Current research and trends, part 2

In AT INTERNATIONAL 3/2010, pages 24–32, we had already reported on the lectures that were in the focus of attention on the first day of the conference “Processing and Recycling 2009”. The following report will highlight the program of the second day, the poster show and the company presentations. 

The second day of the conference started with addresses on waste recycling and valorization. Prof. Dr.-Ing. Daniel Goldmann (Technical University of Clausthal Institute of Mineral and Waste Processing, Waste Disposal and Geomechanics) drew attention in his paper on “Reduction of CO₂ emissions by means of intelligent interlinking of modern waste recycling and valorization processes via utilization of highly processed secondary raw materials in the mineral requisites and energy industries” to the paradigm shift that waste should increasingly no longer be studied only from the disposal, but instead more from the raw-materials supply, point of view (Fig. 7). Efficient recycling and valorization of waste will make it possible to save large quantities of primary raw materials and energy sources throughout the economic chain. The recycling structures applied in the case of life-expired vehicles, electrical and electronic scrap and packaging waste were cited as examples, up to and including the production and use of highly reprocessed plastics and fibers fractions.

Ansilla Bayha, Dr. Jörg Woidasky and Dipl.-Ing. Andreas Stolzenberg (Fraunhofer ICT, Pfinztal) illustrated in their address on “Tried and proven technology in a new process application” that all established reprocessing methods for plastics waste originate from minerals processing and have been adapted to the various reprocessing tasks by means of machine and process design. Hand picking is, for example, the origin of all sorting processes, including those for waste flows, although enrichment stages based on NIR spectroscopy have now very largely taken over this task. A “process tree” consisting of the material digestion, multi-stage dry- and wet-mechanical sorting processes, washing and multi-stage dewatering operations for the recycling of PET was used to illustrate commercial implementation on a 10 t scale. The commercially homogeneously sorted PET flake is compounded, with addition of a selected package of additives, melt-filtered and then processed to extrusion-moulded products, with the potential for 1:1 replacement of primary starting material.

Waste treatment and valorization is increasingly gaining in importance against the background of the current environmental situation. Waste is capable of replacing oil, coal and gas as a secondary fuel, and thus possesses considerable potential for energy-route recycling. Certain quality criteria must be fulfilled in order to permit utilization as substitute fuels (SFs) in industrial combustion systems. The address on „Potentials for experimental analysis of substitute fuels using the compaction and coring method“, by Prof. Dr.-Ing. Sylvia Schade-Dannewitz (Fig. 8), Dr. Jürgen Poerschke and Dipl.-Ing. (FH) Sebastian Döring (University of Applied Sciences, Nordhausen, Environmental and Recycling Technology course), reported on a new sampling method which achieves significantly lower error compared to the standard methods used up to now. This is attained by compressing the sample material in a geometrically defined mould and subsequent probability-proportional sampling by means of core borings directly from the compressed state. Not only the calorific value, but also the chlorine content of the substitute fuels used is of great significance, since this element causes corrosion problems in plant and equipment. Chlorine content is also of particular interest for pricing between substitute-fuel producers and users. Evaluation of organic and inorganic chlorine contents is possible from analysis of the chlorine content of the solids and the liquid, since the liquids contained in the specimens are forced out during compaction in the press.

The paper read by Dipl.-Phys. Bold (Bold-Technoconsult, Kaiserslautern) was entitled “Waste recycling and sorting using the Atritor-Scott turbo separator  and Atritor drying and pulverizing mills and mill classifiers, relatively unknown in Germany”. The turbo separator consists of a shaft fitted with grinding elements and paddles rotating in a horizontal cylinder. This cylinder features crushing bars in its upper and screen decks in its lower section. Its action can be optimized for any specific task by manipulating speed of rotation, tool configuration, tool-to-grinding bed spacing, the number, size and positioning of the paddles, and the type of screen deck used. Typical applications include depackaging of bread, cereals, vegetables, meat products, beverages, cans, cigarettes, ready meals, etc. Further uses extend to the recycling of drywall panels, glass-fiber-reinforced plastic (GRP) panels and paper-industry byproducts. Atritor also serves the waste-treatment sector with its turbo dryer, which is suitable for high-speed drying of sludges.

