The IFC Literature Review

The IFC Literature Review Peter Gogolek CanmetENERGY, Ottawa Natural Resources Canada IFC Purpose  Formed to review and address crucial gaps in the science of flares.  Produce a method of predicting flare efficiency from operating variables: flare gas composition and flow rate; steamassist rate; and wind speed.  Identify optimal operating conditions and identify the operating envelope for flares. IFC Membership  Members: BP, ExxonMobil, Saudi Aramco, Chevron, John Zink, Shell, DuPont, NOVA Chemicals, TOTAL.  Principal Investigators: P. Gogolek, J. Pohl, R. Schwartz, J. Seebold.  Host: CanmetENERGY Literature Review  Review of the published literature on the emissions from elevated flares, assisted or not, for upstream or downstream application in the petroleum and chemical industries.  Mathematical models of flares not treated.  deserves its own review. Structure of Review  Chronological survey of the literature  Detailed analysis of the effects of important operating parameters:     flare gas composition and exit velocity, flare tip size, cross-wind speed, and assist rate.  Data on the trace emissions.  The scaling of flares and the dimensionless groups that may be useful in correlating the emissions from flares. Objective of Literature Review  To identify the reliable knowledge, the apparent contradictions, the errors, and any gaps remaining in the scientific understanding of the emissions from elevated flares. Survey of Literature  Siegel (1980) doctoral thesis     steam-assisted flaring of slip stream of RRG. blower to provide cross-wind commercial tip: 10 t/h, 70 cm diam., SFR from 0 to 1.7 kg/kg  point probe sampling  local conversion efficiency always > 98%  H2 content: Avg = 54.5%-v, Max = 69%-v, Min = 18%-v. CMA (1983)  John Zink STF-S-8 with two pilot burners (8 inch)  Single point sampling above flame tip.  Looked at steam-assist and nitrogen dilution. Steam-assist of propylene flare 100 95 CCE, % 90 85 80 75 70 65 0 1 2 3 4 SFR, kg/kg 5 6 7 8 Dilution of Propylene with Nitrogen 100.5 100 CCE, % 99.5 99 98.5 98 97.5 0 500 1000 1500 Heat Content, Btu/scf 2000 2500 Pohl and coworkers (1980s)  Extensive testing of flare tips and gas compositions.  Correlated stability with minimum heat content.  Final word on flaring for a decade. EER (1997)  DuPont wanted exemption to heat content regulation for hydrogen flares.  Testing on 3" pipe for stability limits of H2/N2.  Range was 6%v to 15%v (15 Btu/scf to 42 Btu/scf) Stability of Hydrogen with Nitrogen 45.0 40.0 35.0 Velocity, m/s 30.0 25.0 20.0 15.0 10.0 5.0 0.0 0.0 2.0 4.0 6.0 8.0 10.0 Hydrogen, vol% 12.0 14.0 16.0 18.0 University of Alberta (1999 - 2004)  Extensive investigations of all aspects of solution gas flaring in Alberta.  Low exit velocities and crosswind give wake-stabilized mode.  Circulating wind tunnel, with small pipes.  Single-pass wind tunnel for scale-up tests. Fuel Slip from Wake Fuel is shed from the wake, and is not combusted. Correlation of Inefficiency 20000 16000 14000 12000 CI (LHVm) 3 Scale-up tests. 1" 2" 4" Equation (2-6) 18000 10000 8000 6000 4000 2000 0 0 BP  2 4 8 BP, - Uw gD U  1/ 3 p 6 f 10 12 14 16 Correlation of Inefficiency 100 1" 2" 4" Equation (2-6) +100% -100% CCI, % 10 Definite size segregation; 4 inch pipe has efficiency > 99%. 1 0.1 0 BP  2 4 8 BP, - Uw gD U  1/ 3 p 6 f 10 12 14 16 Gogolek and Hayden (2003) Dilution 100 20% N2 Dilution with nitrogen and carbon dioxide to same heat content per unit volume 40% N2 60% N2 20% CO2 Inefficiency, % 40% CO2 60% CO2 10 NG 1 0.1 0 2 4 6 Wind Speed, m/s 8 10 12 Remote Sensing  None yet proven on blind tests.  Boden (1996) - DIAL on 42 in and 48 in steamassisted flares. > 98% DE  Open-path FTIR (Haus 1998, Ozumba and Okoro 2000, Blackwood 2000) report > 98% CE.  Mellqvist (2001) - Solar Occultation - ethylene DE from plumes - full load had DE > 98% but high emissions from part-load (<20% of full load). Difficulties for Remote Sensing  Concentration, temperature, and velocity profiles are not known a priori.  There can be spatial and temporal fluctuations of velocity and concentration.  Deconvolution is possible, e.g. tomography, but only if the time for data gathering (traverses) is shorter than the time scale of the fluctuations.  Ambient conditions can cause significant interference with the measurement. Fluid Mechanical Regimes Fr  ln(Fr)  f U 2f (  a   p ) gD p Jetting Wake ln(R) Stabilized Buoyant R  fU 2 f  aU 2 w Combustion Properties of Mixtures  Calculations for flares have to handle mixtures of gases.  Combustion properties should:  be tabulated for a wide range of compounds, or directly calculable from tabulated properties of a wide range of compounds.  have unambiguous mixing rules for each property including the treatment of inert gases  Look at mixing rules for Flammability Limits and Laminar Flame Speed. Flare Gas Exit Velocity  In Jetting regime have correlations of Noble et al. (1984) U f ,max  LHV Va UFL   0.0008    Q (1500 C ) LFL  and Shore (2007) U f ,max D p v  100  LFL  f   0.000066   a   LFL  These are sensitive to errors in the flammability limits. 5 4 Flare Gas Exit Velocity  In wake-stabilized regime, exit velocity dependence is much weaker.  Buoyant Plume parameter has ratio Uw 1/ 3 Uf  Power Factor has same dependence. Wind Velocity  In jetting regime, only Kalghatgi (1981) studied effect of cross-wind on blow-out.  Pipes 2 cm or smaller.  In wake stabilized regime, for 4" pipes, roughly linear decrease of efficiency with wind speed. Flare Tip Diameter  Jetting: efficiency and stability limit appear to be independent of tip size, if big enough (> 3 inch).  Wake stabilized: BP has pipe diameter to 1/3 power; but seems ½ power works better for scale-up data.  3" Rule applies in both regimes. Wake Stabilized - 3 inch rule 3.5 1 inch 3 1 - Carbon Conversion, % 2.5 2 1.5 1 0.5 0 0 1 2 3 4 5 Power Factor, - •Data for 1", 3", 4" and 6" from Canmet FTF. •1" clearly different. 6 7 Gaps      Experimental studies of the flare efficiency in the transition between jetting and wake-stabilized regimes. Experimental studies of the effect of wind on steamassisted flares. Experimental studies on the limiting hydrogen concentration for steam-assisted flares, and wind blown flares. HRVOC and NOx measurements for flares with and without steam-assist. Develop the combination of fuel properties to correlate the flare efficiency with flare gas composition, particularly accounting for the special case of hydrogen, and the inert gases nitrogen and carbon dioxide. Gaps    Develop a treatment of steam-assist rate that includes the flare gas composition, perhaps unifying steam with the handling of nitrogen and carbon dioxide dilution. Need to expand areas of flare performance to include higher capacity flare burners with specific design features that are commonly used in refinery and chemical plants. Need to address environmental regulators' requirements by testing flares similar to those used by industry. Acknowledgements  Funding for this work provided by members of the IFC.  Discussions among members' representatives and PIs.