continuous flow of feed into the membrane modules. A pump 20 controlled by a not shown control device such as a — frequency converter or valve controls the inlet of fluid feed to the liquid recirculating through the membrane modules 1a-1d. The loop of recirculating retentate is provided with an outlet 21, which outlet for retentate may be controlled by a valve 22. If the loop shown in fig. 2 is a first loop in a series of filtration loops providing a further reduction in material content of the circulating liquid, then the loop may be provided with an outlet 23 directing a fraction of the circulating liquid to a second loop. The loop shown in — fig. 2 may be the first loop in a series of loop each comprising an outlet 23 directing circulating liquid to a next loop, in this case normally only the last loop in the series is provided with an outlet 21 for retentate. l.e. the membrane modules 1a, 1b, 1c, 1d are serially connected at the retentate side of the membrane modules 1a, 1b, 1c, 1d, i.e. the same flow of liquid enters all membrane module although the amount is reduced by the amount of permeate leaving from each membrane module. The permeate is removed from — each membrane module 1 through an outlet 6 and may be collected in a joint flow of permeate. The membrane modules 1a, 1b, 1c, 1d provide a segment in a loop through which feed or retentate is continuously pumped by the circulation pump 13 until a desired amount of permeate has been removed via the permeate outlets 6 of the membrane modules. According to this prior art filtration apparatus, it is possible to control the pressure in each membrane module and therefore possible to overcome static pressure, when it is possible to overcome static pressure it is possible to design a matrix comprising a number of segments of membrane modules 1 in two dimensions i.e. it is not necessary to position the membrane modules 1 at the same level, instead membrane modules 1 being serially connected on the feed or retentate side, may be positioned on top of each other providing vertically extending segments.

According to prior art, it is known to connect such segments of membrane modules as shown in fig. 2 parallelly i.e. two or more segments may have a common inlet for retentate or fluid feed. According to the

DK 2023 30177 A1 9 embodiment shown in fig. 2, the pressure is measured by a pressure transmitter 12 at the inlet 2 for fluid feed at each membrane module 1 and the pressure is measured by a pressure transmitter 10 at the outlet 6 for permeate at each membrane module 1, and also, each membrane module 1 is provided with a valve 9 at the outlet 6 for permeat. This makes it possible to control the TMP in each membrane module 1 with great accuracy. However, this is also an expensive solution, especially if an apparatus comprises a large number of membrane modules as each membrane module must be equipped with at least one pressure transmitter at the inlet 2 for retentate/fluid feed. If the pressure transmitter at the inlet is removed, it is necessary to rely on that all the membrane modules react and ages in the same way and then rely on that control can be based on an average behavior of groups of membrane modules. However, it has been shown that this is not always the case, and membrane modules which are expected to be identical may have different pressure loss at a specific flow.

According to the present invention, TMP is controlled by measuring the pressure at each or at a common outlet for permeate and at a common inlet or at a common outlet for fluid feed thereby making it possible to measure TMP for a group of membrane module when each membrane module is not serially connected to any other membrane module. To build large filtration units parallelly connected groups of membrane modules comprising single membrane modules having a common inlet for fluid feed (retentate), also referred to as a section of membrane modules, may then be serially connected to further sections of membrane modules to obtain a matrix of membrane modules.

Fig. 3 discloses an apparatus according to the present invention which apparatus comprises a plurality of membrane modules 1 which membrane modules 1 are connected parallelly in respect of the fluid feed/retentate flow, in the following this flow is referred to as “retentate” as it relates to the flow or liquid being retained on the inlet side of the filter. The apparatus also comprises a circulation pump 13 circulating the retentate through the membrane modules 1 which circulation pump 13 may comprise a single pump or a group of pumps. Each membrane module 1 comprises at least one membrane element 4, an inlet 2 for retentate, an outlet 3 for retentate and an outlet 6 for permeate. Also, each membrane module 1, or as shown in fig. 3, a group of membrane modules 1, comprises pressure control means 9 such as a valve configured to control the pressure and/or flow at the outlet 6 for permeate from one or from a group of membrane modules 1. In case the pressure control means 9 controls the pressure of a group of membrane modules each outlet 6 for permeate from a membrane module 1 being part of the group, also referred to — asa section of membrane modules 1, may be connected to a common outlet or manifold 32 for permeate, and the pressure control means 9 may then be positioned downstream of all outlets 6.

Downstream of the circulation pump 13, the apparatus comprises a common inlet 30 or manifold and the common inlet 30 is connected to the inlet 2 of each of the membrane modules 1 of the first section.

The embodiment of fig. 3 comprises n sections and each of the shown sections comprise 6 membrane modules. In general, the first section may comprise m membrane modules where 1<m<30, or 5 <m < 20.

