Modelling of oxygen-steam gasification of waste feedstock in industrial fluidized bed reactors

The application of a kinetic model to simulate waste gasification in medium and large-sized reactors presents the challenge of having to choose from the different sub-models proposed in the literature, which are often derived for conventional feedstocks, and where some discrepancies still exist. In this work, a one-dimensional non-isothermal model of a bubbling fluidized bed reactor has been developed and validated with data from a pilot-scale gasifier operated on biomass and waste plastic feedstocks. The model accounts for waste feed segregation, devolatilization, char and gas-phase reactions, heat losses through the reactor, and simulates steady-state operation at different operating conditions. A modified two-phase representation of the bubbling bed incorporates bubbles formation and bubbling-induced mixing, mass and heat transfer, and enables the prediction of individual species and temperature profiles within the bed and in the above regions. The model has been successfully applied to the gasification of a plastic-rich waste feedstock in a real pilot-scale reactor operated at different concentrations of steam and oxygen, demonstrating a great accuracy (error < 2.5 %, i.e. lower than average experimental variation). The model was used to predict the effects of various operating parameters on key plant performance indexes, such as the impact of oxygen concentration in the fluidising gas and steam-to-carbon ratios, when using different plastic waste feedstock. The clear advantages of a full steam-oxygen regime, together with challenges associated with residual tar content, are highlighted. The reported results offer interesting insights on the potential adoption of the model for industrial reactors design and process optimization.