Post on 10-Jul-2020
Petrocontrol
FCCU Advanced Control atChevron Pembroke Refinery
ERTC8th to 10th May 2006
Yen Koo CVXZak Friedman Petrocontrol
Steve Park AMT
Petrocontrol
FCC at Pembroke Refinery
• Initial Hydro skim refinery commissioned in 1967• Cracking facilities commissioned in 1983
(Texaco side by side Rx/Rg unit, with a mainfractionator and gas concentration section)
• Can process over 35% resid of total throughputof over 100,000 BPSD (600m3/hr - One of theBiggest FCC in Europe)
• Feed mix variation is in the region of 0.908 to0.92 SG
• Last major turn around is during 2003
Petrocontrol
History of APC at Pembroke
• Pembroke Refinery has a long history of APC since 1987• First MVC controller on FCC – 1988 (DMC) – with
separate cotnroller for Rx/Rg, and Mainfrac• 2001, RMPCT replaced DMC, retained original structure,
and added deeth, debut, napsplit• Very limited success at each time (mainfrac didn’t work,
lack of co-ordination between applications, tray damage)• First Principle Inferentials first used in early 1990’s and
have been deployed across most refinery units
Petrocontrol
FCCU APC Reengineering
• Potentially US$ 4millions/yr yet to be captured (carried astudy on FCC APC during 2004) - Need to completelyrevamp FCC APC
• Scope of the revamp to cover reactor, regenerator,mainfrac, deeth, debut
• Main focus of the application and this paper is theFractionator section due to major difficulties in managingthis section of the unit
• Major feed limiting constraints are mainly in theFractionator section
• RMPCT is the control technology used• New FCCU application commissioned in July 2005
Petrocontrol
True Economic optimum
Hydraulic Const.
Rx/RgTemperature
WGC & others
Column fouling/flooding limitation System Pressure
ProductPurity
Operating within Constraints
Operator'sPreferredOperating
Region
MVCOperatingRegion
Eg. Rx bed Temp.Rg flu gas Temp.Excess O2,Cyclone Vel
Eg. Rx/Rg DP.Mainfrac top PSCSV/RCSV – DPAnd OPMainfrac OVHD P
Eg. Control valve Saturation OP – reflux& cooling system
LCGO draw TY DP, Level,Glitsch grid flow, TPA DP, ICGO wash downMainfrac bottom Temp.
HCN90 & EPHHCN90 & EPLCGO FlashSlurry DensityC2 spec in Ole
Max Tot. feed, Max Resid, ROTMax prod: LCGO (up-grade more HCGO) Max HHCN (match ULSG Capacity)Max Ole (match Alky Capacity) Min usage Air, Min C3 loss to offgas
WGC Anti-surgeAirblower anti-surgeHP steam limitation
Petrocontrol
FCCU application overview
• Applications are as follows:– Rx_Rg/mainFrac/Deeth (better integration and optimisation) –
55CVs,22MVs,11DVs– Single application to cover Debutaniser (8CVs,4MVs,6DVs)
• Large scope application with sub controllers deployed for ease ofmaintenance and operator intervention. (Sub controller switch AM/CL codesupplied by AMT)
• Customised Operator displays developed by CVX and AMT– Easy monitoring and operated upon (by panel operators)– Accommodation for switching access
• First principle Inferential model based on GCC (PetroControl)
Petrocontrol
Overview of Revamp Design
Eg. Rx/Rg DP.Mainfrac top PSCSV/RCSV – DPAnd OPMainfrac OVHD P
Eg. Rx bed TRg flu gas T.Excess O2,Cyclone Vel
LCGO draw DP& LevelGlitsch grid flow,TPA DP,ICGO washdownMF BTM T.cooling duty
HHCN90& EP
LCGOFlash
C2 specin Ole
HCN90 &EP
HCGODensity
WGC Anti-surgeHP STM limitation
Airbloweranti-surge
C5 in Oleprod.
Reboil capacityfrom LCGO PA /Reflux
ICGO PA /RefluxHCGO PA /Reflux
CoolingCapaciy
Down stream units limitation
Typical Constraints
Typical prod. & spec.
RMPCT Application
Petrocontrol
Schematic of Main fractionator
E- 1
P- 2
Reactor Effluent
Slurry Product
606060
P-6
P-7LCGO Product
I-2
P-9
P-10
P-11
ICGO PA
Bottom PA
LCGO PA
E- 3
P-12
P-13
HHCN Product
P-14
E- 7Cold FeedE- 11
TPA
E- 14
E -15
E- 16
Lean Oil to Absorber
Wet Gas
Min Tray Wash Min Grid Flow
Max btm temp Max velocities
Max yield on resid feed
Max to min traywash
Flash point spec
90 % Dist
90% Dist
Max lvl 93 %
Flood limit
Temp min “dew point”
Petrocontrol
Project details Schedule and contract
• Project was completed in a 8 month window.• Inferential model provided by PetroControl, and
implemented and subsequent re-calibrated by CVX(VBA-model for easy maintaining and calibration)
• APC model jointly developed and implemented by CVXand AMT (one engineer each)
• Operator training package jointly developed by CVX andAMT (computer based self-learning, interactive)
• Project completed under budget with benefits higherthan expected
Petrocontrol
FCCU APC Application Success Factors
• New FCCU application commissioned inmid-June 2005
• High operator acceptance• Good average controller uptime (>95%
when process available)• Fractionator control now much improved,
this is a key issue for the FCCU unitoperations.
