Combustion of Thermally Thick Wood Particles: A Study on the Influence of Wood Particle Size on the Combustion Behavior

Abstract

A one-dimensional (1D) comprehensive combustion model for thermally thick wet wood particles, which is also applicable for studying large wood logs, is developed. The model describes drying, devolatilization and char gasification as well as char oxidation.Furthermore, CO oxidation is modeled, in order to account for the fact that exiting gas products can be oxidized and therefore limit the oxygen transportation to the active sites. The challenges for model validation are outlined. Model validation was done against experimental data for combustion of near-spherical wood particles. Furthermore, the validated model was up-scaled and the effect of wood log diameter on the thermal conversion time, the extent as well as the position of drying, devolatilization and char conversion zones were studied. The upscaling was done for cylindrical wood logs with an aspect ratio of 4. The thermal conversion time significantly increased with the size. It was also found that the relative extent of the drying, devolatilization and char conversion zones decreased as wood log size increased. The paper concludes with recommendations for future works.

A Two-Dimensional Study on the Effect of Anisotropy on the Devolatilization of a Large Wood Log

“…Since Grønli did not report any problems arising from their choice of numerical solver, it was assumed that the IDA solver can equally well lead to a suitable simulation tool for the thermochemical degradation of wood and char conversion. A grid independence study for the 1D version of a similar case to that studied here was presented in detail in Haberle et al [11]. In the current work, we performed a similar grid independence study to validate that our resolution was high enough.…”

“…This is why the focus of this work is on the development of 2D models. In addition to the detailed description of the extension of the earlier 1D model developed by Haberle et al [11] to a 2D model, this work also highlights how 2D models compare against common 1D models and outperform them under specific conditions. The development of this 2D standalone code is the first step in developing a wood stove design and optimization tool.…”

“…with h m,0 being the uncorrected mass transfer coefficient. (In earlier works by Haberle et al [11,18], typos were unfortunately present in the definition of the corrected heat and mass transfer coefficients. The correct definition of heat and mass transfer is mentioned here, and its correctness is emphasized.…”

“…The presented equations only consider the devolatilization stage, since in the current test run, drying and char conversion are not modeled. Further details on the model development can be found in earlier works by Haberle et al [11,12]. Table 1.…”

“…Radial gas velocity, u r u r = − κ radial µ ∂P ∂r (7) [13] Longitudinal gas velocity, u z u z = − κ long µ ∂P ∂z + gρ g g (8) [7] Equation of state pV = nRT (9) [11] (1) The reaction rates of wood to non-condensable gases, tar, and char are given by k 1 , k 2 , and k 3 , respectively.…”