In September 2022, Terex Washing Systems (TWS) commissioned an excavation waste processing plant in Dittingen, Switzerland, some 20 kilometres south of Basel. This project was developed on behalf of Antag, a subsidiary of the independent Albin Borer Group. What makes this processing plant unique is that it processes all the materials generated by the Group's construction sites and recycles them into cuts for the concrete that supplies the company's ready-mix plants.
This is the third end-to-end project that TWS has completed in Europe, from design and specification to supplying the machines. The manufacturer worked with its regional distributor, Avesco, for this project, who completed the installation. It has the capacity to process 480,000 t/yr of materials, and it is due to start accepting materials from the Group's partners later this year.
Antag chose a location to the south of Dittingen, near Laufen, in the district of Basel-Landschaft, as the site for its first fixed processing plant, which will be used to process materials from its groundworks sites. It has been designed to process materials with a clay content of up to 30%, most of which originates from the Basel region. Roger Borer, the Group's Technical Director, came up with the idea for the project to supply the company's concrete plants with cuts from this new production unit. "When you put a ton of materials in storage, it costs CHF 10 [equivalent to €10] if it is not contaminated, and CHF 50 if it is. Companies are also duty-bound to process these stored materials," he explains.
For many years, close proximity to France meant that materials could be sent across the border, but lack of space and, more crucially, the cost of materials have prompted the Swiss operators to reconsider this approach. Hence Roger Borer's idea of developing the capability to process these materials so that the reusable portion could be recovered to supply the Group's concrete plants, one of which was nearby in the neighbouring district of Laufen.
To carry out this project, Antag called on the services of Avesco.
Avesco and Terex Washing Systems worked in close collaboration to define the process. Avesco produced the installation plan and handled the overall project management aspect. The core components were identified closely with TWS and specified for a 250 t/hr feed.
Avesco was then responsible for the overall planning of the system and the field management of the project, from installation to commissioning. In terms of the other contributors to the project, Ammann was assigned the electricity and recomposition station, and the German company ABP the production of the conveyors, in accordance with Avesco's installation plans.
Wet processing
The site chosen for building the plant and housing its inventory is a former warehouse extending over almost 2ha, located between an industrial park and the face of a former dimension stone quarry that has not been operational for many years (1).
The plant has been designed to wet process all but the largest materials (>100 mm) discarded from the start.
One of the variables of the processing treatment is the maximum admissible rate of contaminants, which is estimated at 30 %, given that 10 to 30 % of clay is still present in 0/60 mm and that some remain in the 0/4 (50%) before it is put into the cyclone separator. This fraction is removed during the double cycloning stage to ensure that the clay content of the sand is no higher than 3%.
In terms of the treatment process, the installation is fed (0/D) with an excavator, which deposits it in a hopper that feeds a scalping machine (AggreScalp), removing any pieces larger than 80 mm. These larger pieces are not processed on the washed materials line but are sent to the only crusher in the plant (the Terex HSI 3434 impactor). Behind this machine, a reversible conveyor belt returns the dry material (0/80) to a storage container or the washing plant's feed conveyor. A reintegration hopper also sends the material to the crusher for processing.
The washing plant's feed hopper is therefore supplied with 0/80. To prevent overflow, a sensor monitors the material level inside the hopper and reduces the feed to the scalping machine.
An initial underwater screen (2 decks, 6 m x 1.8 m) removes the 0/4 from the feed and directs the 4/80 to a paddle washer (HydroScrub), where the material is separated from the clay. This feed is then rinsed on a two-deck screen. At this point, the >50 mm is returned to a circuit leading to the impact crusher, while the 4/50 is directed to a second screen (with three decks) that is operated dry to produce concrete (2) cuts (4/8 – 8/16 – 16/32 – 32/45).
For this project, the operator expressed the wish to produce crushed material for the asphalt market. Here at the second screen stage, it would be possible to obtain these cuts, provided that the nets are changed.
The 0/4 sand from the feed is sent to a pre-wash tank with an overflow to remove the extra-fine particles (=0.63 µm) and recover sand through pumping. This machine, which has a cone-shaped tank (a kind of sand cone), receives the pulp and injects water under pressure to create vortices via injection nozzles, allowing a large proportion of the extra-fine material to overflow.
This pre-washing stage also allows the removal of a significant proportion of light-density contaminants (mainly roots and wood) before the double-cycloning (3) stage. This stage starts with rinsing the materials, intending to obtain the 1mm cut and mixing it with the 0/4mm to optimise the envelope for concrete production.
At this point, TWS works with what it calls "separators" and not hydrocyclones since they work with the internal pressure of the body of each machine. The distinguishing factor in this installation is that the proportion of sand can vary at the infeed, but what comes out of the dewaterer must have a constant density. This is achieved by creating a vacuum in the underflow by means of a rubber sleeve called a "sock", which closes when there is only a small amount of sand. Conversely, when more sand is inside the body, the vacuum causes the sock to open, but the sand retains a constant moisture level regardless of the feed. The advantage of this system is that it retains the extra-fine material in the body of each machine, which slightly improves the sand's quality.
The dewaterers underneath these separators then make the cuts at 4 mm, then at 1 mm, to obtain the 0/4 and 0/1.
