Zone duty and corrosion environment in steel-plant lime rotary kilns

A steel-plant lime rotary kiln supplies reactive calcium oxide to steelmaking. The hot zone runs hot, and the residence and tumbling of the burden also wear the lining. As in a cement kiln, the duty is organised by zone: the mouths at each end must take the shape of the opening and sudden heating and cooling, while the mid-span sits at high temperature in prolonged contact with fuel ash and calcium oxide.

The kiln mouths often take a corundum or steel-fibre-reinforced castable, so that a short span can absorb thermal shock and mechanical impact. Once the lining enters the hot span, the working layer becomes a high-RUL phosphate brick, or a corundum brick; further along the hot span, a corundum brick can also be laid together with a high-wear phosphate brick, so that corrosion resistance and wear resistance are shared in the same band. The rear mouth returns to a fibre-reinforced castable, to face erosion and temperature swing at the discharge.

If the mid-span uses an MgO working lining, the picture of attack matches what is seen in lime-kiln atmospheres: molten silicates enter along grain boundaries and pores, and silicate phases such as forsterite form; dissolution and cracking are more obvious with coal ash alone, and intrusion is often lighter when ash and quicklime are present together. The temperature and atmosphere of some intermediate spans depend on the kiln’s length-to-diameter ratio and on the burner arrangement, and have to be specified to the duty, rather than copied from the zoning of another kiln. Annular-shaft kilns and ordinary lime rotary kilns follow different thermal paths, and should be considered on their own.