In 2003 QAL installed three 4,500 tpd Gas Suspension Calciners. In 2013, after an overhaul, Calciner 3 began producing up to 2% more particle breakdown that the other two units. In 2015 QAL analysed the problem from the perspective of the fundaments of what causes particle breakdown inside a calciner in order to isolate areas that have the potential to cause such a large difference between the units.
Data collected by QAL on Calciner 3’s hydrate, alumina and Baghouse dust tonnage, size and composition was compared to a model used to calculate dust recycle and particle attrition. The analysis concluded that the shutdown in 2013 had altered the solids flow pattern within one of the vessels and isolated the likely high solids loading areas to the centre three vessels of the unit.
CFD modelling was employed to confirm the cyclone efficiency and expected extent of particle impacts and then to redesign the vessel refractory lining in order to change the air and solids flow patterns. The initial modifications focused on improving the collection efficiency of two cyclones, reducing particle recycle.
The implemented changes significantly reduced the particle breakdown and brought Unit 3 in line with the other two units. Further CFD modelling has identified further modifications that will reduce or prevent the known problem of solids falling into, and restricting, the air duct to the flash furnace.