Determination of Arrhenius parameters for advanced kinetic model used in CFD modeling of the wood pellet combustion process

Abstract

With the increased popularity of using wood stoves for household heating in recent years, numerous experimental research projects have been launched with the goal of generating cleaner and more efficient stove designs. This work is focused on mathematical modeling of combustion process in low-power residential heating appliance (small-scale stove) fuelled by different wood pellets (WP1-Beech (hardwood) and WP2-Pine (softwood)). Kinetic model scheme that encompasses determination of Arrhenius parameters was proposed for applied Finite rate/Eddy Dissipation approach. Types of wood pellets have been combusted on the experimental stand which is equipped with a set of temperature sensors and exhaust analyzer. A comparison of results obtained from combustion in the heating unit has been performed to find relations between established kinetics of devolatilization for various wood pellets and to determine exhaust composition, arising from oxidation reactions. Numerical modeling using computational fluid dynamics (CFD) has been performed for the char and CO oxidations to supplement the experimental results. Due to limitations on installed stove such as poor design, air supply, fume extraction, or heat exchanger can lead to excessive CO emissions or lower energy efficiency. Outcomes show that it is crucial to minimize unused stove volume and to enhance gaseous mixing for reduction of CO emissions, while maintaining sufficiently high temperatures for supporting fast oxidation reactions. Results of comparisons of conducted analyses can be useful in areas related to process optimization and improvement of combustion and devolatilization reaction conditions in the small scale heating units.