SPG Pumps and the ORCA project at OTTO DÖRNER
The processing of primary or secondary mineral raw materials often involves abrasive suspensions loaded with solids. With the “ORCA” project, OTTO DÖRNER Kies und Deponie GmbH is investing in a wet processing plant for soil/construction waste mixtures at its Seevetal site. The aim is to process more difficult material flows to a high standard and, among other things, to provide concrete aggregates of consistently high quality – an important building block for a more circular economy in the construction sector.
The plant is funded as part of the German government’s environmental innovation program and is considered one of the first of its kind in northern Germany. In order to be able to feed the material-laden process water into the closed water and material cycle of the ORCA plant in the first place, robust and appropriately designed pumps from SPG Slurry Pumps Germany GmbH are essential components of the plant.
The development of the robust armored pumps from the Bünde-based company is backed by longtime experience. SPG’s portfolio includes the complete design, service, spare parts supply, and repair of SPG pumps. SPG armored pumps are mainly used in the gravel and sand industry, steel processing, aerated concrete production, and mining, where media with grain sizes of up to 300 mm can be moved. The armored pumps can be configured in a modular fashion to meet customer requirements. These pumps were the perfect fit for the ORCA project, where ORCA stands for OTTO DÖRNER Recycling Plant. SPG supplied a total of 15 pumps for three plant areas.
The Seevetal site (Lower Saxony) is home to the group’s largest single project to date, with an investment volume of around € 22 million, of which around € 2.7 million comes from the Federal Environment Ministry’s “Environmental Innovation Program” funding program. The plant is designed to process rock material and produce high-quality recycled building materials. ORCA is essentially a wet classification plant for mineral building materials, in which the process water is treated and operated in a closed circuit. The mineral waste materials are processed to a fine grain fraction of 0 – 2 mm, and contamination from organic light materials is removed from the process. In this way, the OTTO DÖRNER Group is helping to use mineral construction and demolition waste as a resource for secondary building materials.
The AT MINERAL PROCESSING team spoke on site in Seevetal with OTTO DÖRNER’s technical project manager Simon Gühlstorf and the sales manager of SPG Slurry Pumps Germany GmbH, Andreas Laag, about motivation, plant technology, pump design, and the role of high-quality secondary raw materials in the market.
AT MINERAL PROCESSING: Let’s start with a look at the group of companies: Where does OTTO DÖRNER Kies und Deponie GmbH fit into the group and what role does the Seevetal site play?
Simon Gühlstorf: Within the OTTO DÖRNER Group, we are responsible for the gravel and landfill division. The group is one of the leading companies in the waste disposal industry and mineral building materials in northern Germany – especially in Schleswig-Holstein, Lower Saxony, Mecklenburg-Western Pomerania, and Hamburg. The company is headquartered in Hamburg-Stellingen.
Here in Seevetal, we operate a large site with raw gravel extraction including washing, a DK I class landfill, a composting facility, and a recycling plant. Our portfolio includes the classic range of a gravel plant: sand suitable for concrete, fill sand, and various grain sizes from 2/8 to 8/16 to 16/32. Via a transshipment port in Hamburg-Harburg, we can also offer gravel and grit products that we are unable to extract ourselves due to geological conditions.
In addition, we offer typical recycled products such as recycled gravel base courses, frost protection layers, and mixed recycled materials for construction roads. We operate a composting facility with compost and substrates for landscaping, and accept mineral waste via the DK-I landfill. Everything that can still be usefully recycled is recycled via our dry processing facility – and in future also via the new ORCA wet processing plant.
Around 65 employees currently work at the Seevetal site; the group has a total of around 1300 employees.
AT MINERAL PROCESSING: Why did you decide to build a wet processing plant – and what is ORCA designed for?
Simon Gühlstorf: We wanted to tap into material flows that have previously disappeared into the ground. The background is clear: in a linear economy, we lose valuable resources. Of course, you could say that “excavating gravel and backfilling” is a form of circular economy – and that’s true. But especially with building construction waste and soil/construction waste mixtures, there are many material flows that we have not yet been able to return to circulation in as high a quality as would actually be possible.
