p10 introduction to coking process
TRANSCRIPT
Introduction to Coking Process
Gary GianzonHeavy Oil Technologist
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Crude Oil Cuts
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Heavy Oil Characteristics
Characteristics of Atmospheric and Vacuum Resid
Crude Atmospheric
Bottoms
Vacuum
BottomsBoiling Range, F Whole 680 1000+API Gravity 34.0 15.7 6.4Sulfur, wt% 1.8 3.2 4.2Yield, Vol % 100 40.6 16.3Pour Point, F 50 101Carbon Residue, wt% 8.9 20.1Nickel, PPM 10 25Vanadium, PPM 37 89
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Process Options for Resid
Sold as Products
Visbreaking
ROSE
Catalytic Cracking – FCC
Hydrotreating / Hydrocracking
Delayed Coker
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Sold As Products
Road and Roofing Asphalt
Fuel Oil
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Visbreaking
Milder form of thermal cracking.
Used to reduce viscosity and pour point of vacuum resid to meet specification for heavy fuel oil.
Reduces Distillate Cutter requirement
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ROSE Unit
Residual Oil Supercritical Extraction for production of metal free gasoil, asphaltenes, and resin.
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Resid FCCU
Similar to Gas Oil FCC but processes heavier feed. Feed concarbon limited to 10 wt%. Catalyst circulation and regeneration section much larger than conventional FCCU.
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H-Oil & LC Fining
Resid Hydrotreater/Hydrocracker. Uses catalyst and hydrogen to convert resid to valuable products. Significantly better yield than coker but much higher investment cost.
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Delayed Coking
Thermal cracking process
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History of Delayed Coker
1860
Petroleum coke was first made by Pioneer Oil Refinery in northwest Pennsylvania. This primitive refinery boiled oil in iron stills to recover kerosene using wood and coal fires. Coke accumulated at the bottom of the still where workers dug out the coke and tar before the next run.
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History of Delayed Coker
1880
Several Stills were operated in series with the first still producing the coke.
Used chains in the sump to break up coke, formed during run, for removal.
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History of Delayed Coker
1929
Standard Oil of Indiana built the first delayed coker.
Coke was removed using steel cables on a holding devise in the drum.
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Lesson 4: History of Delayed Coker
1930
Shell Oil patented hydraulic decoking.
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Delayed Coker
Delayed coking is a thermal cracking process which upgrades / converts petroleum resid into lighter liquid & gas products while accumulating petroleum coke material in the drum.
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Delayed Coker Process
Heavy Oil
Heat
Liquid and Gas Products
Petroleum Coke Product
Delayed
Coker
Unit
(DCU)
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Delayed Coking Process
A fired heater is used for the process to reach the thermal cracking temperature of 910 F to 940 F.
The short residence time in the heater tubes (around 50 seconds), delays the coking of the resid until it reaches the coke drum.
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Delayed Coking Process
Coking Reaction Kinetics
750 F – 16 to 24 hours
800 F – 5 to 6 hours
840 F – 1 ½ to 2 ½ Hours
Reaction rates varies with feed composition
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Process Flow
A delayed coker has four main sections:
Feed, Furnace, and Coke Drum Section
Main Fractionation Section
Gas Recovery Section
Closed Blowdown Section
Feed, Furnace,
and Coke DrumsMain Fractionation
Gas RecoveryClosed Blowdown
Heavy OilProducts
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Process Flow
Coker Feed – Fractionator Bottoms
Feed is Preheated with HCGO product and pumparound
Bottoms of the main fractionator provides feed surge.
Recycle is added to the feed
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Process Flow
Furnace
Charge pump boost pressure to 300 to 400 psig
Velocity steam is added to the furnace charge (500 to 1000 lbs/hr)
Heater outlet temperature to 915 to 930 F
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Process Flow
Coke Drum
Coke drum inlet above 900 F
Endothermic Reaction
Drum Outlet around 825 to 840 F
Antifoam Injection at the end of the drum cycle
Coke level Detection, Nuclear or Continuous
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Process Flow
FZGO Section
Feed preheated by the HGO product and pumparound before entering the bottom of the main fractionator.
Coke drum vapors enters the flash zone section. HGO sprays contact the coke drum vapor. This controls the C7 insoluble in the HGO product.
Flash Zone Liquid is filtered and mix in with the feed.
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Process Flow
Heavy Coker Gas Oil Section
Wash sprays to control C7 insoluble.
Heavy gasoil pumparound remove heat from the column.
Heavy gasoil product is routed to the hydrocracker or gasoil hydrotreater for further processing.
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Process Flow
Distillate Section
Distillate pump‐back controls endpoint of distillate.
Distillate pumparound for heat removal.
Distillate product process further in the distillate hydrotreater.
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Process Flow
Main Fractionator Overhead
Reflux to control endpoint.
Fractionator Overhead is cooled using fin fans and water cooler.
Continuous water wash to remove salts.
Overhead liquid and vapor is further process in the coker gas plant.
