Effect of volatile–char interactions on PM10 emission during the combustion of biosolid chars under air and oxyfuel conditions

Abstract

This study reports the significant effect of volatile–char interactions on the emission of particulate matter (PM) during the combustion of biosolid chars in drop-tube furnace at 1300 °C under air and oxyfuel conditions. Slow and fast heating chars were prepared from biosolid pyrolysis and then interacted with the volatiles produced in situ from the pyrolysis of polyethylene (PE) and double acid-washed biosolid (DAWB) in a novel two-stage quartz reactor at 1000 °C (limited by the operating temperature of quartz). The results clearly show that under the experimental conditions, the interactions between chars and small non-oxygenated reactive species in both volatiles substantially decrease the yield of PM with aerodynamic diameter < 1 µm (i.e. PM1), dominantly PM with aerodynamic diameter < 0.1 µm (PM0.1) during char combustion. The interactions between oxygen-free volatiles (produced from PE pyrolysis) and char also reduce char macroporosity, leading to a reduction in the yield of PM with aerodynamic diameter between 1 µm and 10 µm (i.e. PM1-10). However, the interactions between O-containing reactive species (produced from DAWB pyrolysis) and char significantly increase char macroporosity. Higher heating rate with shorter aging process during pyrolysis significantly weakens the effect of volatile–char interactions on PM1 emission but intensifies its effect on PM1-10 emission during char combustion. The combustion atmospheres have little effect on the net yield of PM contributed by volatile–char interactions. Combustion of chars interacted with the oxygen-free volatiles lead to a reduction in the yield of refractory elements (i.e. Mg, Ca, Al, Si, Fe, Ni, Co, Cu, Mn, V and Zn) in PM1-10 but those interacted with the O-containing volatile resulted in an enhanced yield of these elements in PM1-10. Furthermore, the interactions between O-containing reactive species and chars significantly decrease Cr yield in PM0.1 due to formation of volatile chromium oxyhydroxides. In addition, volatile–char interactions have little influence on the forms of alkali and alkaline earth metallic (AAEM) species and P in PM10, i.e. as (Na, K)PO3 in PM1 and (Mg,Ca)3(PO4)2 in PM10.