Combustion of a Single Particle of Biomass

Abstract

Biomass is one of the important renewable energy sources. Biomass fuels exhibit a range of chemical and physical properties, particularly size and shape. Investigations of the behavior of a single biomass particle are fundamental to all practical applications, including both packed and fluidized-bed combustion, as well as suspended and pulverized fuel (pf) combustion. In this paper, both experimental and mathematical modeling approaches are employed to study the combustion characteristics of a single biomass particle ranging in size from 10 µm to 20 mm. Different subprocesses such as moisture evaporation, devolatilization, tar cracking, gas-phase reactions, and char gasification are examined. The sensitivity to the variation in model parameters, especially the particle size and heating rates, is investigated. The results obtained from this study are useful in assessing different combustion systems using biomass as a fuel. It helps to clarify the situations where the thermally thin and thermally thick cases interface. It is clear that simple models of particle combustion assuming constant particle temperature are sometimes inadequate and that for large particles a more detailed mathematical representation should be applied.

Single particle flame-combustion studies on solid biomass fuels

“…We make a definition that the start of devolatilisation is the point of ÒignitionÓ which, in the model above, has been taken to be coincident with a particle temperature of 500K even though there may have been a small amount of devolatilisation before the appearance of a volatile flame. The rate of devolatilisation may be modelled in a simplified form as a first-order, single step Arrhenius reaction [8] as:…”

“…[8]). This approach requires the model of the single particle combustion to be refined before meaningful larger scale combustion can be extrapolated.…”

“…Yang et al [8] developed a computational model including heat transfer, mass transfer and chemical kinetics for cylindrical shaped particles in the range 0.5 Ð 20mm. While this compared favourably to experimental data presented for a single particle burning in entrained gas flow, a more robust validation would require more extensive experimentally derived data to be produced, covering the range of particle sizes.…”

One way of representing the size and shape of biomass particles in combustion modeling

“…However, as the fuel particle shape becomes more complex, at least two parameters (width and length) are necessary to describe the particle size. Despite numerous studies on biomass particles [7,13,14,[9][10][11], there is no consensus on how to represent a biomass particle in combustion models. The common way involves approximating of the particle shape to regular geometrical bodies (e.g.…”

“…parallelepiped, cylinder, cubes, ellipsoids). In combustion models from Yang et al [14] and Yin et al [13], particles are represented by cylindrical and spherical shapes, whereas Thunman et al [7] treat particles in a onedimensional model as plates, cylinders, and spheres. The accuracy of particle models depends on both correct size distribution and characterization of fuel inhomogeneity in terms of shape and structure.…”