Flares Overview

By Yolanda Fernández

MECANICA__________
Transferencia de Calor
CONTENTS

 Objective of Flaring

 What is a flare?

 Types of Flares systems

 Design Considerations

 Equipment for Elevated Flares

 Enclosed Flares

 Multi-point Ground Flares

 References

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Objective of Flaring

 Safe and effective disposal of waste gases at an

affordable cost.
 Eliminate excess process gas by burning it in an open
flame.
 Protect operating facility, plant employees and
surrounding community.

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What is a Gas Flare?

 Pressure device used to proper, safety and efficient

disposal of relief gases in an environmentally manner
through the use of combustion.
 Flare is considered as:
– Last line of defense for most plants.
– Plant safety system.
 Flare is required to:
– Be reliable.
– Operate over a wide range of conditions.
– Work continuously for large periods without shut
down.

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 Type of Flare systems

Elevated flares
Enclosed flares

Multipoint ground flares

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 Type of Flare systems

Elevated flares Enclosed Flares Ground flares

Flame Open & visible No visible No visible
Radiation High Low Low
Noise High Low Low
Steam High Low Low
consumption
Smokeless As per condition design Yes Yes

Plot Area Medium Medium High

Applications Refineries Refineries Refineries
Chemical / Food Chemical plants Chemical plants
processing
Truck loading terminals
LNG
Marine loading facilities
Bio-gas disposal
Bio-gas disposal
…

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Type of Flare systems

Pit flares
Offshore flares

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 Design Considerations

 Major factors influencing flare system design are:

– Flow rate.
– Gas composition.
– Gas temperature.
– Gas pressure available.
– Utility costs and availability.
– Safety requirements.
– Environmental requirements (noise and emissions).
– Geographical conditions (Seismic and wind conditions,
ground type).
– Social requirements.

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Design Considerations

 Major design parameters to calculate a flare are:

– Reliable/Stable ignition
• Exit velocity.
• Gas composition.
• Tip design.
– Hydraulic capacity
• Allowable pressure drop for all conditions.
• Increasing allowable pressure drop allows:
• Smaller flare system size.
• Reduction /elimination of utilities.
• Increasing operating life.

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 Design Considerations

 Major design parameters:

– Air infiltration
• Define purge utilities requirements.
• Air infiltration due to:
• Stack exit.
• Wind action.
• Gas contraction.
• Piping leaks.
• Composition of waste gas.
– Noise requirements
• Local regulations, client spec.
• Noise owes to:
• Gas exits.
• Smoke suppression system.
• Combustion.
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 Design Considerations

 Major design parameters:

– Smoke requirements
• Local regulations, client spec.
• Measured by Ringleman
scale (0 to 5)
• 0  20% opaque.
• 5  100% opaque.

• Smoke suppression methods:

• Energy transformation.
• Steam injection.
• Air addition.

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Design Considerations

 Major design parameters:

– Flame radiation intensity
• Calculation methods
• Calculations are guidance for:
• Flare location.
• Stack height.
• Type of flare.
• Radiation limits

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 Design Considerations

Flame Radiation Intensity (Calculation Methods)

T.A. Brzustowski and E.C. Sommers (B&S Method)

API ST 521 Simple Method
Kent Method
Shell Thornton
Vendors Proprietary methods

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Design Considerations

 Elevated Flare Sizing

– Flare diameter sized on:
• Velocity exit gas.
• Pressure drops.
– Flare stack sized on:
• Radiant heat intensity at grade.
• Wind velocity.
• Required data:
• Gas flow rate.
• Gas composition.
• Gas Temperature.
• Low heating value (LHV) of the gas.
• Wind velocity pattern.
• Stack diameter.

 Aspen FLARENET 2006.5 & FLARESIM 2.12

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Design Considerations (Summary)

 Process Data Sheet shall establish:

– Required flow rates.
– Waste gas compositions.
– Molecular weights.
– Lower heating values.
– Temperatures of the gases.
– Allowable pressure drop.
– Maximum allowable heat radiation at ground level.
– Local solar radiation (if apply).
– Prevailing wind direction and velocity.
– Noise level limitations.
– Utility design conditions.
– Smokeless capacity.
– Ambient Conditions.
– Area classification.

