| Summary: | One of the aims of the environmental and energy policy of the European Union is to reduce the emission of air pollutants, primarily from heat and electricity production, e.g., using renewable energy sources. An example of such a fuel is agricultural biomass including animal manure, which can be used to produce energy in many ways, inter alia direct combustion. The aim of the study was to measure the concentration of NO, NO<sub>x</sub>, CO, dust and boiler efficiency during the combustion and co-combustion of wood and manure pellets. The research was conducted in the laboratory of the Poznań University of Technology using a 15 kW domestic boiler at maximum power. Manure pellets had higher moisture—9.2%, lower high heating value—17.25 MJ·kg<sup>−1</sup>, lower low heating value—16.45 MJ·kg<sup>−1</sup>, and higher ash content—11.23% than wood pellets. The average concentrations of CO, NO, NO<sub>x</sub> and dust for 100% wood pellets were 198 ± 27 mg·m<sup>−3</sup>, 129 ± 5 mg·m<sup>−3</sup>, 198 ± 8 mg·m<sup>−3</sup> and 8.7 ± 0.5 mg·m<sup>−3</sup>, respectively. For this, the fuel boiler power was 13.6 kW (air–fuel ratio 1.48), and it was close to the maximal nominal power. Increasing the share of manure pellets in the burning mixture worsened the stability of the combustion process, and the occurrence of incomplete combustion was observed, which resulted in an increased concentration of CO and dust. Additionally, NO and NO<sub>x</sub> concentrations also increased. The average boiler power during the combustion of 100% manure pellets was 7.8 kW (air–fuel ratio 2.2), and the average concentrations of CO, NO, NO<sub>x</sub> and dust were 1548 ± 555 mg·m<sup>−3</sup>, 355 ± 53 mg·m<sup>−3</sup>, 554 ± 88 mg·m<sup>−3</sup> and 482 ± 63 mg·m<sup>−3</sup>, respectively.
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