Influence of Bed Height on the Quality of Rice Husk Ash in a Fluidised Bed Combustor

The turbulence during the combustion of rice husk in a fluidised bed is largely governed by the mixing behaviour in the inert sand bed, which in turn is governed by the bubble formation characteristics. Further, the retention time among the reactants (air and rice husk) and the heat source is also dependent on the turbulence in the bed. Thus, the purpose of this study was to investigate the effect of bed height (from 0.25 to 0.75 Dc (column diameter) on the quality of rice husk ash during the combustion of rice husk in a 210 mm I.D. fluidized bed combustor and a height of 2000 mm. The degree of rice husk burning in the fluidized bed could be deduced from the temperature of the combustor, as a higher temperature indicated that a higher portion of the rice husk was being burnt in that region. Moreover, the particle size of the resulting rice husk ash is also able to give indication of the degree of rice husk burning in the bed as the turbulence in the bed was known to break down the char skeleton of the rice husk, thereby, resulting in ash with finer size. From this study, the bed height of 0.5 Dc was found to give the lowest residual carbon content in the ash (1.9%) and the highest bed temperature (670 °C) among the other range of bed heights investigated. The problem of contamination of rice husk ash with sand increased as the bed height was increased, however the rice husk ash samples retained their amorphous structure at all bed heights