During operation, the retentate enters into the common inlet 30 or manifold and is then distributed to the inlets 2 of each membrane module 1. In the shown embodiment, the pressure is measured by a pressure transmitter 34 downstream of the retentate circulation pump 13 and , the upstream of the common inlet 30 i.e. upstream of the first inlet 2 or the first connection to an inlet 2, the pressure measured by the pressure transmitter 34 may be used to control the flow into the first section and therefore the crossflow through the membrane modules of all the sections.

After having entered a membrane module 1, a part of the retentate flows through the membrane element and ends up as permeate. The part of the retentate which does not pass through the membrane element to the permeate flow, passes through the membrane module 1 to the outlet 3 of the membrane module 1 and thereafter enters into a common outlet 31 for retentate. The permeate is collected and led to the outlet 6 for permeate and each outlet 6 of the membrane modules in the first section is connected to a common outlet 32 for permeate in which common outlet 32 all permeate from the section is collected during operation in the embodiment shown in fig. 3. Downstream of the last outlet 6 for permeate the pipe or connection comprises pressure control means 9 in form of a valve which may be used to control the pressure in the common outlet 32 for permeate and therefore the TMP in the membrane modules of the first section.

The flows from each of the common outlets 32 from the 1% , the 2" and the n"" sections are joined and flow to a joined permeate outlet 33. — The apparatus of fig. 3 also comprises an outlet 21 for retentate which outlet 21 is positioned between the last section or the n'" section and the retentate recirculation pump 13.

Each outlet 3 of membrane modules 1 of the first section is connected to a common outlet 31 for retentate where the retentate from all the membrane modules 1 of the first section is collected and forwarded to the common inlet 30 or manifold for the second and following section. — The second section and possible following sections comprise the same parts and units as the first section.

However, following section may comprise fewer or smaller membrane modules as the amount of liquid decreases through the sections.

In general, the membrane modules 1 of a single section is normally positioned at same height, the second section and possible following sections may be placed at a different height, e.g. lower or higher than the previous section, which makes it possible to provide a compact apparatus with a large number of membrane modules.

Figs. 4, 5 and 6 illustrate different ways of connecting inlet for fluid feed to the common inlet 30 as well as different ways of connecting the outlet for retentate from the common outlet 31. To make it easy to compare the apparatuses of the different embodiments the apparatuses all comprise 3 sections (n=3) and each section comprise 4 membrane modules (m=4).

Fig. 4 illustrates how the inlet for fluid feed to the common inlet 30 is positioned closest to the membrane module 1 which is furthest to the right in the figure. This is also the membrane module 1 which is closest to the outlet for retentate from the common outlet 31. This system provides the most unified pressure loss per membrane module in a section.

Fig. 5 illustrates how the inlet for fluid feed to the common inlet 30 is positioned closest to the membrane module 1 which is positioned furthest to the left. This is also the membrane module 1 which is further away from the outlet for retentate from the common outlet 31. This system provides the fastest through-flow of retentate and may be referred to as First-In-First-Out.

DK 2023 30177 A1 11

In fig. 5 it is also illustrated how the common outlet 31 or common inlet 30 may comprise an inlet 35 for liquid e.g. used during a CIP (Cleaning-In-Place) procedure where a cleaning liquid is added or for diafiltration where a diluting component such as water is added.

Fig. 6 illustrates how the inlet for fluid feed to the common inlet 30 is positioned in the middle of the common inlet 30, and the outlet for retentate from the common outlet 31 is also positioned in the middle.

Like in fig. 4, this system provides membrane modules 1 with a unified pressure loss per membrane module in a section.

Fig. 7 illustrates an embodiment of an apparatus according to the invention where the different types of common inlet 30 and common outlet 31 are mixed for the three shown sections. In the first section i.e. the first section downstream of the recirculation pump 13, the common inlet 30 has a central position of the inlet for fluid feed to the common inlet 30. On the outlet side for retentate, the membrane modules 1 are separated in two groups, and the retentate from the first group comprising the two membrane modules furthest to the left is collected and connected to a common inlet 30 for two membrane modules in the second section. The second group comprises the two membrane modules furthest to the right wherefrom retentate is collected whereafter the retentate is directed to another common inlet 30 for two membrane modules in the second section. The second section comprises a common outlet 31 where the retentate from all four membrane modules 1 of the section is collected and directed to a third section via an outlet for retentate from the common outlet 31 which is positioned in the middle of the common outlet 31. The third section of the apparatus comprises common inlet 30 and common outlet 31 identical to the first — section.

Fig. 8 shows three embodiments of common inlets 30 where outlets 38 for retentate from a previous section corresponding to inlets 36 for retentate are positioned either offset or directly opposite relative to outlets 37 for retentate from the common inlet 30 to the membrane modules 1 of a following section.

