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PresentationOnDelayed Coking TechnologyBIRENDRA KUMAR (CTSM)BARAUNI REFINERYBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERTopics of Discussion• Thermal Cracking•Brief Overview of Delayed Coker• Feedstock• Operating variables• Coking reactions• Products• Coke formation and type of coke.• Coke Drum Cycle• Safety Hazards• Modern Delayed Coker Design FeaturesBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERThermal Cracking ProcessBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERAdvantages of Thermal Cracking•Thermal Cracking – It is simple and cost effective process. However,rapid uncontrolled thermal cracking produces undesirable products s likegas and coke.• Limitations of Catalytic Cracking for Resid Processing – In resid feedstock presence of high molecular weight compoundslike resins, asphaltenes and metals make it unsuitable for catalyticcracking. RFCC can process resid feed only upto a certain limit. Metals and sulphur compounds present in resid feedstock act ascatalyst poison.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERVarious Thermal Cracking Processes• VISBREAKING It is a thermal cracking process producing gas, distillates and visbroken residue(FO).• DELAYED COKING Continuous thermal cracking process which generates coke and produces variousdistillates in fractionator from vacuum residue. Coke drum temperature remainsaround 415 °C – 450 °C.• FLUID COKING Continuous coking process where residuum is sprayed on to fludised bed of hotcoke particles. Here cracking takes place at much higher temperature ture than delayedcoking (temperature upto 565 °C).• FLEXI COKING Continuous coking process like Fluid Coking which includes a gasification section ofcoke produced in Fluid Coking Operation.Among the above processes Delayed Coking is most popular.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERThermal Cracking Reactions•Thermal cracking reactions take place due to application of heat.During the cracking process, large molecules decompose and formsmaller (lighter) molecules.• In thermal cracking generally two types of reactions take place – Primary reactions by decompositions of large molecules to smallermolecules. Secondary reactions by which active products from primarycracking reactions further crack or react to form other molecules s orpolymerize to generate heavy products (coke).Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERThermal Cracking Reactions•Thermal cracking of long chain oil molecules into shorter chainsproceeds through a free radical mechanism -C nH2n+2 C n-2H 2n-3 + C 2H 5Initially formed free radicals readily combine with otherhydrocarbons/free radicals/decomposed to form olefins.C 2H 5+ C nH 2n+2 C nH 2n+1 + C 2H 6C nH 2n+1 C n-1H 2n-2 + CH 3C nH 2n+1 C nH 2n + HC n-2H 2n-3 + H C n-2H 2n-2C n-2H 2n-3 C (n-2)/2n-2+ C (n(n-2)/2H n-1Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERThermal Cracking Reactions•Aromatics & polyneuclear aromatics undergo condensation reaction withthe formation of Asphaltenic compounds (coke forming compounds).Some typical reactions are –+ + H 2+ 2H 2CH 3 CH 3CH 3 CH 3+ + H 2+ 2H 2Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKER• Delayed Coking is the most commonly used carbon rejection processthat upgrades residues to a wide range of lighter hydrocarbon gasesand distillates through thermal cracking.• The byproduct of delayed coking process is petroleum coke.• The goal for delayed coker operation is to maximise the yield of cleandistillates and minimise the yield of coke.• Delayed coking technology is preferred for upgrading heavierresidues due to its inherent flexibility to handle even the heaviestresidues while producing clean liquid products.• The main products of delayed coker operation is off-gas (from whichLPG is recovered), naphtha, Light Gas Oil (LCGO) and Heavy Gas Oil O(HCGO). LCGO is sent to Hydrotreater for production of Gas Oil andHCGO to refinery FO Pool/ RFCC feedstock/ OHCU feedstock.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKER• The yield slate for a Delayed Coker can be varied to meet a refinerner’s s objectivethrough the selection of operating parameters.• Three operating parameters govern the yield pattern and product quality ofDelayed Coker –‣ Temperature‣ Pressure‣ Recycle Ratio (RR)• Increasing coking temperature decreases coke production and increases liquidyield and gas oil endpoint. However, temperature can be adjusted d only anarrow range to control volatilities left in coke.• Increasing pressure and/or Recycle Ratio (RR) increases gas and coke makeand decreases liquid yield and gas oil endpoint. RR can be varied d from 0% to120%.