Chambéry, France — A new Danieli-patented system for gas cleaning and controlling volatile organic compounds (voc) emissions has been commissioned successfully to RMB Brescia, Italy. The shredder at RMB treats a mixed charge of scrap, including compacted vehicles; for this reason a need was identified for a fume-treatment plant to treat the volatile organic compounds. The innovative solution achieved all the project targets, with total voc emissions lower than 5 mg/Nm3, advancing this new technology as the new benchmark for dedusting systems for automotive recycling.
It should be noted that the abatement of voc has become mandatory only recently in the car recycling industry, and this requirement involves other pollutants, too. One suitable technology for voc control is oxidation at high temperature, but this method is not economically viable in this case because the voc concentration is so low that it cannot support the selfcombustion of voc, thus external fuel must be used to increase the fume temperature to approx. 900 °C. It is not possible to treat the air directly with a bed of activated carbon due to the risk of water vapour condensation from the pretreatment stage involving a wet scrubber (which is necessary for dust abatement). Dry pre-treatment with a bag filter is not feasible due to the potential fire hazard (Flying burning materials must be quenched with the water sprayed in the scrubber).
The Danieli technology involves controlling voc with a bed of activated carbon and processing the primary air flow from the shredder, together with a secondary flow coming from the air separation equipment installed at the fluff separator. The primary fumes are dedusted with a cyclone and then with a wet scrubber. The secondary flow is pre-filtered with a bag filter and heated by an external fuel burner prior to mixing with the primary air flow (from the shredder). The temperature of the mixed flow is higher than ambient temperature, thus the risk of condensation in the carbon bed is prevented.
The advantage of this technology is that a free flame can be safely used to heat only the secondary flow of air, which does not contain voc. The flow rate of air treated by the activated carbon bed does not increase significantly because the secondary flow is only one fifth (approx.) of the primary flow. The combination of the two lines (primary flow from the shredder and secondary flow from air separation unit) is economically advantageous because it allows using only one induced draft fan and one stack instead of two, as it would be required with two independent lines. The project was successful and all the targets have been reached, with total volatile organic compounds lower than 5 mg/Nm3. Due to the innovative solution this technology will become the new benchmark for dedusting systems for the car recycling industry.
Quelle: Danieli Cento Recycling