WO2016129986A2

WO2016129986A2 - A method for treating effluent produced from palm oil milling process

Info

Publication number: WO2016129986A2
Application number: PCT/MY2015/050156
Authority: WO
Inventors: Teng Ye NGAN; Teng Han NGAN; Teng Chee NGAN
Original assignee: Ngan Teng Ye; Ngan Teng Han; Ngan Teng Chee
Priority date: 2015-02-10
Filing date: 2015-12-22
Publication date: 2016-08-18
Also published as: NI201700102A; MX2022014393A; BR122018076810B1; PH12017501407A1; CO2017008041A2; DOP2019000289A; PH12017501407B1; DOP2017000187A; PE20220606A1; GT201700176A; PE20180264A1; MY163847A; CR20170368A; ECSP17052464A; WO2016129986A3; BR112017017097A2; MX2017010196A; BR112017017097B1

Abstract

The present invention relates to a method for treating effluent produced from palm oil milling process, comprising the steps of removing solid (20) from the effluent, wherein the removed solid are formed into dried products, removing water (30) from the effluent for reusing the water in the palm oil milling process, extracting oil (40) from the effluent to form a residual sludge, wherein the steps of removing solids, removing water, and extracting oil are carried out in sequential order of solid, water and oil.

Description

A METHOD FOR TREATING EFFLUENT PRODUCED FROM PALM OIL

MILLING PROCESS

Field of the invention

The present invention relates to a method for the treatment of effluent produced from palm oil processing, and more particularly, the present invention relates to a method of processing the palm oil mill effluent for reducing or eliminating discharge into the environment.

Background of the invention

Palm oil is an important commodity which has widespread applications from producing cooking oils, food, confectioneries to oleochemical products such as soaps and lubricants as well as biodiesel. The palm oil is derived from fresh fruit bunches (FFB) of the oil palm trees, Elaeis guineensis. The FFB harvested from oil palm plantation, will be processed in palm oil mill to extract the crude palm oil and palm kernels as the main products. During the processing of FFBs to recover crude palm oil and palm kernels, large volume of sludge is also produced in the mill at various stages. Sterilizer condensate is produced during sterilization process of FFB. Pressing of the mesocarp produced a thick sludge composed of crude palm oil, water and solid. Water is added to this sludge during the clarification process to assist in the recovery of crude palm oil. When empty fruit bunch (EFB) is pressed, EFB press liquor is produced which contains oil, water and solid. All 3 fractions can be process separately or together to recover the crude palm oil. The residual sludge which normally contains <1 % oil, 3-6% solid and 93-96% water is normally termed as palm oil mill effluent (POME). The total volume of the sludge is normally at 60% ratio to quantity of FFB processed. Other by-products and wastes being produced include palm kernel shell, empty fruit bunches, mesocarp fiber, and decanter cake. Palm oil mill effluent (POME), contains high concentration of organic matters and needs to be subjected to treatment to comply with the standard as required by the relevant authorities. However, due to the high concentration of organic matters, treatment of the POME has been always a challenge in the palm oil milling industry. Treatment of POME is non-income generating, requires a substantial cost to palm oil mill and occupies large area of land. An average size mill with capacity of 45 MT/hr FFB often requires pond treatment systems occupying 5-10 acres land.

Recent development in POME treatment includes trapping and utilization of biogas generated during an anaerobic treatment process. Biogas can be used to generate electricity, and contribute revenue from certain mills by selling harvested power to the national grid. Otherwise the biogas can be used as boiler fuel or simply flared. Apart from that, there has been continuing efforts in searching for new and better treatment method in the palm oil milling industry to reduce environmental pollution and to comply with the more stringent standard as set out by the local authorities on the milling effluent. Furthermore, as the oil palm planting acreage has been increasing over the years, the effluent treatment system of palm oil mills are required to be upgraded to handle the increasing quantity of FFB needed to processing.

International application publication no. WO 2013/169091 A1 discloses a method for processing the POME, which comprises the steps of pre-treatment, biological treatment, and membrane separation. The pre-treatment step includes subjecting the POME to rotary screen, grit separator, and oil water separation. The biological treatment in the method produces methane gas which requires further treatment to reduce the greenhouse gas emission into atmosphere. International application publication no. WO 2014/05415 A1 discloses a system for recovering oil from POME, comprising a screening machine, a heater, a catalyst feedstock, a reactor, and a centrifuge, wherein the system is mounted in a vehicle for portability. The system recovers crude palm oil from POME after centrifugation. However, the system does not address the problem of effluent discharge as solid and water phase will be produced as a by-product.

Malaysian patent no. MY-144226-A discloses a method for extracting crude palm oil from press liquor to reduce effluent discharge comprising the steps of removing solid phase, water phase, and oil phase from the press liquor. The method requires modification to the existing palm oil milling equipment and processes, as the method uses press liquor as the starting substrate.

In view of the above, it is therefore desirable to provide a method for treating POME to effectively reduce or eliminate effluent discharge by recovering solid phase, water phase, and oil phase of the POME so that each phases can be recycled for other uses.