This is exactly where ORCA comes in. We want to recycle materials for which we still have difficulty finding meaningful recycling channels today. At the same time, we want to manufacture products of a quality that is clearly suitable for building construction – especially concrete aggregates.
The plant is designed for soil/construction waste mixtures, i.e., primarily concrete, bricks, and corresponding mixed materials. As a classic washing plant, it is particularly useful for soil-containing, “difficult” materials that are difficult to process to a high standard when dry. Clean, pre-sorted concrete rubble can also be processed well when dry – but to achieve our goal of converting more problematic material flows into high-quality products, we need the equipment required for wet classification.
AT MINERAL PROCESSING: What were you unable to achieve with dry processing in the past that is now possible with ORCA?
Simon Gühlstorf: In dry processing, we work with crushers, screening plants, metal separators, and air separators. This works very well up to a certain point. However, screening plants quickly reach their limits when there is a high proportion of silt, as they become clogged. Air separators can separate by density, but they cannot differentiate sand-containing fractions to the extent that we need for high-quality products.
In short, with certain mixtures, we are unable to separate the materials cleanly enough in dry processing to end up with a truly high-quality recyclable fraction.
It’s different in wet processing. There, we combine several density and grain size separations:
In the grain size range, we work with a wind sifter and a settling machine.
Washing gives us a float-sink separation.
In the sand area, we use several cyclone stages and an upflow separator for density separation.
The result is low-silt materials that are defined by both density and grain size. To be honest, we wash our raw gravel for exactly the same reasons. However, raw gravel is usually “cleaner” due to geogenic conditions. Recycled material requires a little more equipment, but we felt this investment was worthwhile in terms of a sustainable circular economy.
AT MINERAL PROCESSING: What stage is the plant currently at (as of mid-September 2025)?
Simon Gühlstorf: We are in the middle of commissioning. Cold commissioning has taken place and all units have been started up individually. The water cycle is about 95 % operational – that means everything is working in principle, but there are still a few adjustments to be made in some areas.
The selection and design of the pumps is just right, which we are naturally very pleased about. Once the closed water cycle is running smoothly, the next step will be to switch on the material and test the plant in warm operation.
AT MINERAL PROCESSING: You are very focused on high-quality secondary raw materials. How do you assess the market: Is there demand, or is there a lack of acceptance in planning and tendering?
Simon Gühlstorf: The figures clearly show that demand is higher than current output. Additional natural resources continue to be bound anthropogenically – i.e., newly added to the inventory – and are not sufficiently replaced by secondary materials.
Nevertheless, reluctance in tenders and among builders is a key issue: not as much recycled material is being used as could be. The bottom line is that we would certainly sell more material if secondary raw materials were used consistently.
In the end, a lot of this is reflected in the price: how expensive is it to dispose of low-quality materials, how expensive is it to process them, and at what price can we sell them in competition with natural products?
If I have poor-quality raw materials, low disposal fees, and high processing costs, I cannot offer them on the market at a competitive price. Then processing is not worthwhile.
It is not possible to say across the board whether recycled products are more expensive than primary materials. For our plant, we deliberately calculated using market prices for concrete aggregates. If we were to double the prices, we would immediately have a sales problem.
In addition, there are reservations in practice: The Substitute Building Materials Ordinance and the relevant TL regulations specify clear applications, e.g., for RC2 or RC3 material under sealed surfaces. We would like to see even more courage in this area. In the area of recycled concrete, we have had a classic chicken-and-egg problem up to now: large quantities of recycled aggregates were rarely kept in stock because they were only in sporadic demand – and vice versa.
With ORCA, we are taking the next step: we want to operate like a “real” gravel plant that can also deliver defined quantities from construction waste every day – for example, 1000 tons of aggregate – with the quality that a ready-mix concrete plant needs in order to be able to plan reliably.
