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WO2022003161A1 - Control for filtration process - Google Patents

Control for filtration process Download PDF

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Publication number
WO2022003161A1
WO2022003161A1 PCT/EP2021/068341 EP2021068341W WO2022003161A1 WO 2022003161 A1 WO2022003161 A1 WO 2022003161A1 EP 2021068341 W EP2021068341 W EP 2021068341W WO 2022003161 A1 WO2022003161 A1 WO 2022003161A1
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WO
WIPO (PCT)
Prior art keywords
flow
pressure
loop
set point
controller
Prior art date
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PCT/EP2021/068341
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French (fr)
Inventor
Michael BERTELSEN
Keld B. ANDREASEN
Ulrik Johansen
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SD Filtration AS
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SD Filtration AS
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Publication of WO2022003161A1 publication Critical patent/WO2022003161A1/en
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/12—Controlling or regulating
    • A—HUMAN NECESSITIES
    • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23C—DAIRY PRODUCTS, e.g. MILK, BUTTER OR CHEESE; MILK OR CHEESE SUBSTITUTES; MAKING OR TREATMENT THEREOF
    • A23C21/00—Whey; Whey preparations
    • A—HUMAN NECESSITIES
    • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23C—DAIRY PRODUCTS, e.g. MILK, BUTTER OR CHEESE; MILK OR CHEESE SUBSTITUTES; MAKING OR TREATMENT THEREOF
    • A23C9/00—Milk preparations; Milk powder or milk powder preparations
    • A23C9/14—Milk preparations; Milk powder or milk powder preparations in which the chemical composition of the milk is modified by non-chemical treatment
    • A23C9/142—Milk preparations; Milk powder or milk powder preparations in which the chemical composition of the milk is modified by non-chemical treatment by dialysis, reverse osmosis or ultrafiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/14—Ultrafiltration; Microfiltration
    • B01D61/22—Controlling or regulating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D63/00—Apparatus in general for separation processes using semi-permeable membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B11/00—Automatic controllers
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B13/00—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion
    • A—HUMAN NECESSITIES
    • A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23C—DAIRY PRODUCTS, e.g. MILK, BUTTER OR CHEESE; MILK OR CHEESE SUBSTITUTES; MAKING OR TREATMENT THEREOF
    • A23C2210/00—Physical treatment of dairy products
    • A23C2210/20—Treatment using membranes, including sterile filtration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2311/00—Details relating to membrane separation process operations and control
    • B01D2311/14—Pressure control
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2311/00—Details relating to membrane separation process operations and control
    • B01D2311/16—Flow or flux control
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2311/00—Details relating to membrane separation process operations and control
    • B01D2311/20—Power consumption

Definitions

  • the present invention relates to an apparatus and a method for controlling a crossflow membrane filtration process used for filtration processes requiring a specified Transmembrane Pressure (TMP).
  • TMP Transmembrane Pressure
  • 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.
  • MF microfiltration
  • UF ultrafiltration
  • NF nanofiltration
  • RO reverse osmosis
  • An apparatus for crossflow membrane filtration normally comprises one or more feed pumps feeding fluid from a feed tank to an inlet point 6 of a loop, and a loop circulation pump recirculating retentate through one or more crossflow membranes.
  • the feed pumps normally comprise a controller keeping e.g. the level in the feed tank constant, or keeping the flow into the loop constant, or keeping the base line pressure constant
  • the loop circulation pump comprises a controller maintaining a constant difference pressure over the crossflow membrane, i.e. the difference between the pressure before the membrane(s) P2 and the pressure after the membrane PI - where PI is also known as the baseline pressure - is kept constant.
  • Such a control set up makes it possible to maintain a constant production or capacity for the apparatus, where the capacity may be determined by the relation between permeate and retentate, or the content of e.g. salts, protein, or other component of the permeate or retentate.
  • US 5.069.792 A1 relates to optimization of concentrate flow in a filter system which system uses actual sensed operating curve data to optimize plasma flow in a plasmapheresis system.
  • the US-document discloses an adaptive filter concentrate flow control system and method, which method includes a filter system, a pumping system driving feed fluid, concentrate and filtrate flowing through the filter system and a flow control system controlling the pumping system to maintain optimum filtrate flow rates or minimum feed flow rates along a control surface in a three-dimensional transmembrane pressure-feed fluid rate- filtrate flow rate space.
  • Actual sensed operating point data is used to locate the control surface so as to assure an optimized filtrate flow rate or minimized feed flow rate at which reversible blocking of the membrane has begun to occur without irreversible blocking or plugging.
  • the system is employed to control and maximize the flow of plasma in a plasmapheresis system or to minimize the rate at which blood is withdrawn from a donor and introduced into the system while achieving a fixed rate of plasma flow.
  • the system does not suggest how to minimize energy consumption during operation which is an important factor in an industrial processes.
  • US 2005/126961 A1 discloses a multipurpose hemofiltration system and method for removal of fluid and/or soluble waste from the blood of a patient.
  • the system continuously monitors the flow rates of drained fluid, blood, and infusate. When necessary, the pumping rates of the infusate, drained fluid and blood are adjusted to remove a preselected amount of fluid from the blood in a preselected time period.
  • a supervisory controller can monitor patient parameters, such as heart rate and blood pressure, and adjust the pumping rates accordingly.
  • the supervisory controller uses fuzzy logic to make expert decisions, based upon a set of supervisory rules, to control each pumping rate to achieve a desired flow rate and to respond to fault conditions.
  • An adaptive controller corrects temporal variations in the flow rate based upon an adaptive law and a control law. However, neither this system suggest how to minimize energy consumption during operation.
  • the present invention not only makes it possible to maintain a constant capacity in a crossflow membrane filtration apparatus; the present invention also makes it possible to reduce energy consumption compared to a traditional driven membrane filtration apparatus applied in an industrial process as well as increasing the operational lifetime of the membranes.
  • TMP- Trans Membrane Pressure pressure difference between feed and permeate.
  • the TMP is calculated according to the formula: TMP where r, h is the fluid feed/retentate pressure before or at the inlet of a membrane module and p out is the fluid feed/retentate pressure after or at the outlet of a membrane module. p perm is the permeate pressure at the permeate outlet of the module.
