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SEPERATION PROCESSES
FOR PETROLEUM REFINING
Basics of Separation Operations
Thermodynamics: Phase Equilibrium Mass Transfer and Efficiency of Separation
Operations
st at on Absorption and Stripping
Liquid Liquid Extraction
Crystallization Adsorption
Membrane Separation
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Basics of Separation Operations
Function of Separation
Operation in Refining Crude oil: complex
mixture of a very large of
components Given specifications
petroleum products
Necessary to separate outthe different fractions(cuts)
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I. Basics of Separation Operations
Three mains functions:
Fractionation
Recycling
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Fractionation
Recycling
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I. Basics of Separation Operations Homogeneous Mixtures
Two phases thoroughly mixed in the contact stage Separation factor:
Theoretical stage
mEquilibriu
ABAB
Real stage: separation factor depending on masstransfer kinetics
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I. Basics of Separation Operations Homogeneous Mixtures
Classification according to the separating agent and
the nature of the phases in contact: Distillation
Crystallization by cooling
Li uid Li uid extraction for se aratin com onents whose volatilities are
close and belong to different chemical families) Extractive distillation (Combination of the effect of a phase change by energy
input with the effect of solvent addition)
Adsorption (for difficult separation operations and deeppurification)
Membrane separation based on kinetic selectivity, notinvolving a change in phase (gaseous permeation (gas), Ultra filtration,reverse osmosis (liquid))
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I. Basics of Separation Operations Classification
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I. Basics of Separation Operations Implementation of separation processes
Thermodynamics equilibrium Boiling, Crystallization points, Equilibrium constants
Kinetic factor
Molecular diffusion, Hydrodynamic factors
Mass transfer driving force (C-C*)
Mass flux through the interface
N = K(C C*)
Overall diffusion coefficients (K)
Contact between phases
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I. Basics of Separation Operations Implementation of separation processes
Contact between phases
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I. Basics of Separation Operations Implementation of separation processes
Certain examples
Gas purification operation by means of solvent Separation by fixed-bed adsorption
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I. Basics of Separation Operations Implementation of separation processes
Membrane separation:
Still seldom used in refining
Potential application: Ultra-filtration, Pervaporation andGaseous Permeation
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I. Basics of Separation Operations
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I. Basics of Separation Operations Membrane separation:
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I. Basics of Separation Operations Exercise 1: Relation between the separation
operations processes in the oil refining
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II. Thermodynamics: Phase Equilibrium
Vapor-Liquid Equilibrium
General Description:
Describing a mixture: P, T and [Zi] or P, Vap% and [Zi] orT, Vap% and [Zi]
For binary and ternary mixture
Isobaric Vapor - Liquid Equilibrium Diagrams
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II. Thermodynamics: Phase Equilibrium
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II. Thermodynamics: Phase Equilibrium
Vapor-Liquid Equilibrium
Isothermal Vapor Liquid Equilibrium Diagram
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II. Thermodynamics: Phase Equilibrium Vapor-Liquid Equilibrium
Two phase envelope
Ethane Benzene mixture
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II. Thermodynamics: Phase Equilibrium Vapor-Liquid Equilibrium
Azeotrope:
Ex: n-Hexane and Acetone system
A. Isothermal diagram (T = 50C) B. Isobaric diagram (P = 1.013 bar)
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II. Thermodynamics: Phase Equilibrium Vapor-Liquid Equilibrium
Azeotrope:
Existence only in limited pressure domain (Ex: C2H
6-CO
2)
Exercise 2: Using the SRK model with
ki,j = 0.13 for drawing up isothermal
vapor-liquid equilibrium curves for
the Ethane CO2
system at 263,15K.
