Consequence Assessment of Pipeline

Explosion in Farashband

Gas Refinery by Phast Software

Presenter: Amin Avazpour

Dalan Gas Field Production Superintendent

Outline:

• Introduction

• Modeling

• Results and Figures

• Conclusion

• References

Impacts on People, Process and

Facilities , Environment and

Finances is being assessed in

Consequences Modeling

Many things can go wrong on a hazardous industrial facilities, leading

to an unintended release of hazardous materials or an uncontrolled

release of energy.

Consequence assessment is a

methodical examination of the direct

undesirable impacts of a loss of

containment of material or energy.

Introduction:

• Applications:

• design of new facilities: suggest optimal separation distances

• risk assessment of a facility for safety case

• emergency planning and land use planning: estimate impact distances for

• major accident scenarios

• Highly technical area, requiring detailed process safety expertise

PHAST version 7.3 Software (DNV Corp.) was adopted in

order to model the accident. PHAST examines the progress

of a chemical process incident from initial release through

formation of a cloud or pool to final dispersion calculating

concentration, fire radiation, toxicity and explosion

overpressure.

Modeling:

• Whole aim of this study is consequence assessment of explosion

caused by leakage occurred at the critical pipeline system

located in unit-4500 of Farashband Gas Refinery during the

start-up of the plant after annual Overhaul by PHAST. High

pressure (more than 100bars), makes the estimation of

probable explosion consequence more important.

Plant Description :

• Farashband Gas Refinery is located in Fars Province and is a subsidiary of South Zagros Oil and Gas production Company

• The major Process of the Refinery is to Dehydration of Gas and Stabilization of Gas Condensate which is produced in Aghar and Dalan Gas Fields and is transported to the Refinery.

• Climate

• Farashband has hot and humid weather. The temperature of this district

in the hottest month of the year is about 49 degrees centigrade

(August) and in the coldest month of the year is about 8 degrees

centigrade (December).

• The maximum humidity in Farashband is 67 percent in December and

its minimum humidity is about 46 percent in May.

Average value of essential weather variable for Farashband Gas Refinery

Atmospheric temperature 9.85◦C (The average of the minimum temperature

of the 6 colder months).

Relative humidity 64% (the average of the relative humidity for the 6

same months).

Solar radiation 0.50 kW/m2

Wind speeds (based on probable wind speed

of location)

1.5/D, 5/D and 1.5/F

Wind Condition:

For gas dispersion modeling detailed wind and weather data

were obtained from a local weather station and these were

used to define two representative weather conditions to be

used in the modeling.

These being Pasquill-Gifford categories D5 (atmospheric

stability class D with 5m/s wind speed) and F 1.5 (stability F

with 1.5 m/s wind).

D5 represents the most commonly found condition on the site

occurring >65% of the time and F 1.5 a worst case for gas

dispersion (stable conditions with low wind speed).

Gas Analysis Used For Modeling

AREA ACF (MOL%)

N2 6.82

CO2 1.42

C1 88.499

C2 1.52

C3 0.44

IC4 0.13

NC4 0.19

IC5 0.11

NC5 0.10

totalC6 0.38

totalC7 0.26

totalC8 0.10

totalC9 0.02

totalC10 0.01

C11+ 0.001

H2S(PPM) 138

SP.GR 0.64

MOL.WT (gr/mol) 18.42

PRESSURE (BAR) 101

TEMP. (c) 47

RATE (mm/day) 12.17

Figure shows the late Explosion Overpressure in adjacent of equipment.

Category 1.5F and 1.5D have overlap to each other but category 5D has a

40m delay for its maximum overpressure. 0.02068bar over pressure that

is one of the critical thresholds for unsafe distance occur in 500m distance

downwind of explosion

Figure shows the distance of late explosion in which the radii of circles for

various wind speed categories are between 1250 to 1320m downwind.

Figure on top shows the dose radii of jet fire and the other figure shows

that the lethality radius of jet fire which is about 360m.

Explosion radiation vs distance of jet fire showed in this figure. Level of

radiation varies between 360 to 380 KW/𝑚2 for wind speed categories.

Figure shows late explosion worst case distance due to modelling.

The radius of following circle is about 1300m.

Figure shows the flash fire envelop distribution due to explosion.

Category 5D has the smallest radius of flash fire and 1.5F includes the

largest zone between the other categories.

Conclusions:

1- Paying attention to HSE issues during Overhauls will cause to prevent from

losing huge cost of untimely shutdown and production interruption.

2- Consequence assessment will provide a good time for engineering analysis to

perform complete cost assessment for future remediation technique such as

pipeline intelligent pigging and inspection tests for replacing or maintenance of

the pipelines.

3- In safety issues radiations of 20.0 kW/m2 and 37.5 kW/m2 is very important

because the radiation of 20.0 kW/m2 cause damage to human, and 37.5kW/m2

cause damage to equipment and cause Annie's death, from the PHAST result the

radius of 37.5 kW/m2 is about 400m.

4- Concentration of released fluid reaches to 22000ppm in 900m far from

explosion for category 1.5F. This result clearly shows that pipeline explosion can

be extremely mortal for personnel that are working in mentioned distance.

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