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.

It has been known for a long time that hydrogen in the gas phase tends to inhibit gasification of char at low and intermediate temperatures. At higher temperatures, however, there are indications that hydrogen may speed up gasification. The mechanisms behind these effects are currently not understood. In this work, a newly developed detailed chemical kinetics model for char has been used in order to study the mechanisms behind the hydrogen inhibition and speed-up of char gasification. For conditions assumed in this work, the hydrogen inhibition is found for T < 2000 K, while for T > 2000 K the hydrogen in the gas phase speeds up the char conversion. By studying * To whom correspondence should be addressed † Silesian ‡ NTNU ¶ SINTEF 1 the species reaction rates together with the individual rate of every heterogeneous reaction, the reasons for hydrogen influence on char gasification are attempted explained for a wide range of different temperatures in this paper. The focus is not on investigating a real gasifier, but rather to understand the fundamental mechanism behind hydrogen inhibition of char.