Effects of pelletizing pressure and particle size on flame characteristics and potassium release in volatile combustion of biomass pellets

While biomass palletization improves fuel properties, the effects of particle size and pelletizing pressure on volatile combustion characteristics and potassium (K) release remain poorly understood, hindering optimization of pellet quality and combustion efficiency. To clarify the effects of particle size and pelletizing pressure on volatile combustion characteristics (flame height, temperature distribution, etc.) and K release in biomass pellets, a combustion system using multi-wavelength imaging colorimetry and radiation spectroscopy was developed to investigate rice husk pellets (RHP), corn straw pellets (CSP), and poplar wood pellets (PWP) with varying particle sizes (210–420 μm, 125–210 μm, <125 μm) and pelletizing pressures (14.2 kN, 42.7 kN). The results show that higher pressure (42.7 kN) in RHP accelerates volatile release, advancing peak flame height by 3.4 s and increasing maximum side temperature by 114 K. RHP exhibit a unique trend where decreasing particle size increases flame height (from 74-79 mm to 100–102 mm), contrasting with CSP/PWP, whose flame heights decrease by 25–43 mm as particles refine. PWP combustion time shortens by 15–22 s for small particles, while their maximum flame temperature remains stable (1415–1453 K), differing from CSP, where small particles increase maximum temperature by 43–19 K despite reduced flame height. K release patterns also diverge: large-sized RHP/CSP emit 1.34–2.71 times higher K radiation than small-sized RHP/CSP, whereas medium-sized PWP exhibit the highest K radiation intensity (1.57 times large-sized PWP and 1.37 times small-sized PWP). These findings offer insights into biomass pellet utilization and equipment development.