**1. Introduction**

Forests and the wood industry's residues represent an extraordinary source of energy for enterprises and communities located near areas where wood is harvested, and wood byproducts are produced. Currently, there is a clear conviction about the need to make rational use of this energy resource. Therefore, interest in the development of renewable energy studies will continue in the coming years. In the case of biofuels, it is a significant field for applied research.

Among the alternatives for using these resources, there is the possibility of combustion or gasification to generate thermal and/or electrical energy, or the option of producing fertilizer products. The process of densifying wood from forest residues or the wood industry can also be an important alternative due to its low density, low calorific value, and in some cases, high moisture content, which results in high biomass consumption. In industrial processes, the reuse of waste for transformation into byproducts with higher added value, such as particleboard or wood fibers, also generates environmental benefits.

In thermochemical processes such as the combustion of forest biomass, the limitation is the low calorific value of the fuel due to its high moisture content. For this reason, burning them without prior drying requires the use of large volumes of combustion chambers to process the fuel. In this sense, a drying process is important as a preliminary stage to combustion to reduce the volume of the combustion chamber, achieve an adequate combustion temperature, and improve the thermal efficiency of the process.

On the other hand, biomass gasification and pyrolysis processes are normally carried out with low humidity. Thus, for example, according to [1, 2] sawdust gasification in a fluidized bed requires moisture contents of 8–12% and 8.5%, respectively.

In the field of particle board manufacturing, briquettes or pellets require very low levels of humidity. Indeed, the transformation of green wood into particles is done with moisture contents that can vary between 35 and 150% d.b., but the subsequent processes of gluing and pressing the particles require that the moisture be between 5 and 10% to the outer layers and from 2 to 6% for the middle layer. In this context [3], carried out a study on the drying of wood particles in rotary equipment with a humidity of 65% to leave the biomass with a final moisture content of 9–11% d.b., thus allowing hot pressing of the particles for the manufacture of MDF boards. Zabaniotou [4] also studied the drying of forest biomass in rotary equipment but with low initial moisture levels (13% d.b.).

It can then be seen that in all the industrial applications mentioned, the humidity values required for the various transformation processes of the residual biomass are well below the humidity with which it is normally available and that can be 150–170% d.b. It is not always possible to have these residues in a dry state and among the preparatory treatments that are required is the drying of the biomass, which has motivated this research.

Fluidized bed technology has become one of the most successful worldwide. It currently finds applications not only in thermal processes such as combustion, gasification and drying, but also in others on roasters, calciners, classifiers and reactors within the metallurgical, chemical, and pharmaceutical sectors.

In a previous work [5] the authors carried out a thermal study on the drying of biomass particles in a mechanically stirred fluidized bed equipment; the objective of the study was to determine the production rates of forest biomass particles, the evaporation rates, the specific energy consumption, and the thermal efficiency of the drying process. The most important results of this study reveal that the specific energy consumption is 3040 kJ for each kg of water evaporated in the bed, which corresponds to a thermal efficiency of 80%.

In this research the first objective is to experimentally analyze the aerodynamics of the fluidized bed, in order to obtain minimum fluidization velocities, pressure drops in the bed and the specific surface of the gas-particle contact. The second objective is to study the phenomena of heat and mass transfer that occur simultaneously during the drying of the biomass particles, in order to determine the convective coefficients

*Experimental Investigation on Drying of Forest Biomass Particles in a Mechanically… DOI: http://dx.doi.org/10.5772/intechopen.113973*

of heat and mass transfer in the contact surface between the biomass particles and the fluidizing gas.
