Lime kilns · 2026-10-31
Thermal duty and material selection in twin-shaft lime kilns
The two shafts alternate calcining and preheating, and the gas reverses periodically. The preheating, calcining and cooling zones, and the arches and channels, each see a different temperature swing and burden movement.
A parallel-flow regenerative twin-shaft kiln (often called a Maerz kiln) works the two shafts in turn: one is calcining while the other is preheated by gas from its neighbour, and then the flow is reversed. For the lining, that means a given position is heated and cooled periodically, rather than sitting at one temperature for a long campaign.
The preheating and cooling zones run cooler than the calcining zone, but burden movement and wear are more obvious, and thermal shock returns with every reversal. A wear-resistant, thermally shock-resistant phosphate-bonded high-alumina brick is a natural working lining for those two zones. The calcining zone is the hottest; calcium carbonate decomposes here, and the brick face meets both high temperature and calcium oxide. A high-strength anti-spalling brick, or a phosphate brick of higher refractoriness under load, is a usual choice. The supporting columns stand at the meeting of load-bearing and high temperature, and often take the same family of materials as the calcining zone.
The supporting arches and the ring channel also carry structural load and gas erosion. Corundum-mullite, magnesia-alumina spinel, and high-alumina, mullite or magnesia bricks appear in these positions according to temperature and atmosphere. The temperature field at the distributor and at other connections depends on the particular drawing, and has to be read in the same thermal picture as the main zones.