Effect of water vapour on particulate matter emission during oxyfuel combustion of char and in situ volatiles generated from rapid pyrolysis of chromated-copper-arsenate-treated wood

This paper reports the effect of water vapour on particulate matter (PM) during the separate combustion of in situ volatiles and char generated from chromated-copper-arsenate-treated (CCAT) wood at 1300 °C. Combustion of in situ volatiles produces only PM with aerodynamic diameter <1 µm (i.e., PM1), dominantly PM with aerodynamic diameter <0.1 µm (i.e., PM0.1). Water vapour could significantly enhance the nucleation, coagulation and condensation of fine particles and reduce the capture of Na and K by the alumina reactor tube via reduced formation of alkali aluminates, leading to increases in both yield and modal diameter of PM0.1. Water vapour could also enhance char fragmentation hence increase the yield of PM with aerodynamic diameter between 1 and 10 µm (i.e., PM1–10) during char combustion. For trace elements, during in situ volatiles combustion, volatile elements (As, Cr, Ni, Cu and Pb) are only presented in PM1 and water vapour alters the particle size distributions (PSDs) but has little effect on the yields of these trace elements. During char combustion, As, Cr, Cu and Ni are present in both PM1 and PM1–10 while the non-volatile Mn and Ti are only present in PM1–10. Increasing water vapour content increases the yields of As, Cr, Cu, Ni, Mn and Ti in PM1-10 due to enhanced char fragmentation. During char combustion, water vapour also originates less oxidising conditions locally for enhancing As release, promotes the generation of gaseous chromium oxyhydroxides and inhabits the production of NiCl2 (g), leading to increased yields of As and Cr and decreased yield of Ni in PM0.1.