BCR: Profiling Kiln Temperature with Telemetry

August 1, 2002
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A new telemetry-based kiln profiling system can provide the ability to accurately monitor temperature profiles in real time.

A Kiln Tracker Telemetry system in place beneath the kiln car.
Kiln profiling with radio frequency (RF) telemetry is not a new concept. The technology was first introduced in the U.S. many years ago, but it met with limited degrees of success. While the early RF systems enabled kiln operators to collect a range of useful data from inside the kiln, the systems also tended to pick up interference from local radio stations overnight, and large chunks of data from the run were often lost.

Today, most companies rely instead on conventional (non-RF) kiln profiling systems, such as Datapaq’s Kiln Tracker, and hundreds of such systems are successfully operating in kilns around the world. But there is still a desire to see instantly what is happening to the ware on the kiln car. The ability to monitor temperature profiles in real time would be especially useful to brick manufacturers that are experiencing firing problems with a particular product batch. Although kiln cars can be carefully monitored using a conventional kiln profiling system, the problem batch of brick has often completed its firing cycle by the time the data logger is recovered at the end of the run and the firing curve has been examined. Since the next similar batch may not be scheduled for several weeks or months down the road, it may not be possible to determine what specific kiln setting changes would be needed to correct the problem.

To overcome these challenges, researchers at Datapaq set out to develop a next-generation telemetry-based kiln profiling system that would meet the following objectives:

  • It should be the same size as the existing data logger to be able to retrofit into existing Kiln Tracker evaporative thermal barriers.
  • It should be able to run within the existing Kiln Tracker software.
  • It must operate within recognized U.S., European and Japanese transmission specifications.
The company recognized that developing this new product would require more than just technical expertise. A great deal of experimentation and testing in “real life” situations would also be needed, as well as close cooperation with a brick manufacturer.

The thermal barrier can be quickly fixed in place using this detachable basket.

Developing the New System

Because of the technological advantages of telemetry in monitoring kiln temperature profiles, Hanson Brick took an immediate interest in the project. The company nominated Chris Lowe from its Technical Department to liase with Datapaq during the development process.

Initial trials were carried out at Hanson’s Waingroves plant in Derbyshire, U.K., where conditions were typical of those found in many brick plants. The long process cycle and limited space beneath the kiln car made it necessary to use a phased evaporation thermal barrier to protect the data logger.

In this type of barrier, the logger normally operates at a temperature of 100C (212F). However, this operating temperature created two challenges that had to be overcome in developing the new transmitter. The first challenge was a “signal drift” that occurs when the crystal inside the transmitter changes temperature from ambient to 100C within the thermal barrier. The temperature range in which the transmitter has to operate causes the transmission frequency to change slightly, making reception difficult. The second challenge was to find a battery that would be small enough to fit inside the data logger and be able to operate at high ambient temperatures, yet would have enough power to transmit the signal back to the computer. In typical batteries, power drops off quickly at high temperatures.

After several months of development, an advanced version of a telemetry-based kiln profiling system was ready to be tested. Trials carried out at the Waingroves plant with the prototype transmitter indicated that the signal drift and battery problems had been successfully overcome. However, further work was required on the transmitting and receiving antennas that would be supplied with the system.

The power output of a transmitter is limited by law, but the signal carrying the information on the ware temperatures has to be strong enough to escape the confines of the steel underside of the kiln car, as well as the thick, insulated kiln walls. The transmitting antenna also has to be able to function in the high temperatures beneath the kiln car, which, in some cases, can reach 250C (480F). For this reason, the antennas both inside and outside the kiln are crucial to the performance of the system and must operate at peak efficiency.

After several more months of development, new transmitting and receiving antennas were available for the new transmitter, and successful trials proved the feasibility of the project.

Testing the System’s Limits

The focus next switched to Hanson’s Kirton plant. Here, the firing conditions are similar to those in the Waingroves plant, but the kiln cars are much wider, and the bricks pass through a pre-heater before entering the tunnel kiln. At this site, the researchers decided to try to position a second telemetry system two or three kiln cars behind the first. The advantage of this set-up is that if changes are made to the kiln settings, and these changes have an effect downstream of the first test car, they will be picked up by the following car. Using telemetry systems on more than one car also allows more time for the conditions in the kiln to “settle” before the data is further assessed.

Those trials proved successful, so it was decided to run another set of trials at Hanson’s Desford plant, where a steel-clad kiln provided a formidable test. Researchers thought that the steel casing of the kiln might make it difficult for the transmitted signal to get out from beneath the kiln car. However, by using a sensitive receiving antenna, it was possible to receive 100% of the information that was transmitted.

Next-Generation Telemetry

Additional trials in the pottery industry in the U.K., and in the brick and sanitaryware industries in the U.S., have proved that real-time temperature profiling in tunnel kilns is now a reality. Telemetry profiling provides the ability to see precisely what is happening to the ware during the firing process and to adjust the kiln settings on problem brick while the batch is still in the tunnel kiln. It also provides instant access to data that can be vital for problem solving. Thanks to the close cooperation of Hanson Brick, today’s kiln operators can now have a high level of control over even the most difficult firing processes.

For More Information

For more information about kiln temperature profiling with telemetry, contact Datapaq, Inc. at 187 Ballardvale St., Wilmington, MA 01887; (978) 988-9000; fax (978) 988-0666; e-mail sales@datapaq.com; or visit http://www.datapaq.com.

For more information about Hanson Brick, contact the company at Stewartby, Bedford, UK, MK43 9LZ; (44) 8705-258-258; fax (44) 1234-762040; e-mail info@hansonbrick.com; or visit http://www.hanson-brickseurope.com.

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