Delayed Coker Process

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Coking is an old process but one that is becoming more important as the quality of the world’s crude supply deteriorates. As the sulfur, metals, and conradson carbon contents of crudes increase, coking the bottom of the barrel is looking better to many refiners. The greater part of the barrel of resid produced from a crude unit can be converted to gasoline, distillate, and gas oil in a coker. Thus, in the current economic environment, the coker is frequently the most important unit in the refinery. By far the largest amount of coking capacity is represented by the delayed coking process. While delayed coking is simple enough, the cyclic nature of the process gives ample scope to the talents of the troubleshooter.

Delayed Coker Process Schematic

Figure above illustrates a simplified flow diagram of a delayed coker. Hot resid feed flows to the bottom of the combination tower. The combination tower bottom section acts as surge drum from which the coking heater is charged.

The heater raises the resid temperature to 900°F. The resid then flows into the bottom of one of a pair of coke drums, where it thermally cracks to gas, gasoline, gas oil, and solid coke. The coke gradually fills the drum-usually over a period of 24 hours—while the lighter products pass on as a vapor to the combination tower. Since the coking reaction is endothermic, the vapors leaving the top of the coke drum are roughly 110°F colder than the heater outlet temperature.

In the combination tower, the coke drum vapors are condensed and fractionated into four products: gas, wild gasoline, furnace oil, and heavy gas oil.

 

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