System and method for filtration of liquids

Abstract

A normal flow filtration system having a housing with one or more filters contained within a bowl and attached to the outlet of the system. Liquid enters the bowl, contacts the surfaces of the one or more filters. Impurities are trapped in the filter and the filtered liquid flows through to the outlet. Parameter(s) such as flow rate, transmembrane pressure drop and/or time are measured and when met, filtration ceases. A backflushing occurs through the filter(s) so as to remove the impurities from the filter. This backwashed material is directed to an outlet of the bowl that is connected to a drain. Additionally a port formed in the side of the housing adjacent an outer surface of the filter(s) can be used to provide a lateral washing of the filter(s). The system is then recirculated in a downstream manner to reestablish equilibrium and filtration is then restarted.

Claims

1. A system for the normal flow filtration of liquids comprising a source of fluid to be filtered, a first conduit connecting the source to an inlet of a filtration device, the filtration device comprising one or more housings containing one or more filters, the one or more housings having a head and a bowl portion, the one or more filters being in fluid communication with a housing outlet in each of the one or more housings which outlet is in fluid communication with a second conduit leading to a downstream component, the downstream component being selectively closable to flow from the second conduit by a normally open first valve, a selectively closable recirculation loop for the fluid from the first valve via a third conduit back to the inlet of the first conduit in each of the one or more housings wherein the recirculation loop is normally closed off from the housing outlet in each of the one or more housings by a second valve, the inlet and the outlet being located in the head of each of the one or more housings and a drain being located at a lowermost portion of the bowl of each of the one or more housings, one or more ports formed in the side of each of the one or more housings adjacent the one or more filters, the one or more ports being connected to a side of each of the one or more housings adjacent an outer surface of the one or more filters, the port(s) being connected to the first conduit by a port conduit, the first conduit having a third valve which is selectively closable downstream of the port conduit, the port conduit having a selectively openable port valve to direct the fluid to be filtered against the outer surface of the filters for cleaning of the filters when the port valve is selectively opened and the third valve is selectively closed.

2. The system of claim 1 wherein the one or more ports are tangential to a substantially vertical outer surface of the one or more filters.

3. The system of claim 1 wherein the one or more ports are at an angle φ to a substantially vertical outer surface of the one or more filters, wherein the angle φ is formed between the centerline of the one or more filters and the centerline of the one or more ports and wherein the φ is selected from the group consisting of an angle from about 15° to about 165°.

4. The system of claim 1 wherein the one or more ports are at an angle φ to a substantially vertical outer surface of the one or more filters, wherein the angle φ is formed between the centerline of the one or more filters and the centerline of the one or more ports and wherein the φ is selected from the group consisting of an angle from about 30° to about 150°.

5. The system of claim 1 wherein the one or more ports are at an angle φ to a substantially vertical outer surface of the one or more filters, wherein the angle φ is formed between the centerline of the one or more filters and the centerline of the one or more ports and wherein the φ is selected from the group consisting of an angle from about 45° to 135°.

6. The system of claim 1 wherein the one or more ports are at an angle φ to a substantially vertical outer surface of the one or more filters, wherein the angle φ is formed between the centerline of the one or more filters and the centerline of the one or more ports and wherein the φ is about 90°.

7. A system for the normal flow filtration of liquids comprising a source of unfiltered fluid to be filtered, a first conduit connecting the source to an inlet of a filtration device, the filtration device comprising one or more housings containing one or more filters, the one or more filters being in fluid communication with a housing outlet in each of the one or more housings which is in fluid communication with a second conduit leading to a downstream component, the downstream component being selectively closable to flow from the second conduit by a normally open first valve, a selectively closable recirculation loop for the fluid from the first valve via a third conduit back to the inlet of the first conduit in each of the one or more housings wherein the recirculation loop is normally closed off from the housing outlet in each of the one or more housings by a second valve, the inlet and the outlet being located at an uppermost portion of each of the one or more housings and a drain being located at a lowermost portion of each of the one or more housings, one or more ports formed in the side of each of the one more housings adjacent the one or more filters, the one or more ports being connected to a side of each of the one or more housings adjacent an outer surface of one or more filters, the port(s) being connected to the first conduit by a port conduit, the first conduit having a third valve which is selectively closable downstream of the port conduit, the port conduit having a selectively openable port valve to direct the unfiltered fluid against the outer surface of the filters when the port valve is selectively opened and the third valve is selectively closed to clean the outer surfaces of the one or more filters.

