FRUIT BUNCHES

TECHNICAL FIELD

The present invention relates to a method for continuous processing of oil palm fresh fruit bunches (FFB) in palm oil mills, and more particularly to a method for continuous sterilisation of FFB to render them amenable to the extraction of palm oil and palm kernels by downstream processes in the palm oil mill.

BACKGROUND ART

The sterilisation process is one of the key processes in the palm oil mill. Fresh fruit bunches (FFB) are cooked using steam to: (i) deactivate the oil-splitting enzymes to prevent an increase in free fatty acid; (ii) loosen the fruit in the bunch to facilitate the stripping process; (iii) soften the fruit pulp for easier further treatment of the fruit during digestion and pressing; (iv) heat and partially dehydrate the nuts in order that the nuts may be cracked more readily; (v) coagulate the protein in oil bearing cells and prevent the formation of colloidal complexes to facilitate the separation/clarification of the oil in the oil recovery process; and (vi) hydrolyse/decompose the mucilaginous material to also facilitate the oil clarification process. The close-knit arrangement of oil palm fruits in FFB makes steam penetration to the inner layers of the bunch difficult.

In the conventional sterilization process, it is necessary to use steam at a pressure of 3 bar and multiple-peak sterilization cycle to facilitate deaeration and steam penetration into bunches. The FFB are loaded into fruit cages that are then transported to the sterilizers. The sterilizers are horizontal steam autoclaves of cylindrical shape of approximately 2 metres diameter. Loading and unloading the sterilizer is by rail. Sterilization is usually carried out using a triple peak sterilization cycle, which requires about 75 to 90 minutes for completion. An additional 10 to 30 minutes may be required for loading and unloading the sterilizers. It will be realised that the prior art process of sterilisation is carried out in a batch-wise manner. There are numerous short-comings and disadvantages in this system. In addition to the sterilisers, cages are needed to contain and transfer bunches in and out of sterilisers, and equipment such as overhead cranes, tippers, conveyors, transfer carriages, tractors, capston and wire rope, and rail tracks are needed for the handling of the cages.

In view of the problems faced with the handling of fruits in the conventional batch sterilization process, a method for continuous sterilization has been developed as described in Malaysian Patent MY-121530-A. In this method, the fresh fruit bunches are first crushed to facilitate steam penetration into inner layers of the fruit bunches and then heated at atmospheric pressure in a single heating step using saturated steam to an extent sufficient to facilitate stripping of the fruits. Since the main objective of heating using this method is to facilitate stripping of fruits from bunch stalks, it is only necessary for the steam to penetrate to the points of attachment of fruits to stalks so that hydrolysis of the binding tissues can occur. The heating time required for this is generally less than 90 minutes. To attain this retention time in a steam-heated continuous sterilisation chamber, the bunches are moved initially forward and then backwards using a double-deck scraper conveyor. The heating time is not extended beyond 90 minutes to achieve the other known objectives of the sterilization process because of concerns about the mechanical reliability of the conveying system. Increased product loading and high temperature can cause the chain to elongate and this increases the likelihood of the chain disengaging from the sprocket. It is, therefore, timely to consider the introduction of a new system that addresses and overcomes the weaknesses of all prior systems proposed for the sterilization of FFB to facilitate the continuous extraction of palm oil and palm kernel in palm oil mills. DISCLOSURE OF THE INVENTION

It is an objective of the present invention to provide a simple and cost-effective method for continuous extraction of palm oil and palm kernels based on continuous sterilisation.

It is a further objective of the present invention to provide a simple and cost- effective method for continuous sterilization that is less susceptible to breakdowns due to chain breakages and derailments compared to the prior art method.

It is a further objective of the present invention to provide a method for continuous sterilization that facilitates more effective cooking of the FFB compared to the prior art method. The above objectives are achieved in the present invention by a method for continuously sterilization of oil palm fresh fruit bunches (FFB) comprising the steps of:

(a) feeding the FFB to a bunch conditioner to produce conditioned bunches to enhance steam penetration into inner layers of the FFB; and (b) heating the conditioned bunches using live steam while they are conveyed continuously and progressively;

The heating in step (b) above is characterised in that it is a two-step process where the conditioned bunches are heated in a first heating step to raise the temperature of the bunches to the steaming temperature, and are further heated in a second heating step to cook the bunches to facilitate extraction of palm oil and palm kernels by downstream processes.

