Comprehensive Evaluation of Combustion Performance and Emissions from Commercial Pellets in Small-Scale Boilers

The combustion of fossil fuels is a major source of greenhouse gas emissions, drives climate change, and has intensified the search for cleaner energy alternatives such as biomass. Biomass derived from renewable organic materials, is considered a sustainable and carbon-neutral energy source. While biomass represents a renewable and clean energy source, its combustion, especially in pellet form, can produce various pollutants such as CO2, SO2, NO2, CO, and PM. This study focuses on analyzing the combustion of six different pellet brands and the emissions they produce. A dedicated experimental procedure was designed and implemented to evaluate the combustion performance. The temperature shows a gradual increase in ambient temperature around 2.5 °C across all tests, with a similar behavior, the temperature of flue gas shows a similar behavior between tests with temperatures peaking around 300 °C and 340 °C. In the tests conducted, all pellets complied with the legal emission limits defined by legislation. The efficiency calculated using the direct method was lower by around 55%, primarily due to the use of an older boiler (manufactured in 2004) and short duration of the test. The indirect method shows better efficiency, around 70%, influenced by lower moisture content of the pellets. The results indicate that B pellets had a superior performance compared to the others evaluated.