Crystallisation of Organic Materials

Abstract

The deposition of organic crystals onto a heat transfer surface is usually associated with the “freezing” of the organic fluid itself, on surfaces at a sufficiently low temperature. For this reason the process is often called “freezing” or “solidification” fouling. Deposition from waxy hydrocarbons onto cooled surfaces is a problem which has existed in the oil industry for many years and may be regarded as a typical example of “freezing fouling”. The transport of crude oil in pipelines in the North Sea has produced some severe problems of this nature, partly due to the relatively long distances involved and partly due to the relatively low temperatures encountered, coupled with the composition of the crude oil. Although in this particular example the crystals deposited on the surface are not strictly of the identical character of the fluid stream as a whole, they do represent organic material; the fluid stream itself being a mixture of different substances. The deposits consist mainly of n-paraffins with smaller amounts of branched and cyclic paraffins and aromatics.