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Coker Process Variables
Furnace Outlet Temperature/Coke Drum Inlet Temperature
Higher Temperature increases gas and naphtha yields while decreasing the gasoil and coke yields.
Higher Temperature reduces the volatile material that gets trapped in the coke (VCM), resulting in harder coke.
Increasing the temperature towards the end of the coking cycle reduces upsets caused by drum switches.
Temperature Affect on Coker Yield
0
10
20
30
40
50
60
70
% Coke % Liquid % Gas
Yield (wt%
)
900 F930 F
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Coker Process Variables
Coke Drum Pressure
At a higher pressure, more of the material in the drum remains in the liquid phase and can therefore be involved in the reactions that lead to coke formation.
Low pressure can affect drum velocity and increase the tendency of coke carryover.
Coker Yield @ 930 F
0
10
20
30
40
50
60
70
80
% Coke % Liquid % Gas
Yield (w
t%)
6 psig15 psig40 psig
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Coker Process Variables
Natural Recycle
Higher increases the quality of HCGO.
Higher increases coke yield/decrease LV yield.
Higher can increase furnace runlength.
Higher natural recycle improves the quality of coke.
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Coke Drum
Coke drum operation
Beginning of drum cycle
Drum is cold
Volatiles condense on the walls
Condensate trapped in coke
Pools forming at the bottom
Low boiling VCM
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Coke Drum
Coke drum operation
Middle of the cycle
Drum temperature steady
No volatile condensation
Lowest VCM coke
Pool level at steady state
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Coke Drum
Coke Drum Operation
End of cycle
Some volatile left
Pool liquid soaks into coke
Suspended coke particle remain on top
High boiling VCM
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Coke Drum and Structure
Coke Drum Level Detector
Design consideration
Level indication–Neutron backscatter
– Point source level detection.
•Detector penetrates around 1 ft from the source.
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Coke Drum and Structure
Coke Drum Level Detector
Gamma Detection
Continuous Level Detection
Source and Detector on Opposite sides of the drum.
Optimizes Antifoam Usage
Charge Rate Advance Controls
Coke Drum Outage Management
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Petroleum Coke
Three physical structure of petroleum coke: Shot
Sponge
Needle coke
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Petroleum Coke
Shot Coke
Feeds with high level of asphaltene, nitrogen, sulfur, and oxygen predominately make shot coke.
Small, tight, non attached clusters that look like pellets, marbles or BB’s
Usually very hard (i.e., low HGI)
Less desirable to end users –Difficult to handle and grind–During Calcining process Shot Coke tends to “pop” in the kiln reducing the thermal stability.
Shot coke is predominately used as fuel
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Petroleum Coke
Shot Coke Operational IssuesUnquenched hot spot in the coke bed resulting in blowouts and eruptions
Coke Dumps
Poor Drainage
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Petroleum Coke
Sponge Coke
Resembles a sponge– bubbly looking
Sponge Coke Usage– Electrodes for Electric Furnace– Anodes for Electrolytic Cells– Chemical Carbon Source– Graphite Manufacturing– Fuel
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Petroleum Coke
Needle Coke
Special quality coke produced from aromatic feed stocks.
Has crystalline structure with more unidirectional pores.
Used for high quality graphite anodes – Steel industry electric arc furnaces.– Electrode Manufacture
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Petroleum Coke
Typical Properties of Coke
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Coker Drum Cycle
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Coke Drum Cycle
Operation Time Ranges Comment
Switch 5 to 20 min. Use slow switch
Steam to Fractionator 0.25 to 1 hr.
Depressure 10 to 30 min. Avoid foamover
Steam to Blowdown 0 to 1 hr.
Quench & Fill 4 to 7 hrs. Slow = low stress
Vent & Drain 0.5 to 2 hrs.
Unhead 10 to 30 min.
Coke Bore & Cut 1.5 to 6 hrs. Shot coke = short
Rehead; Steam; Test 0.75 to 1.5 hr.
Warm‐up 1.5 to 3.5 hrs.
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Switch
Open backwarm butterfly valve
Close backwarm valve to main fractionator
Open inlet isolation valve
Open Spool Steam
Swing 4 way switch valve to halfway
Swing 4 way switch valve to warm‐up drum
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Small Steam to the Main Fractionator
Open steam valve
Slowly raise steam rate (10 to 15 mlbs/hr)
Close feed isolation valve
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Steam to the Blowdown
Open line to blowdown
Close overhead vapor valve
Raise steam rate
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Water Quench and Fill
Open water isolation valve
Slowly open water control valve
Close steam valve once water flow has been stablish
Set water ramp program
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Drum Vent
Depressure the drum to blowdown
Stop water addition and isolate water valve
Isolate the drum to blowdown
Open vent valve
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Drum Drain
Open the drain valve
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Unhead and Cutting
Open the top head
Open the bottom head
Turn on the eductor
Turn on top water quench
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Air Free and Pressure Test
Close vents
Close eductor
Close drain
Close delta valve
Pressure the drum with steam
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BackWarm to Quench Tower
Balance pressure of the blowdown tower and the main fractionator
Open overhead vapor valves
Open backwarming valve to blowdown
Pinch in backwarm butterfly valve
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Backwarm to Main Fractionator
Temperature above 350 F before backwarm to fractionator
Close backwarm valve to blowdown
Open backwarm valve to main fractionator
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Coke Cutting System
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Hydraulic Decoking System
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Hydraulic Decoking System
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Coke Cutting System
Hydraulically Remove Coke Out of the Drum
Coke Cutting Mode
Pilot Mode, Bore 6 ft pilot hole
Cutting Mode
Cut coke from top down on 10 ft increments
Coke Cutting Time Varies from 2 to 6 Hours
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Coke Cutting System
Coke Cutting System Design Consideration
Coke Type and VCM content
Coke Drum Diameter
Cutting time Target
Coke Handling System Design
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Coke Cutting Safety System
Limit switches to prevent live drill bit from exiting the drum.
