If heavy components of crude oil are to be converted into lighter ones, cracking processes come into play. The desired conversion effect is achieved by overheating the distillation residues under pressure. Such thermal cracking can be done in a coker. Therefore, a mixture of preheated fresh feed (residual oil) is passed from the frac-tionator via a heater to one of the large coker drums. Here the cracking and expansion of the fluids is allowed. The lighter cracked hydrocarbons are taken off at the top of the drums to the fractionation tower, while cracking heavy hydrocarbons results in their conversion into a vapour due to the high temperature.
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