  • Cross flow - Linear flow along the membrane surface A purpose of the cross flow is to minimize or control the dynamic layer on the membrane surface and the cross flow is determined by the pressure difference Pin — Pout on the retentate side of the membrane.
  • Pressure loss per membrane element or dP per membrane element or dP/element - is the driving force for the above-described cross flow.
  • dP/element is the difference in pressure between p in , pressure of the fluid feed/retentate pressure before or at the inlet of a membrane module, and p out , pressure of the fluid feed/retentate pressure after or at the outlet of a membrane module.
  • dP/element r, h - P out .
  • Membrane - a membrane provides a barrier allowing permeate to pass through the membrane and preventing retentate from passing through.
  • a membrane element may be a spiral wound membrane, where permeate flows from a peripheral position to a central opening of the membrane element.
  • Membrane module or module - assembly of one membrane housing including or comprising one or more membrane elements and 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 from the one or more membrane elements of the one membrane housing is removed.
  • the outlet for retentate and the outlet for permeate may be positioned at the same end of the housing, i.e. opposite the inlet for feed/retentate providing concurrent flow of retentate and permeate.
  • the present invention provides an improved method for controlling a crossflow membrane apparatus.
  • the invention relates to a method for controlling a crossflow membrane filtration apparatus comprising
  • the loop comprises one or more membrane modules (3) and a conduit system allowing recirculation/circulation of fluid through the membrane module (3) and a retentate outlet (5), and a loop circulation pump (2) circulating fluid through the loop,
  • a first pressure sensor measuring a baseline pressure PI and a transmitter (PT1) positioned upstream of the loop circulation pump (2) and downstream of the membrane module (3),
  • a second pressure sensor measuring a pressure P2 and a transmitter (PT2) positioned downstream of the loop circulation pump (2) and upstream of the membrane module (3),
  • a level sensor measuring a level L and a transmitter (LT) measuring and transmitting a value for the content in the feed tank (7)
  • a first controller controlling the output to the feed pump (1) comprising 1) a level controller receiving an input from the level sensor/transmitter LT, or 2) a flow controller receiving an input from one or more flow sensors (FT1), or 3) a pressure controller receiving an input from the first pressure sensor (PT1),
  • the set point for the pressure difference dP in the second controller may depend on the flow FI in such a way that if the flow FI exceeds a value Fl
  • the set point for the pressure difference dP in the second controller may be either increased or decreased stepwise depending on a plurality of values for either the flow FI, or the level L, or the baseline pressure PI.
  • the set point for dP may be based on the same relative % increasing or decreasing as the relative % increasing or decreasing of the output for the feed pump.
  • the first controller controlling the output to the feed pump (1) may comprise a flow controller receiving an input from the first flow sensor (FT1) measuring flow into the loop, or an input from flow sensors (F2, F3) measuring flow of retentate (FT3) and permeate (FT2) out of the loop.
  • the first and/or the second controller is/are PID-controllers.
  • the membrane module (3) may comprise an outlet for permeate (4) and this outlet may comprise a third flow sensor measuring the flow F3 and a transmitter (FT3).
  • the loop may comprise a flow sensor and transmitter (FT4) measuring a flow F4 positioned upstream of the loop pump (2) and downstream of the inlet point (6).
  • FT4 flow sensor and transmitter
  • Figure 1 shows a crossflow membrane filtration apparatus which may be controlled by the method of the invention.
  • FIG. 1 shows an embodiment of a crossflow membrane filtration apparatus which may be used according to the invention.
  • the crossflow membrane filtration apparatus comprises a feed pump 1 feeding fluid to an inlet point 6 of a filtration loop.
  • the feed pump 1 is normally a variable pumping capacity type pump.
  • the feed is contained in a feed tank 7 and the feed pump 1 may either function as a master or as a slave i.e. either the feed pump 1 continuously controls the flow into the filtration loop and the feed tank 7 is filled when necessary, or the feed pump 1 reacts when feed is added to the feed tank in response e.g. to the level of fluid in the feed tank.
  • the filtration loop comprises one or more membrane modules 3 indicated by a single block in fig. 1, and a conduit system allows recirculation/circulation of retentate through the membrane module(s) 3, i.e. the retentate outlet(s) of the membrane module(s) 3 is/are fluidly connected to the inlet(s) of the membrane module(s) 3.
  • the filtration loop comprises a retentate outlet 5, a loop circulation pump 2 circulating the feed/retentate through the loop.
  • the loop circulating pump 2 is normally a variable pumping capacity type pump but may be an on-off pumping capacity type pump in combination with a control valve.
  • the plurality of membrane modules may be either parallelly connected, i.e., one flow of feed/retentate is split and fed to two or more membrane modules, or serially connected, i.e., the feed/retentate having passed through a first membrane module enters into a second or following module(s).
  • the crossflow membrane filtration apparatus therefore comprise controllers primarily in order to maintain production capacity for the apparatus.
  • the production capacity is maintained by increasing PI (the baseline pressure) and/or increase dP.
  • control also provide a reduction in used energy, thereby providing a cheaper process.
  • the apparatus comprises
  • PS1 measuring a baseline pressure PI and a pressure transmitter PT1 positioned upstream of the loop circulation pump 2, upstream of the inlet point 6 and downstream of the membrane module 3 and downstream of the last membrane module 3 if there are more than one membrane module 3,
  • PS2 second pressure sensor measuring a pressure P2 and a pressure transmitter PT2 positioned downstream of the loop circulation pump 2 and upstream of the membrane module 3 and at least upstream of the first membrane module 3 if there are more than one membrane module 3,
  • LS level sensor
  • LT level transmitter
  • the feed pump 1 may be operated at between 0% and 100%. According to the invention, the feed pump - depending on which filtration process the feed pump is part of (MF, UF, NF, RO)
  • the feed pump may start at around 60% of the maximum pumping rate.
  • the pumping rate of the feed pump 1 is after start-up controlled through a simple feedback from a measurement of the level in the feed tank 7, the flow after the feed pump, or the base line pressure PI.