8. A system for the normal flow filtration of liquids comprising a source of unfiltered fluid to be filtered, a first conduit connecting the source to an inlet of a filtration device, the filtration device comprising one or more housings containing one or more filters, the one or more filters being in fluid communication with a housing outlet in each of the one or more housings which is in fluid communication with a second conduit leading to a downstream component, the downstream component being selectively closable to flow from the second conduit by a normally open first valve, a selectively closable recirculation loop for the fluid from the first valve via a third conduit back to the inlet of the first conduit in each of the one or more housings wherein the recirculation loop is normally closed off from the housing outlet in each of the one or more housings by a second valve, the inlet and the outlet being located in a head of each of the one or more housings and a drain being located at a lowermost portion of the bowl of each of the one or more housings, one or more ports formed in the side of each of the one or more housings adjacent the one or more filters, the one or more ports being connected to a side of each of the one or more housings adjacent an outer surface of one or more filters, the port(s) being connected to the first conduit by a port conduit, the first conduit having a third valve which is selectively closable downstream of the port conduit, the port conduit having a selectively openable port valve to direct the unfiltered fluid against the outer surface of the filters when the port valve is selectively opened and the third valve is selectively closed to clean the outer surfaces of the one or more filters and wherein the one or more ports are at an angle φ to a substantially vertical outer surface of the one or more filters, wherein the angle φ is formed between the centerline of the one or more filters and the centerline of the one or more ports and wherein the φ is selected from the group consisting of an angle from about 15° to about 165°.

9. The system of claim 8 wherein the angle φ is formed between the centerline of the one or more filters and the centerline of the one or more ports and wherein the φ is selected from the group consisting of an angle from about 30° to about 150°.

10. The system of claim 8 wherein the angle φ is formed between the centerline of the one or more filters and the centerline of the one or more ports and wherein the φ is selected from the group consisting of an angle from about 45° to 135°.

11. The system of claim 8 wherein the angle φ is formed between the centerline of the one or more filters and the centerline of the one or more ports and wherein the φ is about 90°.

Description

IN THE DRAWINGS

(1) FIG. 1 shows a housing useful in a system according to the present invention in cross sectional view.

(2) FIG. 2 shows a close up of a portion of the housing of FIG. 1 according to the present invention in cross sectional view.

(3) FIG. 3 shows the flow path for filtration in a system according to the present invention in cross sectional view.

(4) FIG. 4 shows the flow path for backflushing in a system according to the present invention in cross sectional view.

(5) FIG. 5 shows the flow path for recirculation in a system according to the present invention in cross sectional view.

(6) FIG. 6 shows the flow path lateral flushing in a system according to the present invention in cross sectional view.

(7) FIG. 7 shows the flow path for water washing or cleaning in place (CIP) in the reverse direction in a system according to the present invention in cross sectional view.

(8) FIG. 8 shows a system of the present invention using two such housings either in parallel or alternately.

DETAILED DESCRIPTION

(9) By “port(s)” it is meant that one or more ports exist or can be used. By filter cartridge(s) it is meant that one or more cartridges can exist or be used.

(10) FIG. 1 shows a filter housing 2 according to the present invention. It is formed of two major components, a head 4 and a bowl 6. The head contains an inlet 8 and an outlet 10. The bowl 6 has a drain 12 formed at or near its lowermost point 14.

(11) The bowl 6 may have a frustoconical bottom 16 as shown or it may have a rounded, a tapered or even a flat bottom if desired. Preferably, it is a frustoconical rounded or tapered shape. By having such a shape adjacent and/or at its lowermost point 14, the drain 12 can work more efficiently to remove debris and impurities from the housing 2 as will be described further in. Often these shapes allow for the concentration of the impurities so that minimal amounts of product are lost from the system when the impurities are removed from the housing.

