Too hot to handle

Derek Stuart, AMETEK Land, discusses how effective temperature measurements are able to enhance cement kiln performance and longevity.

Temperature monitoring across the cement manufacturing process is essential for supporting process efficiency and cement quality. It can also help to prolong the life of the kiln by detecting refractory issues or insufficiently quenched clinker at an early stage – which could lead to production stoppages if left unchecked. Temperature monitoring at the kiln also supports safety and emissions control.

Controlling a cement kiln underpins the efficient and consistent production of high-quality cement with the lowest environmental impact. However, this can be challenging to achieve, as it requires close attention to several factors such as the raw mix feed rate, the fuel-to-air ratio, and the temperature distribution throughout the kiln.

Conditions within the kiln make it difficult to measure many of these key operational parameters, particularly temperature. Kiln rotation, high temperatures, and the movement of the sintering material along the kiln make thermocouples and other contact temperature sensors impractical. Radiation thermometers (pyrometers) provide a non-contact temperature measurement, but their effectiveness is limited by the high-dust conditions, especially within the burning zone.

Accurate measurements of the Burning Zone Temperature (BZT) are critical, because this shows whether or not there has been a complete transformation from dicalcium silicate (C2S) to tricalcium silicate (C3S), which occurs in the region of 1300 – 1450°C (2372 – 2642°F). Many kilns use a ratio pyrometer to measure the BZT. This is much less susceptible to errors caused by obscuration from dust because it uses the ratio between the radiation intensity at two wavelengths instead of the absolute intensity at a single wavelength.

Combined with a peak-picker algorithm, a ratio pyrometer can give an accurate temperature measurement even when there is 95% obscuration of the field of view.

A viewing port within the firing hood located below and to the side of the burner allows the best measurement of clinker temperature, but this is a very aggressive location, so usually the pyrometer must be installed with a water-cooled jacket to prevent damage to the electronics, and an air purge to protect the delicate optical surfaces from hot and dusty process gases.

However, the ratio thermometer gives only a single measurement value from a small part of the kiln, so its readings can be deceptive if the target area is not optimised.

A short-wavelength thermal image, using a near-infrared sensor and borescope probe, gives a lot more information about the conditions within the burning zone.

Source: World Cement, Published by David Bizley, Editor

Post time: Aug-19-2022