Simulating Industrial Ethylene Flares

Air quality models (CAMx, CMAQ) often significantly under-predict observed peak O3 with the current VOC emission inventories in HGB/BPA. Even though this could be due to the inaccuracy of the photochemical models used, it is also likely that some VOC emissions may be under-reported or unreported due to the assumption of robust destruction efficiencies of industrial flares. According to TCEQ's 2007 HRVOC special inventory, industrial flares are a major source of highly-reactive VOCs (HRVOCs). From rigorous combustion chemistry, incomplete combustion of hydrocarbons is a likely source of free radicals such as perhydroxyl and radical producing species such as formaldehyde. All together, these pollutants may be responsible for the particularly high ozone formation in the Houston-Galveston-Brazoria area. Our simulations of industrial-sized ethylene flares based on FLUENT and combined San Diego /GRI mechanisms show the carbon-based flare efficiency (CBFE) decreases with cross wind speed even though the destruction and removal efficiency (DRE) stays relatively constant. Over-aeration also reduces the average flame temperature, therefore increases the incomplete-combustion-product emissions. The studies are aimed at finding the relationship between flare efficiencies/emissions and flare operating/meteorological conditions. Another important goal is to help petroleum/chemical industries to establish flare operation guidelines if enough simulation data are generated and validated with available experimental flare/flame data.