Prof S. A. Abbasi - Proses Güvenliği · control of MPFs as compared to stand-alone ... Individual pool fires start to burn more intensely with higher flames ... –Extra precautions

Multiple pool fires

Prof S. A. AbbasiEmeritus Professor

Centre For Pollution Control and Environmental Engineering

Pondicherry University

Dr S. M. TauseefAssistant Professor

Department of Health, Safety and Environment

University of Petroleum and Energy Studies (UPES)

Dr Tasneem AbbasiAssistant Professor

Centre For Pollution Control and Environmental Engineering



Multiple Pool fires (MPFs)

When two or more pool fires burn in close enough proximity to influence one another, they are termed ‘Multiple Pool Fires’ (MPFs)


MPFs may burn brighter than stand-

pool fires but there is little work that

can throw light on them

● Even though MPFs have known to occur fairly often in process industries, much lesser work has been done towards simulation, modeling and control of MPFs as compared to stand-alone pool fires

● Past accident analysis reveals that MPFs have huge destructive potential and have been responsible for some of the worst process industry accidents

● Surprisingly few studies exist on the mechanism of MPF development and the factors that control it

● Of special concern is the paucity of knowledge about such interactive effects of pool fires which can make MPFs more destructive than non-interacting pool fires of identical numbers and sizes


MPFs vs stand-alone pool fires

Different forms of interactive effects distinguish MPFs in contrast to stand alone pool fires

● Individual pool fires start to burn more intensely with higher flames as the distance between them is decreased

● The interaction of number of fires burning in close proximity has substantial effect on

– the burning rate of the fuel,

– the size of the flame, and

– the rate of heat transfer from the flame to the surroundings


A commonly observed sequence of

events in incidents leading to MPFs

Ignition source

Vapor cloud explosion

Pool fireMultiple pool fires

Pool formation

Vapor cloud formation

Overfilling


MPF accidents that have

occurred since 1975


1975 Beek, Netherlands

Naphtha, propylene

None 14 / 107 Not reported

Not reported

22.8

1977 Umm said, Qatar

Liquid propane, butane

37,521

19,873

7 / 13 100 7 76.35

1981 Shuaiba refinery tank farm, Kuwait

Petrochemicalgrade naphtha

Not reported

1 / 1 50 6 42

1983 Milford Haven, UK.

Crude oil 47,000 0 / 20 150 3 7.3

1983 Newark, New jersey, US

Gasoline 6,677 1 / 0 50 1 10

1985 Naples, Italy Gasoline, diesel, and fuel oil

27, 000 5 / 170 Not reported

6 51

1986 Thessaloniki,Greece

Crude oil, fuel oil and gasoline

Not reported

Not reported

Not reported

Not reported

Not reported

1987 Lyon, France Domestic fuel and diesel fuel

1,900

1,200

2 / 14 200 1 26

Year Location Material/ substance

Quantity (KL)

Dead / injured

Reported maximum flame height (m)

Duration (days)

Economic losses (million US $)


A recent example of an MPF accident

Jaipur, India, 2009

Leak from a pipeline during the transfer of

petrol

Vapour cloud explosion

11 pool fires initiated

Flames visible from a distance of 30 KmFire raged for about 2 weeks till all the fuel was burnt off

12 killed200 injured$ 32 million worth of damage caused


Factors governing MPFs

● Separation distance

● Wind effect

● Characteristics and quantity of fuel present in the pools

● Combustion products


Huffman et al 1969Effect of separation distance on flame interactions

Individual fires

Interacting fires

Merged fires

Fuel: n-hexane, Burners: 9, Burner dia: 4-in

Dec

reas

ing

sep

arat

ion

dis

tan

ce

S

D


Huffman et al 1969Burning rates of interacting 4-in cyclohexane fires

Center burner

Outer burners

Dimensionless separation distance, S/D

Bu

rnin

g ra

te p

er

un

it a

rea,

lb/h

rft

2

S

D


Observations from tests

Decreasing separation distance

Flames interact

Increases the burning rate, heat release rate, flame height

Critical separation distance

Flames merge

Burn with maximum heat release rate and flame height

Burning rate and heat release rate fall, but remain at much elevated levels compared to individual fires


Controlled experiments on MPFs

Summary of findings

● Overall flame length as well as the mass burning rate increased with decrease in the separation distance between MPFs (Liu et al., 2009; Fukuda et al., 2004; Huang and Lee, 1967; Vincent and Gollahalli, 1995; Liu et al., 2007)

● The rate of flame propagation, depth of the burning zone and the mass burning rate increases with increasing wind velocities (Rios et al. 1967)

● Closer proximity also contributed to higher flame height and heat release rate (Weng et al., 2004; Delichatsios, 2007; Vincent and Gollahalli, 1995; Fukuda et al., 2004; Liu et al., 2007)


Modeling of MPFs

Only a few empirical and field models have been developed to model MPFs


Modeling of MPFs

● The empirical models for MPFs developed so far have aimed to correlate the total thermal energy radiated by the MPFs with the physical characteristics of fire, aspects of overall combustion chemistry, and variation of the thermal output from different parts of MPFs

