When a Swiss customer needed an end-to-end excavation wash recycling system, Terex Washing Systems and their Dealer, Avesco, answered the call.
With thousands of tonnes of Construction and Demolition (C&D) and excavation waste being stockpiled each year, a system that can recycle this waste into a saleable product, has environmental as well as financial benefits to aggregates producers is exactly the solution Albin Borer AG, a Swiss Group in Construction, infrastructure and material treatment had been seeking when they began to investigate a way to recycle the waste they were sending to landfill.
Terex Washing Systems were tasked with finding a solution to this problem for this customer, which resulted in the design, manufacture and installation of a complete end to end excavation wash recycling system. Everything from the feeder to the filterpress was included in this installation, which manages to achieve throughputs of 250 tonnes per hour of C&D and excavation waste and producing 9 saleable products. The close working relationship between Albin Borer AG, our Dealer, Avesco and Terex Washing Systems, along with a high level of aftersales support has resulted in this unique project being commissioned successfully.
Albin Borer AG is an independent family-owned company, that has been in business since 1932. They are a strong, future-oriented business that provide high quality products for infrastructure, roads and they concentrate their strengths on a wide range of services in the construction industry. From their locations in Erschwil, Laufen, Bolligen and Basel, they operate in the cantons of Solothurn, Aargau, Bern, Jura and Basel. Many members of the family are still very active in the company and are very much part of the innovative advancements they have made over the decades.
Albin Borer AG wanted to start to process their own waste material, that was accumulating from infrastructure work that was happening in the region. Ultimately, they wanted to generate a saleable product and open up a new revenue stream for the business. One
major part of the overall plant design was based around high capacity on a small footprint, due to site space restrictions. In addition there was also not a lot of water available on the site, coupled with environmental legislation around water use, which demanded additional design expertise on Terex Washing Systems for the final solution. This state-of-the-art washing solution was achieved by the innovation team of applications and engineers at Terex Washing Systems in partnership with our dealer, Avesco, who designed this bespoke solution suited to their specific needs. This is a full ‘Feeder to Filterpress’ solution also incorporating crushing capability from our Terex Group Company, Terex MPS, as well as Terex Washing Systems AquaClear, full water treatment solution, incorporating a Terex designed and manufactured Filterpress, with the capability of processing 250tph of feed material, with the ability of processing 25 tons of sludge/final waste per hour.
From Feeder to Filterpress - The DORO site, in DIttingen, Switzerland, an installation of the Albin Borer AG
This installation is testament to the expertise within the team at Terex Washing Systems in conjunction with our Dealer in Switzerland, Avesco, have installed many wash plants in Switzerland. Right from the start of the process Terex Washing System worked extremely closely with Avesco and the customer Albin Borer AG to acquire their specific solution. The in-house applications team worked with the customer and dealer to carry out extensive laboratory testing to determine the material to be processed. From here the dedicated bespoke project engineering team designed a full the plant and solution to their needs, which was completely project managed by Terex Washing Systems and Avesco for the complete delivery install and commissioning of the plant. And it doesn’t stop there, as Terex Washing Systems and Avesco continue to provide 24/7 aftercare support as and when it may be required.
C&D and Excavation Waste
The Terex Washing Systems plant features all Terex designed and manufactured equipment for the key stages in the Wash Recycling process. The plant combines the process of Material Feeding, Rinsing, Crushing, Aggregate Scrubbing & Sizing and Sand Production all coupled with a full Terex Washing Systems AquaClear water treatment offering, ensuring that 95% of the water is recycled and reused within the wash plant. All of this is achieved on a relatively compact footprint, due to limited site space, made possible with unique and innovative design choices.
The feed material is made up of excavation from Albin Borer AG other businesses. An AggreScalp 125 receives feed material from the loading shovel and removes oversized stones (larger than 150mm) from the material, which is achieved by the 150mm gaps in the finger bars installed. These oversized stones are stockpiled for later use. Medium size 150/80 mm are sent via a side chute into a feed hopper, feeding the Terex MPS crusher, a Horizontal Shaft Impactor, HIS 3434. Since occasional pieces of metal were present within the feed material, an over-band magnet has been installed after each of the feed hoppers.
Out of the Terex MPS HSI impact crusher, the crushed stones are either passed to a dedicated stockpile, a dry 0-40 mm, or onto the main conveyor sending the raw material to the washing plant.
Screening, Scrubbing and Classifying
After oversized stone and any metals are removed from the feed material, it makes it’s way up the main conveyor and enters into a Terex 20 x 6 (6m x 1.80m) 3 Deck Rinsing Screen. This 20 x 6 “Pre-screen” Rinser gives the material an initial wash before the various fractions is split with different apertures on the screen mats. The sand (0-4mm) and water from the rinsing screen passes to the “Prewash” tank. The Terex Washing Pre Wash has a unique design features which allows the operator to process difficult or dirty material and ensures production of sand products that confirm to strict specifications. The 4 aggregrate fractions passes (4-80 mm) into the new Terex patented “HydroScrub” logwasher.
