Numerical models for thermochemical degradation of thermally thick woody biomass, and their application in domestic wood heating appliances and grate furnaces

Abstract

This paper reviews the current state of the art of numerical models used for thermochemical degradation and combustion of thermally thick woody biomass particles. The focus is on the theory of drying, devolatilization and char conversion with respect to their implementation in numerical simulation tools. An introduction to wood chemistry, as well as the physical characteristics of wood, is also given in order to facilitate the discussion of simplifying assumptions in current models. Current research on single, densified or non-compressed, wood particle modeling is presented, and modeling approaches are compared. The different modeling approaches are categorized by the dimensionality of the model (1D, 2D or 3D), and the one-dimensional models are separated into mesh-based and interface-based models. Additionally, the applicability of the models for wood stoves is discussed, and an overview of the existing literature on numerical simulations of small-scale wood stoves and domestic boilers is given. Furthermore, current bed modeling approaches in large-scale grate furnaces are presented and compared against single particle models.

Development of a detailed kinetic model for the combustion of biomass

“…The current global warming issues, especially the concerns about the alarming rise of atmospheric CO2 [1], have increased the importance of the use of fuels from renewable resources, primarily biomass. The use of wood and biomass for domestic small combustion installations (fireplaces, stoves and boilers) is widely widespread in countries where heating is needed in winter [2]. Residential wood burning significantly affects the air quality because it is one of the largest sources of fine particles (PM2.5, particulate matter of aerodynamic diameter below 2.5 m).…”

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

“…(3) Indicates that the continuity equation has been transferred to cylindrical coordinates from Cartesian coordinates. (4) Indicates that the original equation given in the reference has been extended to 2D by the authors and a correction regarding the porosity was included in the convective term.…”

“…The correct definition of heat and mass transfer is mentioned here, and its correctness is emphasized. The correct definition of the heat and mass transfer coefficients including the blowing effect can also be found in the literature review by Haberle et al [4].) The Nusselt and the Sherwood number are required for the calculation of the uncorrected heat and mass transfer coefficients,…”

“…During the last years, there has been an increased focus on modeling of thermochemical wood degradation as well as on conversion of the resulting char. One-dimensional (1D) models were, and still are, one of the main tools [4]. This is because they allow for fundamental studies on conversion-related physical processes, while at the same time remaining computationally efficient.…”

“…Furthermore, even though research is focusing on the modeling of thermochemical wood conversion and char consumption, the developed models rarely focus on large wood logs that are comparable in size to wood logs used in wood log heating appliances (e.g., stoves and boilers [4]). There are, however, some exceptions [9,10] A one-dimensional pyrolysis model for large wood logs (with a radius of 25 mm and a length of 300 mm) was developed by Larfeldt et al [9].…”