JSC “Chelyabinsk Zinc Plant”, Chelyabinsk, Russia:

P. A. Kozlov, Head of Engineering Center, pak@zinc.ru

Formation of skulls is one of main disadvantages of the processes, carried out in rotary kilns (productivity decrease, process chemistry violation). Analysis of skull formation process reveals the main causes of their growth:
– chemical composition of charge mixture (containing slagforming compounds — CaO, SiO₂, FeO);
– kiln rotation speed;
– feed material quantity;
– temperature conditions;
– grain size composition of charge mixture.
Setting operating conditions of rotary kiln in accordance with charge material composition makes possible to avoid skull formation. At the same time it is necessary to make the skull-formation in kiln as a means of the furnace refractory protection from chemical and thermal “corrosion”. It is possible to solve the problem of the furnace operation without any skulls and refractory time facing more than 12 months by rotary kiln operating in variable silica ratio mode:
– Period 1, silicate unit (C/S) — 0,4–0,6 (skull is not formed).Duration is 2–4 days. Skull is removed if the furnace operation is more than 4 days;
– Period 2, silicate unit (C/S) — 1,4–1,6 (skull is formed). Duration is 1 day. Skull can be increased if the furnace operation is more than a day.
Provision of operation mode requires the variable silicate module:
– installation of thermal imager, controlling the furnace body temperature, which allows to estimate the skull thickness;
– repeating the furnace operation with the silicate module 1,4–1,6.

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