Further, there is a need to provide a method for treating POME which can be incorporated into the existing operation of palm oil extraction. The method is configured to be added after the last process in the normal oil recovery, so that the current operations used in the palm oil mill will not be affected in terms of quality of oil recovered and oil loss by the incorporation of POME treatment method.

Summary of the invention It is an objective of the present invention to provide a method for treating the effluent produced from the palm oil milling process.

It is also an objective of the present invention to provide a method for eliminating the effluent discharge from the palm oil milling process by treating the POME and recovering the solid, water, and oil phase of the POME.

It is further an objective of the present invention to provide a method for extracting the crude palm oil from the POME.

It is yet another objective of the present invention to provide a method which is economically viable for achieving zero discharge from the palm oil milling process, thereby reducing or eliminating the release of methane gas from conventional effluent treatment ponds.

It is also an objective of the present invention to provide a method of treating the POME which can be incorporated into the existing palm oil extraction process without changing the process thereof. The present invention relates to a method for treating effluent produced from palm oil milling process, comprising recovering solid, water, and crude palm oil from the effluent to produce a residual sludge, wherein the recovering of solid, water and crude palm oil is carried out in sequential order in the sequence of solid first, water next and finally crude palm oil, and each of the recovered solid, water, crude palm oil, and the final residual sludge are recycled or formed into usable products.

In one aspect of the invention, the separation of the solid phase is selected from the group comprising filtration, pressing, centrifugation, or any combination thereof, wherein at least 50% - 90% of the suspended solid are removed from the effluent. In one aspect of the invention, the separation of the water phase comprises multi-effect evaporation using multiple evaporating units at different pressure or vacuum to achieve efficient energy usage. The water phase removed can be used in boiler or palm oil mill processing for the saving of cost of raw water treatment.

In one aspect of the invention, the sequence of the evaporating units in a system of multiple effect evaporation is changed after a predetermined time or upon detection a predetermined value of viscosity, moisture content, solid content, or oil content of the effluent to reduce the fouling issue of the evaporators.

In one aspect of the invention, the separation of the oil phase from the effluent comprises mechanical separation of the oil phase from the residual sludge by settling in a buffer tank and centrifugation. The oil recovered from POME can contribute revenue to the palm oil milling plants.

Brief description of the invention

Figure 1 is a flow chart illustrating a process for treating the effluent from palm oil milling process according to the present invention.

Figure 2 is a flow chart illustrating a process of a pre-conditioning stage in treating the effluent from palm oil milling process according to the present invention. Figure 3 is a flow chart illustrating a process of removal of solid in treating the effluent from palm oil milling process according to the present invention.

Figure 4 is a flow chart illustrating a process of removal of water in treating the effluent from palm oil milling process according to the present invention. Figure 5 is a flow chart illustrating a process of extraction of oil in treating the effluent from palm oil milling process according to the present invention.

Figure 6 is a flow chart illustrating a method for treating residual sludge from palm oil milling process according to the present invention.

Figure 7 is a flow chart illustrating a solvent extraction process on the dried solid as recovered from the removal of solid and residual sludge processing. Detailed descriptions of the preferred embodiments

The present invention will now be described in more detail with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. With reference to Figure 1 , the present invention relates to a method for treating effluent produced from palm oil milling process. Figure 1 shows that the process comprises three main steps of removing solid (20), removing water (30), and extracting oil (40) from the effluent to produce a residual sludge. The three main steps of the method are tightly integrated and designed to work in this particular sequential order of removal of solid, water, and oil. The three main steps are inter-related in the sense that each step enables the subsequent step to have a higher performance in an economically feasible condition. Residual sludge is produced after the oil extraction (40), and is subjected to a step of recycling, drying, or combination thereof (50). The solid removed from the effluent are formed into dried products, whereas the water removed from the effluent is re-used in the palm oil milling process. The extracted oil from the effluent is crude palm oil, with similar oil quality to that recovered in the oil milling process, and which can be further processed to obtain palm oil products. In a preferred embodiment, the effluent which is being treated in the present invention is palm oil mill effluent (POME). The POME is the wastewater produced from processing the fresh fruit bunches (FFB). The POME comprises sludge after clarification or oil recovery process from sterilizer condensate, pressed liquid from fruitlet and pressed empty fruit bunch (EFB) liquor. The POME is usually a thick, brownish colloidal slurry of water which has high biochemical oxygen demand and high levels of suspended and dissolved solids. The normal average ratio between suspended and dissolved solids is between 1 :1 and 1 : 2, actual ratio varies from mill to mill due to factors such as soil, clone, handling and milling process.