The FFB are fed to a bunch conditioner to facilitate heating using live steam at atmospheric pressure. The bunch conditioner disrupts the close-knit arrangement of fruits in the FFB to facilitate steam penetration into the FFB. The bunch conditioner that is most suitable for this application is the double-roll bunch crusher. This crusher consists of two parallel contra-rotating rollers at slightly different speeds. The FFB are drawn through the gap between the rollers by the inward rotation of the rollers. The FFB are squeezed and deformed as they pass through the crusher and this disrupts the close-knit arrangement of the spikelets. The shearing induced by the difference in rotating speeds of the rollers also leads to tearing, and a significant percentage of bunches are tom into two or more pieces. An advantage of using the double-roll crusher is that the crushing can be achieved in a manner that minimises the bruising of fruits and the breakage of nuts.

Although the bunches discharged from the bunch conditioner may be heated using a plurality of heating means operating in series, there are two distinct heating steps in the new process. Ideating during the first heating step is specifically aimed at quickly raising the temperature of the bunches to the steaming temperature, whereas heating during the second heating step is specifically aimed at ensuring that the bunches are sufficiently cooked. Heating during the second heating step may be carried out for a sufficiently long time for hydrolysis of the binding tissues at the points of attachment of fruits to the bunch stalks to be completed to facilitate complete, or almost complete, subsequent stripping of the fruits from the bunch stalks. Alternatively, heating during the second heating step may be extended to ensure that the other objectives of heating the oil palm fruits to facilitate oil and kernel extraction are also partially or completely achieved. If the heating of the oil palm fruits during the second heating step is insufficient, the fruits are further heated using a third heating step after they have been stripped from the bunch stalks.

The main difference between the present invention and the prior art method (Malaysian Patent No. MY-121530-A) for continuous sterilisation is the use of two steps for heating bunches in the present invention, compared to the use of a single step or a plurality of identical heating means operating in series in the prior art method. The use of the two-step process provides the flexibility to use more than one heating method to address the shortcomings in the prior art method. Another significant difference between the present invention and the prior art method (Malaysian Patent No. MY-121530-A) for continuous sterilisation is the use of either saturated steam or superheated steam for heating. This will not make any difference on the method used for the first heating step, but it can have a significant impact on the method used for the second heating step. It can also have an impact on the heating time required.

According to a preferred embodiment of the present invention, the bunches discharged from the bunch conditioner are heated in the first heating step using either saturated or superheated steam while they are conveyed continuously and progressively through one or more heating means in a manner that facilitates quickly raising the temperature of the bunches to the steaming temperature. The thickness of the bunch layer inside each heating means should not be greater than the height equivalent of three bunches stacked end-to-end as this will impede steam penetration and prolong the heating time. The bunches are conveyed through the heating means using mechanical conveying means such as scraper chain conveyors, screw conveyors or belt conveyors. The system may be designed to facilitate heating using a plurality of heating means, or a multi-deck conveyor inside a single heating means.

According to another preferred embodiment of the invention, the bunches discharged from the first heating step are heated in the second heating step using saturated steam while they are conveyed continuously and progressively through one or more heating means in a manner that facilitates maintaining the bunches at the steaming temperature. Since the bunches have already been heated to the steaming temperature in the first heating step, it is only necessary to maintain the temperature of the bunches at the steaming temperature long enough for the bunches to be cooked. Compared to the first heating step, the steam consumption required for the second heating step can be significantly reduced by effectively insulating the heating means to minimize heat losses. Other methods of heating the bunches can be used that are more suitable than the method used for the first heating step for extending the overall heating time beyond 90 minutes. For example, the heating means may be specifically adopted to facilitate stacking bunches to much greater heights than that used for the first heating step and the bunches may be conveyed through the heating means using mechanical conveying means only or a combination of gravity and mechanical conveying means. A mechanical conveying means that can be advantageously applied for conveying the bunches inside the heating means if saturated steam is used for the second heating step is an apron conveyor. In this method, the bunches may be stacked to much higher heights than that used for the first heating step and conveyed in one direcdon only. The use of multi-deck conveyors for conveying the bunches inside the heating means, as proposed in the prior art method, is not necessary. This will lead to significant improvement in the mechanical reliability of the conveyor chains. The proposed conveyor design ensures that the product is always pulled towards the drive end. This is inherently a better conveyor design as it significantly reduces the possibility of sprocket disengagement due to pushing of product. The use of an apron conveyor instead of a scraper conveyor implies that no force is directly applied to the bunches for conveying. This will minimize oil loss and iron pick-up and wear and tear of the apron plates. By using side boards, the carrying capacity of the apron conveyor can be significantly increased. By avoiding the use of scraper bars, the apron conveyor is also made more reliable and less susceptible to breakdowns due to snags. By isolating the conveyor chain from the bunches being conveyed using the side boards, the chain is free from wear and tear by abrasive material such as sand.

