APPLICATION AREA — CEMENT, LIME AND BUILDING MATERIALS PRODUCTION

Cement and lime production are among the fundamental pillars of the construction industry. Crushing, grinding and firing limestone in rotary or shaft kilns produces clinker, cement, lime and hydrated lime — raw materials for concrete, dry mortar and plaster mixes as well as the chemical industry.

An increasingly important role is also played by the combustion of solid recovered fuels (SRF) made from sorted waste. It is precisely this combination of heavy-duty operation and waste-derived fuels that makes magnetic separation an essential part of the technology.

Did you know that modern cement plants already replace more than half of the heat previously obtained from coal by burning SRF? However, with every tonne of alternative fuel, metal contaminants also enter the operation and must be reliably separated.

WHERE WILL YOU FIND OUR MAGNETIC SEPARATORS IN CEMENT, LIME AND BUILDING MATERIALS PRODUCTION?

Limestone quarrying and crushing

Limestone is transported from the quarry to primary and secondary crushing. This is where the risk of metal contamination is greatest: loader bucket teeth and edges, drill bits from blasting operations, bolts and fragments from bucket-wheel excavators. These pieces of iron head straight into the crushers.

The following equipment is most commonly used in limestone quarrying and crushing:

Magnetic plates are suspended above the belt conveyor before the primary crusher — for occasional metal occurrence, the manually cleaned plate DND-MC is sufficient; for large amounts of contamination, we recommend the self-cleaning plate DND-AC. For high material layers on wide belts, the electromagnetic overband DND-AC E with a deep-reaching magnetic field is intended.

Because non-magnetic metals (manganese steel, stainless steel) are dangerous too, a tunnel metal detector is installed after the magnetic separator. This order is important: ferromagnetic metals are removed by the magnet, so the detector only stops the belt in exceptional cases, avoiding unnecessary downtime. We also supply the detector in a version with special treatment for outdoor environments.

Problems this solves: puncturing and longitudinal slitting of the conveyor belt, destruction of crusher jaws and hammers, shutdowns of the whole line.

Benefit for the customer: reduced repair costs, smooth operation and a fast return on investment.

Interesting fact: At a customer processing limestone, we deployed a combination of a magnetic plate and a METRON 05 D detector on a belt 1,200 mm wide at a speed of 2 m/s with a limestone layer of 250 mm — mill damage from metal was completely eliminated!

Grinding of raw materials and cement — mill protection

Crushed limestone, together with correction materials, is ground into raw meal; after firing, clinker with additives (slag, gypsum) is ground into cement. Mills and roller presses are among the most expensive machines in a cement plant and metal particles in the grinding circuit cause serious operational problems.

The following equipment is most commonly used when grinding raw materials and cement:

A magnetic drum MBZ is installed in chutes and transfer points before the mill, continuously removing iron particles from falling material without stopping the line — its robust design is built for bulky and abrasive materials. An elegant solution is also the conveyor head roller MV, which replaces the drive roller of an existing conveyor and separates metals without requiring additional space.

Problems this solves: accumulation of metal particles in the grinding circuit and air ducts, slowed material transport, damage to roller presses and mills.

Benefit for the customer: a stable material flow, fewer stoppages and more reliable operation.

Interesting fact: At a cement plant where coarse metal particles were accumulating in the grinding circuit after a change in the input raw material composition, the problem was solved by a magnetic drum MBZ 304 N 300 GRIZZLY with a 5-year warranty. The customer was so convinced by its performance that they ordered a second, identical drum for another part of the line!

Combustion of solid recovered fuels (SRF)

Modern cement and lime plants are replacing coal with solid recovered fuels (SRF/RDF) made from sorted waste. However, SRF contains large amounts of both ferrous and non-ferrous metals, which damage dosing paths, burners and the calciner. Customers therefore carefully evaluate the quality of the fuel supplied.

The following equipment is most commonly used when processing and burning SRF:

A self-cleaning magnetic plate DND-AC is suspended above the belt conveyor carrying pre-crushed SRF. For high material layers, we recommend the strongest range, MxF BEAST, with ferrite magnets, which can be suspended up to 500 mm above the conveyor and separates Fe particles from 0.5 to 300 mm. Non-ferrous metals (aluminium, copper) are separated by the eddy current separator ECS — a precondition for effective separation is an even, thin layer of material, ensured by the vibrating conveyor placed before the separator. The metal detector at the dosing inlet then serves as a final safeguard before the burner. For environments with explosion hazard, we supply equipment in ATEX design.

Problems this solves: damage to dosing technology and combustion equipment, customer complaints about SRF quality, aluminium in the fuel.

Benefit for the customer: safe combustion of cheaper fuel and demonstrable SRF quality.

Interesting fact: At a leading Czech SRF producer supplying fuel to cement and lime plants, metals are separated from the 0–300 mm fraction on a belt 1,400 mm wide by a DND-AC Mx8 F BEAST magnetic plate suspended 500 mm above the belt — with a 10-year warranty!

Lime and hydrated lime production

In lime plants, graded limestone is fired in shaft or rotary kilns into quicklime, which is further ground or slaked into hydrated lime. Finely ground materials place specific demands on separation — they tend to bridge and require the capture of even fine iron particles from mill wear.

The following equipment is most commonly used in lime and hydrated lime production:

Before the kiln, vibrating screens ensure the required limestone fraction — correct grading is a precondition for even firing. For chutes carrying ground lime and hydrated lime, we recommend the rotational magnetic separator MSR-MC: the rotating magnetic grate keeps poorly free-flowing powder in motion and prevents bridging. Where no obstruction can be tolerated in the material flow, chute magnets ML (magnetic lanterns) with magnets positioned along the sides of the chute are used.

Problems this solves: clogging of chutes by bridging hydrate, iron particles from mill wear in the product, uneven firing due to poorly graded fraction.

Benefit for the customer: a clean product meeting the requirements of construction and chemical industry customers, and a smooth material flow without clogging.

Production of dry mortar and plaster mixes

Dry mortar, plaster and concrete mixes are made by blending graded sand, cement, hydrated lime and additives. Iron contaminants here cause rust stains on finished plasters — and thus complaints.

The following equipment is most commonly used in the production of dry building mixes:

Vibrating screens grade dried sand into precise fractions, break up lumps of cement, limestone and gypsum, and ensure even flowability of powders before dosing. Into the chutes of individual components as well as the finished mix, magnetic grate separators in housing MSS-MC are installed — for large amounts of contamination, in the self-cleaning version MSS-AC, whose cleaning cycle runs fully automatically without human operation. Where the material has poor flow properties, we use enclosed magnetic drums MBZ.

Before bagging, a gravity free-fall style metal detector QUICKTRON 05 A is installed as a final check.

Problems this solves: rust stains on plasters, complaints from builders' merchants and end customers, damage to bagging machines.

Benefit for the customer: documented purity of every batch and fewer quality complaints = higher profit.

Site maintenance

Cement plant, lime plant and quarry premises are full of sharp metal contaminants that cause tyre damage on loaders, dumpers and trucks.

The following equipment is most commonly used for site maintenance:

A magnetic sweeper attached to a forklift's forks or towed behind a vehicle collects nails, wires and sharp fragments from service roads — significantly reducing tyre damage on heavy equipment.

Problems this solves: downtime of handling equipment due to tyre damage.

Benefit for the customer: lower operating costs for tyres.