Dual role of O concentration on the reducing gases produced and NO reduction during sewage sludge combustion in pilot scale cement precalciner.

The reducing gases produced and NO reduction by sewage sludge combustion were investigated in a self-made cement precalciner. The dual role of O concentration (0-5 vol%) in the production characteristics of reducing gases and the reduction efficiency of NO were evaluated experimentally. TG-FTIR analysis demonstrated that the key reducing gaseous species produced by sewage sludge combustion were HCN, NH, CO, and CH. And experiments demonstrated that O concentration had pronounced effects on NH distribution, the maximum production rate was obtained at an O concentration of 3 vol%. Meanwhile, the reducing gases NH and CO were the key species for NO reduction in the cement precalciner, and the reduction efficiency of NO, when reduced by NH, increased with an increase in O concentration, while the reduction performance of NO by CO was limited by O concentration. Therefore, O concentration greatly influences NO reduction efficiency by sewage sludge combustion; the maximum NO reduction efficiency was 61.67% at an O concentration of 3 vol%. The difference in NO reduction by sewage sludge combustion under different O concentrations was primarily attributed to NH production rate and NO reduction by NH and CO, which is greatly affected by O concentration. Sewage sludge combustion can result in NO reduction in the cement kiln flue gas and resource utilisation of sewage sludge.