According to another preferred embodiment of the present invention, gravity is used for conveying the bunches through the heating means used for the second heating step that is heated using saturated steam. The heating can be achieved using either a vertical or a slightly inclined vessel to facilitate the passage of bunches through the vessel by gravity. To facilitate continuous flow of bunches through the heating means using gravity, the discharge of cooked bunches out of the heating means is assisted mechanically using either shafted or shaftless screw conveyors. This provides a simple, robust and cost- effective conveying system for extending the retention time beyond 90 minutes and the use of the extremely long drive chains, as proposed in the prior art method, is avoided. The method is suitable for use in both low and large capacity palm oil mills, if there is a need to reduce the foot print. The use of a tall vessel can lead to excessive pressure build- up at the base of the vessel, which can lead to oil being released from the cooked bunches and eventually lost with the condensate and empty bunch stalks. This problem can be minimized by carrying out the headng using multiple vessels operating in series or by using inclined vessels instead of vertical vessels.

According to another preferred embodiment of the present invention, the bunches are heated in the second heating step using superheated steam in heating means that is specifically adopted to facilitate good contact between the steam and the bunches, as in the first heating step. Superheating the steam to a temperature in the range 140°C to 200°C prior to its use for continuous sterilization provides various benefits. The use of superheated steam implies that the bunches will be momentarily subjected to temperatures higher than the saturated steam temperature. It is expected that the steam temperature will quickly drop to the saturated steam temperature when it is in contact with the bunches, hence the need to have good contact between the steam and the bunches. The effectiveness of heating using superheated steam will depend on how well the superheated steam is distributed inside the heating means. Distributing the superheated steam using multiple steam injection points along the conveying path implies that the bunches will be repeatedly subjected to heating using superheated steam, thus multiplying the benefits of heating with superheated steam. The system may be designed to facilitate heating using a plurality of heating means, or a multi-deck conveyor inside a single heating means.

It has been observed that heating the bunches using superheated steam in the manner described above leads to improvements in cooking effectiveness, thus shortening the steaming time required. Another benefit that has been observed is less condensate formation. The improvement in cooking effectiveness leads to better bunch strippability and lower oil losses from downstream processes in the palm oil mill. There will also be less need for further heating of the fruits after they have been stripped from the bunch stalks using a third heating step.

The reduced condensate formation during the sterilization process could be due to the higher enthalpy of the superheated steam compared to saturated steam. Nevertheless, a significant amount of steam may be lost before it condenses due to steam leakages from the continuous sterilization system, making the overall steam consumption for sterilization higher if superheated steam is used. Another disadvantage of using superheated steam is the additional cost incurred for superheating the steam. To minimize the superheated steam consumption and costs, one option is to only use superheated steam for heating in the heating means used for the second heating step.

If the extent of cooking of the oil palm fruits carried out while they are still attached to bunch stalks is insufficient, the fruits can be further heated after they have been stripped from the bunch stalks using live steam in a third heating step. According to another preferred embodiment of the invention, the fruits are conveyed through the heating means used for the third heating step using a combination of gravity and mechanical conveying means. The fruits would already have been considerably cooked by prior processes, and the additional retention time and steam consumption required for the third heating step is expected to be small. The steam condensate will be trapped with the fruits and transferred to downstream processes, thereby minimizing oil loss. A set of expeller arms, similar that used in digesters in a palm oil mill, should be sufficient to facilitate discharge from the heating means.

The present invention has clear advantages over the traditional batch sterilization process where fruit bunches are transferred in and out of the sterilizers necessitating the use of cages for holding the bunches, rails, conveyors and cranes, among others. The present invention is more environmentally friendly as there is less energy usage, less oil loss and better oil quality. The present invention is also more cost effective and safer as it is highly automated and therefore requires less labour. The present invention also makes it cost-effective to build and operate small and mobile mills at a fraction of the cost of conventional mills to process small quantities of fresh fruit bunches from smallholders.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates schematically the preferred embodiment of the present invention.

Figures 2 and 3 illustrate schematically specific examples showing the application of different heating means used for the second heating step.