• Recycle Ratio is defined as –(Composite feed to Coker Heater)/ (Primary feed to Fractionator bottom)Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKER• Modern trend of Delayed Coking technology is to minimise the cokingpressure and recycle ratio within the economic and technicalconstraints for designing a unit while producing clean Heavy CokerGas Oil (HCGO) product within following quality – Low contaminant level of carbon residue.Low contaminant level of metal. End point within acceptable level.• Delayed Coker products typically require further downstreamhydroprocessing because of hydrogen deficiency and sulphurcontamination.• Fuel grade coke is a low value byproduct. However it has significantdemand as a clean and economic fuel.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERDelayed Coking Feedstock –• Delayed Coker can process a wide variety of feedstocks :-‣ Feedstock can have considerable amount of metal (Ni + V), Sulphur,Resins and Asphaltenes.‣ Contaminants present in feedstock mostly gets eliminated with coke. c•Most typical feedstock is Vacuum Residue (530 °C C +). It can also processrefinery slop oil/ sludge.• Atmospheric residue is also occasionally processed.• Typical feed composition –‣ Sulphur – 5 to 6 % wt‣ Metals 1000 ppmw.‣ CCR – 20 TO 30 % wt.• Properties of coke mostly depends on feed quality.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERDelayed Coking ProcessBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERChemical Reactions of Carbonization –•There are three types of chemical reaction processes which occur continuouslywithout any distinct steps in the coking process –‣ Dehydrogenation – The initial reaction in carbonization involves the lossof hydrogen atom from an aromatic hydrocarbon and formation ofaromatic free radical intermediate.‣ Rearrangement Reactions – Thermal rearrangement usually leads toformation of more stabilised aromatic ring system which forms buildingblock of graphite growth.‣ Polymerisationof aromatic radicals – Aromatic free radicals getpolymerised in the process of coking reaction. This process is initiated inthe liquid phase and continued in different steps.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERREACTOR485 O C420 O C485 O CREACTORLDO / SLOPQUENCHBFWBFWQUENCHCOL nFLUE GAS410 O CMP STEAMBFWRFOMPSTEAMBFW240 O C115 O CMAINFRACTIONATOR200 O C330 O C280 O CMPSTEAMBFW1.8 kg/cm 2 g45 O C405 O C 45 O C95 O CIRFO IRCRSOUR WATERNAPHTHA45 O CLCGO - IMP STEAMLCGO - IIBFWMP STEAM95 O CBFWOFFGASFRESH FEEDHCGOFURNACE340 O C340 O CPETROCOKE502 O CBOTTOM PUMPBOTTOM PUMPDCU FLOW DIAGRAMBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERTypical Drum Cycle Time –Drum CycleHoursSteam to Fractionator 0.5Steam to Blowdown 1.5Low range cooling & water quench 4.5Depressurisation & Drain 2.0Unheading top and bottom cover 1.0Coke Cutting 3.0Reheading/ steam testing/ purge 1.0Drum warm-up/ Vapour heating 4.0Change-over / Drum Switch 0.5Total 18.0Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERCYCLIC PROCESS OFDELAYED COKINGLITTLE STEAMBIG STEAMLITTLE WATERBIG WATERWATER DRAINCOKING CYCLEOF A COKE DRUMDECOKING CYCLEOF A COKE DRUMCOKINGCOKE DRUM PREHEATCOKE DRUM STEAM PR. TESTCOKE DRUM STEAM PURGECOKE DRUMUNHEADINGHYDRAULICDECOKINGCOKE DRUMHEADINGBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERCoke Drum Warm-upup–•To prepare the empty coke drum for receiving feedstock ex process s heater, hotvapors from online drum are circulated into the empty drum for preheating pof cokedrum.•The hot vapours (at around 415 °C) condenses inside the cold vapour drum,heating the drum to a target temperature of around 340 °C.•Condenservapours are continuously drained out of the drum initially through theblowdown circuit and later to main fractionator.•Aftervapour heating the drum for few hours, hot oil (RCO/ VR) ex furnace (ataround 485 °C) is switched to drum.•Most of the vapour condenses on the colder wall of the drum , liquid remaining asboiling pool of oil at the bottom.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERSteam Stripping –•Steam must be flowing before the switch and immediately after the e switch andimmediately after the switch otherwise the neat unconverted feedstock on thetop of coke bead will run down the channels which will solidify and plug thechannels.•This will lead to isolation / plugging of the coked portion from steam andcooling water resulting in formation of hot spots.•These hot spots may result in dangerous steam eruption during cutting of cokewhich is a potential safety hazard.•Steam stripping also serves to transfer heat from the hot bottom portion of thecoke bed to unconverted liquid present at the top of the coke drum.