Separation and Upgrading of Fine Lignite in Pulsed Fluidized Bed. 1. Experimental Study on Lignite Drying Characteristics and Kinetics

摘要

The pulsating flow was introduced into the gas solid fluidized bed to enhance the diffusion and stratification of lignite particles and avoid channeling and short circuits with an attempt to achieve a better drying effect for fine lignite. A pulsed fluidized bed system was established, targeting the analysis of the drying and segregation characteristics of fine lignite. With the thermal input characterized by inlet temperature, thermal energy was transported into the fluidized bed and lignite particles, which accelerates the evaporation of surface water and interior water of lignite particles. Under the combination effect of thermal and pulsating energy, the drying efficiency was significantly improved. This paper mainly focuses on the influence of various operating factors on the drying characteristics of fine lignite in a pulsed fluidized bed and exploring the appropriate kinetic model for the drying process under different inlet temperatures in a pulsed fluidized bed. In the drying process, the drying rate was influenced dramatically in a positive way by the inlet temperature, gas velocity, and pulsating frequency, while the drying rate decreases with the increase of bed height. The increase of inlet temperature, gas velocity, and pulsation frequency reduced the moisture content and increased the drying rate. When the inlet temperature, air velocity, pulsating frequency, and bed height, which are 100 degrees C, 1.09 m/s, 3.06 Hz, and 120 mm, the water content of -6 + 3 mm lignite decreases dramatically from 31.66% to approximately under 8% after 12 min of drying. The water content of 3 + 1 mm lignite plummets from 29.99% to around 4% after 12 min of drying when inlet temperature, air velocity, pulsating frequency, and bed height are set as 100 degrees C, 0.61 m/s, 2.62 Hz, and 80 mm, respectively. An infinitesimal effect on the lignite drying can be detected when the gas velocity and the pulse frequency exceed a certain range. In the study of drying kinetics, fitting results under different temperatures combined with a thin layer drying model showed that the logarithmic model was the optimal model for interpreting the drying characteristic of fine lignite. After drying and separation, the calorific capacities of -6.+3 mm lignite and -3 + 1 mm lignite increase by up to 60% and 67%, respectively. Hence, drying of fine lignite with a pulsed fluidized bed offers a feasible and economical method to enable further industrial application of lignite.