Effects of SO2 and H2O on the ash deposition and NO emission during oxy-fuel combustion of high-alkali coal
Lin Zhao, Chang’an Wang, Tianlin Yuan, Liangxu Dai, Yingchao Nie, Guowei Ma, Lei Zhou, Maoyun Luo, Defu Che
Abstract
The oxy-fuel combustion is promising to realize the large-scale CO 2 capture and effective reduction of nitric oxides . The recirculation of flue gas in oxy-fuel combustion can lead to high concentrations of SO 2 and H 2 O, which probably affects the ash deposition of high-alkali coal because SO 2 and H 2 O are important for the transformation of alkali and alkaline earth metals (AAEMs). In the present work, the effects of SO 2 and H 2 O in recycled flue gas on the ash deposition and NO emission during the oxy-fuel combustion of high-alkali coal were experimentally evaluated in a vertical two-stage furnace system. The conversion ratio of fuel-nitrogen to NO ( C NO ) and ash deposition efficiency were measured, and then the ash deposits were subjected to a couple of tests for further analyses. The experimental results show that SO 2 helps to reduce the NO emission and its impact on ash deposition depends heavily on its concentration. In the case with modest SO 2 addition, the sulfations of sodium and calcium are enhanced to some extent. Consequently, the amount of small sticky particles (NaCl and sodium aluminosilicates) that attached to large particles decreases, and the large particles mainly made of calcium aluminosilicates become smaller and less sticky. The newly generated Na 2 SO 4 and CaSO 4 are insufficient to overcome the inhibiting effects, thus the ash deposition efficiency decreases. Under the condition of excessive SO 2 addition, the sulfations are further promoted. The small particles rich in Na 2 SO 4 and CaSO 4 are substantially more, which can not only serve as the initial ash layer on the heating surface, but also strengthen the stickiness of large particles by attaching to their surfaces. Therefore, the ash deposition efficiency increases·H 2 O can reduce the NO emission, while it aggravates the ash deposition because H 2 O enhances the sulfation.