Presentation on theme: "Refinery Structure- Evolution"— Presentation transcript:
1Refinery Structure- Evolution Mainly fractionation by distillationFor production of industrial fuelsTopping RefineryHydro treating units added for fuelsquality improvementHydroskimming RefineryAddition of several conversion processesto improve: fuels recovery efficiency,further quality improvement, processheavier fractions / crudes & energyefficiencyConversion Refinery
2Processing 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.
3Processing 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 < original crude. The value of the products decreases in the order: gasoline> kerosene/gas oil > crude oil > fuel oil.Bottom of the barrel treatment is vitalChallenge – Meeting Strict Quality standards & Increasing Demand
12Petroleum 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 ProcessesChanging the size and/or structure of hydrocarbon molecules via different processes:Decomposition (dividing) by thermal and catalytic cracking;Unification (combining) through alkylation and polymerization; andAlteration (rearranging) with isomerization and catalytic reforming.Treatment ProcessesFor 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 precipitationDesalting, drying, hydro de-sulfurization, sweetening, solvent refining, solvent extraction, and solvent de-waxing.
14Petroleum - Properties DensitySpecific gravity - Ratio of mass of specific volume to mass of the same volume of water, both at the same temperatureAPI GravityDegrees API = (141.5/Specific gravity at 60/60 °F) – 131.5Viscosity- cP- Flow characteristicsKinematic viscosity/fluidity = Viscosity/ Specific gravityCarbon residue (wt%)Carbonaceous residue left out after destructive distillation- non-volatile part of petroleum/petroleum productsRamsbottom method- ASTM D 189 IP3Conradson method - ASTM D 189 IP4Viscosity and Asphaltenes, Nitrogen & Sulfur contents increase withincreasing carbon residueIndicates the potential for coke formationSignify Light/Heavy character of Crude oil
15Petroleum - Properties Aniline pointTemperature at which exactly equal parts of two components areMiscible- Aniline & Any petroleum fraction/oilIncreases slightly with molecular weightIncreases rapidly with paraffinic character/Higher the aniline point- lower is the aromatics content in the fractionReid vapor pressure (RVP)A measure of the volatility of gasoline. It is defined as the absolutevapor pressure exerted by a liquid at 100 °F (37.8 °C) as determinedby the test method ASTM-D-323.RVP differs slightly from the True Vapor pressure (TVP) of a liquiddue to some small sample vaporization and the presence of watervapor and air in the confined space of the test equipment, i.e. the RVPis the absolute vapor pressure and the TVP is the partial vapor pressure
16Petroleum - Properties Cloud pointThe temperature of the test specimen at which wax crystals have formed sufficiently to be observed as a cloud from a petroleum fractionApplicable for petroleum products and biodiesel fuelsAn index of the lowest temperature of their utility for certain applications.Petroleum blending operations require a precise measurement of the cloud point.Smoke pointProvides 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. aromaticsMore 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.
17Petroleum- Properties Pour pointThe 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 = 3√ TB/ S TB- Average molal BP in Deg.Rankine ; S- Sp.gravity at60°F
18Crude Assay- Properties that determine the processibility, product pattern &hence the cost of the crude
19These fractions need go through regular refining processes to yield fuels of acceptable grade
21Desalting Objectives Process Effective desalting Removal of water, inorganic salts, water soluble metals & suspendedsolids from crude oil –Prevention of corrosion, fouling & plugging of equipmentsProcessTwo stage desalting is carried out, with removal of most of the water at firststage, followed by addition of dilution water in the second stage to extractsoluble salts & metals. Process conditions are °C and psi.Surfactants are added to demulsify & achieve proper separation and removewater by settling. Application of electrostatic coalescing is also adoptedEffective desalting1 kg salt/1000 bblChlorides ppm
24Thermal cracking Dubbs process- Universal Oil Products (UOP) Thermal cracking of reduced crude at °C & psiMajor products- Gasoline & middle distillatesSoaking of light & heavier fractions & further crackingThermal cracking of Reduced crude oilFeedstock; API gravity 25 °C ; IBP- 227°CCracking parameters- 500 °C ; Soaker pressure; 225 psiProduct yields (Vol%)With recycle of H. Oil W/o recycle of Heating oilGasNaphthaHeating oilResiduum
