回转窑传热模型与数值模拟

对回转窑内传热过程进行了分析 ,在已有研究基础上归纳了各项换热系数的关联式 ,尤其结合热渗透模型完善了回转壁面与料床之间传热机制的研究 ,并提出通用的计算关联式。进而提出了内热式炉型的一维轴向传热模型 ,并根据已发表的试验数据验证了该模型和各换热系数的适用性。计算表明在窑内低温段 ,物料的受热主要来自其覆盖的回转壁面对其加热 ;而在高温段 ,气体的辐射热量成为加热料床的主要热源。此外 ,由物料进口端沿轴向窑壁散热增大 ,在窑内高温段窑壁的散热甚至高于物料吸热量 ,因此在回转反应器的设计中应充分考虑窑壁散热造成的热效率降低并采取相应措施。

Axial Heat-Transfer Model and Numerical Simulation for Rotary Kiln

Heat transfer process in rotary kiln was analyzed, and a review of the recent research results of the heat transfer coefficients in rotary kiln was proposed. Especially, the mechanism of heat transfer between the rotating covered wall and the bed material based on the penetration model was analyzed, and the rotating influence on the convective coefficients was discussed. On this basis, one demensional axial heat transfer model for a rotary kiln was presented. The model predictions show good agreements with the experimental data in literature, which validate the applicability of employed heat transfer coefficients. Heat transfer between covered wall and the covered bed plays an important role in the total energy transferred to the bed at relatively low temperature period of the kiln. While radiative exchange between the freeboard gas and the exposed bed surfaces take great fraction with increasing temperature along axial distance. Furthermore heat loss through kiln wall increases and is higher than the net heat transfer to bed along axial distance, which causes the inefficiency in most period of the rotary kiln and should be fully taken into account in rotary kiln design.