生物质湿颗粒干燥特性实验与模拟研究

Experimental and numerical investigation on drying characteristics of wet biomass particles

生物质作为一种新型的绿色清洁可再生燃料,常常因为水分含量过高而大大降低利用效率。本文采用实验与数值模拟相结合的方法,对细丝状生物质颗粒在旋转滚筒内干燥预处理过程展开研究,分析了滚筒倾角、气流温度和气流速度对生物质能量传递和水分迁移过程的影响规律。结果表明:气流速度对颗粒与气流之间的对流换热量影响较大,流速增加强化了颗粒与气流之间的对流换热和水分蒸发过程,降低颗粒与滚筒热内壁面之间导热换热量的比重;滚筒倾角在3.5°~4.5°的范围内,颗粒出口温度和含水率均随滚筒倾角的增加而增加;提高气流入口温度,能够增加促进颗粒与气流之间的对流换热和颗粒表面水分汽化速度,使得颗粒在出口处的温度升高,含水率降低。

Biomass resources are widely used as a form of sustainable and renewable energy due to pollution-free and no emission. However, the utilization efficiency of biomass fuels often sharply decreases because of high moisture content. Therefore, the drying characteristics of fibrous biomass particles in a rotating dryer are studied in this paper. Both tests and numerical simulations were employed to investigate the influence of the slopes of drum, temperatures and velocities of gas flow on heat and mass transfer processes of the biomass. The results show that, the heat and mass transfer characteristics were significantly affected by the gas flow velocity. Convective heat and mass transfer between biomass particles and gas flow could be enhanced by increasing the velocity of gas flow. Meanwhile, the proportion of heat conduction between particles and hot inner wall reduced with the increase of gas velocity. The temperature and moisture content of fibrous biomass particles increased with the drum slope at the range of 3.5°~4.5°. Increasing the temperature of gas flow can strengthen the convection heat transfer and increase the evaporation rate of particles surface moisture. As a consequence, the temperature of particles at the outlet increased and the moisture content reduced.