Abstract:

The reducing gases produced and NO reduction by sewage sludge combustion were investigated in a simulated cement precalciner. The dual role of O₂ concentration (volume fraction is 0~5%) in the producing characteristic of reducing gases and the reduction of NO was studied systematically. Characteristic analysis of TG-FTIR demonstrated that the reducing gases produced by sewage sludge combustion were mainly HCN, NH₃, CO and CH₄. Further experimental studies showed that O₂ concentration had pronounced effects on the distribution of HCN and NH₃, and the maximum producing rate of HCN and NH₃ was obtained at an O₂ volume fraction of 3%. Meanwhile, O₂ concentration had significant influence on the NO reduction by sewage sludge combustion. When the combustion temperature was of 900℃, the CO₂ volume fraction of 25%, the NO concentration of 600mg/m³, the SO₂ concentration of 200mg/m³, and the O₂ volume fraction was 3%, respectively, the maximum NO reduction efficiency was achieved at 55.8%. The experimental studies on the NO reduction by reducing species (NH₃, CO, CH₄ and sludge char) further showed that NH₃ and CO were the key species for NO reduction in the process of sewage sludge combustion, and the NO reduction by NH₃ increased with the increase of O₂ concentration, while the reduction performance of NO by CO was limited by O₂ concentration. The comprehensive analysis showed that the effects of O₂ concentration on NO reduction by sewage sludge combustion were mainly attributed to the difference in the producing rate of NH₃, the dominant role of NH₃ and CO in the reduction of NO and it was greatly affected by O₂ concentration. Sewage sludge used as a reducing agent for NO reduction was efficient and a higher NO reduction efficiency was obtained by controlling the O₂ concentration in cement production.

Key words: sludge combustion, two-phase flow, O₂ concentration, gas, reduction

摘要：

在模拟水泥预分解炉装置上研究污泥燃烧过程中还原性气体的产生及其对NO的还原，并系统研究了O₂浓度（体积分数为0～5%）对还原性气体产生及NO还原的双重影响。TG-FTIR特征分析表明，污泥燃烧产生的还原性气体主要为HCN、NH₃、CO和CH₄。进一步实验研究发现O₂浓度对HCN和NH₃的产生有明显影响，HCN和NH₃在O₂体积分数为3%时产生速率最大。同时，O₂浓度对污泥燃烧还原NO有较大影响。在污泥燃烧温度为900℃，烟气中CO₂体积分数为25%、NO浓度为600mg/m³、SO₂浓度为200mg/m³、O₂体积分数为3%时，NO还原率可达到最大（55.8%）。通过还原性物质（NH₃、CO、CH₄和污泥焦）对NO的还原实验研究进一步发现，NH₃和CO是污泥燃烧过程中NO还原的关键物质，且NH₃对NO的还原随着O₂浓度的增加而增加，而CO对NO的还原受O₂浓度的限制。综合分析表明，O₂浓度对污泥燃烧NO还原的影响主要是由NH₃的产生速率差异、NH₃和CO对NO的还原起主导作用且受O₂浓度影响较大等多种因素综合导致。采用污泥作为还原剂进行NO还原是一种高效的方法，在水泥生产中可通过控制O₂浓度获得较高的NO还原率。

关键词: 污泥燃烧, 两相流, O₂浓度, 气体, 还原