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1
Emergency Relief
Gary Van SciverSeptember 16, 2008
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Gary Van Sciver
Process Engineer – 8 years
Risk Analyst – 22 years
ETC – 2 ½ years
3
Presentation Overview
ERSNormal Vent
1
23
4
5
1. Normal vent2. Design basis3. Mechanical4. Discharge
5. MOC
4
Terminology (ERS)
EmergencyReliefSystem
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1. Normal Vent
ERSNormal Vent
1
23
4
5
1. Normal vent2. Design basis3. Mechanical4. Discharge
5. MOC
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What is the difference between the normal vent & the
emergency vent?EmergencyVent
Normal Vent
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What are the differences? (between the normal & emergency vents)
• No blocking devices in ERS• No flame arresters in ERS• ERS usually bigger• Normal vent also handles vacuum• Pollution abatement for normal vent• Normal vent opens first• Manifolding for normal vent .
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VPRV (conservation vent)
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VPRV(vacuum pressure relief valve)
To/fromvessel
Fromatmosphere
Discharge
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ManifoldsOne pollution abatement device will normally
handle the discharge of multiple vessels
PollutionAbatement
Device
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VPRV(vacuum pressure relief valve)
To/fromvessel
Fromatmosphere
Discharge
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Storage Tank Under Vacuum
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Plastic Bag Over Vent
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2. Design Basis
ERSNormal Vent
1
23
4
5
1. Normal vent2. Design basis3. Mechanical4. Discharge
5. MOC
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Upset Scenario...
Series of events leading to high vessel pressure
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What do we want the ERS to protect against?...
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Concept Sciences1999 Allentown, PA 5 fatalities hydroxylamine
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Concept Sciences
• The plant was designed to concentrate hydroxylamine (HA) up to 50%
• HA is known to be explosive above 70% concentration
• Due to startup problems, the actual concentration was 86% HA .
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Concept Sciences
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Flammable Discharge
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BP - 2005
Texas City, Texas 15 fatalities
Vapor cloud explosion of hexane/heptane (44ºC)
7700 gallons released < 2 minutes from 35 m height
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BP - 2005Tower – 170 feet tall Blowdown drum – 115 feet tall
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BP - 2005Truck parked,
but idling about 25 feet from
blowdown drum
Eyewitness saw engine over-revving and
backfiring sparks
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BP - 2005
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Toxic Discharge
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Bhopal - 1984
>2000 off-site fatalities due to toxic relief valve discharge
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Bhopal
Taloja
Delhi
Kolkata(formerlyCalcutta)
Chennai(formerlyMadras)
Mumbai(formerlyBombay)
Bhopal
IndiaNH 12
NH 12
Upper Lake
NH 86NH 86
UnionCarbide
Toxic GasCloud
Highly-Populated Region of Bhopal
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Bhopal1984
•Relief valve on an MIC storage tank lifted in the middle of the night releasing 80,000 lbs
•>2,000 people died within a short period
•~30,000 people were permanently or totally disabled
•MIC reacted with water, source of contamination uncertain
•Incident had long-term ramifications for Union Carbide and the chemical industry as a whole .
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Bhopal - 1984
MICStorage Refrigeration Scrubber Flare
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Design Basis Procedure
1. Identification 2. Sizing 3. Selection
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How do we identify upsets?
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2 important upsets
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Fire ExposureRD
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Runaway reactionHigh
temperatureor unusual
composition
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Some other non-reactive upsets
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Excessive heating(steam valve failures, coil leaks)
Steam wide open
RD
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Pressurized liquid addition
Liquid
RD
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Pressurized gas addition(line blowing, pressure transfers, pads or purges)
RD
Air, Nitrogen or Steam
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Some reactive upsets
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Inadequate cooling
Coolingwaterfails
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Inadequate heat sinkWater NOT
charged
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Excessive reactant
Reactant
Bypass open
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Poor reactivityAgitator off
Reactant
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Design Basis Procedure
1. Identification 2. Sizing
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Sizing vents is straightforward but we do need kinetics
data for reactive scenarios
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Types of runaway reaction
• Vapor Pressure• Gas Generating .
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Vapor PressureRunaway Reaction
• Pressure related to temperature• Control temperature by
evaporative cooling .
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Emulsion Runaway
• 1995, one-shot emulsion process• Water charging system failed• New operator being trained, batch not stopped• 2,000-gallon, 120-psig reactor • Broke 35-psig, 18-inch rupture disk• ~1200 lbs ethyl acrylate released.
35% EA 70% EA
Normal Upset
90C max 190C max
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Emulsion Runaway
France
Germany
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Emulsion Runaway
France
Germany
Rohm & Haas Karlsruhe
RheinRiver
Odor complaints 13 miles away in
Karlsruhe, Germany
France
Germany
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Gas GeneratingRunaway Reaction
• Pressure related to amount of gas• Can’t control temperature by
venting• Only control is depletion of reactants
.
