3.4. OIL EXPELLING MACHINES

3.4.1. Batch type hydraulic jack operated oil expeller

The batch Cottage level oil expeller (Photo 16) is operated by a 10 MT Hydraulic Jack. The expeller unit, consists of a hollow cylinder made out of stainless steel, a piston, a handle, a pressure indicator gauge and a mounting frame to house all the above. The amount of crushed seed kernel that the expeller can accommodate per batch is 1.5 - 2 kg. After loading a batch into the cylinder the piston (in the form of a circular disc)- which is fitting quite perfectly with the inner walls of the cylinder with minimum clearance and is attached to an arm - is pressed by a hydraulic jack. This forces the oil to be expelled from the feed through the perforated holes. The oil is then collected for filtration and further processing. After complete expulsion, the hydraulic press is released and the residue cake is removed from the cylinder for further processing. The whole operation takes about 30 - 45 minutes per batch.

3.4.2. Continuous Screw Expeller

The first stage of oil expelling is pre-pressing, using a high pressure continuous screw press called the expeller. Continuous screw expellers have a rotating screw inside a horizontal cylinder (barrel) that is made out of mild steel with 1 - 0.05 mm slots in each 25mm. (The discharge end is open and clearance can be adjusted to suit different kind of raw material.) The screw forces the seeds through the cylinder, gradually increasing the pressure on the crushed seed pulp, slowly moving it to the discharge end. The material gets heated due to friction and the oil escapes from the cylinder through small slots while operating the machine, and pressed residue emerges from the end of the cylinder.

First stage of extraction is pre-pressing; that is passing the crushed raw material through the continuous screw expeller in order to preheat the sample. The pressure can be adjusted to suit different kinds of seeds in order to get the highest oil yield. Two or three passes might be required depending on the type of raw material. Extracted oil is filtered, and the material removed from the oil is fed back into the stream (new batch) along with the fresh material. The material which is finally discharged from the pressure residue is called 'pressed cake' (poonack).

The screw type expeller was selected for seed oil expelling at the Gurugoda site.

3.4.3. Reasons for selection of the Continuous Screw Expeller

The capacity of a continuous screw expeller is approximately 4.5. litres/hr. for domba seed oil, 2.5 litres/hr. for rubber seed oil, 2.25 litres/hr. for neem seed oil and 3.00 litres/hr for jatropha seed oil. The batch type hand operated oil expeller's capacity is approximately 2.0 litres/hr for domba seed oil and 0.75 litres/hr for jatropha seed oil. Thus, the continuous screw expeller can be recommended for the project site.

3.4.4. Oil from Pressed Cake

After expelling the seeds, it is necessary to use solvent extraction to get the final traces of oil from the pressed cake. Solvent extraction is a 'high technology' process that has to be carried out on a comparatively large scale. Capital costs are high. Essentially the process is one of continuous counter-current extraction with the raw material flowing in one direction against a solvent; usually hexane. The crude oil then passes on for refining. For the present study it was therefore decided not to extract the oil from the press cake but to use the oil within the press cake for uses such as candles, biogas feed stock etc.

3.5 EXPELLING

3.5.1 Jatropha seeds expelling

Jatropha fruits are mechanically / manually de-hulled. From the fruits the extracted jatropha seeds have a thin hard shell, (Photo 17) which can directly be fed to the eontinuous expeller at the NERDC.

The oil content in jatropha seeds (with seed cover) is reported to be in the range of 30 - 50% by weight of the seed and ranges from 45 - 60% weight of the kernel itself.

Jatropha seeds expelling using Continuous Screw Expeller

Jatropha seeds collected from Practical Action were expelled with seed cover. Approximately 16 - 17% w/w oil was recovered. As a mechanical extraction method was only used for oil extraction, the oil content recorded here was comparatively less than that reported in literature. Some oil might have been lost in the expeller and the seeds were very old. The efficiency of extraction depends on the moisture content of the nuts and the percentage of shell present. The best yields are obtained with 8 - 9%(w/w) moisture. Trial tests were limited, mostly due to a lack of raw materials.

Another sample of fresh seeds (fresher than the earlier batch collected by Practical Action) was collected from near the NERDC premises and manually de-hulled to get kernel. The solvent extraction from this second sample of jatropha seeds kernels gave a 43 - 44% w/w oil yield from the seed sample.

3.5.2. Neem Seeds Expelling

Approximately 16 - 17% w/w oil was recovered from neem without removing seed cover. Whole dried seeds directly passed through to the expellers.

A sample of fresh seeds was collected from Dambulla area and tested for total available oil content. The solvent extraction from this sample of neem kernels gave a 38 - 39% w/w oil yields from the seed sample.

The results obtained are higher as the samples are fresher than the samples used earlier. Due to its bitter taste, the pressed cake generated after extraction of the oil from neem seed has no value for animal feed.

