OVERALL REFINERY FLOW

The crude oil is heated in a furnace and charged to an atmospheric distillation
tower, where it is separated into butanes and lighter wet gas, unstabilized
light naphtha, heavy naphtha, kerosine, atmospheric gas oil, and topped (reduced)
crude (ARC). The topped crude is sent to the vacuum distillation tower and separated
into vacuum gas oil stream and vacuum reduced crude bottoms (residua,
resid, or VRC).
The reduced crude bottoms (VRC) from the vacuum tower is then thermally
cracked in a delayed coker to produce wet gas, coker gasoline, coker gas oil, and
coke. Without a coker, this heavy resid would be sold for heavy fuel oil or (if
the crude oil is suitable) asphalt. Historically, these heavy bottoms have sold for
about 70 percent of the price of crude oilThe atmospheric and vacuum crude unit gas oils and coker
gas oil are used
as feedstocks for the catalytic cracking or hydrocracking units. These units crack
the heavy molecules into lower molecular weight compounds boiling in the gasoline
and distillate fuel ranges. The products from the hydrocracker are saturated.
The unsaturated catalytic cracker products are saturated and improved in quality
by hydrotreating or reforming.
The light naphtha streams from the crude tower, coker and cracking units
are sent to an isomerization unit to convert straight-chain paraffins into isomers
that have higher octane numbers.
The heavy naphtha streams from the crude tower, coker, and cracking units
are fed to the catalytic reformer to improve their octane numbers. The products
from the catalytic reformer are blended into regular and premium gasolines for
sale.
The wet gas streams from the crude unit, coker, and cracking units are
separated in the vapor recovery section (gas plant) into fuel gas, liquefied petroleum
gas (LPG), unsaturated hydrocarbons (propylene, butylenes, and pentenes),
normal butane, and isobutane. The fuel gas is burned as a fuel in refinery furnaces
and the normal butane is blended into gasoline or LPG. The unsaturated hydrocarbons
and isobutane are sent to the alkylation unit for processing.
The alkylation unit uses either sulfuric or hydrofluoric acid as catalyst to
react olefins with isobutane to form isoparaffins boiling in the gasoline range.
The product is called alkylate, and is a high-octane product blended into premium
motor gasoline and aviation gasoline.
The middle distillates from the crude unit, coker, and cracking units are
blended into diesel and jet fuels and furnace oils.
In some refineries, the heavy vacuum gas oil and reduced crude from paraffinic
or naphthenic base crude oils are processed into lubricating oils. After removing
the asphaltenes in a propane deasphalting unit, the reduced crude bottoms
is processed in a blocked operation with the vacuum gas oils to produce lubeoil
base stocks.
The vacuum gas oils and deasphalted stocks are first solvent-extracted to
remove the aromatic compounds and then dewaxed to improve the pour point.
They are then treated with special clays or high-severity hydrotreating to improve
their color and stability before being blended into lubricating oils.
Each refinery has its own unique processing scheme which is determined
by the process equipment available, crude oil characteristics, operating costs, and
product demand. The optimum flow pattern for any refinery is dictated by economic
considerations and no two refineries are identical in their operations..