APPLICATION FIELD – ENERGY AND HEATING INDUSTRY

The energy and heating industry is currently undergoing a fundamental fuel transformation – from coal to biomass, solid recovered fuels (SRF/RDF) and energy recovery from waste (waste-to-energy). All these fuels have one thing in common: they travel in large tonnages along fast conveyor belts, pass through crushers, mills and feeders, and contain unwanted metal objects – so-called tramp metal: nails, screws, wires, pieces of steel from handling and fragments of tools.

Metal contamination damages expensive equipment, causes unplanned downtime and reduces fuel quality. SOLLAU s.r.o. is a Czech manufacturer of magnetic separation technology that designs and produces tailor-made equipment for this sector – from capturing coarse tramp metal on fast belts to recovering both ferrous and non-ferrous metals from incinerator bottom ash. All production takes place in the Czech Republic.

Did you know…? Bottom ash from energy recovery from waste contains 8.5–10.3 % ferrous scrap and 1.6–2.2 % non-ferrous metals – a modern separation line can sort up to 80 kg of iron and 25 kg of non-ferrous metals from a single tonne of bottom ash. What used to end up in landfill turns into a secondary raw material.

Introducing magnetic separation into energy and heating plants protects crushers, mills, feeders and boilers, increases both fuel purity and calorific value, and turns metals from bottom ash into a secondary raw material. This has a positive impact on the profitability and efficiency of production.

WHERE IN THE ENERGY AND HEATING INDUSTRY WILL YOU FIND OUR MAGNETIC SEPARATORS?

Biomass combustion – wood chips, sawdust, straw and pellets

Biomass from forest logging, handling and especially from crushed pallets and recycled wood contains nails, screws, wires, stones and sand. Before it reaches the boiler, it passes through a chipper, crusher, mill and a series of conveyors – and in each of them the metal admixture causes harm. Moreover, the calorific value of forest wood chips fluctuates with the season, so every loss of fuel quality counts.

The following equipment is most frequently used in the preparation and transport of biomass:

Overband plates and electromagnets are installed transversely above the biomass conveyor belt, or longitudinally above the discharge point (head pulley), where the material loosens as it falls and the magnetic field penetrates deeper – this is advantageous with hard-to-flow wood chips and thick layers on the belt. Enclosed and semi-closed drums are placed at the outlet of the crusher/chipper or into the hopper before the boiler feeder. Magnetic lanterns ML are suitable for sawdust prone to bridging, where grate magnets cannot be used.

For abrasive materials, the drum shell can be made of manganese steel or with a replaceable cover shell that can be changed through an inspection opening without dismantling the whole drum. A damaged crusher = unnecessary repair costs, an idle boiler = loss of heat supply – the automatic cleaning of DND-AC plates works without interrupting the material flow and without manual operation. SOLLAU also supplies magnetic technologies to leading manufacturers of mobile crushers and screeners.

Advantages of DND-AC overband plates:

• Strong field from an installation height of up to 500 mm (ferrite BEAST range), capture of Fe particles 0.5–300 mm
• Automatic cleaning without interrupting the material flow, all-stainless design, no blind spots
• 10-year warranty

Coal-fired power and heating plants – coal transport, crushing and milling

Tramp iron (rail spikes, screws, nuts, tools, steel fragments) from the mine or from transport damages coal feeders and pulverisers. Metal cannot be ground and causes extreme stress on bearings, shafts and grinding rings; a large piece can break a segment of the grinding ring and put the mill out of operation. Added to this is the dusty and explosive environment of coal dust, which requires equipment in an ATEX design.

The following equipment is most frequently used in coal transport and milling:

Magnets are placed above the fast reclaim and feed coal conveyors, preferably at the point of free fall above the discharge, where the coal layer opens up and the metals separate more easily. For deep layers and wide belts, the electromagnetic overband DND-AC E with an installation height of up to 600 mm is ideal; the magnetic head roller MV replaces the end (drive) pulley of the conveyor and captures metal from the bottom layers. Before the coal mill, the enclosed drum MBZ in ATEX design proves effective.

From practice: the German energy company RWE deployed an extremely strong neodymium drum MBZ 304 N 1000 certified for the most explosive zone 20 (ATEX) in a lignite power plant. We placed the drum before the coal mill – it met the strict requirements of the Mining Authority, captures ferromagnetic objects from as little as 0.5 mm and, compared to the original worn ferrite drum, significantly increased the overall capture rate and thus the protection of downstream equipment.