Atritor’s drying and pulverizing mills and mill classifiers, initially developed as early as the 1930s, made it possible to dry and grind moist coal breeze in a single operation and inject it directly into the combustion system. Atritor Ltd. nowadays supplies a whole series of air-swept mills with and without drying functions and with and without the classifying function. A number of mill types and their typical applications were examined. Atritor drying and pulverizing mills can process products up to a Mohs hardness of around 4.5. The dryer pulverizer is also capable of drying explosion-hazardous materials, thanks to the facility for drastic reduction of the oxygen content in the dryer achieved by means of systematic air recirculation. Glutinous products can be routed through a remixing circuit. At its facilities in Coventry, UK, Atritor operates pilot systems incorporating a full-scale turbo separator and all the mill types mentioned.

Regenerable feed materials are currently used for the generation of energy, in particular. The development of innovative technologies for “Preparation of regenerable feed materials”, examined by Prof. Dr. Ulrich Teipel (Fig. 9), Herbert Winter (Georg-Simon-Ohm University, Nuremberg, Mechanical Process Engineering/Particle Technol­ogy), Gerd Unkelbach and Rainer Schweppe (Fraunhofer Institute for Chemical Technology [ICT], Pfinztal), is in future to permit the use of regenerable feed materials for the production of special materials, fine chemicals and chemical feedstocks. Only the cellulose content of lignocellulose-containing materials (e.  g. wood, at approx. 40 to 50  % cellulose, 20 to 30  % hemicellulose, 20 to 30  % lignin and 2 to 6  % other constituents), used for production of papermaking pulp, in particular, has been of interest up to now, and the other main constituents – hemicellulose and lignin – in many cases remain unused. This address discussed the preparation of regenerable feed material via a range of comminution processes, focusing on the example of wood.

Dipl.-Wirtsch.-Ing. Christian Hein (BHS Sonthofen) provided in his paper, entitled “Digestions of shredder lights by means of combined comminution”, an insight into the problems of processing this difficult material (Fig. 10). The type of feed material, shredder design, degrees of shredder filling, and also exhauster intensity, determine composition, and correspondingly necessitate flexible processing. It has become apparent that sorting without prior mechanical preparation will not produce the desired result. The fine-particled to dusty ma­terial, in particular, has a great proneness to clogging in foam, and to adhering to plastics and metals. It is thus extremely difficult to overcome these adhesion forces simply by means of screening, sifting and separation. Combined comminution impact applying percussion and shearing forces makes it possible to process this heterogeneous mixture and, depending on depth of sorting, to produce final fractions ­possessing defined and largely homogenous properties.

The development of the patented UNI-CUT^® QZ universal cross flow shredder has provided a new, in principle simple and extremely effective recycling technology in terms of the processing result, for the field of materials recycling. Dr. Siegmar Schäfer and Dipl.-Ing. Andre Schäfer (MeWa Recycling Maschinen und Anlagenbau GmbH, Freiberg office) reported on “New recycling applications for the QZ universal-cross flow shredder”.

The functional principle of the cross flow shredder is based on input of energy via rotating flexible tools, or “working elements”, which accelerate the feed product and generate a special product motion in the cylindrical working chamber. The geometry, particle size and degree of digestion of the end product are determined by the machine’s mode of operation (batch or continuous), rotor speed and the product‘s residence time in the working chamber. The machine can be used for recycling of refrigerators and freezers with adherence to the strictest environmental standards. High-quality metal fractions and a plastics fraction suitable for further processing are generated in a single operating stage. The HCFCs so problematical for the environment can be separated from the PUR foam down to residual contents of <  0.2  %, and then recovered. The machine has also proven its capabilities in processing of electrical and electronics scrap. New recycling applications for the cross flow shredder include processing of metal/plastics fractions from waste-incineration and substitute-fuels plants, cleaning of steel and non-ferrous scrap from incineration plants, recycling of beverage-can scrap from the DSD dual-system collection program, removal of composites from used wood/metal mixtures, digestion of values fractions from recycling of life-expired vehicles (catalysts and metal/plastic composites) and other waste fractions, and also optimization of the processing of bio-waste and regenerable feed materials (Nawaro) upstream biogas plants. The principal benefits of the cross flow shredder can be found in its broad range of potential applications, the machine‘s insensitivity to solids in the feed material, low specific wear costs, fast and easy tool changing, facility for generation of a shielding atmosphere in the working chamber, and therefore for processing of problematical materials under an inert atmosphere, and the ability to match mechanical and process-engineering parameters to the feed material.

