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1. GAS FLARE
STACK PROCESS
Shad B. Ibrahim
MohammedA. Abdulkadir
Rabar M. Mahmood
1

2.  Introduction
 What is Flaring?
 Purpose of Flaring
 Flare Stack Classification: Height of the Flare
Method to Enhance Mixing
 Flare Stack Process (P&ID Drawing)
 Process Description: Knock out Drum
Liquid Seal
Gas Seal
BurnerTip
Pilot Burner
Steam Jets
Controls
 References
CONTENT
2

3. INTRODUCTION
The flame at the top of an oil production site is an iconic image for the oil and
gas industry. Yet few people know why the flare is there and its purpose. The
flare is a last line of defense in the safe emergency release system in a
refinery or chemical plant.
It provides a means of safe disposal of the vapor streams from its facilities,
by burning them under controlled conditions such that adjacent equipment
or personnel are not exposed to hazards, and at the same time obeying the
environmental regulation (EPA) of pollution control and public relations
requirements.
3

4. WHAT IS FLARING ?
 Flaring is a high-temperature oxidation process used to burn
combustible components (mostly hydrocarbons) of waste gases
from industrial operations.
 Natural gas, propane, ethylene, propylene, butadiene and butane
constitute over 95 percent of the waste gases flared.
 In combustion, gaseous hydrocarbons react with atmospheric oxygen to form carbon
dioxide (CO2) and water (H2O).
 Presented below, as an example, is the combustion reaction of propane.
C3H8 +5O2 → 3 CO2 +4H2O
4

5. PURPOSE OF FLARING
Flares are used extensively to dispose:
1) Purged and wasted products from refineries.
2) Unrecoverable gases emerging with oil from oil wells.
3) Vented gases from blast furnaces.
4) Unused gases from coke ovens.
5) Gaseous wastes from chemical industries.
5

6. Flares
Height of the
flare
Elevated
Self Supported Stack
GuyWired Supported
Stack
Derrick Supported
Stacks
Demountable Derrick
Supported Stacks
Ground
Open
Enclosed
Method to
enhance
mixing at
flare
Steam-Assisted
Air-Assisted
Non-Assisted
PressureAssisted
FLARE STACK CLASSIFICATION
6

7. HEIGHT OFTHE FLARE
Elevated Flare
1-Self supported stacks
 This is the simplest and most
economical design for applications
requiring short-stack heights.
 Their installation space required is
relatively less .
 Simple to erect reducing capital
costs.
 Under 50 meters overall height.
2-Guy wired supported stacks
 Sets of 3 wires are anchored 120º
apart at various elevations (1 to 6).
 It’s Investment is generally lower
than the other types.
 Their installation require large
amounts of land to accommodate
the wires.
 50 – 150 meters height range.
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8. HEIGHT OFTHE FLARE
Elevated Flare
8
3-Derrick supported stacks
 Can be the optimum solution for flare
systems installed inside plants.
 When higher elevation is required to
limit ground radiation, thermal
expansion
 A single-diameter riser supported by a
bolted framework of supports which
offer greater support than guyed
stacks.
 Cost 50 to 100% more to build.
 Stack heights above 200 meters.
4-Demountable derrick
 Multiple flares can be installed in a
single derrick structure.
 Require three or four additional
foundations for the derrick legs.
 Allows one flare to be worked on or
replaced while the other flare(s) remain
in service.
 Flare tip can be lowered to grade level
for maintenance, inspection, or repair
activities.

