# Control System Modification of a 5-kW Pellet Stove: Study and Analysis
## 4 Conclusions  
The main findings of this work were the following:  
* This work focused on the improvement of combustion yield in a pellet stove by using a programmable logic controller (PLC). The innovation lies in the capability of the stove to adapt to different kinds of biomass. Moreover, the use of PLC allows for a higher precision when controlling pellet supply and air flow, resulting in more efficient combustion with lower CO emissions. This approach offers a direct implementation to improve commercial devices, making them more efficient and sustainable. Figure 19: Ostwald diagram including different flue gas compositions according to different rotation speeds. Figure 18: Combustion performance according to different rotation speeds of the flue gas fan. * The best combustion performance was achieved when the flue gas fan worked at 320 rpm, as it was the operating condition at which almost all the carbon contained in the biomass were completely oxidized. * CO2 emissions increased when the flue gas fan speed decreased. On the contrary, O2 percentage decreased in this case. * NO content in combustion gas resulting after combustion of biomass waste was relatively low. * The CO percentage was considerably low in fumes once biomass was burned. Compared to previous studies where the abovementioned improvements were not included, the efficiency of the process was considerable, reducing CO emissions. * Concerning poplar pellets, the highest power supplied by the stove was 8.77 kW with a flow of 0.037 kg\(\cdot\)min\({}^{-1}\). This was the highest power obtained in this experience for all the different raw materials. * Regarding holm oak pellets, the highest power was 5.66 kW with a flow of 0.0215 kg\(\cdot\)min\({}^{-1}\). In this case, it was the lowest value found in this work. * Considering sugar cane bagasse, the highest power found was 6.23 kW with 0.0269 kg\(\cdot\)min\({}^{-1}\). * In the case of pear trees, the highest power was 6.32 kW with a flow of 0.0232 kg\(\cdot\)min\({}^{-1}\). Along with the modifications included in the facility to improve the combustion performance of the different biomass samples, further studies or improvements can be proposed to reduce particle matter and gas emissions and improve the power supplied by the stove, such as the following:  
* The implementation of a speed controller in the motor of the flue gas fan to regulate the air inlet in the system and, subsequently, improve the combustion process. * Possibility of automatic disposal of fuel in the hopper before or after each experience in order to change biomass without completely emptying the hopper. * Possibility of changing the rotation direction of the worm screw to unblock this device if required. According to the results obtained in this present work, it can be concluded that this facility, with the abovementioned considerations, could be a suitable alternative for the pre-established working parameters in this biomass system. With this adjustment, the combustion process can be carried out in optimum conditions, increasing the yield of this facility. Conceptualization, A.A.-M. and J.F.G.G. ; methodology, A.A.-M. and J.P.C. ; validation, A.A.-M. and J.F.G.G. ; formal analysis, A.A.-M. and J.P.C. ; investigation, A.A.-M. and J.P.C. ; resources, J.F.G.G. ; data curation, A.A.-M. and S.N.-D.; writing--original draft preparation, A.A.-M., J.P.C. and S.N.-D.; writing--review and editing, A.A.-M. and S.N.-D.; visualization, A.A.-M., J.F.G.G. and S.N.-D.; supervision, A.A.-M. and J.F.G.G. ; project administration, A.A.-M. and J.F.G.G. ; funding acquisition, J.F.G.G. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. Not applicable. Not applicable. Not applicable. Data Availability Statement: The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.