A NEW TWIN-SCREW PRESS DESIGN FOR OIL EXTRACTION OF DEHULLED SUNFLOWER SEEDS

Transport of material in a single-screw press depends mainly on friction between the material and the barrel's inner surface and the screw surface during screw rotation. Thus, a solid core component, like seed hulls, is often necessary to produce the fraction. This sometimes causes excess frictional heat, large energy consumption and oil deterioration. Furthermore, if single-screw presses are not configured with breaker bars or other special equipment, they provide inadequate crushing and mixing. A twin-screw oil press can be expected to solve these problems because of the higher transportation force, similar to a gear pump, and better mixing and crushing at the twin-screw interface. A twin-screw press (screw diameter = 136 mm, length/diameter = 6.5, screw speed 15-100 rpm, feed rate = 50-150 kg/h) was designed with partially intermeshing and counter-rotating screws and was tested on dehulled sunflower seed. The results were compared to a single-screw lab-scale press. Dehulled sunflower seed (wt, 6.0%; oil, 58.6%) without pretreatments (crushing or cooking) gave 93.6% oil recovery with the twin-screw press, in contrast to 20% oil recovery with the single-screw press. The oil expressed with a twin-screw press had less foreign material than the oil from the single-screw press. Other properties of the oil were also good. Energy consumption of the twin-screw press was more efficient. All results suggested that oil production from dehulled sunflower seed with a twin-screw press is highly efficient.