# Investigation of Inner Lining Loss and Correlation with Steel Structure Quality in Rotary Kilns
## 1 Introduction
It does this by taking a picture of the drum's 3D surface profile, which gives a detailed picture of the drum's surface. It works with the help of a set of sensors that are placed around the kiln. At different points around the shell's diameter, the sensors measure how far away the shell is from the sensors. This enables the ovalness of the shell to be calculated [23; 24; 25]. High temperature around a total station, scanning the operating rotary kiln, affects the accuracy of the measurement. Refraction must be taken into account by using a thermal camera to measure the air temperature [26]. The total station can be used to determine how straight the shell's rotation axis is, where the bearing rollers and tyres are in relation to each other, and where their rotation axes are. When the rotating kiln is cold, it is possible to obtain better results [27]. One popular technique for measuring complex objects is laser scanning. Using laser scanning technology, a large number of 3D data points are collected, and then this information is used to make a detailed map of the building surface. It is possible to use point clouds to determine the displacement, curvature, spin, and so on [28]. Measuring with a terrestrial laser scanner (TLS) is faster than with a total station, but it takes longer to process the data. For further research, it is important to get rid of all (redundant points/data) [29]. By comparing two point clouds, it is possible to detect structural changes in time [30; 31]. Some studies used the segmentation of raw point clouds to reduce the amount of time it took to process. The point cloud is broken up into different shapes, such as rotary rings, circular shells, and others. Geometric factors such as shape, size, symmetry, ovality, displacement, curvature, and twist can be estimated using segmented point clouds [29]. The laser tracker and high-precision total station is mostly used for rotary kiln drive alignment, which includes the position of the furnace axis, the centre-to-centre distance of the gears of the crown pair, radial and axial beats of the ring gear, etc. [31]. Another system made up of a laser system, a hall sensor, and a magnet is used to figure out the eccentricity of the radius, the deformation of the surface of the cylinder, and the eccentricity of the centre of the cross-section from the rotary kiln axis. The magnet and Hall sensor are placed on the meshing gear to make a pulse signal to start and stop laser data acquisition. Laser data are used to determine the coordinates of 3D points for further research [11]. After the annual lime firing process, the loss of the lining inside the rotary lime kiln was recorded. The people in charge of a rotary kiln have to check the loss every year and figure out where repairs need to be made. Each year, the readings of the wells show how much of the lining has been lost. The inner lining is drilled every two metres along the 42 m closest to the fire flame, which are the parts of the kiln that undergo the most wear. The drill bit is pushed through the brick until it hits the steel structure. The height of the rest of the inner cover is then decided. The loss can only be calculated at the point of drilling by comparing the ideal inner lining with the actual inner lining. Laser scanning is the best way to obtain information from the inside of a rotary kiln while limiting the number of useless cement points [32]. One of the most effective methods for thermal measurement in rotary kilns is infrared thermography. This non-contact, non-destructive technique uses infrared cameras to capture and analyse the thermal radiation emitted from the kiln surface. The resulting thermal images provide valuable information on the temperature distribution and potential hotspots. [33] Hotspots can develop in rotary kilns due to a variety of factors, such as the uneven wear of the lining, blockages, or mechanical problems. Thermal imaging can be used to identify hotspots early, allowing for timely corrective action to prevent damage to the kiln or product quality issues.