Transcript Design Basis

Emergency Relief
Gary Van Sciver
September 16, 2008
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·
Gary Van Sciver
Process Engineer
– 8 years
Risk Analyst –
22 years
ETC – 2 ½ years
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Presentation Overview
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4
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ERS
Normal Vent
3
2
1. Normal vent
2. Design basis
3. Mechanical
4. Discharge
5. MOC
3
Terminology (ERS)
Emergency
Relief
System
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1. Normal Vent
5
4
1
ERS
Normal Vent
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2
1. Normal vent
2. Design basis
3. Mechanical
4. Discharge
5. MOC
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What is the difference between
the normal vent & the
emergency vent?
Emergency
Vent
Normal Vent
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What are the differences?
(between the normal & emergency vents)
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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)
Discharge
To/from
vessel
From
atmosphere
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Manifolds
One pollution abatement device will normally
handle the discharge of multiple vessels
Pollution
Abatement
Device
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VPRV
(vacuum pressure relief valve)
Discharge
To/from
vessel
From
atmosphere
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Storage Tank Under Vacuum
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Plastic Bag Over Vent
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2. Design Basis
5
4
1
ERS
Normal Vent
3
2
1. Normal vent
2. Design basis
3. Mechanical
4. 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 Sciences
1999 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 - 2005
Tower – 170 feet tall
Blowdown drum – 115 feet tall
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BP - 2005
Truck parked,
but idling about
25 feet from
blowdown drum
Eyewitness saw
engine overrevving 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
Highly-Populated Region of Bhopal
Union
Carbide
Delhi
N
H
12
Bhopal
Mumbai
(formerly
Bombay)
Taloja
India
Kolkata
(formerly
Calcutta)
NH 86
NH 86
Upper Lake
N
H
12
Chennai
(formerly
Madras)
Toxic Gas
Cloud
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Bhopal
1984
•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
MIC
Storage
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 Exposure
RD
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Runaway reaction
High
temperature
or unusual
composition
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Some other nonreactive upsets
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Excessive heating
(steam valve failures, coil leaks)
RD
Steam wide open
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Pressurized liquid addition
RD
Liquid
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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
Cooling
water
fails
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Inadequate heat sink
Water NOT
charged
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Excessive reactant
Bypass open
Reactant
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Poor reactivity
Agitator 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 Pressure
Runaway Reaction
• Pressure related to temperature
• Control temperature by
evaporative cooling .
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Emulsion
Runaway
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Normal
Upset
35% EA
70% EA
90C max
190C max
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.
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Emulsion Runaway
Germany
France
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Emulsion
Runaway
Germany
France
Rhein
River
Rohm & Haas
France
Germany
Karlsruhe
Odor complaints
13 miles away in
Karlsruhe,
Germany
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Gas Generating
Runaway 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
RD
PC
T
Fill
P
X
X
X
X
X
X
X
X
X
X
X
120 cc
test cell
X
X
X
X X X X X X
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Temperature or Pressure
Temperature vs time
time
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Pressure
P vs T
Cool down
Heat up
Temperature
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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”
3”
12”
18”
24”
1.Liquid filling
2.Fire case
3.Half charge runaway
4.Full charge runaway
5.Full charge runaway, no water heel .
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Selection Approaches
1. Codes
2. Tradition
3. Risk .
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Codes
NFPA 30 requires ERS
protection against fire for
aboveground storage tanks
of flammables &
combustibles
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Fire Case Requirement
Fire Case Heat Input
Q (Btu/hour)
1.0E+08
>1 psig
1.0E+07
<1 psig
1.0E+06
1.0E+05
10
100
1,000
10,000
Area (sq feet)
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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
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4
1
ERS
Normal Vent
3
2
1. Normal vent
2. Design basis
3. Mechanical
4. Discharge
5. MOC
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Vessel Failure
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Vessel Failure
With 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
Hydrostatic
Test Pressure
MAWP
0
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
Vacuum support
goes under the RD
Flow
Rupture Disk
Holder
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Compression-loaded RD
(Reverse Buckling)
Knife blade (if necessary)
goes on top of the RD
Flow
Rupture Disk
Holder
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Relief Valves
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Weak Seam Roof
(part of API 650)
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Weak Seam Roof
Weak seam roof should prevent this
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Weak Seam Roof
Install with relief device to protect the roof
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Ambient Temperature
Design Pressure
Vess
e
ERS
l
Design Temperature
Design Temperature
Temperature
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Thrust forces
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Thrust forces
Rupture
Disk
Reactor
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Thrust forces
For 24” RD, Area = 452 sq in
Opposing forces on
support lugs
& structural steel
Pmax = 165 psi
Thrust = 2 Pmax A = 150,000 lbs
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Piping – Thrust forces
(initial & established)
Initial load
Established load
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4. Discharge
5
4
1
ERS
Normal Vent
3
2
1. Normal vent
2. Design basis
3. Mechanical
4. Discharge
5. MOC
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Dispersion Zones
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1
3
1.
2.
3.
4.
High momentum
Less momentum
Gravity
Atmospheric
turbulence
4
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2-phase Flow
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6
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2-phase Flow
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PHAST – Emulsion Reactor RD
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Gooseneck
To
atmosphere
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
2002
runaway
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Toll Incident
2002
runaway
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Toll Incident
2002 runaway
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TNP
(Thrust Neutralization Plate)
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TNP
Thrust Neutralization Plate
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TNP or Gooseneck
wind
typical flammable region
building
air inlet
With an obstruction
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Catch Tank
Gravity 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
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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
110
Straight up
wind
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Rain Protection - Cover
112
5. MOC
5
4
1
ERS
Normal Vent
3
2
1. Normal vent
2. Design basis
3. Mechanical
4. Discharge
5. MOC
113
Why document?
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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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