Put bluntly, the ORCA in Hittfeld produces sand and stones, says Simon Gühlstorf, the plant manager. New ones, it should be added. What is delivered there is legally classed as waste: demolition waste from deconstruction projects, excavated soil, and mineral material from demolition contractors and construction firms. What ends up in the wheel loader at the other end of the plant has to hold its own alongside gravel from the gravel pit. On one day in mid-September, the amount came to around 500 tons.
ORCA stands for Otto Dörner Recyclinganlage (Otto Dörner recycling plant). The family-owned company from northern Germany, with around 1,300 employees, operates it as a wet processing plant for mineral construction and demolition waste. Gühlstorf had already examined the process together with Dörner in his master's thesis at TU Hamburg. He describes the working style at the company in two words that suit the region: direct and dependable. People say what they think, and they move from talking to doing. The plant's name follows the same pragmatism: “Nassklassierungsanlage” (wet classification plant) and “Baustoffwaschanlage” (aggregate washing plant) are simply a mouthful in everyday project work. So it became ORCA, a name that gives laypeople a way in and carries the right message. The abbreviation RC for recycling is seen everywhere in the industry anyway.
From waste to product
The material comes from demolition contractors and construction firms and is analysed and declared before it is accepted. At the reception area, the articulated lorry tips its load, and the wheel loader checks it and feeds the plant. In pre-treatment, the maximum particle size is limited, and steel, films and light materials are removed beforehand.
Then water comes into play. It separates the sand, which by definition ends at two millimetres, from the coarser aggregates. A density separation removes light material, and the water washes the grains. The wash water takes with it whatever the material picked up during its life, from chemicals used in operations to commercially available building products. It must not be discharged and has to be cleaned again. That is why half of the plant consists of water treatment, and why Gühlstorf is particularly proud of the closed water circuit. For the following process steps, what matters is what washing does to the material: the soil and sand that previously gave the input a uniform brown colour have been rinsed off, and each grain shows its own surface again.
A screen can arrange these grains by size. It classifies, says Gühlstorf, but it does not sort. It knows how big a grain is, but not what it is.
Where colour decides
At this point, two MSort AP units are at work, one for the particle size range of 8 to 16 millimetres 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 the colour of the surface, and compressed air nozzles direct each grain into the stream that matches its colour. Because the grains have just been washed, the camera sees differences that would be invisible under a layer of soil. The MSort AP is also built for moist material and needs no artificial drying.
One target product, two usable streams
An example: basalt was the target product, and it ran on both particle size ranges. Alongside the dark rock, the stream contained red brick, glass, asphalt and concrete, which have to be removed from the basalt product. The camera detects them by their colour, the compressed air separates them, and at the end the wheel loader loads the basalt. Separating the wheat from the chaff, as Gühlstorf puts it: one input stream becomes two output streams. What is separated off is therefore not automatically reject material, because what is good and what is bad depends on the target. Which stream is treated as the target product depends on the input and the sorting programme. Changing the programme gives a different material mix, with properties that suit other uses better. This makes it possible to remove red rock, produce black aggregate deliberately or separate glass and asphalt: anything with a colour that is characteristic of its material.
What comes out can be used in construction like a primary raw material, for example as an aggregate for concrete. The quantity is enough to supply a concrete plant continuously, so that it does not receive material one day and none the next.
For Gühlstorf, the standard is what counts
Gühlstorf describes himself as good-natured, but he is precise when it comes to quality: for him, the standard is what counts, and if the material meets the standard, he is satisfied. For red brick in grey or black material, the ORCA achieves an impurity content of less than 10 per cent. For glass, the share of impurities in the product is even below one per cent. With asphalt and glass he does not rest on his laurels: there, for him, more is more.
Dörner did not have to wait until the plant was running to know that the sorting would manage this. Before the first machine was bought, the team tested the plant's main sorting tasks at the STEINERT Test Center in Wedel, the place 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 had even been ordered. Construction and assembly also went without complaints, deadlines were kept and the installation instructions were sensible.
A plant that keeps learning
The day Gühlstorf felt a weight lift from his shoulders was the day the theoretical process worked in practice. Commissioning has been under way since autumn of last year, and technically the plant has reached normal operation. The basic sorting tasks deliver what he had in mind. Now it is a matter of fine-tuning with the technicians from STEINERT and of things that cannot be planned on paper: belt transfers, bearings, points where dirt collects or wear is too high. Performance is measured by throughput, product quality and the range of products.
Gühlstorf assumes that recycling will sooner or later replace the conventional gravel deposits, because the pressure on land is rising. In his view, the 1960s and 1970s, when large areas near major cities could be bought cheaply and an opencast operation could be started, are over. His advice to others facing a similar project: simply get started and do not lose heart. Then it will be fine in the end.