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II. Thermodynamics: Phase Equilibrium Equilibrium conditions
Chemical potential and fugacity
Second principle of thermodynamics
Gibbs energy decreases to minimal: dGT,P = 0
Material balance imposing the condition: so
that we can deduce:
At equilibrium, the chemical potential of any component
has the same value in the liquid and vapor phase
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II. Thermodynamics: Phase Equilibrium Equilibrium conditions
Heterogeneous methods to calculate the K value:Apply different models to the liquid and vapor phase
Methods usin the Re ular Solution model
Chao and Seader, Model 1961
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II. Thermodynamics: Phase Equilibrium Equilibrium conditions
Heterogeneous methods to calculate the K value
Methods using the Concept of Local Composition
The NRTL Model (Non-Random Two Liquid)
The UNIQUAC Model (Universal Quasi Chemical)
Models Using Groups Contribution: ASOG and UNIFAC Models
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II. Thermodynamics: Phase Equilibrium Equilibrium conditions
Homogeneous methods to calculate the K value
Representation of the phases at equilibrium by the same
equation of state
Equations of state derived from the Van der Waals theory
For a mixture: ki,j: interaction parameter determined fromexperimental phase equilibrium data
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II. Thermodynamics: Phase Equilibrium Equilibrium conditions
Homogeneous methods to calculate the K value
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II. Thermodynamics: Phase Equilibrium Equilibrium conditions
Homogeneous methods to calculate the K value
Mean relative deviations (%) in the calculation of vapor pressures and densities by the EOS
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II. Thermodynamics: Phase Equilibrium Equilibrium conditions
Relation between Homogeneous and
Heterogeneous Methods
Liquid Liquid Equilibrium
Liquid Liquid Vapor Equilibrium
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II. Thermodynamics: Phase Equilibrium Equilibrium conditions
Solid Liquid Equilibrium: Crystallization
Formulation of lube oils dewaxing
Purification de paraxylene (Tf= 14C), Tf(m-xylene) = -47C
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II. Thermodynamics: Phase Equilibrium Equilibrium conditions
Solid Liquid Equilibrium: Crystallization
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II. Thermodynamics: Phase Equilibrium Equilibrium conditions
Complex mixture
Small number of pseudo-component
Based on TBP distillation
Detailed chromatographic analysis (simulated
Parameters calculated for the model used (critical
coordinates) according to the data available (Tb, S)
Widely used to calculate distillations
Applied seldom to non-ideal due to the presence ofpolar components mixture or liquid liquid equilibrium
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III. Mass Transfer and efficiency of separation operations
Introduction Sizing the various pieces of equipment
Kinetics of transfer of mass
Efficiency of each of the stages
Height of packed column: transfer coefficient betweenphases in contact
Membrane separation: rate of diffusion of each component
Diffusion in a homogeneous phase
Mass transfer between two phases though theinterface
Efficiency of equipment for contact between phases
COMPLEX MECHANISM NEED THE EMPIRICAL DATA
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III. Mass Transfer and efficiency of separation operations
Diffusion in the homogeneous phase
For binary solution
NA, NB (mol.m-2.s-1): Mass transfer to a fixed point of reference
CA, CB: molar concentration (mol.m-3), vA, vB: velocities (m.s
-1)
The average volume velocity v is given by the equation:
Diffusion law: Ficks law
DAB: Molecular diffusion coefficient (m2.s-1)
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III. Mass Transfer and efficiency of separation operations
Diffusion in the homogeneous phase
For binary solution
Mass flow NA in relation to a fixed point of reference
By using C to stand for the total molar concentration:
Correlation designed to predict the value of a diffusion
coefficient (DAB)
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III. Mass Transfer and efficiency of separation operations
Diffusion in the homogeneous phase
In the gaseous phase: Chapman and Cowling (1964)
()A and ()A : diffusion volumes calculated by
summing the contributing terms
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III. Mass Transfer and efficiency of separation operations
Diffusion in the homogeneous phase
In the liquid phase: Wilke and Chang (1955)
D0AB: Diffusion coefficient of solute A at infinite dilution in solvent B (m2.s-1)
.
