Development of a circulating fluidized bed for a 100 kg/day waste plastic pyrolysis-combustion system

The aim of this study was to develop a 100 kg/day plastic waste pyrolysis-combustion circulating fluidized bed (CFB) system. The CFB was designed to provide heat from the combustor (semi-riser type) to the pyrolyzer (bubbling fluidized bed (BFB)) through heat carriers in high efficiency. A 100 kg/day scale system, including an oil condensation facility, was constructed and operated continuously for 34.5 hrs. Pelletized polypropylene was supplied to the pyrolyzer as plastic waste. The temperature in the pyrolyzer and plastic feeding rate were experimental variables. The weight percentage of low (C₁–C₁₂) and middle (C₁₃–C₂₂) carbon number components of the produced oil in CFB operated at 512-551 °C was 65.3 and 23.2 %, respectively. These were significantly higher than 34.6 and 28.4 % of the BFBs with similar temperatures previously, implying that the heat transfer in the CFB was more intense than that in the BFB. Compared to the BFB, only subtle differences in the pyrolysis gas yield was observed for CFB, which signified that the gas mixing between two reactors was minimized during the operation. Although no blockage was found in the CFB, clogging of condensers and pipelines occurred during low-temperature operation owing to the relatively low pour point of the product oil. The results in this study provide detailed and practical information on the temperature, pressure, product gas, oil, and clogging issues to better understand plastic pyrolysis in CFB.