Petrocontrol

FCCU Advanced Control atChevron Pembroke Refinery

ERTC8th to 10th May 2006

Yen Koo CVXZak Friedman Petrocontrol

Steve Park AMT

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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

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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

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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

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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

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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)

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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

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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”

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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

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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

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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

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Highlight - Inferential models

CVX VBA modelBased on GCC

AM/CL model

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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

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Highlight - LCGO Flash Point control

LCGO Flash Point Control

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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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HCN90_Lab02MFN90.PVHCN90_Lab.stdev

Average Standard deviation is reduced by 1DegC

HCN90 spec control

Controller Commissioned

Highlight – HCN90 spec control

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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

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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

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Highlight - LCGO Section dP Sensitivity to Flood

LCGO Section dP

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LCGO Section dPStd Dev

Flood point

Unit being pushed and stability retained

Controller commissioned

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Highlight - LCGO Draw Tray Level

LCGO Draw Self Regulating Level

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20Draw tray levelLevel stdevTray Full, LCGO section

flooded

Project KO and Pretest and dynamic test

Phase

Controller Commissioned

Unit being pushed

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Highlight - Fractionator BTM T Critical Unit imitation

Fractionator bottom temperature

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Bottom TempStdev

355°C is High Operating Limit

Controller Commissioned

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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)

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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.

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Unit Feed and Yields in M3/HRShows increase in recovery of LCGO whilst sustaining bottom conditions

Feed with LCGO and ICGO Wash

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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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02AR2451.PV02AR2451.PV.stdev

Controller Commissioned

Unit is pushed to the limit

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Highlight – Deeth Optimisation

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DEETH OFF GASC2 IN LPG02DC2C2V.PV.stdev

Controller Commissioned

Deeth Offgas minimisation

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Feature – operator Acceptance

• Easy & user friendly APC monitoringdisplay

• Comprehensive operator’s training

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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

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Highlight – sample training slide

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Thank you

Questions