Hydrogen flares: the DuPont-EER-EPA test program, amendment of the EPA requirements, and related developments

HYDROGEN FLARES: The DuPont-EER-EPA Test Program, Amendment of the EPA Requirements, and Related Developments Peter M. Walsh*, David K. Moyeda, W. Steven Lanier§, C. Michael Booth, E. E. (Gary) Folk, and John Maxwell GE - Energy and Environmental Research Corporation Morrisville, NC and Irvine, CA Wilfred K. Whitcraft§ E. I. du Pont de Nemours and Company Wilmington, DE Roger K. K Noble†, Jeff M. M Clopton‡, Tracy Rogers¶, and Chris Nicely‡ Callidus Technologies Inc. Tulsa, OK Robert E. Rosensteel§ and C. Andrew Miller U.S. Environmental Protection Agency Research Triangle Park, NC ------International Flame Research Foundation Topic Oriented Technical Meeting 36: Industrial Flares Maui, Hawaii, September 30 - October 1, 2010 ________________________ § Retired Present addresses: *University of Alabama at Birmingham, Birmingham, AL 35294 †Continuum Engineering, LLC, Tulsa, OK 74136 ‡John Zink Company, LLC, Tulsa, OK 74116 ¶ 222 South First, Morris, OK 74445 Motivation for the Work Non-Assisted Flares (~1995) ( ) Flares of waste gases containing ~15 vol% hydrogen, having heating values of only 50 -100 Btu/scf, were known to be stable and expected to have high destruction efficiencies at velocities of ~100 ft/s. Supplemental fuel required to meet regulation. 1000 Lower Heatin L ng Value (Btu u/scf) Regulation g for non-assisted flares required combinations of heating value and velocity in the region at the upper left. 40 CFR 60.18 Non-Assisted Flares 800 Permitted 600 400 Not Permitted 200 0 10 20 50 100 Velocity (ft/s) 200 500 The DuPont-EER-EPA Test Program N A i t d Fl Non-Assisted Flares Analysis A l i b by D David id M Moyeda d and d Mik Mike B Booth th off EER (1993) (1993), b based d upon published bli h d work, k showed that waste gas flares containing hydrogen were stable and expected to give high destruction efficiency at heating values well below the existing requirement. A test t t program was planned, l d having h i th the ffollowing ll i objectives: bj ti Determine flame stability limits as functions of hydrogen content of otherwise inert waste gas. Establish criteria for high destruction and removal efficiency. Establish strong enough case for a request to U.S. EPA for review of the regulation. g U.S. EPA provided valuable input, through comments on the experimental approach, review of the Quality Assurance Project Plan, and a visit to the test site while the work was in progress. p g EER/EPA Flare Test Facility J. H. Pohl, R. Payne, and J. Lee, "Evaluation of the Efficiency of Industrial Flares: Test Results," U.S. EPA 600/2-84-095, NTIS PB84-199371, May 1984. Criterion for High Combustion Efficiency Flares burning propane/nitrogen mixtures with no pilot flame J. H. Pohl, R. Payne, and J. Lee, "Evaluation of the Efficiency of Industrial Flares: Test Results," U.S. EPA 600/2-84-095, NTIS PB84-199371, May 1984. Flare Characteristics Tip i.d. 2.9 in. (74 mm), Re = 105 Stable flames were firmly anchored at the pipe tip. Lift off: permanent separation of any part of the flame from the tip. (No stable flames completely separated from the tip were observed.) Blow out in absence of pilot: fl flame extinguished. ti i h d Stabilizing tabs had no significant effect on the H2 contents at lift off and blow out. Measurements Callidus Technologies Test Facility Stability limits: Establish a stable flame with H2-N N2 mixture near the tip velocity of interest, then reduce the H2 content to observe lift off and blow out. With and d without ith t pilot. il t Destruction efficiency: Add a known concentration of hydrocarbon to the flare gas and measure its concentration in the combustion products products. The blue color of the flame is due to emission from electronically excited CO2: CO + O + M → CO2* + M Stability in the Absence of Pilot Even without pilot, flares are completely stable (no lift off) down to: 7.6 vol% H2 at 20 ft/s 15 4 vol% 15.4 l% H2 att 120 ft/ ft/s Blow out occurs at H2 contents approximately 0.8 vol% lower. Interaction between Pilot and Flare Lift off: (same as before) permanent separation of any part off the th flame fl from f the th tip. ti Blow out: no propagation of flame a e from o the ep pilot o into oo or around the jet. Lifted ↑ ← Completely stable Effect of Pilot Flame on Stability Three pilot burners were tested: 1. Burner from propane hand torch. Heat output 120 - 240 W; 0.05 - 0.1% of flare heat input. 2. Natural gas-fired venturi burner. Heat output 700 - 2700 W; 0.3 to 1.0% of flare heat input. 