Online Repair of Refractory Brick Lining in the Calcining Zone of Lime Kilns

In lime kiln operation, refractory brick damage in the calcining zone can cause serious problems, including hot spots, flame leakage through the kiln shell, increased heat loss, and even the risk of large-scale lining collapse. When the kiln is approaching its maintenance period but cannot be shut down for a major overhaul, castable refractory can be used together with other repair methods to restore the damaged lining while the equipment remains in service.

Why Does Flame Leakage Occur in the Calcining Zone?

A shaft lime kiln normally contains several refractory and insulation layers. During operation, limestone passes through three main zones: preheating, calcining, and cooling. The calcining zone is generally the hottest section, with operating temperatures commonly around 1,150–1,200°C.

Several factors can accelerate refractory damage.

First, impurities in limestone may cause deposits or accretions to form on the kiln lining. When these deposits become large, they can fall with the material and pull refractory bricks away from the wall. The bonding mortar may also lose strength after long-term high-temperature service.

Second, the refractory lining is exposed to chemical attack. The high-temperature environment and alkaline components associated with lime production can gradually weaken the inner refractory layer.

Third, incorrect brick alignment or excessive deviation in verticality and kiln radius can create local stress. Over time, these weak areas may develop into missing bricks or gaps. Once the inner and outer refractory layers are damaged, high-temperature flames can escape through the damaged section and heat the steel shell.

Method 1: External Steel Box Repair

For relatively limited damaged areas, an external steel box can be installed around the affected section of the kiln shell.

The steel structure is fabricated in advance and welded securely to the outside of the kiln. New refractory bricks are then installed inside the box, with the joints filled using high-alumina refractory mortar.

After brick installation, an insulation layer is bonded to the outer surface. A curved steel plate is then installed and welded to the surrounding structure, compressing the insulation and creating a stable repair assembly.

This method has several advantages:

• Relatively fast installation

• Limited work inside the kiln

• Lower exposure to falling refractory materials

• Good structural support for localized damage

However, the additional external structure increases wind resistance. Therefore, when the repair area becomes very large, the effect on the overall mechanical performance of the kiln should be evaluated carefully.

Method 2: Castable Refractory Injection Repair

When the damaged area is large and the remaining refractory bricks have insufficient support, simply repairing the surface is not enough. In this situation, castable refractory can be used to fill the damaged cavity and reinforce the remaining lining.

The repair begins by installing steel guide frames outside the damaged area. Steel rods are inserted through the kiln shell and into the refractory layer. These rods provide temporary support and help prevent loose bricks, ash, and other debris from suddenly falling during cleaning.

Small openings are then made sequentially from the bottom of the damaged area. Loose refractory bricks and debris are carefully removed until stable brickwork is exposed.

Temporary steel formwork is installed after cleaning. The castable refractory is then introduced through the prepared openings. During placement, mechanical vibration is used to reduce internal voids and improve compactness.

After one section has gained sufficient support, the temporary steel rods can be removed and the next section repaired. The same procedure is repeated layer by layer until the entire damaged area has been stabilized.

For large damaged sections, this staged approach is particularly important. It prevents uncontrolled collapse while allowing the existing refractory lining above the repair area to remain supported.

How to Choose the Right Repair Method

The two methods are suitable for different site conditions.

The external steel box method is generally preferable for localized damage where fast repair and relatively simple construction are important. The castable refractory injection method is more suitable when the damaged area is extensive and additional structural reinforcement of the refractory lining is required.

In actual kiln maintenance, the repair method should be selected according to the damaged area, remaining brick condition, kiln structure, operating temperature, and available maintenance time.

A properly designed online repair can reduce unplanned shutdowns, prevent flame leakage, extend the service life of the refractory lining, and postpone a costly major overhaul.