● These models can be used to estimate

– Flame geometry

Sugawa and Takahashi, (1993); Weng et al., (2004); Delichatsios, (2007); Huang and Lee, (1967)

– Burning rate

Huffman et al., (1969); Rios et al., (1967); Liu et al., (2009)

– Radiation from an MPF

Weng et al., (2004); Fukuda et al., (2005); Delichatsios, (2007)


“Knowledge gaps”


Controlled experiments on MPFs

Fuels tested

• Fuels tested were mostly clean burning fuels

• Such flames give rise to optically thin flames with little soot

Diameter of individual pools

• Largest size of pool studied is 0.8 m

• All other studies are on smaller pool sizes (0.02 m to 0.15 m)

• At diameters>0.2 m, heat transfer is dominated by radiation, as in large scale pool fires

Limited applicability of the data from these tests for

extrapolating results to simulate larger

MPFs


Comparison of the predictions for flame height, burning rate, and HRR by various

empirical models with corresponding experimental data reported by Vincent

and Gollahalli (1995) and Koseki and Yumoto (1989) for MPF involving pool fires of

diameter 25.4 cm and 80 cm respectively

Models Diameter of

the pool

fires used in

the

experiment

on which

the model is

based (m)

MPF with 25.4 cm diameter pool fires

as used in experiment by Vincent and

Gollahalli (1995)

MPF with 80 cm diameter pool fires as

used in experiment by Koseki and Yumoto

(1995)

Model

predictions

Percentage error

(deviation from the data

reported by Vincent and

Gollahalli (1995))

Model predictions Percentage error

(deviation from the

data reported by

Koseki and Yumoto

(1989))

Flame height

Sugawa and

Takahashi, 1993

0.12 0.859 20 % 6.1 22 %

Weng et al.,

2004

0.0015 0.823 23% 6.4 28 %

Delichatsios,

2007

0.15 0.921 14 % 5.8 16 %

Performance of the empirical models


Comparison of the predictions for flame height, burning rate, and HRR by various

empirical models with corresponding experimental data reported by Vincent

and Gollahalli (1995) and Koseki and Yumoto (1989) for MPF involving pool fires of

diameter 25.4 cm and 80 cm respectively

Models Diameter of

the pool

fires used in

the

experiment

on which

the model is

based (m)

MPF with 25.4 cm diameter pool fires

as used in experiment by Vincent and

Gollahalli (1995)

MPF with 80 cm diameter pool fires as

used in experiment by Koseki and Yumoto

(1995)

Model

predictions

Percentage error

(deviation from the data

reported by Vincent and

Gollahalli (1995))

Model predictions Percentage error

(deviation from the

data reported by

Koseki and Yumoto

(1989))

Burning rate

(Huffman et al.,

1969)

0.05, 0.10

and 0.15

0.0295 44% 0.0276 49%

(Liu et al., 2009) 0.05 0.0458 13% 0.0431 19%

HRR

(Weng et al.,

2004)

0.0015 174 26% - -

(Fukuda et al.,

2005)

0.048 104 24% - -

(Delichatsios,

2007)

0.15 118 14% - -


Work we have done

Over the last 3 years the we have:

● Carried out a close study of all previous efforts to model MPFs and elucidate their mechanism

● Carried out CFD-based simulations using experimental data reported earlier by other authors to ascertain the efficacy of CFD in pool fire modeling and simulation


CFD studies

● Evaluated several CFD turbulence models for the simulation of pool fires

● The standard k-ε model was found to simulate the experimental results most closely


CFD studiesSimulation of a multiple pool fire involving two different fuels

Comparison of experimental results and CFD results of MPF using iso octane and kerosene

T (K) Radiation

(W/m2)

Average burning rate

(kg/m2s)

Experimental MPF with iso

octane as fuel

- 3100 0.0527 (central pool)

0.0410 (outer pools)

CFD MPF with iso octane

as fuel

1789 3806 0.03754 (central pool)


Experimental MPF with jet

A as fuel

1490 2000 0.0270 (central pool)


CFD MPF with jet A /

kerosene as fuel

1315 2572 0.0217 (central pool)



Comparison of temperature profile

(diagonal plane) of MPF using

octane as fuel


Comparison of temperature profile

(diagonal plane) of MPF using

kerosene as fuel


CFD-based simulation of multiple pool

fires occurring at differing elevationsComparison of temperature profiles

SPF diameter = 48 mm MPFs at x = 60 mm, y = 20 mm MPFs at x = 60 mm, y = 0 mm


Prevention/control of MPFs

● As of now no accident prevention/control strategies and codes of practice exist that are specific to MPFs

● The following aspects are particularly relevant to MPFs, in addition to all other measures associated with the prevention and control of stand-alone pool fires:

– Keeping adequate provision to ensure safe and quick drain-off of the fuel in case a fire starts

– Positioning of the storage tanks in a manner that ensures safe distance between the tanks based on the considerations of local meteorology, especially wind directions and speeds

– Extra precautions against overfilling/spillage – Pumping stations should be provided with drainage systems capable of

quickly and safely draining away the flammable liquid

Thank You

Documents

Prof S. A. Abbasi - Proses Güvenliği · control of MPFs as compared to stand-alone ... Individual pool fires start to burn more intensely with higher flames ... –Extra precautions