dc.description.abstract | This research aims to evaluate the energy conversion efficiency and heavy metal partitioning and emission characterization in pyrolysis of Automobile Shredder Residue (ASR) using fixed bed and fluidized bed gasifier. Meanwhile, the feasibility of separation and purification of ASR by density separation controlling at liquid to solid ratio (L/S) of 5 L/kg, stirring time of 10 minutes and standing time of 10 minutes was also discussed. The major components of ASR could be included plastic-rigid, plastic-foam, textile, leather and rubber.
According to the analysis results of density separation, the major density range of plastic-rigid was less than 1.00 g/cm3 with corresponding the weight percentage was approximately 68.21%. The light fractions of plastic-rigid were mainly composed of polyethylene and polypropylene. Approximately 21.82% of plastic-rigid was ranged between 1.00 g/cm3 and 1.20 g/cm3. The major components were including acrylonitrile butadiene styrene, polymethyl methacrylate, polystyrene or nylon. Approximately 6.61% and 3.36% of plastic-rigid were ranged between 1.20 g/cm3 and 1.35 g/cm3 or higher than 1.35 g/cm3, respectively. The polyethylene terephthalate, polyoxymethylene, and polyvinyl chloride were identified by separation and purification process. In the case of plastic-foam and textile separation, the major density range was less than 1.00 g/cm3 with corresponding the weight percentage was approximately 97% and above. However, the leather and rubber was only 18.45 wt% which the density was less than 1.00 g/cm3. The weight percentages of leather and rubber were relatively average in tested density ranges that of 27.45% (1.00-1.20 g/cm3), 26.43% (1.20-1.35 g/cm3), and 27.67% (higher than 1.35 g/cm3), respectively. Based on the density separation results, the heavy metals, gravels, glasses, and PVC plastic in ASR could achieve the objectives of separation and purification by the tested density separation process.
The experimental results indicated that the bio-char and bio-oil produced from ASR and their derived components in fixed bed gasifier were approximately 22.49~55.97% and 29.44~57.14%, respectively. Especially for bio-oil, its higher heating value (HHV) was ranged between 8,200 kcal/kg and 11,200 kcal/kg. Due to the good heat transfer characteristics of fluidized bed gaifier, the yield of pyrolysis gas was increased to 20.6% with corresponding the yield of bio-char and bio-oil decreased to 36.66 % and 34.27 %, respectively. However, the HHV of bio-oil was slightly increased from 9,300 kcal/kg to 10,300 kcal/kg.
The heavy metals partitioning characteristics results showed that cadmium in ASR was mainly partitioned in bio-oil using the fixed bed gasifier which it was approximately 99%. However, in the case of fluidized bed gasifier, the Cd partitioning characteristics of syngas was increased to 0.06% resulting in rapidly thermal reaction and gas turbulent in the fluidized bed gasifier. The heavy metals, such as chromium, copper, lead and zinc, were approximately 90% and above partitioned in bio-char. It implied that the above metals partitioning percentage was less 5% partitioned in bio-oil and gas, respectively. This is because the volatilization temperature of the above heavy metals was relatively high, the less amounts of the above metals will partition in the bio-char during ASR pyrolysis process operated at temperature 500℃. The analysis results of chlorine and sulfur partitioning characteristics in ASR pyrolysis showed that the speciation containing chlorine and sulfur were mainly distributed in bio-char which their partitioning percentages were 79.58% and 63.53%, respectively. Meanwhile, the Cl and S partitioning percentages of bio-oil were 17.68% and 19.06%, respectively. The heavy metals speciation of gaseous products was simulated by chemical equilibrium model. The simulation results indicated that heavy metals chloride and sulfide speciation was presented in solid phase during the lower pyrolysis temperature range of 300-500℃. However, the pyrolysis temperature increased to 800℃, heavy metals chloride and sulfide speciation was mainly partitioned in gaseous phase. In summary, the basic properties of ASR and its energy conversion by pyrolysis were conducted. Meanwhile, the tested heavy metals emission and partitioning characteristics were also well established during ASR pyrolysis process. Therefore, the results of this research could provide the good information for selection of pyrolysis technologies and control strategies of metals emission in the future.
Keywords: Pyrolysis, automobile shredder residue (ASR), separation and purification, heavy metal, partitioning characterization | en_US |