THE INFLUENCE OF BED DEPTH ON SECONDARY REACTIONS DURING SLOW PYROLYSIS OF COAL

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 t he effect of bed depth on secondary reactions. The final pyrolysis tem perature was also varied together with bed depth according to a factor ial 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 eac h volatile component and is dependent on the final pyrolysis temperatu re. At 1000 degrees C, all volatiles displayed a decrease in yield wit h increase in bed depth with the exception of tar, which experienced a corresponding increase in yield with increase in bed depth. Consumpti on and production of volatiles with increasing bed depth occurred at 8 00 degrees C to varying extents depending on the volatile component. A t 600 degrees C, the influence of bed depth was minimal. Fixed carbon yields displayed an optimum yield at 800 degrees C. These observations are explained in terms of the enhancement of secondary reactions of t he nascent volatiles in the void spaces after release from the coal pa rticles.