Experimental study on nitric oxide reduction through calcium propionate reburning

Performances of calcium propionate (CP) on nitric oxide (NO) reduction are experimentally investigated on a drop tube furnace system from basic reburning (BR), Thermal De-NOx and advanced reburning (AR) and it is demonstrated to be feasible of using CP as reburning fuel. BR could supply about 80% efficiency with reburning fuel fraction (Rff) and residence time (τ) kept 20–25% and 0.7 s, respectively. Also, oxygen concentration is required to be less than 4%. However, initial NO concentration is not important to reduction. Characteristics of Thermal De-NOx are also studied. The maximum efficiency of 85.34% could be achieved at 1273 K with mole ratio of ammonia to nitric oxide (β) equaling to 1.75. The corresponding “temperature window” is 1215–1341 K. From 2% to 6% of oxygen concentration, the efficiency of Thermal De-NOx is constantly depressed by 16.17%. The performances of advanced reburning are greatly optimized and higher efficiency could be achieved using less calcium propionate and ammonia. At 1273 K, efficiency of 93.37% is supplied by AR with Rff = 19.83% and β = 0.8. Also, the corresponding “temperature window” is broadened to 1195–1355 K which is 1.27 times of the one in Thermal De-NOx at β = 1.75. Meanwhile, the impact of oxygen concentration on NO reduction is weakened in AR.

Research highlights
► Calcium propionate reburning for NO reduction is performed from aspects of basic reburning (BR), ammonia-based SNCR of Thermal De-NOx and advanced reburning (AR) on a drop tube furnace system.
► BR presents about 80% NO reduction efficiency if reburning fuel fraction (Rff) and residence time (τ) are kept at 20–25% and 0.7 s, respectively. Also, O2 is required to be less than 4%.
► Thermal De-NOx could present the maximum efficiency of 85.34% where temperature is 1273 K and mole ratio of NH3 to NO (β) is 1.75. However, the efficiency is constantly depressed by 16.17% as O2 is increased from 2% to 6%.
► The performances of advanced reburning are greatly optimized and higher efficiency could be achieved using less calcium propionate and ammonia. At 1273 K, efficiency of 93.37% is supplied by AR with Rff = 19.83% and β = 0.8.