WO2016067177A1

WO2016067177A1 - Improved filtration plant and relative method

Info

Publication number: WO2016067177A1
Application number: PCT/IB2015/058234
Authority: WO
Inventors: Osman Omer SAGMANLI
Original assignee: TMCI PADOVAN SpA
Current assignee: TMCI PADOVAN SpA
Priority date: 2014-10-27
Filing date: 2015-10-26
Publication date: 2016-05-06
Anticipated expiration: 2017-04-27

Abstract

An improved plant, in particular for the filtration of organic liquids in the food sector, comprising: - a feed tank (3), - a filtration bell (5) provided with filtering means (6) rotating inside it, said bell (5) communicating with said feed tank (3), on one side via a feed pipe (1) for the product to be filtered, and on the other side via a return pipe (15) for the retentate, said filtering means (6) communicating with an outlet pipe (11) for the permeate, a first valve (14) positioned along said outlet pipe (11), a second valve (16) positioned along said return pipe (1 5), the opening of said second valve ( 16) being able to be modulated to create a pressure difference (Dp) between said return pipe (15) and said outlet pipe (11), a command and control unit (19) connected in signal communication to said first valve (14) and to said second valve (16), characterised in that, at preset time intervals (TPR), the filtration process is interrupted for a predetermined time (TR), said command and control unit (19) being configured to cause closure of said first valve (14) and com plete opening of said second valve (16) to start a recycling cycle between said feed tank (3) and said filtration bell (5) along said feed pipe (1) and said return pipe (15) such as to make the degree of concentration between said filtration bell (5) and said feed tank (3) substantially uniform.

Description

IMPROVED FILTRATION PLANT AND RELATIVE METHOD

The present invention relates to an improvement in a filtration plant and m ethod , particularly intended for use in the food sector for fi ltering organic liquids, for example in the wine industry for wine filtration.

Plants for organic liquid filtration are known comprising a filtration bell containing a filtering device in its interior and connected on one side to a feed tank containing the product to be filtered, and on the other side to a tank for collecting the filtered liquid; generally the filtration bell is provided with two outlets: a first outlet for the filtered liquid or "permeate", which is fed to the collection tank, and a second outlet for the product not completely filtered, and hence sti l l conta in ing suspended solid fraction, technically known as "concentrate" or "retentate"; the second outlet is connected to the feed tank via a return circuit through which the retentate is transferred, to be again introduced into the feed circuit and be filtered.

Known filtering devices include systems com prising a plural ity of membranes in the form of discs of microporous material stacked in series and rigid with a shaft rotating relative to the filtration bell; the purpose of rotating the shaft rigid with the membranes is to facilitate product filtration through the membranes such as to make the filtration process more effective, and also to reduce adhesion of the filtration residues to the membrane surfaces.

An example of a plant of this type is provided by European Patent EP 2326409 in the name of the present applicant, on which the introduction of the accompanying claim 1 is based.

Although it is particularly effective in filtration, in the plant known from EP 2326409 for certain types of product to be treated, a discrepancy can arise between the retentate quantity measured in the filtration bell and the retentate quantity in the feed tank upstream of the bell. In this respect, in the filtration bell an accumulation of solid fraction may arise which is greater than the solid fraction of the product contained in the feed tank. This drawback can cause a reduction in the fi ltered product quantity in that the rotating mem brane efficiency is reduced, besides a greater energy consumption required by the m otor to rotate the membranes; if the accumulation is excessive, the membrane rotation can slow down until the membranes are completely blocked, with consequent damage to the plant.

Consequently, to prevent their clogging, the membranes are periodically washed in counter-current. In particular, to achieve this, the normal filtration cycle is interrupted at determ ined time intervals defined on the basis of suitably measured pressure or flow rate values, to implement a reve rse f i ltrati on stag e (o r backwas h i n g ) . I n parti cular, during the backwashing stage, a back-pressure is created such that the previously filtered liquid (or permeate) is returned to the cycle in the reverse direction to the l iqu id to be fi ltered ; hence in this m anner, the forced passage of the permeate through the mem branes causes removal of the sol id deposits accumulated on their surface.

