Insights into the role of CaO addition on the products distribution and sulfur transformation during simulated solar-powered pyrolysis of waste tires

Solar-powered pyrolysis of waste tires has been extensively studied because it can rapidly convert waste tires into valuable gas products using sustainable energy. However, the emitted sulfurous pollutants during this fast pyrolysis process would significantly reduce the economic feasibility of disposal waste tires. In order to investigate and regulate the sulfur transformation behavior, a large-load thermogravimetric analyzer and an optical rapid thermal processor were adopted to characterize and simulate the solar-powered fast pyrolysis behavior. The sulfur fixation effect of CaO was also evaluated in this study. Results showed that CaO addition could increase the emission of H2 and CO by promoting the cracking of organic compounds in tar. In comparison, it could decrease the CO2 emission by adsorption or transformation. Also, an excellent sulfur fixation rate in char was achieved with 10 wt% CaO addition, but accompanied by increasing emission tendency of SO2, especially at 650 °C-6000 °C/min. It was attributed to the competition reaction between H2S and SO2 in the gas phase and interaction between CaS and CaSO4 in the condensed phase. Our findings could be beneficial to develop an in-situ sulfur removal method during the pyrolysis of waste tires in the industry.