3. Industrial pilot with reduced natural gas orifice. Heat output 3000 - 12000 W W; 1 - 10% off flare heat input. Heat input to DuPont pilots is 0 0.05 05 to 0.6% of the flare heat input. Stability in the Presence of Pilot H2 content at lift off is the same as without pilot. Blow outt occurs att H2 content Bl t t approximately 2 vol% lower than that at lift off. H2 content at blow out extrapolated to zero velocity (4.3 vol%) in good agreement with lean flammability limit for H2-N2-O2 mixtures (4.8 vol%). No Effect of Pilot on Lift Off Conditions at lift off in the presence and absence of the pilot are indistinguishable. Equation for the line: XH2 (%) = 0.078 u (ft/s) + 6.0 Pilot for Destruction Efficiency Tests Venturi burner chosen as the pilot for the destruction efficiency tests tests. 2680 Btu/hour; 0.27 to 0.48% of flare heat input. Destruction efficiency also measured without pilot. Difficulty of Destruction Use Union Carbide correlation (Lee et al., 1979) to compare difficulty of destruction of typical compounds to be destroyed and candidates for the h measurements. Correlation gives the temperature required to achieve 99% destruction in a specified residence time. Parameters: P t Numbers N b off C, C N N, O atoms, C=C groups, vinyl chloride groups, whether aromatic or not, H/C ratio, and autoignition g temperature. Benzene* Acetonitrile* Ethylene H d Hydrogen cyanide* id * Acrylonitrile* Propylene Propane p 1,3-butadiene* iso-butane n-butane Formaldehyde* Formaldehyde Carbon monoxide* Acetylene 1384 oF 1383 1383 1366 1353 1340 1319 1314 1302 1247 1246 1244 1116 Determination of Destruction Efficiency Hood used to capture combustion products products. 0.19 - 1.66 vol% ethylene for destruction measurements. t 10 vol% CO2 added as tracer to determine dilution by excess air. Pilot heat input 0 - 0.5% of flare flare. Tip velocity 96 - 120 ft/s. 13 - 19 vol% H2. Measurements Ambient Conditions Relative humidity T Temperature t Barometric pressure Wind speed Carbon dioxide in air Flare and Pilot Nitrogen flow Hydrogen y g flow Carbon dioxide in flare gas Ethylene in flare gas Pilot flame natural gas flow Flare gas temperature Products Carbon dioxide in stack Ethylene in stack Stack temperature Stack flow Measurement of Stack Flow Rate Traverse stack using Pitot/static probe. p Velocity distribution is wellbehaved and symmetric. Integrate profiles to determine flow rate. Construct a calibration curve from measurements over the range of flow rates. Monitor Pitot/static ΔP on stack centerline during all runs. Destruction Efficiencies Measurements repeated 4 to 7 times. Error bars indicate minimum d t ti efficiency destruction ffi i att 95% confidence level. Destruction efficiencies are above 98% at a level of 95% confidence in all cases. Destruction efficiency increases with increasing ethylene content. Correlation of Destruction Efficiencies Behavior of hydrogen flares dominated by hydrogen content rather than heating value. Adapt stability ratio of Pohl and coworkers k to hydrogen h d flflares using H2 content. Choose reference condition as H2 content at lift off, because it is well-defined and independent of pilot. Destruction efficiencies are well above 98% at stability ratios of 1 and higher. g Recommendations and Outcome Non-Assisted Flares Hydrogen contents and velocities at lift off of the flame from the 2.9-inch diameter flare were recommended as criteria guaranteeing greater than 98% destruction efficiency in hydrogen flares 3 inches in diameter and larger. Recommended that any flare having a combination of hydrogen content and tip velocity making it more stable than at lift off of 2.9-inch diameter flare be considered a hydrogen flare, flare irrespective of the concentrations of other waste gases. gases The General Provisions for New Source Performance Standards (40 CFR 60.18) and General Provisions for National Emission Standards for Hazardous Air Pollutants for Source Categories (40 CFR 63.11) were amended to include a separate specification for hydrogen-fueled flares, effective June 23, 1998 (Federal Register, May 4, 1998). Code of Federal Regulations, 40 CFR 60.18 ( ) An owner/operator (3) p has the choice of adhering g to either the heat content specifications in paragraph (c)(3)(ii) of this section and the maximum tip velocity specifications in paragraph (c)(4) of this section, or adhering to the requirements in paragraph (c)(3)(i) of this section. (i)(A) Flares shall be used that have a diameter of 3 inches or greater, greater are nonassisted, have a hydrogen content of 8.0 vol%, or greater, and are designed for and operated with an exit velocity less than 37.2 m/s (122 ft/s) and less than the velocity, Vmax, as determined by the following equation: Vmax = (XH2 - K1) · K2 Where: Vmax = K1 = K2 = XH2 = Maximum permitted velocity, m/s. Constant, 6.0 vol% H2. Constant, (3.9 m/s)/(vol% H2). Volume-percent of hydrogen, on a wet basis, as calculated by using the American Society for Testing and Materials (ASTM) Method D1946 D1946-77. 