With the maturity of calcination technology, rotary kilns are developing better and better in the field of calcination. However, many customers do not have a thorough understanding of how to use rotary kilns. Today, we will summarize and discuss the determination and control of the horizontal displacement and vertical settlement of rotary kilns.

Determination and Control Method of Horizontal Displacement Control Parameters

Determination of Horizontal Displacement Control Parameters: The rotary kiln is the main equipment for clinker calcination in cement plants. Its specifications are indicated by the inner diameter and length of the cylinder, which ranges from 30 to 180 meters in length and 1.8 to 6 meters in diameter. It floats on 2 to 6 pairs of support rollers, the number of which depends on the kiln’s diameter and length. The kiln load is transferred to the foundation through the support roller bases. Depending on the production process, wet-process kilns generally require 6 foundations, while precalciner kilns only need 2-3 foundations. Their structural forms are generally large-block concrete foundations and reinforced concrete wall foundations. To ensure the normal and effective operation of the rotary kiln, a safe and reliable foundation is essential. The rotary kiln is driven by a motor through a reducer and large and small gears, with a very low rotational speed, generally around 3 rpm. The rotary kiln body has an inclination of 3% to 5%. Material enters from the high-end kiln tail, while fuel is injected from the low-end kiln head, creating convection between the material and high-temperature flue gas. Due to the high temperature in the calcination zone of the kiln, the kiln body deforms, sometimes causing a support roller to detach, resulting in uneven stress on the foundation.

To ensure the safe and normal operation of the rotary kiln, it is necessary to control not only the bearing capacity of the foundation and subgrade but also the deformation of the entire foundation. However, there is a lack of parameters for deformation control. Neither design specifications nor design manuals, nor even equipment manufacturers, provide clear requirements, especially regarding the stiffness of the foundation itself. Designers typically refer to conventional engineering examples, assume a cross-section, and then perform strength calculations, often neglecting deformation calculations. If the designed foundation is similar to the engineering example, there are generally no problems. However, if the designed foundation differs significantly from the engineering example, the designer must recalculate everything. This necessitates a clearly defined control parameter, which currently lacks one. For large-block foundations, the stiffness is already high, and displacement is generally small, so deformation is not a major issue. For wall-type foundations, designers generally calculate based on reinforced concrete closed frames, and the deformation control parameter only refers to the requirements for frame structures, namely, the horizontal displacement of the foundation top surface should not exceed 1/550 of the foundation height. For example, when the foundation height is 5000-7000 mm, the horizontal displacement of the top surface of the foundation should not exceed 9-13 mm. When the foundation height is 17500 mm, the horizontal displacement of the top surface of the foundation should not exceed 32 mm. This is not a problem for general reinforced concrete frame structures. However, it is a problem that cannot be ignored for the foundation of a rotary kiln that is subjected to horizontal forces for a long time.

The rotary kiln’s shell floats on support rollers, which are fixed to the foundation. The reducer driving the rotary kiln is also fixed to the foundation, and the reducer and the kiln shell are connected by gear transmission. When the rotary kiln starts up, the instantaneous horizontal force exerted by the reducer on the kiln shell is large, forcing the kiln shell floating on the support rollers to move in the direction of the horizontal force. As the amount of movement gradually increases, the horizontal force exerted by the reducer on the kiln gradually decreases, and the kiln shell returns to its original position. At this point, the horizontal force exerted by the reducer on the kiln increases again. This process repeats, generating a constantly changing horizontal force on the top surface of the foundation, resulting in varying displacements and causing the rotary kiln foundation to sway. When the foundation rigidity is high, the horizontal displacement is small and the swaying is barely noticeable; conversely, this swaying can be very uncomfortable and sometimes even affect the normal operation of the equipment. Therefore, determining a reasonable and feasible horizontal displacement control parameter based on the characteristics of the rotary kiln’s operating process is crucial. Especially in recent years, with some projects featuring rotary kiln foundations reaching heights of 16-18 meters, this parameter has become even more crucial. However, determining this parameter is not easy. Setting it too small inevitably increases investment and is technically impractical; setting it too large will certainly affect the safe operation of the kiln. Several years ago, we conducted design follow-ups on dozens of completed projects and found that in projects where the calculated horizontal displacement of the foundation top did not exceed 3mm, the equipment operated normally, and the foundation did not exhibit significant shaking. We adopted 3mm as the control parameter for the horizontal displacement of the rotary kiln foundation. Currently, we have designed dozens of production lines according to this parameter, including the UAE uCClO 5000t/d clinker production line, which is now operating normally.

Horizontal Displacement Control Methods: To control the foundation top displacement to within 3mm, we must ensure the foundation has sufficient rigidity. Specific methods include: using large-block foundations; for wall-type foundations, increasing the wall thickness or directly adding transverse shear walls—all very effective methods.

Determination of Rotary Kiln Settlement Differential Control Parameters

The rotary kiln settlement differential refers to the difference in settlement between the rotary kiln foundation and the kiln head and tail. This parameter directly affects the normal operation of the rotary kiln. A safety accident occurred where excessive settlement differential between the rotary kiln foundation and the kiln tail led to damage to the sealing ring and smoke chamber. The determination of this parameter was based on two factors: firstly, our follow-up surveys of some cement manufacturers, and secondly, our exchanges with large international cement equipment manufacturers. Currently, we control the rotary kiln settlement differential within 5mm in our designs. Practice has proven that this design fully meets the requirements for equipment operation.