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How Accurate Thermal Measurement Can Reduce Maintenance Costs: Part Two

World Cement,

New fuels

Pulverised tyres are increasingly being used as a fuel because they are universally available at attractive prices and have a higher calorific value than most coals. They are usually blended with coal to achieve a higher temperature with a view to improving clinker quality. However, as they are a more volatile source of energy, they can cause issues within the kiln, which is why it is essential that thermal imaging scanners are used. Latest technology means it is now possible to view thermal images of the rotating kiln, along with temperature profiles and zone alarms. Up to eight kiln scanners can be integrated within the software, with all scanner inputs being displayed simultaneously, providing a highly integrated overview of multiple kilns.

Refractory lining issues generally develop over time as the refractory brickwork wears and degrades, however, if a refractory brick falls out a hot spot can develop quickly. In these situations, the remote monitoring instantly identifies the exact location on the kiln shell and a hot repair could be carried out, therefore minimising any further or permanent damage.

Burning zone

Popular measurements in the burning zone include burning zone temperature, visualisation of flame shape and length and the detection of ash ring formation.Measurement of the temperature in the kiln-burning zone is vital for maintaining both product quality and kiln efficiency. Burning zone temperature in the past has been problematic due to the large amount of dust present in the area. Traditional optical methods of measuring the temperature have many times resulted in lower readings than actual, caused by dust interference.

Infrared ratio thermometers, also known as 2-colour thermometers avoid the interfering dust and achieve accurate temperature measurements even when dust interference may seem overwhelming. A typical ratio thermometer can accurately measure temperatures in conditions that have over 95% of dust obscuration.

Taking things one step further, an Infrared Process imager like the Land NIR-b borescope, is inserted through the firing hood. Not only does it measure temperature but it also sees the flame propagation and can easily detect developing ash rings.

The NIR-b has a 90° field of view within the kiln, yet only requires access through a nominal 3 in./76 mm dia. hole in the hood. The clear, live thermal image consists of over 300 000 temperature measuring pixels allowing temperature to be measured anywhere within the scene. The Lens tube is water cooled and air purged to enable it to continuously measure the scene in the burning zone. An auto retract mechanism withdraws the borescope thermal imager, if the cooling water or air purge fails, or if the lens tip temperature sensor detects an over temperature situation.

The NIR-b is used in conjunction with Image Processing software that enables the operator to measure areas of interest and live data points, as well as storing and trending this data for future analysis. By monitoring the live thermal video, it allows operators to easily optimise the burner resulting in improved fuel efficiency and clinker quality.

The NIR-b thermal imager replaces both traditional video cameras and single point infrared thermometers, doing both jobs better and with less complexity.Temperature measurements taken further up the kiln from the burning zone can be achieved by using an online infrared thermometer that looks into a closed ended sighting tube that is installed in the kiln. The tube is installed through the shell and refractory and the thermometer looks into it each rotation. A peak picking algorithm holds the reading until the next rotation and then updates it.

This is part two of a three-part article written for World Cement’s August issue and abridged for the website. Subscribers can read the full August issue by signing in, and can also catch up on-the-go via our new app for Apple and Android. Non-subscribers can access a preview of the August 2016 issue here.

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