Trace Elements Release and Particulate Matter Emission during the Combustion of Char and Volatiles from In Situ Biosolid Fast Pyrolysis

This paper presents a systematic study on the emission of trace elements (e.g., As, Cu, Cr, Ni, V, Co, Cd, and Pb) during the combustion of char, volatiles, and biosolid at 1300 °C using a two-stage pyrolysis/combustion reactor system. Over 50% As, Cd, and Pb in biosolid are released with volatiles during fast pyrolysis at 800–1000 °C, while other elements are mostly retained in char. During biosolid combustion, PM 10 consists of mainly major elements and the contribution of trace elements is <0.5 wt %. Particulate matter (PM) produced from the combustion of volatiles produced in situ from biosolid fast pyrolysis at 800–1000 °C is dominantly PM 1, contains only volatile elements (As, Cd, and Pb), and has a unimodal distribution with a fine mode diameter of 0.043 μm. Char combustion produces both PM 1 and PM 1–10, with the PM having a bimodal distribution (a fine mode at 0.043 μm and a course mode at 6.8 μm). It is also found that As, Cd, and Pb only contribute to PM 1 emission even during char combustion. While Ni, Co, Cu, and part of V are responsible for PM 1–10 emission, most Cr and some V presented in char also contribute to PM 1 emission during char combustion. Significant differences are also observed in the PM between direct biosolid combustion and the sum of PM from char and volatile combustion. The results suggest that direct biosolid combustion may have produced substantially different char and volatiles, which may have experienced significant interactions during combustion.