Steam cracking of heavy oil fractions revisited

摘要

There is an increasing tendency to use heavy oil fractions such as gas oils, vacuum gas oils and waxes as steam cracking feeds because of their lower price compared to naphtha. Therefore the cracking behavior of a number of heavy oil fractions (middle distillate, vacuum gas oil and naphtha/wax mixtures) has been studied in the LCT pilot plant for steam cracking. To gain a better insight in the cracking behavior of these heavier feeds a dedicated GCxGC set-up has been implemented. The latter allows the characterization of heavy petroleum feedstocks and steam cracking effluents with an unseen level of detail. By adopting the set-up off-line detailed molecular information about feedstock composition is obtained enabling proper assessment of feedstock quality. Used on-line for the analysis of steam cracking effluents, over 150 different components are identified and quantified. Our results show that cracking of naphtha/wax mixtures shows great potential for industrial application as the ethylene yield is higher compared to the cracking of pure naphtha at the same severity. The naphtha/wax mixtures also show a lower coking tendency than the pure naphtha resulting in longer run lengths.