Demonstration of Hydrogen Use in Steam-and Air-Assisted Flares

Demonstration of Hydrogen Use in Steamand Air-Assisted Flares Alexis McKittrick, Ph.D. Combustion R&D Praxair, Inc. June 9, 2009 www.praxair.com Hydrogen as a Fuel for Flaring • Current EPA flare compliance options • Praxair pursuing modification of 40 CFR 60.18 and 40 CFR 63.11 to extend the current specification to include steam- and air-assisted flares • Potential benefits: - Non-assisted Flares: • 200 Btu/scf minimum OR • 8 volume % hydrogen minimum - Assisted flares • 300 Btu/scf minimum • • Natural gas added to "sweeten" low-Btu streams and comply with regulations Much less hydrogen than natural gas is needed to comply with EPA requirements for low-Btu flare streams - Lower operating cost - 50% to 70% reduction - Lower environmental emissions - CO2, CO, NOx - Lower net natural gas consumption 2 Low-Btu Flaring for Assisted Flares Currently, many flare operators add natural gas to the waste stream to comply with 300 Btu/scf regulation + NATURAL GAS (420 scf) Using Praxair's proposed regulation, flare operators could add Hydrogen to 11.5 vol% to comply WASTE GAS 30 Btu/scf (1000 scf) + HYDROGEN (130 scf) 3 Benefits Example Assisted Flare - 100k scfh stream @ 30 Btu/scf Natural Gas 300 Btu/scf Hydrogen 11.5 vol.% Reduction (%) 42,000 13,000 69 $1,400,000 $425,000 70 NOx emissions (ton/yr) 11.8 1.9 84 CO emissions (ton/yr) 60.2 9.9 84 CO2 emissions (ton/yr) 19,363 2,605 87 Fuel gas required for compliance (scfh) Annual fuel costs (24/7 operation, 340 d/y) $4/MMBtu Natural Gas ~$1MM/year in potential annual savings 4 Steam-Assisted Assisted Flares - Emissions Reduction with Hydrogen 20,000 70 Emissions (ton/yr) 60 Natural gas fuel 18,000 Hydrogen fuel 16,000 50 14,000 40 12,000 Natural gas fuel Hydrogen fuel 10,000 30 8,000 6,000 20 4,000 10 2,000 0 0 NOx CO CO2 Stream assumptions: waste gas volume = 100,000 scfh; waste gas heating value = 30 BTU / scf; H2 volume % required = 11.5% NOx & CO Calculations: Based on Standard Emissions Index from TCEQ's Air Permit Technical Guidance for Chemical Sources: Flares and Vapor Oxidizers, October 2000, RG 109 (Draft) pg 18-19 Thermal NOX - 0.068 lb/MMBTU for steam assisted CO - 0.3465 lb/MMBTU for steam assisted CO2 Calculations: Based on 9.5lbs of CO2 for 1lb H2 produced from SMR; 113lbs CO2 for 1000scf of Natural Gas 5 Testing Hydrogen Addition to Assisted Flares • Flare testing facility built in Tonawanda, NY - 1H 2008 - Variety of fuels - Assist / non-assist operation • Goal: Add hydrogen compliance option for assisted flares to EPA regulations • Critical parameters: - >98% destruction efficiency of hydrocarbons - Flame stability - No visible emissions / smoke 6 7 8 Assisted Flare Diagrams Pilot Gas Inlet Air Outlet Side View Steam Outlet 5' Air Inlet Steam Inlet Waste Gas Inlet Top View Pilot Gas Inlet Pilot Conduit Connection Steam Inlet Air Inlet Waste Gas Inlet 9 Additional Considerations • Mirrored previous flare studies wherever possible - Flame Stability and Destruction Efficiency tests - Flare diameter - 3 inches - Ethylene used as surrogate HAP - Use of emissions capture hood - CO2 used as a tracer to determine amount of captured flare emissions • Simplification of assist - test "worst case scenario" - Steam assist is simple 5 nozzle ring design - Air assist will not use advanced mixing aides • Baseline measurements - Test 300 Btu/scf waste stream for each assist setting (mimics current operation) - Replicate non-assisted hydrogen-fueled fueled flare flame stability tests to demonstrate equivalency of Praxair's testing 10 Test Variables for Assisted Flares Variable Range / Value Tested H2 volume % 5 - 25% Hydrocarbon heating value 30, 100, & 200 Btu/scf Velocity 20 - 150 ft/s Steam Assist 0.4 lb steam / lb ethylene Air Assist 20% of stoichiometric air requirement 11 Flame Stability Images (A) (B) Not Lifted Lifted Flame No Flame Pilot Flare Tip Pilot Flare Tip Flare Pipe Flare Pipe 12 Flame Stability Results - Air-Assisted Flare Hydrogen Volume Percent (%) 20% 18% 16% 14% 12% 10% 8% 6% 4% 2% 0% 0 50 100 Exit Velocity (ft/s) 150 200 13 Flame Stability Results - Steam-Assisted Assisted Flare Hydrogen Volume Percent (%) 20% 18% 16% 14% 12% 10% 8% 6% 4% 2% 0% 0 50 100 Exit Velocity (ft/s) 150 200 14 Flame Stability Results • Fitting linear equations to the flame stability data results in the following: Air-assisted flare: X H 2 (%) = 0.0489 * v( ft / s) + 10.3 Steam-assisted flare: X H 2 (%) = 0.0575 * v( ft / s ) + 9.83 Where: X H 2 (%) = Hydrogen volume percent in the waste gas exiting the flare v( ft / s ) = Exit velocity of the flare (excluding assist gas), not to exceed 150 ft/s • These equations can be used to determine the amount of hydrogen required to ensure a stable flame at a given exit velocity 15 Destruction Efficiency Results Using Hydrogen Heating Value Assist of Waste Gas Used (Btu/scf) Runs n Destruction Efficiency (%) Average 95% Confidence Exit Velocity (ft/s) Flame Stability 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 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 99.90 150 1.02 16 Assisted Flare Testing Results How Much Hydrogen? • Slightly more hydrogen required for assisted flares than non-assisted • These numbers must be approved by the EPA • Assuming any new regulation will be equation-based (similar to current compliance options) Exit Velocity (ft/s) Hydrogen Requirement (vol%) 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 17 Praxair Study Conclusions • Hydrogen use in assisted flares study mirrored previous flare testing as closely as possible • Results established a flame stability envelope for assisted flares over a range of velocities • Destruction efficiencies above 99% were observed for all hydrogen-fueled fueled conditions tested • Requesting that 40CFR 60.18 & 63.11 be amended to include hydrogen as a compliance option for steamsteam and air-assisted assisted flares based on these findings 18