WO 2013/031237 describes instead a method for preparing antibodies by ultrafiltration. In particular, this method com prises monitoring the feed pressure during filtration then, when this reaches or exceeds a certain value, a suitable recycling step is inserted to prevent the feed pressure reaching too high values during the subsequent filtration step. It should be noted that the feed pressure is a particularly critical parameter in the case of ultrafiltration, in that feed pressures which are too high can damage the integrity of the ultrafiltration membrane. Not only, but the ultrafiltration membrane is particularly thin and delicate, and is consequently fixed (i.e. it is not subjected to movement or rotation).

The main aim of the present invention is to provide an improved filtration plant and a relative method, in particular for the filtration of organic liquids in the food sector, for example wine, able to overcome the drawbacks deriving from the aforesaid state of the art.

Within the aforesaid aim, one object of the present invention is to provide a plant and method by which the retentate quantity associated with the feed tank and filtration bell is made substantially uniform and homogeneous during the filtration process.

Another object is to provide a plant and method by which the degree of efficiency of the filtering membranes remains substantially constant during the filtration process, to maintain the filtered product quantity constant.

A further object is to provide a plant and method by which the process reliability is increased and the energy consumption is maintained within economically convenient limits.

A further object is to provide a plant and method by which backwashing is replaced by an alternative solution to maintain the membrane efficiency substantially constant.

A further object is to provide a constructionally more simple plant, in terms of the required number of components and in the configuration of the control unit, and a relative method. A further object is to provide a plant, and a relative filtration method, by which the aforesaid aim and objects are attained at competitive costs and are attainable by usual known machines and equipment.

The aforesaid aim and objects, and others which will be apparent hereinafter, are attained by an improved filtration plant as defined in claim 1, and by an improved filtration method as defined in claim 7.

Further characteristics and advantages of an improved filtration plant and relative method according to the present invention will become more apparent from the ensuing description of a particular but non-exclusive embodiment thereof, illustrated by way of non-limiting example with reference to the accompanying figures, in which:

Figure 1 shows schematically a plant according to the present invention during the normal filtration step;

Figure 2 shows schematically the plant during the recycle step for achieving a uniform degree of concentration;

Figure 3 shows schematically a second method for achieving a uniform degree of concentration;

Figure 4 shows schematically a third method for achieving a uniform degree of concentration.

The filtration plant according to the present invention, particularly intended for use in the food sector for filtering organic liquids, such as in the wine industry for wine filtration, is illustrated schematically in the accompanying figures, and comprises:

- a feed pipe 1 through which the product to be filtered is withdrawn from a tank and fed to a filter unit; - a pump 2 advantageously controlled by an inverter 20 positioned in the feed pipe 1 ;

- a feed tank 3;

- a filter unit 4, comprising a filtration bell 5 containing in its interior one or more filtering means 6; each of the filtering means 6 preferably consists of a series of fi ltering mem branes 7 , in the form of discs of m icroporous material which rotate relative to the filtration bell 5; in particular, the filtering mem branes 7 are stacked in series and are rigid with a shaft 8 rotating relative to the filtration bell 5; the shaft 8 is provided internally with a cavity 9 communicating at one end 10 with an outlet pipe 1 1 for the filtered liquid and closed at the opposite end; the cavity 9 also communicates with the filtering membranes 7 via one or more channels within the membranes 7 and disposed substantially in an axial direction to enable the filtered liquid to flow out from the filtration bell 5; the shaft 8 is rotatably supported by the filtration bell 5, the rotational movement being impressed on the shaft 8 by an actuator 12, for example an electric motor; the filter unit 4 can be provided with one or more shafts 8 disposed in parallel and supporting respective series of membranes 7, as shown for example in Figure 1 .

