During the refining of crude petroleum, the sulfur component of the crude oil reacts with the specialty alloy steel processing equipment producing iron sulfide scale. Pyrophoric iron sulfide scale, when exposed to air, reacts exothermically and can result in a fire. Toxic sulfide odors can also be formed during these turnarounds.
Permanganate oxidizes pyrophoric iron sulfide to iron sulfate eliminating the potential for exothermic reactions and fires or explosions during shut downs for maintenance of refinery process equipment. Permanganate treatment also controls toxic odors by oxidizing the sulfides to odorless sulfates.
Permanganate (NaMnO4 or KMnO4 ) is added to the process equipment as a 0.1% to 1.0% aqueous solution. The units are filled with the permanganate solution and the solution is recirculated, or agitated depending on the design of the process. Control is visual. As the solution turns from purple to brown in color, the permanganate is being used up. The spent permanaganate solution can be discharged directly to the sanitary sewer.
Due to the variability of the amount of iron sulfide present on the equipment, an exact dose of permanganate cannot be calculated. It is recommended that the permanganate solution be fed until a faint purple to pink color is observed in the finished water.
Proper mixing tanks and feed pumps compatible with a permanganate solution are required. Operators should be trained in making up the permanganate solution and in monitoring permanganate residuals. Operators should be given appropriate safety and emergency training.