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8/17/2019 Section 04 Shutdowns & Interlocks CAPC
1/31
BASIC SHUTDOWN SYSTEMS & INTERLOCKS
PT Chandra Asri Petrochemical Company
Ciwandan, Cilegon, Indonesia
July 2007CAUTIONARY NOTICE
This document contains information which is proprietary to Kellogg Brown & Root, Inc. This information is to be held in confidence. No disclosure,
reproduction or other use of this document is to be made without the prior written consent of the Kellogg Brown & Root, Inc.
8/17/2019 Section 04 Shutdowns & Interlocks CAPC
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CONFIDENTIAL
Shutdown System / Permissives
• Low Fire Trip
• Complete Trip
• Permissives for Hydrocarbon Cracking
• Permissives for Decoking
• Permissives for Burner Lightoff
• Burner Lightoff Procedure
• Permissives for MOV Switching
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CONFIDENTIAL
Furnace Shutdown Systems
• Low Fire Trip – Not a complete shutdown
– Furnace remains hot (so-called hot standby condition)
– Rarely results in mechanical work
• Complete trip
– No firing – Furnace cold
– May require mechanical work if furnace has been cracking more
than ~10 days
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CONFIDENTIAL
Furnace Shutdown Systems
LOW FIRE TRIP ACTIONS – 6376-IC3522-01 Sheet 1 of 9
– Isolates HC Feed
– Trips Main Burners Leaving Decoke Burners On – Resets Fuel Gas Control Valve Set Point
– Dilution Steam Flow Set Same As SAD
– Purge Steam To FPHT I Coil Initiated
– Firing Rate Reduced To LFT Setpoint – Isolates Decoke Air (If In SAD Prior To LFT)
– Isolates Decoke Water (If In SWD Prior To LFT)
– Isolates Cracked Gas Analyzer
– Disables Total Feed Controllers
– Isolates DMDS
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CONFIDENTIAL
Low Fire Trip
• Avoids a complete trip!
• Furnace sent to “safe condition” (similar to decoke)
• Thermal swing reduced
– Furnace remains hot (no shut down)
– Possibility of mechanical work reduced
• Hydrocarbon operation resumed after decoking
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CONFIDENTIAL
Furnace Shutdown Systems
COMPLETE TRIP ACTIONS – 6376-IC3522-01 Sheet 1 of 9
– Close Decoke Burners – Pilots Remain On
– Open Main Burner XV-10850 – Isolates HC Feed
– Isolates Decoke Air (If In SAD Prior To CT)
– Isolates Decoke Water (If In SWD Prior To CT)
– Dilution Steam Flow Reset To Complete Trip Rate – Isolate Quench Oil – Purge Quench Oil Nozzles
– Isolates Cracked Gas Analyzer
– Isolates DMDS
– Pilots Typically Stay Lit – Exception If CT Initiated By Operator or High-High-High Furnace Arch Pressure
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CONFIDENTIAL
Complete Trip
Furnace is shut down
• Furnace is cold (pilots typically firing)
• Mechanical work probably required.
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CONFIDENTIAL
Low Fire Trip
• Initiators for Low Fire Trip:
– Low-Low hydrocarbon feed pass flow (any pass)
– Low-Low dilution steam pass flow (any pass)
– Low-Low SHP steam drum level
– High-High SHP steam temperature
– High-High arch pressure (Hot Furnace Only)
– High-High transfer line temperature (either side of furnace)
– Manual trip
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CONFIDENTIAL
Low HC Feed Flow Trip
LOW HC FEED
FLOW
LOW
FIRE
TRIP
IF IN SWD, ADD HC
FEED, DS, DECOKE
STEAM & DECOKEBFW FLOW RATES
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CONFIDENTIAL
Low Dilution Steam Flow Trip
LOW DILUTION
STEAM FLOW
LOW
FIRE
TRIP
IF IN SAD,
ADD DIL STEAM
& PURGE STEAMFLOW RATES
IF FURNACE
COLD, DISABLE
IF IN SWD,
RESET
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CONFIDENTIAL
Low Steam Drum Level Trip
LOW STEAM
DRUM LEVEL
LOW
FIRE
TRIP
60 SEC
DELAY
COMPLETE
FURNACE
TRIP
REQUIRED TO PROTECT PQE’S
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CONFIDENTIAL
High SHP Steam Temperature Trip
HIGH-HIGH
STEAM
TEMP
LOW
FIRE
TRIP
8 MIN
DELAY
COMPLETE
FURNACE
TRIP
HIGH STEAM
TEMP
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CONFIDENTIAL
High Arch Pressure Trip
COMPLETE
FURNACE
TRIP
30 SECDELAY
FIREBOX
COLD?
