Technical field

The present invention is in the field of vegetable oil recovery from natural sources. More particularly, it concerns a process for the recovery of crude vegetable oil from its natural sources, the use of a corrugated plate interceptor or a cross flow interceptor for vegetable oil recovery, a coiled pipe reactor for enzymatic vegetable oil recovery, and an apparatus which can suitably be used for this process.

With the term vegetable oils is meant oils that can be retrieved from fruits, nuts and plants. Examples of vegetable oils are palm oil, rapeseed oil, soybean oil, sunflower oil, palm kernel oil, peanut oil, olive oil, linseed oil, sesame oil, castor oil, coconut oil. In the description, the invention is explained using palm oil for illustration an example, but it must be kept in mind that other vegetable oils are included.

With natural sources is meant the fruits, nuts and plants from which the vegetable oils are extracted.

Background

The invention concerns a process for the separation of crude vegetable oil such as crude palm oil and crude from the press liquor .

The extraction of edible oil from oil palm fruits typically involves mechanical processing at temperatures ranging from 90 - 140°C. Generally, the FFB (fresh fruit bunches) undergo a sterilization process at 140°C for some 75 to 90 minutes in order to deactivate hydrolytic enzymes responsible for the breakdown of oil to free fatty acids. In addition, the

sterilization process loosens up the fruits on the bunch, facilitating stripping or threshing. Threshing takes place in a rotary drum. The drum rotates and so the bunches get lifted up and drop when they reach the top of the drum. This action causes the fruits to detach from the bunches. The separated fruits fall through slots in the rotary drum onto a conveyor.

The separated fruits are conveyed to a digester equipped with a rotating paddle impeller to mash the fruits at a temperature of 85 - 90° C. This results in the release of 20 to 30% of free oil from the fruit mesocarp. From the digester the mashed fruits are transferred to a screw press in which the crude palm oil is extracted under high pressure. The resulting extracted oil is mixed with fruit particles, water, sand and dirt. This mixture is called the press liquor. The press liquor is first passed through a vibrating screen for removing the coarse fibers and other dirt. From the collection tank below the screen the press liquor is then pumped to the settling tank for clarification

The settling tank is a heated vertical tank in which the crude oil is separated by gravity from the water, fruit fibers, sand and other dirt. The clarification process takes place at a temperature of 90°C and takes about 6-12 hours. The clarified CPO is skimmed off at the top of the tank, while the underflow, called sludge, is sent to a de-sanding cyclone and from there to a centrifuge to recover as much as possible CPO.

Before de-sanding the resulting mesocarp sludge contains about 40 % palm oil. The centrifuged mesocarp sludge still contains about 10% Palm oil.

Several attempts have been made to increase the crude palm oil yield.

In for instance WO 2017/183955 a method is described to remove more crude palm oil from the final sludge. It involves a Solid Removal Oil Recovery System (SRORS) for oil recovery and suspended solids removal from palm oil mill and related refinery raw sludge wherein said SRORS comprises at least a holding tank and into which said raw sludge is discharged and stored, a plurality of filtration assemblies or filtration modules that are connected in series, a slurry tank and a decanter system and with said components suitably connected. The palm oil mill and related refinery raw sludge in the holding tank is subsequently transferred to the plurality of filtration assemblies for treatment, specifically cross flow filtration and with filtrate and slurry being the main products of said treatment and with said slurry transferred to the slurry tank. The slurry from the slurry tank is fed to the decanter system for oil recovery and suspended solids removal.

WO 1989/9009255 concerns the extraction of oil and fats from natural product using a cell disruption device which contains enzyme, the process is further followed by first and second cross-flow filtration device for extraction at a temperature of 45 to 65 ° C.

In comparison with the conventional palm oil production process, the process according to the invention has an improved CPO (crude palm oil) yield. Further, the process requires less water and is less time consuming and owing to the controlled reaction conditions the formation of by-products such as free fatty acids is inhibited.

