Cement kilns · 2026-11-04

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.

Preheating and calcining run cooler than the burning zone, but they are long, and the shell area available for heat loss is large. In the steady state, the flux through the lining is given by Fourier’s law: the lower the effective thermal conductivity, the less heat reaches the shell for the same temperature difference.

q = - λ \frac{d T}{d x}

Equation (1). One-dimensional Fourier’s law. Lowering the effective conductivity λ of the working lining is a direct way to cut the flux to the shell.

Figure 1. Heat flow from the hot face through the working lining to the shell.

Lightweight does not have to mean weaker. Replacing part of the dense aggregate with a light aggregate such as spinel hollow spheres can lower bulk density and conductivity while cold strength and high-temperature modulus of rupture are maintained, or even raised; resistance to cement-clinker attack need not suffer. The pores must be closed inside the aggregate, not linked as infiltration paths in the matrix. A brick with a lightweight composite layer puts the insulating layer and the working face in the same unit: the hot face stays dense and wear-resistant, and the shell side takes the insulation.

The burden is still moving in the preheating zone, and alkali vapor has not gone away, so a lightweight lining has to be weighed together with spalling and thermal-shock resistance. Once the conductivity is down, the shell temperature follows, and both the heat consumption of the kiln and the working environment around it improve.

Back to Industry Insights

Related insights

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.