Presentation on theme: "Refinery Structure- Evolution Topping Refinery Hydroskimming Refinery Conversion Refinery Mainly fractionation by distillation For production of industrial."— Presentation transcript:
Refinery Structure- Evolution Topping Refinery Hydroskimming Refinery Conversion Refinery Mainly fractionation by distillation For production of industrial fuels Hydro treating units added for fuels quality improvement Addition of several conversion processes to improve: fuels recovery efficiency, further quality improvement, process heavier fractions / crudes & energy efficiency
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.
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 kerosene/gas oil > crude oil > fuel oil. Bottom of the barrel treatment is vital Challenge – Meeting Strict Quality standards & Increasing Demand
Diesel Specs- India
Structure of refinery
Flow Scheme of modern oil refinery
Catalytic processes in refinery
Petroleum refining processes
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.
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) – 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
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
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.
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 = 3 √ T B / S T B - Average molal BP in Deg.Rankine ; S- Sp.gravity at 60°F
Crude Assay- Properties that determine the processibility, product pattern & hence the cost of the crude
These fractions need go through regular refining processes to yield fuels of acceptable grade
Thermal Processes: Cracking & Coking
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 °C and 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 ppm
MS Rana et.al. Fuel,86,1216,2007
Thermal cracking Dubbs process- Universal Oil Products (UOP) Thermal cracking of reduced crude at °C & 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- 227°C 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 Heating oil Residuum
Visbreaking Process Viscosity-breaking- Cracking to reduce the viscosity A mild form of thermal cracking of the residue (10% conversion), at psig pressure at °C 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
Visbreaking- Yield pattern Luisiana Vacuum Residue Arabian Light Atm. residue Feed stock Gravity API Carbon residue Sulfur wt % Product yields Naphtha Light gas oil6.3 Heavy gas oil70.8 Residuum Gravity API Carbon residue Sulfur wt % FeedstockFromProcess Typical productsTo ResidualAtmospheric tower & Vacuum tower DecomposeGasoline or distillate Hydrotreating VaporHydrotreater ResidueStripper or recycle GasesGas plant
Visbreaking- Process variations Hydrovisbreaking Treatment with hydrogen at mild conditions 3 reactors: 1. Visbreaking- Mild cracking with H 2 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 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
Delayed coking The feed is subjected to thermal cracking, in a coke drum, under high pressure & temperature psig & °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 % Product yields Naphtha Light gas oil Heavy gas oil Coke Sulfur wt %
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 °C;residence time 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/m 3 ) gas in one integrated processing step that can virtually eliminate petroleum coke production. ~ 95 % coke conversion is achieved Fluid Coking & Flexi Coking
Fluid coking- Flexibility Feed Quality- Conradson carbon- 15.5; Gravity I°API- 6.4, LV below 1000°F- 8.0%; S- 2.6 %; N- 1.0 %; Ni- 283 ppm; V-126 ppm Low ReactorTempHigh ReactorTemp Yields Hydrogen sulfide H C 1 -C C C °F °F °F to End point Gross coke Net coke Coke Sulfur % Ni ppm V ppm
Flexicoking- Product pattern Vac.Residue propertiesArabia n Light Iranian Heavy Gravity °API Conradson carbon wt % Sulfur Wt % Nitrogen wt % V+Ni ppm90525 Yield across Flexicoking ( Wt %) C 3 gas C 4 saturates0.6 C 4 unsaturates1.3 C °F naphtha °F Gas oil Gross coke Purge coke Coke gas (vol%) PropertyFlexicokeFluid coke Bulk density lb/ft Particle density lb/ft Surface area m 2 /g 7012 Av.Particle size μ Sulfur wt % After particulate removal After sulfur removal H 2 S vppm7100<10 COS vppm150<5 NH 3 vppm<3 HCN vppm<3Nil Solids lb/Mscf0.0042Nil Sulfur wt%9.7,0.04
Thermal Processes-Comparison VisbreakingDelayed cokingFluid coking Mild heating at psi; °C Reduction in viscosity Low conversion `10% Heated coil or drum Moderate heating at °C & 90 psig Soak drums at °C.Processes continues till complete coking occurs Coke removed hydraulically Coke % Yield 30% Severe heating at 10 psi °C Fluid bed with steam Cracking on fluidized coke Higher yield of < C 5 Less/no coke yield Fuel grade gas
MS Rana et.al. Fuel,86,1216,2007 Liquid products from thermal processing require further treatments for use as fuels
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 Propane deasphalting
DAO from propane de-asphalting has the highest quality but lowest yield, possibly due to low critical temp.97°C & 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
Propane deasphalting Propane/Oil ratio- 6:1 to 10:1 by vol.
Deasphalting process - Data ParametersFeedstockDeasphalted OilAsphalt Crude Vol % Vol% feed50.2 Vol% feed Gravity, °API Conradson carbon wt % SUS at 210°F Ni wppm V wppm Cu+Fe wppm SUS-Sabolt Universal Seconds –ASTM D 2161-Related to kinematic viscosity