Response Surface Modeling and Setpoint Determination of Steam- and Air-Assisted Flares

摘要

Federal Regulation 40 CFR <>63.670 requires flare operators to specify smokeless design capacity for flares with no visible emissions. Alternatively, 96.5% combustion efficiency (CE) or 98% destruction efficiency must be achieved with threshold limits of minimum combustion zone net heating value (NHVcz) >= 270 British thermal unit/standard cubic feet (BTU/scf) for steam-assisted and net heating value dilution parameter (NHVdil) >= 22 BTU/ft(2) for air-assisted flares. There is still no guarantee for smokeless flaring (SLF) or CE >96.5%. Robust response surface models developed in this study expressed %CE and %Opacity as a function of operating variables for air- and steam-assisted flares. Opacity and CE test data from 1983 to 2016 were analyzed. General quadratic models with transforms of CE and Opacity showed R-2 > 0.90, and bivariate sigmoid models for CE showed R-2 > 0.87. Two-dimensional (2D) contours illustrate the trends of major operating parameters. Operational setpoints at the incipient smoke point (ISP) and SLF were determined by solving the models subject to NHVcz and NHVdil threshold limits specifying Opacity at 3% (ISP) and 2% (SLF). The predicted steam/air assists/makeup fuel, NHVcz (or NHVdil), and CE at ISP and SLF conditions are compared with the experimental 1984 Environmental Protection Agency (EPA) and 2010 Texas Commission on Environmental Quality flare study ISP test data. These setpoints would help flare operators to establish ISP or SLF conditions either by adding makeup fuel to vent gas with low heating value or by minimizing the assist without adding makeup fuel for steam- and air-assisted flares.