Assisted Flaring• Flare emissions are controlled by injection of air or steam into the flame.

• Air/steam is intended to suppress soot formation and reduce luminosity.

Motivation• Overuse of air/steam in flaring has led to major regulatory violations.

• Too much air/steam smothers the flame allowing waste gas to escape.

• Recent studies show that assist requirements may be overstated.

• Over-aeration/steaming compromises combustion efficiency (<96.5%).

Principles of Operation• Wide variety of flare designs exist. Purpose is to improve combustion.

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Steam-to-Flare Gas Mass Ratio

FG = 937 lb/hr FG = 2,342 lb/hr 96.5% CE

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Air-to-Flare Gas Mass Ratio

FG = 902 lb/hr FG = 353 lb/hr 96.5% CE

Flare Design• A coflow burner was designed with an inner tube for air or steam assist.

• Thermocouples at burner tip measure exit flow temperatures allowing for

estimates to be made of fuel and air/steam exit velocities.

Test Facility• Facility was designed to handle fuel flow rates equivalent to ~50 kW.

• Fuel options include methane, propane, and natural gas.

• 300 SLPM of air and 408 g/min of steam is available for assisting flame.

Conclusion• Assisted flaring is necessary for emissions control but has limitations.

• A test facility was established to evaluate emissions from lab-scale flares.

• Emissions data is used to estimate carbon conversion efficiency and

emission indices for CO2, unburned hydrocarbons, soot, and NOx.

1. The John Zink Hamworthy Combustion Handbook, Chapter 11 – Flares

2. https://www.epa.gov/sites/production/files/documents/flaringviolations.pdf

3. https://www.google.com/patentsUS7967600/

4. Allen, D. T., & Torres, V. M. (2011, August 1). TCEQ 2010 Flare Study Final Report

Abbas Ahsan, Hamza Ahsan, Jason S. Olfert, Larry W. Kostiuk

Reacting Flow Laboratory, University of Alberta, Edmonton, AB, Canada

Establishing a Test Facility for Measuring the Carbon

Conversion Efficiency and Emissions Indices for

Lab-Scale Air and Steam Assisted Flares

No steam

John Zink flare with varying steam injection flow rates [1]

Upper Ring

Nozzles

Center

Nozzle

Lower

Nozzle

(steam)

Flare Gas

Promote

turbulence and

entrain air

Increase flare

gas momentum

Common design features of an assisted flare [3]

Combustion efficiency trends for air- and steam-assisted flares [4]

Properly operated flare (left) and over-steamed flare (right) [2]

Venting methane!

Lab-scale flare with varying quantities of steam-assist

John Zink steam- (right) and air-assisted (left) flare [4]

109 cm OD 91 cm OD

Minimum

operating

set point

Starting steam Full steam

No steam Starting steam Full steam