Figure 2 illustrates the method of the pre-conditioning stage prior to the step of solid phase separation. The pre-conditioning stage (10) is an optional stage which is dependent on the actual setup of the palm oil mill. In a preferred embodiment, this pre-conditioning stage (10) can be multi-stages with the objective to remove coarse fibrous solids, sands and excessive solids in the effluent. Hence, the pre-conditioning stage, by way of non-limiting example, involves a vibrating screen (11 ) follow by de-sanding cyclone (12) to pre-condition part or all of the effluent which still contains coarse fibrous solids and sand. The pre-conditioning stage (10) may further involve a decanter (13) to remove excessive solids such as fine sands and organic matter if no solids have been removed in the milling process.

With reference to Figure 3, the removal of solid (20) comprises one or more separation apparatuses (21 ) for removing solid from the effluent. In a preferred embodiment, removal of at least 50% - 90% of the solid is required. In a more preferred embodiment, at least 60% - 90% of the solid is removed. Taken into consideration of technical results and cost factors, removal of 90 - 95% solid is preferred. A removal of 99% of solid would be ideal, but would also incur higher costs. The removal of solid (20) comprises a single step or multiple steps of equipment operating in series or in parallel to remove the solids. The use of multiple steps of equipment has advantages as it allows for the separation of solid of different physical properties. An example of the multiple steps equipment includes multiple filters having screen or membrane with different mesh or pore sizes.

The removal of solid in the present invention can be carried out by using a method selected from the group comprising filtration, pressing, centrifugation, or any combination thereof. Any other equipment capable of performing a two phase separation of solid and liquid can be used in the solid phase separation. The solid separated need not be fully dry, and a moisture content of less than 80% would be acceptable.

The filtration equipment can be chosen from, but not limited to, continuous filters comprising vacuum belt filter, rotary drum filter, rotary disc filter, and belt press filter, tangential flow filter, or batch filters comprising filter press, membrane filter press, horizontal disc filter, leaf filter, tube filter, tower filter and multi-element candle filter, and bag filter.

An example of the pressing means for separating the solid phase is the rotary press. Alternatively, centrifuge such as 2 phase decanter/separator which can perform a solid and liquid separation with the separated solid with moisture of less than 80% can be used.

Depending on the method used to remove the suspended solid, a portion of the dissolved solid will be removed simultaneously in the form of the moisture in the wet solid removed. As a result of this effect, it may be advantages to have a high moisture content in the solid removed to simultaneously reduce the dissolved solid in the residual sludge. In a preferred embodiment, the moisture content of the solid removed is as high as 80%. In another preferred embodiment, the moisture content of the solid removed can be just 40%.

The solid removed is dried into dried products with a moisture level of less than 15% in bulk form and stored in separate silos for ease of storage, transportation and sale or further processing.

Figure 4 illustrates removing of water (30) in the treatment of the POME by using evaporating units (31 ) according to the present invention. In a preferred embodiment, a plurality of multi-effect evaporator may be employed using any combination of, but not limited to, the common evaporator design such as falling film evaporator, forced circulation evaporator, natural circulation evaporator, batch pan evaporator, wiped film evaporator, rising film evaporator, plate type evaporator, falling film tubular evaporator and rising/falling film tubular evaporator. All these evaporators can be arranged as feed forward configuration or feed backward configuration.

Multi-effect evaporation uses the steam produced from one evaporating unit to provide the heat to evaporate product in a second evaporating unit, in which the second evaporating unit is maintained at a lower pressure. In a two effect evaporator, it is possible to evaporate approximately 2kgs of steam from the product of each kg of steam supply. As the number of effects is increased, the cost efficiency of providing steam to the evaporation process increases.

The evaporation in the present invention may be incorporated with use of thermo vapor recompression (TVR) and mechanical vapor recompression (MVR) for improving the economy of the evaporation. The water evaporated or removed by from evaporation will be clear and clean water that can be recycled to either the mill process or boiler in the palm oil milling process. The specification of the water is as follows: PH of 5-6, TS ~1 50ppm, BOD ~20ppm. The evaporation is carried out to remove at least 50% of the moisture, and more preferably, the evaporation should remove between 60-75% of the moisture. Theoretically, depending on the percentage of suspended and dissolved solid in the input solid, it is possible to remove more than 85% moisture by evaporation method.

Table 1 Approximate ratio of oil, solid and water at various stages without removal of solid

Table 1 shows that the percentage of oil increases as higher percentage of water is being removed. Theoretically, the recovery of oil is possible without removal of solid. However in practical, there are 4 issues in recovery of oil without removal of solid. Referring to the case where the concentration of solid in the initial solid percentage is 6%. Firstly, at 75% removal of water, the percentage of water is too low, resulting in the sludge becoming too viscous to flow in the evaporating units. Therefore, the removal of water will be subjected to an upper limit of approximately 60 - 75%.

Secondly, at more than 60% water removal, the percentage of solid is too high for most of the current centrifugal equipment. Therefore, oil recovery is an issue at higher percentage of water removal, but efficiency of oil recovery will be badly affected at lower percentage of water removal.

Thirdly, since it is only possible to target around 60% water removal without first removing the solid. Not only will this reduce the oil recovery, it will also result in higher quantity of residual sludge. The eventual drying process will require more heat energy, or otherwise, there may be too much sludge to recycle.