This HydroScrub is a unique design logwasher for aggregate scrubbing, patented by Terex which allows operators to hydraulically adjust the hull angle from 9° to 16°, depending on the raw material to be treated. This gives the operator the ability to process a wider range of feed materials and is ideally suited for recycling applications.
Whether the raw material is containing a lot of “light density” contaminants like wood, roots, plastics etc, then the angle is set up “high”, and floating elements are easily removed.. Likewise, if the raw material is containing more clay conglomerates, then the angle is set “low”, which results in a better ‘stone on stone’ scrubbing giving better throughputs and a cleaner aggregate product and eliminates the need for secondary scrubbing on high clay bound or dirty material.
The post-screen of the HydroScrub classifies the material into two different sizes - 4-40 mm and 40-80 mm. The 40 -80 mm can be sent back to the crusher, or it can be sent to the dry classifying screen. The 4-40 mm is also conveyed to the set of dry screens (see below).
Fine Sand Cleaning
The water that has washed the aggregates up until this point in the process along with the sand, is collected in the Terex Washing Systems PreWash tank. This unique solution is receiving all of the process water from the upstream process, with the sand, and the extra fines, clay, and contaminants, and light density particles:
The Terex Washing Systems PreWash tank allows the ability to produce sand products into specification from materials with a high silt content and is a must for recycling applications and plant operators. The principal of it is to pump less volume out than is entering the tank. It is designed to “overflow”, gently separating out extra fines, and the light density contaminants, keeping only the sand 0-4 mm, that will be sent by a centrifugal pump to the sand washing Hydro-cyclones module.
The Terex Washing Systems FM200 Sand Plant is part of the wider solution and it is fitted with separators, high performance cyclones, which are also specially design for recycling applications. The use of separators means the plant can handle the variability of material that is often the case with Construction, Demolition and Excavation material, and results in a reduction in losses of valuable sand product, and the production of an in-specification material.
The FM200 also features a double wash process. The Terex washing systems double wash process to maximum recovery of sand through the removal of silt, slimes and clays below 63μm.The sand slurry (0-4mm and water) is pumped to the primary separator for an initial wash. The underflow discharges onto the dewatering screen where it receives a further rinse. Any fine sand which passes through the screen is collected in the sump and pumped to the secondary separator for a final wash. It was necessary to double wash the material at the Albin Borer AG site due the high percentage passing 63-micron in the feed, which was identified in the initial laboratory testing.
After this double wash process, the two in specification grades of sand are dewatered onto the high frequency dewatering screen, which reduces residual water content in the final product to 10-15%. The water from both separators containing the minus 63-micron material is collected in a ground sump and pumped into the thickener tank—where the water management process begins.
Sludge & Water Management
The waste water is pumped into a low level thickener with flocculent added, from the central control room housing unit. Within the low level thickener, the waste particles of silt (minus 63-micron ) and clay combine with the “co-polymer”, or flocculent, to create a larger heavier particle that sinks towards the base of the cone. The flocculent dramatically speeds this process up and allows the clean water to weir over the top weir of the thickener into a collection tank, where it is recycled back into the wash plant.
The sludge that has been collected at the bottom of the deep cone thickener is pumped into a buffer tank, where it is stored until enough volume is gathered. At this point it is transferred into a filterpress. The Filterpress on this Albin Borer site is the Terex Washing Systems 165 plate press, with a plate size of 2m x 2 m. The function of the press is to recover the last remaining water within the thickened sludge.
The Filterpress has a working pressure of 16 bar (232 psi). Each plate is covered in a nylon filter cloth, which when filled with sludge under pressure, forces the remaining water to be removed from the sludge. This water is then recycled back into the wash plant to be used for washing aggregates and sand once again.
After the water has been removed from the sludge, bomb doors below the filterpress open and the hydraulic ram begins to decompress. The slurry cakes are then rapidly discharged into the bay below the filterpress. Particularly sticky cakes are removed with a pneumatic plate shaker that ensures all the plates are ready for the next cycle. The cakes below can then be re-used for several applications, such as lining for ponds.
Albin Borer AG opted for an automatic cloth wash system on their Filterpress, so that the lifespan of the filter cloths could be extended while optimum performance is ensured. This system cleans each cloth individually using a high-pressure water jet.
Johnston Patterson, Product & Applications Manager at Terex Washing Systems explained that, “This water management system recycles 95% of the water used for this application. Albin Borer AG only needs a small tank of water to top up the system every so often. This has a hugely positive impact on the environment and has financial benefits.”
The result for Albin Borer is the sustainable production of usable and saleable sand and aggregate product from C&D and excavation waste. This also has the environmental benefit of being diverted from landfill. Additionally, the water management products recycles the dirty water from the process and returns a clean water back to the process again for use.
Johnston Patterson explained that, “the customer is very pleased to have a solution in place to recycle their C&D and excavation waste. The working relationship between Terex Washing Systems, Avesco and Albin Borer AG has played a huge part in achieving a high level of performance for this plant.”