Nox removal from Small-Scale biomass combustion in DC Corona: Influence of discharge polarity on plasma chemical kinetics

Abstract

Direct current corona discharge was investigated to reduce nitrogen oxide (NOx) emissions from a 15-kW smallscale biomass boiler. The electrostatic precipitator was designed and operated under different regimes with both positive and negative polarities. A reduction in NOx concentration from 200 mg/m3 to 44/46 mg/m3 for positive/negative polarities was achieved, corresponding to a NOx removal efficiency of approximately 78 %. However, the specific input energy required for a positive corona (35.7 J/L) was lower than that for a negative corona (48.4 J/L), indicating an energy efficiency advantage for positive polarity. The results were analysed for NO decontamination involving reactions with OH radicals, ground-state oxygen atoms, and ozone. Positive corona favoured NOx removal via reactions with OH (21 % efficiency) and oxidation by oxygen (12 % efficiency), whereas negative corona promoted NO oxidation by ozone (75 % efficiency). The distinct distribution of electrons and active species, influenced by the non-uniform electric field and polarity, governs plasma chemical kinetics.