Combustion characteristics of millimeter-sized wood biomass particles in high-temperature turbulent environments
Biomass co-firing in coal-fired power plants represents a viable technology for efficient and low-cost CO2 reduction.The high energy consumption for crushing biomass fuel results in relatively large particle sizes entering the furnace.The burnout of these large parti-cles in the high-temperature turbulent environment within the furnace is a matter of concern.A four-fan opposed high-temperature turbu-lent experimental apparatus was employed to create a nearly homogeneous and isotropic turbulent flow field.Woody biomass particles of two sizes(dp,0=2.5 and 6.0 mm)were used as the research subjects,the effect of turbulent fluctuation velocity urms on the combustion charac-teristics of millimeter-sized biomass particles were examined by varying the furnace temperature(Tgas=500,700,900 ℃)and turbulent fluctuation velocity(urms=0-1.8 m/s).The particle temperature using a particle surface-center temperature measurement system was used and the entire combustion process using a color image capture system was captured.The biomass particle's combustion time,ignition mode,flame shape,and particle size change under different conditions could be determined.The results indicate that biomass par-ticles tend to undergo homogeneous ignition,with the mode of ignition shifting to heterogeneous only at Tgas=500 ℃ when urms increases.The particle heating rate before ignition rises by nearly 30％,and the particle surface temperature during the volatile combustion stage in-creases by approximately 300 ℃,when urms increases to 1.8 m/s.The increase in urms causes the volatile flame front to wrinkle and de-form,intensifying homogeneous combustion and slightly shortening the volatile combustion time.The porosity development of biomass char becomes more rapid,allowing a large amount of oxygen diffuse into the particles and react with carbon matrix,significantly shortening the char burnout time by over 40％and increasing the char combustion temperature.The larger the particle turbulent Reynolds number,the more significant the impact of turbulent fluctuation.Raising the furnace temperature weakens the effect of increasing urms on particle temperature but strengthens its effect on shortening the combustion time.
homogeneous and isotropic turbulentbiomasssingle particle combustionturbulent fluctuation
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