Abstract
Slow pyrolysis experiments were performed on Waterberg 1.4 coal using a fixed bed reactor with a bed depth range of 25–250 mm to determine the effect of bed depth on secondary reactions. The final pyrolysis temperature was also varied together with bed depth according to a factorial design. Results show that bed depth has a significant influence on the yield of volatiles comprising hydrogen, carbon monoxide, methane, carbon dioxide and tar. Further, the bed depth effect varies with each volatile component and is dependent on the final pyrolysis temperature. At 1000 °C, all volatiles displayed a decrease in yield with increase in bed depth with the exception of tar, which experienced a corresponding increase in yield with increase in bed depth. Consumption and production of volatiles with increasing bed depth occurred at 800 °C to varying extents depending on the volatile component. At 600 °C, the influence of bed depth was minimal. Fixed carbon yields displayed an optimum yield at 800 °C. These observations are explained in terms of the enhancement of secondary reactions of the nascent volatiles in the void spaces after release from the coal particles.