Pressure distillation depropanizer

In the separation train, the gas stream is partially liquefied before entering the demethanizer at 320 bar. The overhead vapor, containing methane and hydrogen, is sent to a membrane separator in which these products are separated. The pressure of the bottoms product is reduced to 270 bar and fed to the deethanizer. In this column, the ethylene and ethane are removed in the distillate, whose pressure is reduced to 160 bar before the species are separated in the C-2 splitter. The bottoms product from the deethanizer, containing propylene, propane, and the heavier species, is throttled to 190 bar, mixed with the bottoms product from the condensate splitter, and fed to the depropanizer. The overhead product of the depropanizer is a mixture of propane and propylene and the bottoms product is throttled to 50 bar and sent to the debutanizer. In this column, the butylenes and butadiene are separated from the SCN. 

Depropanizers , which remove propane, are also part of the distillation sequence illustrated in figure 6.7, and they too are operated at an elevated pressure. With a pressure of about 15 bar, the temperature at the top of the column is sufficiently high for ordinary water or air to be used as the coolant for the condenser. 

The bottoms liquid from the depropanizer is fed to the debutanizer. The primary function of this column is recovery of all C-4 compounds from the feed. This column usually operates at a pressure from 70 to 130 psia and is equipped with 25 to 40 actual trays. The distillate product contains 98% to 99% of the C-4 hydrocarbons present in the feed. This distillate also contains all the propane present in the feed, plus a small amount of C-5 hydrocarbons. 

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