Waste Metal Decoating System For Aluminium Scraps

The de-coating is a thermal treatment applied on the aluminium scrap, used to remove from the surface of the material all the contaminants as paper, oil, links, paint, plastic.

The aluminium scrap is used as “raw material” to produce new aluminium but before to be molten again has to be “cleaned”, i.e. treated inside a de-coating unit, in order to reach the specific characteristics requested. If the scrap is not cleaned (de-coated) and is molten directly inside the furnace, the metal loss increases and the presence of contaminants in the furnace might create problems to the use of the regenerative burners, producing at the same time an additional cost of the natural gas used in the melting. The cleaning process is based on heating the aluminium scraps in a controlled low oxygen atmosphere, through direct convective exchange with exhaust fumes, which have been processed into post-combustion chamber. The experience on existing pyrolysis plants, allow to cover the following scraps: turning, cover, ground, cans, tubes or caps, cables, sheets laminated with paper or plastic, sheets coated.

Environmental and economic advantages:

• Key role into the main loop of aluminium recycle: after treatment, treated scraps are ready to be melted again to make new raw material
• Reduce metal loss and energy consumption in the melting process
• Complete oxidation of organic pollutant
• Fuel saving through regenerative ceramic beds
• Comply with the most restrictive environmental regulations.

Hengyang system main components are: . The Rotary Kiln for processing the dirty scraps. . The Post-combustion chamber, for the incineration of the gases generated in the rotary kiln. . The recirculation fan between both equipments, in order to reuse part of the hot gases generated in the Postcombustion chamber. . The intermediate cyclone, for removing the small particles from the process, such as fines, dust, ... Economical & environmental benefits: . Very low overall energy consumption. . Reduce the metal losses and energy consumption in the melting process. . Improved the Foundry safety (no water). . Controlled volatilization of the VOC. . Full incineration of the generated gases. . Reduces emissions to the environment.

Kiln discharge and temperature

The temperature at the kiln discharge is controlled to ensure a well cleaned final product. The Hengyang tube, acts as a heat exchanger giving up heat to the scrap and kiln exit gases by radiation. The Gases enter the Hengyang tube at afterburner temperature and by the time they reach the end have been cooled, and so used to control the temperature at the discharge end of the kiln, with temperatures below 550º C.

Cyclone & recirculation fan

A high efficiency cyclone unit is employed to remove any particulate from the kiln prior to the recirculation fan and afterburner. The recirculation fan provides the required gas flow from the Afterburner. The fan is fitted with a variable speed drive unit, and the speed of the fan is modulated automatically to maintain the kiln gas exit temperature at the selected control set point.

Kiln Speed and residence time

The kiln rotational speed is adjusted by the kiln drive motor. Each material has an ideal residence time within the kiln barrel.

Kiln gases pressure control

The Hengyang kiln pressure is controlled to ensure that process gases remain within the system and that the infiltration of air into the drum is kept to a minimum. Kiln free O2 level The Hengyang free oxygen level is controlled to ensure the thermal process occurs in the required conditions, avoiding the generation of CO gases.