Refinery Structure- Evolution

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Refinery Structure- Evolution
Mainly fractionation by distillation For
production of industrial fuels
Topping Refinery
Hydro treating units added for fuels quality
improvement
Hydroskimming Refinery
Addition of several conversion processes to
improve fuels recovery efficiency, further
quality improvement, process heavier fractions /
crudes energy efficiency
Conversion Refinery
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Processing of light crude
Processing of light crude, even in a
complex/modern refinery with FCC, hydrocracking
etc. does not yield a satisfactory product
distribution. The amounts of fuel oil are too
high.
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Processing of heavy oil

• For heavy oil the situation is even worse with
  50 fuel oil being produced even in a complex
  /modern refinery.
• Fuel oil is worth lt original crude. The value of
  the products decreases in the order gasolinegt
  kerosene/gas oil gt crude oil gt fuel oil.

Bottom of the barrel treatment is vital Challenge
Meeting Strict Quality standards Increasing
Demand
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Gasoline Specs-India
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Diesel Specs- India
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Structure of refinery
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Flow Scheme of modern oil refinery
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Catalytic processes in refinery
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Petroleum refining processes
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Petroleum Refining- Types of Operations

• Fractionation (distillation)-
• Separation of crude oil in atmospheric and vacuum
  distillation towers into groups of hydrocarbon
  compounds of differing boiling-point ranges
  called "fractions" or "cuts."
• Conversion Processes
• Changing the size and/or structure of hydrocarbon
  molecules via different processes
• Decomposition (dividing) by thermal and catalytic
  cracking
• Unification (combining) through alkylation and
  polymerization and
• Alteration (rearranging) with isomerization and
  catalytic reforming.
• Treatment Processes
• For additional processing and to prepare finished
  products.
• Removal or separation of aromatics / naphthenes/
  impurities / undesirable contaminants.
• Chemical or physical separation e.g. dissolving,
  absorption, or precipitation
• Desalting, drying, hydro de-sulfurization,
  sweetening, solvent refining, solvent
  extraction, and solvent de-waxing.

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Processes in Oil Refining Processes in Oil Refining Processes in Oil Refining
Physical Thermal Catalytic
Distillation Visbreaking Fluid Catalytic Cracking
Solvent extraction Delayed coking Hydrotreating
Solvent dewaxing Fluid cocking Catalytic Reforming
Propane deasphalting Flexi coking Catalytic dewaxing
Blending Hydrocracking
Isomerization
Alkylation
Etherification
Polymerization
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Petroleum - Properties

• Density
• Specific gravity - Ratio of mass of specific
  volume to mass of the same volume of water, both
  at the same temperature
• API Gravity
• Degrees API (141.5/Specific gravity at 60/60
  F) 131.5
• Viscosity- cP- Flow characteristics
• Kinematic viscosity/fluidity Viscosity/
  Specific gravity
• Carbon residue (wt)
• Carbonaceous residue left out after destructive
  distillation- non-volatile part of
  petroleum/petroleum products
• Ramsbottom method- ASTM D 189 IP3
• Conradson method - ASTM D 189 IP4
• Viscosity and Asphaltenes, Nitrogen Sulfur
  contents increase with
• increasing carbon residue
• Indicates the potential for coke formation

Signify Light/Heavy character of Crude oil
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Petroleum - Properties

• Aniline point
• Temperature at which exactly equal parts of two
  components are
• Miscible- Aniline Any petroleum fraction/oil
• Increases slightly with molecular weight
• Increases rapidly with paraffinic character/
• Higher the aniline point- lower is the aromatics
  content in the fraction

• Reid vapor pressure (RVP)
• A measure of the volatility of gasoline. It is
  defined as the absolute
• vapor pressure exerted by a liquid at 100 F
  (37.8 C) as determined
• by the test method ASTM-D-323.
• RVP differs slightly from the True Vapor
  pressure (TVP) of a liquid
• due to some small sample vaporization and the
  presence of water
• vapor and air in the confined space of the
  test equipment, i.e. the RVP
• is the absolute vapor pressure and the TVP is
  the partial vapor pressure

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Petroleum - Properties

• Cloud point
• The temperature of the test specimen at which wax
  crystals have formed sufficiently to be observed
  as a cloud from a petroleum fraction
• Applicable for petroleum products and biodiesel
  fuels
• An index of the lowest temperature of their
  utility for certain applications.
• Petroleum blending operations require a precise
  measurement of the cloud point.
• Smoke point
• Provides an indication of the relative smoke
  producing properties of kerosines and aviation
  turbine fuels in a diffusion flame.
• Related to the hydrocarbon type composition of
  such fuels, esp. aromatics
• More aromatic the fuel the smokier the flame.
• A high smoke point indicates a fuel of low smoke
  producing tendency.
• The smoke point is quantitatively related to the
  potential radiant heat transfer from the
  combustion products of the fuel.

