2014 Volume 54 Issue 12 Pages 2737-2745
The generator gas of melter gasifier inevitably carries a lot of dust, which would be transported to the freeboard for recycling, as a result of the existence of the fluidized bed. The recycling dust, with an attractive concentration of C and Fe, is considered as a useful secondary material, thus it is important to investigate the inherent characteristics and behavior of recycling dust in the freeboard. In the present work, the recycling dust characteristics are investigated through the granulometry, chemical, mineralogical and micro analysis. The recycling dust has an irregular shape and an uneven granulometric distribution with the following primary minerals: Fe, FeO, SiO2, 2CaO·SiO2 and 2CaO·Al2O3·SiO2. Furthermore, a three-dimensional mathematical model at steady state is developed to describe the recycling dust combustion and the freeboard temperature distribution, which significantly influences the recycling dust behavior. The region of high temperature above 3000 K can be observed in front of DB due to the combustion of C in the recycling dust, with a combustion ratio of almost 100%. Based on the above analysis, the recycling dust behavior is complex. Fe and FeO in the recycling dust may be oxidized and finally smelts into liquid iron, while other minerals smelt into molten slag. It is worth noting that the phenomena of circulation and accumulation of alkali metals, ZnO and S could occur, despite that most of them are discharged out of the melter gasifier through the generator gas and molten slag.