Solar-Thermal Pyrolysis of Mallee Wood at High Temperatures

This study reports solar-thermal pyrolysis of mallee wood powders driven by direct concentrated solar radiations at different temperatures (1540, 1740, and 1930 °C), heating rates (320, 800, and 3200 °C/min), and holding times (0 and 5 min). Under such severe pyrolysis conditions, solar-thermal pyrolysis of mallee wood produces predominantly volatiles (≥90 wt %), with very low char yields (≤10 wt %), as reported on a dry basis. Majorities of inherent alkali and alkaline earth metallic (AAEM) species are also released into the gaseous phase. The severe pyrolysis conditions also lead to the low reactivity of char products as a result of not only the char carbon structure becoming ordered and graphitized (as evidenced by the Raman data) but also significant losses of catalytic AAEM species in the char. For example, during the solar-thermal pyrolysis of mallee wood at 1930 °C, 800 °C min–1, and 5 min holding time, the char yield is only ∼5 wt %, the retentions of Na and Mg are ∼1%, the retentions of K and Ca are only 13 and 35%, respectively, and the char is less reactive. Therefore, despite the low char yield, char conversion is still a critical consideration in the design and operations of solar-thermal reactors under these conditions because the char is very inert.