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

• Combination of pilot ignition and air staging for utilizing LCG. • Pilot flame produces H 2 O and NO to facilitate LCG ignition. • NO promotion on CH 4 based LCG is from NO/NO 2 cycle to enhance CH 3 oxidation. • Whether steam exists determines the NO influence on CO based LCG reactivity. 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 NO x emission. Present work proposed to combine the pilot ignition and air staging approach, to respectively overcome the difficulty in LCGs ignition and reduce its NO x emission. Experiment and numerical simulation were conducted to explore combustion characteristic of LCG during pilot ignition. Some previous proposed kinetics models for CH 4 or CO combustion were evaluated that whether they capture the NO or H 2 O influence, respectively, within this complex flue gas atmosphere, and the mechanisms were further explored. Adding 0.04 vol% NO reduces the ignition temperature of CH 4 based LCG from 750 to 510 °C under pilot ignition condition. This promotion is via a NO/NO 2 cycle of NO + HO 2 → NO 2 + OH and CH 3 + NO 2 → CH 3 O + NO , to enhance CH 3 oxidation rate by ∼ 30 times. In that cycle, the NO formation (NO 2 consumption) rate is higher than the NO 2 formation (NO consumption), causing only NO but no NO 2 was preserved in flue gas under pilot ignition condition. The effect of adding NO to CO based LCG is dependent on H 2 O presence, where it makes no difference without H 2 O presence, but has an improvement on "moist gas" reactivity. Neither the commonly used kinetics models of CH 4 combustion nor those for CO contained syngas gas can predict reactivity of "dry CO contained LCG" under pilot ignition condition. [ABSTRACT FROM AUTHOR]