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Flare System: Types, Segregation, Tips, Purge System and More 2 Comments
1. Types of Flare 2. Segregation of Flares 3. Flare Knock-Out Drum 4. Flare KOD Liquid Removal 5. Flare KOD sizing depends on two aspects 6. Liquid Seal Drum 7. Purge reduction seals 8. Flare Purge system 9. Flare stack 10. Flare Structure 11. Flare Tip
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12. Ringlemann Chart 13. Pilot burner 14. Pilot Ignition 15. Other Accessories
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is defined as a process of controlled burning of exhaust gases which generates heat and noise. Flaring is a common practice in oil/gas exploration, production and processing operations. A flare system consists of a flare stack and pipes that feed gas to the stack. The type and amount of gas or liquids in the flare stack governs the sizing & brightness of the flare. There are many function & reason for flaring, During well production testing after drilling is completed For safety and during emergencies and maintenance For managing gas during compression and processing
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4. Flar Flaring ing at well well sites to recover recover oil oil
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1. Ele Elevat vated ed Flare Flare 2. Ground Ground Flar Flare e 1. Enc Enclos losed ed Flare Flare 2. Ope Open n Flar Flare e
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Google+ Elevated Flare
Enclosed Flare
Open Flare
Typical Flare System with Elevated Flare
1. Serv Servic ice e 1. Aci Acid d gas fla flare re 2. Col Cold d dry dry flare flare 3. Wa Warm rm wet wet flare flare 2. Press Pressure ure 1. Atm Atmosp ospher heric ic 2. Low pre pressu ssure re 3. Hi High gh pressu pressure re
1. 1. Separ Separate ate bulk bulk liquid liquid from gas 2. Limit liquid liquid droplet size size entrained with with gas to the flare flare 3. Provide adequate adequate residence residence time time for liquid 2. 1. Bas Based ed on API API 521 521 2. Separation of liquid droplet droplet size of 300-600 300-600 microns considering considering the design case for the flare 3. 20-30 minutes of liquid liquid hold-up time based based on a relief case that results results in maximum liquid 4. No internals internals to facilitate separation 5. Many orientations orientations / options possible, possible, horizontal horizontal KODs most most preferred
Flare KO Drum elevation
3. 1. KO drum elevati elevation on decides decides pipe rack elevation rack elevation based on 1:500 slope of main flare header
Flare KO Drum elevation 2. KO drum elevation elevation determined determined by pump NPSH requirement 3. To reduce pipe rack elevation options are 4. Reduce Reduce KOD elevation elevation (option (option 1) 1. Use verti vertical cal can can pump pump 2. Locat Locate e pump pump within within pit 3. Locat Locate e KO drum drum within within pit 5. Use intermediate intermediate KO KO drums (option 2) 2)
>Flare KO Drum elevation arrangement (Option 1)
Flare KO Drum elevation arrangement (Option 2)
Remove liquid from flare KOD after relief to avoid overfill during future relief event 1. 1. Draining to evaporation pond or closed closed drain drums 2. Liquid removal by by flare KOD pumps pumps 3. Heater to be installed installed in KOD where freezing, pour pour point issues exist exist 4. Rate of liquid removal to to consider frequency and amount amount of liquid release 5. High level in flare KOD to be be considered for plant plant shutdown 2.
Flare KO Drum
1. LLLL shall be sufficiently sufficiently high to avoid any sludge sludge deposition impacting impacting LT nozzle (150 mm in above figure not correct, consider 300 mm minimum for services which are not clean). 2. LLLL shall be minimum minimum 700-300 in in case flare drum electrical electrical heaters need to be installed. 3. LLLL Level Level at which pump pump trips. trips. 4. LLL Level at which both pumps pumps stops 5. HLL Level at which first first pump starts 6. HHLL Level Level at which which second pump pump starts 7. HHHLL Level Level at which entire entire plant goes into into pressurized pressurized trip.
