Screw heat exchangers that cool sand, a residual stream from the processing of tar-containing asphalt granulate (TAG), within a few hours from 1050°C to 50°C? That sounds like an impossible mission! But Van Beek has succeeded in creating this technologically advanced process with Celsius screw heat exchangers for the new asphalt processing plant of Recycling Kombinatie Reko in the Rotterdam port area.
TAG is a combination of sand, gravel and the contaminating binder, tar. Asphalt granulate is produced by breaking up an asphalt road and according to the law may only be recycled when it has been cleaned. Reko, as one of the biggest processing companies in the world, can fully recycle this type of contaminated building material. How? By the thermal cleaning of TAG, an environmentally-friendly technique that according to the German Fraunhofer Institute offers many ecological advantages and guarantees a considerable CO2 saving.
Direct cooling effect
It is an innovative recycling process, to which several Celsius screw heat exchangers and Van Beek screw conveyors make a considerable contribution. They are used to re-cool the sand coming out of the boiler economizer (heat exchanger) and afterburner in Reko’s new asphalt processing plant, which processes some 4000 kg of sand an hour. The re-cooling is carried out in four streams of 250°C and 1050°C to an acceptable temperature of around 50°C. The boiler economizer collects the energy released in the form of steam, after which Reko delivers the electricity generated to the electricity grid.
It is the shared circular economy vision and innovative mind-set that brought Van Beek and Reko together before. In 2008 Van Beek had already supplied Celsius screw heat exchangers for a Reko asphalt processing plant. The highest temperature in the old plant was 850°C, while in the new plant this involves re-cooling from 1050°C°. “This time we supplied the cooling screws for an afterburner, a boiler economizer and we also incorporated a number of screw conveyor systems into the project to create a connecting production line”, says Bas Boerboom, sales engineer at Van Beek.
According to him innovation has not stood still since 2008. For example the capacity of the new processing plant is ten times greater and the combustion temperature has increased quite a bit: from 850°C to 1050°C now. The higher the temperature, the cleaner the material. “The Celsius screw heat exchangers were adapted for the higher temperatures. They are fitted with a twin-walled cooling jacket through which the water flows. Water also flows out through the inner tube of the screw itself. The sand swirls downwards through the boiler economizer and arrives at the cooling screw”, explains Boerboom.
Innovative prestige project
Van Beek was closely involved from an early stage in designing and implementing Celsius screw heat exchangers for the new plant. “We knew our cooling screws could be adapted for the extremely high temperatures and by mixing in cold sand, we were able to reduce the input temperature of the cooling screw. As a result the screw will wear less. It is a wonderful big project of which we at Van Beek can be really proud!”