(12) As shown the one or more filter cartridges 18 are attached to the outlet 10 of the housing 2. The cartridge(s) 18 are arranged so that the cartridge(s) 18 hang vertically from the outlet 10 of the head 4 into the bowl 6. These cartridge(s) 18 are well known in design and have a closed end 19 which in this embodiment is farthest from the outlet 10 and an open outlet end 21 which is attached to the outlet 10 of the housing 2. The cartridge(s) 18 contain one or more layers of filter material which may be pleated porous plastic membrane, spun or wound fibers such as of plastic, glass and the like and/or non woven materials. If desired various support and protective layers such as an outer porous protective cage, an inner porous core and one or more layers of filter support materials such as porous non-woven scrims and the like.

(13) Typical plastics for the filter material include but are not limited to polyolefins such as polyethylene and polypropylene, polyvinylidene fluoride (PVDF), polyvinyl alcohols, polyvinyl chlorides, polysulfones, polyarylsulfones, polyethersulfones, polyphenylsulfones, PTFE resins, PFA resins, polyesters, nylons, polyamides, polyimides, and celluloses and modified cellulosic materials such as cellulose acetate.

(14) The pore size of the filter will vary depending upon the filter type chosen, the impurities to be filtered and the like. They may range from about 0.1 micron average pore size to 10 microns pore size. Typically, a 2.0, 1.0, 0.65, 0.45 or 0.22 micron pore size are used for membrane type filters depending on the application, the impurities to be removed, the amount of impurities present and the like. Preferably filter having a pore size between about 0.65 and 2.0 microns is used. Non-wovens and depth filters such as wound filters and the like are not often rated by pore site but the extent that they are the same pore sizes as tier membranes can be used.

(15) The housing may also contain one or more additional port(s) 20 in the side of the housing 2 adjacent the filters 18 that is used in the cleaning process described further below. The port(s) are tangential to the substantially vertical surface of the filter cartridge(s) and may be at an angle φ formed between the centerline (A-A) 23 of the cartridge(s) and the centerline (B-B) 25 of the port 20 as shown in FIG. 2. Preferably the angle φ is from about 15° to about 165°, more preferably from about 30° to about 150° or 45° to 135° and most preferably it is substantially perpendicular or about 90°. The port(s) 20 are in fluid communication with the source 26 of unfiltered fluid by a port conduit 27 which branches off of the conduit 28. This port conduit 27 is generally closed by a port valve (not shown) and only opened for a lateral flushing step explained below at FIG. 6.

(16) FIG. 3 shows such a housing 2 and the system into which it is incorporated. A pump 22 is connected at its inlet 24 to a source of liquid 26 to be filtered. A conduit 28 connects the outlet 30 of the pump 22 to the inlet 8 of the housing 2. Liquid enters the bowl 6 and is drawn through the filter 18 and through the outlet 10. Drain 12 is connected to a waste line 32 and closed off from the waste line by a valve (not shown).

(17) Optionally a first sensor 36 is located at the inlet 8 and a second sensor 38 is located at the outlet 10. The two sensors 36, 38 in combination can measure the transmembrane pressure in the one or more filter cartridges 18 or the flow rate of the system as will be described below. The sensors may be pressure sensors when determining transmembrane pressure differential or flow meters when determining flow rates. Any pressure sensor may be used, be it dial or analog or digital read out. The pressure sensor may be “dumb” requiring the operator to monitor the gauge or read out to determine it a desired parameter has been met as will be explained below) or it may be intelligent and provide a signal to the system when the parameter is reached. Likewise any flow sensor may be used, such as a paddle wheel flow sensor that determines flow by counting the revolutions of the wheel or propeller in the sensor. It may be a dial or analog or digital read out. The sensor may be “dumb” requiring the operator to monitor the gauge or read out to determine if the desired parameter (flow rate) has been met (as will be explained below) or it may be intelligent and provide a signal to the system when the parameter is reached.

(18) Filtrate (liquid that has passed through the filter layer(s) of the cartridge(s) 18) exits the housing 2 through outlet 10 to conduit 40 and through valve 44 to a next step or storage tank 42. Also shown is valve 46 in conduit 48 that selectively allows filtrate to flow to backflushing tank 50 for storage and use as described below. Valve 46 is normally closed off allowing filtrate to flow through valve 44.

(19) In operation, liquid, to be clarified or filtered is supplied from the source 26 such as a vat, tank or bin to the pump inlet 24. The pump 22 moves the liquid through conduit 28 to the inlet 8 of the housing 2. The liquid enters the bowl 6 outside of the filter cartridge(s) 18 and passes through the filter layer(s) of the cartridge(s) 18 to the outlet 10 of the housing 2. Then through conduit 40 and valve 44 to a downstream component such as a next step or storage tank 42.

