Influence of phosphorus based additives on nitrogen and sulfur pollutants emissions during densified biochar combustion.

Biomass is a carbon neutral fuel and can effectively replace fossil fuels. However, its large scale application is limited by disadvantages such as low calorific value, low energy density and high alkali content. Densification, pyrolysis and adding additives are available methods to upgrade biomass fuels. Nevertheless, emission rules of nitrogen and sulfur oxides in combustion of densified biochar need to be clarified. This paper focuses on the emission and transformation mechanisms of nitrogen and sulfur pollutants during pyrolysis and combustion of biomass with phosphorus based additives by means of thermodynamic calculation and experimental research. The addition of additives promoted the emissions of H 2 S, COS and NH 3 during pyrolysis, so the treatment of H 2 S and COS needs to be considered particularly. During combustion of densified biochar at 1000 °C, increased pyrolysis temperature accelerated SO 2 emissions, while it had no obvious influence on NO emissions. NH 4 H 2 PO 4 accelerated organic sulfur release, NH 4 H 2 PO 4 and Ca(H 2 PO 4) 2 slightly reduced the emission of NO. The maximum values of NO and SO 2 release rates were about 2.81 and 1.55 g/kg, respectively, which were lower than those of most typical fuels. The upgraded densified biochars have benefits such as high calorific value, low melting point and low pollutant emission. • Emission rules of nitrogen and sulfur oxides of densified biochar were studied. • Influences of phosphorus additives on transformation of N and S were studied. • Additives promoted H 2 S and NH 3 release during pyrolysis. • SO 2 and NO emissions of densified biochar during combustion were lower than most fossil fuels. [ABSTRACT FROM AUTHOR]