The co-current process is the least complicated. Bleaching earth is added in two consecutive stages in the oil, with a filtration after every stage.
In the counter-current bleaching process, the spent bleached earth from the second bleaching stage is re-used in the first stage. The efficiency of the counter-current process is largely affected by the way the filtration with spent bleaching clay is performed. The easiest way is to use a third filter operating in counter-current at the inlet of the bleacher. The pre-filtration of the oil through the spent bleaching clay cakes in the filter, built up during the second bleaching stage, already results in a saving of 10–15% bleaching earth as compared to single stage bleaching