TABLE OF CONTENTS Physical separation techniques separate a mixture such as a crude oil without changing the chemical characteristics of the components. The separation is based on differences of certain physical properties of the constituents such as the boiling and melting points, adsorption affinities on a certain solid, and diffusion through certain membranes.
The important physical separation processes, discussed here, are distillation, absorption, adsorption, and solvent extraction.
Atmospheric distillation separates the crude oil complex mixture into different fractions with relatively narrow boiling ranges. In general, separation of a mixture into fractions is based primarily on the difference in the boiling points of the components. In atmospheric distillation units, one or more fractionating columns are used.
Distilling a crude oil starts by preheating the feed by exchange with the hot product streams. The feed is further heated to about 320 C as it passes through the heater pipe (pipe still heater).
The hot feed enters the fractionator, which normally contains 30 50 fractionation trays. Steam is introduced at the bottom of the fractionator to strip off light components. The efficiency of separation is a function of the number of theoretical plates of the fractionating tower and the reflux ratio. Reflux is provided by condensing part of the tower overhead vapors. Reflux ratio is the ratio of vapors condensing back to the still to vapors condensing out of the still (distillate). The higher the reflux ratio, the better the separation of the mixture.
Products are withdrawn from the distillation tower as side...
