Cement, Energy and Environment

, because the shredder could be damaged by unshreddable items or explosions and fires which could be caused by the impact on certain hazardous waste. In many cases, when processing filled steel drums, these must be emptied to eliminate any potentially explosive waste residue. Satrind machines, thanks to the low speed of their blades, are particularly well-suited to shred loose heterogeneous waste such as metals, flammable and hazardous chemical waste and sludges sealed into IBCs or steel drums without any prior selection, to obtain the small final material shred-size specified for optimal combustion in cement kilns. RDF from end of life tyres Satrind has supplied different solutions for production of RDF for cement kilns from end of life tyres. It is important to consider that fuels like coal and coke are known to release great quantities of heat when they are burned because of a high presence of carbon. Tyres are also a great source of hydrocarbons (carbon and hydrogen) and burning tyres in a cement kiln produces 25 per cent more energy than coal. The typical Satrind plant can guarantee 5-8 tph output with a pre-defined 'chip' size 50 - 80 mm depending on customer's requirements. This plant would be composed of a first and eventually a second stage slow speed-high torque shredder (s). Since the two shaft models cannot guarantee a specific final size, a size selection system must be used to return to the shredder for further processing all the tyre pieces which are larger than the desired dimension. Traditionally the selection system was done with a rotating trammel which required a frequent periodical maintenance to free the holes from being clogged by the tyre pieces. A much more efficient size section system has been adopted in the plants designed by Satrind through the use of disk screens which avoid the problems encountered with the previous solutions. These rectangular screens are composed of several steel disks fitted on parallel shafts. The desired chip size can be obtained using pre-determined disk thickness and specific shaft speeds. The chip suitable for RDF will fall by gravity under the screening table while the longer pieces are discharged at the end of the table and are further reintroduced into the shredder with conveyor belts closing the loop. Advantages of using RDF The use of alternative fuel is a well known and consolidated technology that guarantees numerous environmental benefits. Primarily, avoiding to consume non-renewable precious resources and consequentially lowering emissions of gases since the traditional fuel is actually replaced by a fuel derived from waste which would otherwise require other forms of disposal. The burning waste produces toxic gases such as hydrogen chloride and sulphur dioxide which would require extremely expensive filters to avoid their release in the environment. The raw material, used to produce cement, contains a high degree of lime and alkaline material which when they are introduced into a kiln at very high temperatures (from 1600' C to 2000 'C) absorbs and neutralized directly the hazardous gases in the kiln chamber. The filters traditionally installed in the cement plants are therefore sufficient to reduce any toxic emissions. Moreover cement kilns are able to use the energy generated by the waste material, while many traditional waste incinerators are less efficient converters of the heat content of wastes. 67