Brickmaking sustainability driven by technology and material development

Clay Technology magazine
,
7 Jun 2019

Brick manufacture is an energy-intensive process, but power and resource savings can be made throughout the cycle to build up sustainability. We take a look. 

Raw materials

The optimal raw materials are paramount for achieving high-quality and consistent bricks and clay products. A fundamental aspect of this is moisture control. Having the right amount of water in the clay mix is vital – too little water and the mix will be coarse and difficult to extrude, potentially causing damage to machines, too much water and it will easily lose its shape and require greater amounts of energy during drying and firing stages. Therefore, achieving accuracy at each stage will ensure minimal waste and energy consumption.

One option for doing this is to use near infrared instruments along the production process which, when coupled with data processing equipment, not only monitor moisture content throughout but record and supply data into a central system for constant management and quality control. Moisture levels can be monitored in real-time in order to ensure the energy-intensive spray drying process is performed more efficiently, bulk density variations, and to produce consistent products with the desired moisture content. In tiles, press efficiency can be managed for better formation, minimising rework or scrap, and final product yields can be optimised.

Near infrared gauges are available in forms including on-line measurement of powders, coarse particles, slurry, flakes or granules. They emit a light that is absorbed by the liquid in the material being assessed and the amount of unabsorbed light is measured by a sensor, to determine the moisture level. Basic and continuous machines provide options depending on the needs of the operation, and can be placed on the conveyor line to quickly test materials as they pass by.

Though technical and non-essential, the accumulative cost savings can mount up significantly over only a few months.

Energy-efficient kilns

Firing is one of the most high-power stages of clay product production and is an obvious target area for energy savings. While the majority of industrial kilns have to be able to operate continuously at very high temperatures, there are still ways to reduce power consumption and make savings. Starting from scratch, several manufacturers are building new types of kilns that enable a larger amount of product to feed into the space, while others are exploiting heat exchange to redirect the heat to other functions – although these don’t reduce the initial energy output, they ensure it is not wasted but can go on to support functions such as drying.

Other alternative approaches include investigating integrated high-temperature ventilation modules, heat exchangers for preheating combustion air or producing hot water, self-recovering burners, high-efficiency refractory insulation, and the substitution of energy sources such as replacing fossil fuels with biogas. But rather than bandaging up the flaws, a promising field is new and innovative kiln design. A partnership between engineering firms Ceritherm, Direxa Engineering and Seipia has set out to create a new concept kiln, called the skate-kiln (SK). It has no tracks or cars, instead having small devices that support the products and drive them through the tunnel.

Without a full wagon or track, there is more space available inside the kiln for products, and the tunnel can be made as wide and/or deep as desired to reduce the area that needs to be heated up. Kiln cars themselves represent a parasitic mass, as they absorb a great deal of heat and require time to come to temperature with the clay, then need further time to cool down before they can be reused. Removing them is estimated to provide energy savings of up to 40%, as well as cutting down the lost time on each cycle. The Ceritherm-Direxa-Seipia partnership is developing this new concept kiln as a way to serve the future needs of the clay industries, using this as an opportunity to make a list of top desirables in the ideal industrial kiln.

The SK model is being designed to provide optimal tunnel tightness from the inlet along to the outlet, identical and effective insulation of all four faces of the roof, sole and lateral walls, and the ability to manage specific atmospheres inside the tunnel. Also, as well as eliminating parasitic mass, there is no risk of causing damage to mechanical parts exposed to repetitive firing temperatures. In addition to consistent and more economical operations, it is aimed to reduce the time of overall firing cycles, enabling shorter and more frequent runs.

Packing it up

A cover designed to stretch around a brick pallet is helping reduce the total material used to protect them for transportation. Gordian Strapping’s low-density polyethylene (LDPE)-based cover, called a stretch hood, has an elasticity to help exert force onto bricks for as long as they sit on a pallet. The triple-layered hood has an ethylene-vinyl acetate inner layer, which naturally wants to retain its original shape and in turn, pulls onto the bricks. The methodology for covering the bricks is similar to a shrink hood, which covers the bricks by being placed above the pallet and then heated to shrink to the pallet’s size.

Sales and Marketing Director, Daren Spice, said, ‘The hood is produced so it is smaller than the brick pallet. After the hood has been stretched and pulled over the pallet, it will naturally want to snap back to its natural form. The snapping back action puts pressure on the five faces of the pack – the top and the four side faces.

Once a shrink hood is on, it is shrunk to the size of the pack and is inert. So once it's shrunk, it stays that size. So if the bricks settle a little bit inside, that film won't continue to exert pressure on the pack – it will just stay in the same shape and the bricks may have extra room to move under the bag.’

The stretch hood is in a better position to offer stability to the pack so it can handle several lifts – from the line to a yard, then a truck, a builder’s merchant, another truck and finally the construction site. ‘The stretch hood will help more than a shrink hood could because it is continually exerting some pressure on the sides of the pack,’ Spice said.

Its plastic thickness achieved about 50-70micrometre, compared with 120 for a shrink bag. Spice said when using 100micrometre film, about 262g of plastic is used in the packing, but if the micron count were smaller, the total plastic used would be about 105g.

Gas is also not required to help expand the bag as it is a mechanical process. ‘On a cost per pack basis, you’d be allowing about 5p per pack in gas for the shrinking process. So immediately, by moving from gas shrink to stretch, you’ve got a cost saving and a carbon footprint advantage as well,’ Spice said. The material can be recycled or turned into residual-derived fuel.

Plastic strapping is also getting thinner while still holding mechanical properties to support a 500 brick pack – measurements have gone down to 15mm-wide to 0.9mm-thick.

Gordian Strapping is challenging plastic film producers and machine manufacturers to get the shrink wrap as thin as possible. Spice said more testing needs to be done to ensure the brick pack corners do not tear the film. Spice would like to see bags made with a portion or wholly of recycled content, but the material would need to be consistent and able to support the weight.