Nano-Silica Production by Rice Husk Combustion in a 0.7 MW Double-Circulating Fluidized Bed after Acid Pretreatment

Abstract

Rice husk is an organic silicon source for amorphous nano-silica particles. This paper reports the experimental study on the industrial production of nano-silica by rice husk combustion in a specially-designed 0.7 MW double-circulating fluidized bed (DCFB) based on acid pretreatment process. The physicochemical properties of RHA were characterized by various testing instruments. Results showed that acid pretreatment removed a large amount of metal impurities in the rice husk and thus inhibited the formation of crystalline silica or the agglomeration during the fluidized bed combustion process. The combustion efficiencies were as high as 99.5%. The obtained RHA comprised white fine particles and exhibited an amorphous structure, but factors such as collection point and acid type had certain influences on the quality of RHA. The highest SiO2 purity was greater than 98.6 wt.%, the lowest content of unburned carbon was 0.2 wt.%, the specific surface area reached 178 m2/g, and the pore size reached 5 nm. The circulating fluidized bed combustion of rice husk based on acid pretreatment can prepare nano-silica while providing heat for industrial processes, which is a highly energy-rich process.