Agglomeration Characteristics of Alumina Sand-Rice Husk Ash Mixtures at Elevated Temperatures

Abstract

The agglomeration characteristics of alumina sand-rice husk ash mixtures were investigated at various levels of temperature (750, 850, 900, 950, and 1000°C) and ash content (0·0, 5·0, 10·0, 15·0, 20·0, and 25·0%) using light microscopy, scanning electron microscopy, and energy dispersive X-ray analysis techniques. The scanning electron microscopy and X-ray analysis were also used for the identification of the rice husk and elemental makeup of rice husk ash. There was no indication of melting at all the levels of temperature and ash content studied. However, weak and friable agglomerates were observed at 950 and 1000°C. The structure of the particles was not altered, and bonding by surface diffusion may be a possible mechanism for the formation of the weak, friable agglomerates. Physical entrapment by minute whiskers at the surface of rice husk ash may also be a factor. The use of alumina sand as an inert fluidizable material in fluidized bed systems will prevent the formation of these easily breakable structures because of particle friction caused by mixing and fluidization. Thus these friable structures are not expected to cause any problem during the normal operation of fluidized bed gasification systems that are normally operated at temperatures in the range of 700-800°C.