(20) Impurities either are kept in the bowl 6 or become trapped in the filter layer(s) of the cartridges) 18. After a while the filtration rate will decline and/or the transmembrane pressure differential will increase above the accepted parameter and the filter cartridge(s) 18 will need to be backflushed. When this backflushing is to occur can be determined by a variety of parameters, including but limited to time, transmembrane pressure and flow rates.

(21) As to the use of a time parameter, one can simply apply a timer to the controls for the pump 22 and/or valves into and out of the housing 2 if any. At a predetermined schedule, the pump 22 is shut off and filtrate is pulled from tank 50 through pump 52 and conduit 54 and valve 56 which is opened and back through the filter(s) 18 to dislodge any impurities that are adjacent or embedded in the filter(s) 18. The impurities then settle out toward the lowermost portion 14 of the bowl 6. Valve 58 is also closed at this time. The backflushed liquid is then preferably sent to drain so that all clogging material is removed from the system. This step and its flow path are shown in FIG. 4.

(22) The period of backflushing does not need to be long. It merely needs to provide a pulse of backflow and pressure sufficient to clean the filter cartridge(s) 18 to a degree sufficient to allow further filtration to proceed. In a preferred embodiment, the period of time for backflushing is from about 2 to 20 seconds, more preferably from about 5 to 10 seconds.

(23) The pressure of the backflushing can be about the same as the filtration pressure differential (generally around 1 bar over the actual downstream pressure). If desired additional pressure may be applied to the backflushing operation.

(24) Then the pump 22 is turned back on and the remaining fluid from the backflushing step above in FIG. 4 is moved through conduit 28 into the housing 2 and out through conduit 40 as in the filtration step of FIG. 3. Valves 44 and 46 are closed and valve 60 is opened to allow the liquid to recirculate back to the inlet 24 of the pump 22. Optionally and preferably, new unfiltered liquid is also drawn into the system at the same time from source 26. This recirculation need only occur for a short period of time so that the liquid is reequilibrated and/or any filtration cake that is needed for filtration to occur is formed. Valve 60 is then closed and valve 44 is reopened and filtration resumes. Additionally, at some point during the filtration process, valve 46 is opened and valve 44 is closed to allow tank 50 to refill for the next flushing cycle.

(25) The period of recirculation does not need to be long. It merely needs to provide a filtration cake if needed for filtration and/or equalize all the liquid within the system before filtration can begin again. In a preferred embodiment, the period of time for backflushing is from about 20 seconds to 60 seconds, more preferably from about 20 to 40 seconds and most preferably about 30 seconds.

(26) The pressure of the recirculation should be about the same as the filtration pressure differential (generally around 1 bar over the actual downstream pressure). If desired additional pressure may be applied if desired for example to generate a filtration cake).

(27) Preferably, in one embodiment of the present invention where time is used as the parameter, one sets a schedule based upon the load of impurities in the stream, the titter cartridge(s) 18 selected and the volume of material to be filtered. Typically, it has been found that a schedule set between every 10 to every 20 minutes is useful for most applications. For most the preferred time parameter is every 10 minutes. The same process of valve openings/closing and pump movements are used as described above to create the backflushing and recirculation steps.

(28) The period of backflushing and the pressure used is the same as described above.

(29) As to the use of a transmembrane pressure parameter, one can simply select a transmembrane pressure upper limit that corresponds to a certain level of clogging of the filters. One can use pressure sensors as sensors 36 and 38 to measure the upstream and downstream pressures of the filter layer(s) and determine when the transmembrane pressure the difference between the upstream or inlet pressure and the downstream or the outlet pressure) is too great. When that parameter value is met or exceeded the same backflushing and recirculation steps occur.

(30) Preferably, in one embodiment of the present invention where transmembrane pressure is used as the parameter, one sets a limit of from about 0.2 bar (20 KPa) to about 5.0 bar (500 KPa) depending upon the impurities in the stream, the filter(s) 18 selected and the volume of material to be filtered. Typically it is between about 0.2 bar (20 KPa) and 1 bar (100 KPa) difference (but again, the pressure differential chosen is dependant of the quality of impurities, and therefore of the fluid to be filtered). For most applications, the preferred transmembrane pressure differential parameter is 0.2) bar (20 KPa).