In general, a common inlet 30 comprises a volume such as a pipe with at least one inlet 36 for fluid feed and at least two outlets 37 for fluid feed, i.e. one outlet 37 for fluid feed for each membrane module being connected to the common inlet 30. Between the inlet 36 for fluid feed and the nearest outlet(s) 37 for fluid feed may be a mix zone or at least the outlets 37 for fluid feed are fluidly connected.

The embodiments of figs. 3 and 6 illustrate how a single inlet 36 for retentate may be positioned relative to the outlets 37 for fluid feed to the membrane modules 1 of the downstream section in order to obtain the above-described effects.

The common inlet 30 shown in fig. 3 comprises a pipe 30 comprising one open end providing one inlet 36 for fluid feed and six outlets 37 for fluid feed, one outlet 37 for fluid feed for each membrane module. All the sections 1%, 2™ and n'"", shown in fig. 3 comprise the same embodiment of a common inlet 30. For the 1%, 2" and n'"" sections, a common outlet 31 from a previous section may be distinguished from the common inlet 30 of a following section as the common outlet 31 for each section comprises a pipe with six inlets 38 for retentate and one outlet 39 for retentate which common outlet 31 is positioned upstream of the inlet 36 of the common inlet 30. The outlet 39 for retentate from the common outlet 31 is fluidly connected to the inlet 36 for the common inlet 30 of the following or downstream section.

In figs. 3-6 it is illustrated how the inlet 36 of the common inlet 30 of the first section, is connected to a recirculation pipe through which the recirculation pump 13 forces the retentate.

Figs. 8A, 8B and 8C illustrate alternative embodiments where it is not possible to distinguish a common outlet 31 from a previous section from the common inlet 30 of a following section because the outlets 38 for retentate from the membrane modules 1 of the previous section are not positioned upstream of the inlets 36 of retentate for the common inlet 30. . The common inlet 30 and the common outlet 31 between two sections according to these embodiments are constituted of one volume shown as a pipe, and the inlets for retentate 36, corresponds to the outlets or retentate from the previous section.

According to these three embodiments, the common inlet 30 and the common outlet 31 for neighboring sections coincide and are constituted by the same volume such as a pipe, the inlets 36 for fluid feed to the common inlet 30 correspond to the six inlets 38 for retentate to a common outlet 31.

Fig. 8A shows an embodiment of a common inlet 30 for one section which also constitute a common outlet for a previous section. Each membrane module 1 of the previous section directs retentate through an inlet 36 for retentate to the common inlet. The outlets 37 for retentate from the common inlet 30 which direct retentate to the membrane modules 1 of the following section are positioned offset relative to the inlets 36.

Fig. 8B shows an embodiment of common inlet 30 for one section which also constitute a common outlet for a previous section. Like the embodiment of fig. 8A, each membrane module 1 of the previous section directs retentate through an inlet 36 for retentate to the common inlet 30. The outlets 37 for retentate from the common inlet 30 directing retentate to the membrane modules 1 of the following section from the common inlet 30 are positioned directly opposite relative to the inlets 36.

Fig. 8C shows an embodiment of a common inlet 30 for one section also constituting a common outlet 31 for the previous section which common inlet 30 comprises six inlets 36 for retentate and five outlets 37 for retentate. The inlets 36 and the outlets 37 are positioned offset relative to each other.

In general, if the common inlet 30 comprises a several inlets, the common inlet 30 may comprise an inlet for each outlet 3 from membrane modules in a previous section, or for a group or plurality of outlets 3 from a plurality of membrane modules in a previous section, if there are more than one inlet 36 to the common inlet 30, the inlets 36 may be placed offset relative or direct opposite to the outlets 37 for retentate connected to each membrane module 1 of the section fed from the common inlet 30.

In general, if the common inlet 30 does not provide a certain degree of mixing, therefore if the common inlet 30 is constituted by a pipe it may comprise a static mixer upstream or downstream of the first outlet 37 from the common inlet 30, or the common inlet 30 may comprise a volume with increased diameter where mixing may be increased.

The invention also relates to a method for controlling the TMP in an apparatus according to the invention where TMP, Trans Membrane Pressure, is the pressure difference between feed and permeate. . . int .

The TMP is calculated according to the formula: TMP = Pin "Font Pperm where pin is the retentate pressure before or at the inlet of a membrane module and pow is the retentate pressure after or at the outlet of a membrane module. Pperm is the permeate pressure at the permeate outlet of the module.