VA: Molar volume of A at its normal boiling point (cm3
.mol-1
) MB: Molar mass of the solvent (g.mol-1)
B: Association parameter (2.6 for water, 1.9 for methanol, 1.5 for ethanol
and 1 if the solvent does not give rise to any association
Case of concentrated solution
Vignes equation (1966)
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III. Mass Transfer and efficiency of separation operations
Transfer between phase:
Phase 1 and 2 in contact
Mass transfer takes place if they are not at thermodynamic
equilibrium
Driving force of transfer: (C C*) leading the equation:
C* corresponding to equilibrium with the concentration C
K [m.s-1]
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III. Mass Transfer and efficiency of separation operations
Transfer between phase:
Phase 1 and 2 in contact
An individual transfer coefficient relative to phase 1
N = k(C Ci)
An individual transfer coefficient relative to phase 2N = k(Ci C)
C* = mC + q
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III. Mass Transfer and efficiency of separation operations
Predicting Transfer Coefficients Transfer coefficient depends on the diffusion coefficient
Assumed that the concentration gradient limited to a very
thin stagnant film in the neighborhood of the interface
The interface renewal model: limited contact time,transfer in a transient state:
ONLY IN THE STAGNANT MEDIUM OR BOUDARY LAYER EQUATIONIN THE CASE OF A LAMINAR SYSTEM
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III. Mass Transfer and efficiency of separation operations
Predicting Transfer Coefficients In practice: Complexity of hydrodynamic conditions
Impossible to determine the coefficient of transfer of mass
Using the dimensionless numbers
Reynoldss :
Schmidts number:
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III. Mass Transfer and efficiency of separation operations
Predicting Transfer Coefficients
Calculate of Sho(Re,Sc) inside a spherical particle
(Diffusion only)
For a short contact time (Dt/d2 < 0,035):
For fairly large contact time:
Calculate of Sho(Re,Sc) outside a spherical particle
(Diffusion and convection)
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III. Mass Transfer and efficiency of separation operations
Predicting Transfer Coefficients
Calculate of Sho(Re,Sc) outside a spherical particle
(Diffusion and convection)
By Hughmark (1967)
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III. Mass Transfer and efficiency of separation operations
Efficiency and Transfer Coefficients
Tray efficiency
(viscosity in cP or mPa.s)
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III. Mass Transfer and efficiency of separation operations
Efficiency and Transfer Coefficients HETP for packed column
i ill i b i d i i
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IV. Distillation, Absorption and Stripping
IV Di ill i Ab i d S i i
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IV. Distillation, Absorption and Stripping
IV Di till ti Ab ti d St i i
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IV. Distillation, Absorption and Stripping
Realized in the tray column or packing column
Comparison the factors in favor of Tray and PackingTray Column Packed Column
, , ,
(manholes)
Complex column (feed injection product
draw off)
Low liquid retention
Large diameter column Operation when residence time minimized
Overly high/low liquid flow rate - flexibilityof tray design (perforation, use cap, valve)
Small diameter column: Easier install ofcontact equipment
Star-up and shut-down: attenuated
mechanical phenomena
Minimize the tendency to foam
Minimize the column weight
IV Di till ti i th P t l I d t
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IV. Distillation in the Petroleum Industry
Atmospheric distillation of crude oil, including the
important desalting operation
Vacuum distillation of the atmospheric residue
Gasoline distillation and gas fractionation
IV Distillation in the Petroleum Industry
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IV. Distillation in the Petroleum Industry
Atmospheric distillation of crude oil (Topping)
Producing the cuts:
Gasoline cut: feed for the gasoline and gas fractionation
Naphtha cut for the petrochemical industry
Kerosene cut for use in producing aviation fuel
Atmospheric residue as feed to the vacuum distillation unit
Eventually:
Distillate cut drawn off between HGO and the flash zone
for use as a fluxing agent for FO Possible to draw off a light gasoline cut in the distillation
unit at the top and heavy naphtha laterally via stripper
(corrosion problem at the top)
IV Distillation in the Petroleum Industry
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IV. Distillation in the Petroleum Industry
Atmospheric distillation of crude oil (Topping) Designed to allow crudes of different characteristics
A base crude, representative of the refinerys average oil supply
A lighter crude, which sizes the top of the scheme and furnace zones
A heavier crude, which sets the dimensions of the bottom of the
column and the exchanger train
Allowing the variation in the cut points amounting to about twenty
degree Celsius on TBP
Unit able to operate properly at approximately 60% of its normal
capacity
IV Distillation in the Petroleum Industry
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IV. Distillation in the Petroleum Industry
Atmospheric distillation of crude oil (Topping) Description of the process - Pressure: 1 3 barg.
