PLASMA-ARC TECHNOLOGY FOR THE THERMAL TREATMENT OF CHEMICAL WASTES

摘要

Plasma-arc technology is developed to dispose chemical wastes from a chemical plant by the Institute of Mechanics, Chinese Academy of Sciences. A demo system with this technology is constructed to destroy two sorts of chemical wastes from production process in a chemical plant of Chenguang Research Institute of Chemical Industry, Zigong, Sichuan, China. The system includes shredding, mixing and feeding sub-systems, plasma-arc reactor of 150 kW, off-gas burning and scrubbing sub-system. To form the vitrified slag, some additives, such as CaO, SiO_2 and Fe, etc., are added into the reactor. The average temperature in the graphite crucible space is in the range of 1400-1500 ℃, so the hazardous organic wastes with chlorine are rapidly pyrolyzed and the additives are heated up to molten state to capture the hazardous elements, then the slag is quickly quenched to form amorphous glass structure. A DC experimental facility of 30 kW with plasma-arc technology is also set up to study the pyrolysis process in the laboratory, and the experimental results show the cooling speed is the most important factor for good vitrified structure of the slag. According to previous tests, the destruction and removal efficiency (DRE) for these chemical wastes is more than 99.999%, and the PCBs concentration in the solid residues is in the range of 1.28 to 12.9 mg/kg, which is far below the National Emission Limit for hazardous wastes. A simplified electro-magneto model for numerical simulation is made to estimate the temperature and velocity fields. This model can make very satisfied maximum temperature and velocity distributions in arc region, as well as the results by magneto hydrodynamic approach.