Dilute Oxygen Combustion

A novel burner system, in which fuel (natural gas) and oxidant (oxygen or air) are separately injected into a furnace, shows promise for achieving ultra-low NOx emissions for commercial furnace applications. The dilute oxygen combustion (DOC) burner concept achieves ultra-low NOx through in-furnace dilution of the oxidant stream prior to combustion, resulting in low flame temperatures, thus inhibiting thermal NOx production. The results of a fundamental and applied research effort on the development of the DOC burner system are presented. The fundamental aspects of the burner development program involved examining the entrainment and flame lift-off characteristics of a natural gas jet in a high-temperature (-1366 K) oxidant (7-27% O2 vol. wet). The measured entrainment rate of the fuel jet decreased with increasing oxygen content in the surrounding high-temperature oxidant. As expected, the flame lift-off height decreased with increasing oxygen content and increasing temperature of the surrounding gas. Several DOC burner configurations were tested in a laboratory-scale furnace at fIring rates of 185 kW (0.6 MMBtu/h). The flue gas composition was recorded as a function of furnace nitrogen content, furnace temperature and burner geometric arrangement. NOx emissions increased with increasing furnace nitrogen content and furnace temperature. NOx emissions below 5.10-3 g/MJ (10 ppmd-air equivalent at 3% O2 dry) were obtained for furnace temperatures below 1533 K (2300°F) and furnace nitrogen levels between 1 and 40%. CO emissions were typically low (<35 ppmd).