Pre-refining the crude oils before entering the process of biodiesel or before using it as a bio-carburant is essential. The general process is composed of the following sections:
- acid degumming in order to reduce the phosphorus content to an acceptable level, then
- stripping of the free fatty acids under deep vacuum.
Physical refining - also called steam refining - is the neutralisation of fats and oils by steam stripping under vacuum.
This process is well suited to most edible oils provided they are thoroughly degummed and purified.
Main advantages of the physical refining system towards the conventional one are:
- the refining factor of the whole refining process is superior in physical refining than in chemical refining mode;
- moreover, in physical refining, there is no production of soapstock, a main source of pollution in alkali refining;
- production costs as well as investment costs are lower in physical refining;
- the requirements for effluent water treatment are minimised.
To properly neutralise the oil in the stripper, it is essential that the oil entering the neutraliser/stripper is free of impurities.
The "degumming" process is sufficient to get an oil free of impurities and with a reduced phosphatide content. Some oils require some partial neutralising in the degumming step to remove unwanted minor components