Kilns and filled bricks help sustainability

Clay Technology magazine
7 Jun 2019

Keller ICS discussed the benefits of filled bricks and next-generation kilns that can help bring heavy clay into the sustainable and economical era of Industry 4.0

The future of construction lies in filled bricks. This is an emerging and useful trend in construction and is growing in popularity due to the simplicity of applying this process to common household bricks and the multiplicity of benefits it brings, both to home builders and home owners.

Rising use of filled bricks is coming from several places at once – market demands for quicker erection of walls is a primary driver, as the process is carried out inside the factory so by the time the bricks are delivered to the site, they are ready for use and remove the need for additional time to install insulation.

For the resident, the filling ensures an economical form of building insulation that is just as effective at blocking ingress of excess heat in the summer months as it is for trapping in the warmth during the winter. In addition, it provides natural humidity protection, increases the bricks’ ability to absorb radiation – up to 90% - and crucially, it improves overall fire resistance. When using filled bricks, even a thin wall can withstand a fire for at least 1.5 hours before incurring sufficient damage to cause collapse.

Choose your filling

Generic house bricks of any size and hole pattern can receive a filling to improve their performance. Three preferred brick filling materials are perlite, mineral fibre and mineral granulate. Each of these options gives a similar degree of performance and, in fact, the filling material is chosen depending on the design of the brick itself - the plant machinery is calibrated according to the size, depth and hole pattern, and then the process can begin.

Perlite is the go-to material for brick filling. This amorphous volcanic glass is the most widely used material as it is versatile and requires no special handling, so can be applied to any hole pattern with consistent, high level insulating results. Adding perlite to heavy clay makes the product lighter and provides a degree of moisture flexibility - it increases aeration of the material, expands with heat and as it retains a lot of water, it can help regulate moisture content over the brick’s lifetime.

If the hole pattern is uneven or inconsistent, mineral fibre is the better choice. When the machinery is adjusted for the variance, fibre mats can be stuffed into the bricks to achieve the right level of insulation. As the fibre is porous, it absorbs air and moisture to provide an excellent level of heat capture, and also protects against sound vibrations.

Finally, mineral granulate is used for bricks that have finepored hole patterns, in order to get an adequate fill.

Building a reputation

For Keller, any brick design can be filled and wall thicknesses can be accommodated up to 300mm. All
of these filling materials are natural, so at the end of their life, the bricks can be reclaimed and reused without problems.

More and more manufacturers are exploring the use of filled bricks and it is likely to become standard practice for fast and reliable housebuilding. This is being helped by their practical aspects and other complimentary factors. For instance, building is quicker as it requires thin mortar, and when using a special mortar that allows for handling at very low temperatures – down to 0°C – house building can continue year-round even in poor weather conditions.

Additionally, movement joints are generally not required in walls less than 20m-long, clay blocks are lighter than concrete blocks, and they have no sharp edges.

Sustainable firing

Another consideration for Keller is the focus on sustainability across all aspects of production.
For brickmakers, this inevitably means paying closer attention to high-energy stages of manufacture,
such as firing.

Whether as part of a new plant or a retrofit, measures such as cogeneration plants with combined electricity and waste heat recovery, the use of tunnel kiln waste heat for drying or the regenerative thermal oxidation of flue gas and low-temperature carbonisation gas are just three examples of efforts being made to advance environmentally sustainable technologies for the future of the heavy clay industry.

Keller supplies products, machinery and entire brickmaking plants, so has many years’ experience optimising the production line. In light of the need to refine energy consumption, the company recently developed a more efficient method, the Enviro Kiln.

This new model has been designed to ensure the solid-solid energy transfer operates successfully. Initial considerations revealed that the product flows travelling side by side were limited in their geometry, that the convection could work as forced convection, and that the heat transfer by means of radiation would need to be used as efficiently as possible.

In order to comply with these requirements, Keller cut the kiln cars into slices and lined them up next to each other, thus forming a large number of kiln cars where products to be both heated and cooled were placed side by side but moving in opposite directions. Trials indicated that these were the optimal conditions for heat transfer. Recirculation fans were then arranged in the convection area over the length of the kiln to provide transverse circulation. From approximately 700°C and upwards, these recirculation fans are no longer needed, as the radiation is then predominant and takes over as the main heat exchange. Final firing would take place in the firing zone, as with any conventional kiln.

Extensive theoretical considerations, supported by Fluent software, in close cooperation with the University of Applied Sciences in Osnabrück, Germany, preceded the studies for the redesign of this counter-travel kiln design. In order to put the theory into practice, prove the findings and to gather real-world measurement data, Keller built a pilot kiln that was 5m-wide, 16m-long and 5m-high, used to record extensive measurement data. Results of the pilot phase indicated it is possible to obtain significant marketable energy savings by using the Enviro Kiln.

On to the fourth

This new future-focused technology has been planned for implementation in various projects across Europe. But for now, Keller is preparing to carry out the first practical tests of the kiln, anticipating it to cause a large and positive impact on the heavy clay industry. This is only one of the technology projects the company is working on, as it moves the brick making sector into Industry 4.0.

Developments in brick machinery and robotics have accelerated in the last few years. Although considered conservative, progress, while perhaps slower than other industries, can be seen creeping into the brick making sector. Today more plants are operating with smaller numbers of staff and are aiming for absolute minimum, there is increasing integration of teleservice and augmented reality control systems with visualisation tools for uses such as fault diagnostics, and the emergence of mobile remote control and monitoring of human-machine interface systems. The drive for sustainability has not come alone, and is infiltrating all aspects of the sector, bringing with it a need for new and improved brick making technologies that are robust, efficient and futureproof.