CRUDE DISTILLATION Purpose To recover light materials ... · Crude Stabilizer/Preflash Column...

2/16/2015 NPTEL :: Chemical Engineering Petroleum Refinery Engineering

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CRUDE DISTILLATION Overview Purpose

To recover light materials.Fractionate into sharp light fractions.

Configuration —May be as many as three columns in seriesCrude Stabilizer/Preflash Column

Reduce traffic in the Atmospheric ColumnAtmospheric ColumnVacuum Column

Reduced pressure to keep temperatures below 650o F Crude Oil Fractionation / Distillation

Crude oil is heated to 750 oF (400 oC)Heated crude is separated into rough "cuts“

Different boiling point are drawn from the distillation tower.Light compounds (fuel gas and LPG) rise to the top of the tower, Heavy material(asphalt) falls to the bottom of the tower.

Petroleum Refining Operations.

Petroleum refining begins with the distillation, or fractionation, of crude oils intoseparate hydrocarbon groups like Light ends, naphtha/gasoline kerosine dieseland residue etc.The resultant products are directly related to the characteristics of the crudeprocessed.(T 650750 deg oF) or (310 oC350 oC)Most distillation products are further converted into more usable products bychanging the size and structure of the hydrocarbon molecules through cracking,reforming, and other conversion processes.



Fig 1.10 Atmospheric Distillation[19]

Fig:1.11 Typical Configuration Atmospheric Column w/o Preflash[19,20]



Fig:1.12 ADU & VDU OVERVIEW [24,25]

Wash Zone

Couple trays between flash zone & gas oil draw.Reflux to wash resins & other heavy materials that may contaminate theproducts.

Condenser

Typically 0.5 to 0.2 psig.Balancing act

Low pressure reduce compression on overhead system.High pressure decrease vaporization but increases flash zone temperature &furnance duty: affects yields.

Pumparounds

Reduces overhead condenser load & achieves more uniform tower loading.provides liquid reflux below liquid draws.

Side draws & strippers cut point related to final boiling point of draw steam.



Side strippers remove light component tail & return to main column.Steam strippers traditional.Reboiled strippers reduce steam usage & associated sour water.

Trays & pressure profile [19,20,24,25]

Typically 32 in tower 0.1 to 0.2 psi per tray.Condenser & accumulator 3 to 10 psi across condenser liquid static head inaccumulator.Typically 6 to 16 psi across entire column.

Fig:1.13 A typical configuration of Atmospheric column with stripping section

and reflux drum arrangement.



Fig:1.14[19]A typical configuration of two stage hydrocracking unit.

Table:1.4

Typical Crude Tower Cut Points[19,20]

CUT TBP IBP(oF) TBP EP(oF)

Light Naphtha(LSR Gasoline) 80 to 90 180 to 220

Heavy Naphtha 180 to 220 330 to 380

Distillate (Kerosene) 330 to 380 420 to 520

AGO(Atm Gas Oil) 420 to 520 650

LVGO(Light Vac Gas Oil) 650 800

HVGO(Heavy Vac Gas Oil) 800 950 to 1100

Vaccum Resid 950 to 1100

CRUDE DISTILLATION Purpose To recover light materials ... · Crude Stabilizer/Preflash Column...

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