## Materials and Methods
### Identification of Faults, Malfunctions and Process Conditions
#### 2.3.2 Second Testing Phase (2014-2015)  
After solving the problems identified during the first testing phase, the second phase started, with the objective of having the unit in operation for the maximum possible continuous time. The intention was to identify other problems that might only occur after some time, and that might somehow condition the operation of the production unit. In this way, the process began, stipulating a temperature considered low, so as to more easily control any sudden temperature rises. Over the following days, with the process stabilized and with the product presenting some interesting characteristics without, however, achieving the desired results as torrefied biomass pellets, it was possible to verify and prove the success of the improvements introduced in the system, since none of the situations described above occurred again during the second testing phase. Meanwhile, the monitoring of aspects related to the mechanical functioning of the production unit was intensified in order to identify any situation that might be considered critical for normal functioning. It was found that, after about four days of continuous operation, the first auger of the cooling system, which connects the discharge chamber to the second auger, began to show an increase in amperage, indicating an abnormal effort that had not been registered thus far. For this reason, the decision was made to interrupt the test, initiating the stopping procedure and ensuring the safe cooling of the system. In order to gauge the reason for the large effort, and because it was thought that it could be caused by a warping of the central shaft, it was disassembled, as shown in Figure 11. As is clearly visible in the image, there was a layer of carbonized material mainly in the corresponding section of the shaft that was in contact with the discharge chamber area of the reactor. This situation immediately raised a suspicion regarding the origin of this encrustation of carbonized material located in this area of the auger, mainly because another indication appeared at several points of the production line, associated with the permanent exhaustion of gases in transition zones. This revealed multiple leaks, through which gases escaped, condensing along the surface of the equipment, as can be seen in Figures 12 and 13, where the atmosphere inside the production unit is perfectly visible, completely filled with exhaled gases, as well as runoff along the surfaces of the equipment. The verification of the two situations, first, the fact that something was agglutinating the solid material, causing it to adhere to the propeller and the central shaft of the first cooling auger and,  
Figure 11: Propeller of the first auger in the cooling system. Both the shaft and the propeller are covered in a black material, similar to coal, indicating that the material may have been exposed to high temperatures, or an excessive residence time. Figure 12: View of the atmosphere inside the production unit, with the gases occupying the space completely and exiting through several holes along the production line. Figure 13: Condensation of gases forming runoff along the surface of the equipment. Left: runoffs from the manhole door of the reactor discharge chamber. Right: runoffs on the door of the pelletizer itself, that is, in the final section of the production line. second, the fact that there were gas leaks along the entire production line, indicated that the volume of gases produced during the torrefaction process was higher than what had initially been admitted. Above all, it was evident that the gas extraction system had been dimensioned in a deficient way and was, therefore, not able to eliminate all the gases produced. This allowed them to follow the solid fraction, since the temperature difference of approximately 80 \({}^{\circ}\)C was sufficient to condense some of the gases when they passed from the reactor to the discharge chamber.