BLEVE Fireballs 2010

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BLEVE & FireballsBLEVE & Fireballs

Roger DeoRoger Deo

BLEVE (Video) BLEVE (Video)

BELEVE & FireballsBELEVE & Fireballs 22

BLEVE & fireballsBLEVE & fireballs

A boiling liquid expanding vapor cloud A boiling liquid expanding vapor cloud explosion (BLEVE) occurs when there is a explosion (BLEVE) occurs when there is a sudden release of confinement of a sudden release of confinement of a


pressure vessel containing a superheated pressure vessel containing a superheated vessel or liquefied gas. A BLEVE can vessel or liquefied gas. A BLEVE can occur due to any mechanism that results occur due to any mechanism that results in the sudden failure of containment.in the sudden failure of containment.

BLEVEBLEVE

Path Length


receptor

g

Height

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Empirical equationsEmpirical equationsThe determination of the fireball’s height, The determination of the fireball’s height, diameter and duration are given by the diameter and duration are given by the following empirical equations.following empirical equations.Maximum fireball diameterMaximum fireball diameter


Maximum fireball diameterMaximum fireball diameter

Fireball combustion durationFireball combustion duration

31

max M8.5D =

31

BLEVE M45.0t =6

1

BLEVE M6.2t =

For M<30000

For M>30000

Empirical equations Empirical equations

Center height of fireballCenter height of fireball

MAXBLEVE D75.0H =


Initial ground level hemisphere diameterInitial ground level hemisphere diameterMAXBLEVE

MAXINITIAL D3.1D =

RadiationRadiationThe emissive radiation flux is represented The emissive radiation flux is represented by the Stefanby the Stefan--Boltzmann lawBoltzmann law

4max TE σ=


–– WhereWhere

––σσ is the Stefan Boltzmann constant is the Stefan Boltzmann constant

–– TTff is the absolute temperatureis the absolute temperature

–– EEmaxmax is the maximum radiative fluxis the maximum radiative flux

max σ

For real sources the maximum emissive For real sources the maximum emissive

radiation is given by the followingradiation is given by the following

E = E = εε EEmaxmax


Where Where

εε is the emissivity of a black bodyis the emissivity of a black body

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For fireballs Beer’s law can be used For fireballs Beer’s law can be used

to determine the emissivityto determine the emissivity

kDe1 −−=ε


–– WhereWhere

K is the extinction coefficientK is the extinction coefficient

EmittanceEmittanceThermal radiation is usually calculated using Thermal radiation is usually calculated using

surface emitted flux. Typical energy fluxes are surface emitted flux. Typical energy fluxes are

much higher than that of pool fires much higher than that of pool fires


The surface heat flux based on the radiative The surface heat flux based on the radiative

fraction on the total heat of combustion is fraction on the total heat of combustion is

given by:given by:

BLEVEmax2

c

rDRMHE

π=

Where Where

–– E is the radiative emissive fluxE is the radiative emissive flux

–– R is the radiation fraction of the heat of R is the radiation fraction of the heat of

combustioncombustion


–– M is the initial mass of fuelM is the initial mass of fuel

–– HHcc is the heat of combustion per unit massis the heat of combustion per unit mass

–– DDmaxmax is the maximum diameter of the fireballis the maximum diameter of the fireball

Radiative flux Radiative flux

The radiative flux received by a receptor The radiative flux received by a receptor

at a distance L can be determined from at a distance L can be determined from


this empirical equation.this empirical equation.

2c

32

ca

X4MRH2.2E

πτ

=

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Radiative flux Radiative flux WhereWhere–– EErr is the radiative flux received by the is the radiative flux received by the

receptorreceptori th t h i t i i iti th t h i t i i it


–– ττaa is the atmospheric transmissivityis the atmospheric transmissivity–– R is the radiative fractionR is the radiative fraction–– M is the initial mass of fuel in the fireballM is the initial mass of fuel in the fireball–– XXcc is the distance fireball center to the is the distance fireball center to the

receptor.receptor.