Summary

To this end the present invention is directed to a process for the recovery of vegetable oil from natural sources, wherein oil is separated from the natural source by comprising the following steps:

a pressing step to form press liquor and press cake, a clarifying step wherein the press liquor is fed in a corrugated plate interceptor and/or to an incubator.

Optimally, the press liquor is fed to the clarification step by means of rotary positive displacement pumps.

In an embodiment, the clarifying process comprises a primary clarifying step wherein the press liquor is fed in a corrugated plate interceptor and an incubating step. The primary

clarification step may be conducted prior to the incubating step or vice versa, the incubating step prior to the primary

incubation step.

In an embodiment, the clarifying step also comprises a secondary clarifying step, which is conducted subsequent to the incubating step or the primary clarification step. Said

secondary clarification step may be conducted in a corrugated plate interceptor.

Optionally the corrugated plate interceptor is provided with a hopper bottom. In an embodiment, the temperature in the

corrugated plate interceptor is kept between 80 and 120 °C, preferably between 85-95 °C. Preferably the corrugated plate interceptor is a cross flow interceptor. In one embodiment, the cross-flow interceptor has its plates arranged in an out-of- phase plate configuration.

In another embodiment, the clarification step comprises an incubating step wherein press liquor is intimately mixed with enzymes that are able to release oil entrapped in cell material present in the press liquor.

The enzymes may be added to the press liquor prior to

entering the incubator or during passing the incubator by means of enzyme dosage points provided in the incubator.

Usually the temperature in the incubator ranges from 20 to 70 °C, preferably 25-60 °C, more preferably 30-50 °C.

Preferably the incubator is a coiled pipe reactor. Also or alternatively, the incubator may comprise a spiral element with a spiral thread along which the material to be separated is passed, e.g. the spiral element being arranged in a conduit, which conduit may be a pipe segment of a coiled pipe reactor, and/or wherein the spiral element may have an outer diameter corresponding to an inner diameter of the conduit such that the spiral element spans a lumen of the conduit and any material flowing through the conduit has to pass along the spiral thread in a flow direction determined by the spiral thread.

In one embodiment the process for the recovery of vegetable oil from natural sources, wherein oil is separated from the natural source comprises the following steps:

a pressing step to form press liquor and press cake, a primary clarifying step wherein the press liquor is fed in a corrugated plate interceptor, and

an incubating step wherein press liquor coming from the corrugated plate reactor is intimately mixed with enzymes that can free oil from cell material present in the press liquor, and

- a secondary clarifying step wherein the press liquor coming from the incubating step is fed to a corrugated plate

interceptor .

The invention is further directed to the use of a corrugated plate interceptor for the recovery of vegetable oil from natural sources, the use of a cross flow interceptor and/or the use of a coiled pipe reactor and/or a spiral element containing reactor for the enzymatic recovery of vegetable oil from natural

sources. The invention is further directed to an apparatus that can suitably be used for the process according to the invention.

Detailed Description

The present invention is directed to a process for the recovery of vegetable oil from natural sources, wherein oil is separated from the natural source by comprising the following steps :

a pressing step to form press liquor and press cake, a clarifying step wherein the press liquor is fed in a corrugated plate interceptor and/or to an incubator.

Thus, in the process according to the invention the settling tank that is used in conventional processes is replaced with a specific type of plate separator and/or an incubator. With conventional settling tanks/decanters only relatively low portions, e.g. about 40 %, of the mass of the press liquor can be retrieved, e.g. as crude palm oil (or equivalent, dependent on the natural source used) , while with the use of a corrugated plate interceptor about 50 % of the mass of the press liquor may be retrieved as crude palm oil (or equivalent) . Furthermore, the press liquor as received from the press may be subjected to the clarifying step without any dilution with water. This is in contrast to a settling tank/decanter, wherein large amounts of water have to be added during the decanting process.