(31) As to the use of the flow rate parameter, one can simply select a sensor to measure flow rate such as flowmeter preferably on the downstream or outlet side of the system. A reduced flow rate that equates to a certain level of clogging of the filter(s) is determined and when that reduced flow rate is reached the backflushing operation described above in relation to the transmembrane pressure differential or time system above is utilized.

(32) Preferably, in one embodiment of the present invention where flow rate is used as the parameter, one sets a limit of from about 50% to about 80% of the initial flow rate depending upon the impurities in the stream, the filter cartridge(s) 18 selected and the volume of material, to be filtered. Typically it has been found that a reduction in flow rate of between 20 and 40% from the initial flow rate is useful for most applications.

(33) At some point in the process or as an alternative to the backflushing step (although the backflushing step of FIG. 4 is preferred and this optional step is an additive step that may be used as desired either before or after the backflushing step), one may use a lateral flushing step by introducing liquid through port(s) 20 in the side of the housing 2 rather than through the inlet 8. Impurities are pushed of off and out of the filter cartridge(s) 18 and then are discarded through the drain 12 in a manner described above. This optional step is shown in FIG. 6. Fluid from source 26 flows into conduit 27 through one or more ports 20 and against the outer surface of the cartridges 18. From there, the fluid and any impurities removed from the cartridges are flowed out of the system to the drain 12.

(34) The period of lateral flushing does not need to be long. It merely needs to provide a pulse of liquid at a pressure sufficient to clean the filter cartridge(s) 18 to a degree sufficient to allow further filtration to proceed. In a preferred embodiment, the period of time for lateral flushing is from about 2 to 20 seconds, more preferably from about 5 to 10 seconds.

(35) FIG. 7 shows a step for cleaning, the system after use or flushing the system before use to remove any potential contaminants that may have entered the system during assembly. Water be it cold 70 or hot 72 or optionally steam instead of one or the other waters 70,72 is supplied by conduit 74 through tank 50 pump 52 and conduit 54 to conduit 40 and outlet 10 of the housing 2. Various valves such as 76 are closed to cause the water or steam to flow through the housing 2 and it can be returned to the tank 50 via conduit 80 for recirculation. After the desired time, the water or and/or steam is but off and valve 78 is shut to close off the water return conduit 80 and the water/steam is drained through conduit 82 to a water/steam drain. Optionally, the conduits used in this step may also be subjected to pressurized air to cause the water/steam to drain out more efficiently as is well known in the art.

(36) FIG. 8 shows a system having more than one or two or more housings 2A and B. The operation of the system is similar to that explained in FIGS. 3-7 and would be obvious to one of ordinary skill in the art the only addition being a dedicated water/steam tank 100. This allows one to use one housing 2A while the other is being regenerated through the process described in FIGS. 4 and 5 and optionally 6 and/or 7. Alternatively, the two or more housing can be run in parallel at the same time if desired.

(37) Preferably the temperature of the process in any embodiment is kept at a range between about −6° C. and about 20° C. (minus temperatures may be used for liquids that contain alcohol or salts that depress their freezing point or are formed of materials that have freezing points below 0° C.). For many applications, such as wine filtration, fruit juice filtration, biological filtration, the process takes place in chilled rooms and in chilled systems with temperatures ranging between about 4° C. and about 10° C. In the case of filtration of wine for removing bitartrate crystals (cold stabilization of wines), the temperature of filtration is as a rule of thumb minus half of the alcohol content (otherwise the crystals would redissolve). This means for alcohol of 11% one would conduct the filtration at temperatures of about −4° C. or −5° C.

(38) The liquid can be prechilled before entering the system. The system may be insulated if desired but generally it is not needed as the time spent in the system is relatively low. Alternatively, the system may be run in a cooled or “cold” room to minimize any shift in temperature within the liquid while being processed. In some extraordinary situations, the system can be affirmatively cooled by cold water circulation systems or chilling blankets as are well known in the art.

(39) The filter is a normal flow polymeric filter such as a Polygard® CE filter available from Millipore Corporation of Billerica, Mass. which contain a glass fiber/diatomaceous earth/polypropolene fiber blend of materials. However any normal flow filter that can withstand backflushing pressures on repeated cycles can be used in the present invention.

