Full scale treatment of ASR wastes in a modified rotary kiln

- The Automobile Shredder Residue was effectively thermo-valorized in a rotary kiln.
- All the emission parameters have been kept below the regulatory limits.
- ASR pretreatment can increase the heat of combustion and reduce fines.
- Slag recycling is suggested as an important step to fulfill the ELV Directive.

A plant, designed for the thermo-valorisation of tyres, was specifically modified in order to treat Automobile Shredder Residue (ASR). Results from two full-scale combustion experiments, carried out on large ASR feeding lots (thousands of tons) indicate the proposed technology as a potential route to help the fulfilling of impending 95% reuse and recovery target set by the End of life Vehicle (ELV) Directive (January 2015). The paper describes the main operational troubleshot occurred during the first experiment (emissions at the stack out of regulatory limits and problems of clogging on the conveyer belt) and the consequent upgrading solutions (pre-treatment, introduction of waste double low-flow screw feeder and a cyclone prior to the main fan, modification of rotatory kiln inlet) adopted to allow, during the second long-term experiment, a continuous basis operation of the plant in full compliance with the discharge limit to the atmosphere. Characterization of both ASR and combustion residues allowed to quantify a 18% of combustion residues as not dangerous waste while only the 2% as hazardous one. A pre-treatment for the reduction of fines in the ASR was recommended in order to achieve the required energy recovery efficiency.

Layout of the gasification-combustion plant. Red numbers indicate the location of the prevalent plant/process modifications undertaken to make the plant environmentally and energetically effective for the treatment of ASR wastes: 1. Reduction of fines in the ASR feed to avoid fly ash deposition and increase the heat load of the kiln; 2. Substitution of the original belt feeder with screw feeder to avoid clogging problems at the feed location and consequent difficulties in the air intake control; 3. Better sealing of the kiln to avoid excessive air intake; 4. Introduction of a cyclone ahead of the main fan to avoid its damaging by fly ashes; and 5. Increase of sodium carbonate injection rate to cope with higher than usual HCl emissions from the kiln.