Pressure distillation debutanizer

Samples containing Hght components must be debutanized in a preliminary step. In the method, a weighed sample of 1-10 hters is distilled in a fractionating column having an efficiency at total reflux of 14-18 theoretical plates. A reflux ratio of 5 1 is maintained throughout except at the minimum pressure of 2mmHg, where a ratio of 2 1 can be used. The mass and density of each fraction are used to prepare distillation curves either by mass or volume. This method is often referred to as the 15-5 method. 

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. 

A debutanizer column is considered as a typical case. A mixture of 50 mol% -butane ( C4) and 50mol% -pentane ( C5) is separated in a column with 61 stages. The feed flow rate is lOOkmol/h and the feed is introduced on Stage 23 (using the Aspen notation that the condenser is Stage 1). The design specifications are 1 mol% C5 impurity in the distillate and 1 mol% nCA impurity in the bottoms. The reflux-drum pressure is set at... 

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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