Atmospheric transmissivityAtmospheric transmissivityThe atmospheric transmissivity is an The atmospheric transmissivity is an important factor radiation is absorbed and important factor radiation is absorbed and scattered by the atmosphere. This causes a scattered by the atmosphere. This causes a reduction in radiation received by target reduction in radiation received by target


locations If the atmospheric transmissivity is locations If the atmospheric transmissivity is ignored ignored ττaa = 1. This can result in substantial = 1. This can result in substantial error since at distances greater than 20m error since at distances greater than 20m this would account for 20% to 40% of the this would account for 20% to 40% of the radiation absorbed.radiation absorbed.

A recommended correlation formula that A recommended correlation formula that accounts for humidity is given byaccounts for humidity is given by

( ) 09.0cxa XP02.2 −=τ

( ) ⎟⎠

⎞⎜⎜⎝

⎛−=w T

53284114.14exp(RH101325P


WhereWherePPww is the vapor pressure of water (Pa)is the vapor pressure of water (Pa)

RH is the relative humidity (%)RH is the relative humidity (%)

TTaa is the ambient temperature is the ambient temperature

XXcc si the distance from the center of the si the distance from the center of the

⎠⎝ aT

Radiative fluxRadiative flux

A more empirical equation for the A more empirical equation for the

radiative flux was proposed by Robert radiative flux was proposed by Robert


2c

771.03

XM1028.8E ×

=

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Radiative fluxRadiative fluxThe radiation received for the duration The radiation received for the duration of the BLEVE incident is given byof the BLEVE incident is given by

21ar EFE τ=


WhereWhereEr is the emissive radiative flux received by a Er is the emissive radiative flux received by a black body receptorblack body receptorττa a si the atmospheric transmissivitysi the atmospheric transmissivityF is the geometric view factorF is the geometric view factor

Geometric view factorGeometric view factorFor a horizontal surface the geometric view For a horizontal surface the geometric view factor is given by:factor is given by:

( )( ) 2

322

2

21HL

2DHF+

=


For a vertical surface the geometric view For a vertical surface the geometric view factor is given by:factor is given by:

( ) 222 HL +

( )( ) 2

322

2

21HL

2DLF+

=

Pool firesPool fires

A pool fire can result from a number of A pool fire can result from a number of

scenarios. If the material is a scenarios. If the material is a


flammable liquid stored below its flammable liquid stored below its

boiling point the subsequent release boiling point the subsequent release

and ignition would result in a pool fireand ignition would result in a pool fire

Pool firePool fireFire


Receptor

Pool

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Burning rate Burning rate For burning liquids the radiative heat For burning liquids the radiative heat

transfer and subsequent boiling rate would transfer and subsequent boiling rate would

increase with the pool diameter. For pool increase with the pool diameter. For pool


diameters greater than 1m the radiative heat diameters greater than 1m the radiative heat

transfer dominates and the flames geometric transfer dominates and the flames geometric

view factor is constant. Thus a constant view factor is constant. Thus a constant

burning rate can be expected burning rate can be expected

For pool diameters greater than 1m For pool diameters greater than 1m Burghs showed that the rate of Burghs showed that the rate of decrease of the height of the liquid is decrease of the height of the liquid is given by:given by:

*HH1027.1y c6

max ∆∆

×= −


Where Where ––∆∆HcHc is the net heat of combustionis the net heat of combustion––∆∆H* is the modified enthalpy of H* is the modified enthalpy of

vaporization of vaporization of hyhy liquid at its boiling liquid at its boiling point (equation on the next slidepoint (equation on the next slide

*H∆

WhereWhere

––∆∆Hv is the enthalpy of vaporizationHv is the enthalpy of vaporization

dTCH*HTbp

TapV ∫+∆=∆


∆∆Hv is the enthalpy of vaporizationHv is the enthalpy of vaporization

–– Cp is the heat capacity of the liquid Cp is the heat capacity of the liquid

integrated between ambient temperature integrated between ambient temperature

and that of the boiling pointand that of the boiling point

If the density is not available the mass If the density is not available the mass

burning rate is then given byburning rate is then given by

*HH101m c3

B ∆∆

×= −


WhereWhere

–– MMbb is the mass burning rate in (kg/sec)is the mass burning rate in (kg/sec)