AT MINERAL PROCESSING: How did the connection with SPG come about and what role do the pumps play in the plant?
Simon Gühlstorf: Once the basic plant concept was in place and we had clarified approvals and budget, we moved on to selecting suppliers. Everyone knows each other in the pump market – there aren’t an infinite number of suppliers operating in this segment.
SPG was a contender for us for several reasons: its proximity – Bünde is “just around the corner” for us, the good reputation of its pumps, the availability of spare parts from the factory in Bünde, and, most importantly, the technical support it provided during the design phase.
I joined the project in 2021, and we entered into discussions with SPG at a very early stage. The collaboration was pleasant and constructive from the outset. Our colleagues supported us in selecting the sizes, materials, and seals, which is a real added value in such a complex wet processing plant.
AT MINERAL PROCESSING: Mr. Laag, what do you think was crucial to the success of the project?
Andreas Laag: It was very positive for us that we were involved in the project at a very early stage. If we are involved in the pipeline planning from the outset, we can optimally tailor the design of the pumps to the plant.
The most important factors here are:
Flow velocity and sinking velocity in the pipelines: If the pipeline is oversized, there is a risk of solids settling. This would result in blockages and an “ever-decreasing” pipeline.
Pressure losses and geodetic height differences: Together with the desired flow rate, these determine the operating point of the pump.
Once we know which mixture – i.e., how much water with what proportion of solids – needs to arrive at which point, we can say very precisely which pipe diameter and which pump type are appropriate.
Of course, pipe routes, heights, and lengths sometimes change during the course of a project. In the case of ORCA, however, we were able to largely stick with the original pump selection; in the end, it was mainly the speeds that were adjusted. This suggests that the concept was right from the start.
AT MINERAL PROCESSING: How well are the pumps now performing in commissioning?
Andreas Laag: We are very satisfied with the performance. Cold commissioning showed that the pump sizes were well chosen. A controller is only as good as the unit it controls – if the pump does not fit the system, even the best control system is useless.
Currently, we are really satisfied. The pumps start up cleanly, they deliver the required flow rates and we do not have to artificially “throttle” them because they are oversized.
This is important for two reasons: on the one hand, the pumps operate in the optimum efficiency range, and on the other hand, we avoid unnecessary energy losses due to oversized pumps.
And if something should happen during later operation, we have an extensive inventory in Bünde – both complete pumps and spare parts. This is a key point for operators: in the event of a malfunction, replacements must be available quickly.
AT MINERAL PROCESSING: A quick look at SPG Slurry Pumps Germany GmbH: How long has the company been in existence and what are its main areas of focus?
Andreas Laag: SPG was founded just over ten years ago by Reinhard Langer. He later handed SPG over to his son Jens Langer, who took over the company during economically challenging times and has consistently developed it further.
Today, we are in a comfortable position: despite the difficult construction market, our business is growing because, as a relatively small company, we can already make significant gains with just a few additional percentage points of market share.
Three points are central to us:
Large stock of pumps and spare parts to ensure short delivery times.
Intensive consultation: We coordinate piping, flow rates, materials, and sealing concepts closely with our customers.
Specialization in abrasive media, such as those encountered in the ORCA project.
AT MINERAL PROCESSING: What are your hopes for the future –
in terms of technology and the market?
Simon Gühlstorf: From a technical perspective, we naturally want a stable, robust plant that delivers the expected quality. The initial tests give us cause for optimism.
On the market side, it would be important for planners and clients to be even more open to secondary raw materials – especially where regulations already allow this today. If tenders consistently specify recycled materials, it will also be easier to justify investing in high-quality processing technology.
With ORCA, we believe we are building a bridge: we are showing that “difficult” soil/construction waste mixtures can be used to manufacture high-quality products, including concrete aggregates. And we can supply these qualities in relevant quantities. If this is accepted by the market, much will be gained – for us as a company, but above all for the circular economy in construction.