  • the first controller may comprise:
  • a level controller having a set point L feed receiving an input from the level sensor/transmitter LT, or
  • a flow controller having a set point Fl feed receiving an input from one or more flow sensors (FT1) or
  • a pressure controller having a set point Pl feed receiving an input from the first pressure sensor (PT1).
  • the apparatus comprises a second controller controlling the output to the loop circulation pump 2 and thereby controlling the pumping rate of the loop pump 2.
  • a dP min and a dP max which values depend on the application of the filtration, i.e. the product produced by the apparatus.
  • the loop pump 2 may be operated at between 0% and 100%. According to the invention, the loop pump - depending on which filtration process the loop pump is part of (MF, UF, NF, RO) - may start at between 20% - 60%, e.g. 25%-50% of the maximum pumping rate.
  • the pumping rate of the loop pump 2 is after start-up controlled through feedback from a measurement of P2 and PI from which a dP is calculated.
  • the pressure difference dP depends on the type of membrane module(s) 3 used, the number of membrane module(s) 3, the flow through the membrane module(s) 3, and the fouling level of the membrane module(s) 3. For a given membrane filtration apparatus the type and number of membrane module(s) is constant, while the flow through the membrane module(s) and the fouling of the membrane module(s) are variable parameters.
  • the driving force is also influenced by the permeate pressure, P permeate , however the permeate pressure is not controlled by the loop circulation pump.
  • the set point for the pressure difference dP may depend on
  • the set point for the pressure difference dP in the second controller may depend on
  • dP min is defined as a minimum dP necessary to deliver a crossflow neutralizing fouling of the membranes of the membrane module(s) 3.
  • the dynamic set point for dP for the loop circulation pump 2 will not exceed dP max i.e. the maximum difference pressure dP which is defined primarily by data provided by the membrane manufacturer for the membrane(s) used in the apparatus.
  • the set point for the pressure difference dP in the second controller may be increased or decreased stepwise i.e. a plurality of set points may be provided for the second controller and these set points may each depend on different values for either the flow FI, or the level L, or the baseline pressure PI.
  • the first controller controlling the output to the feed pump 1 may comprise a flow controller receiving an input from the first flow sensor/transmitter FS1/FT1 which measures the flow FI entering into the filtration loop, or alternatively, the flow controller may receive an input from flow sensors/transmitters FS3/FT3 and FS2/FT2 measuring flow F3 of retentate FT3 and flow F2 of permeate FT2 out of the loop.
  • the first and/or the second controller may comprise PID-controllers e.g. defined as follows:
  • PID5 and PID6 calculating dynamic set points for dP for use in PID4 SP1, SP2, ... , SP6 are set points for the different controllers.
  • the controllers PID1 (SP1), PID2 (SP3) or PID 3 (SP5) control the output to the feed pump 1, i.e. they may either increase or lower the power to the feed pump 1 and consequently increase or lower the pumping rate of the feed pump 1.
  • the PID4 controls the output from the loop circulation pump 2, i.e. the controller may either increase or lower the power to the loop circulation pump 2 and consequently increase or lower the pumping rate of the loop pump 2.
  • the set point for the second controller, PID4, controlling the output from the loop circulation pump may at the start of production be SP6min corresponding to dP min .
  • the feed pump 1 may during a filtration process reach its maximum pumping capacity (either max ampere consumption of the motor or maximum baseline pressure) and the feed pump 1 will not be able to further increase the transport of feed into the filtration loop. Due to the limitation of the feed pump 1, the filtration capacity of the plant will decline resulting in decreasing amount of product, and either increasing level in the feed tank (if the feed pump is controlled by PID1) or decreasing feed flow (if the feed pump is controlled by PID2 or PID3).
  • PID1 having a set point SP1
  • PID5 receiving an input from the level transmitter LT and having a set point SP5
  • PID5 may also contribute to controlling the level in the feed tank 7 and PID5 may be activated when the level of the feed tank 7 exceeds or has exceeded SP1.
  • the feed pump 1 is controlled by PID2 or PID3 having a set point SP2 or SP3, and the feed pump 1 reaches its maximum pumping capacity, the feed flow FI will decrease below the setpoint SP2 or SP3.
  • a further PID controller, PID6 receiving an input from the flow transmitter FT1 and having a set point SP4, may also contribute to controlling the feed flow FI, PID6 may be activated when the feed flow FI decreases below SP4.
  • a program sequence can be used to increase the delta pressure set point in steps when needed i.e., when the level is too high or the flow too low.
  • the outlet for permeate 4 from the membrane module may comprise a third flow sensor FS3 measuring the flow F3 and a transmitter (FT3).
  • the flow F3 may be used to calculate the amount of retentate entering a following loop, as the incoming feed minus the outgoing permeate corresponds to feed entering the downstream loop.
  • the flow sensor/transmitter FT2 positioned at the retentate outlet is normally only positioned after a last loop.
  • the loop may comprise a flow sensor and transmitter FS4/FT4 measuring a flow F4 positioned upstream of the loop pump (2) and downstream of the inlet point (6) in fig. 1, however, the flow sensor and transmitter may be installed anywhere in the loop.
  • the flow F4 may be used to control a flushing step in a CIP process. When knowing the flow F4 it is possible to control the flow being circulated in the loop. During a flushing step it is desirable that as little "retentate" as possible is recirculated in the loop. Normally the flow F4 during CiP should be significantly lower than the flow experience during a filtration process.
  • a controller receives inputs from PT1 and PT2 to calculated dP and inputs from FT4 to control the output from the circulation pump 2.
  • the dynamic set point for the loop circulation pump 2 may be the actual flow FI.
  • the method of the present invention is primarily intended for use within food production.
  • the present invention relates to a method for filtrating a liquid in an apparatus for membrane filtration comprising the following step, a) An amount of fluid feed wherefrom a permeate is separated is continuously pumped through a loop comprising one or more membrane modules, the one or each membrane modules being provided with one inlet and one outlet for fluid feed/retentate and permeate respectively, the inlet for the fluid feed/retentate is positioned at the opposite end of the membrane module as the outlets for respectively the fluid feed/retentate and the permeate, ensuring that the flows of fluid feed/retentate and the permeate are concurrent in the full lengths of the membrane(s) in each membrane module.
