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Thermal imaging and application and performance monitoring in cement kilns

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article image FLIR A-Series cameras make potentially dangerous hotspots clearly visible

Thermal imaging cameras from FLIR Systems are being used to monitor temperatures round-the-clock in cement kilns. The IRTKilnMonitor is an advanced computer system developed by INPROTECIRT, the FLIR Systems distributor for Italy, in partnership with Grayess, a US-based leader in the design, manufacture and marketing of special customised infrared thermal imaging solutions and software for a wide variety of applications. Grayess is based in Bradenton, FL, USA.

The IRTKilnMonitor is an advanced computer system that allows cement production operators to monitor, process and trace data from several kilns simultaneously. The IRTKilnMonitor system includes FLIR A-Series cameras, which monitor the kiln temperature in real time as well as a kiln visualisation module (2D and 3D) and a thermographic analysis module. 

Cement production is a complex process, and involves blending limestone with other components in big rotary furnaces. These furnaces or kilns are a critical asset of a cement production plant, and are heated to temperatures up to 1500°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. 

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 associated with this shell.

Firstly, during operation, a ring of cement coating piles up inside the shell on the refractory brick surface. On the one hand, this is beneficial, because it lowers the shell temperature, reducing heat loss and protecting the refractory material. On the other hand, furnace operators need to ensure this coating doesn’t get too thick, because this will reduce the internal diameter and as a result, impact 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, hotspots are formed inside the shell, resulting in loss of energy and disturbed kiln operation. To protect the steel shell from damage, its temperature should remain below 350°C. This can of course, easily be monitored with thermal imaging cameras. 

The IRTKilnMonitor, developed by INPROTECIRT and Grayess, makes use of three FLIR A315 thermal imaging cameras, each scanning one 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 unfavourable temperature, operators receive dedicated software alerts, which allow them to take the appropriate remedial actions including 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.

Comparing the FLIR A315 thermal imaging cameras with thermal imaging scanners, another often used technology for kiln shell monitoring, INPROTECIRT’s Roberto Ricca says it is clear thermal imaging cameras offer the end customer a less expensive and more flexible solution.

The FLIR A315 and A615 thermal imaging cameras are compact and affordable models, fully controlled by a PC. With a thermal sensitivity of < 50 mK, these thermal cameras capture the finest image details and temperature difference information. 

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