A review of CO emissions during solid biofuel combustion – Formation mechanisms and fuel-related reduction measures

Minimizing carbon monoxide (CO) emissions from the combustion of solid biofuels is essential to improve thermo-chemical conversion efficiencies and avoid impact on human health. This review focuses on the formation mechanisms and subsequent oxidation of CO within the combustion process; for this, the different phases of biomass combustion (i.e., heating up, pyrolysis, gasification, and homogeneous gas-phase oxidation) are considered separately. The comprehensive analysis shows that CO emissions can be mitigated by fuel-related measures (e.g., washing and leaching to eliminate K components) as well as by (mineral) additivation of the fuel to repress the K-release by binding it in temperature-stable components within the ash. Furthermore, the addition of sulfur results in the sulfation of critical K-compounds to less corrosive and non-radical interfering compounds.