Optimized output quality in an innovative standard process

Surrounded by beautiful mountain views of the Alps, you will find the headquarters of the BHS-Sonthofen group of companies on the outskirts of Sonthofen. Even from a distance, you can see the blue company logo and the modern buildings...but the beginnings go way back to 1607. Even back then, there were ironworks here to process the mined iron ore. The first mention of this location is in 1607 as an iron smelter and hammer mill; in 1912, crushers began to be manufactured. BHS-Sonthofen became a state-owned company in 1953. In 1996, Dr. Christof Kemmann took over and continued to run BHS as an owner-managed group of companies. Today Dennis Kemmann heads the company as CEO of BHS-Sonthofen GmbH. Worldwide, the BHS group of companies consists of four production sites in Germany, China, Italy and Slovakia and ten subsidiaries worldwide.

Since 1997, BHS-Sonthofen has also been active in the recycling business - and the area is growing. With an eye on the future in the field of control technology and the buzzword IoT, BHS-Sonthofen took over Thoma Elektrosteuerungsanlagen GmbH from Babenhausen near Memmingen with effect from 1.1.2020 as part of the newly founded subsidiary BHS Control Systems GmbH & Co. KG. „The portfolio expansion in the field of control technology now enables BHS-Sonthofen to offer everything from a single source for small projects and also for large projects such as multi-stage recycling plants. The proven high quality of BHS can thus be guaranteed for even more components and solutions,“ emphasises Dr Steffen Kämmerer, Chief Technology Officer (CTO) of BHS-Sonthofen and Managing Director of the newly founded BHS Control Systems GmbH & Co. KG.

The latest expansion in the recycling sector was a participation by BHS-Sonthofen in the technology area of separating, sorting and classifying technology. Since September 2021, BHS has held a 50 % stake in RW Recycling World GmbH in Switzerland. Founded in 2002, the company has proven technologies for separating, sorting, sifting, screening and separating. For the Recycling & Environment business unit in particular, this represents a significant expansion of process expertise, the technology portfolio and the value chain offers BHS the opportunity to design complete plant lines from a single source.

There are clear ideas for the further orientation of the steadily growing company: Focus as the key to success. The declared goal of BHS is therefore to specialise even further in specific areas of application. „In the future, we will focus primarily on specific applications in the recovery of high-grade metals from a wide variety of waste and residual materials, as well as in battery recycling, in which we are technology leaders or aspire to be. This can only be achieved by clearly focusing on core segments and applications,“ explains Daniel Weber, Vice President of the Recycling Technology & Environment Division.

Recovering valuable metals sorted by type - fine processing by BHS

The topic of resource conservation is on everyone‘s lips - it's high time to use materials as carefully as possible and recovering them to a high degree. Metals in particular are often classified as critical substances whose recovery is absolutely essential for the sustainable use of resources. When processing waste electrical and electronic equipment (WEEE), shredder residues from automobile recycling or waste incineration ash, valuable metals are produced, especially in the small particle range below 25 mm. However, these must be separated from the accompanying materials, such as plastics or minerals, in order to be able to reuse them. For this purpose, BHS-Sonthofen has developed a modular standard processing line in many years of development and testing, the aim of which is to recover pure and ready-to-sell metal concentrates at a high throughput.

The feed material is a fine fraction of 0 - 25 mm. The composition of the material stream can vary depending on the application, country, etc. Thanks to the modular design and the experience of BHS, the fine processing plant can be adapted to the customer‘s input material and expanded according to individual needs. The heart of the plant is the BHS rotor impact mill in the RPMX version. Thanks to its special operating principle, the mill pulverises minerals, exposes metal strands and selectively shapes ductile metals into balls. In addition, it reliably removes cable sheathing and other substances adhering to metals.

Pre-sorting and crushing

In addition to the rotor impact mill, a number of other components are of course part of the innovative fine preparation process from BHS. First, the input material is collected in a hopper before it passes over a protective screen and zigzag classifiers in the first process step of pre-sorting. The protective screen removes impurities and parts with a grain size of more than 25 mm. Afterwards, the zigzag sifters removes the disturbing mineral particles and dust. This streamlines the entire material flow and minimises wear.

