生物质再燃脱硝及其同相还原反应特性

利用固定床反应器研究了稻壳、木屑和玉米秸3种生物质在不同工况〔再燃温度、φ(O₂)〕下的再燃脱硝效率,同时考察了再燃区出口处CO、H₂、碳氢类物质(主要是CH₄)、HCN和NH₃的体积分数随工况的变化规律. 结果表明:生物质类型对再燃脱硝效率有很大影响,木屑再燃脱硝效率最大值达57.0%±2.1%,高于稻壳(50.0%±1.5%)和玉米秸(51.0%±1.1%). 在再燃过程中,生物质产生的热解气能够增强还原性气氛,从而提高再燃脱硝效率,当烟气中φ(O₂)为0%～1%时,再燃脱硝效率较高. 在还原性气氛(800～1 200 ℃)下,3种生物质再燃脱硝效率差异主要来自生物质不同热解气与NO的同相反应. 其中,碳氢类物质对NO的还原起到了关键作用,而CO和H₂所起作用并不大,φ(HCN)与φ(NH₃)之和反映了气相中NO向N₂的转化趋势. 因此,深入了解生物质热解气对其再燃脱硝效率的影响机制有益于燃料再燃脱硝效率的提高. 

Nitrogen Oxide Reduction by Biomass Reburning and Its Reaction Characteristics of Homogeneous Reduction

The nitrogen oxide (NO) reduction efficiencies of three biomass samples (rice husk, sawdust and corncob) by reburning were investigated under different conditions (reburning temperature and O₂ concentration) in a fixed-bed reactor. The variations of CO, H₂, hydrocarbons (mainly CH₄), HCN and NH₃ in the outlet gas from reburning zone under different conditions were evaluated. The experimental results indicated that the biomass type significantly influenced the NO reduction efficiency. The maximum NO reduction efficiency of sawdust reburning was 57.0%±2.1%, which was higher than those of rice husk reburning (50.0%±1.5%) and corncob reburning (51.0%±1.1%). During the reburning process, pyrolysis gases from the biomass could strengthen the reducing atmosphere and thus enhance the NO reduction efficiency by reburning, and highly efficient NO reduction was obtained at oxygen concentrations in the flue gas of 0%-1%. At reducing atmosphere (800-1200 ℃), the difference in NO reduction of the three biomass samples could be ascribed to the difference in yield of pyrolysis products of biomasses through the homogeneous reactions. Hydrocarbons were the key species causing the reduction in emissions of NO, whereas CO and H₂ slightly affected NO reduction. The total concentration, summed by HCN and NH₃, was an index reflecting the tendency of conversion from major nitrogen-containing species to N₂. Thus, understanding the effect of pyrolysis gas on NO reduction by reburning was beneficial to NO reduction.