Thermal imaging cameras from FLIR are being used to monitor temperatures within cement kilns to prevent overheating and damage.

One of the steps in cement production involves the blending of limestone with other components in big rotary furnaces. These furnaces or kilns are a critical asset of a cement production plant, heating their contents to temperatures up to 1,500°C. There is however a risk of overheating, which can cause serious damage to the kiln shell. In order to monitor this delicate heating process and prevent possible damage to the kiln, thermal imaging cameras from FLIR Systems are used to measure temperatures on a 24/7 basis. 

Two companies recently teamed up to develop the IRTKilnMonitor, an advanced computer system that allows cement production operators to monitor, process and trace data from several kilns at once. The first company, INPROTECIRT, is an official FLIR Systems distributor for Italy while the second company, Grayess, based in Bradenton, FL, USA, is a leader in the design, manufacture and marketing of special customised infrared thermal imaging solutions and software for a wide variety of applications. 

The IRTKilnMonitor system incorporates FLIR A-Series thermal imaging cameras, which monitor the kiln temperature in real time. Additionally, a kiln visualisation module (2D and 3D) and a thermographic analysis module are also part of the system. 

Roberto Ricca, Director of Sales at INPROTECIRT said that the FLIR A315 and A615 thermal imaging cameras integrated with the system provide exactly the detailed thermal data needed for this type of application.

A refractory lining inside the rotary kiln insulates the steel shell from the high temperatures inside the kiln and protects it from the corrosive properties of the process material. This lining consists of refractory bricks or cast refractory concrete and needs to be replaced on a regular basis whenever it shows wear. The lifetime of the refractory lining can be prolonged by maintaining a coating of the processed cement material on the refractory surface. The thickness of the lining is generally in the 80-300 mm range. 

A typical refractory layer will be capable of maintaining a temperature drop of 1000°C or more between its hot and cold faces. The shell temperature needs to be maintained below 350°C in order to protect the steel from damage. Thanks to thermal imaging cameras, the kiln shell can continuously be monitored and when needed, early warnings of hotspots indicative of refractory failure can be given.

The shell is critical for the operational performance of the kiln. Thermal imaging cameras can detect at least two different problems regarding this shell.

Firstly, during operation, a ring of cement coating piles up inside the shell on the refractory brick surface. While this is beneficial because it lowers the shell temperature, reducing heat losses and protecting the refractory material, furnace operators also need to ensure that this coating doesn’t get too thick, because it will reduce the internal diameter and lower the furnace’s production performance. By detecting low temperatures on the kiln shell, thermal imaging cameras can make operators aware of this problem.

Secondly, unstable cement coating or sudden detachment of coating material easily leads to problems with the refractory material and can cause refractory bricks to fall off. As the protecting layer is then damaged and its thickness reduced, hot spots are formed inside the shell, which result in loss of energy and disturbed kiln operation. To protect the steel shell from damage, its temperature should remain below 350°C, which can be monitored easily with thermal imaging cameras. 

The IRTKilnMonitor makes use of three A315 cameras, each scanning a third of the 60m long rotary kiln. These thermal video streams are distributed to a visualisation system inside the central control room, and provides operators with a 24/7, real-time view of the kiln operation and performance. The kiln has a rotation time of around 30 seconds and the IRTKilnMonitor is synchronised to the rotation time to build up a thermal image.

Whenever the kiln shell reaches an undesired temperature, operators receive dedicated software alerts, which allow them to take the appropriate remedial actions such as reducing the temperature of the burner or even shutting the system down to prevent severe damage and avoid huge costs.

To give control room operators the best possible view of the situation, the IRTKilnMonitor generates several different viewing modes based on the information received from the FLIR thermal imaging cameras.