- a collection tank 13 for the filtered liquid, technically known as the "permeate", connected to the filter unit 4 via the outlet pipe 1 1 ;

- a first valve 14 positioned along the outlet pipe1 1 for the permeate flowing towards the collection tank 13;

- a return pipe 15 for the incompletely filtered product, technically known as the "retentate"; - a second valve 16 disposed in the retentate return pipe 1 5, the opening of wh ich can be m odu lated to create a substantial ly constant pressure difference Dp between the return pipe 1 5 and the outlet pipe 1 1 to enable the filtration flow to be regulated;

- first means 1 7 for measuring the permeate flow rate, such as a flowmeter, positioned in the outlet pipe 1 1 preferably downsteam of the first valve 14;

- second means 1 8 for measuring the retentate flow rate, such as a further flow meter, positioned in the return pipe 15 upstream or downstream of the second valve 16;

- a command and control unit 19 (PLC) to which the following are connected in signal communication: the first valve 1 4, the second valve 16, the first flow rate measurem ent means 1 7, the second flow rate measurement means 18, and the inverter 20.

The plant operates in the following manner: after a first preliminary step in which the filtration bell 5 is filled with the membranes 7 at rest, in which the product is made to recirculate by the pump 2 between the feed tank 3 and the filtration bell 5 along the feed pipe 1 and the return pipe 15, a second preliminary step takes place in which the rotation of the membranes 7 is started by activating the actuator 12 and the second valve 16 is throttled to create a pressure difference Dp in the filtration bell 5, while the first valve 14 is put into the open position.

After completion of the preliminary filling and start-up steps, the plant is brought to steady working conditions and the filtration cycle begins (Figure 1 ), during which the liquid to be filtered is withdrawn from the feed tank 3 by the pump 2 and fed to the filtration bell 5 through the feed pipe 1 ; the pressure difference across the filtration bell 5 created by the second valve 16 facilitates passage of the product through the fi ltering m em branes 7 , wh ich thus permeates through the discs of microporous material. The rotation of the membranes 7 is aimed at facilitating product filtration through the membranes, such as to make the filtration process more effective, and to reduce adhesion of the filtration residues to the surfaces of the membranes, hence reducing thei r clogg ing , by the self-cleaning effect achieved on the disc filtering surfaces determined by the tangential velocity created by the rotation.

The product filtered through the membranes 7, or permeate, enters the cavity 9 of the shaft 8 through the rad ial channels present with in each membrane 7 and flows along the cavity 9 as far as the outlet of the filtration bell 5 through the open end 1 0 of the shaft 8 which communicates, possibly via a conveyor 21 if several shafts 8 are d isposed in paral lel , with the permeate outlet pipe 1 1 , where it is fed to the collection tank 13.

The incompletely filtered product, or "retentate", which was unable to pass through the filtering membranes 7, leaves the filtration bell 5 through the return pipe 1 5 and returns to the feed tank 3 and mixes with the product to be filtered, to be again fed into the cycle.

At time intervals TPR (Recycle Delay Time) set by the operator in the command and control unit 19, a recycle step of duration TR (Recycle Time) is carried out, also predetermined by the operator and set in the command and control unit 1 9. During the recycle step (Figure 2) the filtration process is interrupted for a time of TR, the closure of the first valve 14 and the complete opening of the second valve 16 being imposed automatically by the command and control unit 1 9. Consequently, the flow of the permeate into the outlet pipe 11 is interrupted, while the flow of the product to be filtered and of the retentate continue, along the feed pipe 1 and return pipe 15 respectively, between the feed tank 3 and the filtration bell 5. During this step the membranes 7 continue to rotate in order both to mix the product and in order not to interrupt the self-cleaning effect on the rotating discs. In this manner, the retentate quantity or "concentration" between the filtration bell 5 and the tank 3 is restored and made uniform by the exchange of product to be filtered originating from the feed tank 3 and the retentate expelled from the filtration bell 5.

In other words, homogeneity is restored between the concentration of suspended solids accumulated in the bell 5 during filtration, and the concentration, which is lower by being diluted by the liquid portion of the product to be filtered, present in the feed tank 3.

At the end of the time TR the command and control unit 19 automatically causes the first valve 14 to reopen and the second valve 16 to undergo modulated closure, to restore the pressure difference Dp in order to resume the normal filtration cycle.

