燃煤机组耦合生物质甚至全燃生物质是高效低成本降碳的可行技术。生物质燃料破碎能耗高导致入炉粒径相对较大,部分大粒径颗粒在炉内高温湍流环境中的燃尽问题值得重视。采用四风扇对冲高温湍流实验装置,构造近均匀各向同性湍流流场。以两种粒径的木质生物质颗粒(dp,0=2.5、6.0mm)为研究对象,通过改变炉温(Tgas=500、700、900℃)和湍流脉动速度(urms=0~1.8m/s),研究湍流脉动速度urms对毫米级生物质颗粒燃烧特性的影响。试验通过颗粒表面-中心温度测量系统记录了颗粒温度,通过彩色图像测量系统捕捉燃烧全过程,确定不同工况下生物质颗粒的燃烧时间、着火模式、火焰形态及粒径变化。结果表明,生物质颗粒通常倾向于发生均相着火,仅在Tgas=500℃时增大urms使着火模式由均相着火转变为异相着火。urms增至1.8m/s,着火前颗粒升温速率提高了近30%,挥发分燃烧阶段颗粒表面温度升高约300℃。urms增加引起挥发分火焰锋面褶皱变形,均相燃烧强度增加,tvol略微缩短;生物质焦炭的孔隙发展更加迅速,大量氧气扩散进颗粒内发生反应,使焦炭燃尽时间大幅缩短40%以上,焦炭燃烧温度亦随之增加。颗粒湍流雷诺数Rep,t越大,受湍流脉动影响越显著。升高炉温,增大urms对颗粒温度的影响将减弱,对缩短燃烧时间的影响越强烈。

Biomass co-firing in coal-fired power plants represents a viable technology for efficient and low-cost CO2 reduction. The highenergy consumption for crushing biomass fuel results in relatively large particle sizes entering the furnace. The burnout of these large particles in the high-temperature turbulent environment within the furnace is a matter of concern. A four-fan opposed high-temperature turbulent experimental apparatus was employed to create a nearly homogeneous and isotropic turbulent flow field. Woody biomass particles of twosizes (dp,0 = 2.5 and 6.0 mm) were used as the research subjects,the effect of turbulent fluctuation velocity urms on the combustion characteristics of millimeter-sized biomass particles were examined by varying the furnace temperature (Tgas = 500, 700, 900 ℃ ) and turbulentfluctuation velocity (urms = 0-1.8 m/ s). The particle temperature using a particle surface-center temperature measurement system wasused 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 particles 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 increases by approximately 300 ℃ , when urms increases to 1.8 m/ s. The increase in urms causes the volatile flame front to wrinkle and deform, intensifying homogeneous combustion and slightly shortening the volatile combustion time. The porosity development of biomass charbecomes more rapid, allowing a large amount of oxygen diffuse into the particles and react with carbon matrix, significantly shorteningthe 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 particletemperature but strengthens its effect on shortening the combustion time.

0 引言

1 试验台与测量装置

2 试验工况与数据处理方法

3 结果与讨论

   3.1 湍流热环境中生物质颗粒温度变化

   3.2 湍流对生物质颗粒着火的影响

   3.3 湍流对生物质颗粒火焰形态与粒径演变的影响

   3.4 湍流对生物质颗粒燃烧时间的影响

4 结语与展望