A Bird Eye View of the Delayed Coker Unit Process Streams

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The DCU derives its name from the fact that the formation of coke does not take place in the furnace tubes but is delayed until it is laid down in the coke drums, where it can be accumulated and removed as a saleable product.
The DCU drums are operated as sets of two coke drums. One drum is emptied (De-coked) while the other is being filled (Coked) with coke.
Each set of drums is supplied by a dedicated feed heater. This allows the DCU to operate at 50% capacity while one heater and pair of drums are shut down for de-coking (Pigging).
The coke drum overhead vapors are separated in the Coker main Fractionator, side strippers, and the Coker Gas Concentration System.
The products of the coking process include sour fuel gas, liquefied petroleum gas (LPG), light Coker naphtha (LCN or LKN), heavy Coker naphtha (HCN or HKN), light Coker gas oil (LCGO or LKGO), heavy Coker gas oil (HCGO or HKGO), and coke. Products leaving the DCU are further treated in other refinery units, consumed as fuel, or sold as product.
DCUs are designed to process heavy residuals to produce distillates (naphtha & gas oils) that may be catalytically upgraded; Hydro-treating, catalytic cracking.
Delayed Coker can process a wide variety of feed stocks which can have considerable metals sulfur, resins, & asphaltenes; Most contaminants exit with the coke.
Typical feed is:
      Vacuum Resid.
     Atmospheric Resid occasionally used.

Feed stock ultimately depends on type of coke desired or processed:

Petroleum coke has uses in the electric power and industrial sectors, as fuel inputs or a manufacturing raw material used to produce electrodes for the Steel or Aluminum industries. 2010 t0 2011 the refining industry supplied approximately 132 million barrels of petroleum coke with most of it subsequently consumed as fuel.

Two types of coking processes exist today "Delayed Coking and Fluid Coking". Both are physical processes that occur at pressures slightly higher than atmospheric and at temperatures greater than 900^oF that thermally crack the feedstock into products such as Coker Gas oils (light & heavy) and Coker Naphtha, leaving behind the petroleum coke. Depending on the coking operation temperatures and length of coking times, petroleum coke is either sold as Fuel-grade petroleum coke or undergoes an additional heating or calcining process to produce anode-grade petroleum coke.

With delayed coking, two or more large coke drums, are used to hold / delay, the heated feedstock while the cracking takes place. Coke is deposited in the coke drum as a liquid and is then cooled to a solid. This liquid thermally cracked coke builds up in the coke drum until it is cooled/quenched and is then removed by hydraulically cutting the coke using water. In order to facilitate the removal of the coke, the hot feed is diverted from one coke drum to another, alternating the drums between coke removal and the cracking part of the process. With fluid coking, the feed is charged to a heated reactor, the cracking takes place, and the formed coke is transferred to a heater as a fluidized solid where some of it is burned to provide the heat necessary for the cracking process. The remaining coke is collected to be sold.

Like other secondary processing units, coking can play an important role in refinery economics depending on the type and cost of the crude oil run at a refinery. As the quality of crude oil inputs to a refinery declines, coupled with greater demands for transportation fuels, coking operations will serve to meet transportation fuel demands and also produce increasing quantities of fuel-grade and anode-grade or needle petroleum coke.