Coking by metal dusting of steels

In process industries coking is an annoying phenomenon, the carbon depositi on causes decrease of heat transfer and hinders gas flow. Coking in a proce ss may indicate metal dusting, i.e. the disintegration of metals and alloys in carbonaceous atmospheres under formation of graphite and fine metal par ticles. The metal particles act as catalysts for vast coke formation. The t hermodynamics, mechanisms and kinetics of metal dusting have been studied o n iron and steels in synthesis respectively reduction gas CO-H-2-H2O, here the aspects are presented of coking due to metal dusting. From the interpla y of the metal disintegration and carbon deposition rather complex coupled kinetics are resulting, even different in a low temperature range where the decomposition of the intermediate cementite is rate determining and in a h igher temperature range where the carbon transfer from the atmosphere is ra te controlling. Coking by metal dusting can be suppressed in the same way a s metal dusting, by sulfur addition to the atmosphere and/or by a stable de nse protective oxide layer.