Shredding slagging

As consequence of the fact that only the organic materials are shredded, both glass bottles and cans remain intact. Maintenance and power consumption are also significantly reduced. In addition, the extremely low glass-content of the RDF minimizes equipment abrasion and reduces potential slagging problems in the thermal conversion process. 

House-hold and industrial waste is shredded in a hammer mill where pieces of 4 inch maximum lump size are carried by a conveyor to screens through which glass, ceramics, slag, ash and other inerts smaller than 3/8" are discarded. Pieces larger than 4" are separated by gravity. 

Magnetic separation is used to separate and recover (1) ferrous metals from scrap and alloys, slag, mixed metals in source-separated waste (e.g., tin cans from aluminum cans), (2) ferrous items from automohile shredding, municipal solid wastes (tin cans, wires, household equipment, etc.) and combustion residues. 

This is typified by the Varta process implemented by Varta Batterie AG at Hannover, Germany and as used by Boliden-Bergsoe AB at Landskrona, Sweden. The batteries are drained and charged with fluxes (lime, silica and shredded scrap iron), coke and an amount of recycle lump slag. The slag has a melting point above 1000°C and maintains an open structure in the shaft until it nears the tuyere zone with a temperature of around 1150°C. 

Feed is composed of battery materials, other lead-bearing residues and scrap, fine coke or coal, and fluxes. The fluxes used depend on the type of slag and can be soda ash (sodium carbonate) and shredded iron scrap for the production of soda slags or limestone, silica and iron for the production of silica slags. Separate bins and weighfeeders for each component are used to continuously blend the feed, which is fed by conveyor into the kiln. 

The shredded PVC waste (20 - 30 mm particle size) is burnt continuously together with brown coal dust, sand and calcium-chloride solution. Brown coal dust and sand improve the burn-out and the recovery of chlorine sand also bonds with heavy metals etc. in the slag. The third additive is a 30% calcium chloride solution, recirculated from the waste water unit. Under incineration conditions calcium chloride is converted to calcium silicate and HCl. 

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