YES
30 SEC
DELAY
TRIP OPENID FAN
DAMPER
LOWFIRE
TRIP
30 SECDELAY
HIGH ARCH
PRESSURE
(PT’s)
HIGH ARCH
PRESSURE(TT’s)
ARCH
PRESSURE
HIGH?
(TT’S)
NO
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CONFIDENTIAL
High Transfer Line Temperature Trip
HIGH TRANSFERLINE TEMPERATURE
(EITHER SIDE)
COMPLETEFURNACE
TRIP
5 MIN.
DELAY
LOWFIRE
TRIP
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CONFIDENTIAL
Manual Low Fire Trip
LOW
FIRE
TRIP
MANUAL LOWFIRE TRIP
CONTROL ROOM
MANUAL LOW
FIRE TRIP
BURNER PANEL
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CONFIDENTIAL
Checks After Low Fire Trip
LOW TOTAL
DILUTION
STEAM FLOW
COMPLETEFURNACE
TRIP
LOW
FIRETRIP
HIGH FLUE
GAS TEMP
5 MIN
DELAY
30 SEC
DELAY
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CONFIDENTIAL
Complete Trip
Initiators for Complete Trip:
• High-High / Low-Low fuel gas pressure
• High-High-High SHP steam temperature
• High-High-High Firebox Pressure
• ID Fan Failure
• Manual trip
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CONFIDENTIAL
Fuel Gas Complete Trips
COMPLETE
FURNACETRIP
LOW FUELGAS PRESSURE
HIGH FUELGAS PRESSURE
MANUAL
COMPLETE TRIPCONTROL ROOM
MANUAL
COMPLETE TRIP
BURNER PANEL
HIGH ARCH
PRESSURE (COLD)HIGH-HIGH-HIGH
ARCH PRESSURE
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CONFIDENTIAL
Pilot Trips
PILOT
TRIP
LOW PILOTGAS PRESSURE
HIGH PILOT
GAS PRESSURE
MANUAL
COMPLETE TRIP
CONTROL ROOM
MANUAL
COMPLETE TRIP
BURNER PANEL
HIGH-HIGH-HIGH ARCH PRESSURE
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CONFIDENTIAL
Interlocks for MOV Switching
Permissives for MOV Switching• Analyzer sample valves closed
• HC feed isolated
• Quench oil isolated
• Decoke air isolated
• In “Decoke” mode
• DMDS isolated
• Steam flow rates above minimum (Administrative)
Permissive failure after decoking commences causes alarm
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CONFIDENTIAL
MOV Switching - From Transfer Line to Decoke Line
• Control room operator activates local panel
• Field operator begins transfer line valve (TLV) closure
– High Transfer line pressure alarm active
• Operator stops TLV movement based on furnace pressure and/or TLV ∆P
• Field operator begins opening of decoke line valve (DLV).
– Low Transfer line pressure alarm active
• Operator stops DLV movement based on transfer line pressure and/or TLV ∆P
• If Transfer Line Low DP or High Pressure Occurs valve movement stopsuntil corrected
• Close TLV - Low TLV ∆P alarm disabled
• Open DLV - High transfer line pressure alarm disabled.
MOV Switching Sequence From Decoke Line to Transfer Line
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CONFIDENTIAL
MOV Switching Sequence - From Decoke Line to Transfer Line
• Control room operator activates local panel
• Field operator begins DLV closure
– High Transfer line pressure alarm active
• Operator stops DLV movement based on transfer line pressureand/or TLV ∆P
• Field operator begins opening of TLV – Low Transfer line pressure alarm active
• If Transfer Line Low DP or High Pressure Occurs valve movement stops
until corrected
• Close DLV - Low TLV ∆P alarm disabled
• Open TLV - High transfer line pressure alarm disabled.