3.5.3. Extraction of Castor Oil

Extraction of oil from castor seeds was done using a similar method as used for most of the other oil seeds. At the beginning direct expelling was done but the yield was very poor. However, oil yield can be increased by steaming and drying the seeds prior to expelling.

Based on literature, the following method was also tried. 3 Anon. No date. Principles of Oil Extraction Publishing. 11.p., available at www.itdgpublishing.org.uk The ripe seeds were allowed to dry to enable them to split open naturally. These seeds were then cleaned, cooked and dried prior to extraction. Cooking was done to coagulate protein (which is necessary to permit efficient extraction) and to free the oil for efficient pressing. This method can only be applied to castor seeds (from the seeds studied). The castor seeds collected from Practical Action were expelled with their seed cover. Approximately 17 - 18% w/w oil was recovered from castor seeds.

3.5.4. Rubber seeds expelling

All the seeds other than rubber seeds can be expelled with their seed cover. At least partial de-hulling is required before the expelling of rubber seeds. Rubber seeds were collected from Practical Action. De-hulling was done at NERDC using a rubber roll sheller with some small adjustment to the rubber rollers. The rubber roll sheller can be driven by coupling it to a two wheel tractor. Foreign particles were removed and seeds were separated from the shells before oil expelling. A single phase, screw type expeller was used for expelling. The best yields are obtained with 8 - 9% moisture and 15 - 20% shell. The kernel makes up 54 - 60% of the rubber seed weight depending on the moisture content.

For rubber seeds the seed cover percentage is comparatively higher than that of the other seed varieties. The study showed that the process of rubber seed extraction could be considerably improved by adding rice husk which improves the friction between particles.

3.5.5 Domba Seeds Expelling (Calophyllum inophyllum)

Domba is a non-edible oil bearing plant. The fruit (the ballnut) is round, reaching 2 to 4 cm in diameter and having a single large seed. The seed has a soft shell and is much richer in the quantity of extractable oil than most of the other seeds. The available oil content is 60-64% w/w oil and 50-54% can be extracted.

The nuts should be well dried before cracking, after which the oil-laden kernel should be further dried. The seeds yield a thick, dark green oil for medicinal use or hair grease. This oil is also suitable for biodiesel processing.

3.5.6. Karanda (Pongamia pinnata) seed expelling

Pongamia oil is a non-edible oil extracted from seeds of Pongamia pinnata. Each pod bears a single seed. The average fresh weight of a matured seed is 1.2 gm.

Seed oil has many traditional uses as well as being resistant to pests. The oil content is 25 - 30%, however by using the continuous screw type expeller only 5 - 7% w/w oil can be extracted.

3.5.7 Summary of Seed oil extraction test

3.6 OIL CLARIFICATION

After extraction, the oil is clarified to remove contaminants such as fine pulp, water and resins. Raw oil can be clarified by allowing it to stand undisturbed overnight and then removing the upper layer which is called crude oil. The crude oil requires further filtering before processing into biodiesel. After removing the upper layer of the oil, the sedimentation (oil + fine particles) is taken from the bottom part of the container for further separation oil. The sedimentation part requires quick separation because trace amounts of moisture remains in the sludge.

The first step, crude oil was transferred to a Gravity Filter (Photo 28) which was fabricated at the NERDC workshop for fine filtering. The total height of the unit is about 2 meters. Oil filtration takes place under hydrostatic pressure through a 100% polyester filter cloth bag (triple layer, 45cm height, 8 - 10 cm wide bag which is attached to the lower end of the pipe). After separation of crude oil and sludge, the oil is poured into the Gravity Filter and the filtered oil is immediately taken for the refining process to avoid it getting rancid.

Further investigations showed that after gravity separation of oil from pulp, the fine particles remaining at the bottom of the cloth bag also need to be taken for oil separation (Photo 29). Therefore as the second step, a quick separation process was developed to separate the remaining oil in the sediment from the oil settling container and fine particles in the cloth bag (Photo 29). In this second step, the sedimentation was put into a suitable type of cloth bag (preferably double layer raw cotton of size 45cm height and 8cm diameter). The bag is then placed in the perforated stainless steel cylinder and pressed by means of a jack operated piston (Photo 30). Due to the resulting pressure exerted into the cloth bag and the built up pressure in the cylinder the oil runs through the pores of the cloth and between the perforated cylinder into the pan or vessel. After the oil has drained (Photo 31), the pressed solid material removed from the bottom part of the cylinder is called oil cake.

3.6.1 Remaining oil in the press cake
Oil in the pressed oil cake, removed from the press equipment was a little bit higher than the oil from the pressed cake (Photo 33) extracted from the continuous type expeller (poonack). Oil pressed cake contains about 15-17% w/w as a remaining oil.
After separation of the oil using the first step and second step, the two end products are filtered oil (ready for processing of biodiesel) and pressed cake (poonack). It is recommended that the pressed oil cakes be fed back into the stream of fresh material (seed) during expelling.
