Crude DistillationCrude DistillationChapter 4Chapter 4
Light Naphtha
CrudeOil
Desalter
Atmospheric
Distillation
Vacuum Distillation
Gas
Separation & Stabilizer
Solvent
Deasphalting
Coking
Visbreaking
Fluidized
Catalytic Cracking
Hydro-cracking
Naphtha
Reforming
Isom-erization
Sat Gas
Plant
Polymer-
ization
Alkylation
Naphtha
Hydro-treating
Treating & Blending
Coke
Fuel Gas
LPG
Aviation Gasoline
Automotive Gasoline
Solvents
Jet Fuels
Kerosene
Solvents
Heating Oils
Diesel
ResidualFuel Oils
Lubricant
Greases
Waxes
Asphalts
HeavyNaphtha
Kerosene
Distillate
AGO
LVGO
HVGO
VacuumResiduum
CatDistillates
Gas Oil
Hydro-treating
DAO
Isomerate
Gas
AlkylFeed
Alkylate
PolymerizationNaphtha
Gases
Butanes
LPG
Reformate
Naphtha
Fuel OilBottoms
Distillates
Distillate
Hydro-
treating
CatNaphtha
Cycle Oils
SDABottoms
CokerNaphtha
HeavyCokerGasOil
Light CokerGas Oil
Sulfur
PlantSulfur
Naphtha
Fuel Oil
SolventDewaxing
Lube Oil
Waxes
Crude Distillation TechnologiesCrude Distillation Technologies
Provider Features
Foster Wheeler
Shell Global Solutions
TECHNIP
Uhde GmbH Vaccum distillation
Complex of atmospheric & vacuum distilation for initial
separation of crude oil. May include preflash column.
Typical Crude Tower Cut PointsTypical Crude Tower Cut Points
950 to 1100Vacuum Resid
950 to 1100800HVGO
(Heavy Vac Gas Oil)
800650LVGO
(Light Vac Gas Oil)
650420 to 520AGO
(Atm Gas Oil)
420 to 520330 to 380Distillate
(Kerosene)
330 to 380180 to 220Heavy Naphtha
180 to 22080 to 90Light Naphtha(LSR Gasoline)
TBP EP (°F)TBP IBP (°F)Cut
OverviewOverview
‣ Crude Stills• Historically the oldest refining process
• Only the first step in crude oil processing
‣ Purpose• To recover light materials
• Fractionate into sharp light fractions
‣ Configuration — May be as many as three columns in series
• Crude Stabilizer/Preflash Column
� Reduce traffic in the Atmospheric Column
• Atmospheric Column
• Vacuum Column
� Reduced pressure to keep temperatures below 650°F
Feed Preheat Train & Feed Preheat Train & DesalterDesalter
‣ Feed Preheat Train• Initial heat exchange with
streams from within the tower� Heat recovery important to
distillation economics!» First absorb part of the
overhead condensation load
» Exchange with one or more of the liquid sides streams, beginning with the top (coldest) side stream.
• Final heating in a direct fired heater� Inlet typically 550°F� Heated no higher than
750°F » Minimize thermal cracking
‣ Desalter• Temperature must be carefully
selected — care taken not to let the water vaporize
� Lighter crudes (> 40°API) @ 250°F� Heavier crudes (< 30°API) @ 300°F
• All crudes contain salts (NaCl, MgCl, …)
� Salt present in the emulsified water� Treated in the field with heat &
chemicals to break oil water emulsions.
• Salt can cause damage to equipment� Scale in heat exchangers can
drastically reduce heat transfer � HCl formation can lead to corrosion� Metals can poison refinery catalysts
• Remove salts & dissolved metals & dirt
� Oil mixed with fresh wash water & demulsifiers.
� Mixed & heated followed by settling
• Separation in electrostatic settling drum
• Wash water up to 10% of crude charge
� ~ 90% of the water can be recovered
• Effluent water treated for benzene
Atmospheric Distillation SummaryAtmospheric Distillation Summary
‣ Column Configuration
• Condenser …
� Partial condenser if no Stabilizer Column.
� Total condenser if Stabilizer Column to remove light ends.
• … but no reboiler.
� Feed preheat exchanger train
» All of the heat to drive the column comes from the hot feed.
o As much as 50% of the incoming crude may be flashed.
• Pumparounds
� Move cooling down column.
� Liquid returned above draw tray
• Side draws
• Side strippers
� “Clean up” side products
• Stripping steam
� Reduce hydrocarbon partial pressure
� Condensed & removed as a second liquid phase.
» Conditions set so it doesn’t condense within the column.
o Can lead to foaming.