• Payback achieved within a month
Petrocontrol
Feature – inferentials/Specs Control
• Fractionator:– LCGO Flash Point– HHCN ASTM 90% & End point– HCN ASTM 90% & End point
• Gas Plant– Deeth bottom % C2 slippage– Olefin % C5– LCN RVP
• Note: no analyser or lab updates used for biasing inferences
Petrocontrol
Highlight - Inferential models
CVX VBA modelBased on GCC
AM/CL model
Petrocontrol
Sample Model – Spec Control MF Top-T MF OVHD-T LCGO prod. HCGO PA LCGO RBL Deeth RBL Ambient-T
HCNpt90
HCN EP
HHCN90pt
HHCNEP
LCGOFP
DeethBottom
C2
Petrocontrol
Highlight - LCGO Flash Point control
LCGO Flash Point Control
0
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0
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Infer LCGO FPLab LCGO FPInfer LCGO FP Sdev
Iinferential recalibrated & new controller commissioned
Average Standard deviation is reduced by 1DegC
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150
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HCN90_Lab02MFN90.PVHCN90_Lab.stdev
Average Standard deviation is reduced by 1DegC
HCN90 spec control
Controller Commissioned
Highlight – HCN90 spec control
Petrocontrol
Feature – mainfrac control
• Optimise where possible the Fract bottoms heat removalControl Fractionator bottom temperature
• Prevent Fractionator flooding• Maximise heat removal and balance duty around the
column• Ensure column packed sections are kept wet• Ensure Slurry oil density remain on control within tight
limits• Minimise fouling probabilities in Slurry system• Sustains Debutaniser on control even though reboiler
(HCGO) exchanger fouling occurs
Petrocontrol
Sample Model – Main Frac control Feed ROT MF Top-T LCGO prod. HCGO PA ICGO PA HHCN prod
MainFrac Bottom Temp.
PackedSection
ICGOWash
LCGODrawLVL
LCGODrawDP
HCGOVisc
HCGODensity
Petrocontrol
Highlight - LCGO Section dP Sensitivity to Flood
LCGO Section dP
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
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0.45
0.5
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0.1
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0.16
0.18
0.2
LCGO Section dPStd Dev
Flood point
Unit being pushed and stability retained
Controller commissioned
Petrocontrol
Highlight - LCGO Draw Tray Level
LCGO Draw Self Regulating Level
50
60
70
80
90
100
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2
4
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10
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14
16
18
20Draw tray levelLevel stdevTray Full, LCGO section
flooded
Project KO and Pretest and dynamic test
Phase
Controller Commissioned
Unit being pushed
Petrocontrol
Highlight - Fractionator BTM T Critical Unit imitation
Fractionator bottom temperature
280
290
300
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360
370
380
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Bottom TempStdev
355°C is High Operating Limit
Controller Commissioned
Petrocontrol
Feature – Optimisation direction
• Maximise Total Feed (match scheduling)• Max Resid processing to Regen limitations• Minimise load on Blower and expander• Stay in safe system delta P range (slide valves)
– max cat circulation• Maximise Conversion• Run to minimum Regen excess O2 (>1%)• Max LCGO draw against MIN internal reflux
• Significant operator issue• Minimises the Deethaniser C3’s loss to offgas
subject to C2 content at bottom (ole prod)
Petrocontrol
Sample Model – Rx/Rg optimisation Tot-Feed Reactor-Temp Resid-Feed Rx/Rg-DP Feed-Preheat MF Top-P Air-blower
ExcessO2
Rx bedTemp
RCSVDP
RCSVOP
AirblowAnti-srg
WGCAnti-srg
Cat.Circ.
Petrocontrol
Unit Feed and Yields in M3/HRShows increase in recovery of LCGO whilst sustaining bottom conditions
Feed with LCGO and ICGO Wash
0
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200
300
400
500
600
700
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Feed to unitTray washLCGO Product
Feed rate conditions dictated by refinery and plant issues, Application ran at >95% from start of
application
Controller commissioned
Increased recovery of LCGO at expence of internal reflux (traywash) and hence
Slurry yield - Gain of 1
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Highlight – Excess O2 optimisation
Excess O2 regen flu gas
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3
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02AR2451.PV02AR2451.PV.stdev
Controller Commissioned
Unit is pushed to the limit
Petrocontrol
Highlight – Deeth Optimisation
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0.6
0.8
1
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1.8
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DEETH OFF GASC2 IN LPG02DC2C2V.PV.stdev
Controller Commissioned
Deeth Offgas minimisation
Petrocontrol
Feature – operator Acceptance
• Easy & user friendly APC monitoringdisplay
• Comprehensive operator’s training
Petrocontrol
Highlight – Custimised Operator Display
Able to switchon/off, betweenSub-controller
Able to drop anyCVs or MVs
Able to changeLow/High Limit
Able to switchon/off the whole
controller
Able to see whichare the critical
variables
Petrocontrol
Highlight – sample training slide
Petrocontrol
Thank you
Questions