摘要
When semi-coke is co-combusted with bituminous coal with higher sulfur content in a circulating fluidized bed(CFB)boiler,the necessity of desulfurization in furnace increases.Meanwhile,limestone,which is a widely used desulfurizing agent,also has an effect on NO emission.In order to explore its effect during co-combustion,the combustion experiments were conducted in both a CFB test rig and a fixed bed reactor.The results show that blending semi-coke with bituminous coal will change the occurrence forms of nitrogen in the fuel and more fuel NO is released during the devolatilization stage.During the desulfurization process,CaO will be generated through the calcination reaction.It has catalytic effects on both the oxidation and reduction reactions of NO,and the catalytic strength in these two types of reactions decides the final effect on NO emission.For the blended fuel with 50%semi-coke and 50%bituminous coal(SC50BC50),the NO emission initially increases and then decreases as the Ca/S molar ratio increases from 0 to 4 at 900℃.Compared to the situation of burning semi-coke alone,semi-coke in the blended fuel has more opportunities to contact with CaO under the same Ca/S molar ratio,leading to the heterogeneous reduction reaction of NO enhanced.As the combustion temperature increases from 800℃ to 1000℃,the effect of limestone on NO emission will change from promotion to inhibition.This is because the higher combustion temperature can intensify not only the catalytic reduction of NO precursors in the dense-phase region,but also the reaction between NO and unburnt char in the dilute-phase region in the CFB.Besides,the lower O_(2) concentration in the atmosphere is also favorable for enhancing the catalytic effect of CaO on the NO-char reduction reaction for semi-coke and SC50BC50,so the conversion of fuel-N/NO will be inhibited compared with the cases without limestone.The achievements of this study are beneficial for the coordinated control of NOx and SO_(2) during the co-combustion of semi-coke and bituminous coal.
基金
financially supported by the Scientific Research Startup Foundation of High-level Introduction Talents of Nanjing Institute of Technology(No.YKJ201914)
National Natural Science Foundation of China(NSFC)(No.51678291).
作者简介
Corresponding author:LIU Yanquan,E-mail:lyqlxx@jit.edu.cn。