» Must be treated as sour water
Atmospheric Distillation SummaryAtmospheric Distillation Summary
‣ Wash Zone• Couple trays between flash zone &
gas oil draw.• Reflux to wash resins & other heavy
materials that may contaminate the products.
‣ Condenser• Typically 0.5 to 20 psig.• Balancing act• Low pressures reduce compression
on overhead system• High pressures decrease
vaporization but increase flash zone temperatures & furnace duty; affects yields
‣ Pumparounds• Reduces overhead condenser load &
achieves more uniform tower loadings
• Provides liquid reflux below liquid draws
‣ Side Draws & Strippers• “Cut point” related to final boiling
point of draw stream• Side strippers remove light
component “tail” & return to main column
• Steam strippers traditional• Reboiled strippers reduce steam
usage & associated sour water
‣ Trays & Pressure Profile• Typically 32 trays in tower• 0.1 to 0.2 psi per tray• Condenser & accumulator• 3 to 10 psi across condenser• Liquid static head in accumulator• Typically 6 to 16 psi across entire
column.
Typical ConfigurationTypical ConfigurationAtmospheric Column w/o Atmospheric Column w/o PreflashPreflash
Refining Overview – Petroleum Processes & Products, by Freeman Self, Ed Ekholm, & Keith Bowers, AIChE CD-ROM, 2000
Crude Electrostatic DesaltingCrude Electrostatic Desalting
Drawings from:Refining Overview – Petroleum Processes & Products, by Freeman Self, Ed Ekholm, & Keith Bowers, AIChE CD-ROM, 2000
OverviewOverview
‣ Crude Stills• Historically the oldest refining process
• Only the first step in crude oil processing
‣ Purpose• To recover light materials
• Fractionate into sharp light fractions
‣ Configuration — May be as many as three columns in series
• Crude Stabilizer/Preflash Column
� Reduce traffic in the Atmospheric Column
• Atmospheric Column
• Vacuum Column
� Reduced pressure to keep temperatures below 650°F
Vacuum DistillationVacuum Distillation
Drawings from:Refining Overview – Petroleum Processes & Products, by Freeman Self, Ed Ekholm, & Keith Bowers, AIChE CD-ROM, 2000
Vacuum Distillation SummaryVacuum Distillation Summary
‣ Column Configuration• Vacuum conditions to keep
operating temperatures low• Large diameter column• Very low density gasses• Condenser for water vapor• Liquid reflux from pumparounds• No reboiler• Stripping steam may be used• Needed for deep cuts (1100°F)
‣ Feed• Atmospheric residuum• All of the vapor comes from the
heated feed stream• Under vacuum (0.4 psi)• Separate higher boiling materials at
lower temperatures• Minimize thermal cracking
‣ Products• May have multiple gas oils• Separate products to increase the
heat recovery in the column• Products recombined downstream• Usually FCCU via hydrotreating• Vacuum resid• Blended — asphalt, heavy fuel oil• Further processing — thermal,
solvent• Choice depends on products & types
of crude
Vacuum Distillation SummaryVacuum Distillation Summary
‣ Dry System• 1050°F+ cut temperature & no
stripping steam • Smaller tower diameters• Reduced sour water production • Pressure profile• Flash zone: 20-25 mm Hg abs & 750
to 770°F. • Top of tower: 10 mm Hg abs
‣ Deep Cut System• 1100°F+ cut temperature & stripping
steam • Steam reduces hydrocarbon partial
pressures• Pressure profile• Flash zone: 30 mm Hg abs• Hydrocarbon partial pressure 10-15
mm Hg abs• Top of tower: 15 mmHg abs
‣ Steam Ejectors & Vacuum Pumps • Vacuum maintained on tower
overhead• Steam systems considered more
reliable• Waste steam is sour & must be
treated• Combinations systems — Last steam
stage replaced with a vacuum pump
SummarySummary
‣ Off spec product can either reprocessed or blended differently at the end.
‣ Pressure drops are important, especially in the vacuum column.
‣ Reuse the heat that you put via heat exchange between the feed & internal column streams.
‣ Refinery capacity is based on how much the atmospheric column can process.
‣ Metals are bad. Can remove some metals via desalters.
‣ Complex column configurations. • No reboilers, heat from feed furnaces.
• Side draws, pumparounds, side strippers.
• Stripping steam.
• 3-phase condensers.
SummarySummary
‣ Increase capacity with a Pre-flash column.
‣ Steam stripping aids in separation without cracking.
‣ Condensed water will have hydrocarbons & dissolved acid gases. Must be cleaned before discharged.
‣ Vacuum gas oils recombined – only separated for operating considerations.
‣ Pumparounds may be required to ensure liquid reflux within the column.
‣ Vacuum columns very wide (short & fat).