Fuel-specific devolatilization parameters for detailed comparison of pulverized biomass fuels

Abstract

Low-grade biomass feedstocks are sustainable alternatives for pulverized fuel applications in the energy industry. Adverse fuel properties can make their adoption challenging due to operational issues such as flame ignition problems and high emissions. These issues can be potentially resolved by Computational Fluid Dynamics (CFD) simulations, where a submodel is needed to describe the fuel devolatilization behavior. In this work, the devolatilization parameters are reported for three pulverized biomass fuels: high-quality industrial wood pellet, lower-grade spruce bark, and steam-explosion pretreated spruce bark. The parameters are determined with a combination of high heating-rate drop-tube reactor experiments and CFD-coupled optimization algorithm. Comprehensive analysis is conducted to examine how the devolatilization reactivity and steam-explosion pretreatment affect the industrially relevant fuel properties. The functionality of the drop-tube devolatilization parameters is further demonstrated in larger-scale combustion simulations of a 120 kW pulverized fuel test rig. The simulations are able to capture the more challenging ignition behavior of the lower-grade bark fuels, and give detailed insight on the phenomenological side of solid fuel ignition. The fuel devolatilization reactivity is shown to have a strong impact on highly nonlinear flame characteristics, such as NO formation. Most importantly, the presented characterization, simulation and analysis methods can be applied to other biomass feedstocks to better understand how reactivity is altered by feedstock pretreatment, and how the process characteristics are influenced by fuel devolatilization reactivity.