  • the TMP may be in the area of 0.02-12 bar, e.g. 0.07-10 bar, or 0.2- 8 bar, or 0.3-2 bar.
  • the method of the present invention can be used in connection with membrane filtration operations within the dairy industry.
  • 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
  • a method according to the present invention can be used in connection with membrane filtration operations of a fluid within the

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Abstract

The present invention relates to an apparatus and a method for controlling a crossflow membrane filtration process used for filtration processes requiring a specified Transmembrane Pressure. In particular, the invention relates to a method for controlling a crossflow membrane filtration apparatus comprising - one or more feed pumps (1) feeding fluid to an inlet point (6) of a loop from a feed tank (7) and having an output from 0% to its maximum 100%, - the loop comprises one or more membrane modules (3) and a conduit system allowing recirculation/circulation of retentate through the membrane module(s) (3), a retentate outlet (5), and a loop circulation pump (2) having an output from 0% to its maximum 100% and circulating retentate through the loop, - a first pressure sensor measuring a baseline pressure P1 and a transmitter configured to measure the pressure upstream of the loop circulation pump (2) and downstream of the membrane module(s) (3), - a second pressure sensor measuring a pressure P2 and a transmitter configured to measure the pressure downstream of the loop circulation pump (2) and upstream of the membrane module(s) (3), - a first flow sensor measuring a flow F1 and a transmitter configured to measure the flow upstream or downstream of the feed pump (1) and upstream of the inlet point (6), - a level sensor measuring a level L and a transmitter measuring and transmitting a value for the content in the feed tank (7), - a first controller controlling the output from the feed pump (1) comprising 1) a level controller receiving an input from the level sensor/transmitter, or 2) a flow controller receiving an input from one or more flow sensors/transmitters, or 3) a pressure controller receiving an input from the first pressure sensor/transmitter, - a second controller controlling the output from the loop circulation pump (2) comprising a pressure controller receiving inputs P1, P2 from the first and second pressure sensors/transmitters and calculating a pressure difference dP = P2 - P1 and then comparing the calculated dP with a set point for the pressure difference dP, for each loop in a crossflow membrane filtration apparatus dPmin and a dPmax, are defined to obtain a desired retentate or permeate product, wherein the set point for the pressure difference dP of the second controller is dynamic and the set point depends on - the flow F1 in such a way that if the flow F1 decreases below a value Floop,low then the set point for dP is increased, or the level L in such a way that if L increases above a value Floop,high then the set point for dP is increased, or - the baseline pressure P1, in such a way that if P1 increases to a value above P1high then the set point for dP is increased.

Description

Control for filtration process
The present invention relates to an apparatus and a method for controlling a crossflow membrane filtration process used for filtration processes requiring a specified Transmembrane Pressure (TMP).
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).
An apparatus for crossflow membrane filtration normally comprises one or more feed pumps feeding fluid from a feed tank to an inlet point 6 of a loop, and a loop circulation pump recirculating retentate through one or more crossflow membranes. To control such a filtration process, the feed pumps normally comprise a controller keeping e.g. the level in the feed tank constant, or keeping the flow into the loop constant, or keeping the base line pressure constant, and the loop circulation pump comprises a controller maintaining a constant difference pressure over the crossflow membrane, i.e. the difference between the pressure before the membrane(s) P2 and the pressure after the membrane PI - where PI is also known as the baseline pressure - is kept constant. Such a control set up makes it possible to maintain a constant production or capacity for the apparatus, where the capacity may be determined by the relation between permeate and retentate, or the content of e.g. salts, protein, or other component of the permeate or retentate. According to a traditional filtration process where the pumping rate or output from the loop pump is controlled through feedback from a measurement of dP, the system is dimensioned to maintain a constant value for dP, such as dP= 0.8 bar for a high-pressure filtration process.
US 5.069.792 A1 relates to optimization of concentrate flow in a filter system which system uses actual sensed operating curve data to optimize plasma flow in a plasmapheresis system. The US-document discloses an adaptive filter concentrate flow control system and method, which method includes a filter system, a pumping system driving feed fluid, concentrate and filtrate flowing through the filter system and a flow control system controlling the pumping system to maintain optimum filtrate flow rates or minimum feed flow rates along a control surface in a three-dimensional transmembrane pressure-feed fluid rate- filtrate flow rate space. Actual sensed operating point data is used to locate the control surface so as to assure an optimized filtrate flow rate or minimized feed flow rate at which reversible blocking of the membrane has begun to occur without irreversible blocking or plugging. The system is employed to control and maximize the flow of plasma in a plasmapheresis system or to minimize the rate at which blood is withdrawn from a donor and introduced into the system while achieving a fixed rate of plasma flow. However, the system does not suggest how to minimize energy consumption during operation which is an important factor in an industrial processes.
US 2005/126961 A1 discloses a multipurpose hemofiltration system and method for removal of fluid and/or soluble waste from the blood of a patient. The system continuously monitors the flow rates of drained fluid, blood, and infusate. When necessary, the pumping rates of the infusate, drained fluid and blood are adjusted to remove a preselected amount of fluid from the blood in a preselected time period. A supervisory controller can monitor patient parameters, such as heart rate and blood pressure, and adjust the pumping rates accordingly. The supervisory controller uses fuzzy logic to make expert decisions, based upon a set of supervisory rules, to control each pumping rate to achieve a desired flow rate and to respond to fault conditions. An adaptive controller corrects temporal variations in the flow rate based upon an adaptive law and a control law. However, neither this system suggest how to minimize energy consumption during operation.
The present invention not only makes it possible to maintain a constant capacity in a crossflow membrane filtration apparatus; the present invention also makes it possible to reduce energy consumption compared to a traditional driven membrane filtration apparatus applied in an industrial process as well as increasing the operational lifetime of the membranes.
Definitions of words:
TMP- Trans Membrane Pressure, pressure difference between feed and permeate. The TMP is calculated according to the formula: TMP where r,h is the fluid feed/retentate pressure before or
Figure imgf000004_0001
at the inlet of a membrane module and pout 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.