Dipl.-Ing. Thomas Krampitz, Dr. H.-Georg Jäckel (TU Bergakademie Freiberg mining and technology academy, Institute for Processing Machinery) and Dr. Georg Timmel (REMONDIS Assets & Services Anlagentechnik, Lünen) presented a “Paper on the design of screening drums for waste reprocessing”. The demands made on the recycling processes used for commercial waste and packaging lights (PL) are increasing continuously, with screen-based grading in screening drums playing an important role as a preparatory processing stage for subsequent sorting. The screening drums used up to now in reprocessing plants, and modified by the manufacturer, exhibit good, but in some cases also unsatisfactory, functioning, depending on the operating parameters. Feed mixtures containing wire and geometrically unstable materials such as films, foils and textiles, which are typically present in commercial waste and packaging lights, have proven to be particularly difficult to screen. This address focused on results obtained during operation and in a pilot plant for improvement of the operating regime and thus for the design of screening drums for practical use, citing the example of the classification of difficult-to-screen flows (commercial waste and packaging lights).

Dipl.-Ing. Martin Steuer (Fig. 11) and Dr.-Ing. Thomas Folgner (TU Berg­akademie Freiberg mining and technology academy, Institute for Processing Machinery) examined the difficult problem of “Sorting of particles by particle geometry”. Particle geometry plays an important role in many production processes, and is subject to strict quality requirements in many sectors. The innovative, high-throughput high-efficiency “serial ­classification” particle-geometry sorting principle developed in the context of a research project was studied in more detail in this paper. In this sorting method, sorting by particle geometry is accomplished by means of chronologically and spatially separate classification on the basis of not less than two characteristic particle dimensions. The process can be configured in such a way that sorting takes place either by the length characteristic, cubicity (“three-dimensionality”) or flatness characteristic of the particles. The principle was illuminatingly illustrated using the example of sorting by cubicity. During sliding motion of the particles over a surface featuring round-section apertures (a perforated plate), the largest dimension of the particle determines the probability of the particle passing through the aperture geometry. The coarse fraction generated can then be classified into sub-fractions of differing particle thicknesses using bar-screen decks at defined spacings in each case.

“The SLon magnetic separator: Advances in wet magnetic separation” was the title of the paper presented by Dr. Udo Jakobs (Dr. Jakobs GmbH, Simbach/Inn) and Dr. Ian Sherrell (Outotec Inc. USA). This magnetic separator has been ­developed in order to overcome the disadvantages of the high-gradient magnetic separators used up to now. The ­functional principle of the separator was explained, and specific applications in the processing of iron ore and quartz examined.

The paper presented by Ferdinand Schmalholz (R-CON-GmbH, Markt­oberdorf) was entitled “EXSOR: Sorting of metals with top-line results – Innovation ‚Made in Germany”. The EX-900 sorter incorporating the EMCAM^® (ElectroMagnetic CAMera) system recently developed by EXSOR, of Hamburg, was examined. The feed material (6 to 80 mm) reaches the machine via a vibrating trough and then passes along a conveyor belt (width: 900 mm) at a speed of 3.2 m/s. The EMCAM^® sensor located beneath this belt recognizes all the materials present and transmits corresponding information to the downstream array of nozzles, which features one hundred and fifty high-output valves. The fractions are air-blasted out at up to two thousand „shots“ per second and separated from residual material via a separation plate. The system recognizes all conductive material and removes ferrous and non-ferrous metals and VA steels from precomminuted fractions at high speed and with high precision, at low energy consumption (compressed air).

Messrs. Gudrun Petzold, Simona Schwarz (Leibniz Institute of Polymer Research, Dresden) and Antje Lieske (Fraunhofer Institute for Applied Polymer Research, Golm) reported on the “Recovery of useful materials from non-aqueous suspensions using innovative polycations”. The research work examined is concerned with monoflocculation using polycations of high molecular mass, and also with hydrophobic molecular contents, which are capable, at optimum dose, of completely removing solids. Specific glycol-containing suspensions from industrial production were used to demonstrate that both the particle and glycol contents can be returned to the process, additionally saving significant costs for disposal of spent process liquids.

“Production of MFP^® via recycling of soft-magnetic ferrite waste”, by Silvio Gablenz and Marko Kloucek (TRIDELTA Weichferrite GmbH, Hermsdorf, Thuringia), provided an example that qualitatively removed soft-ferritic MnZn ferrite cores – so-called „sinter scrap“ – can be recycled into high-quality innovative materials. Potential applications for MFP^® can be found, for example, in the design of inductive sensors, and as a material for components for electromagnetic compatibility applications.

