Emissions of Nitrogen Oxides from Flares Operating at Low Flow Conditions

Abstract

Full scale flare tests have been conducted to test the impacts of flare operating conditions on the fraction of flared gases that are converted to carbon dioxide and water (combustion efficiency, CE) for flares combusting low heating value gases (∼350–600 BTU/scf) at low flow rates (∼0.1–0.25% of maximum flow). Flares produce lower flame temperatures when operating with low heating value gases at low combustion efficiencies than when operating with high heating value gases at high combustion efficiencies. This leads to reduced formation of nitrogen oxides (NOx) in the flame. For a series of tests conducted under low flow conditions, with low heating value gases, NOx emission factors ranged between 10 and 120% of the NOx emission factor reported in AP-42. Emissions of NOx were highest for air assisted flares operating at high CE and lowest for steam assisted flares operating at low CE. In general, emissions were lower in steam assisted flare tests than in air assisted flare tests conducted under similar conditions. Photochemical modeling simulations indicated that these reductions in NOx emissions had relatively small impacts on the ozone formation potential of flares operating at low CE.