固定/鼓泡床中煤沥青球升温过程的CFD-DEM模拟

CFD-DEM investigation of heating process of coal tar pitch in packed and bubbling fluidized beds

为掌握煤沥青球在不同床型结构下的升温规律,采用三维CFD-DEM耦合传热的数值模拟方法,对实验室尺度固定床和鼓泡床内的煤沥青球升温过程展开研究,获得了不同流型(固定床/鼓泡床)、高径比、厚宽比下床层内的气固流动及传热结构、气固对流传热强度、床层升温速率及温度均匀性信息.结果表明,相较于固定床,使用鼓泡床能够有效避免局部高温区域的形成;当床层高径比提升至0.95以上时,对鼓泡床温升的影响较小;跟踪颗粒在床层上方受到空气冷却的时间随高径比的增加而增加,从而导致其出现更大的温降;壁面效应随宽厚比的增加而逐渐减弱,气泡上升速度、颗粒动能均有所增加,使得床层颗粒的内循环速率加快,床层底部气固温差增大,床层颗粒升温速率提升约24.2%.

To grasp the heating characteristics of coal pitch spheres in different bed structures, a 3 D model for computational fluid dynamics-discrete element method(CFD-DEM) with coupled heat transfer was adopted to investigate the gas-solid flow and heat transfer characteristics in packed and bubbling fluidized beds. The following results were obtained: gas-solid flow and heat transfer structure, convective heat transfer intensity, heating rate and temperature uniformity under different flow regimes, the ratio of height to diameter, and the ratio of thickness to width. The results show that avoiding the local high-temperature particle region is less formed in bubbling fluidized beds compared with that in packed beds. When the ratio of height to diameter is greater than 0.95, it has little effect on the temperature rise of particles in the bubbling fluidized bed. The cooling time of the tracking particles in upper region increases with the increasing ratio of height to diameter, resulting in a larger temperature drop. The wall effect gradually decreases with the increase of the ratio of width to thickness, the rising velocity of bubbles and the kinetic energy of particles both increase, making the internal circulation rate of bed particles accelerate, the gas-solid temperature difference at the bottom of bed increases, and the heating rate of bed particles increases by about 24.2%.