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7/27/2019 Honeywell Rodgers Presentation.pdf
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reven on
MeasuresOverview of Explosion Prevention MeasuresSlide 1Oct 2010
Sam RodgersHoneywell
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ExplosionExplosion
Explosion The bursting or rupture of anenc osure or a con a ner ue o e eve opmenof internal pressure from a deflagration
ISO
Oxidant
ATIO
DetectionFuel
Ignition
N
ContainmentContainment
Overview of Explosion Prevention MeasuresSlide 2Oct 2010
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Explosion Protection Systems DocumentsExplosion Protection Systems Documents
NFPA 68 Standard on Ex losion
Protection by Deflagration Venting (2007edition)
NFPA 69 Standard on Ex losionPrevention Systems (2008 edition)
Invoked by other Standards
Overview of Explosion Prevention MeasuresSlide 3Oct 2010
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, , , , ,
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Explosion Protection and PreventionExplosion Protection and Prevention
There are two distinct phases involved in a
Prevention, which deals with the elimination of theconditions which permit the formation of anexp os ve m xture an t e e m nat on o a poss esources of ignition
Protection, which deals with reducin the effects ofan explosion, the basic purpose of this guide
This talk deals with both aspects NFPA 68
methods for both protection and prevention
Overview of Explosion Prevention MeasuresSlide 4Oct 2010
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PerformancePerformance--based approachbased approach
Standards offer option for compliance -
Establish life safety and property protectionobjectives
Define deflagration hazard scenario
See Chapter 5 of NFPA 68 or 69
-Use the equations as presented in Chapters 7, 8,
and 9 to determine vent requirements accordingto NFPA 68
Use the explosion prevention and protectionmethods of Chapters 7 through 14 of NFPA 69
Overview of Explosion Prevention MeasuresSlide 5Oct 2010
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Explosion PreventionExplosion Prevention
Pre-Deflagration Detection and Ignit ion Control Detect using Optical or Concentration sensors Used for Pre-emptive Shutdown or Modification of
operations to Prevent Activating a Protection System
Can be used independently to reduce frequency of
Deflagrations System
Can not interfere with the operation of the ValidatedSystem
Can not be used as the sole detector for a ValidatedSystem
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Overview of Explosion Prevention MeasuresSlide 8Oct 2010
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Oxidant Concentration Control (Inerting)Oxidant Concentration Control (Inerting)
Overview of Explosion Prevention MeasuresSlide 9Oct 2010
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Limiting Oxygen Concentration of Selected Dust SamplesLimiting Oxygen Concentration of Selected Dust Samples
us o .
Pear wood 16.0
Barium dust 13.4
Wood grinding dust 13.0
Zinc stearate 11.5Polyethylene 10.0
Para-formaldehyde 6.0
.
Overview of Explosion Prevention MeasuresSlide 10Oct 2010
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Oxidant Concentration ControlOxidant Concentration Control
on nuous 2 oncen ra on on or For LOC > 5%:
Max% O2 = Worst Credible Case LOC 2 vol%
For LOC < 5%:
Max% O2 = 0.60 LOC
Without Continuous O2 Concentration Monitor
For LOC > 5%:ax 2 = .
For LOC < 5%:
Max% O2 = 0.40 LOC
And O2 Checked on a regularly scheduled basis
Requires Purge Gas Monitoring and
Overview of Explosion Prevention MeasuresSlide 11Oct 2010
Sam RodgersHoneywell
Alarm for Abnormal Operation
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Combustible Concentration ControlCombustible Concentration Control
With Continuous Concentration Monitor ax om us e oncen ra on =
Requires anAlarm, but not automatic action
With Continuous Concentration Monitorand SafetyInterlocks (automatic change to safe condition)
Max Combustible Concentration = 60% LFL MEC Aluminum per NFPA-484 = 50% LFL (MEC)
Requires Instrumentation to Monitor
Overview of Explosion Prevention MeasuresSlide 12Oct 2010
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Predeflagration Detection and ControlPredeflagration Detection and Control
Optical system detectors are sensitive toradiant energy from hot particles, glows,
,
Extinguishing mediums such as water, carbon,
Stop and diverter valves are also common
Gas sensin s stems detect the formation ofthermal decomposition gases
Control can be accomplished with alarms,
automated shutdown, or the release of theextinguishing system
Overview of Explosion Prevention MeasuresSlide 13Oct 2010
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Gas Sensing Equipment ConsiderationsGas Sensing Equipment Considerations
The system shall take air samples at inlets and
concentration for selected thermaldecomposition products.
