Combustion characteristic of low calorific gas under pilot ignition condition—Exploring the influence of pilot flame products

Abstract

Low calorific gas (LCG) is a huge thermal energy resource, but its utilization is poor due to the low reactivity and a tendency of high NOx emission. Present work proposed to combine the pilot ignition and air staging approach, to respectively overcome the difficulty in LCGs ignition and reduce its NOx emission. Experiment and numerical simulation were conducted to explore combustion characteristic of LCG during pilot ignition. Some previous proposed kinetics models for CH4 or CO combustion were evaluated that whether they capture the NO or H2O influence, respectively, within this complex flue gas atmosphere, and the mechanisms were further explored. Adding 0.04 vol% NO reduces the ignition temperature of CH4 based LCG from 750 to 510 °C under pilot ignition condition. This promotion is via a NO/NO2 cycle of NO + HO2→NO2+ OH andCH3+ NO2→CH3O + NO, to enhance CH3 oxidation rate by ∼ 30 times. In that cycle, the NO formation (NO2 consumption) rate is higher than the NO2 formation (NO consumption), causing only NO but no NO2 was preserved in flue gas under pilot ignition condition. The effect of adding NO to CO based LCG is dependent on H2O presence, where it makes no difference without H2O presence, but has an improvement on “moist gas” reactivity. Neither the commonly used kinetics models of CH4 combustion nor those for CO contained syngas gas can predict reactivity of “dry CO contained LCG” under pilot ignition condition.