Natural gas is used as a fuel in all of the refinery processes
that feed high sulfur fuel oil.
For instance a typical pathway for a raw rude oil might be the
following: Atmospheric Distillation, Vacuum Distillation, Solvent
Deasphalting, Visbreaking. The fuel oil is the heavy product of the
visbreaker, which is final step in this particular process.
The bottoms product from each of these refinery processes is
sent to the next process where the oil increases in density and
viscosity as "lighter" components (entrained gases, gasoline,
diesel, gas oils, etc.) are removed. Each of these four processes
requires its own process heater, which often burns natural gas as a
fuel (natural gas is especially used in refineries in developed
nations). While refinery "fuel gas," or gas removed from the crude
oil, is used as a fuel in many of these heaters, some external
supply of natural gas is often needed to supply the balance of
energy needed to run these energy intensive processes.
