Study on the combustion characteristics and pollutant emissions of cold-pressed pellets and pellet powders in fluidized-bed

Abstract

Wood pellets produced by cold-pressing reduces energy consumption, but also generates more pellet powders. In order to achieve the complete utilization of woody biomass, this study analyzed the combustion characteristic parameters, pollutant emissions, and combustion efficiency of wood pellets (WP) and pellet powders (PP–S, PP-L) in fluidized-bed. Thermogravimetric and fluidized-bed experimental results showed that: (1) PP-S presented the highest volatilization and burning rate, with the best combustion characteristic parameters. (2) Material size and excess air coefficient determined the fluidization pattern and temperature profile, the optimal excess air at the highest combustion temperature of PP-S, PP-L, WP was 1.25, 1.5, and 1.75, respectively. (3) The fly ash after combustion was mainly within the range of small (<32 μm) and large (>212 μm) sizes, with PP-S producing more fine ash and WP producing more coarse ash. (4) Increasing size from PP-S to WP and decreasing excess air coefficient both led to reduced emission of NO but increased emissions of CO and CxHy. (5) The combustion efficiency of PP-S was the highest and basically unaffected by excessive air coefficient. Increasing excessive air coefficient reduced the heat loss of PP-L and WP, and promoted their combustion efficiencies.