Cross flow - Linear flow along the membrane surface. A purpose of the cross flow is to minimize or control the dynamic layer on the membrane surface and the cross flow is determined by the pressure difference Pin — Pout on the retentate side of the membrane.
Pressure loss per membrane element or dP per membrane element or dP/element - is the driving force for the above-described cross flow. 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 = r,h - Pout.
Membrane - a membrane provides a barrier allowing permeate to pass through the membrane and preventing retentate from passing through. In the context of the present application a membrane element may be a spiral wound membrane, where permeate flows from a peripheral position to a central opening of the membrane element.
Membrane module or module - assembly of one membrane housing including or comprising one or more membrane elements and 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 from the one or more membrane elements of the one membrane housing is removed. The outlet for retentate and the outlet for permeate may be positioned at the same end of the housing, i.e. opposite the inlet for feed/retentate providing concurrent flow of retentate and permeate.
Summary of invention:
The present invention provides an improved method for controlling a crossflow membrane apparatus.
The invention relates to a method for controlling a crossflow membrane filtration apparatus comprising
- one or more feed pumps (1) feeding fluid to an inlet point (6) of a loop from a feed tank (7) and having an output from 0% to its maximum 100%, - the loop comprises one or more membrane modules (3) and a conduit system allowing recirculation/circulation of fluid through the membrane module (3) and a retentate outlet (5), and a loop circulation pump (2) circulating fluid through the loop,
- a first pressure sensor measuring a baseline pressure PI and a transmitter (PT1) positioned upstream of the loop circulation pump (2) and downstream of the membrane module (3),
- a second pressure sensor measuring a pressure P2 and a transmitter (PT2) positioned downstream of the loop circulation pump (2) and upstream of the membrane module (3),
- a first flow sensor measuring a flow FI and a transmitter (FT1) positioned upstream or downstream of the feed pump (1) and upstream of the inlet point (6),
- a level sensor measuring a level L and a transmitter (LT) measuring and transmitting a value for the content in the feed tank (7),
- a first controller controlling the output to the feed pump (1) comprising 1) a level controller receiving an input from the level sensor/transmitter LT, or 2) a flow controller receiving an input from one or more flow sensors (FT1), or 3) a pressure controller receiving an input from the first pressure sensor (PT1),
- a second controller controlling the output to the loop circulation pump (2) comprising a pressure controller receiving inputs from the first and second pressure sensors (PI, P2) and calculating a pressure difference dP = P2 - PI and then comparing the calculated dP with a set point for the pressure difference dP, for each loop in a crossflow membrane filtration apparatus it is possible to calculate a dPmin and a dPmax, wherein the set point for the pressure difference dP in the second controller is dynamic and the set point depends on the flow FI in such a way that if the flow FI decreases below a value Fli00p,iow then the set point for dP is increased, or the level L in such a way that if L increases above a value L|00 ,high then the set point for dP is increased, or the baseline pressure PI, in such a way that if PI increases to a value above Plhigh then the set point for dP is increased.
According to any embodiment of the invention, the set point for the pressure difference dP in the second controller may depend on the flow FI in such a way that if the flow FI exceeds a value Fl|00p,high the set point for dP is decreased, or the level L in such a way that if L decreases to a level below a value L|00p,iow then the set point for dP is decreased, or the baseline pressure PI, in such a way that if PI decreases to a value below Pl|O then the set point for dP is decreased.
According to any embodiment of the invention, the set point for dP for the loop circulation pump may be set to dPmin at t = 0, where dPmin is defined as a minimum dP necessary to deliver a crossflow neutralizing fouling of the membranes, and wherein the set point for dP for the loop circulation pump does not exceed
According to any embodiment of the invention, the set point for the pressure difference dP in the second controller may be either increased or decreased stepwise depending on a plurality of values for either the flow FI, or the level L, or the baseline pressure PI.
According to any embodiment of the invention, the set point for dP may be based on the same relative % increasing or decreasing as the relative % increasing or decreasing of the output for the feed pump. According to any embodiment of the invention, the first controller controlling the output to the feed pump (1) may comprise a flow controller receiving an input from the first flow sensor (FT1) measuring flow into the loop, or an input from flow sensors (F2, F3) measuring flow of retentate (FT3) and permeate (FT2) out of the loop.
According to any embodiment of the invention, the first and/or the second controller is/are PID-controllers.
According to any embodiment of the invention, the membrane module (3) may comprise an outlet for permeate (4) and this outlet may comprise a third flow sensor measuring the flow F3 and a transmitter (FT3).
According to any embodiment of the invention, the loop may comprise a flow sensor and transmitter (FT4) measuring a flow F4 positioned upstream of the loop pump (2) and downstream of the inlet point (6).
List of figures:
Figure 1 shows a crossflow membrane filtration apparatus which may be controlled by the method of the invention.
Throughout the application identical or similar elements of different embodiments are given the same reference numbers.
Detailed description of invention:
Figure 1 shows an embodiment of a crossflow membrane filtration apparatus which may be used according to the invention. The crossflow membrane filtration apparatus comprises a feed pump 1 feeding fluid to an inlet point 6 of a filtration loop. The feed pump 1 is normally a variable pumping capacity type pump. The feed is contained in a feed tank 7 and the feed pump 1 may either function as a master or as a slave i.e. either the feed pump 1 continuously controls the flow into the filtration loop and the feed tank 7 is filled when necessary, or the feed pump 1 reacts when feed is added to the feed tank in response e.g. to the level of fluid in the feed tank.
The filtration loop comprises one or more membrane modules 3 indicated by a single block in fig. 1, and a conduit system allows recirculation/circulation of retentate through the membrane module(s) 3, i.e. the retentate outlet(s) of the membrane module(s) 3 is/are fluidly connected to the inlet(s) of the membrane module(s) 3.
Further, the filtration loop comprises a retentate outlet 5, a loop circulation pump 2 circulating the feed/retentate through the loop. The loop circulating pump 2 is normally a variable pumping capacity type pump but may be an on-off pumping capacity type pump in combination with a control valve.