Energy recovery from waste (waste-to-energy / incinerators) – separation of metals from bottom ash

After municipal waste is burned, bottom ash remains full of both ferrous and non-ferrous metals. Sorting them out has a twofold benefit: recovery of valuable secondary raw materials and treatment of the bottom ash for construction use. The correct order is key – first iron with a magnet, only then non-ferrous metals via ECS, because iron disturbs the eddy current technology.

The following equipment is most frequently used in bottom ash processing:

The chain is arranged after the wet bottom ash extractor (after ageing and crushing): first a magnetic plate above the conveyor and a magnetic drum or magnetic head roller removes iron, then the ECS separator repels and ejects non-ferrous metals (aluminium, copper, brass).

Wet bottom ash is sticky and therefore standard magnetic drums cannot be used, because the ash would stick to them and thus reduce their efficiency. That is why we often install a set of two magnetic drums in a special configuration, where the drums are placed above the bottom ash conveyor, from which they pull out metal impurities without contact. These are then taken over by another magnetic drum, the ash residues fall off, and the result is clean ferromagnetic contaminants free of ash.

For maximum yield, multi-stage magnetic re-cleaning and optimisation of the magnet tilt prove effective; hoppers are made of non-magnetic steel so as not to disturb the field. A vibrating feeder ensures uniform dosing of the bottom ash.

About 80 % of the ferrous scrap is in particles above 20 mm, whereas 80 % of non-ferrous metals are in particles below 20 mm – that is why ECS separators from SOLLAU achieve an efficiency of over 99 % and separation from 0.5 mm (BUFFALO model), with a 3-year warranty and 3 free service inspections. Ineffective separation = lost raw materials and bottom ash that cannot be used in construction.

Advantages of ECS non-ferrous metal separators:

• Separation efficiency over 99 %, separation of non-ferrous metals from 0.5 mm
• Both concentric and eccentric rotor depending on the fraction and type of metal
• Working width 500–2000 mm, 3-year warranty + 3 free service inspections

Production of solid recovered fuels (SRF / RDF) from waste

Fuel for cement works, lime kilns and glassworks is produced from crushed waste. Metals in SRF/RDF damage the manufacturer's crushers and presses and the customer's combustion technology. Metal components additionally increase boiler corrosion and emissions. Customers therefore carefully assess fuel quality – and impure fuel means a complaint.

The following equipment is most frequently used in the production of alternative fuels:

The magnetic plate is suspended transversely or longitudinally above the belt carrying the crushed waste; for deep layers, the electromagnet DND-AC E is used. Where the belt inclination exceeds 30° (the plate's discharge belt would slip), separation is solved with a magnetic drum between the dosing hopper and the conveyor. Non-ferrous metals and aluminium from laminates and packaging are removed by the ECS separator.

Documented SOLLAU implementation: a leading Czech manufacturer of alternative fuels from sorted waste deployed the overband plate DND-AC Mx8 F BEAST, which separates ferromagnetic impurities from a distance of 500 mm above the belt (fraction 0–300 mm, belt width 1400 mm, layer 300 mm, speed up to 3 m/s). Metal in the fuel = complaint and a damaged boiler at the customer – clean SRF/RDF means higher calorific value, less corrosion and a satisfied customer.

Biogas plants

The input biomass and substrate – especially from waste and agricultural raw materials – carry metal objects that damage pumps, rotary macerators and fermenter agitators. Magnetic separation at the inlet protects this expensive technology and ensures smooth operation of the fermentation.

The following equipment is most frequently used in biogas plants:

Magnets are placed on the substrate inlet conveyor and into the hopper before the feeding, crushing and maceration equipment. For liquid fermented biomass in pipelines, a pipeline magnetic separator is used, which captures wear debris from pipes and fittings. A jammed agitator = an idle fermenter and a loss of biogas production.

Processing of fly ash and bottom ash for the construction industry

Fly ash and bottom ash are used as a substitute for cement or aggregate (road base, concrete elements). However, residual ferrous and non-ferrous metals reduce the quality of the secondary mineral material and prevent its certification, so it is necessary to re-clean them.

The following equipment is most frequently used in the processing of fly ash and bottom ash:

The separators are placed in a gravity chute or on a conveyor after screening and sorting. High-gradient multi-stage rollers VMSV are used for fine and weakly magnetic ferrous particles, and non-ferrous metals are removed by ECS. The benefit is higher purity of the mineral fraction, compliance with standards for construction use and a reduction in the volume of landfilled waste.