The effect of draft tube on the performance of a spouted bed for rice husk combustion

Abstract

The production of paddy in Malaysia is around 2,2 million metric tones which rice husk represents 20% of the weight. Rice mills usually dispose the rice husk through open burning. With the cost increment of fossilized fuel, rice husk would have the potential to be a cheap source of renewable energy, In addition, rice husk ashes also contained a high content of silica, an important raw material for industries. Previous studies on the fluidized bed technology have shown its potential in waste disposal, and energy recovery from biomass. Spouted bed offers several advantages in comparison with the bubbling fluidized bed such as a better solid mixing and low-pressure drop to maintain the bed fluidization.With the low bulk density of rice husk (100kgm(-3)) compared to inert bed material and having a high content of volatile matter (64%), most of rice husk burn in the freeboard region. It is important to burn the husk in the bed to maintain the bed temperature. Mixing study conducted has shown the preferred sand size in the range of 600-800 um with the operating bed height of 1-1.15Dc. Air velocity of 2-3Ums was not feasible due to the nature of the husk. With conventional spouted bed, circulation of particles slowed down at the dense phase of the bed. With a draft tube, it was seen to improve circulation and burning. This paper reports the difference of rice husk combustion with and without the draft tube in a spouted bed combustor.