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Industrial odour control 2 Odour nuisancesOdour from process plants Odorants often appear in connection with chemical processes and form part of the process discharge, unless they are cleaned before emission from the plant. But the most thorough cleaning of discharges cannot prevent odour from a plant in which process equipment is badly maintained, with leakages through which odorous gas emitted in the atmosphere. Gas may also escape in connection with emptying/filling of tanks or with repair and cleaning of manufacturing equipment. Odour sources It is not possible to make a complete list of odour-producing plants. Below are given some examples of plants, processes and activities which are well-known emitters of odorous compounds and, thus, sources of offensive smell: Oil refinery Odour generation Odours are generated in many different situations, in industry sometimes in connection with processing of natural products, e.g. oil distillation or synthesis of chemical compounds. A variety of substances are involved, and special literature should be studied for further details. In some plants smells are generated by microbial decomposition of organic compounds, e.g. hydrogen sulphide, mercaptans, but also nitrogen compounds in the form of ammonia, amines, and skatole may cause malodour. Smell generating reactions often occurs where organic substances are kept in containers without oxygen or in anaerobic water, for instance sewers, wells, settling tanks etc. Some of the problems may be solved by adequate circulation or supply or oxygen or oxidising substances. Problems relating to odour control Odour nuisances are sometimes very difficult to prevent, because even negligible amounts of some odorants are sensed by humans. Hydrogen sulphide and mercaptans for instance can be sensed in concentrations far below concentrations which are harmful to Man. Due to our ability to detect odorants in very small concentrations, otherwise insignificant air pollution sources (valve and joint leakages, small spills, evaporation from wells, sewers or open basins) may give rise to complaints from neighbours.
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