The Gas Plant
Light ends are hydrocarbons boiling at the lowest temperatures including methane, ethane, propane, butanes, and pentanes, which contain from one to five carbon atoms. Light ends are fractionated in distillation towers and treated with amine contacting to remove hydrogen sulfide. The most abundant source of lights ends is cracking operations.
Unsaturated light ends, containing ethylene, propylene, butylenes and pentylenes (from the Fluidized Catalytic Cracking Unit and Coker Unit), are fractionated separately from saturated light ends (from Crude Distillation, Hydrocracking, and Catalytic Reforming).
This allows separate disposition:
- Methane and ethane to fuel gas
- Ethylene and propylene to petrochemical feedstock
- Propylene, butylenes, pentylenes, and iso-butane to alkylation
- Saturated propane and butane for sale
- Saturated butane to isomerization
- Gas plant condensate (pentane and higher) are blended to motor gasoline.
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The Gas Plant
The Gas Plant will remove the light hydrocarbons from the Naphtha Unit product. Lean oil is used to absorb and recover the propane and butane to allow the hydrogen, methane, ethane and hydrogen sulfide to be sent overhead as fuel gas. The remaining liquid will be separated out into propane, iso-butane, butane, light naphtha and heavy naphtha.
Distillation columns are used to separate these gases in the same way as the Crude column. The lighter boiling point materials leave the top and the heavier ones leave through the bottom of the tower. In addition, the mixed butanes and iso-butane are sent the Alklyation Unit. The heavy naphtha is also sent to the Reformer for upgrading.