Low pressure shutdown – shutdown the jet pump on low discharge pressure to prevent exposing personnel to high pressure water during cutting hose failure.
High pressure shutdown – prevents deadheading the pump
Isolation valve position permissive
Low suction pressure shutdown
Cutting water tank level permissive/shutdown
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Delta Valve Top Cutting Containment
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Delayed Coker Safety Incident
At least 40 incident reported since 1993 in North America.
At least 16 fatalities in North American cokers.
The list is not all inclusive
Restricted only to US and Canada
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Delayed Coker Safety Incident
Primary Cause Category
Training and Procedure–Inadequate procedure, no procedure, failure to follow procedure, inadequate training or lack of understanding of the process
Engineering Error–Improper design–Improper metallurgy
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Common Failure Mechanisms Piping Failure Erosion Corrosion Material Selection
Operator Error Opening valve on live drum Improper quenching of Drum Drill Bit Exited the drum during cutting Improper draining resulting in operator exposure to hot water
Equipment Failure Unheading Gasket Leak Flange Leak Pump Seals Valve Leaks
Over-Pressure– Water + Hot Oil
Vapor Release
Lightening
Flare System Failure
Relief System Design
Procedures
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Coker Unit Safety Incidents
South Texas Refinery– 1993
Operator open live drum to drain resulting in fire/explosion
1 fatality resulted in this incident
Unit was shutdown for 6 months for repairs
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Coker Unit Safety Incidents
Louisiana Refinery
Carbon steel joint installed in alloy pipe at the discharge of the coker charge pump
Fire resulted from line failure, east coker destroyed
3 fatalities resulted in this incident
Unit was shutdown for 6 months for repairs
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Coker Unit Safety Incidents
Houston Area Refinery
Opened bottom head on a live drum resulting in fire
Unit was shutdown for 5 months for repairs
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Coker Unit Safety Incidents
South Texas Refinery
Drum Blowout + Fallout of hot coke, water, steam, after deheading prior to raising the chute.
2 operators injured during this incident
Unit shutdown for 2 days
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Coker Unit Safety Incidents
California Refinery
Hahn and Clay devise was found to be inadequately close after the drum was put online resulting in fire.
2 operators were injured during this incident
This also happened in Marathon’s Garyville, luckily the oscillating monitor saves the unit!
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Coker Unit Safety Incidents
Washington State Refinery
Opened interrupted drum, not properly quench (tar ball) resulting in explosion, fire
6 fatalities resulted form this incident. 2 fatalities at the bottom head and 4 at grade under the deck.
Unit was shutdown for 6 months for repairs
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Coker Unit Safety Incidents Louisiana Refinery
Hot work on top of empty drum was not property isolated from the live drum
1 leaking valve use for isolation
Weld slag ignite flamable mixture in the drum causing explosion/fire
Two fatalities resulted from this incident
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Coker Unit Safety Incidents
Indiana Refinery
Drill Bit existed drum in cutting mode, protective limit switch was bypass/not operable
High pressure water causes severe lacerations
One fatality resulted from this incident
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Coker Unit Safety Incidents
Los Angeles California Refinery
Line failure on coke drum vapor line quench piping due to wrong metallurgy resulting in fire
Unit was shutdown for 5 months for repairs
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Coker Unit Safety Incidents
Los Angeles California Refinery
2nd degree burn to operator on unheading cart due to hot water release from the bottom of the drum (multiple occurrence)
1 injury resulted from this incident
Louisiana Refinery
Charge pump seal failure resulting in fire
2 injuries resulted from this incident
Unit was shutdown from 3 weeks for repairs
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Coker Unit Safety Incidents Kansas Refinery
Drill Bit existed drum in cutting mode
1 fatality resulted from this incident
Canadian Refinery (Fort McMurray, AB Canada)
Incorrect metallurgy installed in fractionator bottoms pump piping resulting in a large fire
The unit was shutdown for 9 months for repairs
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SAFETY DESIGN FEATURES
100% PMI on all alloy piping
Water deluge on unheading and cutting deck
Water deluge on coke drum egress routes
Automated unheading system
Remote stair case on top deck
Coke drum safety intelocks
Procedure on dealing with tarball.
Standard operating procedures.
Well trained operators.
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Questions?