Finally, the solids, especially the bigger particles, are prone to stick to the tubes of the evaporating units and cause fouling problem.

For example, without removal of solid, and at 60% water removal, oil recovery is approximately 56% and quantity of residual sludge is approximately 44% to POME.

Table 2 Approximate ratio of oil, solid and water at various stages with 50% removal of suspended solid with 80% moisture

According to Table 2, comparing 50% and 75% removal of water, the concentration of oil increased from approximately 2% - 3.5%. Current method of oil recovery using centrifugal method such as decanter or separator will have a residual oil of 0.6% - 1 % remaining in the sludge. Therefore, the higher concentration of oil implies the percentage of recovery of oil is higher. In conclusion, the removal of water has a direct impact on the recovery of oil from the sludge. Higher percentage of water removal will result in higher percentage of oil recovery.

However, the removal of water is subject to a maximum limit where the sludge will still flow within the water removal process. In the case of evaporators, depending on the design of the evaporators, each design will have a different limit, but the common denominator is the percentage of solid in the sludge, especially the suspended solid.

According to Table 2, although the oil concentration remains similar as without removal of solid, water removal of between 60% - 75% is possible depending on the initial solid content, thereby resulting in better oil recovery and also lesser quantity of residual sludge to dry or recycle.

For example, with 50% removal of suspended solid, and at 75% water removal, oil recovery is more than 70% and the quantity of residual sludge is approximately 29% of POME.

Therefore, the advantages of at least 50% removal of suspended solid include higher oil recovery rate of more than 70%, lower residual sludge of less than 30% of POME, simplified drying and/or recycling of the residual sludge due to lesser residual sludge. Besides that, less solids means that there will be less particles that will stick to the tubes of the evaporating units and cause fouling problem.

Table 3 Approximate ratio of oil, solid and water at various stages with 90% removal of suspended solid at 80% moisture

Table 3 above shows the approximate ratio of oil, solid and water from the effluent, after solid removal of 90% suspended solid at 80% moisture and after 50, 60, and 75% of water removal. From the numbers in the table, it shows the importance of solid removal before the step of evaporation. With the removal of 90% suspended solid in the first stage, the solid content reduced from standard effluent of 3 - 6% down to 2 - 4%.

With 90% suspended solid removal, it is possible to remove more than 75% of the water. Depending on the initial solid content, it is possible to remove 80 - 85% of the water.

At 75% water removal, oil recovery is more than 70% and the quantity of residual sludge is only approximately 28% of POME. At 80% water removal, oil recovery is more than 76% and the quantity of residual sludge is only approximately 23% of POME. In an embodiment of the present invention, the sequence of the evaporating units is changed after a predetermined time in order to reduce the fouling issues of the tubes of the evaporating units^ or upon detection of a predetermined value of viscosity, moisture content, solid content, or oil content of the effluent in the evaporating units. The measurement of the viscosity, moisture, solid, or oil content can be taken at a certain interval to determine whether change of sequence is necessary, The moisture, solid, or oil content can be measured by a 3-5 minutes spinning test on a sample taken from the effluent.

The fouling of the evaporating units normally develops on the last few effects where the liquid is thick and viscous. Therefore, in this invention, the design of the evaporator allows for the sequence of the evaporating units to be changed, making use of the feed effluent which flows easily to clean the evaporator tube without downtime. Other than the temperature and pressure difference which requires a short time of several minutes for adjusting depending on the equipment size, the evaporator still functions and evaporates water as normal, just the sequence of the effect has changed. As such, the sequence changing capability of the evaporating units are advantageous over the conventional multiple effect evaporators where the ducting connecting the multiple evaporating units are permanently fixed without any valve due to the large size of the evaporating units.

In a preferred embodiment, the sequence of the evaporating units is changed by controlling the flow of effluent, vapor, and condensate in conduits interconnecting the evaporators. In a more specific embodiment, to allow the change of the evaporating unit sequence in a multiple effect evaporator, all the input and output of the evaporating unit are changed. The input includes (a) the liquid effluent to be evaporated to remove part of the water and (b) the steam which supplies the heat for the evaporation purpose, and the output includes (c) the residual liquid after some of the water had been removed, (d) the water condensed from the steam supplied to heat up the input liquid, and (e) the water that had been evaporated in the form of steam.

In an embodiment of the present invention, the flow of effluent, vapor, and condensate in the conduits is controlled by at least a valve coupled to the conduits. For the liquid portions of the input and output, changing the sequence of the evaporating units can be achieved with the use of normal valve usually with the size of 5- 30 cm (2-12 inches) to control the feed. However, to control the steam portion of the input and output, use of valve to change the sequence would be very costly, since the normal ducting sizes have diameter of more than 0.6 m (2 feet).

In a preferred embodiment, the evaporating units are provided with smaller diameters of approximately 1 m. With the smaller evaporating unit diameters, the ducting sizes can be reduced to between 25 - 41 cm (10-16 inches). Coupled with the use of common headers to connect those evaporating units of which the sequence need to be changed, it becomes viable to change the sequence and at the same time minimize the actual numbers of valves and interconnecting ducts required.