In addition to the aforedescribed timed recycle procedure, the plant can include a further manner of restoring uniformity of concentration between the filtration bell 5 and the feed tank 3, particularly suitable for products very easy to filter and hence with very quick solids accumulation in the filtration bell 5.

In this second manner, the operator sets a maximum flow rate value Qpmax in the command and control unit 19, referred to the flow rate of permeate flowing along the outlet pipe 11. With reference to Figure 3, whenever the first flow rate measurement means 1 7 measure, in the outlet pipe 1 1 , a permeate flow rate value Qp exceeding the preset value Qpmax, the command and control unit 1 9 feeds a command to the second valve 16, which has been throttled to create the pressure difference Dp, causing it to reduce the throttling extent, i. e. to increase the partial opening, such as to reduce the pressure difference to a value Dpi less than Dp, consequently increasing the retentate flow rate Qc along the return pipe 1 5. At the same time, the permeate flow rate Qp reduces progressively; when the first flow rate measurement means 17 measure a Qp value less than Qpmax, the command and control unit 1 9 causes throttling of the second value 16 to restore the difference Dp.

The aforedescribed method can be summarized as follows:

Qp > Qpmax - Dpi < Dp and increase of Qc

The i ncrease i n th e rete ntate fl ow rate Q c determ i n ed by the aforedescribed method reduces the concentration discrepancies between the filtration bell 5 and the feed tank 3, in particular during the initial hours of the filtration process, favouring concentration uniformity in the plant.

A further aspect of the present invention consists of controlling the retentate flow rate in the return pipe 1 5 to preserve efficiency of the pump 2 and reduce its wear, in addition to favouring retentate uniformity between the feed tank 3 and the filtration bell 5.

With reference to Figure 4, in this third manner, the operator sets a minimum flow rate value Qcm in in the command and control unit 19, referred to the flow rate of retentate flowing along the return pipe 15. Whenever the second flow rate measurement means 1 8 measure in the return pipe 1 5 a retentate flow rate value Qc less than the preset value Qcm in, the com mand and control un it 1 9 causes, via the inverter 20, the velocity of the pump 2 to be increased until the normal flow rate value Qc > Qcmin is restored.

If the flow rate Qc is not restored within a predeterm ined time, the command and control unit 19 senses this irregularity and blocks the filtration process to prevent plant damage, in particular to the pum p 2 in which, for example, cavitation phenomena could arise.

From the aforegoing it is apparent that the present invention attains the in itial ly stated objects and advantages: in this respect, an im proved filtration plant and relative method have been devised, in particularly for filtering organic liquids in the food sector, such as wine, which are able to overcome the drawbacks deriving from the aforesaid state of the art.

I n th is respect, the aforedescribed plant and m ethod enab le the degree of concentration between the feed pipe and the filtration bell to be made uniform and substantially homogeneous by a timed cycle of retentate recycling between the tank and bell at time intervals TPR during the filtration process, possibly aided by control l ing the m axim um permeate flow rate through the outlet pipe and reduction in the pressure difference Dp, a method particularly suitable for easily filtered products, i.e. products for which filtration takes place relatively quickly.

One advantage deriving from the recycling cycle is that the efficiency of the fi lteri ng m em branes du ri ng the fi ltration process is m a intai ned substantially constant to ensure constant filtered product quantity, by the periodical removal of the accum ulation of solid product fraction within the filtration bell.

A further advantage of the plant and method according to the present invention is to increase process reliability and maintain energy consumption within econom ically convenient lim its, by virtue of the greater membrane efficiency during the entire filtration process.

A further advantage of the filtration plant and method according to the present invention is the ability to preserve pump efficiency and considerably reduce its wear, by controlling the minimum retentate flow rate along the return pipe.

The present invention relates in particular to the filtration of organic liquids, for exam ple wine or m ilk, thus preferably using membranes with a pore diameter from 0.1 to 10 pm.