9. Open Ground Flare
 Have a series of headers spaced across open ground with multiple burner tips to distribute the
flame.
 A radiation fence typically surrounding the area.
 Open ground flares are able to burn larger quantities at a time.
 Handling large gas flow rate with smokeless operations.
 Requires large clearances.
 It’s units contain a limited amount of space for the burners. This means that the units must be
kept at a distance for safety reasons.
 Bright light, noise and heat emissions require that the unit be used in a more secluded area.
Enclosed Ground Flare
 More common than an open ground flare.
 It’s burner heads are inside a shell that is internally insulated. This shell reduces noise,
luminosity, and heat radiation and provides wind protection.
 Equipped with a vertical combustion chamber and the height must be adequate for creating
enough draft to supply sufficient air for smokeless combustion and for dispersion of the
thermal plume.
 Suitable for managing low and medium gas flow rates.
 Reliable and high combustion efficiency can be attained under any atmospheric conditions.
HEIGHT OFTHE FLARE
9

10. SteamAssisted
AirAssisted
NonAssisted
PressureAssisted
 Predominant flare
type found in
refineries and
chemical plants.
 For disposal of
heavier waste gases
which have a
greater tendency to
smoke .
 Used where high
efficiency
combustion of
heavy hydrocarbons
is required.
 Steam causes
turbulence which
improves mixing
and combustion
efficiency.
 Can be used where
steam is not
available.
 Dispose of heavier
waste gases which
have a greater
tendency to smoke.
 Combustion air is
provided by a fan in
the bottom of the
cylinder.
 The amount of
combustion air can
be varied by varying
the fan speed.
 Flare tip without any
auxiliary provision to
enhance the mixing.
 Limited to gas
streams that have a
low heat content and
C/H2 ratio, that burn
readily without
producing smoke.
 Where smokeless
combustion of heavy
hydrocarbons is not
required.
 Gases with lower
combustion
temperatures.
 Lower capital cost for
safe disposal of
waste gases.
 Use the actual
pressure of the
waste gas to create
turbulence.
 Pressure-assisted
flares generally have
the burner
arrangement at
ground level.
 They have multiple
burner heads that
are staged to
operate based on
the quantity of gas
being released.
METHODTO ENHANCE MIXING
10

11. FLARE STACK PROCESS (P&ID DRAWING)
11

12. Knock Out Drum
 Remove liquids that may be in the vent gas stream or that have condensed
out in the collection header and transfer lines.
 This drum must be sized for worst case conditions.
 Horizontal drum is more economical when large liquid storage and, high
vapor flow and lowest pressure drop is desired.
 Vertical knockout drums used if the liquid load is low or
limited space is available.
 They are usually quite large.
 Zone 1: Inlet distribution zone.
Zone 2: Fine separation zone.
Zone 3: Liquid collection and drain zone.
PROCESS DESCRIPTION
12

13. PROCESS DESCRIPTION
Liquid Seal
 Process vent streams are passed through a liquid seal before going to the flare
stack.
 Can be downstream of the knockout drum or incorporated into the same vessel.
 Preventing air infiltration in the flare stack and header system.
 Stop flame propagation and prevent possible flame flashback.
 Quenching possible flame with a barrier of water.
 Acts as a large check valve so that gas cannot travel upstream for any reason.
 Dis-entrain liquid droplets.
 Maintains a positive pressure on the upstream system.
13

14. Molecular Seal
 Installed just below the flare tip flange.
 Force the gas travelling up the stack to make a 180° turn down then it must turn
again to go up to the flare tip.
 Light gases collected at the top of the seal creating a barrier to any oxygen.
 Considerably larger and more expensive than velocity seals.
 Also collects liquids which can freeze in cold environments.
Velocity Seal
 A cone or chevron, located inside the flare tip just above the flare tip flange.
 Breaks the flow of air into the system by disrupting the flow passage of the air to
the wall and creates a velocity differential barrier in the purge gas.
 Doesn’t collect liquids or require draining, making it suitable for cold weather
environments.
 They are less expensive than a molecular seal.
 Reduces the operating purge gas requirements.
Gas Seals
PROCESS DESCRIPTION
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15. PROCESS DESCRIPTION
BurnerTip
 Give environmentally acceptable combustion of the vent gas.
 Keep an optimum burn and control over all flow rates.
 The tip does not come into contact with the flame making the tips
reliable and long lasting.
 The maximum and minimum capacity of a flare to burn a flared gas
with a stable flame is a function of tip design.
 With modern flame holder designs, a stable flame can be achieved
over gas exit velocity.
15