For example, last effect evaporating unit becomes 1 st or 2nd effect evaporating unit after certain amount of time in operation. Ideally if all the evaporating units are rotated after certain time, then all the evaporating units will be cleaned by the feed effluent. In practice, not all evaporating units need to be shifted as the purpose of changing the sequence of the evaporating unit is to reduce the fouling issue which mainly occurs in the last few effects. Therefore, by allowing the last and/or second last effect evaporating unit to be change with 1 st or 2nd effect evaporating unit, would be sufficient. To simplify the ducting design where there is change of sequence, common headers coupled with valves can be used to connect the common inlets and outlets of the evaporating units.

In a preferred embodiment, the evaporating units are grouped into a plurality of groups with each group comprising at least two evaporating units adjacent to each other in sequence, and the sequence of the evaporating units is changed by switching between the groups of the evaporating units.

For example, the changing of the first and second evaporating unit with the second last and last evaporating unit simplifies the arrangement of the evaporating units and rendering it more cost effective.

In another example, for a 3-effect evaporator, just swapping the 1 st effect and the 3rd effect evaporating units would be sufficient. For a 5-effect evaporator, just swapping the 4th and 5th effect evaporating units as a whole to replace 1 st and 2nd effect evaporating units would greatly simplify the design and construction.

The evaporating unit described herein should be construed as an evaporator device, evaporator vessel, or a partition in an evaporator of which single effect evaporation is carried out in a system for multiple effect evaporation. The evaporating units may be provided in parallel configuration as set out in the following examples.

It is also possible to construct the evaporator with multiple 1 st or 2nd effect evaporating units operating in parallel, but some of these 1 st or 2nd effect can be made to operate as the last and/or second last effect while that last and/or second last effect will operate as the 1 st or 2nd effect during such times.

For example, for a 3-effect evaporator, it is possible to have 2 or more evaporating units of 1 st effect, and 1 or more of these 1 st effect can change sequence with the last effect. For a 5-effect evaporator, it is possible to have 2 or more evaporating units of 1 st effect and may be also 2 or more units of 2nd effect. In this case, just change the 4th effect or 5th effect unit with 1 st effect units would be sufficient. It is also possible to achieve similar result of reducing fouling by partitioning a evaporator into multiple evaporating units so that multiple-effect evaporation can be carried out within the same evaporator, and change the sequence of the evaporator units as described earlier. Figure 5 illustrates the extraction of oil (40) from the effluent after the removal of water (30), which comprises centrifugation (41 ) of the effluent, heating the effluent, feeding the effluent to a buffer tank, and mechanically separating the oil layer in the buffer tank by skimming the oil layer that floats on top of the tank. The centrifuge which is used for mechanical separation can be 2 or 3 phase decanter or 2 phase separator capable of separation of oil from liquid. At this stage, the oil content of the effluent is reduced to less than 1 %, forming a residual sludge. From Tables 2 & 3, the removal of solid and water enhance the oil concentration from 1 % in the feed to between 2 - 3.7% after 60 - 75% water removal. At this concentration of 2 - 3%, the oil recovery from the effluent after solid and water removal is increased. After the oil phase separation, the residual sludge is produced, which in an example, may still contain approximately 0.5 - 1 % oil, 5 - 9% solid and 90 - 94% water with a volume of between 20 - 40% of the original input. The residual sludge is subjected to further processing as shown in Figure 6. In a preferred embodiment, the residual sludge is subjected to recycling, drying, or a combination of both (50). By recycling the residual sludge back to the process (51 ), it is possible to use this as dilution water for press station or clarification station. This way, no liquid is discharged as effluent and therefore, no oil loss can occur.

Alternatively, the drying of the residual sludge (52) is carried out to reduce the moisture therein to less than 15% for ease of storage, transportation, and sale or further processing. The low moisture content allows the solid to be stored for a period of time without deterioration of quality. The drying apparatus (54) which may be used, include rotary drum dryer, spray dryer , vacuum dryer or any other suitable design of drying machinery along with heat energy from any combination of boiler exhaust, high pressure steam from boiler or low pressure steam from back pressure receiver (turbine exhaust steam) or any other heat source if available.

It is also another embodiment to use a combination of recycling and drying (53) in treating the residual sludge. This way, addition of water to the milling process is minimized, while at the same time, no additional heat energy from steam is needed to dry the residual sludge. In this combination of recycling and drying, more solid is being removed using solid removal system by the use of separation machineries (55) with different specification as compared to the solid phase separation. A percentage of 90 - 99% of solids in the residual sludge is removed. The moisture content of the solid removed may be high so that more solid including dissolved solid is removed, and this moisture content can be adjusted based on the heat energy available from the boiler exhaust. The liquid after the solid removal, will be fed to a buffer and may be reheated to a required temperature prior to the recycle to press or clarification station in the milling process. Temperature of the sludge is a very important parameter throughout the whole process and is tightly monitored, controlled and optimized for performance and energy efficiency. Other than the evaporator stage, the sludge is maintained at 90 degree Celsius or higher where possible. An example of the solid removal system which can be used in the combination of drying and recycling is membrane filter press. By recycling filtrate as dilution water, the actual POME to be removed by evaporator is only at a ratio of 0.4MT per 1 MT of fresh fruit bunches processed instead of the standard 0.6MT per 1 MT of fresh fruit bunches.

