Development of a small capacity double stage compression screw press for oil expression

Mechanical pressing of oilseeds is the most widely used method for oil expression in the world. However, the mechanical oil expellers (screw presses) employed for this purpose leave about 8–14% of the expressible oil in the deoiled cake, so that a large quantity of edible oil is not available for human consumption. To improve the efficiency of oil recovery, a modified oil expeller was designed and developed based on a novel principle of single feed double stage compression. An evaluation of the performance of the developed expeller with moisture conditioned rapeseed samples indicated that in two passes it recovered over 90% of the available oil at a moisture content of 7.5% (w.b.). This is in contrast to normally required 3–5 passes in conventional oil expellers for an oil recovery of about 80%. The throughput capacity of the expeller was 25 kg/h while its effective capacity (two passes) was found to be 15 kg/h. The maximum barrel temperature was 70.3°C which assured production of a good quality oil, and the deoiled cake and the specific energy requirement was 0.05 kWh/kg of feed for the optimized pressing conditions. An economic analysis indicated that the developed screw press could profitably be used for small-scale processing of rapeseed in rural areas of India.