Liquid Hold up requirement during a major liquid or two phase release. Sufficient distance shall be available between inlet device bottom and HHHLL. It is possible to have manually initiated depressurization even after HHHLLL. Any possible liquid shall be accommodated above HHHLL. Distance between HLL and HHHLL shall be designed to accommodate maximum liquid release scenario(?). Some standards this distance is between HHLL and HHHLL. Residence time required for drop of liquid particles of 300-600 micron size. Liquid particles separate When the residence time of the vapor or gas is equal to or greater then the time required to travel the available vertical height at the dropout velocity of the liquid particles and When the gas velocity is sufficiently low to permit the liquid dropout to fall. This vertical height is usually taken as the distance from the maximum liquid level.
1. 1. Prevent flashback flashback from flare flare tip back back to flare headers 2. Avoid air ingress into into flare system during during sudden temperature temperature changes leading to condensation and maintain positive system pressure 2. 1. Used in flare flare gas recovery recovery systems systems 2. Staged flaring between between enclosed flare flare and full size emergency flare flare 3. 1. Water as liquid sealing sealing fluid not recommended recommended for extremely cold releases; releases; waterglycol mixtures of sufficient concentration used instead
Liquid Seal Drum
1. 1. Prevent air infiltration infiltration into flare system at at low flow rates rates 2. Reduce amount of continuous continuous purge gas gas injection into into flare stack 2. 1. Buoyancy seal seal (molecular (molecular / density seal) 2. Veloc Velocity ity seal (fluid (fluidic ic seal)
Purge Reduction Seal
1. 1. Prevent air infiltration infiltration into flare system at at low flow rates rates 2. Prevent vacuum formation formation in flare headers and and system following steaming steaming or large relief event 2.
1. Continuous purge rate with with velocity in stack 1. 1-5 fps : without without molecula molecularr seal 2. 01 : with with molecula molecularr seal 3. 02-0 02-0.04: .04: with with velocity velocity seal seal 2. Approximate purge purge flow rate can be calculated using using section 7.3.3.3 of API 521.
Purge Reduction Seal
Flare P&ID
1.
1. Combustion of relief relief gases at elevation to minimize minimize radiation exposure exposure to personnel/ equipment/ structure 2. Ensure adequate adequate dispersion dispersion of un-burnt hydrocarbons hydrocarbons and toxic toxic components
Flare protection 2. 1. Radiation: Limit Limit radiation, either continuous continuous and peak, on off-site properties properties and persons, equipment, buildings and personnel on the installation installation.. Applicable to impacted area, restricted area and equipment lay-out. 2. Flammable gas: gas: Avoid ignition of a flammable flammable gas cloud released from a cold cold vent or in case of flare flame out. 3. Toxic hazards: (Mainly (Mainly for H2S and SO2, but not limited limited to) limit the risk of a toxic gas cloud to reach off-site population, provide means of alarm and adequate protection to personnel present in the restricted area. 4. Noise: Limit both continuous continuous and peak peak noise 5. Stack height is determined determined by HSE group based on permissible permissible radiation radiation level as per project philosophy or API 521. 6. Taller stack will will result in in smaller sterile sterile zone. 7. Locate process process plant upwind of flare.