After pre-screening, the material goes into the rotor impact mill (RPMX). Here, the remaining mineral fractions are pulverised, metals are broken down, separated and ball shaped. The rubber and plastic components essentially pass through the mill without being crushed. The high peripheral speed of the rotor causes centrifugal forces to act. At the same time, the shredding tools generate impact and shearing forces (see Fig.: Functional principle of the rotor impact mill), which cause a high energy input into the feed material. With the help of a rotor cover plate, the material is additionally directed from above into a narrow gap between the anvil ring armour and the impact hammers. In this way, the entire height of the grinding gap is utilised for comminution, which ensures a longer dwell time and a higher loading frequency of the feed material. An intensive entanglement effect is created between the horseshoe-shaped beaters and the ring armour, which sets the conditions for subsequent, efficient separation and sorting of non-ferrous metals and other materials. According to the desired output result, the feed material is specifically processed in the rotor impact mill.

Further increasing effectiveness

In order to increase throughputs and make maintenance more effective and work-friendly, BHS further developed its rotor impact mill with the help of many tests, theoretical calculations and simulations. A new design of the hammers used ensures even more efficiency: „We examined the impact hammers of the RPMX and checked how we can become even more effective and robust here,“ reveals Jörg Ehrich from the Process Development department. „On the one hand, we are concerned with further optimising the output quality and at the same time reducing wear even more. On the other hand, the replacement and adjustment of the hammers in case of wear has been simplified considerably. The improved maintenance concept makes it easier for customers to make adjustments to the hammers themselves quickly and easily. In addition, we have integrated a special tool called a mandrel for removing the hammers as well as a load-bearing hook into the design. The latter simply hooks into the hammer so that it can be easily lifted out or in by crane, which significantly reduces the physical strain on personnel.“

The shredding process described is run 2-3 times in a cycle by default to achieve optimal preparation of the material. An alternative, more efficient material feed provides for a second rotor impact mill connected in series so that the material is continuously fed through the plant. With this variant, much higher tonnages can be processed. „If sufficient space is available and a higher throughput and continuous operation of the plant is desired, we have, for example, delivered plants with two rotor impact mills. The two machines are then connected in series, so there is no need to return the material,“ explains Ivan Glamuzina, Senior Project Manager at BHS. Whether it‘s a recirculation process or rotor impact mills connected in series: Before each further shredding pass in the RPMX, a zig-zag sifter removes light material and dust so as not to put unnecessary strain on the shredding technology.

Fine screening - the real added value

The final shredding step is followed by the second part of the process: sorting the processed material. For this purpose, it passes through a doser onto a screening machine, which sorts it into different fractions. What these are depends on the further processing. On the separating tables, the individual fractions are separated into „heavy“ - i.e. all metals and metal mixtures - and „light“ - usually plastics and rubber. Magnetic technologies separate the heavy fractions, which contain the valuable metals, into a magnetic and a non-magnetic metal fraction. The latter pass through a further separation step. An eddy current separator sorts the valuable fraction into heavy metals, such as copper, and light metals, for example aluminium. „Due to the fact that the RPMX already has all soft metals shaped into balls and hard metal parts are well separated, the material can be sorted excellently in the eddy current separator,“ explains Jörg Ehrich. All the finished sorted metal concentrates can then be sold directly.

Test investment security beforehand

Due to the large variance in the feed material, more precise knowledge of the material properties is necessary to coordinate the system components and process parameters. In 2019, BHS commissioned a new test centre for this purpose, among others, so that customers can be sure that their materials are optimally crushed and sorted with the fine preparation designed by BHS. The trials with original feed material that Jörg Ehrich and his colleagues carry out together with customers in the Sonthofen Test Centre form the basis for the process recommended and optimised by BHS. In addition, the trials and test results are used for further process optimization and as the basis for detailed plant engineering as well as for an individual profitability calculation.

In the future, further adaptation options could be added with the use of alternative and additional shredding technologies in combination with sensor-based sorting technology. „We are currently examining whether even higher output qualities can be achieved with this, for example in the recycling of lithium-ion batteries,“ adds Ivan Glamuzina. BHS-Sonthofen not only supplies complete and ready-to-use recycling plants. With its in-house technology portfolio – shredding, classifying, and sorting technologies as well as its plant control systems – the company also ensures maximum process efficiency and reliability for the key components of the process.

www.bhs-sonthofen.com