The design shall be based on such factors as:Process mass flowFlow velocityPotential measurement interferences
Air flow and exchange rateSensor response time
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Overview of Explosion Prevention MeasuresSlide 16Oct 2010
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Deflagration Containment Based on PDeflagration Containment Based on Pmaxmax
PR max
test
max .
Ptest = initial absolute pressure during the test (typically 1 bar)
(1) For most gas/air mixtures, the value of R shall be 9.
(2) For St-1 and St-2 dust/air mixtures, the value of R shall
.
(3) For St-3 dust/air mixtures, the value of R shall be 13.
A value for R other than the values specified shall be
ermitted to be used if such value can be substantiated b
Overview of Explosion Prevention MeasuresSlide 17Oct 2010
Sam RodgersHoneywell
test data or calculations.
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Design Strength of Vessels to Contain PDesign Strength of Vessels to Contain Pmaxmax
(1) If permanent deformation, but not rupture, of the enclosurecan be accepted.
ua
mawpF
PPR
P3
20
Pmawp = enclosure design pressure [barg (psig)] according toASME Boiler and Pressure Vessel Code, i.e. the maximum
allowable workin ressure
Fu = ratio of ultimate stress of the enclosure to the allowablestress of the enclosure per the ASME Boiler and PressureVessel Code; For vessels fabricated of low-carbon steel and
low-alloy stainless steel, Fu equals approximately 3.5
P0 = worst case initial vessel pressure
Overview of Explosion Prevention MeasuresSlide 18Oct 2010
Sam RodgersHoneywell
Pa = atmospheric pressure
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Design Strength of Vessels to Contain PDesign Strength of Vessels to Contain Pmaxmax
(2) Ifpermanent deformation of the enclosure cannot beaccepted.
PPR
y
amawp
F
P
32
Fy = ratio of the yield stress of the enclosure to the allowable
stress of the materials of construction of the enclosure per the
ASME Boiler and Pressure Vessel Code; For vesselsfabricated of low-carbon steel and low-alloy stainless steel, Fyequals approximately 1.75
nc osures vesse s a e nspec e aleast every 3 years More frequent than
Overview of Explosion Prevention MeasuresSlide 19Oct 2010
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co e
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Overview of Explosion Prevention MeasuresSlide 20Oct 2010
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2007 Equations Summary2007 Equations Summary
Basic
75.0
154.11101 max4/33/44
0
red
StstatvP
VKPA
Enclosure L/D 2
095.0exp26.0 red
v
v
PDA
Vent Panel Mass2.03.0
5.06.0
0
0075.01red
St
v
v
PVn
KM
A
A
Partial Volume
(locally dusty)
1
31 rr
v XXA
A
Vent Ducts4.08.018.11 KEE
Av
Overview of Explosion Prevention MeasuresSlide 21Oct 2010
Sam RodgersHoneywell
00v
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Basic EquationBasic Equation
154.11101max4/3
3/440
red
StstatvP
PVKPA
where: Av0 = vent area calculated from the basic equation (m2) Pstat = nominal static burst pressure of the vent (bar) KSt = deflagration index (bar-m/sec) = 3
Pmax = maximum pressure of a deflagration (bar) Pred = reduced pressure after deflagration venting (bar)
Overview of Explosion Prevention MeasuresSlide 22Oct 2010
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PPredred and Vent Areaand Vent Area
Overview of Explosion Prevention MeasuresSlide 23Oct 2010
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Enclosure L/D CorrectionEnclosure L/D Correction
)95.0exp(26.012
.
01 redvv PD
LAA
V = 12.35 m3
=
V = 12.35 m3
=
No correction if L/D < 2
..
Overview of Explosion Prevention MeasuresSlide 24Oct 2010
Sam RodgersHoneywell
determines the effective L/D
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Vent Panel InertiaVent Panel Inertia
Correction Threshold is 5% effect on Vent Area
67.1
Panel Inertia Correction
5.0
..67.6
St
redT
K
nP
]0075.01[
5.06.0
23 Stvv
KMAA
Limitations: < 2
..
redn
75 < KSt < 800 bar-m/sec
Overview of Explosion Prevention MeasuresSlide 26Oct 2010
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Partial VolumePartial Volume
Dust concentrations in some process equipment andbuildings are inherently or by housekeeping limitedto only a fraction, Xr, of the enclosure volume.
1
31
34r
rvv XAA
Av4 = vent area for partial volume deflagration
Av3 = vent area for full volume deflagration
=
Ventin is not re uired if Xr