The processing of the rapeseed to obtain SVO to be used as engine fuel is made through three mechanical steps: cleaning of seed, pressing and purification (see Fig. 2). The first step consists of cleaning the seeds from stones, metal pieces and straw. In this process it is very important to reduce the risk of damaging the press.

The second step is a cold pressing of the oil seed with the screw press to obtain oil. This step must be done carefully to reduce the incorporation of undesirable materials from the solid by-product (rapeseed cake) The pressing process influences the content of phosphorus, calcium and magnesium as well as the content and dimension of the particles. The variability of those elements depends on the speed and the pressing temperature. A low speed (low throughput) increases the oil yield and the content of particles. A high speed

(high throughput), produces the opposite effect, decreasing the oil yield and also the particles. It is possible to find an optimal compromise according to the necessities of production and capacity of filtering. The oil yield should be between 32-36% of rapeseed mass, due to the amount of undesirable particles obtained in the oil if the pressure is too high or if a second pressing is done (Ferchau, 2000).

As a final step, purification of raw oil obtained from the press is needed. It is recommended to use a press filter and to perform a security filtration after a decantation. A general filtration procedure must be done after decantation in order to remove the suspended particles from the oil. Usually a pressure filter is used, either a chamber filter or a vertical one. As a final step, a security filtration of a defined pore size (between 1 and 5 pm) is recommended to remove the finest particles that still remain in the oil. In this step is very important to pass the quality control exposed in section 4.5. After this final step and after complying with the quality control, the oil is prepared for combustion in a modified diesel engine.

The cake meal and the filter cake obtained in the process to obtain SVO both have a high content of protein and are suitable for being incorporated as part of animal fodder There is a variation of this process to extract more oil from the seed using a solvent. The abovementioned process is the first step. About 70% of oil from the seed is extracted, leaving 30% in cake meal. The next stage is a process of extraction using hexane as solvent. It reaches up to 95% extraction of the seed oil. In this stage, a solvent (hexane) is mixed with rapeseed cake. The solvent dissolves the oil remaining in the rapeseed cake. After its evaporation, the solvent is recovered for its use. The outline of the process is shown in Figure 3. In case of hexane extraction, the cake meal obtained has less protein than when just pressing the seed. Even though, there is no problem to use it as animal food.