Annually the amount of PWPO (Plastic-Wood-Paper-Organic) waste produced in Italy is approximately 26 million of tons, of which about 27% is constituted by water and 13% by inert components (silicates, salts and metals). The remaining 60% is plastic, paper and wood with a calorific power at least equal to 10 MJ/kg. Nowadays the production of RDF (Refuse-Derived Fuel) does not represent an interesting alternative to the fossil combustibles because of its low calorific power and, more important, because of the presence in high amount of toxic elements, ashes and inert components. In Italy the RDF is classified in two classes (UNI 9903 regulation) with respect to the different qualities. The material of high quality can be employed as industrial fuel because of reduced amount of CO2 and pollutants emissions after combustion. The composition and chemical-physical limitations, established by the UNI 9903 regulation, underline the necessity to subtract the water content in the waste, eliminate the metallic (ferrous and not ferrous, like Fe, Al, Mn, Cu, Zn, Cd, As, etc) and the inert (glass) components; for instance, by recovering them through a simple refinement circuit. Finally, it is necessary to eliminate the halogenated organic (presented in residues of cleansers, herbicides, plastics, etc.) and sulphur compounds, as well as the ammoniacal components (derivatives of polyurethane, fertilizers, etc.). Based on the Author's experience in mechanochemical technology, it was developed a recovery process, called Mechanical Refining, that has been carried out using a mechanochemical reactor able to induce in the treated materials a progressive and irreversible modification of the molecular structures, as well as a strong dimensional reduction of the wastes in micro-spherule with diameter smaller than 100 ?m. Mechanochemical process is based on the use of friction stresses caused by an eccentric mill: the eccentric movement accelerates the grinding masses much more than the traditional mills overlapping the impact to the friction effect. In this way the material is subjected to shear forces that can reach over 15 kbar. Preliminary tests have been performed in a ring mill of 900 rpm. It was used with paper, dry wood, PET and mixed M.S.W. with 35-40% of organic material content. Analysis of the materials after mechanochimical treatment has been carried out in order to study the structure and composition of the new materials after grinding, with scanning electron microscope, laser granulometry, X-ray diffraction , ICP and thermal analysis in oxiding and neutral atmosphere. The main result is an high increase of the calorific power of the waste (between 10% and 40%), followed by a decrease in the chlorine amount (equal to ~ 90%, essential for a drastic reduction of PCDD and PCDF emissions). According to the results obtained in the years 2002-2004, the first prototype of a new industrial planetary mill has been designed and constructed. The grinding mill with capacity of 1500 kg/h has been inserted inside a real circuit of recovery. To get a strong reduction in the amount of inactive material and metals in the final dusts, a complete pre-selection system has been designed, that consists of two magnetic separators for ferrous metals and an eddy current separator for non magnetic metals and a ballistic separator for heavy inerts. The rest of the circuit is constituted by air cyclone for the separation of light and heavy fractions of the dusts and by a system of bag-filling in big-bags. The product obtained is free from inert components and has a significant less concentration of chlorine (< 100 ppm), metals (< 500 ppm), sulphates and PAH < 100 ppm.
The mechanochemical alternative for the recovery of the municipal solid wastes
Plescia P
2007
Abstract
Annually the amount of PWPO (Plastic-Wood-Paper-Organic) waste produced in Italy is approximately 26 million of tons, of which about 27% is constituted by water and 13% by inert components (silicates, salts and metals). The remaining 60% is plastic, paper and wood with a calorific power at least equal to 10 MJ/kg. Nowadays the production of RDF (Refuse-Derived Fuel) does not represent an interesting alternative to the fossil combustibles because of its low calorific power and, more important, because of the presence in high amount of toxic elements, ashes and inert components. In Italy the RDF is classified in two classes (UNI 9903 regulation) with respect to the different qualities. The material of high quality can be employed as industrial fuel because of reduced amount of CO2 and pollutants emissions after combustion. The composition and chemical-physical limitations, established by the UNI 9903 regulation, underline the necessity to subtract the water content in the waste, eliminate the metallic (ferrous and not ferrous, like Fe, Al, Mn, Cu, Zn, Cd, As, etc) and the inert (glass) components; for instance, by recovering them through a simple refinement circuit. Finally, it is necessary to eliminate the halogenated organic (presented in residues of cleansers, herbicides, plastics, etc.) and sulphur compounds, as well as the ammoniacal components (derivatives of polyurethane, fertilizers, etc.). Based on the Author's experience in mechanochemical technology, it was developed a recovery process, called Mechanical Refining, that has been carried out using a mechanochemical reactor able to induce in the treated materials a progressive and irreversible modification of the molecular structures, as well as a strong dimensional reduction of the wastes in micro-spherule with diameter smaller than 100 ?m. Mechanochemical process is based on the use of friction stresses caused by an eccentric mill: the eccentric movement accelerates the grinding masses much more than the traditional mills overlapping the impact to the friction effect. In this way the material is subjected to shear forces that can reach over 15 kbar. Preliminary tests have been performed in a ring mill of 900 rpm. It was used with paper, dry wood, PET and mixed M.S.W. with 35-40% of organic material content. Analysis of the materials after mechanochimical treatment has been carried out in order to study the structure and composition of the new materials after grinding, with scanning electron microscope, laser granulometry, X-ray diffraction , ICP and thermal analysis in oxiding and neutral atmosphere. The main result is an high increase of the calorific power of the waste (between 10% and 40%), followed by a decrease in the chlorine amount (equal to ~ 90%, essential for a drastic reduction of PCDD and PCDF emissions). According to the results obtained in the years 2002-2004, the first prototype of a new industrial planetary mill has been designed and constructed. The grinding mill with capacity of 1500 kg/h has been inserted inside a real circuit of recovery. To get a strong reduction in the amount of inactive material and metals in the final dusts, a complete pre-selection system has been designed, that consists of two magnetic separators for ferrous metals and an eddy current separator for non magnetic metals and a ballistic separator for heavy inerts. The rest of the circuit is constituted by air cyclone for the separation of light and heavy fractions of the dusts and by a system of bag-filling in big-bags. The product obtained is free from inert components and has a significant less concentration of chlorine (< 100 ppm), metals (< 500 ppm), sulphates and PAH < 100 ppm.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
