## 3 Results and Discussion  
From the analysis of the cases described in the previous sections, it is possible to understand the main problems associated with increasing the scale of the biomass torrefaction units, namely those associated with the production of torrefied biomass pellets. It was found that the difficulties encountered by many of the industrial projects over the past few years, especially those related to the ability to produce continuously, without forced stops due to contingencies in the process itself, and to the ability to produce pellets of torrefied biomass with good quality, meeting, for example, the requirements presented in ISO/TS 17225-8: 2016 (Solid biofuels--Fuel specifications and classes--Part 8: Graded thermally treated and densified biomass fuels), are fundamentally due to the fact that not all the variables associated with the thermochemical conversion process used, such as biomass torrefaction, were understood and taken into account. Moreover, the intrinsic characteristics of the raw material, namely their chemical and structural composition, and the behavior of each of these compounds during the torrefaction process, were neglected. If, on the one hand, as seen above, issues related to the elimination of torrefaction gases can interfere with the normal functioning of the industrial process, on the other hand, issues related to the incorrect definition of process parameters directly influence the quality of the final product, being decisive for obtaining good or bad products. In addition to the calorific value, the quality of the final product is also dependent on other factors, such as mechanical durability, bulk density or fines content, all of which are related to operational aspects of the industrial process, but also dependent on the chemical composition of the product's raw material and, above all, on the correct definition of the operating intervals of the fundamental parameters of the torrefaction process, the temperature and the residence time. It is the combination of these two factors that will determine the success or failure of the process, so it is essential, before any other corrective measure, to know exactly all the conditions and specificities related to biomass torrefaction, in order to be able to define correctly the torrefaction concept itself. Currently, it is possible to find dozens of definitions available in the most varied types of publication. However, although the vast majority of them are not incorrect, it can be said that they are at least incomplete, focusing only on the issue of temperature and the absence of oxygen, which, as mentioned above, is manifestly insufficient, as this type of definition can be misleading and give the impression that the greater the temperature or residence time the better, as long as the oxygen-poor atmosphere is maintained. In reality, this may seem true if the objective is only to obtain a product with a high calorific value, but, as already mentioned, this temperature will cause profound changes to the molecular structure of the compounds that make up most of the biomass of vegetable origin. As lignin is a material with an amorphous structure and is the main compound responsible for the agglutination of the particles during the pelletization process, it is important that its structure does not change, because otherwise difficulties will occur during this process. The structural change of lignin from amorphous to crystalline state is widely described in the literature, with temperature and subsequent cooling changing its behavior from ductile to brittle, since the bonds established between the molecules are stronger [41; 42; 43]. A similar situation occurs with cellulose, which adds to the difficulty of the pelletizing process, making the whole set more friable [44; 45; 46].