Experimental study on biomass reburning in one dimensional drop tube furnace

Reburning for nitrogen oxides (NOx) control by corn straw and rice husk as reburn fuels was studied in the current work. Experimental equipment was an isothermal drop tube furnace. Flue gas from the primary zone was simulated by the combustion of propane mixed with NO through premixed burner in horizontal combustion chamber. Reburn fuels were fed from the top of vertical section, flowing from top to down. The vertical isothermal section was used to simulate reburn zone. Flue gas at different resident time was sampled by a water-cooled sampling device, and the gas composition was analyzed with gas analyzer. Considering resident time in reburn zone is less than 0.7s in practical operation, a resident time of 0.5s was used as a benchmark when NO removal effectiveness of different cases was compared. The NO concentration was kept at 800ppm at the outlet of primary zone and the temperature in the reburn zone was controlled approximately at 1200 degrees C for all cases. Different biomasses as reburn fuels and their influence on NO removal were studied experimentally. The results show that NO can be reduced up to 60% when corn straw was used as reburn fuel with 15% reburn fuel fraction and stoichiometric ratio was 0.9. A higher NO reduction can be achieved if the reburn fuel fraction is increased and the SR is decreased. Rice husk is less effective reburn fuel than corn straw under the same conditions. Furthermore, a kind of bituminous coal was also tested as a reburn fuel also. The experimental results suggest that higher NO removal efficiency obtained with two biomasses than that with the bituminous coal. Besides, the influence of various parameters was analyzed by chemical kinetics mechanism to explain the experimental results, which theoretically supports engineering application of the reburning technology.