(40) The system can be used in a process that may be manually operated (by a system operator manually operating the valves, pumps, etc) or automatically (through a series of PIDs, a CPU, computer, computer network or other system that controls hardware and/or software).

EXAMPLE

(41) A system according to that of FIG. 8 which had a twin two 3 round 30″ Polygard® CE filter cartridges (2-micron pore size) available from Millipore Corporation of Billerica, cartridges in parallel was used and incorporated a housing according to that of FIG. 1 such that the outlets of the cartridges were attached to the outlet of each housing via the housing round plate as is well known in the art so that liquid leaving the housing outlets first passed through the filter cartridges.

(42) 500 liters of unfiltered white wine with an alcohol content 12 from a stainless steel tank was supplied to the inlet of the pump at a temperature of −2° C. at an upstream pressure of 0.2 bar (20 KPa) as read by the upstream pressure monitor on the inlet to the housing. Filtrate passed through the outlet of the housing at a pressure of 0.2 bar (20 kPa).

(43) Time was the parameter measured and this was done by a stop watch.

(44) After 10 minutes, the pump was shut of manually and the backwashing step as taught in FIG. 4 was run for 6 seconds at a pressure of 0.17 bar (70 KPa) as read on the pressure sensor of the outlet.

(45) The recirculation step as described in relation to FIG. 5 was run at 0.7 bar (70 KPa) measured at the upstream sensor on the inlet to the housing for 28 seconds to reequilibrate the systems and create the desired filter cake on the filter surface.

(46) The above steps were run in sequence 6 times.

(47) After 5 filtration and backflushing steps were completed a lateral washing step through the side port(s) of the housing was conducted for 6 seconds at a pressure of about 0.7 bar (70 KPa), followed by the recirculation step.

(48) A control system formed of a standard TFF hollow fiber system (Ronfil hollow fiber system, sold by Domnick Hunter Ibética) was run using the same wine and both systems had flow rates, turbidity of wine and clogging index (filterability index) measured.

(49) The Clogging Index is a filterability index is widely used in European wineries to gauge the filterability of a wine. Clogging index is the difference in time between how long it takes to filter from 200 ml and 400 ml as compared to the time it takes to filter the first 200 ml on a continuous experiment at a given pressure and membrane.

(50) The method for calculating it is the following:

(51) T0=initial time of 0 seconds.

(52) T2=time in seconds to filter the first 200 ml (from 0 ml to 200 ml) of wine through a 0.65 membrane at 2 Bar inlet pressure.

(53) T4=time to filter the second 200 ml (from 200 ml to 400 ml) of wine through the same filter and at the same pressure.
CI=(T4−T2)−(T2−T0)=T4−2*(T2)

(54) Units are reported in seconds, but it is normally treated as a index with no units assigned.

(55) The wine filtered according to the control and the present invention had the following characteristics as set forth in Table 1:

(56) TABLE-US-00001 Contro Flow Control Invention Invention Inveution Rate Control Clogging Flow Turbidiy Clogging Time (min) (1/h) Turbidity (NTU) Index Rate (1/h) (NTU) Index 10 120 <1 10 600 <1 11 20 900 <1 12 600 <1 14 30 650 <1 8 600 <1 12 40 450 <1 11 600 <1 14 50 150 <1 10 600 <1 13

(57) The holdup and lost volume for backflushing and lateral back-flushing for the present invention was 5 liters or 1% of the starting volume and the filtration occurred in 50 minutes.

(58) The holdup and lost volume for the control was 35 liters or 7% of the starting volume and the filtration required 66 minutes to complete.

(59) As can be seen for the example the present invention significantly reduced the volume lost to hold up volume of the system and completed the filtration quicker and maintained a high, consistent how rate through out the entire test.

(60) While the above example was with wine, this system can be used equally well with other liquids which need clarification such as beer, water, fruit juices, energy drinks that contain impurities such as fruit pulp or skin, solid impurities, clarification aids such as egg albumin or diatomaceous earth and the like. Likewise it is suitable for use with biological streams such as the output from a bioreactor which contains a protein of desire, such as a monoclonal antibody, along with other impurities including but not limited to clarification aids such as diatomaceous earth or flocculants, cell debris, host proteins and other undesirable cell elements and the like.