DK 2023 30177 A1 13

According to the present invention, the pressure upstream of the common inlet 30 of each section may be determined as well as the pressure downstream of the common outlet 31 of the last section. This makes it possible to determine the Pi, and Pau: for each section. Further, the Pgerm is determined downstream of the common outlet 32 for permeate after each section. — The method of the present invention can be used in connection with membrane filtration operations within the dairy industry. E.g. the feed fluid can be a fluid in the dairy industry and dairy ingredients industry requiring accurate and same-time control of TMP and cross flow to obtain the result in particular protein separation, fat separation, micro-organism separation and protein fractionation on oe cheese whey e+ cheese whey WPC e skim milk e skim milk MPC e raw whole milk e whole milk eo microfiltration permeates

Also, method of the present invention can be used in connection with membrane filtration operations within a fluid in the e liquid food industry or e liquid beverage industry or e liquid life Science industry requiring accurate and same-time control of TMP and cross flow to obtain the result in e protein separation or e fat separation or e micro-organism separation or e protein fractionation or e alcohol separation on e vegetable (green) solutions or e meat solutions or e fish solutions or e beverage solutions or e microfiltration permeates.

DK 2023 30177 A1 14

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Claims (10)

Claims

1. An apparatus for crossflow membrane filtration comprising a plurality of membrane modules (1), and a retentate circulation pump (13) continuously forcing fluid feed through the plurality of membrane modules (1), wherein -each membrane module (1) comprises at least one membrane element (4), an inlet (2) for fluid feed, an outlet (3) for retentate, and an outlet (6) for permeate, - each membrane module (1) or a group of membrane module(s) (1) comprise(s) pressure control means (9) such as a valve configured to control the pressure and/or flow at the outlet (6) for permeate from one or for a group of membrane modules (1), characterized in that the apparatus comprises at least a first section comprising m1 membrane modules (1) where m1 2 2, wherein the inlet (2) of each of the m1 membrane modules (1) of the first section are connected to a common inlet (30) for fluid feed, and the outlet (3) of each of the m1 membrane modules are connected to a common outlet (31) or to a common inlet (30) for a following section i.e. the m1 membrane modules of the first section are parallelly connected on the retentate side, and either the — common inlet (30) or the common outlet (31) comprises a pressure or flow measuring means (12) configured to control the crossflow.

2. An apparatus according to claim 1, wherein the apparatus in addition to the first section comprises a second or more sections each section comprising respectively m2, m3, ..., mn membrane modules (1) > where m2>2, m322,.…, mn 2 2 and where the inlet (2) of each of the membrane modules (1) of one section are connected to a common inlet (30) for retentate, and the outlet (3) of each of the membrane modules (1) are connected to a common volume defined as a common inlet (30) or a common outlet (31)

i.e. all membrane modules of each section are parallelly connected on the retentate side i.e. the membrane modules (1) of each section are fluidly connected upstream and downstream on the retentate side.

3. An apparatus according to any previous claim, wherein the retentate collected in a common outlet (31) of the last n' section is recirculated to the common inlet (30) of the first section.

4. An apparatus according to any previous claim, wherein one or each common outlet (31) for retentate comprises a pressure or flow transmitter (12) measuring the pressure or flow at or through the common outlet (31) for retentate, normally the transmitter (12) is positioned downstream of the last connection to a retentate outlet (3) from a membrane module (1).

5. An apparatus according to any previous claim, wherein each membrane element (4) comprises a central — opening (5) configured to collect permeat and direct the permeate to the outlet (6) for permeate, the outlet (6) for permeate is positioned at the same end of the membrane module (1) as the outlet (3) for retentate providing concurrent flows of the fluid feed and the permeat in full length of each membrane module (1).

6. An apparatus according to any previous claim, wherein the apparatus comprises a feed pump (20) supplying fluid feed to the circulating retentate flow either continuously or in batches.

7. An apparatus according to any previous claim, wherein the apparatus comprises at least two sections, or at least three sections supplied by the retentate circulation pump (13), and/or n sections where 1 <n < 30.

8. An apparatus according to any previous claim, wherein each section comprises m membrane modules where 5 <m < 20, different sections of same apparatus may comprise same number of membrane modules i.e. Miirst section = Misecond section = -... = Mnth section but two subsequent sections need not comprise the same number or dimension of membrane modules (1)

i.e. optionally Mfirst section # Msecond section # ... # Minth section, OF e.g. Mifirst section 2 Msecond section 2 … 2 Mnth section.

9. An apparatus according to any previous claim, wherein the outlets (6) for permeate for a section of membrane modules (1) being parallelly connected on the retentate side are connected to a common outlet (32) for permeate, and a plurality of common outlets (32) for permeate for 2-n sections may be connected to a joined permeate outlet (33) for filtrated liquid.

10. An apparatus according to any previous claim, further comprising an outlet for retentate (21) positioned downstream of the last or nth section and upstream of the retentate circulation pump (13).