- Products drawn off as side streams
by means ofstrippers
- Generally steam stripped or reboiled- Behaving like reflux absorber,
equipped one to three pumparounds
- Overflash Internal reflux of the first
tray above the feed sent back to the
bottom of tower- Overhead condensation total or
partial: residual gas taken up by
compressor and sent to gas plant
- Main column (~50m high): 30 50
conventional trays- Side stripper: 4 10 trays
- Crude preheated in an exchanger
train by recovering heat to 120
160C and desalted
- Desalting takes place at high pressure (~10 bars)
- Heated in a second exchanger train and furnace
to 330 390C
- Into the main column in a partially vaporized
state
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IV Distillation in the Petroleum Industry
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IV. Distillation in the Petroleum Industry
Atmospheric distillation of crude oil (Topping) Fractionation quality: GAP or OVELAP
IV Distillation in the Petroleum Industry
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IV. Distillation in the Petroleum Industry
Atmospheric distillation of crude oil (Topping) Fractionation quality: GAP or OVELAP
- Other internal specifications
- Flash point of kerosene and gas oils
- End boiling point ASTM D86 of heavy naphtha (generally < 185C)
- Cloud point of heavy gas oil
- Flash point of atmospheric residue
IV. Distillation in the Petroleum Industry
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IV. Distillation in the Petroleum Industry
Atmospheric distillation of crude oil (Topping) Computerized calculation
Choose the thermodynamic model
- Deviations between two extreme models
- Amount of vapor generated in the flash zone: 5%- So, thermal load of overhead condenser: 5%
- Off take temperature: 3 5C
- Overflash: 20%
IV. Distillation in the Petroleum Industry
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IV. Distillation in the Petroleum Industry
Atmospheric distillation of crude oil (Topping) Computerized calculation
Entering Data and Analyzing Results
TBP or ASTM D86 of the crude
Hypothetical component or pseudo-component
Density, Boiling point temperature, molar mass
Number of tray
Thermal exchange zone: 2 4 real trays
Pressure drop between the top and flash zones: 0,4 0,6 bar
IV. Distillation in the Petroleum Industry
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IV. Distillation in the Petroleum Industry
Atmospheric distillation of crude oil (Topping) Computerized calculation
Estimating the Overhead pressure
Amounts of stripping steams Kerosene and gas oils: 15 to 30 kg of steam/m3 of product
Residue: 20 to 30 kg of steam/m3 of residue
Regulating the overflash
3 to 5% of the feed
Analyzing the results
TBP and ASTM product curves
Product specifications (gap or overlap) Flow rate of withdrawn products
Amount of heat extracted by various pumparounds
Convergence Difficulties
IV. Distillation in the Petroleum Industry
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y
Atmospheric distillation of crude oil (Topping) Technology
Conventional technology
Ordinary carbon steel except for hot zones steel alloys
Usually clad with 12% weight chromium steel
Zone exposed to cold corrosion (top of the tower, reflux drum):Monel (Ni Cu ( Fe) alloys) or special coatings
Conventional valve trays of steel alloy 12%Cr
Tray efficiency diminishes from the top to the feed inlet Wash zones structured packing
Draw off tray - feed the side strippers and the pumparound:total draw off type (chimney tray)
Main column feed inlet of the tangential type
Furnace of cabin or cylindrical type
Heat exchangers of TEMA type the nominal working pressuredoes not exceed of 30 bars
Diameter 9m for a tower processing 1000 t.h
-1
of crude
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y
Atmospheric distillation of crude oil (Topping) Process variation
Double condensation at the top
of the column
Other flow diagrams
IV. Distillation in the Petroleum Industry
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y
Atmospheric distillation of crude oil (Topping) Crude Oil Desalting:
Essential operation in the refinery
Fouling of exchanger and the furnace
Corrosion of overhead equipment
Atmospheric residue with high sodium content: fouling rate of thevacuum distillation furnace; shorter cycle length for visbreakers,
ata yst po son ng n cata yt c crac ng, ou ng an corros on o
boiler superheaters Severe environment problems
Sources of the salt in the crude (10 80 mg.l-1)
Inevitable
Delibarable contamination (5 to 50 mg.l-1)
Accidental contamination
Concentration in chlorides of overhead water in the towershould not exceed 10 ppm
IV. Distillation in the Petroleum Industry
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y
Atmospheric distillation of crude oil (Topping) Crude Oil Desalting:
Salt content o a number
of crude oils (before andafter transportation)
IV. Distillation in the Petroleum Industry
