(209g) Inferential–MODEL Based FLARE SET POINT Determination
Recent EPA rule (40 CFR parts 60 and 63) finalizes single minimum combustion zone net heating value (NHVcz) operating limit as 270 BTU/scf during any 15â??minute average period for flares subject to Petroleum Refinery Maximum Achievable Control Technology standards to ensure 98% destruction efficiency (DE) or 96.5% combustion efficiency (CE) or higher at all times. In addition, refinery flares meet the flare tip velocity requirements (max. 400 ft/s), visible emission requirements (20% opacity limits) and net heating value dilution parameter (NHVdil) minimum operating limit of 22 BTU/ft2 and corrected vent gas heat content of 1212 BTU/scf for hydrogen to demonstrate the compliance. This study aims at developing robust inferential flare models to express DE, CE and opacity as a function of operating variables and to determine set point for steam and make up fuel at the incipient smoke point operation for NHVcz â?¥ 270 BTU/scf and NHVdil â?¥ 22 BTU/ft2. Multivariate statistical distribution and response surface models were developed for steam and air assisted flares burning propylene, propane, natural gas, methane, ethylene and typical refinery vent gas mixtures. Curve fitting tool box in MATLAB and Minitab were used in modeling. In this study, soot emissions, visible emission scale, DE, and CE test data from 1983 to 2014 (including 1983/1984/1985 EPA, 2010 TCEQ, 2009/2010 Marathon Detroit/Texas City, and 2014 Carleton University) were analyzed. The input variables include measurable variables like exit velocity, lower heating value, flare tip diameter, vent gas species (double bond, carbon to hydrogen molar ratio and molecular weight), and operating variables (NHVcz, NHVdil, steam/air assists, and fuel). Response surface models developed for CE and opacity showed high coefficient of determination (R2) values 0.91 and 0.95 respectively for steam assisted flare data.