蒸汽-兰炭传热及余热回收特性

Heat Transfer and Waste Heat Recovery Characteristics of Steam and Semi-coke

为了提高兰炭余热回收效率,建立了蒸汽-兰炭三维非稳态传热模型,对单颗粒传热机理进行了分析,并研究了兰炭粒径、料层厚度和蒸汽流量对蒸汽-兰炭传热及余热回收特性的影响。通过搭建蒸汽-兰炭换热实验台对所建传热模型进行验证,计算结果与实验结果具有良好的一致性。结果表明:对于单颗粒传热,中层颗粒和顶层颗粒热流量均是随着换热时间先增加后减小,具有相似的变化规律,而底层颗粒热流量的变化规律不同于中层颗粒和顶层颗粒热流量的变化规律,底层颗粒热流量是随着换热时间逐渐减小最后趋于0。蒸汽-兰炭换热初期热交换剧烈,料床整体平均温度下降较快,热回收量显著增加。热回收量随着兰炭粒径的增大逐渐减小,随着料层厚度的增加几乎呈线性增加,随着蒸汽流量的增大先逐渐增大后趋于稳定,在保证余热回收量最大的情况下蒸汽的最佳流量为9.0 kg/h。

To improve the waste heat recovery efficiency of semicoke,a three-dimensional model of unsteady convection heat transfer of steam-semicoke was established to investigate the heat transfer mechanism of single particle.At the same time,the effects of semicoke size,steam flow,and particle bed thickness on the heat transfer and waste heat recovery of steam-semicoke bed were investigated.The heat transfer model was verified by a gas-solid heat transfer test bench and the calculated results are in good agreement with the experimental results.The results show that,for the heat transfer of a single particle,the heat transfer rate of the middle and the top particles first increased gradually and then decreased slowly.The heat transfer rate of bottom particle first decreased rapidly and then tended to 0.The heat transfer rate evolution of the bottom particle was different from those of the middle particle and the top particle,and the heat transfer rate evolution of middle particle and top particle was similar.In the initial stage of heat exchange between steam and semicoke,the heat exchange was violent,the average temperature of the semicoke bed decreased rapidly and the amount of heat recovery increased significantly.The amount of heat recovery decreased with the increase of the particle size,increased almost linearly with the increase of the semicoke bed thickness,and increased gradually at first and then tended to be stable with the increase of the steam flow.The optimal flow rate of the steam was 9.0 kg/h when the maximum amount of heat recovery was ensured.