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Atmospheric distillation of crude oil (Topping) Crude Oil Desalting and topping
IV. Distillation in the Petroleum Industry
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Atmospheric distillation of crude oil (Topping) Crude Oil Desalting: Mechanism
Diffusion of the crudes salts in water (by washing)
The mixture of water and crude through a mixing valve placed atthe desalter inlet - P = 0,5 (viscous) 1,5 bar(light cude)
Sufficiently fine water-crude emulsion from 1 to 10m
oa escence o wa er rop e s y e ec rocoa escence
Asphaltenes and FeS adsorbed on the water-oil interface stabilizing emulsion agents
Settling (by gravity Stokes law)
IV. Distillation in the Petroleum Industry
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Atmospheric distillation of crude oil (Topping) Crude Oil Desalting: Industrial Implementation
E1 = 200 Volt.cm-1
E2 = 1000 Volt.cm-1
Electrostatic desalter with one stage
Electrostatic desalter with two stages
IV. Distillation in the Petroleum Industry
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Atmospheric distillation of crude oil (Topping) Crude Oil Desalting: Industrial Implementation
Desalters performances
Desalting efficiency of 85 95%
Water content in the desalted crude: mower than 0,2% V (0,4 0,5% for
heavy crudes)
Hydrocarbon concentration in the water coming out not exceed 200ppm
IV. Distillation in the Petroleum Industry
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Atmospheric distillation of crude oil (Topping) Corrosion and Erosion
Corrosive agents: Chlorides, organic acids, non-organic salts, sulfur
compound
Corrosion by salts
Injection of caustic
Metals or metal alloys uses: Ti, Monel, Hastelloy
High Temperature sulfur corrosion
T: 300 420C for ordinary carbon steel
5%Cr-5%Mo steel or 12% - 18%Cr steel
Naphthenic Acid corrosion
T: 220C 240C
Severe corrosion above 350C (furnace 18/10/3 steel alloy)
Erosion
Transfer line, overhead line: high velocity and mitered elbow used
IV. Distillation in the Petroleum Industry
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Atmospheric distillation of crude oil (Topping) Precaution to guard against corrosion risks in topping unit
IV. Distillation in the Petroleum Industry
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Vacuum distillation of the Atmospheric residue Purposes:
Extraction of the distillate cuts to feed conversion unit
Feed for bitumen manufacture
Base stocks for lube oil manufacture
Technologies:
Dry vacuum distillation without injection of steam very low pressure(10 15 mmHg at the top)
Wet vacuum distillation with injection of steam in the furnace feed andstripping steam in the bottom of tower (40 60 mmHg at the top)
Semi-wet vacuum distillation with injection only at the bottom of thecolumn
Use of un ejector (called booster ejector)
Fractionation:
Typical cut points for a 350C TBP atmospheric residue: VGO 350 390C(T90 or T95 ASTM D86 360C), Vacuum Distillate: 390 550C (C, Me)
Reduce heavy oil production: to prolong distillates (exceed 585C TBP)
IV. Distillation in the Petroleum Industry
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Vacuum distillation of the Atmospheric residue Definition of terms specific to vacuum distillation:
LVGO
MVGO
HVGO
Cracked h drocarbons
Non condensable Air entering through leaks
Non condensable dissolved in the feed
Light hydrocarbon produced by cracking in the furnace
Slop cut and overflash (3 5% of the feed): internal reflux
IV. Distillation in the Petroleum Industry
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Flow diagram of a dry vacuum distillation unit
IV. Distillation in the Petroleum Industry
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Flow diagram of a wet vacuum distillation unit
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IV. Distillation in the Petroleum Industry
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Crude oil vacuum distillation Configuration of fractionation
Heat Exchange zones:
Random packing of metal ringand grates (grids)
Fractionation zones:
Structured packing: more effective and
expensive
Wash zone
Less sophisticated grates (grids)
Distributors Sprays or Gravity
IV. Distillation in the Petroleum IndustryComparison of two columns
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IV. Distillation in the Petroleum Industry
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Vacuum distillation Vacuum pumps and Ejector Condenser To create the vacuum
Ejector (venturi effect)-low pressure steam about
of 6 bar
Combination ejector and liquid ring pump similar
to eccentric rotor gas compressors with a seal provided
By a ring of cooled water moving around in a closed circuit
with compression ratio of about 10 (eq. to 2 or 3 ejectors)
IV. Distillation in the Petroleum Industry
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Gasoline Distillation and Gas Fractionation Conventional Flow Scheme
