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Monitoring kiln performance

World Cement,

Today, it is impossible to imagine the building industry without cement. As an important component of masonry mortar and concrete, the manufacturing of and use of cement products make cement one of the most valuable and useful mineral products in the world. Cement production is a complex process, in which one of the steps consists of blending 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 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.

FLIR A-Series cameras make potentially dangerous hot spots clearly visible.

Two companies recently teamed up to develop the IRT KilnMonitor®, an advanced computer system that allows cement production operators to monitor, process and trace data from several kilns at once. The first company, INPROTEC IRT, is an official FLIR Systems distributor for Italy. The company has a wide expertise in high-tech equipment for industrial safety applications. The second company, Grayess, based in the US, 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 IRT KilnMonitor® system includes FLIR A-Series cameras, which monitor the kiln temperature in real-time. In addition, it includes, among other things, a kiln visualisation module (2D and 3D) and a thermographic analysis module. "We have designed the system to be integrated with the FLIR A315 and /or A615 cameras. These products provide exactly the detailed thermal data that is needed for this type of application,” said Roberto Ricca, INPROTEC IRT.

IRT KilnMonitor® set-up view.

Protecting the kiln shell

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

Firstly, during operation, a ring of cement coating is piling up inside the shell on the refractory brick surface. On the one hand, this is beneficial, as it lowers the shell temperature, reducing heat losses and protecting the refractory material. On the other hand, furnace operators need to be aware that this coating does not get too thick, as this will reduce the internal diameter and, as a result, reduce 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 results 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.

Kiln monitoring system

The IRT KilnMonitor® makes use of three A315 cameras, each scanning one third of the 60 m 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 IRT KilnMonitor® 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. For example, hot spots in the thermal image of the furnace can indicate that refractory bricks have become detached from the refractory lining and that the protective kiln layer is becoming less thick. This may require the furnace operators to reduce the temperature of the burner or even shut the system down in order to prevent severe damage and avoid large costs.

Accurate thermal views

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

Two-dimensional infrared view (Temperature Map 2D): the IRT KilnMonitor® allows operators to select their own colour palette and temperature range of interest. They can read information about temperature at a specific spot, position of the spot, brick thickness, coating thickness, etc. The software also allows them to zoom in on a specific area in a separate window.

Three-dimesional view of the kiln interior (Kiln Section 3D): this viewing mode virtually cuts the kiln at some position and shows the kiln interior (bricks and coating).

Thermal imaging cameras versus scanners

The image quality is not the only advantage of the FLIR A315 thermal imaging cameras. When comparing them with thermal imaging scanners, another commonly used technology for kiln shell monitoring, it is clear that thermal imaging cameras offer the end customer a less expensive solution.

“When scanners are used, then theoretically one scanner unit can suffice to monitor an entire 60 m rotary kiln,” said Ricca. “However, when using a scanner, the unit needs to be placed at a certain distance and the rotary kiln should be fully visible. In practice, this is not always possible. Thermal scanners can be quite bulky and are not very flexible in terms of installation. In many cases, a rotary kiln is installed inside a dedicated production hall. Taking into account that a thermal imaging scanner has a maximum viewing angle of 120°, it is very often impossible to install a thermal scanner at sufficient distance from the rotary kiln and avoid obstacles that are blocking the view. For example, with many rotary kiln installations, there is a secondary air tube that directs hot air out of the rotary kiln to be used as an energy source. This secondary tube will often be an obstacle.”

“In contrast, thermal imaging cameras are much smaller, much lighter and much more flexible in terms of placement and installation,” Ricca continued. “In fact, they are the preferred solution for installations where space is limited. In our system design, we used a FLIR A315 with 90° lens. In this case, you would need three thermal imaging cameras to cover the total pipe length of 60 m, which is still cheaper than one thermal imaging scanner.”

High resolution

The FLIR A315 and A615 are compact and affordable thermal imaging cameras, fully controlled by a PC. With a thermal sensitivity of <50 mK, it captures the finest image details and temperature difference information. “We definitely need the high resolution,” Ricca added. “For an ideal installation, we often opt for a 90° lens, because then you only need to use two or three cameras to cover the entire kiln length. For a German customer, we integrated the FLIR A315 with 90° lens and it delivered on the promise: very high image quality, very accurate detail.”

“We are also interested in the FLIR A615 for future installations of the IRT Kilnmonitor® system, because this will provide us with even higher resolution. The FLIR A615 has a resolution of 640x480 pixels that allows more accuracy and shows more details at a longer distance. In fact, taking into account a rotary kiln of 60 m long, it would give us an image where each pixel represents 10 cm of the pipe,” Ricca concluded.

Written by FLIR Systems.

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