2.2.1 Oil palm fruit

(see Flowsheet 1)

In West Africa, specialized groups can be found when larger quantities of oil palm fruit have to be processed. These groups are well organized and have been reported to be able to process 3-6 drums (450-900 kg) of fruit per day, using traditional methods.

Handpresses

The main drawback of the traditional process with its large water consumption, has been eliminated by the use of presses. These were initially modified wine presses, e.g. the so-called “Duchscher" curb press, which was at one time built in Luxembourg.

Figure 9: Duchscher Curb Press

Only in Nigeria were these presses made available as privately owned service mills all over the country. The owner of the fruit could come with his fruit and his crew to use the equipment of the mill (as boiling drums, pounding mortar, the press and a clarification drum) or he could bring the fruit to have it processed by the mill. In this last case the owner of the mill would process the fruit with his family. Later on hydraulic presses were introduced but not accepted.

Elsewhere, groups working in the field of Appropriate Technology, took up the design of presses to be manufactured from locally available materials. These groups are for example TCC (Technology Consultancy Centre, Kumasi, Ghana), who designed a press with the spindle in the centre, and ENDA (Environnement et Developpement du Tiers Monde, Dakar, Senegal), who adopted an already existing design for dissemination. Other countries from which activities have been reported are Cameroon, Liberia, Sierra Leone, and Togo.

Hand presses make the traditional process simpler (see Flowsheet 3). However, the need for intensive pounding remains. In order to facilitate the pounding step, KIT (Koninklijk Instituut voor de Tropen, Amsterdam, the Netherlands) has introduced the reheating step, during which the fruit pulp is completely digested. Pounding is only required to remove the pulp from the nuts. The actual digesting of the fruit is carried out by steaming, during which the cell walls are weakened, the protein in the cells denatured and the micro oildroplets, as originally present in the cells, combined to larger droplets, which are more easily pressed out.

Flowsheet 3 Usual Process for Oil Palm Fruit with Hand Press

1 Steaming is advised to prevent the decomposition of intercellular cement.
2 Pounding can be mechanized for example with the TTC palm fruit pounder.
3 To be carried out with any press, sturdy enough to press mixtures of nuts and fibre (see 5.1).

A complete process has been designed, starting with the steam sterilization of the bunches to the final drying of the oil, to improve upon its storage properties. When the fruit is cooked in water, the intercellular cement dissolves, giving a suspension of cells (still intact), from which it is difficult to obtain the oil. This problem is avoided by the designed steam sterilization process. To be able to process aura oil palm fruit with a good recovery, fibre has to be recycled and mixed into the mass to be pressed, to prevent the nuts from touching. As the ratio of fruit pulp to nuts in Tenera fruit is higher, it can be processed without recycling the fibre. However, to obtain maximum oil recovery, it is recommended to reheat and press the fibre (or the fibre/nut mixture) a second time. The complete process, including all process steps, is presented as Flowsheet 4. With this process it is possible to keep apart small quantities to be processed separately; an advantage, because generally women do not want to have their own fruit mixed with that of others.

Flowsheet 4 KIT Process for Oil Palm Fruit with Hand Press

1 When processing aura oil palm fruit it is advisable to reheat the recirculated fibre. This is, however, sometimes very complicated. In that case the fibre can be mixed in immediately before pressing. When processing Tenera oil palm fruit reheating is required in case the fibre (or fibre/nut mixture) is reprocessed.

2 When processing aura oil palm fruit, recirculation of fibre is required to prevent the nuts from touching.

3 To be carried out whith any press, sturdy enough to press mixtures of nuts and fibre.

Details on an oil palm processing project in Togo using this system are given in Chapter 3.

Although the KIT process can improve much upon the oil recovery, this process is not appreciated everywhere. Some reasons are:

- the large quantity of fibre to be recirculated in the case of fruit with an extremely low pulp content;
- the loss of the possibility to obtain a valuable sludge to be used for food.

To overcome these drawbacks, while still improving workload and oil recovery, a semi-traditional process was introduced for instance in The Gambia and Guine Bissau. It includes the traditional separation of fibre, oil-containing cream and nuts in water. The fibrous material however is subsequently steam-heated and pressed. The cream is boiled for oil and sludge, as traditionally.

Mechanized systems

Mechanized systems become feasible when really large quantities are involved and regular processing is possible. The first step to be mechanized is the pounding. TCC has developed a horizontal mechanically-driven pounding machine (see Figure 10). This machine is continuously operated by feeding cooked fruit at one side. Digested fruit, ready for pressing, is produced at the other. The capacity of the pounding machine is 100 kg per hour. TCC supplies a steam sterilization kettle and a clarification kettle as well.

Figure 10: Palm Fruit Pounder (TCC)

The nominal capacity of the TCC system, equipped with a steam sterilization kettle, a pounding machine and two hand presses is 600 kg tenera fruit per day (giving about 144 kg or 24 % of oil). It can be estimated that at least 8 women are required, the equivalent of 8x8 working hours.

Even more than 40 years ago, the French firm “Pressoirs Colin" developed a continuously working press that carried out the actions of digesting and pressing at the same time. This press was originally meant to be operated by two men. However, it has appeared to be far too heavy for continuous manual operation. When engine driven, this press is an interesting possibility, particularly for the processing of tenera fruit on a relatively large scale. In Cameroon, APICA developed a press, based on the same principles. This press is called the “CALTECH" (see Figure 11).

Figure 11: CALTECH Oil Press (APICA) (manual version)

APICA started with a manual version. This press appeared much too heavy as well. It could not be operated by the same men for more than half an hour. Its nominal capacity is 100 kg per hour. The motorized version (2.3 hp = 1.7 kW) has a capacity of 200 kg per hour. The motorized version of the “COLIN" press, presently on the market as the press SPEICHIM M-10 (4.5 hp = 3.3 kW) has a nominal capacity of 300 kg per hour.

Oil recoveries, reported for the traditional process, the KIT process, the CALTECH and the COLIN expeller, are given in Table 8.

Table 8: Palm Oil: Oil Recoveries Obtained with Different Processes and Equipment

1 Source: Traut, G. Use of Colin Press for Traditional Palm Oil Processing. In: Report of the First African Small-Scale Palm Oil Processing Workshop, NIFOR, Benin City, Nigeria 12-16 October 1981, FAO, Rome 1982.

2 Source: UNATA, Report on comparative tests for COPROCO, 1986.

3 Source: KIT, Report on feasibility tests for CONGAT, 1986.

4 ()=Calculated on the basis of fruit to bunches ratio=0.64