What is the difference between filtered oil and refined oil?

For refining the oil, there are three basic processes in the refinery. First process is neutralizing the oil in the neutralizer to remove the Free Fatty Acids (FFA) by adding caustic soda. Oil is heated upto about 60°C by thermic fluid coils and oil is stirred by stirrer. Then soap stock formed due to chemical reaction is allowed to settle at the bottom of the neutralizer from where it is taken out into soap pan.

Neutralized oil is drawn into the second vessel called bleacher where colour of oil is removed by bleaching process with aid of chemicals such as carbon black and bleaching earth. Oil is generally heated upto 110°C by thermic fluid coils. Stirring is also continued. Bleaching process is done under vacuum.

Bleached oil then goes to the filter press where bleaching earth and chemicals are separated and clean bleached oil is then drawn to deodourizer where oil is heated above 110°C through thermic fluid coils and then live steam is given to the oil from the bottom steam nozzles and temperature of oil is raised upto 200 to 220°C through thermic fluid coils.