As was mentioned in previous parts of this series, petroleum refiners go to great lengths to capture as much naphtha as they can.  Two units designed to squeeze out more naphtha are the fluidized catalytic cracking unit (FCCU) and the delayed coking unit.

The residue exiting the bottom of the atmospheric tower is sent to a vacuum fractionator (vacuum distillation tower).  The lower pressure helps the residue to boil at lower temperatures; and thus, enhances the separation process.  Exiting the bottom of the vacuum fractionator is the residual oil and just above that is the heavy vacuum gas oil.

The FCCU takes the heavy vacuum gas oil, heats it to a gas, then reacts it with a catalyst.  The gas and the catalyst mix into a type of pseudo single phase substance.  The catalyst breaks down the long hydrocarbon chains into smaller chains forming products, one of which is naphtha.

In the case of delayed coking, the residual oil  is cracked, not with a catalyst, but with a high temperature furnace.  The residual oil is first passed through another fractionator.  The bottoms from that tower are fed through a furnace where long chain hydrocarbons are broken into smaller ones.  The stream is then fed into coke drums where it is further heated; thus, doing more cracking and ultimately boiling off the light components, including more naphtha.  What is left behind is called coke, and it is hard as a rock.

Think about all the refineries around the world generating all this naphtha.  What will we do with all this naphtha when the world starts moving towards electric and methane cars, trucks, and trains.

 

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