Self supported flare stack Guy wired supported flare stack Derrick supported flare stack More than one flare may be supported on the same structure
Flare Stack Support
Produce desired destruction/combustion efficiency of maximum specified relief gas Establish and maintain proper ignition Pilot gas /Pilot burners/ Ignition system Ensure stable combustion Windshield Retention rings Result in smokeless operation at normal continuous flows or at100% flows Steam Air (high pressure or low pressure) High pressure water No external medium, maintain high pressure at tip by staging
Flare Tip
Flare Tip
Flare Tip: Velocity Seal (top view)
Based on velocity of gas exit from tip, flare tips are considered as sonic and subsonic (pipe flare) type. This is the term used by process designer for high pressure flares and low pressure flares. General stack pressure drops are as given below. Sonic flare – 2 to 4 bar Subsonic flare – 0.2-0.5 bar
Open Pipe flare tips: These are used for combustion of gases that do not produce smoke, gases with a low heating value, or for installations where smokeless combustion of heavy hydrocarbons is not required. These flare tips are one of the lower capital cost options for safe disposal of waste gases. In general these kind of flares have tips with very low pressure drop. Open pipe flare tips with steam injection: Steam injection is provided reduce the smoke formation. Open pipe flare tip with high pressure gas injection: This will increase the turbulence at flare tip and reduce the smoke formation. Fuel gas can be generally used as assist gas. Fuel gas injection can be either continuous or initiated manually based on monitoring of flare tip. Air assisted flare tip: When smokeless flaring is desired and neither steam nor assist gas is available, blowers can be used to inject combustion air directly into the waste gas stream as it exits the flare tip. Combustion efficiency of flared gas is increased by installing air blower which will reduce smoke formation. Multiple nozzle type flares: They are used where high flare gas pressures are available (1 barg and up) and where it is preferred to have some smokeless burning capability and also lower radiation levels. These kinds of flares are used for HP flare application. They have good combustion efficiency and less chances of smoke formation. Coanda flare tip: The Coanda effect is a gas-adhesion principle that dramatically dramatically enhances the combustion process, resulting in maximum destruction of waste gases. Coanda Effect occurs when gas is passed over and adheres to a carefully profiled, curved surface, creating a near vacuum that pulls in substantia substantiall amounts of air. The air turbulently mixes with the gas flow, resulting in high-efficiency combustion.
Open Pipe Flare
Multi Nozzle Flare
Coanda Flare
A series of charts, numbered 0 to 5, that simulate various smoke densities densities by presenting different percentages of black. Ringelmann No. 0 is clear smoke Ringelmann No. 5 is 100 percent black. Ringelmann No. 1 is equivalent to 20 percent black
Ringleman Chart
1. 1. Provide flame for reliable ignition ignition of main flare flare gas at all times 2. 1. Pilot system system to comply with with API 537
2. Pilots designed to remain remain lit and capable of being being relit at wind speeds up up to 160 km/h under dry conditions
Pilot gas line
1. 1. Electrode capable capable of high energy or high high voltage discharge discharge near pilot pilot tip 2. Does not require require propagation of a flame front as in FFG system 3. Does not require require compressed air, air, self aspirating aspirating pilots 4. Simple and easy to use and and automate, require little little training or maintenance. maintenance. Reignition takes few seconds 5. Shutdown of flare system required for for maintenance maintenance 6. Back up FFG ignition ignition (when using using HEI) may be considered for 1. Very tall flares that that are difficult difficult to access 2. Flare systems systems that can be off line only once in in more than 3-5 years 3. Offshore platforms in platforms in corrosive and salt environments
Electrical Ignition Panel 2. 1. Ignition line from panel panel to flare pilot filled with with flammable fuel gasgas- air mixture and spark introduced. Mixtures ignited and flame front travels through piping to ignite pilot at flare tip 2. FFG panel panel located located at at grade 3. Panel operated manually manually or automated to reignite reignite of pilot flame out detection. Re-ignition can take several minutes 4. Moisture accumulation accumulation can lead to corrosion, flame extinguishment extinguishment Ignition Ignition lines to be heat traced
FFG Panel
FFG System
Monitoring relief devices leaks during normal operation Assess flaring of gases due to pressure control operations Note relief flows for assessing flare system adequacy checks and potential for flare gas recovery Non-intrusive ultrasonic ultrasonic flow meters with wide range and no pressure drop is preferred
Proper steam or air control is required By measuring gas being flared and adjusting steam rate / blower capacity Detection smoke using infra-red analyzers
Required when flare heights exceed 61m or when site is close to airport Type and number based on regulations Industrial Boiler OPEN
Boiler Can Run on Coal Oil Gas Biomass Electric Use for Drying Sterilizing Heating Dyeing
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2 COMMENTS
Abhijit August 30, 2016 at 4:37 am
Process plan should be downwind to flare to avoid flammable gases getting to the flair.
YAK October 26, 2016 at 12:49 pm
Thank you, this is really useful data for me!
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