The boiler exhaust would be sufficient to dry off the solid removed from both the solid phase separation and the residual sludge drying to moisture of less than 15%. The decanter cake from the normal oil milling and pre-conditioning stage, if any, can be added to the drying process to increase the quantity of dried solid.

The dried solid will be stored in silos prior to further processing in the mill. The dried solid can also be sold or transported to a centralized processing plant for further processing. The dried solid will have an average protein of 8 - 1 3% and fiber of 3 - 16%, in addition to oil content of 3 - 5%. Therefore, the dried solid can be sold as is for the value of its protein, or the oil can be recovered first using solvent extraction process, and the solid with <1 % oil can be sold separately for its protein value as animal feed. It also contains mineral content such as Calcium (Ca), Phosphorus (P), Magnesium (Mg) and Potassium (K) of between 0.2% - 1 % which makes it possible to be sold as organic fertilizer. The mineral content can be separately recovered to increase the concentration and enhance its nutrient value as organic fertilizer. The dried solid also contains high level of ether extract of between 20 - 40% which will increase its energy content but also creates rancidity problem during storage. In a preferred embodiment, the present invention separates the different fractions of the solid in the residual sludge by making use of the physical properties of each fraction. Since the solid were removed at different stages using equipment of different performance parameters and multiple steps in each stage, it is possible to fine tune the parameters of the solid separation at each stage to remove solid with higher concentration of a certain particle size.

For example, the use of filtration with pores from bigger to smaller size in multiple steps allows for the removal of solid with high concentration of initially sand, subsequently fibre and eventually protein. The use of centrifuge or tangential flow filtration at the later stage after 95-99% suspended solid has been removed, allows for removal of specific mineral if the economics warrants the use of such equipment.

It is possible to handle the solid separately from drying to oil recovery. The drying and storage can be performed either in batches or with the use of smaller drying equipment and silos for each fraction. In a further process, the recovered solid phase is subjected to solvent extraction (60) to recover oil in the solid. The solvent extraction comprises soaking or flushing the solid with solvent, recovering the solvent, and distillation of the solvent to recover oil as shown in Figure 7. Solvent used can be flammable solvent such as hexane, or non-flammable solvent such as Trichloroethylene, depending on the application of the solid and oil after the processing.

Normal solvent extraction plant is designed with an extractor (62) and a desolventising toaster (DT) (64) operating in sequence to recover oil form the solid. In extreme case where the economics warrants, the solvent extraction plant can be designed with multiple sets of extractors (62) and desolventising toasters (DT) (64) operating in parallel to handle the different fraction of the solid. However, the distillation portion can be shared with the multiple extractors (62) and desolventising toasters (DT)(64). The solvent extraction plant can be located at the mill or can be located separately from the mill. Where the solvent extraction plant is located separately from the mill, the dried solids from this invention will be stored in silos in the mill and transported to a centralized solvent extraction plant for the solvent extraction. This centralized solvent extraction plant will normally be located near to a port for ease of export of the dried solid.

In solvent extraction process, dried solids received from the mills may be powders mixed with lumps depending on the drying operation and design of the mill. There may be a need to pre-condition (61 ) the solid to a form suitable for solvent extraction. For example, the solid is crushed to powder and then pelletized. The lumps may be screened out and only the powder needs to be pelletized. Subsequently, in the extraction process, the solvent needs to soak or flush or rinse the dried products in plural cycle and stages, with solvent of oil content from high to low as the solid travels through the extractor (62).

The design of the extractor can be a horizontal bed extractor, rotary extractor or loop extractor. The prepared material enters the solvent extractor through a rotary air seal. Material is then spread across the width of the extractor evenly resting on a perforated plate or screen with suitable size to retain the solid. The solid travels from the inlet to the outlet of the extractor at a speed which can be varied depending on the feed rate.

The flow of the solvent is normally in counter-flow configuration as compared to the dried products flow. Solvent will be fed in from the top of the extractor above the material, and fed evenly across the width of the extractor to soak the dried products with solvent. The solvent is then collected at the bottom of the conveyor. Fresh solvent with low or zero oil content will be fed into the extractor at the material discharge end of the extractor. This low oil content solvent is used to extract the oil in the dried solids at the discharge end which also has low oil content. The oil content in the solvent increase from low to high as it flows from chamber to chamber in the direction against the material flow. The solvent will overflow from one chamber next due to the continuous feeding of fresh solvent at the material discharge end. The solid leaving the extractor will have an oil content of less than 1 %. At the same time, the miscella which is a liquid containing solvent with extracted oil will leave the extractor at the material inlet side with oil content of less than 10%. The miscella will undergo distillation (63) process to recover the oil, while the solvent recovered will be recycled to the extractor.

