Modelling and Simulation of Pulverised Biomass Combustion

Sustainable heat and power generation from biomass is in the focus of scientific and industrial interest. Increasing awareness about the environmental impact caused by greenhouse gas and pollutant emissions related to the use of fossil fuels is the main reason for this interest. The partial or full utilisation of biomass as an energy source in fossil fuel-based power plants can be considered a suitable solution to reduce greenhouse gas emissions.

Numerical modelling of combustion processes together with CFD has proven to be an efficient tool for the calculation and optimisation of firing systems. In this work, a numerical model representing the relevant characteristics of pulverised biomass combustion is developed. A comprehensive CFD framework originally developed for coal combustion is used for this purpose. The main physical-chemical steps of combustion are evaluated taking into account the specific characteristics of biomass fuels.

Considering the typical particle sizes related to biomass combustion, a comprehensive single-particle model is developed to describe pyrolysis and drying. The model combines intra-particle transport phenomena and a detailed chemical mechanism. Predictions of the particle model are compared with experimental data, proving its ability to reproduce temperatures, release rates of gas species, and conversion times.

Char conversion models are examined, including oxidation and gasification reactions. Homogeneous reactions are evaluated, including their interaction with turbulent flow. Global combustion model predictions are compared with experimental measurements conducted in a semi-industrial scale facility. They show an excellent agreement with the measurements in terms of absolute values and profiles of temperatures and gas concentrations.