Throughout the description the term "press liquor" is referred to interchangeably with the terms "press liquor

sludge", "sludge" and "flowable pulp". It refers to the liquid mass resulting from pressing oil from a natural source, in the various stages of further separation from the solid mass also present in the oil after pressing.

Corrugated plate interceptor

Corrugated plate interceptors are known, but were never used for extraction of vegetable oils from the press liquor. In a corrugated plate interceptor corrugated plates are arranged in a plate pack wherein the plates may installed at an angle of between approximately 40 and 70 ° to the horizontal, preferably an angle of 45° or 60 ° is used. The separated oil droplets collect at or near the tops of the corrugations, while solids would deposit in the troughs. Separated solids slide down the plates and separated oil drops adhere to the invert side of the plates and gently move upwards due to their lesser density than water and/or other process fluid.

Preferably, a corrugated plate interceptor is used in which Cross Flow type corrugated plate packs are installed, so-called cross flow interceptors (CFI) . In the CFI, the flow enters the plate pack at the front and leaves at the back, the flow

direction being predominantly horizontal, perpendicular to the corrugations . Preferably, the plates are arranged in an out-of-phase plate profile configuration. This results in alternating flow

velocities between the plates, whereby the high velocities serve to 'squeeze' crude palm oil (CPO) out of pockets in the

mesocarp, while the zones with low velocities promote easy separation of CPO from the mesocarp. The preferred CFI clarifier has 180° out-of-phase plates, with a minimum plate spacing of 15-25 mm, e.g. 20 mm and a maximum plate spacing of 100-130 mm, e.g. 120-125 mm, likel22 mm. The plate inclination may be 45 to 60° .

Preferably the press liquor is fed to the corrugated plate interceptor by means of rotary positive displacement pumps of the progressive cavity type. With this type of pumps, the press liquor can be delivered to the clarifier as 'undisturbed' as possible .

Optionally the corrugated plate interceptor is provided with a hopper bottom. The corrugated plate interceptor may comprise at least two hoppers, preferably three, the first to collect the bulk of the heavier sludge with a high settling velocity. The next two hoppers collect sludge separated in corrugated plate packs installed above them. The function of these sludge hoppers may be up to four-fold:

- Collection of sludge;

- Storage of sludge;

- Prevention of sludge build-up in the plate packs;

- Facilitating on-line removal of collected sludge from the CFI clarifier sludge hoppers.

The hopper bottom combined with the on-line removal of sludge may cause that there is little to no down time of the clarifier for periodic clean out of sludge. On-line sludge discharge can also take place with a conventional settling tank, but then it will not be possible to remove all sludge effectively from the tank's flat bottom. Periodic clean out with associated down time will have to be performed. In the process according to the invention, the press liquor is led over the plate separator maintaining a temperature of between 80 and 120 °C.

The clarification step by means of a corrugated plate

interceptor may either be conducted directly on the press liquor as resulting from the press step, or the clarification step by means of a corrugated plate interceptor may be used subsequent to the enzymatic incubation step. If both clarification methods are used in combination, the temperatures of the feed may be adjusted to a desired temperature in one or each step prior to entering said step.

The invention is also directed to the use of a corrugated plate reactor or a cross flow interceptor for the recovery of vegetable oil from natural sources.

Incubator

In the process according to the invention the press liquor may also be fed to an incubator. In the incubator the press liquor is intimately mixed with enzymes that are able to release oil that is still entrapped in the cell material present in the press liquor. In conventional palm oil extraction the press liquor is first settled in a settling tank and subsequently centrifuged. However, centrifugation only removes free oil and not the oil that is entrapped in the cell material. Moreover, it has surprisingly been found that settled samples rendered a higher yield than centrifuged samples and, accordingly, use of a combination of enzymatically treated liquor with a CFI, which separates liquor in a settling-like manner, provides

unexpectedly high yield.

Suitable enzymes to free the oil are cellulases and cellulase blends. These types of enzymes are commercially available.