Series of column working at different pressure chosen so that the condensation
can be done by air-cooler exchanger or cooling water
First column: stabilization column or debutanizer
After the amine washing, the overhead cut is sent to deethanizer
Stabilized gasoline is usually fractionated into 2 cuts gasoline splitter
are ract onate n a epropan zer
IV. Distillation in the Petroleum Industry
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Gasoline Distillation and Gas Fractionation
IV. Distillation in the Petroleum Industry
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Gasoline Distillation and Gas Fractionation with absorber and stripper
IV. Distillation in the Petroleum Industry
Gasoline Distillation and Gas Fractionation
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Main Operating Conditions
Common Specification
Debutanizer C5 content in butane: 0,5% mass or 1% volume maximum
1% volume maximum C4 in light gasoline
Depropanizer or Deethanizer
Commercial specifications for the products
Propane in Butane: vapor pressure not exceeded 6 bar rel. at 50C Ethane content in propane: vapor pressure not exceeded 14 bar rel at 38,8C
Splitter GAP 20C
IV. Distillation in the Petroleum Industry
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Gasoline Distillation and Gas Fractionation Other configurations
Cryogenic scheme in some applications to recover olefins contained in gas coming
from conversion unit
Set up with a deisobutanizer to recover isobutane for the alkylation unit,
deisopentanizer, de isohexanizer,
Columns for extracting aromatic compound
Gas treatment unit with the diethanolamine (DEA) washing, LPG sweetening,
sulfur trap and drier type in order to meet commercial specification
IV. Distillation in the Petroleum Industry
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FCC Primary Fractionation Similar to a crude topping unit but has two major differences
Totally vaporized and superheated feed (480 540C)
Large proportion of the gases
Feed always contains traces of catalyst Problem of pressure drop to the limits of
capacity of compressor and the activity of
,
A convention configuration includes: HCO
LCO
Heavy naphtha
Overhead vapors: C2-, C3, C4, light gasoline
Eventually an added draw-off of intermediate
gasoline
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IV. Distillation in the Petroleum Industry
f
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Treatment of FCC gas Including the following sequence:
Compressor
Deethanizer, primary absorber/stripper
Debutanizer
C3/C4 separation
Some characteristics
Working at a relatively high pressure (10 20 bars)
High specific liquid load in comparison to vapor loads High vapor gravity low liquid gravity
Favorable for tray
Sour water stripping
Remove H2S and NH3 contained in the water condensed at the top ofatmospheric fractionation column before the biological treatment
Stripping column supplied with the live steam at the bottom
Equipped with random or structured packing
IV. Distillation in the Petroleum Industry
T f FCC
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Treatment of FCC gas
IV. Distillation in the Petroleum Industry
Treatment of FCC gas
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The primary absorber:
To absorb most of LPG contained in the gas coming from HP seperatordrum with FCC gasoline
Equipped with some thirty tray made of 410S
One or two pumparounds to evacuate the heat of absorption
Reflux with a draw-off sump to collect the water or supplying the top ofthe column with the debutanized subcooled FCC asoline
Stripper
Remove th lightest fraction (C1, C2, H2S ) from wild gasoline
Equipped with some thirty tray made of 410S
Reboiled with LCO coming from primary fractionation
Secondary absorber
Gas from the top of the absorber washed with lean oil LCO (T < 40C)
Debutanizer
Adjust the FCC gasoline vapor pressure some forty trays of 410S
Reboiled with HCO coming from primary column
IV. Distillation in the Petroleum Industry
k f
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Coker primary fractionation
Visbreaker primary fractionation
Fractionation of HF Alkylation Effluents
Treatment of Reforming Effluents
V. Liquid Liquid Extraction in the Petroleum Industry
Separation technique based on the differences in solubility
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between the components of a homogeneous liquid feed in a
appropriate solvent
Employed when distillation alone can not provide an
economically satisfactory solution (azeotropy, too small
relative volatility)
Good for separating components by chemical family
In oil and gas industry: dearomatizing gas oil, deasphaltingheavy cut and extracting BTX aromatics
Compose of two main complementary steps:
Extraction implemented in different ways: One-stage, Crosscurrent,single countercurrent, Countercurrent with reflux, Dual solvent
Solvent regeneration generally by distillation