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Petroleum- Properties

• Pour point
• The lowest temperature at which it will pour or
  flow under prescribed conditions. It is a rough
  indication of the lowest temperature at which oil
  is readily pumpable.
• Can be defined as the minimum temperature of a
  liquid, particularly a lubricant, after which, on
  decreasing the temperature, the liquid ceases to
  flow.
• UOP K factor ( Watson Characterization factor)
• K 3v TB/ S TB- Average molal BP in
  Deg.Rankine S- Sp.gravity at
• 
  
  60F

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Crude Assay- Properties that determine the
processibility, product pattern hence the cost
of the crude
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These fractions need go through regular refining
processes to yield fuels of acceptable grade
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• Thermal Processes
• Cracking Coking

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Desalting

• Objectives
• Removal of water, inorganic salts, water soluble
  metals suspended
• solids from crude oil Prevention of corrosion,
  fouling plugging of equipments
• Process
• Two stage desalting is carried out, with removal
  of most of the water at first
• stage, followed by addition of dilution water in
  the second stage to extract
• soluble salts metals. Process conditions are
  90-150C and 50-250 psi.
• Surfactants are added to demulsify achieve
  proper separation and remove
• water by settling. Application of electrostatic
  coalescing is also adopted

• Effective desalting
• 1 kg salt/1000 bbl
• Chlorides 10-30 ppm

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MS Rana et.al. Fuel,86,1216,2007
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MS Rana et.al. Fuel,86,1216,2007
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Thermal cracking

• Dubbs process- Universal Oil Products (UOP)
• Thermal cracking of reduced crude at 455-540C
  100 -1000 psi
• Major products- Gasoline middle distillates
• Soaking of light heavier fractions further
  cracking
• Thermal cracking of Reduced crude oil
• Feedstock API gravity 25 C IBP- 227C
• Cracking parameters- 500 C Soaker pressure
  225 psi
• Product yields (Vol)
• With recycle of H. Oil
  W/o recycle of Heating oil
• Gas - 1.0
• Naphtha 57.5
  42.0
• Heating oil 0.0
  23.0
• Residuum 37.5
  34.0
  

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Visbreaking

• Process
• Viscosity-breaking- Cracking to reduce the
  viscosity
• A mild form of thermal cracking of the residue
  (10 conversion), at 50-300 psig
• pressure at 455-520C to reduce viscosity/
  pour point.
• Liquid phase cracking. Process optimized to
  minimize coke formation
• Water injected with the feed to provide
  turbulance control temperature
• Residue from Atmos. / Vac. distillation units
  can be used
• Coil/Furnace type- high temp. short residence
  time
• Soaker type- Lower temp. longer residence
  time
• Benefits
• 5-10 conversion leads to 5 fold decrease in
  viscosity
• Reduction in pour point
• Less coke formation vis-a vis other processes
• Blending of LHO to FO minimized
• Product stability is the issue- Olefinics

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Visbreaking- Yield pattern
Luisiana Vacuum Residue Arabian Light Atm. residue
Feed stock Gravity API Carbon residue Sulfur wt 11.9 10.6 0.6 16.9 3.0
Product yields Naphtha 6.2 7.8
Light gas oil 6.3
Heavy gas oil 70.8
Residuum Gravity API Carbon residue Sulfur wt 88.4 11.4 15.0 0.6 20.9 1.3 5.0
Feedstock From Process Typical products To
Residual Atmospheric tower Vacuum tower Decompose Gasoline or distillate Hydrotreating
      Vapor Hydrotreater
      Residue Stripper or recycle
      Gases Gas plant
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Visbreaking- Process variations

• Aquaconversion
• Catalytic process in slurry mode
• Oil soluble catalyst and water
• Alkali metal catalysts activate the
• transfer of hydrogen from water as H
• Coke formation is reduced

• Hydrovisbreaking
• Treatment with hydrogen at mild
• conditions
• 3 reactors
• 1. Visbreaking- Mild cracking with H2
• 2. Demetallation
• 3. Hydrocracking
• Reactors 2 3 use Co-Mo-Alumina
• catalyst for removal of metals and
• cracking of heavier molecules.
• Less Coke formation
• Better quality product- demetallized

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Delayed coking

• The feed is subjected to thermal cracking, in a
  coke drum, under high pressure
  temperature-15-90 psig 415-450 C
• Held (delayed) 24 hours for the process to get
  completed
• Two coke drums used, one for processing and the
  other for coke
• removal cleaning
• Virtually eliminates residue fraction-forms solid
  carbon/fuel
• Highly aromatic coke, retains S,N metals
• Naphtha, LGO HGO used for gasoline/diesel/FCCU
  after hydrotreating

Luisiana Resid Kuwait Resid
Feed stock Gravity API Carbon residue Sulfur wt 12.3 13.0 0.7 6.7 19.8 5.2
Product yields Naphtha 22.8 26.7
Light gas oil 18.4 28.0
Heavy gas oil 37.6 18.4
Coke Sulfur wt 23.7 1.3 30.2 7.5
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Fluid Coking Flexi Coking