The enzymes may be added to the press liquor prior to entering the incubator and/or during passing the incubator by means of enzyme dosage points provided upstream of and/or in the incubator .

The temperature maintained in the incubator is adjusted to the optimum working temperature of the enzymes used. Typically, this temperature ranges from 20 to 70 °C, preferably 25-60 °C, more preferably 30-50 °C. The residence time typically ranges from 1 to 1.5 hours.

The incubator is preferably a coiled pipe reactor (CPR) . A coiled pipe reactor may be a static reactor without any moving parts. The tube of the reactor is preferably provided with internals such as baffles, helices or spirals. Flow conditions in a CPR closely resemble plug flow conditions whereby no short circuiting and back mixing occur, thus allowing for a narrow residence time. This gives the CPR incubator the advantage that an ideal incubation time found in a laboratory can be exactly replicated in an industrial scale coiled pipe reactor so there is no need for a longer residence time to overcome adverse mixing conditions, and dosing rates found to be most effective in a laboratory can be replicated in the coiled pipe reactor without the need for overdosing as compensation for an

unfavorable residence time pattern.

The enzymatic incubation step may either be conducted directly on the press liquor as resulting from the press step, or the incubation step may be used subsequent to the primary clarification step in the corrugated plate interceptor. If both clarification methods are used in combination, the temperatures of the feed may be adjusted to a desired temperature in one or more of the steps prior to entering said step. To this end (use of) heating and cooling systems may be incorporated into the process .

The invention is also directed to the use of a coiled pipe reactor for the enzymatic recovery of vegetable oil from natural sources Secondary clarification

Optionally the clarification step comprises a secondary clarification by means of a corrugated plate interceptor in addition to the one described above. This secondary

clarification may be conducted subsequent to the incubation step or subsequent to the primary clarification by means of a

corrugated plate interceptor. The properties and conditions used for the first clarification by means of a corrugated plate interceptor are also suitable for the secondary clarification. However, since the feed in the secondary clarification mainly comprises sludge only one hopper may suffice.

The invention is also directed to a process for the recovery of vegetable oil from natural sources, wherein oil is separated from the natural source by comprising the following steps:

a pressing step to form press liquor and press cake, a primary clarifying step wherein the press liquor is fed in a corrugated plate interceptor, and

an incubating step wherein press liquor coming from the corrugated plate reactor is intimately mixed with enzymes that can free oil from cell material present in the press liquor, and

- a secondary clarifying step wherein the press liquor coming from the incubating step is fed to a corrugated plate

interceptor .

The invention is further directed to an apparatus that can suitably be used for the process according to the invention.

Brief description of the drawings

The above-described aspects will hereafter be more explained with further details and benefits with reference to the drawings showing a number of embodiments by way of example. Elements and aspects discussed for or in relation with a particular

embodiment may be suitably combined with elements and aspects of other embodiments, unless explicitly stated otherwise. Fig. 1 is a flow diagram of a treatment plant for enzyme enhanced recovery of crude palm oil from palm fruits;

Fig. 2 indicates a plate separator for use in a clarifier according to the present concepts;

Figs. 3-4 indicate two plate arrangements for the plates of a clarifier .

Detailed description of embodiments

It is noted that the drawings are schematic, not necessarily to scale and that details that are not required for

understanding the present invention may have been omitted. The terms "upward", "downward", "below", "above", and the like relate to the embodiments as oriented in the drawings, unless otherwise specified. Further, elements that are at least

substantially identical or that perform an at least

substantially identical function are denoted by the same

numeral, where helpful individualised with alphabetic suffixes.

Further, unless otherwise specified, terms like "detachable", "openable" and "removably connected" etc. are intended to mean that respective parts may be disconnected and/or opened

essentially without destruction of either part, e.g. excluding structures in which the respective parts are integral and not intended to be demolished or deformed (e.g. welded or molded as one piece) , but including structures in which parts are attached by or as mated connectors, fasteners, releasable self-fastening features, etc.

