Numerical Simulation and Experimental Research on Drying Behavior of a Single Lignite Particle (SLP) under High-Temperature Flue Gas

Abstract

The drying behavior of a single lignite particle (SLP) in high-temperature (600–900 °C) flue gas was investigated by experiment and numerical calculations. A self-designed horizontal fixed-bed reactor was employed for high-temperature drying experiments. Based on the drying curves obtained from these experiments, no constant-drying-rate stage was found, and the SLP drying process included stages with increasing and decreasing drying rates. To explore the drying process in depth, a mathematical model was developed in which the SLP was simplified into a simple spherical model. Based on the dry–wet zone theory, the heat- and mass-transfer equations were established to describe the drying process. The simulated results calculated using MATLAB agreed well with the experimental data. The model can predict SLP drying behaviors including the effects of the drying time, the surface and internal temperature distributions of the lignite particle, the migration of the evaporation interface inside the particle, and so on. The predicted results indicated that the migration velocity of the evaporation interface and the temperature were linearly dependent and that a temperature of 700 °C was the most suitable temperature for lignite drying. Furthermore, the drying time can be predicted using the model according to practical applications. Thus, the model can be used for the optimization of the drying process parameters and can offer guidance for the development of new drying technologies.

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“…To dry lignite with high efficiency and low energy consumption, it is necessary to study the drying mechanism in more detail. Based on the theory of dry and wet zone, Li et al 8 established heat and mass transfer equations describing the drying process of a single lignite particle (SLP), and successfully predicted the drying behavior of lignite in hightemperature flue gas, including the temperature profile inside the particles and the migration of the dry−wet boundary. Wan et al 9 established a mathematical model to describe the drying process of lignite using the volume average method.…”