**3.3 Modification of the thread shaft fin**

Widely known as "break-mount," the fin located at the end of the biomass screw is intended to push the material down the pipeline, avoiding agglomerations and possible clogging. During the work, it was observed that the angle between the face of the fin and the axis of the screw has a great influence on its performance, and originally, the fin had its face towards the beginning of the screw. With this configuration and direction of rotation of the thread, the fin did not push the material down, but back into the thread, in the opposite direction to the natural flow of transport.

The position of the fin was changed (according to **Figure 7**) so that it pushed the material in the same transport direction. With this new configuration, the fin, in addition to helping to transport the material, prevents the biomass from being trapped at the beginning of the drop duct.

**Figure 6.** *Adequacy of the manhole of the biomass pipeline.*

#### **Figure 7.**

*Thread shaft fin position before (left) and after (right).*

#### **Figure 8.**

*Evolution of the number of cloggs of the M710 screw.*

#### **3.4 Changing the operating logic**

Another important point dealt with in the work was the reactive actions taken after clogging that could prevent new occurrences or reduce the man–machine interaction in the thread unclogging process.

When the screw stops due to clogging (when the sensor is activated), an automatic operating logic was created to rotate the screw in the opposite direction to normal operation, for a few seconds and at low speed. The purpose of this sequence was to loosen any material that might be trapped above the drop duct or sensor rod. With reverse movement, the biomass detaches and falls, freeing the material duct and avoiding the need for human intervention in the machine. With the development of this logic, most of the clogging was resolved soon after the occurrence (sensor activation) and, thus, the machine availability increased significantly, while the humanmachine interaction reduced.

In addition to these actions, others of lesser impact were also applied to contribute to solving other voices of the problem. The result of all the actions together can be

seen in **Figure 8**, where the monthly average number of occurrences of clogs dropped 75% after the implementations. Consequently, the frequency of unclogging interventions dropped from 1.7 times a day to less than 0.5.

It is known that eliminating this type of occurrence is practically impossible for this position, since, due to the structural shape and distribution of the boiler support points, the M710 thread is the one that receives material in a different direction from the natural flow, where the entire biomass line is tortuous.

However, the actions developed were of low cost and did not require the boiler to be stopped, thus configuring a good option for solving this type of problem. In addition, any of the actions can be extended to other positions of the threads in the boiler, making it possible to drastically reduce problems related to clogging.
