The middle biomass solids demonstrated slow heating rate compared to upper biomass solids at 2.4LPM (Fig. 2, Run 6), whereas increase in N2 flow rate to 6LPM and 9.6LPM increases the middle biomass solids heating rate (Fig. 2, Run 7–12 and 13). This suggests that the heat carried with N2 gas from surface carbon solids can contribute heat to the inside carbon solids, which can then be transmitted to the middle biomass solids. Interesting, the upper and middle biomass solids temperature rises at the same heating rate and reached nearly complete uniformity of process temperature at 6LPM (Fig. 2, Run 7–12). This uniform heating behavior of biomass solids demonstrates that heat generated by the carbon and biomass solids, and heat carried with N2 gas from the reaction zone reached equilibrium. This important finding suggests that the uniform process heating can be achieved by controlling N2 flow rate.
The increase in N2 flow rate from 4LPM to 8LPM demonstrated no significant effects on heating rate and final pyrolysis temperature at 300–600 W and 35 wt% carbon loading. However, the heating rate and final pyrolysis temperature reached in biomass solids are influenced by N2 flow rate at 300–600 W with 75 wt% carbon loading. At 300 W and 75 wt% loading, increase in N2 flow rate decreased the heating rate and final biomass pyrolysis temperature. The TUBL and TMBL reached final pyrolysis temperature of 505 °C and 474 °C at 4LPM, which reduces to 389 °C and 412 °C at 8LPM (Fig. 3, Run 15 and 16). However, TUBL and TMBL maintain 492 °C and 622 °C at 4LPM, which changes to 687 °C and 505 °C at 8LPM (Fig. 3, Run 17 and 18) using 600 W and 75 wt% loading, respectively.