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

Abstract

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 °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 °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.

Theoretical Analysis and Optimization of Fine Lignite Drying and Separation with a Pulsed Fluidized Bed

“…23,24 Putra and Ajiwiguna (2017) investigated the relative influence of temperature and air velocity on drying process and concluded that the drying effect at high air velocity (1.6−2.8 m/s) is more significant than that of temperature. 23 An analogical result was also achieved by Sheng et al (2018). In the temperature range of 40−60 °C and air velocity range of 2−6 m/s, the increase of air velocity accelerates the drying of water more significantly than that of temperature, according to the work of Chandramohan (2018).…”

“…Then, the metamodel is evaluated at multiple sample points to determine model parameters by minimizing the error in the model. , The sample experiment points were determined based on an orthogonal experimental design, where four variables, namely, inlet temperature, pulsating frequency, air velocity, and bed height were analyzed. These variables were reported to have a significant effect on the segregation standard deviation of ash contents (σ ash ). − , We implemented the RSM and designed the orthogonal experiments to optimize the operation conditions for drying and simultaneously separating lignite particles.…”

“…These variables were reported to have a significant effect on the segregation standard deviation of ash contents (σ ash ). [23][24][25]27 We implemented the RSM and designed the orthogonal experiments to optimize the operation conditions for drying and simultaneously separating lignite particles.…”

The Influence of Anionic Additives on the Microwave Dehydration Process of Lignite

“…With extensive exploitation, high-quality coal (HQC) reserves have been rapidly decreasing, and the development and utilization of low-quality coal (LQC) has attracted much attention. , Lignite is a typical LQC, with proven reserves of approximately 400 billion tons globally, accounting for approximately 45% of the total coal reserves. , In China, the proven reserves of lignite are approximately 13 billion tons, accounting for 13% of the total reserves . Therefore, reasonable development and utilization of lignite can alleviate the shortage of coal resources to a certain extent and make the transformation from traditional energy to renewable energy more stable.…”

“…3,4 In China, the proven reserves of lignite are approximately 13 billion tons, accounting for 13% of the total reserves. 5 Therefore, reasonable development and utilization of lignite can alleviate the shortage of coal resources to a certain extent and make the transformation from traditional energy to renewable energy more stable.…”