In the beginning of February 2017, Isabel De Schrijver (Project Manager Plastic characterisation, processing & Recycling at Centexbel), and I were invited by Jan Grobet (Manager Public Affairs Belgium and Luxembourg at ROCKWOOL Benelux) to visit the production site of ROCKWOOL in Roermond. After a small “tour de table”, Jan Grobet and Daan de Kubber (Manager Marketing & Business Development at Lapinus-part of ROCKWOOL) started off by giving a presentation. Later on, Jan Grobet guided us through production line 8.
Production proces in summary
Rockwool is produced from a natural rock called basalt. This stone is mixed together with “briquettes” and a solid fuel i.e. cokes into a melting furnace. The primary energy necessary for melting the raw materials is provided by burning the fuel using combustion air, possibly enriched with oxygen. The melt (ca. 1500 ° c) then runs out of the oven onto a spinner and during the spinning process it is converted into fibers. Binder is then added, whereby the loose fibers stick together and turn into flakes.
During our visit to production line 8 at Roermond, we saw how the conveyor belt transports the briquettes” (rock wool, slag wool and cement) and virgin basalt into the furnace. The ratio is 42% up to 50% “briquettes”, 33% basalt, 22% other rocks (cement) and 3% binders. As basalt is a natural product it does not always have the same composition. The use of the “briquettes” permits control of the composition needed for a very specific production line. That way the quality of the endproduct can easily be garanteed. Fun fact: basalt is created more than 38 000 times faster (by the cooling of the Earth’s crust) than mined for all production applications.
Depending on the location of the production site, the melting furnace is usually heated on the basis of coke (to around 1500 C °) and sometimes also on the basis of electricity. The melting furnaces in Roermond do not use electricity for heating, just coke. Through heating a “hot lava” is created that consists out of briquettes and virgin basalt. The recipe should be determined very accurately to obtain the desired product characteristics.
The lava then flows into two flywheels that catapult the lava so fast such that fibers are emerging (spinning process). These fibers are atomised with a binding agent, consisting of a mixture of formaldehyde and phenol, which are completely curing to a thermoset connection, whereby the fibers stick together (cross-linkage). If the product needs water repellent properties, than mineral oil is added simultaneously. The fibers are collected by means of extraction and by a mantel clock with a pendulum movement on a conveyor belt. The opening of the mantel clock can be set as well. It is the speed of the pendulum, in cooperation with the speed of the conveyor belt that determines the shape and thickness of the wool. The rockwool is pressed to the required density, depending on the desired end product.The sides are cut off (and collected for recycling), after which the wool is curred in a curing oven of over 100 °C. This provides hardening and thus a thermoset of the binder, you can compare it to the curing of a plastic billiard ball. The plate is cut in its length by means of a high pressure jet of water. The core is being inspected, through x-rays, to make sure that it is sufficiently cooled.
ROCKWOOL attaches great importance to sustainability (own LCA and EPD calculations), CSR and recycling. For instance, the largest production sites have their own recycling site. The residual product can be dealth with at any of these sites.
ROCKWOOL collects rockwool originating from internal processes but also from rockwool that is recuperated from demolition and renovation sites. If the latter rockwool meets the standards (no contamination) it is collected by Van Gansewinkel i.e. through the ROCKCycle ® system. Considering the temperature in the furnace, other contaminations (such as organic) are of lesser importance. The GRODAN mats for example, are being dosed into the production proces of the “briquettes” because of their high amount of organic material. The repossessed rockwool is sorted according to its characteristics (resin-bearing, moist, filter pads, etc.). The fact is that not all repossessed rockwool is suitable for any production line. Depending on the type, the sorted Rockwool is shredded and the briquettes (which were collected during the production of rockwool) shattered. Then depending on the type, one obtains a dusty mass that again is sorted acoording to their type, collected in silos and added to the feedstock in function of the type of rock wool that is being made. Then, cement and slag are added and mixed. At the very last stage, water is added and everything is poured into the hexagonal form and pressed. The briquettes are hardened at a temperature of 38 degrees and a relative humidity of 90%, after which they start their next life.