It is no secret that infrared technology has been widely embraced by the cement industry for more than 20 years; while all infrared rotary kiln systems offer the basic capabilities highlighted above, newer systems developed in the last decade feature some of the latest technology in the industry and offer expanded functionality to support operator needs.
Some top-tier functionalities, for example, address the concern of shadowed areas that stretch along the length of the kiln. With a wide field-of-view scanner, it can be common to have several obstructions, such as buildings, power poles, and other equipment, which essentially prevent the scanner from ‘seeing’ the entire kiln shell. Several of the top systems available today, for instance the CS210 System from Fluke Process Instruments, incorporate single point sensors, also known as pyrometers, that are located in such a way that they can ‘see’ the areas shadowed from the linescanner.
A linescanning system positioned to monitor a rotary kiln tire slip.
Up to 32 pyrometers can be installed and set up to utilise multi-drop communication, meaning only one connection is necessary for communication back to a PC. Because the software integrates data from multiple sensors into one single image, a ‘dirty lens’ warning can be added. This feature compares each data point with its adjacent points and, if the difference exceeds the defined limits, operators are alerted that the sensor may be partially blocked by a dirty lens or other obstruction.
A ‘false’ colour representation of the kiln surface temperature.
Additionally, top-tier scanning systems typically read frequencies between 3.5 μ and 4 μ. This range enables infrared linescanners to see directly through dust and moisture in order to determine the temperature of the kiln’s surface. In higher micron ranges, such as 8 μ to 14 μ, infrared systems tend to pick up reflections caused by dust and moisture in the air, meaning these solutions can only be used in more controlled facilities. As a result, linescanner systems are the ideal solution for cement manufacture in outdoor, rugged environments.
Other functionalities include monitoring clinker temperatures at the hot end of the process inside the kiln. In this application, an infrared sensor ‘looks’ into the hot part of the kiln end through a viewing port and monitors clinker temperature. The data is displayed on the same screen as the kiln shell imagery, allowing operators to monitor both steps of the process simultaneously.
Some systems, such as the CS210 System, also offer advanced capabilities that will monitor the condition of the brick and report on refractory wear. These software features also include a module database that can store and analyse all necessary data from (at least) the last year to indicate refractory wear during use, enabling engineers to schedule refractory repairs.
While these systems are useful, it is critical that the data entered into the programme by operators is accurate. Because all installations are inherently different, wear rates will also differ; therefore, making generalised predictions on the wear rate of any given material will inevitably lead to installations where the brick simply will not last as long as the system predicts.
One additional development in improving kiln life still utilises kiln monitoring systems, but not temperature measurement. Typically, kilns are driven from one end – which, due to their extensive size and mass, makes homogenous rotation extremely challenging. During this process, and particularly during speed changes, there is a tendency for some of the rotational energy to cause the kiln’s live-rings (or tire slips) to torque (or twist) instead of rotate.
A small amount of torque is not necessarily a problem for the live-rings, however, too much will cause damage to the fragile refractory material. In typical kiln monitoring systems, pyrometers are used to measure each live-ring rotation and trigger the display of each subsequent image of the kiln.
If multiple sensors are installed, the rotational speed of several points along the length of the kiln can be monitored – and if the rotational speed varies along the length, this can be indicative that a twist is occurring, allowing engineers to make corrections before serious damage occurs.