Experiment on NO reduction performance from reburning of agricultural wastes

Abstract: In order to develop clean and efficient utilization technologies of biomass to supplement insufficient fossil energy, the reduction of NO was studied in a drop tube furnace (DTF) using rice husk, straw, and pulverized coal as reburning fuels. The impacts of fuel type, stoichiometric ratio (SR), reburning reaction temperature, residence time in the reburning-zone, the ratio of fuel particle size and reburning fuel on NO removal efficiency were analyzed in this study. The results indicated that NO reduction efficiency of biomass fuels such as rice husk, straw and sawdust of pine were higher than that of pulverized coal. The NO removal efficiency of straw and sawdust of pine was the highest, but the efficiency of the pulverized coal was the lowest among these three fuels. The composition of volatile components in different fuels had major impacts on the efficiency. NO removal efficiency was decreased with SR increasing in reburning zone. As SR was increased, reducing components released during the devolatilization were consumed by oxygen at the same time with NO reduction, which weakened the reduction reaction of NO. The SR had major impacts on the efficiency of NO reduction of agricultural wastes including rice husk and straw than that of the pulverized coal. For the test case of reburning ratio of 20 %, the reduction efficiency of NO using straw and rice husk were decreased by 20.12 % and 20.07 %, respectively if the SR was increased from 0.8 to 0.9. It was decreased by 8.38 % when using the pulverized coal. The sizes of fuel particles affect heating process. Under the same conditions, the fine fuel particles produced more volatile components and supplied more reducing matters of NO, which increased the reduction efficiency of NO. The increase of resistance time also increase the reaction time between reburning fuel and NO, which facilitated the NO reduction. By using straw and rice husk as reburning fuel, reasonable residence time was shorter than 600 ms, which is much lower than that of using the pulverized coal. Adjusting reburning ratio can attain appropriate reduction efficiency of NO. Reasonable reburning ratios of straw and rice husk were preferred to be between 15%-20%.