Janewit Wannapeera, Nakorn Worasuwannarak, and Suneerat Pipatmanomai

pp. 393 - 404

Abstract

Fast pyrolysis of rice husk, rice straw and corncob were investigated in a newly constructed drop-tube/fixed-bed reactor, which enables pyrolysis experiments under conditions closely simulating those occurring in commercial gasifiers such as fluidised-bed gasifiers. Biomass samples were pyrolysed with a fast heating rate (i.e. > 1,000°C s-1), up to 850°C and holding times ranging from 1 to 10,800 seconds. Within 1 second after the biomass was injected into the reactor, considerable weight loss occurred instantaneously, leaving only a small amount of char, i.e. ~10-30 %. For all three samples, the weight loss continued throughout the range of holding times used but at an extremely slow rate, i.e. 1.3 % hr^-1. The weight loss rates observed for the three biomass samples were affected by the proportion of the biomass chemical components as well as the metal species contents. Corncob, which had the lowest lignin content but highest cellulose content, had the highest pyrolysis weight loss rate. On the other hand, rice husk containing a relatively high lignin content, had the lowest
pyrolysis rate. The metal species (Na, K, Ca and Mg) were found to increase devolatilisation yield depending on their contents in biomass. The influence of the metal species was the most pronounced for rice straw, having the highest total metal species content. As the pyrolysis progressed, each biomass exhibited different char characteristics. Scanning electron
microscopy (SEM) pictures clearly showed the individual changes in geometry for all biomass-derived chars as well as their decrease in combustion reactivities. The gas formation profiles for all three biomass samples showed almost the same trend, with CO contributed by cellulose decomposition as the major gas product.