The solid leaving the extractor contains solvent which will also be recovered in a desolventising toaster (DT) (64). Inside the DT (64), the material will be subjected to continuous heating to evaporate the residual solvent contained therein. The dropping of the solid from one layer to the next creates some flipping effect which assists in the recovery of solvent. The vapor from DT contains high concentration of solvent and will be condensed with a condenser (65) to recover the solvent. Miscella, which is a liquid containing solvent and recovered oil, will be fed to the distillation section (63) where solvent will be evaporated from the liquid leaving behind the oil, and the solvent is recovered with another condenser (65). This operation can be multi-stage to gradually increase the concentration of oil as the liquid pass through the distillation apparatus. At the end of the distillation process, the oil is fully separated from the solvent (<100ppm). The quality of this oil may slightly deteriorate due to the exposure to heat from drying process and storage time before processing. But it is still a valuable product with at least 50% value of normal oil. The recovered solvent can be recycled back to the process again. The dried and de-oiled solid may contain less than 1 % of oil, 8-16% of protein and 10-25% of fiber. The solid can therefore be sold as one product or the many different fractions of it can now be sold separately for its high fibre value, high protein value or fertilizer nutrient value.

Although the present invention has been described in a specific embodiment as in the above description, it is understood that the above description does not limit the invention to the above given details. It will be apparent to those skilled in the art that various changes and modification may be made therein without departing from the principle of the invention or from the scope of the appended claims.

Claims

1 . A method for treating effluent produced from palm oil milling process, comprising the steps of:

removing solid (20) from the effluent, wherein the removed solid are formed into dried products;

removing water (30) from the effluent for reusing the water in the palm oil milling process;

extracting oil (40) from the effluent to form a residual sludge;

wherein the steps of removing solid, removing water, and extracting oil are carried out in sequential order of solid, water and oil.

2. A method for treating effluent produced from palm oil milling process according to claim 1 , wherein the effluent is palm oil mill effluent (POME).

3. A method for treating effluent produced from palm oil milling process according to claim 2, wherein the palm oil mill effluent (POME) comprises sludge after clarification or oil recovery process of sterilizer condensate, pressed liquid from fruitlet, and pressed empty fruit bunch liquor.

4. A method for treating effluent produced from palm oil milling process according to any of the preceding claims, wherein the method further comprises a pre-conditioning stage (10) to remove coarse fibrous solids, sands, and excessive solid, prior to the step of removing solid (20) from the effluent.

5. A method for treating effluent produced from palm oil milling process according to any of the preceding claims, wherein at least 50% - 90% of the suspended solid are removed from the effluent.

6. A method for treating effluent produced from palm oil milling process according to any of the preceding claims, wherein the removal of solid (20) is performed by using a method selected from the group comprising filtration, pressing, centrifugation, or any combination thereof.

7. A method for treating effluent produced from palm oil milling process according to any of the preceding claims, wherein the removal of water (30) is carried out by using evaporation.

8. A method for treating effluent produced from palm oil milling process according to claim 7, wherein the evaporation is a multi-effect evaporation which employs a plurality of evaporating units (31 ).

9. A method for treating effluent produced from palm oil milling process according to claim 8, wherein the sequence of the evaporating units is changed after a predetermined time or upon detection of a predetermined value of viscosity, moisture content, solid content, or oil content of the effluent in the evaporating units.

10. A method for treating effluent produced from palm oil milling process according to claim 9, wherein the sequence of the evaporators is changed by controlling the flow of effluent, vapor, and condensate in conduits interconnecting the evaporating units.

11 . A method for treating effluent produced from palm oil milling process according to claim 10, wherein the flow of effluent, vapor, condensate in the conduits is controlled by at least a valve coupled to the conduits.

12. A method for treating effluent produced from palm oil milling process according to claim 10 or 11 , wherein the conduits interconnecting the evaporating units are incorporated with at least a common header for forming at least a common inlet or at least a common outlet for the evaporating units to allow changing of the sequence of the evaporating units.

13. A method for treating effluent produced from palm oil milling process according to any one of claims 9 to 12, wherein the change of sequence of the evaporating units comprises switching at least a first evaporating unit in sequence with at least a last evaporating unit or at least a second last evaporating unit in sequence.

14. A method for treating effluent produced from palm oil milling process according to any one of claims 9 to 13, wherein the change of sequence of the evaporating units comprises switching at least a second evaporating unit in sequence with at least a last evaporating unit or at least a second last evaporating unit in sequence.

15. A method for treating effluent produced from palm oil milling process according to any one of claims 9 to 14, wherein the evaporating units are grouped into a plurality of groups with each group comprising at least two evaporating units adjacent to each other in sequence, and the change of sequence of the evaporating units comprises switching between the groups of the evaporating units.

