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).