If there are more than one membrane module 3, the plurality of membrane modules may be either parallelly connected, i.e., one flow of feed/retentate is split and fed to two or more membrane modules, or serially connected, i.e., the feed/retentate having passed through a first membrane module enters into a second or following module(s).
During filtration, the membranes will gradually foul (become dirty) why first the feed pump 1 and then secondly the loop pump 2 must gradually increase the output, i.e. the pumping rate, to compensate for the increasing resistance. The crossflow membrane filtration apparatus therefore comprise controllers primarily in order to maintain production capacity for the apparatus. The production capacity is maintained by increasing PI (the baseline pressure) and/or increase dP.
According to the present invention, the control also provide a reduction in used energy, thereby providing a cheaper process.
To obtain a both stable and energy optimized process, the apparatus comprises
- a first pressure sensor (PS1) measuring a baseline pressure PI and a pressure transmitter PT1 positioned upstream of the loop circulation pump 2, upstream of the inlet point 6 and downstream of the membrane module 3 and downstream of the last membrane module 3 if there are more than one membrane module 3,
- a second pressure sensor (PS2) measuring a pressure P2 and a pressure transmitter PT2 positioned downstream of the loop circulation pump 2 and upstream of the membrane module 3 and at least upstream of the first membrane module 3 if there are more than one membrane module 3,
- a first flow sensor (FS1) measuring a flow FI and a flow transmitter FT1 positioned upstream or downstream of the feed pump 1 and upstream of the inlet point 6, i.e. the first flow sensor FS1 measures the flow through the feed pump 1,
- a level sensor (LS) measuring a level L and a level transmitter LT measuring and transmitting a value for the content in the feed tank 7,
- a first controller controlling the output to the feed pump 1 i.e. the first controller controls the pumping rate of the feed pump 1. The feed pump 1 may be operated at between 0% and 100%. According to the invention, the feed pump - depending on which filtration process the feed pump is part of (MF, UF, NF, RO)
- may start at between 40% - 70%, e.g. 50%-65% of the maximum pumping rate. For high-pressure filtration processes, the feed pump may start at around 60% of the maximum pumping rate. The pumping rate of the feed pump 1 is after start-up controlled through a simple feedback from a measurement of the level in the feed tank 7, the flow after the feed pump, or the base line pressure PI.
The first controller may comprise:
1) a level controller having a set point Lfeed receiving an input from the level sensor/transmitter LT, or
2) a flow controller having a set point Flfeed receiving an input from one or more flow sensors (FT1) or
3) a pressure controller having a set point Plfeed receiving an input from the first pressure sensor (PT1).
Further, the apparatus comprises a second controller controlling the output to the loop circulation pump 2 and thereby controlling the pumping rate of the loop pump 2. The second controller comprises a pressure controller receiving measured inputs from the first and second pressure sensors/transmitters (PS1/PT1, PS2/PT2), then the controller calculates a pressure difference dP = P2 - PI and compares the calculated dP with a set point for the pressure difference dP. For each loop in a crossflow membrane filtration apparatus, it is possible to calculate a dPmin and a dPmax which values depend on the application of the filtration, i.e. the product produced by the apparatus.
The loop pump 2 may be operated at between 0% and 100%. According to the invention, the loop pump - depending on which filtration process the loop pump is part of (MF, UF, NF, RO) - may start at between 20% - 60%, e.g. 25%-50% of the maximum pumping rate. The pumping rate of the loop pump 2 is after start-up controlled through feedback from a measurement of P2 and PI from which a dP is calculated.
The pressure difference dP depends on the type of membrane module(s) 3 used, the number of membrane module(s) 3, the flow through the membrane module(s) 3, and the fouling level of the membrane module(s) 3. For a given membrane filtration apparatus the type and number of membrane module(s) is constant, while the flow through the membrane module(s) and the fouling of the membrane module(s) are variable parameters.
The pressure difference dP which is controlled by the loop circulation pump 2, partly define the driving force of the filtration process taking place in the membrane module(s) 3 as Pin = P2 and Pout = PI when calculating the transmembrane pressure: TMP = Vm+Vout —
Figure imgf000008_0001
The driving force is also influenced by the permeate pressure, Ppermeate, however the permeate pressure is not controlled by the loop circulation pump.
The second controller
According to the invention, the set point for the pressure difference dP = P2-P1 in the second controller is dynamic during operation of the apparatus, i.e., the set point may be dynamic during start-up and/or closing down of a production process, and during normal production.
The set point for the pressure difference dP may depend on
1) the flow FI in such a way that if the flow FI decreases below a value Fl|00p,iow then the set point for dP is increased, or
2) the level L of the feed tank in such a way that if the level L increases above a value L|00 ,high then the set point for dP is increased, or
3) the baseline pressure PI, in such a way that if the pressure PI increases to a value above Plhigh then the set point for dP is increased.
These conditions 1), 2) or 3) appear in the apparatus when the feed pump 1 is approaching a maximum output, when the feed pump 1 is running at its maximum pumping rate, the first controller is no longer able to influence production, and to maintain a constant output of retentate or permeate, the pumping rate of the circulation pump 2 must then be increased.
In case the feed pump 1 is moving away from the maximum output to an optimal output, the set point for the pressure difference dP in the second controller may depend on
1) the flow FI in such a way that if the flow FI exceeds a value Fl|00p,high the set point for dP is decreased, or
2) the level L in the feed tank in such a way that if the level L decreases to a level below a value L|00p,iow then the set point for dP is decreased, or
3) the baseline pressure PI, in such a way that if the pressure PI decreases to a value below Pl|O then the set point for dP is decreased.
The set point for dP for the loop circulation pump may be set to dPmin at the start (t = 0), i.e. at the beginning of a filtration process where the membrane(s) are clean i.e. without fouling. dPmin is defined as a minimum dP necessary to deliver a crossflow neutralizing fouling of the membranes of the membrane module(s) 3. Also, the dynamic set point for dP for the loop circulation pump 2 will not exceed dPmax i.e. the maximum difference pressure dP which is defined primarily by data provided by the membrane manufacturer for the membrane(s) used in the apparatus.
The set point for the pressure difference dP in the second controller may be increased or decreased stepwise i.e. a plurality of set points may be provided for the second controller and these set points may each depend on different values for either the flow FI, or the level L, or the baseline pressure PI.