Fig. 1 is a flow diagram of a treatment apparatus 1 for enzyme enhanced recovery of crude palm oil from palm fruits. The diagram is also applicable for enzyme enhanced recovery of oils from other vegetable materials such as one or more of press liquor, press liquor sludge and flowable pulp.

The apparatus 1 comprises a supply system 3 for supplying press liquor from a pressing arrangement (generally indicated with "P") , a primary clarifier 5, an incubator 7 and a secondary clarifier 9. First and second incubator feed lines 11 and 13 with optional temperature control systems may be arranged, as shown, between the incubator 7 and the respective first and second clarifiers 5, 9. Here, the first and second incubator feed lines 11 and 13 may be thermally connected, possibly even directly as shown, and/or they may be mutually connected to a common temperature controller 15, which in turn may comprise one or more of pumps 17, storage and/or expansion vessels 19, heaters (not shown) etc. Further, an intermediate collection tank 21 and/or a number of pumps 23 may be provided, as shown, between the primary clarifier 5 and the incubator 7. Further, at least part of the primary and secondary clarifiers 5, 9 may be fluidly connected.

The first clarifier 5 is, preferably, a cross flow

interceptor or CFI, as generally shown in Fig. 2, comprising one or more packs 25 of mutually parallel corrugated separation plates 27 arranged inclined to the horizontal direction, the plates possibly having longitudinal corrugations as shown, and wherein the medium to be separated flows over and between the plates in a flow direction (IN - OUT1) perpendicular to the corrugations of the plates. In such cross flow interceptor, light matter (e.g. oils) collects at or near the crests of the corrugations and rises upwards, leaving the pack at the top (OUT2) . Heavier matter like solids collects in the troughs and slides downwards, leaving the pack at the bottom (OUT3) . Such cross flow interceptor is capable of separating liquid and solids simultaneously, with little or no (risk of) re

entrainment of separated matter into the lighter and/or the continuous phases (flowing in directions IN-OUT2 resp. IN-OUT1).

The cross flow interceptor 5 may, in one or each pack 25, contain a number of parallel plates 27 mounted with the

respective corrugations in-phase so that crests and troughs of adjacent plates are aligned (see Fig. 3) . However, a preferred embodiment of a cross flow interceptor clarifier has its plates 27 mounted mutually out-of-phase, in particular all adjacent plates 27 being mounted mutually equally out of phase, more in particular as 180° out-of-phase plates so that crests of one plate are aligned to troughs of the adjacent plate and vice versa (see Fig. 4) .

With the in-phase plate arrangement of Fig. 3 the flow velocity of the medium between the plates is constant. With the out-of-phase plate arrangement of Fig. 4, the medium flow velocity between the plates varies. When the spacing between the plates contracts the flow velocity increases and when the space between the plates expands the flow velocity decreases. This way of operation facilitates the release of CPO still entrapped in sludge pockets, thus greatly enhancing the separation

efficiency .

Applying an out-of-phase plate profile configuration results in alternating flow velocities between the plates, thus an effect can be created whereby pockets holding oil can be

'massaged' out of fractions of the CPO comprising relatively higher concentrations of large components and/or particulate matter. CPO separation is promoted this way. Heavy CPO

components collect in the corrugation troughs and tend to slide downward along the troughs. By shifting the corrugation phase to a counterphase, the entire troughs are available for collection and transportation of collected/precipitated CPO-components . See figure 4. Then there may be is so much room that settling of heavy components will not be hindered.

For process control, the clarifier 5 may be provided with one or more sensors, e.g. cameras and/or other detectors, like a guided wave radar type level transmitter.

