Characteristics of sodium compounds on NO reduction at high temperature in NOx control technologies

Characteristics of sodium compounds additives on NO reduction at high temperature were investigated in a tube stove and a drop tube furnace. Sodium carbonate, sodium hydroxide and sodium acetate were chosen as Na additives to research the effect on NO reduction. It was found that sodium compounds could reduce NO emission and promoted NO reduction efficiency during pulverized coal combustion, coal reburning and urea-SNCR process. Adding sodium carbonate into crude coal gained 3.2%–34.8% of NO reduction efficiency on different combustion conditions during the coal combustion process. NO reduction efficiency was affected by sodium content and coal rank. Na additive performed NO reduction effect in whole Shenhua coal combustion process and in char rear combustion of Gelingping coal. Adding sodium hydroxide into the reburning coal increased NO reduction efficiency of the reburning technology. NO reduction efficiency was increased to 82.7% from 50.0% when the weight ratio sodium to the reburning coal was 3% and the ratio of the supplied air to the theoretical air of reburning fuel was 0.6. Sodium carbonate, sodium hydroxide and sodium acetate performed the promotion of NO reduction efficiency in urea-SNCR. Sodium acetate promoted NO reduction efficiency best while sodium hydroxide promoted worst at 800 °C. Sodium additives as SNCR promoter performed much better at lower temperature than at higher temperature, and they promoted NO reduction weakly in urea-SNCR when the temperature was greater than 900 °C.