77. Tip Velocity at Lift Off, with or without Pilot Conditions at lift off in the presence and absence of the pilot are indistinguishable. Equation for the line: XH2 (%) = 0.078 u (ft/s) + 6.0 u (ft/s) = [XH2(%) - 6.0] / 0.078 Praxair Demonstration of Hydrogen Use in Steam- and Air-Assisted Steam Air Assisted Flares Alexis McKittrick, 16th IFRF Members' Conference, Boston, 8-10 June 2009. Minimum net heating value for steam- and air-assisted flares (300 Btu/scf) is even higher than that for nonassisted flares (200 Btu/scf). Praxair conducted a test program to validate the use of hydrogen in steam- and air-assisted flares. 1000 Lo ower Heating g Value (Btu/scf) Approximately 80% of flare operators in the U.S. use steam- or air-assisted flares. 40 CFR 60.18 AirAssisted 800 Permitted SteamAssisted 600 400 Not Permitted 200 Non-Assisted 0 10 20 50 100 Velocity (ft/s) 200 500 Praxair Steam- and Air-Assisted Flare Tip i.d. 3 in. Air assist through the annulus surrounding the flare gas tip tip. Steam assist through 5 nozzles at 30o from vertical. No mixing tabs or other stabilizing devices. Natural gas pilot, 28,000 Btu/hr, 0.4 to 19% of total flare heat output. Side and top views of the assisted flare. Alexis McKittrick, 16th IFRF Members' Members Conference, Boston, 8-10 June 2009. Praxair Flare Test Facility Waste g gas: hydrogen, y g , nitrogen, ethylene, and carbon dioxide Steam: 0.4 0 4 lb per lb ethylene Air: 20% of waste gas stoichiometric air Tip velocity: 20 - 150 ft/s Hydrogen: 5 - 25 vol% Waste gas heating value (ethylene only): 30, 100, 200, 300 Btu/scf Alexis McKittrick, 16th IFRF Members' Conference, Boston, 8-10 June 2009. Flame Stability Assisted Flares Hydrogen content of waste gas at lift-off as function of tip velocity, H2-N2 mixtures. Air-assisted XH2 (%) = 0.0489 0 0489 u (ft/s) + 10.3 10 3 Steam-assisted XH2 (%) = 0.0575 0 0575 u (ft/s) + 9.83 9 83 Alexis McKittrick, 16th IFRF Members' Conference, Boston, 8-10 June 2009. Destruction Efficiency Assisted and Non-Assisted Flares N2, CO2, C2H4, H2 Mixtures ________________________________________________________________________________ Waste Gas No. Destruction Efficiency (%) Tip Flame Heating Value Assist of Velocity Stability (Btu/scf) Runs Average 95% Confidence (ft/s) Ratio ________________________________________________________________________________ 30 Steam 3 99.77 99.61 151 1.03 100 Steam 4 99.94 99.92 150 1.04 200 Steam 3 99.99 99.98 151 1.03 300 Steam 3 99 44 99.44 98 88 98.88 60 no H2 30 Air 4 99.26 99.02 150 1.02 100 Air 4 99.90 99.88 150 1.02 200 Air 3 99 92 99.92 99 90 99.90 150 1 02 1.02 300 Air 4 99.39 99.21 60 no H2 ________________________________________________________________________________ Values greater than 1 (1.02 to 1.04), for the ratio of flare gas hydrogen content to the hydrogen content at lift off, were sufficient to achieve greater than 99% destruction efficiency, with 95% confidence, at tip velocities of 150 ft/s. Alexis McKittrick, 16th IFRF Members' Conference, Boston, 8-10 June 2009. Hydrogen Requirement for High Destruction Efficiency Comparison of Non-assisted, Air-assisted, and Steam-assisted Flares ________________________________________________ Tip Velocity Hydrogen Requirement (vol%) (ft/s) No Assist Air Assist Steam Assist ________________________________________________ 25 8.0 11.5 11.3 50 10.2 12.7 12.7 75 12.4 14.0 14.1 100 14.5 15.2 15.6 125 16.4 17.0 150 17.6 18.5 ________________________________________________ The results of this testing justify the extension of current regulations to include the use of hydrogen as a compliance mechanism for steam- and air-assisted flares, in addition to the alternate requirements q already y in p place for non-assisted flares. Alexis McKittrick, 16th IFRF Members' Conference, Boston, 8-10 June 2009. Acknowledgments The work on non-assisted flares was supported by E. I. du Pont de Nemours and Company Thanks to: Alexis McKittrick Praxair John Pohl Energy International Van Brawley, Ellen Lane, Mary Nuxoll, Robert Perry, and Walter Schrimper DuPont Terry Harrison and Gene Riley U.S. EPA Brian Duck, Mike Keller, Roger Poe, Rick James, Chad Ogden, Jim Stockton, and Scott Guthrie Callidus Technologies Frank Stevens, Bob Elliott, Peter Maly, Roy Payne, Jerry Johnson, and Jerry Cole GE Energy