Effects of water vapor and Na/K additives on NO reduction through advanced biomass reburning

• NO reduction of 60.1–73.8% is achieved by biomass AR process at 920–1150 °C.
• Water vapor of 2–6% has an obvious promotion on NO reduction in the AR process.
• Na/K promoters on NO reduction follows the sequence of NaCl > NaOH ∼ Na2CO3 > KCl.
• Na-additives concentration has little effect on NO reduction when it above 50 ppm.
• Water vapor and Na-additives have a significant coupling promotion on NO reduction.

NO reduction through advanced reburning (AR) was carried out in an entrained flow reactor. Four types of biomass fuels, rice husk (RH), camphor leaves (CL), saw dust (SD) and wood charcoal (WC), were selected as reburning fuels. Effects of reaction temperature in the reburning zone (T2), biomass species, water vapor and alkali metal additives (Na2CO3, NaOH, NaCl and KCl) on NO reduction were investigated. The roles of these factors in the reaction pathways and possible mechanism were discussed. Results indicate that NO removal efficiency increases first and then decreases as temperature increases within 850–1150 °C. The maximum NO reduction efficiency is around 60.1–73.8% at optimal reaction temperature in the AR process. NO reduction also appears to increase and then decrease as the water vapor content increase from 0% to 15%, with a peak NO reduction at water vapor of 2–6%. Na/K additives have certain promoting effect on NO reduction in the AR process, following the sequence of NaCl > NaOH ∼ Na2CO3 > KCl. Concentration of Na-additives (NaCl, Na2CO3) has little effect on NO reduction when its concentration is higher than 50 ppm. The improvement of Na-additives in NO reduction can be promoted by water vapor significantly. More than 11.4% increment in NO reduction is achieved by AR with rice husk in presence of 4% water vapor and 100 ppm Na-additives (NaCl, Na2CO3) in comparison to that without water and additives, and the maximum NO removal efficiency gets up to 85.5%.