• Both FLUID COKING (1954) and FLEXICOKING (1976)
  use fluid bed technology
• Thermally convert heavy oils such as vacuum
  residue, atmospheric residue,
• tar sands bitumen, heavy crudes, deasphalter
  bottoms other heaviers
• Heat for the process is supplied by partial
  combustion of coke. Remaining coke is
• withdrawn as product
• Feed is injected into a fluidised bed with hot
  coke particles. Steam is injected at the
• bottom for fluidization
• New coke formed is deposited as a thin layer on
  the surface of circulating coke
• particles Coking vessel temp-480-565Creside
  nce time 15-30 sec.
• FLEXICOKING goes one step beyond FLUID COKING
  in addition to
• generating clean liquids, FLEXICOKING also
  produces a low-BTU (90 BTU/Cu.ft
• or 800 Kcal/m3) gas in one integrated
  processing step that can virtually eliminate
• petroleum coke production. 95 coke
  conversion is achieved

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Fluid coking- Flexibility

• Feed Quality- Conradson carbon- 15.5 Gravity
  IAPI- 6.4, LV below 1000F-8.0 S- 2.6 N-
  1.0 Ni- 283 ppm V-126 ppm
• Low
  ReactorTemp High ReactorTemp
• Yields
• Hydrogen sulfide 0.5
  0.7
• H2 0.1 0.2
• C1-C3 8.0 9.0
• C4 1.6 2.0
• C5-215F 4.2 5.1
• 215-400F 8.6 10.4
• 400F to End point 58.4 51.8
• Gross coke 18.5 20.2
• Net coke 10.0 10.6
• Coke
• Sulfur 3.4 3.4
• Ni ppm 1520 1400
• V ppm 680 620
  

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Flexicoking- Product pattern
Vac.Residue properties Arabian Light Iranian Heavy
Gravity API 6.5 5.1
Conradson carbon wt 19.2 21.4
Sulfur Wt 4.29 3.43
Nitrogen wt 0.34 0.77
VNi ppm 90 525
Yield across Flexicoking ( Wt )
C3 gas 9.8 9.9
C4 saturates 0.6 0.6
C4unsaturates 1.3 1.3
C5- 360F naphtha 11.2 11.0
360-975F Gas oil 53.7 50.8
Gross coke 23.4 26.4
Purge coke 1.1 1.2
Coke gas (vol) 13.1 15.5
Property Flexicoke Fluid coke
Bulk density lb/ft3 50 60
Particle density lb/ft3 85 95
Surface area m 2/g 70 12
Av.Particle size µ 120 170-240
Sulfur wt 2.0 6.0
After particulate removal After sulfur removal
H2S vppm 7100 lt10
COS vppm 150 lt5
NH3 vppm lt3 lt3
HCN vppm lt3 Nil
Solids lb/Mscf 0.0042 Nil
Sulfur wt 9.7 ,0.04
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Thermal Processes-Comparison
Visbreaking Delayed coking Fluid coking
Mild heating at 50-200psi420-490C Reduction in viscosity Low conversion 10 Heated coil or drum Moderate heating at 450-500C 90 psig Soak drums at 450-480C .Processes continues till complete coking occurs Coke removed hydraulically Coke- 20-40 Yield 30 Severe heating at 10 psi 450-565C Fluid bed with steam Cracking on fluidized coke Higher yield of lt C5 Less/no coke yield Fuel grade gas
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Liquid products from thermal processing require
further treatments for use as fuels
MS Rana et.al. Fuel,86,1216,2007
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Propane deasphalting

• Generic name- Solvent Deasphalting (SDA) to yield
  DeAsphalted Oil (DAO)-Feeds- Vac residue/bitumen
• Coke-forming tendencies of heavier distillation
  products are reduced by removal of asphaltenic
  materials by solvent extraction.
• Liquid propane is a good solvent. Butane,
  pentane, Heptane or mixture of solvents are also
  commonly used.
• Vacuum residue is fed to a counter current
  deasphalting tower.
• Deasphalting is based on solubility of
  hydrocarbons in propane, i.e. the type of
  molecule Alkanes dissolve in propane whereas
  asphaltenic materials (aromatic compounds),
  coke-precursors do not.
• Asphalt is sent for thermal processing.
• Deasphalted oil can be used as Lube oil base
  feedstock (LBFS) or as feed to FCCU

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Propane deasphalting

• DAO from propane de-asphalting has the highest
  quality but lowest yield, possibly due to low
  critical temp.97C Max extraction temp-82 C
• Mixtures of propane n-butane more suitable for
  better extraction.
• Using pentane may double or triple the yield from
  a heavy feed, but at the expense of contamination
  by metals and carbon residues that shorten the
  life of downstream cracking catalysts due to
  their increased solubility.
• Choice of solvent extraction conditions are
  critical

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Propane deasphalting
Propane/Oil ratio- 61 to 101 by vol.
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Deasphalting process - Data
Parameters Feedstock Deasphalted Oil Asphalt
Crude Vol 23 49.8 Vol feed 50.2 Vol feed
Gravity, API 6.8 18.1 -1.3
Conradson carbon wt 15 5.9
SUS at 210F 75000 615
Ni wppm 73.6 3.5
V wppm 365 12.4
CuFe wppm 15.5 0.2

SUS-Sabolt Universal Seconds ASTM D 2161-Related
to kinematic viscosity