Coking/decoking sequences, coke

The coke drums are typically installed in pairs for each fired heater. When the on-line coke drum is full of a high-density hydrocarbon residue known as petroleum coke, the heated feed is switched to an empty drum. After being filled, the full coke drum is isolated from the process flow and goes through a sequence of steps to remove the coke and prepare the drum for the next cycle, which can be from as little as 10 hours to more than 24 hours. Therefore, DCU is a semi-batch operation, in which the batch stage is represented by the filling and decoking steps sequence of the drums. Table 1 presents the sequence of typical steps and the associated duration of a 20 hours cycle DCU. 

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