V. Liquid Liquid Extraction in the Petroleum Industry
Solvent characteristics
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Solvent properties related to the thermodynamics of L L equilibrium
Capacity or Solvent power
Selectivity
Physical properties Viscosity: pumping, dispersion energy, mass and heat transfer, settling velocities
Density: density of the extracted phase, difference between the densities of
extract and raffinate for operating the extractor
Surface tension: low surface tension promotes the dispersion of one phase in theother, large interfacial surface area favorable to mass transfer, stable emulsion
Boiling point: differences in volatility great enough to avoid azeotropic
phenomena, minimize equipment size and energy consumption
Other properties Thermal stability
Chemical inertia
Low toxicity, Biodegradable and high flash point
VI. Solvent Extraction in the Petroleum Industry
Extraction of aromatic compound from lube oil stocks in order to produce
lubricants
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lubricants
Deasphalting of distillation residues to produce both DAO and Asphats
Extraction of Aromatic compound from lighter stocks: gasolines or
kerosenes in order to comply with present and future regulation
VI. Solvent Extraction in the Petroleum Industry
Extraction of aromatic compound from lube oil stocks in order to produce
lubricants
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lubricants
VI. Solvent Extraction in the Petroleum Industry
Choice of solvent
S l t (S l t it )
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Solvent power (Solvent capacity)
High selectivity for aromatics molecules
Other points enter into consideration in the choice of a solvent
VI. Solvent Extraction in the Petroleum Industry
Extraction of aromatic compound Furfural Extraction
Extraction solvents are numerous among which furfural meet the target
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Extraction solvents are numerous, among which furfural meet the target
criteria adequately
Examined different variables:
External variables: Solvent, Extractor, feed composition, extraction
efficiency
Internal variables : Solvent ratio, Extraction temperature, Temperature
, ,
Furfural
Phenol N-methyl-2-
pyrrolidone (NMP)
VI. Solvent Extraction in the Petroleum Industry
Furfural Extraction - Comparison
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VI. Solvent Extraction in the Petroleum Industry
Furfural Extraction Points to consider for understanding
Water and furfural form a heteroazetrope
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ate a d u u a o a ete oa et ope
The mutual solubility of water and furfural are not negligible
The solvent power of furfural increases when the temperature increases anddegreases with the molecular mass
The selectivity of furfural toward aromatics degreases when the temperatureincreases
Furfural is chemical compound that is sensitive to oxidation, acids andtemperature.
Inhibitors such as amines protect furfural during the storage against the action ofoxidizing agents but they are difficult to use in a unit in operation
Metal such as copper accelerate the oxidation process that form acids, they inturn make furfural break down into resins
Rate of degradation is proportional to the concentration in H+, so water can alsoaffect furfural
Furfural has tendency to break down with temperature (at 230C, 5% is degradedin 80h) with the formation of resin insoluble in aromatics
Furfural is not inert toward some components of feeds so giving rise to complexpolymers
VI. Solvent Extraction in the Petroleum Industry
Furfural Extraction Choice of extractor
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Present-day trend is to use the high efficiency RDC (Rotating Disc Contactor)
-High number of theoretical stages (up to 10 compared with 5-7 conventional
columns)
-Very clear-cut raffinate/Extract interface- Raffinate yield 3 to 5% higher
-Possibility of optimizing extraction quality depending on the type and flow rate
of feed by using rotating disc
VI. Solvent Extraction in the Petroleum Industry
Furfural Extraction - Flow Scheme
Feed deaeration
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DAO, thermal exchange with the extract to 100C, 50mmHg, eliminate the moisture and air,furfural sensible to oxidation and to presence of water
Extraction Extractor working under pressure (6 bar at the top)
Introduction of feed at the bottom of the extraction zone, solvent at the top of column
Adjusting the feed temperature by an exchanger
Mixed extract side stream drawn off under the feed inlet, cooled in exchanger and sent backto t e tower
Regulated Top/feed/bottom temperature gradient with the set point of the temperature of
the top
Recovery of solvent in the raffinate Equipped exchanger and furnace to heat the raffinate to 200C for vaporizing the furfural in
flash drum and recovering the solvent trace in the steam stripping zone.