The primary clarifier 5 may be fed in any suitable manner. E.g., the primary clarifier 5 may be fed by means of one or more pumps 3. A centrifugal pump may be used, but by the nature of their working principle, in centrifugal pumps high shearing forces are generated. These high shearing forces can cause water present in the press liquor to disperse into very small droplets that are difficult to separate. Therefore, rotary positive displacement pumps, preferably rotary positive displacement pumps of the progressive cavity type, are preferred. With this latter type of pumps 3 press liquor can be delivered to the clarifier 5, relatively, as 'undisturbed' as possible preventing (further) undesired dispersion.

The flow through the CFI clarifier 5 may have a uniform pattern with laminar conditions in the plate packs 25. This promotes an optimal separation process. A uniform, let alone a laminar flow pattern, cannot be achieved and maintained in other separators, such as (large) settling tanks, in which short circuiting and back mixing due to temperature gradients is unavoidable, leading to poor separation efficiency. In the clarifier 5, baffles (not shown) may be provided that extend downward from the plate packs 25 into the sludge hoppers, so as to prevent short-circuiting underneath the plate assemblies 25.

The primary clarifier 5 may comprise a number of Cross Flow plate packs 25 (see Figs 2 and 4, not shown in Fig. 1) and it may have a so-called hopper bottom, divided in hoppers 29a-29c: the first hopper 29a collects the bulk of heavier components of the CPO with a high settling velocity. The next two hoppers 29b, 29c collect CPO-components separated in the respective Cross Flow plate packs (25) installed above them. The collected CPO- mass or sludge may be drawn off via valves (not shown) at the bottoms of the hoppers 29a-29c, and transported to the

intermediate collection tank 21.

Optionally, an inlet chamber 29 of the clarifier 5 may be devoid of plates 27 and/or a hopper bottom, acting as a settling tank for large and/or very heavy CPO-components. In case of high concentrations of such CPO-components, plate packs 25 could otherwise become clogged.

The press liquor stream may enter a clarifier's inlet/flow distribution chamber, e.g. chamber 29, via an inlet nozzle. In, or near and upstream of, this chamber 29 a heater, e.g. a steam heater (not shown) , can be installed for heating the press liquor stream to a desired temperature, e.g. 80 - 90°C, e.g. in case the inlet temperature turns out to be too low for a proper separation process. Also, a cooler may be provided in case of the opposite. E.g. in case of a low inlet velocity, e.g. in a range of 0.2-0.3 m/s at 13-20 m ³ /h, prevailing conditions in the inlet chamber 29 may be quiescent.

Via an underflow weir and/or an adjustable plate overflow weir (collectively indicated with 33) clarified CPO may flow into a clarified CPO outlet chamber 35. The underflow weir prevents liquid to short circuit through the upper part of the plate pack assemblies. The overflow weir is to prevent water or other relatively heavy fractions (when present) from entering into the CPO outlet chamber 35.

The heavy fraction of the CPO collected at the hoppers 29a- 29c of the primary clarifier 5, also referred to as "sludge", is discharged from the clarifier 5 and collected in the

intermediate collection tank 21. This may serve for levelling out any discharge peaks and/or other flux variations from the primary clarifier 5. Thus, the incubator 7 can be fed at a continuous flow rate, possibly controlled by one or more

incubator feed pumps 23.

In and/or upstream of the incubator 7 enzymes are mixed into the CPO. Enzyme dosing may be effected by any suitable means, progressive cavity type metering pumps being preferred (not shown) . With this type of dosing pumps there is no requirement for one or more of calibration pots, pulsation dampeners and back pressure valves, although these may be provided as desired. Multiple pumps may be provided, e.g. one pump is being a duty pump and one pump being stand-by.

The incubator 7 may have any suitable construction; a coiled pipe reactor or CPR may be preferred. Flow conditions in a CPR may closely resemble plug flow conditions whereby short circuiting and back mixing may be prevented, thus allowing for a well-defined residence time.

Operating conditions of the clarifiers 5, 9 may be closely similar. The operating conditions of the clarifiers 5, 9 may, however, differ starkly from those of the CPR incubator, in particular where temperature is concerned. E.g. for optimal clarification of palm oil a medium temperature of some 90°C is required, while the temperature for incubation of enzymatic processes should preferably not be much higher than 50°C.

