Study On Ring-forming Of Calculating Zn-bearing Dust In Rotary Kiln

At present,metallurgical zinc-containing solid waste,such as dry ash,electric arc furnace ash,zinc-containing sludge,etc.is mainly processed by rotary kiln process.Rotary kiln process has the property of large processing capacity and high efficiency.But there is the shortcomings ring-forming,which causes uneven material layer,systematic resistance of rotary kiln increasing,and kiln effective cross-sectional area reducing.All these seriously affect the kiln capacity,and shorten service life of rotary kiln lining.However,there are few reports on the formation mechanism of the ring in the process of zinc-containing dust roasting in rotary kiln.This paper focuses on the problem of ring formation in rotary kiln in the process of zinc dust treating.the characteristics of raw materials,such as the chemical composition of raw materials and the soft melting performance were studied.The mineral phases and chemical composition of the ring from rotary kiln were analyzed by XRF,SEM and EDS.The consolidation strength of the ring was determined by the compression device.The melting temperature of the ring was measured by ash melting point meter.On this basis,the causes and influencing factors of the ring formation in rotary kiln during the treatment of Zn-bearing dust in rotary kiln are analyzed and summarized,and the main measures to suppress the ring formation are proposed.The results show that the ring consists of iron and FeOt,and has relative high contents of CaO,SiO2,Al2O3.The internal layer is mainly composed of iron wustite and calciclase,mainly caused by solid phase sintering,complemented liquid phase bonding.The middle layer contains much liquid iron,and some iron wustite,the melilite and the spinel.The outer layer is mainly composed of liquid phase,iron wustite and calcium silicate.It is mainly caused by liquid phase bonding.The bond phase is predominantly liquid metallic iron and silicate phase with low melting point.Based on the obove results,the following formation mechnism of the ring was proposed,the accumulation of coal ash and the various oxides from the material form a low melting point compounds in the kiln,in turn the liquid and solid particle form high viscosity fluids adhereing to the wall of rotary kiln.