•Adequate steam stripping increases the quantity of recovered gas oil as well asreduce the amount of volatile matter present in the bottom section of the cokedrum.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERDelayed Coking ProductsBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERProducts of Delayed Coking –•Delayedcoker produces desirable liquid products (naphtha and gasoil) and byproducts coker gas and solid coke.•Coker off-gas goes to the gas plant where C3 and C4 is recovered asLPG and the lighter end can be used as fuel gas in the refinery.•Naphtha ex coker unit contains high olefin content and this stream isusually sent to hydrotreater for stabilisation.•Light Coker Gas Oil (LCGO) is sent to diesel hydrotreaterforproduction of diesel. Typical end point of this stream is around 370 °C.•Heavy Coker Gas Oil (HCGO) is sent to FCC/ RFCC for production of ovaluable distillate products. Typical end point of this stream is around538 °C.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERTypical Yield Pattern of Delayed Coking –PARTICULARS PR BRFeed Quality :-Feed CCR, % wt 22 11Feed “S”, % wt 4.8 1.2Yield Pattern (% wt) : -Gas + H 2S 5.0 8.0LPG 3.0 4.0Light Naphtha 6.0 8.0Heavy Naphtha 5.0 -LCGO 32.0 40HCGO 19.0 15Coke 30.0 25Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERType of Coke –Coke formed in Delayed Coker Unit can be classified into threedifferent types–‣Sponge Coke‣Needle Coke‣Shot CokeBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERSponge Coke –• Sponge Coke is porous, irregular shaped lumps.•It was named by its sponge like appearance.•Vacuum Residue with low to moderate asphaltene produces spongecoke.• Most of the sponge coke is used as fuel.•Some sponge coke with low sulphur (< 2% wt) and metal content canbe used to make anodes used in aluminium industries.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERNeedle Coke –•It is a premium coke from Delayed Coker named by its needle likeappearance.•Feedstock with aromatic component (without much asphaltene) ) helpsto produce needle coke. FCCU decant oil after hydrodesulphurisation forremoval of sulphur used as needle coke feedstock.• It has microscopic, elongated, needle like structure.•It has very low coefficient of thermal expansion (CTE) and electricalresistance suitable for using as electrodes in steel making.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERShot Coke –•It is formed from high asphaltene content feedstock present at highcoke drum temperature.• Shot coke is undesirable product in delayed coking.•With the light ends flashing-off small globules of tar are formed whichrapidly converted to coke due to huge heat generation duringexothermic asphaltene polymerisation reaction.• Shot coke is usually blended with sponge coke to use as fuel.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERComparison of Different Types of Coke –Sponge Coke Needle Coke Shot Coke• Porous, irregularshaped.• Feed – Moderateasphaltene level.• High “S” – FuelGrade.• Low “S” – AnodeGrade.• Needle likestructure.• Feed – Low “S”,verylowasphaltene witharomaticcomponent.• Premium GradeCoke.• Very low CTE.• Undesirable.•Feed – HighAsphaltene.•Difficult andunsafe to handle.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERThumb Rule for Yield Prediction –• Coke and liquid yields can be predicted by simple equationa as under -• Coke Yield (wt%) = 1.6 X (wt% feed CCR)• Gas (C4 - ), wt% = 7.8 + 0.144 X (wt% feed CCR)• Gasoline (wt%) = 11.29 + 0.343 X (wt% feed CCR)• Gas Oil (wt%) = 100 – wt % coke – wt % gas – wt % GasolineBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKEREffect of Operating VariablesBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKEREffect Of Coke Drum Temperature –•At constant pressure and recycle ratio, the coke yield decreases anddistillate yield increases as drum temperature increases.•If the temperature is too low, the coking reaction does not proceed farenough and pitch and soft coke formation occurs.•When the temperature is too high the coke formed generally is veryhard and difficult to remove from the coke drum with hydraulicdecoking equipment.•The temperature is used to control the Volatile Combustible Matter(VCM) of coke. At higher temperature VCM is reduced.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKEREffect Of Coke Drum Pressure –•Coke yield decreases by reducing coke drum pressure. Every 0.5kg/cm2 reduction in coke drum pressure increases liquid yield by 1.3%vol and reduces coke yield by 1 % wt of fresh resid feed.•For producing premium grade coke, coke drum should operate athigher pressure. Raising the pressure suppresses vaporisation of gas oilin the coke drum. It extends the retention time of aromatic compoundsoundswhich favours the formation of better quality coke.