Design and performance analysis of vegetable seed oil expellers: A review

For cooking and eating purposes, oils expelled from vegetable seeds such as cashew nuts, sunflower, soybean, and olives have been in use for centuries. The increase in demand of the oils has prompted the drive for the development of more efficient methods to extract oil from these vegetable oilseeds. At large scale production, the modern most preferred method has been solvent extraction, which is expensive and requires sophisticated technical expertise to both set up and operate. However, for small production operations the mechanical extraction method is mostly preferred because mechanical screw expellers are easy to use and the investment capital is low. The mechanical extraction method is therefore, favourable for small producers and farmers in the rural areas and marginalised communities. Nonetheless, because of the low energy efficiency of the mechanical expellers and high electricity tariffs, there has been a need to develop more energy efficient expellers, which can incorporate the use of renewable energy (Solar) for use in the under developed areas. Various research studies have been done in the past by either altering the processing parameters (temperature, pressure, screw speed or the moisture content of seeds) and or trying different design properties of the screw and pressing-barrel namely the pitch size, tapered screw or the grilled barrel. Different authors have also developed mathematical models to describe and predict the performance of the expellers for various designs and processing conditions in relation to the produced yield of oil and energy efficiency. An analysis of these mathematical models and an evaluation of recommendations from previous designs of expellers, as well as research in this area are presented in this paper.