The first controller
The first controller controlling the output to the feed pump 1 may comprise a flow controller receiving an input from the first flow sensor/transmitter FS1/FT1 which measures the flow FI entering into the filtration loop, or alternatively, the flow controller may receive an input from flow sensors/transmitters FS3/FT3 and FS2/FT2 measuring flow F3 of retentate FT3 and flow F2 of permeate FT2 out of the loop.
Control system
The first and/or the second controller may comprise PID-controllers e.g. defined as follows:
- PID1 controlling level (LT) in the feed tank
- PID2 controlling feed flow (FT1) to the circulation loops
- PID3 controlling baseline pressure (PT1) in the circulation loops
- PID4 controlling dP (PT2 - PT1) in the circulation loops
- PID5 and PID6 calculating dynamic set points for dP for use in PID4 SP1, SP2, ... , SP6 are set points for the different controllers.
The controllers PID1 (SP1), PID2 (SP3) or PID 3 (SP5) control the output to the feed pump 1, i.e. they may either increase or lower the power to the feed pump 1 and consequently increase or lower the pumping rate of the feed pump 1.
The PID4 (SP6) controls the output from the loop circulation pump 2, i.e. the controller may either increase or lower the power to the loop circulation pump 2 and consequently increase or lower the pumping rate of the loop pump 2.
The set point for the second controller, PID4, controlling the output from the loop circulation pump may at the start of production be SP6min corresponding to dPmin.
Due to a decreasing dP in the loop (resulting from a lower capacity of the membranes normally due to fouling) the feed pump 1 may during a filtration process reach its maximum pumping capacity (either max ampere consumption of the motor or maximum baseline pressure) and the feed pump 1 will not be able to further increase the transport of feed into the filtration loop. Due to the limitation of the feed pump 1, the filtration capacity of the plant will decline resulting in decreasing amount of product, and either increasing level in the feed tank (if the feed pump is controlled by PID1) or decreasing feed flow (if the feed pump is controlled by PID2 or PID3). If the feed pump 1 is controlled by PID1 having a set point SP1, and the feed pump 1 reaches its maximum pumping capacity, the level L in the feed tank 7 will increase to above SP1. A further PID controller, PID5 receiving an input from the level transmitter LT and having a set point SP5, may also contribute to controlling the level in the feed tank 7 and PID5 may be activated when the level of the feed tank 7 exceeds or has exceeded SP1. PID5 may have an output between 0% and 100%, and may be used to calculate a dynamic setpoint SP6 for PID4, the calculated dynamic set point may be linear and have values between SP6min and SP6max, meaning that if the output from PID5 is 0% the setpoint SP6 for PID4 is SP6min, and if the output from PID5 is 100% the setpoint for PID4 is SP6max, and if the output is 50%, then SP6 = (SP6max-SP6min)*0.5+SP6min.
If the feed pump 1 is controlled by PID2 or PID3 having a set point SP2 or SP3, and the feed pump 1 reaches its maximum pumping capacity, the feed flow FI will decrease below the setpoint SP2 or SP3. A further PID controller, PID6 receiving an input from the flow transmitter FT1 and having a set point SP4, may also contribute to controlling the feed flow FI, PID6 may be activated when the feed flow FI decreases below SP4. PID6 may have an output between 0% and 100% and may be used to calculate a dynamic setpoint SP6 for PID4, the calculated set point may be linear between SP6min and SP6max, meaning that if the output from PID6 is 0% the setpoint SP6 for PID4 is SP6min, and if the output from PID6 is 100% the setpoint SP6 for PID4 will be SP6max, and if the output is 50%, then SP6 = (SP6max-SP6min)*0.5+SP6min.
As an alternative to using further controllers PID5 and PID6, a program sequence can be used to increase the delta pressure set point in steps when needed i.e., when the level is too high or the flow too low.
The outlet for permeate 4 from the membrane module may comprise a third flow sensor FS3 measuring the flow F3 and a transmitter (FT3). The flow F3 may be used to calculate the amount of retentate entering a following loop, as the incoming feed minus the outgoing permeate corresponds to feed entering the downstream loop. The flow sensor/transmitter FT2 positioned at the retentate outlet is normally only positioned after a last loop.
The loop may comprise a flow sensor and transmitter FS4/FT4 measuring a flow F4 positioned upstream of the loop pump (2) and downstream of the inlet point (6) in fig. 1, however, the flow sensor and transmitter may be installed anywhere in the loop. The flow F4 may be used to control a flushing step in a CIP process. When knowing the flow F4 it is possible to control the flow being circulated in the loop. During a flushing step it is desirable that as little "retentate" as possible is recirculated in the loop. Normally the flow F4 during CiP should be significantly lower than the flow experience during a filtration process. During CIP, a controller receives inputs from PT1 and PT2 to calculated dP and inputs from FT4 to control the output from the circulation pump 2. The dynamic set point for the loop circulation pump 2 may be the actual flow FI.
Example illustrating reduction in energy consumption relative to traditional filtration process Power consumption: E, pressure loss membrane(s): dP, circulation flow in loop: V Simple calculation of power consumed: E = dP * V (i)
At frequency control, the connection between circulation flow and pressure loss is as follows: dP = V2 => \l = dP~ (ii) Combining (i) and (ii): E = dP * dP = /dP3
(1) Traditional method where the system including pumps, filtration membranes etc., is dimensioned to maintain constant maximum dP both during start up and operation: dPmax = 5 bar, the loop pump and the feed pump together maintain a constant dP : El= 5^ = 11,2
(2) Method according to invention where the system is dimensioned to start at a lower dP and maintain a lower dP at least during part of operation: dP = 50% of dPmax = 2,5 bar, where E2= V2.53 = 3,95 l.e. a reduction of dP with 50% will result in a reduction of the power consumption to around:
E2/E1 = 3,95/11,2 = 0,35 = 35%
The method of the present invention is primarily intended for use within food production.