In describing the preferred embodiments of the invention, which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

MODES FOR CARRYING OUT THE INVENTION

Figure 1 illustrates schematically our invention for a method for continuous sterilization of oil palm fresh fruit bunches (FFB). The FFB is stored in FFB hoppers when it is delivered to palm oil mills. The FFB can have a high trash content due to mechanization of fruit collection in the field. The high trash content can lead to increase in the operating and maintenance costs of the machinery used for continuous sterilization, as well as other critical machinery in the palm oil mill.

Referring to Figure 1, the FFB 100 discharged from FFB hoppers is optionally treated using one or more screening means 101 to reduce its trash content. The use of screening means 101 generates two phases. One phase is trash 102 that is easily disposable. Another phase is screened FFB 103 with significantly reduced trash content. Equipment that can be used for this purpose are rotary drums, vibrating screens and slots in FFB conveyors. FFB 100 or screened FFB 103 is fed to bunch conditioner 104 to disrupt the close-knit arrangement of fruits in the FFB and to downsize some of the FFB into two or more pieces to facilitate the heating process. The bunch conditioner that is most suitable for the present application is the double-roll crusher. This crusher consists of two parallel contra-rotating rollers at slightly different speeds. An advantage of using the double-roll crusher is that the bunch conditioning can be achieved in a manner that minimises bruising of fruits and breakage of nuts.

The conditioned bunches 105 are continuously fed using pre-heating conveyor 106 to the first heating step 110. Pre-heating conveyor 106 is steam-sealed and the conditioned bunches fed to the first heating step 110 through steam lock 108. The steam lock 108 could be a rotary valve, flap valve, a screw feeder, or some other device that is adopted for this purpose. To minimise steam loss, the length of pre-heating conveyor 106 should preferably allow a retention time sufficient for the complete condensation of the steam that escapes from the first heating step 110.

Pre-heating 106 facilitates heating the conditioned bunches 105 immediately after they have passed through bunch conditioner 104 to a temperature above 60°C to deactivate the lipolytic enzymes responsible for the formation of free fatty acid. Pre- heating 106 also facilitates deaeration and minimizes the amount of air that enters into subsequent processing steps, thereby ensuring that the temperature in subsequent processing steps is close to the saturated steam temperature. By utilizing the steam that would otherwise be wasted, pre-heating helps to minimize the overall steam consumption. The use of an inclined conveyor for conveying the conditioned bunches 105 upwards will facilitate the removal of the condensate generated during pre-heating 106 in a downward direction to ensure that bunches fed to the first heating step 110 is free of condensate. Condensate that is carried over to the first heating step 110 from pre-heating step 106 is not so easily removed. This may reduce the effectiveness of heating using live steam and may also lead to higher oil loss with the condensate. Conditioned bunches 105 are heated during the first heating step 110 using live steam 111 while they are conveyed continuously and progressively through a heating means. According to a preferred embodiment of the invention, the heating can be achieved using either saturated or superheated steam. The steam is superheated to a temperature in the range 140°C to 200°C before it is used. Since the main objective of the first heating step 110 is to facilitate quickly raising the temperature of the conditioned bunches 105 to the steaming temperature, the method used is the same for both types of steam. The thickness of the bunch layer inside the heating means is limited to a maximum of three bunches, stacked end to end, to enable steam to easily penetrate the bunch layer. The bunches are conveyed through the heating means using mechanical conveying means such as scraper chain conveyors, screw conveyors or belt conveyors. The system may be designed to facilitate heating using a plurality of heating means, or a multi-deck conveyor inside a single heating means. The bunches 112 leaving the first heating step 110 then enter the second heating step 113 where it is heated using live steam 114. As with the first heating step, the heating can be achieved using either saturated steam or superheated steam.

If saturated steam is used for heating the bunches in the second heating step 113, the heating means may specifically be adopted to facilitate stacking the bunches to heights much greater than that used in the first heating step. Since the bunches have already been heated up to the steaming temperature using the first heating step, it is more important during this step to maintain the bunches at the steaming temperature for a long enough period for the cooking to be completed to facilitate the extraction of palm oil and palm kernels by downstream processes in the palm oil mill. The bunches are conveyed through the heating means using mechanical conveying means only or a combination of gravitational and mechanical conveying means.