*H∆

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Pool sizePool sizePool sizes are fixed are fixed by the size Pool sizes are fixed are fixed by the size of the release and that of physical of the release and that of physical barriers. For a continuous release on an barriers. For a continuous release on an


infinite flat plate the maximum diameter infinite flat plate the maximum diameter is reached when the product of the is reached when the product of the burning rate and surface area is equal to burning rate and surface area is equal to the leakage area.the leakage area.

Where Where

–– Vl is the volumetric liquid spill rateVl is the volumetric liquid spill rate

yV2D l

max π=


Vl is the volumetric liquid spill rate Vl is the volumetric liquid spill rate

(volume/time)(volume/time)

–– y is the liquid burning rate (length/time)y is the liquid burning rate (length/time)

Flame heightFlame heightFor a circular pool the flame height is given For a circular pool the flame height is given by:by:

61.0

b

gDM42

DH ⎟

⎠

⎞⎜⎜⎝

⎛

ρ=


WhereWhere–– ρρzz is the air densityis the air density–– g is the gravitational constantg is the gravitational constant

a gDD ⎠⎝ ρ

Geometric view factorGeometric view factorThis geometric view facto is for the point This geometric view facto is for the point source. If the solid plume is to be used a source. If the solid plume is to be used a different more complex geometric view factor different more complex geometric view factor is requiredis required


is required.is required.

WhereWhere–– X is the distance from the center to the targetX is the distance from the center to the target

2P x41Fπ

=

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Received thermal flux Received thermal flux If the point source model is selected then If the point source model is selected then the received thermal flux is determined from the received thermal flux is determined from the total energy of combustionthe total energy of combustion

AFHMFQE ∆


If the solid plume radiation model is selected If the solid plume radiation model is selected the selected the received flux is based on the selected the received flux is based on surface surface

pcbaprar AFHMFQE ∆ητ=τ=

21car FHE τ=

Jet firesJet firesJet fires typically result from the Jet fires typically result from the

combustion of material as it is being combustion of material as it is being

released from the pressurized process released from the pressurized process


unit. The main concern is localized unit. The main concern is localized

effects. The model is used mostly to effects. The model is used mostly to

specify am exclusion zone for flares.specify am exclusion zone for flares.

Flame heightFlame heightFlame height for turbulent gas jets in Flame height for turbulent gas jets in still air is given by:still air is given by:

⎤⎡


( )⎥⎥⎦

⎤

⎢⎢⎣

⎡−+=

f

aTT

T

jf

Tj MMCC

aTT

CdL 13.5

WhereWhere–– L is the length of the visible turbulent flameL is the length of the visible turbulent flame–– ddii si the diameter of the jet, the physical si the diameter of the jet, the physical

diameter of the nozzlediameter of the nozzle–– CCTT is the fuel mole fraction ratiois the fuel mole fraction ratio-- the the

stoichiometric ratio of the fuel air mixturestoichiometric ratio of the fuel air mixture


–– TTff si the adiabatic flame temperaturesi the adiabatic flame temperature–– TTi i is the jet fluid temperature respectivelyis the jet fluid temperature respectively–– Ma is the molecular weight of airMa is the molecular weight of air–– MMff Is the molecular weight of the fuelIs the molecular weight of the fuel–– aaTT is the moles of reactant per mole of productis the moles of reactant per mole of product

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The flame height was also given by the The flame height was also given by the

following expression from Mudan & following expression from Mudan &

CroceCroce


f

a

Tj MM

C15

dL` =

Radiant fluxRadiant flux

The radiant flux reaching the receiver is The radiant flux reaching the receiver is

then given by;then given by;


pcbaprar AFHMFQE ∆ητ=τ=

BLEVE Fireballs 2010

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