•Higher pressure improves the coke quality w.r.t lowering of Co-efficient of Thermal Expansion (CTE) and electrical resistivity.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKEREffect Of Recycle Ratio (RR)–•Increase in Recycle Ratio (RR) increases coke make and improves cokeproperties.•Increase in Recycle Ratio lowers the combined feed resin asphaltene contentand in turn also provides a higher concentration of aromatics in coke drums.•High RR – Results in more coke, more gas & gasoline, less distillate, lessdeposition of coke in heater tubes.•Low RR – Results in less coke, less gas & gasoline, more distillate, moredeposition of coke in heater tubes.•HCGO quality deteriorates at lower RR w.r.t its density, CCR, metal content,end point etc.•ModernCokers operate at 10% or less RR to increase unit throughput.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKEREffect Of BFW Injection in Heater Coils –• Used as a turbulising water in heater coils.• Reduces partial pressure of hydrocarbon in the coke drum.• Leads to formation of loose coke.•Normallyturbulising water is kept @ 1% of pass flow. However, itdepends on heater design.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERSummary of Impact of Operating Parameters –Increasing Gas Yield C5 + LiquidYieldPressureRecycle RateCoil TemperatureVelocity MediumCoke YieldHCGOQualityImprovesImprovesDeterioratesDeterioratesBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERProcess Licensors of Delayed Coker –Some of the well known process licensors of Delayed Coker Unitare as under–‣ Foster Wheeler‣ Lummus Technology‣ Conono Philips‣ Exxon Mobil etc.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERSafety Hazards & MitigationBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERDelayed Cokers – Safety Hazards :–:• Coke drum switching –‣ Severe accidents reported due to faulty valve operation duringcoke drum switching operation.• Coke drum head removal –‣ Hot eruptions due to inadequate coke bed cooling.‣ Incomplete draining before bottom head removal.‣ Avalanche of shot coke during bottom head removal.• Coke cutting operations –‣ Cutting tool raised out of coke drum without isolation.‣ Bursting of water hose.‣ Failure of wire rope supporting the drill stem.• Others –‣ Dust irritation, toxic exposure, coke handling by o/h cranes,conveyors, crushers pay loaders etc.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERDelayed Cokers – Mitigation of Safety Hazards :–:• Coke drum switching –‣ Remote operated system for removing faulty operation.‣Colourcoding of valves to avoid faulty operation.‣ Employees working in pair – “buddy system”• Coke drum head removal –‣Remote opening/ closing of coke drum head.‣Restricted movement of people on coke drum top and bottomplatforms.• Coke cutting operations –‣Interlocks to prevent drill stem to come out of the coke drum w/oisolation.‣Remote switch off for jet pump.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERModern Delayed CokersDesign FeaturesBarauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERModern Trend in Delayed Coker Technology –• Maximize the production of liquid distillate.• Minimize the production of coke.• Produce heavy gas oil suitable for downstream catalytic processing.• Optimize number and size of coke drums.• Optimize energy recovery.• Optimize feed pre-heat system and heater duty.• Maximize air cooling and minimize water cooling.• Low pressure operation i.e 1.05 kg/cm2-g g drum pressure.•Reduction in Recycle Ratio (10% or lower) for maximizing distillateyield.• High CCR feed processing.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERModern Trend in Delayed Coker Technology –• Shorter coke drum cycle (18 hours or lower).• No sloping from blowdown.•Refinery slop (with reactor o/h quench) and sludge (during coke drumquench) processing.•Increased heater run length ( 1 Yr +) and online spalling.• No quench column/ RFO generation.• Double fired heater with online spalling and decoking facility.• Automatic heading and deheading system.• Hydrocyclone for recovery of coke cutting water.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERIn NUTSHELL –Delayed Coking is an attractive option for upgradation ofresidual fractions.Coking is a severe thermal cracking process aimed at distillateand lighter production during which coke is also formed.Modern trend is to go for low recycle, low pressure DelayedCokers for maximizing liquid yield.Barauni Refinery – In harmony with nature

PRESENTATION ON DELAYED COKERTHANK YOUBarauni Refinery – In harmony with nature