Delayed coker coke drum pressure

Three operating control variables in a delayed coker dictate the product quality and yields for a given feedstock. These variables are the heater outlet temperature, coke drum pressure and the ratio of recycle to fresh feed. 

A decrease in pressure has the effect of vaporizing more heavy hydrocarbons. As the production of desirable liquid hydrocarbons is increased at low pressures, the coke yield is correspondingly decreased. Thus, most modern delayed cokers have been designed to operate at a low coke drum pressure. 

The solvent contained in the asphalt and deasphalted oil is condensed in the fractionator overhead condensers, where it can be recovered and used as lean oil for a propane/butane recovery in the absorber, eliminating the need for lean oil recirculation from the naphtha stabilizer. The solvent introduced in the coker heater and coke drums results in a significant reduction in the partial pressure of asphalt feed, compared with a regular delayed coking unit. The low asphalt partial pressure results in low coke and high liquid yields in the coking reaction. 

A delayed coker consists of a furnace to heat the feedstock to around 500 °C, two pressure vessels (coke drums) with a diameter of 4 to 7 m and 20 to 30 m high, together with a distillation system to separate the volatile components. Figure 13.8 shows the flow diagram for the delayed coking process. 

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