If superheated steam is used for heating the bunches in the second heating step 113, the heating means may specifically be adopted to ensure good contact between superheated steam and the bunches, as in the first heating step. The steam is superheated to a temperature in the range 140°C to 200°C before it is used. The use of superheated steam implies that the bunches will be momentarily subjected to temperatures higher than the saturated steam temperature. The steam temperature will quickly drop to the saturated steam temperature when it is in contact with the bunches. To improve the effectiveness of heating, the superheated steam is distributed inside the heating means using multiple steam inlet points along the conveying path of the bunches so that the bunches will be in contact with superheated steam for a longer period, thus multiplying the benefits of heating with superheated steam. The system may be designed to facilitate heating using a plurality of heating means, or a multi-deck conveyor inside a single heating means. The cooked bunches 115 are eventually discharged to post-heating conveyor 118 that is adopted to facilitate post-heating of bunches by utilizing the steam that escapes from the second heating step 113. As in the case of pre-heating step 106, by utilizing the steam that would otherwise be wasted, post-heating step 118 helps to minimize the overall steam consumption. The cooked bunches 115 are discharged to post-heating conveyor 118 through steam lock 116 that is similar in design to steam lock 108 to minimize steam leakages.

Stripping 120 is carried out using a drum stripper to lift and drop the cooked bunches several times to shake out the fruits. The bunch stalks 121 leaving the drum stripper may be further stripped using a second-stage drum stripper or a beater stripper and provision may be made for recycling partially stripped bunches.

Stripped fruits 122 leaving stripper 120 may be further heated using third heating step 123 to optimize the extraction of palm oil and palm kernels by downstream milling processes. The fruits are conveyed by gravity through a cylindrical- shaped vessel and discharged using a set of expeller arms mounted to a central drive shaft, similar to that used with digesters in palm oil mills.

Figure 2 illustrates schematically one preferred embodiment of the present invention, wherein the second heating step is carried out using an apron conveyor. In this mode, the bunches 200 discharged from the heating means used for the first heating step are further heated in a second heating step using saturated steam. The bunches 200 enters the rectangular box-shaped vessel 202 used for the second heating step through inlet chute 201 and falls onto apron conveyor 203. The length of the vessel 202 and the apron conveyor 203 are adjusted to suit the retention time required. The vessel 202 is properly insulated to minimize heat losses and heated using steam injection points mounted to steam distribution pipe 208 located above apron conveyor 203. The bunches are stacked to much higher heights than that used for the first heating step and conveyed in one direction only using apron conveyor 202. The apron conveyor consists of a continuous line of pans or slats, with beaded front and rear edges, which overlap to form a steel belt when mounted on two or more strands of chain. The apron conveyor can have pans mounted on roller chains with extended side bars to form the ends of the pans. With the addition of skirt plates or side boards, they can be designed to handle large capacities. Specially designed roller chains with outboard-mounted rollers can be used for ease of maintenance. Outboard rollers can be supplied with either plain bearings or bushes. Figure 3 illustrates schematically another preferred embodiment of the present invention, wherein the second heating step is carried out using a vertical silo-type vessel to facilitate the passage of bunches through the vessel by gravity. In this mode, the bunches 300 discharged from the first heating step are further heated in a second heating step using saturated steam. The bunches 300 enters the silo-type vessel 302 from the top through inlet chute 301 and leaves from the bottom. The top of vessel 302 is covered to minimize steam losses. The vessel 302 may either have a rectangular or cylindrical shape and the height of the vessel is adjusted to suit the retention time required. The vessel 302 is properly insulated and heated using multiple steam injection points from the side of the vessel. To ensure continuous flow through the vessel 302, the displacement of cooked bunches out of the vessel must be achieved mechanically using one or more screw conveyors 304 located at the bottom of the vessel. This provides a simple, robust and cost-effective conveying system for heating bunches, and the use of the extremely long drive chains is avoided. The embodiments of the invention described herein are only meant to facilitate understanding of the invention and should not be construed as limiting the invention to those embodiments only. Those skilled in the art will appreciate that the embodiments of the invention described herein are susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications which fall within the scope of the inventive concept thereof.

INDUSTRIAL APPLICABILITY

The present invention finds ready industrial applicability in the palm oil industry as it is a method for continuous processing of fresh fruit bunches that facilitates radical changes in the design and operation of palm oil mills. Mills using the new method can be operated at close to steady-state conditions, making possible significant reduction in manpower, facilitating automation and minimizing the loss of palm oil and palm kernel. By eliminating the use of sterilizer cages, rail tracks, overhead cranes, tippers, transfer carriages and tractors, it also provides significant savings in operating and maintenance costs.