Recovery of solvent in the extract Complex circuit to reduce the energy consumption involved in vaporizing furfural
Made up of four consecutive vaporization stages and ends with steam stripping
Water removal and azeotropic distillation section
Drainage system and Inert Gas system
VI. Solvent Extraction in the Petroleum Industry
Furfural Extraction
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10-15% Furfural
20% Furfural
recovery
60% Furfural
recovery
90-85% Furfural
10% Furfural
recovery
VI. Solvent Extraction in the Petroleum Industry
Furfural Extraction
Azeotrope: 35% Furfural 65% H2O
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Azeotrope: 35% Furfural 65% H2O
VI. Solvent Extraction in the Petroleum Industry
N-methyl-2-pyrrolidone (NMP) Extraction
In comparison with furfural, it has the following advantages
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p , g g
Better stability
Better oxidation resistance
Less carryover in the raffinate and the extract Higher solvent power toward aromatics
Lower process temperature
Less toxicity
The following drawbacks
Lower specific gravity
Less selectivity
Higher boiling point
VI. Solvent Extraction in the Petroleum Industry
N-methyl-2-pyrrolidone (NMP) Extraction
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VI. Solvent Extraction in the Petroleum Industry
N-methyl-2-pyrrolidone (NMP) Extraction Dehydration section
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VI. Solvent Extraction in the Petroleum Industry
Deasphalting Purpose of process
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Oily fractions
Production of bright stock and waxes
Preparation of FCC feed with or without an intermediate hydrorefining stepFeed specs for FCC unit: 2000ppm Maxi. Basic nitrogen,
2% Maxi. Conradson carbon content
20ppm mass Maxi. metal
Preparation of hydrocracking feeds to increase the production of high quality
middle distillates
Asphaltic fractions
Production of road quality
Use as components in industrial fuel oil or solid fuels
Feed for conversion unit as visbreakers, oxyvapogasifiers and cokers
VI. Solvent Extraction in the Petroleum Industry
Deasphalting Incorporation of deasphalting process in the lube oil
stock production process
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VI. Solvent Extraction in the Petroleum Industry
Deasphalting Incorporation of deasphalting process es an extra
conversion unit
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VI. Solvent Extraction in the Petroleum Industry
Deasphalting Products and properties
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VI. Solvent Extraction in the Petroleum Industry
Deasphalting Solvent characteristics and operating conditions
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VI. Solvent Extraction in the Petroleum Industry
Deasphalting Solvent characteristics and operating conditions
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VII. Crystallization in Oil Industry
Solvent Dewaxing
Most common Oil/Wax separation based on crystallization with
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a solvent
Ideal solvent: Dissolve the Oil and Precipitate all the Wax
Solubility and selectivity: good solubility for the oil and goodcrystallization selectivity for the wax
Low heat of vaporization
Low congeal point: remain liquid at filtration temperature
No toxicity or corrosivity
Low price and wide availability
In the industry using the mixture of Methyl Ethyl Ketone (MKE)and Toluene (80%) or Methylisobutylketone
VII. Crystallization in Oil Industry
Solvent Dewaxing
Physical properties of MEK and Toluene
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VII. Crystallization in Oil Industry
Dewaxing Process Using an MEK-Toluene Mixture as solvent Crystallization in presence of solvent
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Filtration
Separation between the solvent and the oil or the wax by distillation
VII. Crystallization in Oil Industry
Dewaxing Process Using an MEK-Toluene Mixture as solvent
Products
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- Dewaxed oil and
-Wax with oil content of 10 20%
(slack wax or petrolatum wax)
-Deoiling (wax with very low oilcontent and foots oil)
VII. Crystallization in Oil Industry
Dewaxing Process Using an MEK-Toluene Mixture as solvent(Without in line deoiling)
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VII. Crystallization in Oil Industry
Dewaxing Process Using an MEK-Toluene Mixture as solvent
Four main section:
Crystallization section to cool the
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- Crystallization section to cool the
raffinate and solvent, thereby
crystallizing the waxes
- Filtration section to separate the
dexaed oil from the wax cake
-- D st at on sect on w t two
operation for dewaxing unit without in
line deoiling and three with in line
deoiling to separate the solvent from
de dewaxed oil, the wax and the foots
oil
- Solvent system recovering the
solvent exiting the distillation
operation and redistrubuting it in the
form of dilution