蒸汽-兰炭传热及余热回收特性

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。

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

In order to improve the waste heat recovery efficiency of semi-coke, the unsteady convection heat transfer three-dimensional model of steam and semi-coke was established to investigate the heat transfer mechanism of single particle. At the same time, the effects of semi-coke size, steam flow and particle bed thickness on the heat transfer and waste heat recovery characteristics of steam and semi-coke 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 particle and top particle first increase gradually and then decrease slowly. The heat transfer rate of bottom particle first decreases rapidly and then tends to 0. The heat transfer rate evolution of the bottom particle is different from that of the middle particle and the top particle, and the heat transfer rate evolution of middle particle and top particle is similar. In the initial stage of heat exchange between steam and semi-coke, the heat exchange is violent, the average temperature of the semi-coke bed decreases rapidly and the amount of heat recovery increases significantly. The amount of heat recovery decreases with the increase of the particle size, increases almost linearly with the increase of the semi-coke bed thickness, and increases gradually at first and then tends to be stable with the increase of the steam flow. When remaining the amount of heat recovery is maximum, the optimum steam flow rate is 9.0 kg/h.