Construction Process of Rotary Kiln Lining

Large rotary kilns are mostly lined with refractory bricks. The main methods for lining construction are as follows.

Template Method

The template method is mostly suitable for circumferential continuous joint masonry. See the diagram below:

Figure: Schematic diagram of rotary kiln lining construction using the template method
(circumferential continuous joint lining)

The lining is constructed from the lowest point of the cross-section in two circumferential directions. When the height exceeds the kiln's centerline, a mold is set up, and the lining is closed from both directions towards the highest point of the cross-section, with support provided as construction progresses until the locking is complete.

The mold shown in the diagram is a relatively simple one, entirely manual, resulting in low construction efficiency. To improve efficiency, many companies have adopted pneumatic support rings. The equipment has two rows of pneumatic support devices, significantly improving construction efficiency.

Because the template method requires circumferential continuous joint construction, its applicability is limited. It cannot be used in rotary kiln lining construction requiring staggered joint construction.

Objectively speaking, the service life of staggered joint rotary kiln linings is superior to that of circumferential continuous joint rotary kiln linings. In the middle and later stages of the lining's service life, a V-shaped phenomenon can be clearly observed at the circumferential joints. This is mainly due to two reasons:

① The circumferential erosion caused by material sliding within the kiln is severe, and the circumferential continuous joints provide favorable conditions for this erosion, leading to early damage to the lining.

② Due to significant temperature differences across different zones in a rotary kiln, the temperature variations within the kiln's metal shell are substantial. Taking a rotary kiln with equal diameter as an example, although the inner diameter of the shell is uniform during manufacturing, temperature differences within the metal shell during use result in varying degrees of thermal expansion. The inner diameter of the zone with higher temperatures is larger, while the inner diameter of the zone with lower temperatures is smaller. As the lining rolls within the metal shell, differences in angular velocity exist between the lining rings. This causes rubbing of the refractory bricks between the rings, leading to premature damage to the refractory bricks at the ring joints.

In contrast, staggered-joint rotary kiln linings do not suffer from the aforementioned drawbacks. Staggered-joint rotary kiln linings offer better overall integrity and a longer service life.

Support Method

When constructing the rotary kiln lining using the support method, start from the lowest point of the cross-section and build layer by layer towards both sides. When more than half of the cross-section is reached, install supports. Then, continue building from the lowest point to the highest point, building layer by layer. When more than one-quarter of the cross-section is reached, install supports a second time, and then rotate the kiln a second time. Continue building layer by layer from the lowest point to the highest point, and when approaching the locking position, rotate the kiln a third time to begin locking, gradually completing the lining construction.

The support method for constructing the rotary kiln lining can be used for either continuous circumferential joint construction or staggered joint construction. The advantage of this process is that it uses simple tools and is easy to operate. The disadvantage is that the support installation causes elastic deformation of the kiln shell. When the supports are removed, the strong compressive stress within the lining during the shell's return to its original shape causes premature damage to the brick masonry lining, shortening its service life.

Design of a Distributed Support Method Mold

Early rotary kilns had relatively small diameters, mostly no more than two meters, and their linings were primarily constructed using a distributed support method. When more than half of the lining was in place, a simple support rod was used to secure each brick in place to prevent slippage. After the interlocking was completed, all support rods were removed. This process allows for both continuous and staggered lining construction of rotary kilns. However, this method is too inefficient and time-consuming for larger diameter rotary kilns, making it unsuitable. An alumina company designed and manufactured a platform and support system. The platform components were constructed using a modular approach, facilitating transportation, assembly, and disassembly. All components were made of wood, making them lightweight and easy to transport within the kiln.

Template-based staggered-joint construction of rotary kiln lining

The lining construction begins at the bottom of the lower half. A template is installed when the lining reaches the level opening.

The template consists of several parts, including crossbeams, through beams, and supporting arched plates. The crossbeams and through beams are on the same plane, and their height should be 150mm-200mm below the kiln's centerline. Assembly of the crossbeams and through beams must be quick and convenient for on-site assembly inside the kiln. The supporting arched plates are made of assembled wooden planks, with a radius 25mm-30mm smaller than the inner radius of the lining.

During use, the supporting arched plates are fixed to the through beams in a suitable manner. To improve the lining construction speed, the working platform should be at least 6 meters long. A supporting arched plate must be installed for each brick to ensure proper support for each brick laid. After the template is securely installed, the upper half of the lining is laid. After each brick is properly laid, it must be firmly secured with wooden wedges to ensure the stability and strength of the refractory bricks. The masonry sequence is upwards from both sides, gradually approaching the top.

When reaching the top locking position, a small jack is placed within the pre-reserved space at the locking point, slowly pressing down on the refractory bricks at both ends. After the lining is tightened, the jack is removed, and then, according to the size of the gap at the locking point, the lining at that location is completed using modular locking bricks. The supporting arc plate can only be removed after the refractory mortar has initially set.

When constructing the upper part of the rotary kiln lining using the above process, the bonding and setting times of the refractory mortar must be appropriate to ensure smooth construction according to schedule. If the bonding time of the refractory mortar is too long, the refractory mortar in the brick joints will flow due to its own weight, causing deformation, loosening, or even collapse of the lining after the supporting arc plate is removed.