A lining must carry mechanical load, chemical attack and temperature change together. Zone design, thermal-shock parameters, heat flow and slag infiltration decide which material belongs in each band.
Industry Insights
The materials science of kiln linings — zones, thermal shock, heat flow and corrosion — in cement, lime, glass and non-ferrous furnaces.
Cement kilns
Zone linings in cement rotary kilns: mechanical, chemical and thermal loads
Temperature, coating and gas chemistry differ from the burning zone to the transition and preheating zones. There is no universal brick for every position.
Cement kilns
Corundum linings in the high-temperature and transition zones
Corundum linings offer high-temperature strength, thermal-shock and wear resistance, and relatively low conductivity. They address spalling of basic bricks on stop/start, and oxidation cracking in the transition zone and cooler.
Cement kilns
Magnesia-iron spinel and coating in the burning zone
Well-developed iron-alumina spinel gives the brick flexibility and coating adhesion, so the burning zone can take the complex stresses of a rotary kiln and keep the hot face under a coating.
Cement kilns
Magnesia-alumina spinel in the upper transition zone: thermal shock and alkali attack
The upper transition zone has an unstable coating, large temperature swings, and often alkali and sulphur dioxide. The thermal-shock stability and chemical resistance of magnesia-alumina spinel make it a characteristic material for this band.
Cement kilns
Alkali-vapor attack and spalling of silica-mullite bricks in the transition zone
Alkali vapor and liquid enter silica-mullite bricks through the pores; calcium and potassium dissolve alumina and silica. On cooling, gehlenite, potassium feldspar and potassium chloride precipitate, and expansion mismatch cracks and spalls the altered layer.
Cement kilns
Monolithic linings at the kiln mouth, hood, tertiary air duct and cooler
These positions see sharp thermal shock and strong erosion, and some are prone to build-up. Corundum–mullite, low-cement high-alumina, steel-fibre-reinforced and anti-skinning castables each answer a different hot-face condition.
Cement kilns
Lightweight, low-conductivity linings in the preheating zone
The preheating zone is long, cooler than the burning zone, and yet a substantial source of shell heat loss. Lightweight aggregates or a composite layer lower the effective conductivity, so heat flow to the shell can fall without giving up strength and thermal-shock resistance.
Cement kilns
Phosphate-bonded alumina linings in preheating and calcining
Phosphate-bonded high-alumina–mullite bricks have high strength, low porosity and good thermal shock, and suit preheating and calcining — cooler than the burning zone, yet still subject to burden movement and alkali.
Cement kilns
Stress and masonry in the lining of a large clinker rotary kiln
A rotary-kiln lining is not only a choice of brick. It is the art of keeping the brick ring intact under alternating mechanical stress and thermal expansion. Parallel, cross and rotary masonry change the path along which stress travels around the ring and along the axis.
Lime kilns
Lime-kiln linings under thermal load and chemical attack
The hot face of a lime kiln meets high temperature, fuel ash and calcium oxide at once. Molten silicates infiltrate MgO brick along grain boundaries and pores; the fuel, and whether quicklime is present, change the manner of attack.
Lime kilns
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.
Lime kilns
Zone duty and corrosion environment in steel-plant lime rotary kilns
The mouth, the calcining span and the rear mouth of a steel-plant lime rotary kiln face, respectively, thermal shock in the castable, ash attack on an MgO or high-alumina working lining, and erosion at the discharge. Whether fuel ash and quicklime are present together changes how far slag can infiltrate.
Non-ferrous metallurgy
Slag corrosion and thermal shock in the reaction zone of zinc oxide rotary kilns
The reaction zone meets molten slag, gas erosion and temperature swings at once. The lining has to balance resistance to slag ingress with toughness, and the arrangement changes with the raw materials and the slag.
Non-ferrous metallurgy
Toughness, spalling and erosion in slag-resistant linings
The reaction zone of a non-ferrous furnace must resist slag ingress, thermal-shock spalling, and erosion by gas and burden at the same time. The damage parameter R‴ is a reminder that how much strength remains after cracking depends on whether the brick is tough enough.
Non-ferrous metallurgy
Magnesia-chrome and magnesia-alumina-chrome spinel in non-ferrous furnaces
From sintered and direct-bonded to fused rebonded, magnesia-chrome grades follow the severity of temperature and slag attack. Magnesia-alumina-chrome spinel resists sulphur dioxide, ferrous oxide and lead oxide, while keeping a moderate density and spalling resistance.
Glass furnaces
Material systems for glass-furnace linings
The regenerator crown, the checkerwork and the other positions in a glass furnace do not see the same flue gas, carryover or fuel. Chrome-corundum, magnesia-zirconia, magnesia, mullite, zircon-mullite and magnesia-chrome are material systems divided along those conditions.
Glass furnaces
Chrome-corundum at the regenerator crown under petroleum-coke firing
Petroleum coke brings vanadium and sulphur into the flue gas. Low-melting silicates and vanadates can form between MgO crystals, and the volume change on melting and solidification cracks and spalls the checkers. Chrome-corundum takes this crown duty with resistance to V₂O₅ and SO₂, and with excellent thermal shock.
Glass furnaces
Magnesia and magnesia-zirconia in regenerators: fuel and flue gas
Magnesia brick stores heat in periclase and resists erosion, and is the foundation of the regenerator. Magnesia-zirconia, with zircon added, gains thermal-shock resistance and resistance to sulphur dioxide, and suits the crown of a large float-glass furnace that is not fired with petroleum coke.
Glass furnaces
Mullite and zircon-mullite in glass furnaces
Low-porosity mullite offers excellent thermal shock, high strength and resistance to erosion and corrosion, and is used in glass furnaces as well as in lime and non-ferrous kilns. Zircon-mullite, with corundum, mullite and ZrO₂ as its main phases, holds high-temperature, thermal-shock and corrosion resistance in the same structure.