The combination of such methods as treatment by clays and distillation is considered to be one of the modifications of contact filtration. It is applied by some refineries to process reduced oils and other fractions with a low content of asphalt. The implementation of the combined filtration and distillation process requires clay to be first mixed with an original product. Further, this mixture of oil and clay is pumped into a distillation column that is equipped with a tube-type furnace. When passing through a tube-type furnace, fractions from the upper part of the column make contact with the clay. This process results in the accumulation of clay in dead oil at the bottom of the column.
No additional filtration is required to remove the clay. Oil that contains used clay is supplied to a filter of an oil filtration unit to be separated. Pure oil is cooled down and pumped into special tanks for further storage. Also, it is necessary to dispose of waste clay.
In some cases, a combination of clay treatment and distillation prevails over a usual percolation, contact filtration and distillation if used separately. But generally speaking, the final results of purification are the same.