The solution of WO 201 3/031237 consists of alternating the filtration with a recycling step to prevent the feed pressure reaching too high values which could damage the integrity of the ultrafiltration membrane; in contrast, in the present invention the recycling step is provided to make the solid particle concentration uniform between the feed pipe and the filtration bell. In this respect, in WO 2013/031237, interrupting the filtration process in order to start the recycling step is based on measuring the feed pressure, whereas in the present invention it takes p lace at predefi ned tim e intervals TP R; moreover, in the present invention the purpose of measuring the pressure, when required, is merely to identify an irregular situation such as to provide an alarm signa l to interru pt fi ltration, and is therefore not used for any adjustment/control purpose. Moreover, the present invention differs from EP 2326409 in that, in order to maintain constant efficiency of the filtering membranes, in does not use backwash i ng as the fi ltered l i q u i d (permeate) is not returned to recirculation in counter-current; instead during the recycling step, the valve positioned along the permeate outlet pipe is closed.

In addition, in contrast to EP 2326409, in the present invention the filtration process is automatically interrupted at preset intervals TPR; in other words, in the present i nvention , neither the acqu is ition nor continuous monitoring of the pressure and flow rate signals is envisaged, neither is their processing for determining when to interrupt the filtration step.

From the aforegoing it is apparent that the plant and the method according to the invention are much more advantageous than the traditional art as they can be implemented more simply and economically than traditional plants and methods, and moreover their operation is more simple, reliable and economical.

Claims

C L A I M S

1 . An improved plant, in particular for the filtration of organic liquids in the food sector, comprising:

- a feed tank (3),

- a filtration bell (5) provided with filtering means (6) rotating inside it, said bell (5) communicating with said feed tank (3), on one side via a feed pipe

(I ) for the product to be filtered, and on the other side via a return pipe (15) for the retentate, said filtering means (6) communicating with an outlet pipe

(I I ) for the permeate,

- a first valve (14) positioned along said outlet pipe (1 1 ),

- a second valve (16) positioned along said return pipe (1 5), the opening of said second valve ( 16) being able to be modulated to create a pressure difference (Dp) between said return pipe (15) and said outlet pipe (1 1 ),

- a command and control unit (19) connected in signal communication to said first valve (14) and to said second valve (16),

characterised in that, at preset time intervals (TPR), the filtration process is interrupted for a predetermined time (TR), said command and control unit (19) being configured to cause closure of said first valve ( 1 4) and com plete opening of said second valve (16) to start a recycling cycle between said feed tank (3) and said filtration bell (5) along said feed pipe (1 ) and said return pipe (15) such as to make the degree of concentration between said filtration bell (5) and said feed tank (3) substantially uniform.

2. A plant as claimed in claim 1 , characterised in that the rotating filtering means (6) comprise a series of filtering membranes (7) stacked in series and rigid with at least one rotating shaft (8) supported by the filtration bell (5).

3. A plant as claimed in one or more of the preceding claims, characterised in that said at least one rotating shaft (8) is internally provided with a cavity (9) in communication, at one end (10), with said outlet pipe (11) for the filtered liquid and closed at the opposite end, said cavity (9) of said shaft (8) being also in communication with the filtering membranes (7).

4. A plant as claimed in one or more of the preceding claims, characterised in that said rotating filtering means (6) comprise a series of filtering membranes (7) in the form of discs of microporous material.

5. A plant as claimed in one or more of the preceding claims, characterised in that said filtering membranes (7) comprise at least one internal channel (7) disposed substantially in a radial direction to enable the filtered liquid to flow out of the filtration bell (5).

6. A plant as claimed in one or more of the preceding claims, characterised in that, during the filtration process, said filtering means (6) are rotated in order both to facilitate product filtration and to reduce the adhesion of the filtration residues to the surfaces of said means.

7. A plant as claimed in one or more of the preceding claims, characterised in that said filtering means (6) continue to rotate during the recycling cycle.

8. A plant as claimed in one or more of the preceding claims, characterised in that the time intervals (TPR) for interrupting the filtration process and/or the time (TR) of interruption of said filtration process, and hence the duration of said recycling cycle, are predetermined by the operator and are set in the command and control unit (19) by the operator.

