The physicochemical properties of substances taking part in processes of diesel fuel cleaning with ammonia water and washing with water are studied. It is shown that ammonia water containing similar to 2 wt. % of petroleum acids should be used as the reagent. For steady operation of the plate column, the optimal rates of fuel discharge through the plate holes are found to be 0.15 m/sec for cleaning and 0.30 m/sec for washing of the fuel. In this case, the disperse phase layer heights under the plate are 12-16 mm and 75-85 mm, respectively.