Characteristics of Syngas from Pyrolysis and CO2-Assisted Gasification of Waste Tires

The growing number of waste tire generated worldwide every year can be converted from a major environmental issue to a valuable energy source by thermochemical conversion processes. CO2 gasification can offer a prominent position in the tire waste to energy panorama since it offers high quality syngas production and direct mitigation pathway for GHG emissions. An evaluative study of syngas yield and quality between pyrolysis and CO2 assisted gasification has been carried out in a laboratory scale fixed bed reactor and is presented in this work. Pyrolysis was performed in the temperature range of 673 to 1173 K and gasification at temperatures of 973 to 1273 K in steps of 100 K. The effect of reactor temperature on the flow rates of syngas and its major gaseous components (CO, H2, CH4) for the both processes and on the CO2 consumption in case of gasification was investigated. A comparison between pyrolysis and gasification carried out on the basis of cold gas efficiency and overall process efficiency over the investigated temperature range was provided as well. Results showed that gasification temperature strongly affects the syngas yield, quality, and energy content. Gasification reactions below 973 K were negligible. Char reactivity even at higher temperature was found to be low. Gasification resulted in 3.3 times increase in CO yield at 1073 K and 2.8 times increase at 1173 K as compared to pyrolysis. The increase in gasification temperature from 1173 to 1273 K enhanced CO yield by 1.5 times. While pyrolysis provided higher efficiency from a merely energetic point of view, gasification still presented high cold gas efficiency that reached 62.6% at 1273 K and an overall efficiency greater than 30%. In addition, CO2 assisted gasification of waste tire provided a direct pathway to utilize GHG emissions, showing a carbon dioxide consumption of 0.75 g for each gram of scrap tires gasified at 1273 K, and produced a significant amount of CO, which is valuable for both energy production and fuel and value-added products synthesis