9. A plant as claimed in one or more of the preceding claims, characterised in that on termination of said predefined time (TR), said command and control unit (19) causes complete opening of said first valve (14) and the throttling of said second valve (16) such as to restore said pressure difference (Dp) in order to restart the filtration process.

10. A plant as claimed in one or more of the preceding claims, characterised by also comprising permeate flow rate measurement means (17) positioned in said outlet pipe (11) and connected in signal communication to said command and control unit (19).

11. A plant as claimed in one or more of the preceding claims, characterised in that said command and control unit (19) is configured to compare the permeate flow rate value (Qp) measured by said permeate flow rate measurement means (17) positioned in said outlet pipe (11), with a preset maximum flow rate value (Qpmax).

12. A plant as claimed in one or more of the preceding claims, characterised in that said command and control unit (19) is configured to increase the partial opening of said second valve (16) in order to reduce said pressure difference (Dp) by increasing the retentate flow rate along said return pipe (15) and progressively reduce the permeate flow rate along said outlet pipe (11), when the value of the permeate flow rate (Qp) measured by said means (17) exceeds the preset maximum value (Qpmax).

13. A plant as claimed in one or more of the preceding claims, characterised by also comprising: - a pump (2) controlled by an inverter (20) and positioned in said feed pipe (1 ), said inverter (20) being in signal comm unication with said command and control unit (19),

- retentate flow rate measurement means (18) positioned in said return pipe (15) and in signal communication with said command and control unit (19), said command and control unit (1 9) being arranged to compare the value of the retentate flow rate Qc m easured by said m eans ( 1 8) with a preset minimum flow rate value (Qcmin).

14. A plant as claimed in one or more of the preceding claims, characterised in that said command and control unit (19) increases, via said inverter (20), the velocity of said pump (2) when the value of the retentate flow rate (Qc) measured by said means (18) is less than the preset minimum value (Qcmin).

15. An improved method for the filtration of organic liquids in the food sector, comprising a filtration process with a pressure difference (Dp) and at least one recycling cycle, characterised by comprising the steps of:

- setting a filtration time interval (TPR) and a recycle time interval (TR) in a command and control unit (1 9) of a filtration plant claimed in one or more of the preceding claims;

- interrupting the filtration process on termination of the filtration time interval (TPR);

- at the beg i nn i ng of the recycle tim e interva l (TR) , wh ich essential ly coincides with the end of said time interval (TPR), closing said first valve (14) and completely opening said second valve (16) of said filtration plant to interrupt the permeate flow and enable the retentate, and the product to be filtered, to flow between said feed tank (3) and said filtration bell (5); - at the end of said recycle time interval (TR), opening said first valve (14) and throttling said second valve (16) to restore said pressure difference (Dp) and resume said filtration process for a subsequent filtration time interval (TPR).

16. A method as claimed in the preceding claim, characterised that the filtering means (6) are rotated both during said filtration time interval (TPR) and during said recycle time interval (TR).

17. A method as claimed in one or more of the preceding claims, characterised by also comprising the following steps:

- setting a maximum permeate flow rate Qpmax in said command and control unit (19);

- measuring the instantaneous permeate flow rate Qp in said outlet pipe (11);

- comparing said instantaneous flow rate Qp with said maximum value Qpmax;

- if Qp > Qpmax, increasing the partial opening of said second valve (16) to reduce said pressure difference Dp and progressively reduce said permeate flow rate Qp;

- when Qp < Qpmax, reducing the partial opening of said second valve (16) to restore said pressure difference (Dp).

18. A method as claimed in one or more of the preceding claims, characterised by also comprising the following steps:

- setting a minimum retentate flow rate value Qcmin in said command and control unit (19);

- measuring the instantaneous retentate flow rate Qc in said return pipe (15);

- comparing said instantaneous flow rate Qc with said minimum value Qcmin; - if Qc < Qcmin, increasing the velocity of the pump (2) as in claim 5 until > Qcmin.