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. 0 20 40 60 80 100 0.0 0.5 1.0 1.5 2.0 2.5 Combustion Efficiency (%) Steam-to-Flare Gas Mass Ratio FG = 937 lb/hr FG = 2,342 lb/hr 96.5% CE 0 20 40 60 80 100 0 50 100 150 200 250 Combustion Efficiency (%) 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 CO 2 , unburned hydrocarbons, soot, and NO x . 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