Dual role of O2 concentration on the reducing gases produced and NO reduction during sewage sludge combustion in pilot scale cement precalciner.

ABSTRACT

The reducing gases produced and NO reduction by sewage sludge combustion were investigated in a self-made cement precalciner. The dual role of O2 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, NH3, CO, and CH4. And experiments demonstrated that O2 concentration had pronounced effects on NH3 distribution, the maximum production rate was obtained at an O2 concentration of 3 vol%. Meanwhile, the reducing gases NH3 and CO were the key species for NO reduction in the cement precalciner, and the reduction efficiency of NO, when reduced by NH3, increased with an increase in O2 concentration, while the reduction performance of NO by CO was limited by O2 concentration. Therefore, O2 concentration greatly influences NO reduction efficiency by sewage sludge combustion; the maximum NO reduction efficiency was 61.67% at an O2 concentration of 3 vol%. The difference in NO reduction by sewage sludge combustion under different O2 concentrations was primarily attributed to NH3 production rate and NO reduction by NH3 and CO, which is greatly affected by O2 concentration. Sewage sludge combustion can result in NO reduction in the cement kiln flue gas and resource utilisation of sewage sludge.