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Equipment for Elevated Flares

 Flare systems are compounds per:

– Main elements.
– Optional elements.
– Auxiliary equipment.
 Main required elements:
– Flare burner with or without
steam suppression.
– Flare pilots.
– Pilots igniter.
– Pilots flame detection.
– Support structure.
– Associated Piping.

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Equipment for Elevated Flares (Main)

Flare Burner
 General main requirements
– Wide operation range.
– Reliable operation under all weather conditions.
– Low pressure drop.
– Low noise level.
– Minimum utilities requirement.
– Long service life.

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Equipment for Elevated Flares (Main)

Flare burner
 Unassisted pipe flare
– Non smokeless burning.
– Ignition of the flare flame by pilots.
– Flame retention device.

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Equipment for Elevated Flares (Main)

Flare Burner con’t

 Steam assisted pipe flare
– Low radiation levels.
– Low smoke emissions.
– High noise level.
– Steam injected by a top ring or a center injector.

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Equipment for Elevated Flares (Main)

Flare Burner con’t

 Air assisted pipe flare
– Adjustable smokeless burning rates.
– Hazard of over-aerate flame.
– Limited application.

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Equipment for Elevated Flares (Main)
Flare Burner con’t
 High pressure flares tip
– Short flame length.
– Low smokeless rate.
– Low radiation levels.
– High gas exits velocity.
– High noise.

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 Equipment for Elevated Flares (Main)

Flare Pilots
 Pilots shall ensure
– Continuous and reliable operation.
– Flare ignition and stable flame under all operation
conditions.
– Fast re-ignition.
– Long service life.
 Pilot energy level depends on:
– Waste gas composition.
– Waste gas exit velocity.
– Flare burner design.
– Atmospheric conditions.
 Minimum heat release 13.2 kW required for stable
operation.

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 Equipment for Elevated Flares (Main)

Flare Pilots con’t Igniter Pilot tip

 Type of pilots to be used:

– Self inspirating pilot.
– Air compressed pilot.

Mixer

Strainer

Pilotsnumber depends on flare

burner diameter.

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Equipment for Elevated Flares (Main)

Pilots ignition system

 Flame front Generator (FFG)
– Safe and reliable ignition if properly maintained.
– Manual/ Automatic operation.
– Controls and sparking device located at grade.
– Special maintenance.

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Equipment for Elevated Flares (Main)

Pilots ignition system con’t

 Spark ignition (High energy igniter)
– Safe and reliable ignition.
– Automatic re-ignition.
– Manual / Automatic operation.
– Control by a PLC or a push button.

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Equipment for Elevated Flares (Main)
Pilot flame detection
 Checking and monitoring flame presence at each pilot
as per emitted energy during combustion.
 Thermocouples
– Type K thermocouples.
– Pilot mounted .
– Slow response time.
 Optical systems
– UV and IR systems.
– Located at grade (maximum range 150-300 m).
– Fast response time.
– False flame failures.

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Equipment for Elevated Flares (Main)

Pilot flame detection con’t

 Flame Ionization
– Two electrodes mounted on the pilot.
– Short response time.
– Detectors exposed directly to the flame.
 Acoustic systems
– A sensor unit and a signal-processing unit.
– Located at grade (max.150 m from pilot).
– Fast response time.

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Equipment for Elevated Flares (Main)

Pilot flame detection con’t

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Equipment for Elevated Flares (Main)

Support Structure
 Self Supported
– Most expensive solution.
– Large land area for foundations.
– Stack height of 60 m to 90 m.

 Guy-wire-supported:
– Least expensive solution.
– Largest land area requirements.
– Stack height of 180 m to 250 m.

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Equipment for Elevated Flares (Main)

Support Structure con’t:

 Derrick supported:
– Larger stacks.
– Maintenance allowed from grade.
– Multiple stacks on the same derrick.

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Equipment for Elevated Flares

 Optional elements:
– Purge seal.
– Knock-out drum.
– Liquid seal.
– Aircraft warning lights and painting.
 Auxiliary equipment:
– Smoke suppression control system.
– Ladders and platforms.
– Flame detonation arrestor.
– Blowers.

