Investigation of the Waelz oxide calcination process in tubular rotary kilns

Abstract

At the Chelyabinsk Zinc Plant of the Ural Mining and Metallurgical Company, oxidized zinc and lead-containing raw materials are processed in Waelz kilns. Waelz oxides, containing chlorine and fluorine, are calcined in tubular rotary kilns. The results of studies on the halide removal are provided

– in the calcination process, chlorine is removed mainly in the form of zinc and lead chlorides, while in calcined oxide, chlorine remains in multicomponent difficult-to-digest substances;

– at an increase in the specific volume of exhaust gases from 300 to 820 m³/kg of chlorine, charged into the kiln, the residual chlorine content in the calcined Waelz oxide decreases from 5.2 to 0.05%;

– at the pilot kiln (length of 1.9 m, diameter of 0.2 m), tests were carried out to determine the specific volumes of exhaust gases and the gas flow velocity.

The following results were established

– within 1 h from the beginning of the experiment, the reaction proceeds in the diffusion-kinetic mode;

– when the velocity of gases at the outlet of the kiln decreases to 3 m/s, the sublimation occurs in the forced diffusion mode. This correlates with the data on the velocity of gases in a real industrial kiln;

– the capacity of the industrial kiln (L = 41 m, D = 2.5 m) is 8.0 t/h of waelz oxide using the calcined product (chlorine content of 0.05%) with a volume of kiln exhaust gases of 12–18 thous. Nm³/h at a temperature of 500–550 °C and the size of the charged waelz oxide pellets of 6–10 mm. When the pellet size is reduced to 2–4 mm, the kiln capacity increases from 8 to 10 t/h, while the chlorine content decreases from 0.05 to 0.04%.

On the basis of pilot tests, a cyclone cooler, capable of cooling 18,000–19,000 Nm³/h of gases with a temperature of 600 °C, was developed for the kiln.