Optimising the lifespan of essential assets, such as the kiln, is vitally important to any cement plant. With the replacement of the kiln shell one of the greatest capital expenditures to a plant, identifying and integrating technologies that maximise its longevity and reduce damage is essential.
Thermal monitoring of the outer kiln shell is key to ensuring that the inner refractory lining is protecting the kiln shell. Continuous thermal imaging of the shell shows the development of any hot area which may be a sign of missing refractory lining or refractory damage or wear. Early detection of these hot spots is vital to facilitate running repairs, thereby avoiding costly maintenance or an unplanned shutdown.
In the past hand-held infrared thermometers were widely used for monitoring the kiln shell, however, they had a number of limitations including the fact they are subject to human error. Due to the continuous imaging capability of the line scanner systems they are becoming increasingly popular for monitoring the rotating kiln, as they detect and trend any developing hot areas precisely and consistently.
Today’s infrared line scanners typically sample 1000 data points per line at scan frequencies up to 150 Hz, providing a continuous high resolution scrolling thermal image of the kiln shell.
Many of these line scanners have high levels of connectivity, for example, with an Ethernet connection straight from the sensor head, removing the requirement for a separate processor. From a practical point of view, the adoption of Power over Ethernet technology (PoE) means all local electrical connections are made with a single cable – this simplifies and lowers installation costs. The local Ethernet connection is then extended to the control room over a standard fibre optic Ethernet cable. The use of fibre optics from the field to the control room also isolates and prevents potential control room damage during electrical storms.
Infrared line scanners are designed to be able to operate in the harsh environment found in the vicinity of a cement kiln. Design details like the flush, flat sapphire protection window and air purge ensure the scanner has a long and low maintenance life. As these line scanners are generally a more cost effective solution than other alternatives, they are an attractive option for many cement plants.
An additional benefit of using fully integrated infrared technology is that the data can be logged and analysed to identify slowly developing problems.Maintaining accurate measurement of the temperature of the kiln shell is an integral part of ensuring its efficient operation. Infrared technology is becoming more widely used, mainly as it can give a plant a competitive advantage in terms of reducing maintenance costs and less downtime.
Tyre slip monitoring
An additional benefit of line scanning in kiln monitoring applications is that the thermal data can also be used to monitor the tyre creep. The minimum heating-up period is determined by the time required to stabilise the temperature difference (and hence the clearance) between the kiln shell and the tire, since the shell will heat up faster than the tire. The line scanning solution has the facility to monitor up to seven tyres for slip continuously allowing the operator the most accurate control of the heating-up schedule.
Inductive sensors are installed at each tyre close to the kiln surface while a reference sensor is used for the speed of rotation. For each tyre which is being monitored for slip it is possible to configure tolerance values, any slip outside of the tolerance values will be highlighted to the user. The thermal expansion for each unit can be controlled so that deformation of the kiln or the tyre can be avoided.
Infrared non-contact temperature measurement and thermal imaging technologies provide accurate data that is helping to extend Mean Time Between Failure (MTBF) and is protecting the cement plant’s valuable assets.
This is part one 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.
Read the article online at: https://www.worldcement.com/special-reports/02082016/how-accurate-thermal-measurement-can-reduce-maintenance-costs-part-one-35/