Gasification of Waste Tires

Gasification is a thermochemical pathways used to convert carbonaceous feedstock into syngas (CO and H2) in deprived oxygen environment. The process can accommodate conventional feedstock such as coal as well as discarded waste including plastics, rubber, and even MSW due to the high reactor temperature of 1000 to 1600oC. Pyrolysis is another conversion pathway yet it is more selective to the carbonaceous feedstock as it proceeds at relatively lower process temperature (350 to 550oC). Discarded tires can be subjected to pyrolysis, however the yield involves the formation of intermediates radicals that remaining in additional to unconverted char that require further distillation and upgrading. Also due to continuous Random Fission/Radical Recombination, β-Scission/Radical Addition, Depropagation/Propagation, Hydrogen Abstraction devlatilization and recombination, pyrolysis fails to follow equilibrium and is very complex to predict and thereby model. Gasification, however, due to their higher temperature and shorter residence time is more opted to follow quasi-equilibrium and predictive. In this work tire crumbs are subjected to two levels of gasification modelling, i.e. equilibrium zero dimension and high fidelity multidimensional computational reactive flow. The objective is to investigate the effect of the oxidizer amount on the conversion of tire granules and syngas composition in compute process metrics. The simulation is carried out in a small 20kw cylindrical gasifier of 19in height by 10.75in diameter. Initially the chemical composition of several tire samples are measured following Standard ASTM procedures for proximate, ultimate and heating value. The measured data are used to define the tire properties and carry out equilibrium based gasification subjected to different equivalence ratio. This followed with reactive flow analysis to gain more details of the species distribution and reaction kinetics as twelve reactions including combustion, reduction, and methanation additional gas and water shift reactions are considered with their appropriate kinematics. The result shows that both models are reasonably predictive averaging 68% gasification efficiency, the devolatilization is less sensitive than the char conversion to the equivalence ration as complete devolatilization is always achieved. In view of the plausibly attained efficiency, it is suggested that tire gasification system is economically viable.