Corrosion in Fractionation Systems

摘要

All data collected to date suggest that chlorine, as water-soluble chlorides, is necessary, albeit not sufficient, to cause the accelerated corrosion observed in pilot plant fractionation columns. We thus have proposed mechanisms for the transportation of chlorine to the fractionation columns, for the concentration of chlorine in these columns, and for the corrosion of the materials of construction of these columns. The source of the chlorine is the coal feed. When the coal is fed to the dissolver vessels, hydrogen chloride may be formed by volatilization or by hydrolysis of chloride salts followed by volatilization. The latter mode of hydrogen chloride formation and evolution is described by chemical equations. Recent analyses of the aqueous portion of a pilot plant stream (specifically, RPWT water) used infrared spectroscopy to confirm the presence of amine hydrochlorides. These amine hydrochlorides are transported in liquid streams to the fractionation area. Once fed to the fractionation column the amine hydrochlorides may concentrate on particular trays in the column. The concentrating mechanism we have proposed consists of volatilization, with dissociation, of the amine hydrochlorides, movement of the volatile amines and hydrogen chloride to cooler regions of the column where reassociation occurs, then flow of the amine hydrochlorides back down the column. The result of this reflux action is the concentration of amine hydrochlorides at various tray levels. Washing the coal liquids with water to remove the water-soluble chlorides and the addition of certain amines are proposed as methods for reducing the corrosion. (ERA citation 07:010132)