| Summary: | In this study, the co-combustion of coal and biomass, and the tri-combustion of coal, biomass, and oil sludge in a 130 t h<sup>−1</sup> circulating fluidized bed (CFB) boiler are investigated via the computational particle fluid dynamics (CPFD) approach. Furthermore, the effect of biomass feeding position is also comprehensively evaluated. The results show that for the co-combustion of coal and biomass, the O<sub>2</sub> mole fraction at the furnace outlet rises from 0.0541 to 0.0640 as the biomass blending ratio enhances from 40% to 100%, while the CO<sub>2</sub> mole fraction reduces from 0.1357 to 0.1267. The mole fraction of NO<i><sub>x</sub></i> and SO<sub>2</sub> at the furnace outlet decreases from 4.5867 × 10<sup>−5</sup> to 3.9096 × 10<sup>−5</sup> and 2.8253 × 10<sup>−4</sup> to 4.6635 × 10<sup>−5</sup>, respectively. For the tri-combustion of three fuels, the average NO<i><sub>x</sub></i> mole fraction initially grows quickly and then declines gradually, ranging from 4.1173 × 10<sup>−5</sup> to 4.2556 × 10<sup>−5</sup>. The mole fraction of SO<sub>2</sub> at the furnace outlet increases from 3.5176 × 10<sup>−4</sup> to 4.7043 × 10<sup>−4</sup> when the ratio of oil sludge rises from 10% to 20%. The uniformity of temperature and gas components distribution is “new inlet > secondary air inlet > feed inlet”. As for the three inlet positions, the mole fractions of NO<i><sub>x</sub></i> at the furnace outlet are between 3.9096 × 10<sup>−5</sup> and 5.1537 × 10<sup>−5</sup>, while those for SO<sub>2</sub> are between 2.5978 × 10<sup>−4</sup> and 2.5278 × 10<sup>−4</sup>.
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