Adapting to Complex Configurations

28/11/2014 09:27

Installation of a wide-angle scanner for thermal kiln shell monitoring at ARM Cement Ltd’s Kaloleni plant.

ARM Cement Ltd, one of the major East African cement producers, has selected HGH’s KILSCAN to operate the thermal monitoring of the kiln shell at its Kaloleni plant near Mombasa. With a scan angle of 140˚, KILNSCAN was adapted to the required installation confi guration at the plant, with a free space of only 10 m between the shell and the scanner.

ARM to cement Kenyan economic ambitions

ARM Cement Ltd is the second largest cement producer in Kenya, with a 1 million tpa capacity in the country, It operates two plants; one in Athi River, a few kilometers from the country’s capital, Nairobi, and one in Kaloleni, north of Mombasa – the second largest city in Kenya and featuring one of the main ports in East Africa. With Kenya’s claimed ambition to become the hub of the regional trade through the completion of its “Vision 2030” development programme, signifi cant economic growth has been forecast for the region. This development process includes a series of improvements to local infrastructure, such as the construction of new terminals at the Port of Mombasa, which will double the port’s container handling capacity by 2020.

The kiln and preheater at the Kaloleni cement plant

ARM aims to meet growing demand in the region, and plans to double its annual production capacity to about 5 million t over the next six years through the construction of new plants in Tanzania and a capacity increase in Rwanda. The firm produces Portland Pozzolana Cement and Ordinary Portland Cement, with the commitment to deliver the finest quality product with the best quality-to-cost ratio. It should be noted that ARM is one of the few cement companies in the region that manufactures its own premium quality clinker, managing the full value chain of the manufacturing process for greater control of production costs, process efficiency and product quality.

Kaloleni plant installation

With total process control in mind, ARM needed to accurately and reliably monitor the 45 m long rotary kiln at the Kaloleni plant, to prevent any interruption in production due to hot spots and to control the burning process. Even though the kiln is relatively small, this project was a challenge because the scanner had to be set up at a very close distance from the shell – less than 10 m. To measure the temperature on the entire surface of the rotary kiln shell with a single sensor it was necessary to install a system with a scan angle greater than 130˚.

Thermal scanner installed at 10 m from the kiln shell at ARM’s Kaloleni plant.

With a field of view (FOV) of up to 140˚, the KILNSCAN thermal scanner from HGH Infrared Systems can provide a simple and effective solution to this type of demanding configuration. At such a reduced distance from the shell, two traditional scanners with a FOV of 90˚ would have been necessary to provide complete thermal monitoring from the output of the preheater tower to the input of the cooler. Obviously, the use of two systems implies additional costs and installation complexity. Indeed, in the case of the Kaloleni kiln, with quite a large slope with respect to the ground, the scanner had to be tilted accordingly. This ensures that its line of sight is parallel to the rotation axis of the shell. The straightforward operation in the case of a single system becomes more complex when it comes to aligning multi-sensors; to allow for a thermal map display without impairment the scanners have to be jointly aligned so that the measurement line is unique and undistorted. In addition, difficult operations in terms of image linearization and fusion have to be performed for an accurate representation of the temperature at the correct scale.

The KILNSCAN, with a wide scan angle of 140˚, perfectly meets ARM’s request for a cost effective thermal monitoring system adapted to the limited space between the scanner protection cabin and the shell.

Thermal scanner monitoring in the control room

Flexibility in the face of complex configurations

This kind of complex project is not unusual. The KILNSCAN has already proven its flexibility to adapt to even more difficult configurations, two examples of which are outlined below.

Lafarge, UK

In the UK, HGH provided Lafarge with a system to monitor a long kiln (110 m in length) that operates inside a building. Again, thermal scanners had to be positioned at a very short distance from the shell surface. In this configuration, HGH proposed a system based on three KILNSCANS, each with a FOV of 140˚, in order to be able to monitor the entire kiln. In this particular case, in addition to the geometric constraints, the installed equipment also had to adapt to high ambient temperatures of up to 50 ˚C.

kiln inside a building

Tasek, Malaysia

An installation for Tasek in Malaysia is another example of a complex configuration. Not only was the protection cabin close to the kiln, but the scanners’ line of sight was also obstructed by several posts and pillars. A special configuration had to be designed with three KILNSCAN scanners with a FOV of 140˚, in order to display a thermal map with no dead zone. In this specific case, wide-angle scanners are aligned with an overlap in their line of sight. The thermal image is then reconstructed by combining the data from the three scanners, eliminating shadows in the display for full monitoring of the shell.

kiln masked with several posts and supports

Wide angle on specification

Covering the entire surface of the kiln shell is not the only challenge to meet. Over 1000 KILNSCANS are in operation worldwide, and in all the projects with which HGH has been involved, the main concern is to obtain reliable indicators on refractory bricks and kiln shell status, and on clinker quality. The same was true of ARM Cement. Maintenance of the kiln shell is an important contributor to the production costs. Considering the consequences of an unplanned kiln shutdown, which can cause several days of lost production, it is essential to select a reliable high-performance thermal scanner.

The first important parameter is spatial resolution, i.e. the smallest size of a hot spot that can be detected by the scanner. Late warning can occur with scanners with low resolution, because of the averaging on the thermal map, smoothing temperature peaks. As a result, alarm thresholds cannot be reached sufficiently in advance for kiln shell distortion to be avoided. The KILNSCAN features a single brick resolution, enabling rapid and efficient action to re-build the coating (such as locally cooling down the shell with fans or modifying the burner settings) to prevent kiln shut down. When several bricks are missing such action becomes useless, resulting in unavoidable kiln shutdown and therefore loss of production, costly repair, and the reduced lifetime of the brick lining because of thermal shock.

3D thermal map of a kiln, with hot spot and copper rings, highlighting the Kilnscan high spatial resolution

In addition to high spatial resolution, the KILNSCAN has high thermal sensitivity – better than 0.05 ˚C. This means that the lowest rise in temperature will be immediately detected and the configurable alarm system will warn the control room of any emergency. Maintenance operators will then be able to react quickly before irreversible damages occur.

In the three case studies detailed above the installed scanners had a FOV of 140˚, which is unique on the market and very useful for adapting to any type of configuration. Of course, this wide-angle scanning is performed without compromising the high spatial resolution and thermal sensitivity.

KILNSCAN also features another unique advanced function – the Thermal Warp computation. This involves calculating the kiln distortion induced by temperature changes over the shell in order to infer the cyclical overloads and associated stresses suffered by the shell, tyres and roller stations. The evolution of the thermal distortion of the kiln provides information on the process evolution inside the kiln: evolution of coatings, kiln push of unburnt material, flame adjustment, etc.

Kaloleni plant ready for long-term operation

Maintenance operators at ARM’s Kaloleni plant expressed their satisfaction following the commissioning of their new thermal monitoring system. With the largest field of view available on the market (140˚), KILNSCAN is able to display the full thermal map of the kiln in real time, with high accuracy and reliable output and with one single sensor at a limited distance from the shell. Today, KILNSCAN is a leader in the line scanner industry in terms of spatial resolution and thermal sensitivity. Its advanced and unique software features allow for unmatched monitoring, ensuring that plants receive a good return on investment for years to come.