Temperature Measurement


Non-contact temperature measurement in the cement industry

January 2022 Temperature Measurement

Industrial IR sensors and systems for non-contact temperature measurement are vital to the cement industry and can be employed throughout the plant for process monitoring and predictive maintenance. Sensors for non-contact thermometry detect the energy radiated from the object and measure its temperature with high accuracy within a temperature range of -50 to 3000°C.

Common problems in a kiln

Careful management of kilns contributes to a plant’s success, however, there are several problems which may shorten the lifetime of a kiln.

Early detection of hot or cold spots is essential to avoid costly maintenance or an unplanned shutdown. Continuous monitoring of the kiln shell along its length, for example, will provide the earliest possible indication of potential problem areas. Spot monitoring of the rotary burn zone temperature is also vital for maintaining both product quality and kiln efficiency. Monitoring of the temperature on and after the clinker cooler section allows proper cooling levels and safeguards against fire hazard and conveyor belt burn out can be set.

Non-contact thermometers have a response time in milliseconds, much faster than thermocouples and RTDs and can be used from an optimal distance with high accuracy. Measuring temperature at a distance from the object means that the sensor can be located in a more acceptable environment with less heat, vibrations, or interferences.

Ratio, or two-colour, pyrometers are special versions of non-contact temperature measurement instruments often used in harsh environments. The ratio of energy detected in two different narrow spectral bands is used to calculate the true temperature even through dust smoke and vapour. Mounted in a water-cooled rugged thermojacket, the sensor can be used in very high ambient temperatures, making it ideal for measuring clinker temperature in the sinter zone of a kiln.

One of the most common problems relates to the build-up of coating inside the kiln shell. This coating provides protection for the shell and so it is essential that it remains even across the kiln wall. However, if there is an imbalance within the kiln, perhaps due to poor flame position, the coating may become thin, thus reducing its protective property. Even worse, the coating may fall away from the wall and bring refractory bricks with it. This is a sign of impending kiln failure, unless the operator can cool the kiln locally at the problem point and promote the build-up of new scale.

Another problem, which can significantly reduce productivity, is the build-up of excessive deposits within the kiln. Ring-like formations towards the entrance of the kiln can seriously reduce the throughput of raw materials into the kiln. Early detection is absolutely essential to enable the operator to remove them before they become too restrictive. A final problem relates to the position of the flame within the kiln. While it is important to ensure its correct position, length and form for optimum combustion, it is equally important that refractory bricks in the vicinity of the flame can respond correctly by promoting acceptable levels of protective coating.

By monitoring the temperature of the kiln surface, it is possible to detect each of the above problems before they become too serious. While localised areas of cool temperatures equate to high levels of coating or deposits, relatively higher temperatures indicate low coating and hence poor protection of the kiln shell. By monitoring how much the temperature changes and over what distances, it is even possible to identify the exact nature of the fault, be it a ring around the circumference of the kiln shell, or a localised area of poor coating.

For more information contact R&C; Instrumentation, +27 11 608 1551, info@randci.co.za, www.randci.co.za


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