Improvements in or relating to the purification of waste waters from petroleum hydrocarbon processing

摘要

Waste water from petroleum hydrocarbon processing is purified by contacting a stream of the water with a stream of a stripping gas so that the water is substantially freed of voltatile contaminants, and then contacting the water stream with a stream of liquid hydrocarbon so that non-volatile contaminants are transferred from the water stream to the hydrocarbon stream. The purified water may be discarded into a body of water or it may be used in further hydrocarbon processing. The stripping gas may be sweet natural gas, flue gas or mixtures thereof, and the stripping gas may remove such volatile contaminants as hydrogen sulphide, mercaptons and ammonia. The liquid hydrocarbon may be a polymerization unit feed stream, (e.g. a butane-butylene mixture) an overhead fraction from the product fractionator of a catalytic cracking unit (e.g. the gasoline-containing fraction boiling below 225 DEG C. and resulting from the cracking of gas oil of other heavy hydrocarbon oil fraction), gasoline, naphtha or kerosene; the liquid hydrocarbon may remove such non-volatile contaminants as phenols from the water. Where the liquid hydrocarbon contains volatile contaminants, at least a portion of these may transfer to the water stream, and in this case the water should be returned to the gas stripping zone for further removal of volatile contaminants. Apparatus is described in which the water circulates continuously around a closed circuit, water from the stripping zone contacting in turn contaminated liquid p hydrocarbon polymerization unit feedstock, contaminant-free liquid hydrocarbon polymerization unit feedstock, and the overhead fraction from the product fractionator of a unit for the catalytic cracking of hydrocarbons, before returning to the stripping zone. Means are provided for continuously discarding a small portion of the water and continuously adding a small portion of fresh water.