A chamber filter press recovers the sediment from the thickener cone and presses it at a rate of 30 t per cycle. Each press produces 165 filter cakes weighing 180kg after a 55-minute cycle. This machine is manufactured under a TWS licence and includes a container housing a flocculation control cabinet, which adjusts the flocculant dosage in the treated water. The unit is also equipped with an automatic flocculant mixture preparation system. Depending on the sites where the materials are recovered, the quality of the clay can vary. To process all the sediment, TWS has integrated a milk of lime preparer, which has not yet been implemented. Pressing is sufficient to achieve the right level of dry content (up to 80 %).
Dittingen Gold
This is the third installation carried out by TWS with the support of a local partner. The first was commissioned in Sweden for the construction company Peab, and the second near Geneva in Switzerland for SAPA, a subsidiary of the Implenia Group, which is active in real estate services and construction (4). According to Jean-Noël Potin, Area Sales Manager at TWS, "End-to-end processing solutions are being implemented on an industrial scale within Europe for TWS, and we are handling projects with an ever-greater level of complexity". And there are more to come, including two in England and one in the Paris region, as part of the Grand Paris Express works. "These projects are also in the area of processing materials generated by construction sites, which require special treatment to extract the recoverable fraction", he explains.
Antag has invested a significant amount in its first fixed processing plant. The plant must be able to keep up with the increase in the number of materials being processed from the sites where the Group operates, which equates to 1 mt a year, as well as the materials that will be brought in by partners wishing to dispose of excavation waste.
Since it was commissioned, "It has been operating as planned, 9 hours a day and 5 days a week", notes Michael Schöni, Project Manager at Avesco. He oversaw this project and regularly visits Dittingen to ensure that the required tonnage output is achieved and that the machines were running at the correct rate. He knows that Roger Borer will call on him when changes need to be made to the process – the Swiss Government grants a 3-year authorisation for a plant of this type, but when this is renewed, there may be new rules to follow, particularly in relation to the control of materials.
Roger Borer has named this production facility 'Doro'. D stands for Dittingen, and oro means 'gold' in Italian. Because in Switzerland, although materials are not rare, they are becoming more and more scarce.
Future developments are in the pipeline that will improve processing capabilities and open up new opportunities. As previously noted, these include integrating a crushed aggregate production station for asphalt. There will also be a blending device, similar to those found in quarries, with a conveyor belt weighing system and mixing before loading. This will enable suppliers to make up a formula for customers upon request, all from a deposit now worth its weight in gold. Like Midas from Greek mythology, he turned everything he touched into gold, including the sand in the waters of the Pactolus... You could say it's a kind of allegory for the recycling industry in Switzerland.
Number references
1. The site is adjacent to a quarry that the Albin Borer Group took over 4 years ago when it set up the Barock Naturstein subsidiary. This operation is located just in front of the processing platform. A yellowish Jura limestone is extracted here, which is rich in fossils. This so-called Schachental quarry is located within a region known for quarrying since ancient times. This stone from the Birs Valley has been used to clad several of the region's buildings, such as in Basel and Geneva, as well as in New York. Mining activity peaked in the 19th century when a great many quarries and processing companies were in operation.
2. These materials manufacture all types of concrete (unclassified concrete, classified concrete, special concrete, concrete for highway infrastructure, etc.). The company performs checks on its production line, including particle size analysis, kurtosis, blue value, Los Angeles coefficient, sand equivalent, density, and water absorption coefficient.
3. Generally, the ratio used for washing 1 t of sand is 2.5 to 5 m3 of water. For alluvial sand, however, this ratio is 1:2, i.e. 2 m3 of water to wash 1 t of sand. If there is a clay content of 15 %, the volume of water required is 1:3, and double cycloning will also be required, using fresh water for the second cycloning cycle. However, double cycloning may not be sufficient, in which case a pre-wash tank or an upflow separator would be required.
4. This unit was produced on behalf of SAPA ("Public limited company for asphalt products"), a subsidiary of the Implenia Group located in Satigny, near Geneva. It has a 150 t/hr feed. The clay content in the processed material ranges from 23 to 30 %.
Albin Borer – the fourth generation at the helm
The origins of this Swiss holding company date back to 1932, when Heribert Borer set up a building and road construction business. In 1960, he transferred the company to his brothers, Albin and Arnold Borer, who relocated it to Erschwil, around 20 kilometres southwest of Basel, in the Soleure district. In 1964, the company began to specialise in construction and civil engineering. In 1988, it built its first mobile crushing and sorting plant to process construction materials.
Anton Borer, the current Managing Director, took over the reins of the family business in 1990 and set about expanding and developing it. He increased its workforce to 150 employees in 1998, obtained ISO 9001 certification in 2001, and to date, has renewed this certification regularly. The scope of its activities is increasing through external growth in the construction sector and the recycling sector, which saw the establishment of the Antag Recycling subsidiary in 2007. In 2011, it took over the Schachental depot in Dittingen, where the Doro plant was built in 2022.
Roger Borer is the fourth generation to lead the company, which has 11 subsidiaries and employs 500 people – including 300 in the construction sector – and generates a turnover of CHF 130 M.
Avesco, TWS’ Swiss partner
Avesco has been TWS' Swiss distributor for the last 7 years. They were tasked with installing and commissioning the plant. The company is well known in the Swiss Confederation as a distributor of many construction equipment brands, including Caterpillar, which it has distributed in Switzerland for 90 years, in addition to the Baltic States, Finland and Austria. In the construction sector, Avesco also represents Ammann, Thwaites, Rufener, Terex-Finlay and Evoquip.
The company represents Sandvik, Bauer and Klemm equipment in the tunnel construction, civil engineering and geothermal energy sectors. And in concrete transport, it represents Schwing, Stetter and Fliegl.
