Waste tyres valorisation through gasification in a bubbling fluidised bed: An exhaustive gas composition analysis

Abstract

Waste tyres gasification in a bubbling fluidised bed reactor is evaluated by means of a complete characterisation of the product gas. The experiments are carried out at two temperatures, 700 and 850 °C, and various equivalence ratios (ER) while using air as a gasifying. Additionally, the effect of steam is also studied at 850 °C. High temperature and low ER increase the production of H2, CH4, and C2H4. Steam addition mainly affects H2 and CO production. Low carbon conversion (CC) into gas and cold gas efficiency (CGE) are obtained, increasing with temperature and ER. The lower heating value (LHV) of the gas decreases with the ER because of the higher partial combustion rates. LHV values range between 12 MJ/Nm3 with steam addition at ER = 0.13 and 850 °C to 5.3 MJ/Nm3 at ER = 0.33 and 700 °C using air only. Along with a major permanent gas (CO2, CO, H2, CH4, and C2Hn), up to 25 short-chain hydrocarbons (non-aromatic hydrocarbons ranging from C3 to C6+) and two light aromatics are present in the product gas. Among short-chain hydrocarbons, C3 and C4 compounds are present in the highest yields. All these minor hydrocarbon species (i.e., C3 to C6+), not usually reported in biomass or waste gasification studies, yield up to 13 %vol. on a N2-free basis. Their contribution to the gasification performance is important because they account for half of the energy content in the product gas. Therefore, it is important to consider them in the gasification process, not only for energy purposes but also for the chemical industry.