Sustainable conditions for waste tires recycling through gasification in a bubbling fluidized bed

Abstract

Gasification in a bubbling fluidized bed reactor was introduced as sustainable technology to treat waste such as tires. However, uncertainty arises when defining the most sustainable gasification process conditions. In this paper, eight experimental conditions were analyzed. The experiments were carried out at 700 and 850 °C with different equivalence ratios (ER) while using air as a gasifying agent. At 850 °C the effect of steam addition was also studied. A Life Cycle Assessment (LCA) was assessed to the product gas and its energy content by the following environmental impacts: Climate Change (CC), Ozone Depletion (OD), and Particulate Matter (PM). LCA methodology revealed that optimal gasification conditions provide 74, 69 and 66% environmental impact reductions in CC, PM, and OD, respectively by comparing the best and the worst-case scenarios. The combination of high temperature, low ER, and steam addition offered the most environmentally sustainable process, achieving 8.3·10−2 kg CO2 eq/MJ in CC, 1.3·10−8 kg CFC-11eq/MJ in OD and 4.9·10−5 kg PM2.5eq/MJ in PM. Despite the great savings in environmental impacts, additional efforts are still needed to reduce the energy consumption of the preheating system to ensure the product gas is levelled to conventional natural gas.