Therefore, the cooling/re-heating system 11, 13, 15, 17, 19 is provided (Fig. 1) .

Sludge from the primary clarifier 5 is received in the intermediate sludge collection tank 21. The associated discharge piping from the clarifier hoppers 29a-29c to the sludge tank 21 may be provided with heat insulation. The tank 21 itself may have heat insulation or not, and the tank may be equipped with an agitator. From the tank 21 the CPO is transferred to the CPR incubator by means of the incubator feed pumps 23. In an

enbodiment multiple pumps may be provided, e.g. one duty pump and one stand-by pump. As indicated before, the pumps may be progressive cavity pumps. The pumps may be provided with

variable speed drive.

The collected heavy CPO-fraction may be warm from the primary clarifier 5. And the contents of the intermediate sludge

collection tank 21 may be (still) warm as well. The material from the tank 21 is pumped to the incubator 7 via a primary incubator feed line 11. This primary incubator feed line 11 is provided with an optional jacket tube through which cooling water is flown or pumped (co-flow or counter-flow as desired, relative to the CPO flow direction) . The temperature of the cooling water will increase on its trajectory along the

incubator feed line. From the jacket tube of the primary incubator feed line 11 the warm cooling water is transferred to the jacket tube of the secondary feed line 13 (co-flow or counter-flow as desired, relative to the CPO flow direction) . The temperature of the CPO flowing through this feed line will therefore increase by the heat transfer of the warm water flowing through the jacket tube. Thus, the temperature of the CPO in the incubator 7 may be lowered with respect to its temperature upstream and downstream of the incubator 7. See the flow diagram in figure 1. The cooling/re-heating system may include a common temperature controller 15, which in turn may comprise one or more of pumps 17, storage and/or expansion vessel 19, a heater (not shown) etc. and be a closed circuit as shown. This causes that the hot mesocarp sludge is cooled before it enters into the CPR

incubator, wherein the heat absorbed by cooling water is used for (re-) heating the enzyme-treated mesocarp sludge before it enters into the secondary clarifier. Also or alternatively, other thermal control systems may be provided.

The incubation step may include centrifugation before or after the incubation but this is not needed and may add

complexity and costs to the system.

From the incubator 7 the treated CPO material (sludge) may be directly fed to the secondary clarifier 9, although secondary clarifier feed pumps may be provided as desired.

In the secondary clarifier 9 the treated CPO is separated like in the primary clarifier 5 and any oils may be combined with the oils separated in the primary clarifier 5 and/or be fed a second time into the primary clarifier 5 for further

refinement and/or process control.

The secondary clarifier 9 may have the same construction as the primary clarifier 5, although differences in the number and/or dimensions of the plate packs 25 and/or plates 27 therein may exist. The plates may be arranged at different mutual separation and/or different angle to the horizontal. Also, more or less bottom hoppers may be provided as shown.

Any heavy CPO fraction intercepted with the secondary clarifier 9, and from which the desired fraction CPO is removed, may be drawn off from (a bottom segment e.g. a bottom hopper of) the secondary clarifier 9 and transported to an effluent

treatment plant (ETP) for further processing. For that, in the secondary clarifier 9 waste sludge is collected in the large sludge hopper underneath the last part of the separation

chamber. From this hopper the sludge is discharged in a

controlled manner to the ETP. Controlled discharge may be desired to keep the recovered CPO/sludge interface within a certain level range so that recovered CPO can be continuously skimmed off. Sludge discharge can be effected by sludge pumps and/or by a control valve.

The disclosure is not restricted to the above described embodiments which can be varied in a number of ways within the scope of the claims. For instance, the materials used, the temperatures, the dimensions, and angles may be adjusted to the process at hand e.g. with different types of vegetable oils.