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MAA Rail Car
July 1988 (R&H) Deer Park, Texas
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VSP(Vent Sizing Package)
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VSP
120 cctest cell
P FillT
RDPC
XXXXXXX
XXXXXXX
X X X X X X
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Temperature vs time
time
Tem
pera
ture
or P
ress
ure
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P vs T
Temperature
Pre
ssur
e
Heat up
Cool down
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Design Basis Procedure
1. Identification 2. Sizing 3. Selection
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List the scenarios in
order of increasing relief
device size requirement
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Example Scenario List
2” 1.Liquid filling 3” 2.Fire case12” 3.Half charge runaway18” 4.Full charge runaway24” 5.Full charge runaway, no
water heel .
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Selection Approaches
1. Codes2. Tradition3. Risk .
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NFPA 30 requires ERS protection against fire for
aboveground storage tanks of flammables &
combustibles
Codes
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Fire Case Requirement
Fire Case Heat Input
1.0E+05
1.0E+06
1.0E+07
1.0E+08
10 100 1,000 10,000
Area (sq feet)
Q (B
tu/h
our)
<1 psig
>1 psig
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Tradition
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Take advantage of our previous experience
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For example: batch reactor ERS sized for a full-charge
runaway
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Risk
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Risk Management Services(RMS)
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Rohm and Haas Risk Criteria
Community 1 in 100,000 per year
Employees 1 in 40,000 per year
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3. Mechanical
ERSNormal Vent
1
23
4
5
1. Normal vent2. Design basis3. Mechanical4. Discharge
5. MOC
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Vessel Failure
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Vessel FailureWith increasing pressure, flat surfaces become rounded,
vessel resembles a sphere.
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Bottom Seam Failure
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Hold Down Lug - Older
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Hold Down Lug - Newer
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Hold Down Lug - Newer
Vessel
Concrete
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Failure Pressure
Safety Factor
HydrostaticTest Pressure
MAWP0 1X 1.5X 2X 3X 4X
Pressure
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Relief Devices
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Rupture Disk
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Tension-loaded RD
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Tension-loaded RD
Flow
Rupture Disk
HolderVacuum support goes under the RD
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Compression-loaded RD(Reverse Buckling)
Flow
Rupture Disk
Holder
Knife blade (if necessary) goes on top of the RD
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Relief Valves
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Weak Seam Roof(part of API 650)
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Weak Seam RoofWeak seam roof should prevent this
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Weak Seam Roof
Install with relief device to protect the roof
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Design Temperature
ERS
Vessel
Temperature
Des
ign
Pre
ssur
e
Am
bien
t Tem
pera
ture
Des
ign
Tem
pera
ture
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Thrust forces
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Thrust forces
RuptureDisk
Reactor
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Thrust forces
For 24” RD, Area = 452 sq in
Pmax = 165 psi
Thrust = 2 Pmax A = 150,000 lbs
Opposing forces onsupport lugs
& structural steel
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Piping – Thrust forces(initial & established)
Initial load
Established load
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4. Discharge
ERSNormal Vent
1
23
4
5
1. Normal vent2. Design basis3. Mechanical4. Discharge
5. MOC
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Dispersion Zones1. High momentum2. Less momentum3. Gravity4. Atmospheric
turbulence
1
2 3
4
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2-phase Flow
1 3
4 5 6
2
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2-phase Flow
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PHAST – Emulsion Reactor RD
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Gooseneck
Toatmosphere
From vessel
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Toll Incident• Wisconsin - 2002• Leaky steam valve heated a completed
batch from 40C to 150C in 3 hours• Resulting decomposition (>200 psig)• MSDS: “This material is considered
stable”• No fatalities or injuries .
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Toll Incident
DistillateReceiver
Condenser
4000 GallonReactor
RuptureDisk
Building
Building Roof
Steam
2002 runaway
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Toll Incident
2002 runaway
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Toll Incident2002 runaway
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TNP(Thrust Neutralization Plate)
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TNPThrust Neutralization Plate
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TNP or Gooseneckwind
typical flammable region
buildingair inlet
With an obstruction
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Catch TankGravity Separator
Vapors still escape from a separator,
but at a lower
velocity.
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Catch Tank
From reactor Cyclone separator
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Catch Tank Incident
107
Catch Tank Incident• Illinois 2001• Runaway reaction
broke 135 psi RD• Blew off catch tank
top & damaged piping
• No injuries or fatalities .
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Catch Tank Incident
Catch tank roof failed
Low-pressure vessel with
insufficient vent
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Catch Tank Incident
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Quench Tank
111
Straight up
wind
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Rain Protection - Cover
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5. MOC
ERSNormal Vent
1
23
4
5
1. Normal vent2. Design basis3. Mechanical4. Discharge
5. MOC
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Why document?
• Required by OSHA PSM (Process Safety Mgmt)• Required by EHS 536 (Process Safety Mgmt)• For future Management of Change (MOCs)• For future HAZOPs• Avoid reconstructing the design• Information can be used on other systems .
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Vent System Analysis
Follow the ERS procedure for every vessel & every relief device
Store the results in a safe place
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Questions?
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