Emissions of Hazardous Air Pollutants and Ozone Precursors from a Natural Gas-Fired Burner

Due to heightened environmental concerns about air quality, urban areas around the world are shifting to the use of natural gas for continuous stationary combustion systems. However, USEPA regulations concerning hazardous air pollutants (HAPs) and ozone precursors (OPs) may pose challenges in the design and operation of advanced gas-fired combustion systems. As natural gas systems switch to lean, premixed operation to reduce NOx formation and maintain high combustion efficiency, the emissions of HAPs and OPs - specifically of volatile organic compounds (VOCs) - may potentially increase. A study was conducted to investigate the effect of low - NOx operating conditions on VOC emissions for a scaled, generic, low - NOx, natural gas-fired burner. The exhaust samples were analyzed for C2 - C10 aliphatic, aromatic, and carbonylic hydrocarbons using USEPA-sanctioned methods. Most VOCs were emitted in relatively low concentrations (< 100 ppbv). However, certain very lean and high air velocity conditions generated relatively high total VOC levels (2 - 118 ppmC). To address concerns regarding the release of VOCs from stationary combustion systems, a performance function based on NOx, CO, and VOC emissions was developed to identify an optimal set of conditions where all pollutant emissions are minimized. If natural gasfired systems operate at these optimal conditions, a significant regulatory concern with respect to VOC emissions can be mitigated. Achieving and maintaining this level of performance may require active control and the use of indicator species. The data show a positive correlation between VOCs, CO, and total hydrocarbons (THCs), suggesting that CO and THCs could potentially serve as surrogates for VOC emissions under lean burn conditions.