Monitoring Chlorine Concentrations in Distillate Hydrotreater Feedstocks

For distillate and gas oil streams the goal is to reduce the sulphur content of blend stocks used in diesel fuel and/or downstream upgrading units. In the case of heavy naphtha, the primary objective of hydrotreating is to clean up the feed before sending it to the reformer. The key concern with organic chlorides in refineries is its conversion to hydrochloric acid within hydrotreaters. Since as a rule, these units operate with very little water, there is a tendency to have any of the produced HCl accumulate in the very small water volumes present in the hydrotreater effluent. The end result is a severe drop in pH and aggressive corrosion of metallurgies. For this reason, ppm levels of organic chlorides in crudes can potentially be quite problematic.

The CLORA Online Analyser from XOS (USA) provides an analytical solution to monitor chlorine concentrations in hydrotreater feedstock with sub-ppm detection limits. ASTM D 4929 (a lab based method for organic chlorine determination by distillation and biphenyl reduction or micro-coulometry) is limited in its ability to measure organic chlorides in compounds with boiling points below 400 deg F. It is unable to provide any quantification of organic chlorides in heavier streams such as distillates or gas oils. Some refiners have reported evidence of organic chloride induced corrosion in distillate and gas oil hydrotreaters. The availability of equipment capable of measuring organic chlorides in both distillate and gas oil feeds is beneficial from a corrosion management viewpoint.