Coating On Refractory Brick Lining

Though refractory brick lining is installed with a purpose to protect the metallic shell of the kiln but often it is practised to have a good layer of coating on the brick lining. A majority of experts attribute it to the skills of a kiln operator.

A good protective coating on the refractory lining in the burning zone is always preferred to prolong the life of a refractory. Replacement of refractory bricks costs a large amount of money, loss in production while the kiln is down for lining replacement. In short replacement of refractory is an undesirable condition in any kiln.

Although refractories in the burning zone have to be replaced from time to time, a kiln operator has the capacity to increase or decrease the life of the lining by his ability to control the coating in the burning zone.

TYPES OF COATINGS

Coating is a mass of clinker or dust particles that sticks to the wall of the kiln, having changed from a liquid or semi liquid to a solidified state. The solidified particles stick to the surface of the coating (CS in Fig. 1), or the refractory surface (BS) when no coating exists, as long as the temperature of the surface of the coating is below the solidifying temperature of the particles. Coating continues to form until its surface reaches this solidifying temperature. When the kiln operates under such condition at equilibrium, the coating will maintain itself.

There is a temperature drop between the coating surface (CS) and the kiln shell (KS), the heat flowing in the direction indicated by the arrow (Fig. 1) (Heat always travels from a place or body of high temperature to a place of body of lower temperature). This heat transfer is governed to a great extent by the conductivity of the refractory and the coating. The better the conductivity of the refractory, the better the chance of coating formation, explained by the fact that the more heat that travels in the direction of the arrow. A kiln feed with a high liquid content at clinkering temperatures is more effective in coating formation than a feed low in liquid.