Physical Modelling of Thermal Stratification, Bottom Build-Up and Mixing in Submerged ARC Electric Smelting

A one-tenth scale model of a portion of a submerged arc electric furnance for nickel smelting is constructed. By using a 52 wt% aqueous calcium solution to simulate the matte, solid calcium chloride hydrates are precipitated on the bottom of the furnace in an analogous manner to metallic precipitation from a matte phase. Mineral oil is used to simulate the slag. Reasonable similarity compared to the full scale furnace is achieved in the Prandtl, Grashof and Froude groups for both the calcium chloride solution and the oil phase. Furthermore, electric resistance heating from the top electrodes and cooling from a bottom water jacket are arranged to simulate conductive heat transfer in the full-scale furnace. It is found that with the imposed heat flux, the oil and calcium chloride solutions behave as if they are stagnant. Gas injection significantly reduces the thickness of the precipitate layer, and reduces the stratification in the oil and calcium chloride. Thermal mixing times are found to be considerably longer with electrical heating because the thermal stratification opposes mixing. Consequently, previous work on mixing in isothermal water models cannot be applied to top-heated vessels, such as electric and reverbatory furnaces.