Coking - continued.

Delayed Coking

The figure provided here illustrates a schematic diagram for a delayed coking process.

In a delayed coking process, the heated charge (typically residuum from atmospheric distillation towers) is transferred to large coke drums. These drums provide the long residence time, which is needed to allow the cracking reactions to proceed to completion.

Initially the heavy feedstock is fed to a furnace which heats the residuum to high temperature (900-950 deg F or 480-510 deg C) at low pressures (25-30 psi).

The heating furnace is designed and controlled to prevent premature coking in the heater tubes. The mixture is passed from the heater to one or more coker drums where the hot material is held approximately 24 hours (delayed) at pressures of 25-75 psi, until it cracks into lighter products.