light products that might remain in the residual oil are distilled out. The oil is then pumped through a furnace, where it is heated to the required coking temperature. From the furnace, the hot oil is discharged into the bottom of the coke drum. The oil undergoes thermal cracking and polymerization for an extended period, resulting in the production of hydrocarbon vapors and porous carbonaceous coke that remains in the drum. The vapors leave the top of the drum and are returned to the fractionation tower, where they are fractionated into the desired cuts. This process is continued until the drum is substantially full of porous coke. Residual oil feed is then typically switched to a second parallel drum, while steam is introduced through the bottom inlet ofthe first drum to quench the coke.
The steam strips out the remaining uncracked oil in the drum. During the early stage of steaming, the mixture of water and oil vapors continues to pass to product recovery, as during the coking stage. Thereafter, the effluent from steaming is diverted to blow-down facilities, where it is condensed and transferred to settling basins. In the settling basins, oil is skimmed from the surface of the water.
After steam cooling to about 700.degree.-750.degree. F., water is introduced to the bottom of the coke drum to complete the quench. The first portions of water are, of course, vaporized by the hot coke. The resultant steam plus oil vapor is passed to blow-down for condensation and skimming to separate oil. Water addition is continued until