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CONFIDENTIAL
Interlocks for Hydrocarbon Service
• Decoke line MOV 100% closed
• Decoke air isolated
• Transfer line MOV 100% open
• Decoke/Cracking Mode Switch in Cracking position
• Steam flow rates above minimum (Administrative)
Permissive failure after cracking commences causes an alarm
I l k O D k Ai (SAD)
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CONFIDENTIAL
Interlocks to Open Decoke Air (SAD)
• Transfer line MOV 100% closed
• Decoke line MOV 100% open
• HC feed isolated
• Quench oil isolated
• Decoke/Cracking Mode Switch in Decoke position
• Chromatograph isolated
• Steam flow rates above minimum (Administrative)
Permissive failure after decoking commences causes an alarm
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CONFIDENTIAL
Burner Lightoff System
• Checks permissives
• Purges firebox
• Checks for burner fuel gas cock closure
• Includes temporary bypasses for:
– High fuel gas pressure
– Low fuel gas pressure
• Firebox purge & fuel gas cock closure tests run in
parallel to save time
• Includes bypass switch for pilots usage
I t l k / P d f B Li ht ff
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CONFIDENTIAL
Interlocks / Procedure for Burner Light-off
Burner Purge Panels:
• ESD Console Panel
• Outside Burner Panel• DCS Switches, Lights
F l G C t l
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CONFIDENTIAL
Fuel Gas Control
QIC
AI
ATM @ SAFE
LOCATION
Burner Header
PIC
FO
Burner Light Off Sequences
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CONFIDENTIAL
Burner Light-Off Sequences
There are four separate burner light-off sequences
1. Pilot, Main, and Decoke Burner Light-Off
1. Furnace is cold or Complete Trip with Pilot Trip
2. Pilots lit first then Main and Decoke burners can be tested and lit
2. Main & Decoke Burner Light-Off
1. Furnace has had Complete Trip but Pilots remain lit
2. Main and Decoke burners tested together and enabled
3. Main Burner Light-Off 1. Furnace has had Low Fire Trip but Pilots and Decoke burners remain lit
2. Main burners are tested and enabled
4. Main & Decoke Burner Light-Off – Pilots Bypassed
1. Furnace has had Complete Trip or is Cold
2. Main and Decoke burners tested together and enabled
All three sequences follow a similar pattern
Burner Light Off Sequence Firebox Purge
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CONFIDENTIAL
Burner Light-Off Sequence – Firebox Purge
• If furnace is hot and permissives satisfied, firebox purge
starts automatically.
• If furnace is cold, operator must initiate firebox purge.
• Must satisfy all permissives for 15 minutes.
• Purge complete light illuminates.
Burner Light Off Sequence Cock Closure Test
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CONFIDENTIAL
Burner Light-Off Sequence – Cock Closure Test
• Field operator closes all burner fuel gas cocks
• Check that burner fuel gas header pressure is low
• Operator starts 5 minute timer: – Fuel gas commissioned to spring loaded valve
– Open isolation valve upstream of spring loaded valve
– Operator holds spring loaded valve open
– Fuel gas flows through RO into burner fuel gas header
– Fuel gas header pressure rises to set point?
– Close isolation valve upstream of spring loaded valve
Burner Light Off Sequence Light Burners
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CONFIDENTIAL
Burner Light-Off Sequence – Light Burners
• Firebox purge & cock closure tests successful• 5 minute timer starts automatically
– Low & High fuel gas pressure trips bypassed for 5 minutes
– Fuel gas commissioned to fuel gas header
– Operator adjusts fuel gas vent to stabilize pressure between Low
& High fuel gas pressure trip set points (PCV-1082
recommended setpoint ~ 0.4 kg/cm2g)
– Light burners as required
– Close vent valve when sufficient burners are lit to allow CV to
control