Handling delayed coker disturbances with APC

摘要

A delayed coker unit (DCU) is an established candidate for the application of advanced process control (APC) with an attractive return on investment. The challenge in DCU-APC lies in handling the big disturbances that occur during drum switch-over and vapour heating events when the vapour enthalpy feed to the main fractionator is suddenly reduced. Timely actions need to be taken on several control loops to minimise the effects of sudden cooling of the column, which leads to large variations in coker gas oil quality as well as flow rates. The exact occurrences of these events are unmeasured and a conventional control system is not adequate to handle such big disturbances. The resulting economic losses due to quality give-away and off-spec product generation are substantial, not only in the DCU but also in downstream units where the disturbances are propagated. Hence continuous operator attention is required for managing these events.