## Materials and Methods
### Identification of Faults, Malfunctions and Process Conditions  
#### 2.3.1 Start-Up and First Testing Phase (2013-2014)  
After the completion of the construction and equipment assembly work, the unit was started with the first tests and tests to fine-tune the process. However, it quickly became apparent that the unit was not able to operate efficiently in a continuous process, since there was a set of considerations that, despite being apparently minor, in reality threatened to endanger the entire operation. An example of this was the sample collection windows, located in the main transitions between equipment, which caused several ignitions during the operation, because they were not watertight and thus allowed oxygen-rich air to enter the system in areas where the temperature was high. It was also quickly verified that the cooling system installed was neither sufficient nor efficient to reduce the temperature, since there was ignition of the material, even after the cooling zone, which was initially constituted only by a double-walled auger, where water circulated and was cooled by a radiator with air ventilation, thus demonstrating that the temperature reduction was not sufficient for the amount of mass and heat present in the system. All these issues indicating that it was not possible to operate the system safely led to the decision to stop the tests and to correct the problems identified. Therefore, changes were made to the cooling system, with three more double-walled augers (Figure 8). The cooling system was also replaced usinga radiator with ventilated air, with a cooling tower. Finally, all the non-watertight sampling windows were eliminated, and these were replaced by a watertight sampling system. Regarding the quality of the final product, at this stage, no results were obtained that would allow the process to be fine-tuned, since the permanent insecurities caused by ignitions made it necessary to interrupt the process many times. Therefore, it was difficult to maintain its stability and thus guarantee the repeatability of the results obtained for the final product. As the temperature considered to be optimal for the process was often exceeded, and the material appeared more carbonized than torrefied, there were frequent problems in pelletizing, causing great wear and tear to the components of the pelletizing equipment. Figure 9 shows examples of this wear caused by the abrasiveness of excessively torrefied material. This information was extremely important, as it prompted the development of a line of research on the pelletization of the torrefied biomass. At this stage, a lot of data were collected, both on the process itself, namely temperatures and other system variables related to the individual operation of each  
Figure 8: Cut of one of the double-walled augers of the cooling system, in which the chamber where the cooling water circulates is visible. The heat is dissipated by conduction through the cooled walls of the auger in contact with the material that circulates inside. Figure 9: Left: the appearance of a new layer of a pelletizer roll. Center: the wear caused on the cover of a pelletizer roll after 200 h in the production of conventional biomass pellets. Right: the wear caused on the cover of a pelletizer roller after 50 h of processing torrefied biomass. equipment, and also on the products at different stages of the process. These data were subsequently analyzed and led to the first optimizations of the pelletization process, namely the definition of the type of die to be used for the processing of torrefied biomass. Initially, the degree of torrefaction was defined only by the temperature of the process, since in this testing phase the residence time and the type of raw material used, which was always Pinus pinaster wood, were kept constant. As all previous experience was based on the production of conventional biomass pellets, the first matrices used in the tests were the same, with high compression rates.