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Equipment for Elevated Flares (Optional)

Purge Seal
 A permanent purge gas is used to avoid flashback.

 Purge gas rate is calculated as:

D =Flare stack diameter [m]

y = Column depth at which the oxygen concentration (O2) is
predicted [m]
O2 i= oxygen volume fraction [%]
Ci = volume fraction purge gas [%]
Ki = Constant for purge gas.

 Considering O2 = 6 % and y =7,62 m.

 For hydrogen, higher purge gas rates to be considered.

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 Equipment for Elevated Flares (Optional)

Purge Seal con’t:

 Purge seals reduce purge gas rate.
Velocity seals:
– Purge gas velocity reduced to 0,006 - 0,012 m/s
– Oxygen concentrations 4 - 8 % .
– Not special maintenance.

Buoyancy seals:
– Purge gas velocity reduced to 0,003 m/s
– Oxygen concentrations less than 0. 1 %.
– Drain required for liquid collection.
– Special maintenance.
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 Equipment for Elevated Flares (Optional)

Knock out drum

 Avoid large amount of liquid entry to flare stack.
 Separate liquid (entrained or condensate) from gas to be
flared.
 Droplets cause not desired phenomena:
Smoking increase  600 - 1000 μm
Flaming particles rainout  1000 μm and over

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Equipment for Elevated Flares (Optional)
Knock out drum con’t
 KO Drums design based on size particles to separate.

New works  400 μm

Revamp works  600 μm

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 Equipment for Elevated Flares (Optional)

Hydraulic Seal
 Main purposes of hydraulic seal
– Avoid flashback propagation.
– Prevent air ingress.
– Staged operation.
 Type of fluid to be used shall be carefully studied.
 Emplacement shall consider:
– Cost.
– Regularly maintenance.
– Client operating practices.

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 Equipment for Elevated Flares (Optional)
Aircraft warning lights and painting:
 Painting according to International Civil Aviation Organization
(ICAO) Aerodromes Annex 14.
 Aircraft warning lights:
– To be used if:
• Flare heights exceed 61 m (API 521).
• Locations closed to airports.
• Client specifications.
– Number, type and location as per (ICAO) Aerodromes Annex
14.
– Fixed or retractable devices can be used.

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Equipment for Elevated Flares (Auxiliary eq.)

 Smoke suppression control system

– Manual control.
– Television monitoring with manual control.
– Control system for pressure, mass flow or velocity.
– Control system by infrared sensor.

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 Equipment for Elevated Flares (Auxiliary eq.)

Smoke flare

Smokeless flare

Oversteamed flare

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Equipment for Elevated Flares (Summary)
Pilots burner
Flare Burner

Purge Seal

Flare Stack

Ignition device

KO Drum Liquid Seal

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 Enclosed Flares

 Enclosed flares are used to:

– Maintain flame hidden from direct
view.
– Reduce noise and minimize radiation.
– Monitoring emissions.
 Main characteristics:
– Wide turndown.
– Low level radiant heat.
– Multiple burners arranged to operate
in stages.
– Limited capacity.
– Elevated cost investment.

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Enclosed Flares

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Multipoint Ground Flares

 Main characteristics:
– High smokeless rates.
– High Pressure.
– Lower radiation levels.
– Capacity limited to available plot area.
– Multiple burners arranged in arrays.
– Staging operation.

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Multipoint ground flares

 Staging P&ID for a multipoint ground flare.

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Summary

 Why is flaring important.

 Required parameters to design a flare.
 Different types of flares.
 Elements of an elevated flare.
 Introduction to enclosed flares
 Introduction to multipoint ground flares.

44
References

- “Pressure-relieving and Depressuring Systems” ANSI/API

STANDARD 521 - Fifth Edition; Incorporates Errata: 6/2007 and
Addendum: 5/2008.
- “Flare Details for General Refinery and Petrochemical Service”
ANSI/API STANDARD 537 2nd Edition, December 2008.
- “Process Design Manual Relief & Flare System” Fluor Manual
000.225.9048
- Zeeco Company.(Flare System Emissions Control conference).
- Callidus Technologies Company (Course September 2008).
- John Zink Company.
- “The John Zink Combustion Handbook” Charles E. Baukal J.R.
CRC Press.

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Questions and discussion

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