Despite the high anticipated service-life of twenty-five to thirty-five years for thin-film photovoltaic modules on a cadmium-telluride (CdTe) and copper-indium diselenide/disulfide (CIS) basis, recycling strategies which satisfy both ecological and economic criteria are required even now. Information on the status of this work was provided in two series of posters, “Recycling of thin-film photovoltaic modules using a vacuum-suction blasting process”, by Messrs. Jürgen Wolf and Sigurd Ruhland (GP innovation GmbH, Lübbenau), Wolfgang Berger and Kerstin Meissner (BAM Federal Institute for Materials Research and Testing, Berlin), Ulrich Riebel and Jörg Perwin (Technical University of Brandenburg, Cottbus), and “Wet-mechanical processing of thin-film photovoltaic modules: Initial results from an AiF project”, by Messrs. Wolfgang Berger, A. Bredow, J. Freywald, S. Lang and Kerstin Meissner (BAM Federal Institute for Materials Research and Testing, Berlin, Specialist Group IV.3 Waste Treatment and Remediation of Existing Pollution). Removal of the semiconductor films is based on vacuum-suction blasting technology, for which purpose a pilot plant, using which the useful materials can be recovered with the lowest possible abrasion of the substrate materials, must be developed, constructed and tested. Following removal of the thin films by means of vacuum-suction blasting, the values – tellurium and indium, in particular – are to be concentrated as effectively as possible from the remaining mixture of semiconductor materials, abraded glass and blasting agent. The best results up to now in laboratory-scale flotation tests have been achieved with the use of the potassium amylxanthate (PAX) foaming agent for concentration of indium from the mixture of CIS semiconductor material, glass and blasting agent (glass shot of < 50 µm).

The „Analysis of crushing element motion and energy distribution in agitator mills and planetary ball mills“ poster, by Messrs. Stefan Strege, Stefan Rosenkranz, Sandra Breitung-Faes and Arno Kwade (Institute for Particle Technology, Technical University of Braunschweig), provided an overview of research projects in this field, which is important for the production of micro- and nanoparticles. The progress of comminution in mills with freely mobile grinding elements is dependent on the frequency and intensity of particle loading. The discrete element model (DEM) makes it possible to precisely describe conditions in these mills and to simulate the progress of comminution.

Numerous new and further developments were unveiled in the context of the company presentations. “Machines for comminution and recycling of plastics”, by Herbold Meckesheim GmbH, focusing in particular on the recycling of waste from the plastics-using industry, the processing of used, mixed and contaminated plastics, and the fine grinding of plastic granulates and waste. Dr. Jakobs GmbH, of Simbach am Inn, specializes in the physical and physico-chemical separation processes of “magnetic separation – electrical separation – flotation”, representing the Outotec (USA) Inc., company and its machines, primarily for use in the separation and processing of minerals, and for recycling. GRAINsoft GmbH (Dipl.-Math. Volker Reinsch) has developed, in the form of its PMP (Particulate Materials Processing) software, an effective tool system which supports qualified, practically orientated analysis, planning, optimization and diagnosis of comminution and classifying processes, and also grinding circuits, for the “Process-engineering modeling of grinding circuits”. CeramTec-ETEC GmbH, of Lohmar, presented its Alotec^® materials for use as wear-protection, structural ceramics and composite systems. IMRO Maschinenbau GmbH, Uffenheim, specializes in the handling and separation of waste, and in the planning and construction of complete recycling plants. IMRO’s latest developments include its RCSX non-ferrous-metal separator, featuring an eccentric pole system. The same company’s new, sensor-assisted separation system, employing metal detec­tors, in the form near-infrared separators or X-ray sorting systems, permits efficient and highly selective removal of the most diverse materials from the flow of recycled useful materials. EUROFINS-AUA GmbH, Freiberg office, showcased its portfolio of services for the detection, measurement and evaluation of environmental contamination in the soil, water and air,
for definition of existing pollution, for ecotoxicology, ­environmental and quality management, and for the analysis of soil, water, liquid and solid products, etc. Further ­
exhibitors included Hosokawa Alpine AG, Augsburg,
AKW Apparate + Verfahren GmbH, Hirschau, Atritor-boldtechnoconsult, Kaiserslautern, HAVER & BOECKER OHG Maschinenfabrik, Münster, ITE GmbH, Alsdorf, and the host company, UVR-FIA GmbH, of Freiberg.