16. A method for treating effluent produced from palm oil milling process according to claim 15, wherein the first group of the evaporating units in the sequence is switched with the last group of the evaporating units in the sequence.

17. A method for treating effluent produced from palm oil milling process according to any of the preceding claims, wherein at least 50% of the water is removed.

18. A method for treating effluent produced from palm oil milling process according to any of the preceding claims, wherein the extraction of oil (40) is carried out by using a method comprising heating the effluent, centrifugation of the effluent, feeding the effluent to a buffer tank, mechanically separating the oil layer in the buffer tank, or any combination thereof.

19. A method for treating effluent produced from palm oil milling process according to any of the preceding claims, wherein the extraction of oil (40) reduces the oil content in the effluent to less than 1 %.

20. A method for treating effluent produced from palm oil milling process according to any of the preceding claims, wherein the residual sludge is subjected to drying to form dried products, or recycling to the palm oil milling process, or a combination of both.

21 . A method for treating effluent produced from palm oil milling process according to claim 20, wherein all the residual sludge is subjected to drying, recycling, or a combination of both, without any discharge into the environment.

22. A method for treating effluent produced from palm oil milling process according to claim 21 , wherein no methane gas is released from the processing of the residual sludge.

23. A method for treating effluent produced from palm oil milling process according to any of the preceding claims, wherein the dried products from removed solid and residual sludge are subjected to solvent extraction (60) to recover oil in the dried products.

24. A method for treating effluent produced from palm oil milling process according to claim 23, wherein the solvent extraction comprises soaking the dried products with a solvent to extract oil from the dried products, collecting the solvent, and distillation of the solvent to recover the extracted oil.

25. A method for treating effluent produced from palm oil milling process according to claim 23, wherein the solvent extraction is carried out with the dried products placed on a perforated plate or screen with suitable size to retain the dried products inside an enclosed chamber and as the dried products travel from the inlet to a discharge end of the enclosed chamber on top of the perforated plate or screen, the dried products are provided with solvent of increasingly lower oil content towards the discharge end of the enclosed chamber.

26. A method for removing water from effluent produced from palm oil milling process, comprising:

performing multiple effect evaporation on the effluent with a plurality of evaporating units;

characterized in that the method further comprises changing the sequence of the evaporating units for performing the multiple effect evaporation.

27. A method for removing water from effluent produced from palm oil milling process according to claim 26, wherein the sequence of the evaporating units is changed after a predetermined time or upon detection of a predetermined value of viscosity, moisture content, solid content, or oil content of the effluent in the evaporating units.

28. A method for removing water from effluent produced from palm oil milling process according to claim 26 or 27, wherein the sequence of the evaporating units is changed by controlling the flow of effluent, vapor, and condensate in conduits interconnecting the evaporating units.

29. A method for removing water from effluent produced from palm oil milling process according to claim 28, wherein the flow of effluent, vapor, condensate in the conduits is controlled by at least a valve coupled to the conduits.

30. A method for treating effluent produced from palm oil milling process according to claim 28 or 29, wherein the conduits interconnecting the evaporating units are incorporated with at least a common header for forming at least a common inlet or at least a common outlet for the evaporating units to allow changing of the sequence of the evaporating units.

31 . A method for treating effluent produced from palm oil milling process according to any one of claims 26 to 30, wherein the change of sequence of the evaporating units comprises switching at least a first evaporating unit in sequence with at least a last evaporating unit or at least a second last evaporating unit in sequence.

32. A method for treating effluent produced from palm oil milling process according to any one of claims 26 to 31 , wherein the change of sequence of the evaporating units comprises switching at least a second evaporating unit in sequence with at least a last evaporating unit or at least a second last evaporating unit in sequence.

33. A method for removing water from effluent produced from palm oil milling process according to any one of claims 26 to 32, wherein the evaporating units are grouped into a plurality of groups with each group comprising at least two evaporating units adjacent to each other in sequence, and the change of sequence of the evaporating units comprises switching between the groups of the evaporating units.

34. A method for removing water from effluent produced from palm oil milling process according to claim 33, wherein the first group of the evaporating units in the sequence is switched with the last group of the evaporating units in the sequence.

35. A method for recovering oil from dried products from removed solids and residual sludge produced from drying of palm oil mill effluent, comprising performing solvent extraction on the dried products.

36. A method for recovering oil from dried products from removed solids and residual sludge produced from drying of palm oil mill effluent according to claim 35, wherein the solvent extraction comprises soaking the dried products with a solvent to extract oil from the dried products, collecting the solvent, and distillation of the solvent to recover the extracted oil.

37. A method for recovering oil from dried products from removed solids and residual sludge produced from drying of palm oil mill effluent according to claim 36, wherein the solvent extraction is carried out with the dried products placed on a perforated plate or screen with suitable size to retain the dried products inside an enclosed chamber and as the dried products from the inlet to a discharge end of the enclosed chamber on top of the perforated plate or screen, the dried products are provided with solvent of increasingly lower oil content towards the discharge end of the enclosed chamber.