16. PROCESS DESCRIPTION
16
Pilot Burners
 Flame and pilot gas supply should be stable and continuous
(also required by EPA regulations).
 Positioned around the outer perimeter of the flare tip .
 The number and duty of the pilot burners should be
determined by the size of the flare and its application.
 Maintenance or replacement is not possible while the flare is in
operation.
 Features three main components (mixer, orifice and burner
nozzle).
 Reliable operation of the pilot burner is governed by achieving
the right air fuel ratio.
 Withstand extreme weather conditions (along with direct
flame from the flare tip).
 Ignited by an ignition source system.

17.  High velocity steam injection nozzles.
 Positioned 1-15 around the outer perimeter of the flare tip.
 Increase gas turbulence in the flame boundary zones, drawing in more combustion
air and improving combustion efficiency.
 Reducing the temperature in the core of the flame and suppress thermal cracking.
 To optimize steam usage infrared sensors are available that sense flare flame
characteristics and adjust the steam flow rate automatically to maintain smokeless
operation.
 Automatic control, based on flare gas flow and flame radiation, gives a faster
response to the need for steam and a better adjustment of the quantity required.
 Disadvantages of steam usage are the increased noise and cost.
Steam Jets
PROCESS DESCRIPTION
17

18. PROCESS DESCRIPTION
Controls
Flame Front Generator Electronic Spark Ignition Ballistic Pellet Ignition
 Originally developed for offshore
use.
 Instead of a fireball, it comprises a
launching cabinet containing the
ignition pellets.
 The fuse is released and the pellet
explodes producing a shower of
sparks over the flare tip thereby
lighting the gas.
 Found in production facilities but
not very often in process plants.
 Mixes plant or air with pilot
ignition gas at grade and fills a
line running up to the pilot
burner.
 At grade an electrically generated
spark ignites the mixture and the
resulting fireball travels up to the
pilot and ignites the gas.
 Disadvantage is that moisture or
solids can block the fireball from
making it up to the pilot.
 Gas/air mixture could get too lean
or too rich and the spark doesn’t
ignite.
 Advantage is that all items need
maintenance are at grade and
can be serviced while the flare is
in operation. 18
 Becoming the preferred system.
 Two basic forms of these
systems; high energy (HE) and
high tension (HT).
 The most common and primary
method of pilot ignition for newer
systems.
 HEI systems use an electric probe
inserted near the pilot burner to
create a spark and ignite the pilot
fuel gas/air mixture.
 A capacitor is used to discharge
the spark across a low tension
spark plug in a short time and
with a high current.
 Full automatic systems.

19. REFERENCES
 A L Ling, July 2007. FLARE SELECTION AND SIZING (ENGINEERING DESIGN GUIDELINE), Johor Bahru:
KLMTechnology Group.
 Leslie B. Evans, William M. Vatavuk, Diana K. Stone, Susan K. Lynch, Richard F. Pandullo, September
2000. VOC Destruction Controls, North Carolina, Durham: Office of Air Quality Planning and Standards,
U.S Environmental ProtectionAgency.
 Ludwig, Ernest E., 1999. APPLIED PROCESS DESIGN FORCHEMICAL AND PETROCHEMICAL PLANTS,
Volume 1,Third Edition, United States of America: Gulf Publishing Company.
 Charles E. Baukal, JR., 2014. The John Zink Hamworthy Combustion Handbook, Second Edition:Volume
3 – Applications, Boca Raton, Fort Lauderdale, USA:Taylor & Fransic Group LLC.
 Nicholas P. Cheremisinoff, Apr 1, 2013. INDUSTRIALGAS FLARING PRACTICES, New Jersey USA: John
Wiley & Sons Cooperation.
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20. THANKYOU
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