Page 306 - Introduction to Petroleum Engineering

THE DOWNSTREAM SECTOR: REFINERIES 295
TAblE 15.1 Downstream Sector Products
Liquefied petroleum gas (LPG) Asphalt
Liquefied natural gas (LNG) Synthetic rubber
Propane Plastics
Gasoline Lubricants
Diesel oil Pharmaceuticals
Jet fuel Fertilizers
Heating oil Pesticides
Other fuel oils Antifreeze

FIguRE 15.4 Distillation towers at a Texas refinery. (Source: © energy.fanchi.com (2015).)

15.2.1 Separation
Refining changes crude oil into finished products using three major processes: separa-
tion, conversion, and purification processes. The first step in refining is separation with
one or more distillation towers. A distillation tower, which is also known as an atmo-
spheric crude fractionator, separates crude oil into mixtures of components based on the
boiling points of the mixtures. Figure 15.4 shows some distillation towers at a refinery.
Figure 15.5 is a schematic of a distillation tower system. A furnace is used as a
heat source to heat and vaporize liquid crude oil. The liquid phase that remains in the
lowermost section of the tower after heating is a mixture of components with the
highest boiling points, while the vapor phase that rises in the tower is a mixture of
components with lower boiling points. A table of boiling point (B.P.) ranges and
hydrocarbon components for several fractions is shown in Figure 15.5 (Olsen, 2014).
Each fraction is a mixture of hydrocarbon components that can be used to make
different products. For example, naphtha is used to make gasoline for vehicles and
kerosene is used to make jet fuel.
The temperature in the distillation tower is hottest in the lowermost section
because of the furnace. The hot vapor cools from approximately 700°F in the