Delayed Coking - continued.

Vapors from the drums are returned to a fractionator where gas, naphtha, and gas oils are separated. The heavier hydrocarbons produced in the fractionator are recycled through the furnace.

The figure shows the feed going to both of the drums. This indicates the direction of feed to the drums. In reality only one coker is in service at any one time, while the other is being cleaned out. In some cases there may be multiple units similar to that shown, in which case the feed may be routed to both of the units at one time.

After the solid coke reaches a predetermined level in one drum, the flow is diverted to another drum to maintain continuous operation. The full drum (full of coke) is steamed to strip out uncracked hydrocarbons, cooled by water injection, and decoked by mechanical or hydraulic methods. The coke is mechanically removed by an auger rising from the bottom of the drum. Hydraulic decoking consists of fracturing the coke bed with high-pressure water ejected from a rotating cutter.