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Thermal conversion revamp boosts diesel production
Thermal conversion is cost effective, versatile and can handle a wide range of feed stocks for helping refineries margins along, with visbreaking, explains Okke de Boks – Technical Director, Refining and Chemical Licensing, Shell Global Solutions International B.V.
Thermal conversion revamp boosts diesel production
Thermal conversion offers flexible and cost effective opportunities to boost margins, by selective, phased investment based on incremental economic analysis.
There are two distinct elements in a thermal gas unit (TGU): visbreaking, to convert the residual part of the cut, and thermal cracking which takes distillates and cracks them into diesel and other products. The two elements can be combined into one efficient process unit, called the thermal conversion process.
Thermal cracker units revamps have been carried out by Shell since the 1960s and fit into multiple refineries configurations: from simple to
complex, creating opportunities for continuous optimisation.
The basic feature of a standard thermal gas unit (TGU) is the residue furnace, which is fed by atmospheric or short residue. Some have an optional soaker or reaction chamber to extend the residue residence time for continuous cracking (operating temperatures rise to 450oC). The cracked products flow to a cyclone (used to separate the vapour and liquid efficiently at high temperature and prevent coking in the atmospheric column). Vapour from the cyclone is routed to the atmospheric distillation column and unconverted material is cooled to a lower temperature and fed into a vacuum distillation column.