25Visbreaking Process Benefits Viscosity-breaking- Cracking to reduce the viscosityA mild form of thermal cracking of the residue (10% conversion), at psigpressure at °C to reduce viscosity/ pour point.Liquid phase cracking. Process optimized to minimize coke formationWater injected with the feed to provide turbulance & control temperatureResidue from Atmos. / Vac. distillation units can be usedCoil/Furnace type- high temp. & short residence timeSoaker type- Lower temp. & longer residence timeBenefits5-10% conversion leads to 5 fold decrease in viscosityReduction in pour pointLess coke formation vis-a vis other processesBlending of LHO to FO minimizedProduct stability is the issue- Olefinics
26Visbreaking- Yield pattern Luisiana Vacuum ResidueArabian Light Atm. residueFeed stockGravity APICarbon residueSulfur wt %11.910.60.616.93.0Product yieldsNaphtha6.27.8Light gas oil6.3Heavy gas oil70.8ResiduumSulfur wt %88.411.415.020.91.35.0FeedstockFromProcessTypical productsToResidualAtmospheric tower & Vacuum towerDecomposeGasoline or distillateHydrotreatingVaporHydrotreaterResidueStripper or recycleGasesGas plant
27Visbreaking- Process variations AquaconversionCatalytic process in slurry modeOil soluble catalyst and waterAlkali metal catalysts activate thetransfer of hydrogen from water as H+Coke formation is reducedHydrovisbreakingTreatment with hydrogen at mildconditions3 reactors:1. Visbreaking- Mild cracking with H22. Demetallation3. HydrocrackingReactors 2 & 3 use Co-Mo-Aluminacatalyst for removal of metals andcracking of heavier molecules.Less Coke formationBetter quality product- demetallized
28Delayed cokingThe feed is subjected to thermal cracking, in a coke drum, under high pressure & temperature psig & °CHeld (delayed) ~24 hours for the process to get completedTwo coke drums used, one for processing and the other for cokeremoval & cleaningVirtually eliminates residue fraction-forms solid carbon/fuelHighly aromatic coke, retains S,N & metalsNaphtha, LGO & HGO – used for gasoline/diesel/FCCU after hydrotreatingLuisiana ResidKuwait ResidFeed stockGravity APICarbon residueSulfur wt %12.313.00.76.719.85.2Product yieldsNaphtha22.826.7Light gas oil18.428.0Heavy gas oil37.6CokeSulfur wt %23.71.330.27.5
29Fluid Coking & Flexi Coking Both FLUID COKING (1954) and FLEXICOKING (1976) use fluid bed technologyThermally convert heavy oils such as vacuum residue, atmospheric residue,tar sands bitumen, heavy crudes, deasphalter bottoms & other heaviersHeat for the process is supplied by partial combustion of coke. Remaining coke iswithdrawn as productFeed is injected into a fluidised bed with hot coke particles. Steam is injected at thebottom for fluidizationNew coke formed is deposited as a thin layer on the surface of circulating cokeparticles; Coking vessel temp °C;residence time sec.FLEXICOKING goes one step beyond FLUID COKING: in addition togenerating clean liquids, FLEXICOKING also produces a low-BTU (90 BTU/Cu.ftor 800 Kcal/m3) gas in one integrated processing step that can virtually eliminatepetroleum coke production. ~ 95 % coke conversion is achieved
34Thermal Processes-Comparison VisbreakingDelayed cokingFluid cokingMild heating at psi; °CReduction in viscosityLow conversion `10%Heated coil or drumModerate heating at °C & 90 psigSoak drums at °C .Processes continues till complete coking occursCoke removed hydraulicallyCoke % Yield 30%Severe heating at 10 psi°CFluid bed with steamCracking on fluidized cokeHigher yield of < C5Less/no coke yieldFuel grade gas
35Liquid products from thermal processing require further treatments for use as fuels MS Rana et.al. Fuel,86,1216,2007
36Propane deasphaltingGeneric name- Solvent Deasphalting (SDA) to yield DeAsphalted Oil (DAO)-Feeds- Vac residue/bitumenCoke-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
37Propane deasphaltingDAO from propane de-asphalting has the highest quality but lowest yield, possibly due to low critical temp.97°C & Max extraction temp-82 °CMixtures 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
38Propane deasphaltingPropane/Oil ratio- 6:1 to 10:1 by vol.
39Deasphalting process - Data ParametersFeedstockDeasphalted OilAsphaltCrude Vol %2349.8 Vol% feed50.2 Vol% feedGravity, °API6.818.1-1.3Conradson carbon wt %155.9SUS at 210°F75000615Ni wppm73.63.5V wppm36512.4Cu+Fe wppm15.50.2SUS-Sabolt Universal Seconds –ASTM D 2161-Related to kinematic viscosity