<P> Below is a schematic flow diagram of a typical crude oil distillation unit . The incoming crude oil is preheated by exchanging heat with some of the hot, distilled fractions and other streams . It is then desalted to remove inorganic salts (primarily sodium chloride). </P> <P> Following the desalter, the crude oil is further heated by exchanging heat with some of the hot, distilled fractions and other streams . It is then heated in a fuel - fired furnace (fired heater) to a temperature of about 398 ° C and routed into the bottom of the distillation unit . </P> <P> The cooling and condensing of the distillation tower overhead is provided partially by exchanging heat with the incoming crude oil and partially by either an air - cooled or water - cooled condenser . Additional heat is removed from the distillation column by a pumparound system as shown in the diagram below . </P> <P> As shown in the flow diagram, the overhead distillate fraction from the distillation column is naphtha . The fractions removed from the side of the distillation column at various points between the column top and bottom are called sidecuts . Each of the sidecuts (i.e., the kerosene, light gas oil and heavy gas oil) is cooled by exchanging heat with the incoming crude oil . All of the fractions (i.e., the overhead naphtha, the sidecuts and the bottom residue) are sent to intermediate storage tanks before being processed further . </P>

When was oil first broken down into fractions