In general, the present invention relates to a method for filtrating a liquid in an apparatus for membrane filtration comprising the following step, a) An amount of fluid feed wherefrom a permeate is separated is continuously pumped through a loop comprising one or more membrane modules, the one or each membrane modules being provided with one inlet and one outlet for fluid feed/retentate and permeate respectively, the inlet for the fluid feed/retentate is positioned at the opposite end of the membrane module as the outlets for respectively the fluid feed/retentate and the permeate, ensuring that the flows of fluid feed/retentate and the permeate are concurrent in the full lengths of the membrane(s) in each membrane module. This causes a well-defined flow behavior inside the membrane module without appearance of a dead leg in the central tube of the membrane. b) generated permeate is continuously drained from the one or each membrane module 3 through the permeate outlet, c) optionally, the permeate pressure at the permeate outlet in one or in each membrane module is controlled keeping TMP within a desired range, the pressure (P2, PT2) is measured at the feed inlet end of the membrane module 3.
During microfiltration or ultrafiltration, the TMP may be in the area of 0.02-12 bar, e.g. 0.07-10 bar, or 0.2- 8 bar, or 0.3-2 bar.
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
• cheese whey
• cheese whey WPC
• skim milk
• skim milk MPC
• raw whole milk
• whole milk
• microfiltration permeates Also, a method according to the present invention can be used in connection with membrane filtration operations of a fluid within the
• liquid food industry or
• liquid beverage industry or
• liquid life Science industry to obtain
• protein separation or
• fat separation or
• micro-organism separation or
• protein fractionation or
• alcohol separation on/from
• vegetable (green) solutions or
• meat solutions or
• fish solutions or
• beverage solutions or
• microfiltration permeates
Figure imgf000012_0001

Claims

1. Method for controlling a crossflow membrane filtration apparatus comprising
- one or more feed pumps (1) feeding fluid to an inlet point (6) of a loop from a feed tank (7) and having an output from 0% to its maximum 100%,
- the loop comprises one or more membrane modules (3) and a conduit system allowing recirculation/circulation of retentate through the membrane module(s) (3), a retentate outlet (5), and a loop circulation pump (2) having an output from 0% to its maximum 100% and circulating retentate through the loop,
- a first pressure sensor (PS1) measuring a baseline pressure PI and a transmitter (PT1) configured to measure the pressure upstream of the loop circulation pump (2) and downstream of the membrane module(s) (3),
- a second pressure sensor (PS2) measuring a pressure P2 and a transmitter (PT2) configured to measure the pressure downstream of the loop circulation pump (2) and upstream of the membrane module(s) (3),
- a first flow sensor (FS1) measuring a flow FI and a transmitter (FT1) configured to measure the flow upstream or downstream of the feed pump (1) and upstream of the inlet point (6),
- a level sensor (LS) measuring a level L and a transmitter (LT) measuring and transmitting a value for the content in the feed tank (7),
- a first controller (PID1, PID2, PID3) controlling the output from the feed pump (1) comprising 1) a level controller receiving an input from the level sensor/transmitter LS/LT, or 2) a flow controller receiving an input from one or more flow sensors/transmitters (FS1/FT1) or 3) a pressure controller receiving an input from the first pressure sensor/transmitter (PS1/PT1),
- a second controller controlling the output from the loop circulation pump (2) comprising a pressure controller receiving inputs PI, P2 from the first and second pressure sensors/transmitters (PS1/PT1, PS2/PT2) and calculating a pressure difference dP = P2 - PI and then comparing the calculated dP with a set point for the pressure difference dP, for each loop in a crossflow membrane filtration apparatus dPmin and a dPmax, are defined to obtain a desired retentate or permeate product, characterized in that the set point for the pressure difference dP of the second controller is dynamic and the set point depends on
- the flow FI in such a way that if the flow FI decreases below a value Fl|00p,iow then the set point for dP is increased, or
- the level L in such a way that if L increases above a value L|00p,high then the set point for dP is increased, or
- the baseline pressure PI, in such a way that if PI increases to a value above Plhigh then the set point for dP is increased.
2. A method according to claim 1, wherein the set point for the pressure difference dP in the second controller depends on - the flow FI in such a way that if the flow FI exceeds a value Fl|00p,high the set point for dP is decreased, or
- the level L in such a way that if L decreases to a level below a value L|00p,iow then the set point for dP is decreased, or
- the baseline pressure PI, in such a way that if PI decreases to a value below Pl|O then the set point for dP is decreased.
3. A method according to any preceding claim, wherein the set point for dP for the loop circulation pump is set to dPmin at t = 0, where dPmin is defined as a minimum dP necessary to deliver a crossflow neutralizing fouling of the membranes, and wherein the set point for dP for the loop circulation pump does not exceed d P max
4. A method according to any preceding claim, wherein the set point for the pressure difference dP in the second controller may be either increased or decreased stepwise depending on a plurality of values for either the flow FI, or the level L, or the baseline pressure PI.
5. A method to any preceding claim, wherein the set point for dP is based on the same relative % increasing or decreasing as the relative % increasing or decreasing of the output for the feed pump.
6. A method according to any preceding claim, wherein the first controller controlling the output to the feed pump (1) comprises a flow controller receiving an input from the first flow sensor (FT1) measuring flow into the loop, or an input from flow sensors (F2, F3) measuring flow of retentate (FT3) and permeate (FT2) out of the loop.
7. A method according to any preceding claim, wherein the first and/or the second controller is/are PID- controllers.
8. A method according to any preceding claim, wherein the membrane module (3) comprises an outlet for permeate (4) and this outlet may comprise a third flow sensor measuring the flow F3 and a transmitter (FT3).
9. A method according to any preceding claim, wherein the loop comprises a flow sensor and transmitter (FT4) measuring a flow F4 positioned upstream of the first membrane module (3) or upstream of the loop pump (2), and downstream of the inlet point (6).
10. A method according to any preceding claim, wherein the method is applied with an industrial process to reduce energy consumption during operation of the crossflow membrane filtration apparatus.
11. Use of a method according to any of the claims 1-10 for high-pressure filtration such as microfiltration (MF), ultrafiltration (UF), nanofiltration or reverse osmosis.
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DE102024106402A1 (en) * 2024-03-06 2025-09-11 B.Braun Avitum Ag Method for operating a reverse osmosis system

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