Otto Dörner's ORCA wet plant turns demolition waste into washed aggregate

Roughly 500 tonnes of mineral demolition waste moved through the ORCA wet processing plant in Hittfeld on a single day in mid-September. Plant manager Simon Gühlstorf puts the output plainly: the facility produces sand and stones — new ones. The material has to hold its own against gravel from the pit, and Gühlstorf's quality standard is set accordingly.

ORCA stands for Otto Dörner Recyclinganlage. The family-owned company from northern Germany, with around 1,300 employees, operates the site as a wet processing plant for mineral construction and demolition waste. The name is pure pragmatism: "Nassklassierungsanlage" and "Baustoffwaschanlage" — wet classification plant and aggregate washing plant — are a mouthful in daily project work, so the company chose ORCA.

How does the plant turn waste into product?

Trucks arrive from demolition contractors and construction firms carrying demolition waste, excavated soil and mineral material. Every load is analysed and declared before acceptance. At reception, the articulated lorry tips its load and a wheel loader checks it and feeds the plant. Pre-treatment caps the maximum particle size and removes steel, films and light materials.

Water then does the separation work. It splits the sand — which by definition ends at two millimetres — from the coarser aggregates. Density separation removes light material, and the wash water carries off whatever the grains picked up during their service life, from operational chemicals to standard building products. That water cannot be discharged and must be cleaned again. Half of the plant consists of water treatment, and Gühlstorf is particularly proud of the closed water circuit.

Washing changes what the sorting cameras can see. The soil and sand that gave the input a uniform brown colour rinse away, and each grain shows its own surface. A screen downstream classifies the grains by size but, as Gühlstorf notes, does not sort them: it knows how big a grain is, not what it is.

Where does colour decide the separation?

Two STEINERT MSort AP units handle the sorting, one for the 8-to-16-millimetre fraction and one for 16 to 32 millimetres. The ranges are deliberately narrow so that size and other material properties overlap less during detection. Dörner already knew the technology from its sister facility in commercial waste sorting.

The grains fall past a camera that detects surface colour, and compressed air nozzles direct each grain into the matching stream. Because the grains have just been washed, the camera sees differences that a layer of soil would hide. The MSort AP is built for moist material and needs no artificial drying.

Basalt illustrates the method. It ran as the target product on both fractions, with red brick, glass, asphalt and concrete in the stream requiring removal. The camera detects them by colour, the air nozzles separate them, and the wheel loader loads the finished basalt. Gühlstorf frames it as separating the wheat from the chaff: one input stream becomes two output streams, and neither is automatically reject material. What counts as product depends on the input and the sorting programme. Changing the programme yields a different material mix suited to other uses — deliberate production of black aggregate, removal of red rock, separation of glass and asphalt. Anything with a colour characteristic of its material is a candidate.

What quality does the output reach?

The product can be used in construction like a primary raw material, for example as aggregate for concrete. The quantity is sufficient to supply a concrete plant continuously, so the buyer does not receive material one day and none the next.

Gühlstorf describes himself as good-natured but is precise on quality: the standard is what counts, and if the material meets it, he is satisfied. The numbers back the position:

• Red brick impurities in grey or black product: below 10 per cent
• Glass impurities in the product: below 1 per cent
• For asphalt and glass, Gühlstorf keeps pushing: "more is more"

Dörner did not wait for the plant to run before verifying the sorting performance. Before the first machine was purchased, the team tested the plant's main sorting tasks at the STEINERT Test Center in Wedel — the town where Dörner started in 1932 as a transport company. The result: with the MSort units, the standard is met. Gühlstorf recalls a lot of patience and advice before anything was ordered. Construction and assembly went without complaints, deadlines were kept, and the installation instructions were sensible.

What happens next at Hittfeld?

Commissioning has been under way since autumn of last year, and the plant has technically reached normal operation. The basic sorting tasks deliver what Gühlstorf had in mind — the day the theoretical process worked in practice, he said, a weight lifted from his shoulders. The current phase is fine-tuning with STEINERT technicians and addressing what cannot be planned on paper: belt transfers, bearings, points where dirt collects or wear runs too high. Performance is measured by throughput, product quality and product range.

Gühlstorf expects recycling to replace conventional gravel deposits sooner or later because pressure on land is rising. The 1960s and 1970s, when large areas near major cities could be bought cheaply and opened as gravel pits, are over in his view. His advice to others facing a similar project: get started, do not lose heart. Then it will be fine in the end.

The milestone to watch is the completion of fine-tuning at Hittfeld, and with it the plant's move from commissioning to fully steady production of washed, standard-compliant aggregate for concrete supply.