基于钛铁矿的热态增压流化床水平埋管传热特性

Heat transfer characteristics of horizontal immersed tubes in hot pressurized fluidized bed with ilmenite as bed materials

为提供工业规模增压流化床锅炉密相区埋管传热系数,提出一种灵活的换热关联式。首先,采用夹套式布置方法,研制热态增压流化床实验平台;其次,利用钛铁矿和石英砂为床料,探究运行工况对密相区传热特性的影响;最后,根据实验结果,提出密相区水平埋管传热关联式。研究结果表明:随着炉膛压力和床层温度上升,埋管平均传热系数呈现上升趋势;随着流化风速上升,埋管平均传热系数呈现出先增大后减小的趋势;在4~6倍流化数时,埋管平均传热系数达到最大值;以钛铁矿为床料,埋管周向传热系数的分布规律与石英砂保持一致,即水平埋管两侧的传热系数高于埋管底部和顶部。考虑床料导热系数的影响,提出了增压热态流化床密相区水平埋管传热经验关联式,经过本文和公开文献中实验数据验证,传热经验关联式在现有传热模型中精度较高。

To provide heat transfer coefficient of immersed tubes in the dense zone of pressurized fluidized bed boiler,a flexible heat transfer correlation was proposed.Firstly,the experimental platform of thermal pressurized fluidized bed was designed and built by using the jacketed arrangement method.Secondly,the influence of operating conditions on the heat transfer characteristics of dense zone was explored by using ilmenite and silica sand as bed materials.Finally,according to the experimental results,a heat transfer correlation of horizontal immersed tube in dense zone was proposed.The results show that the average heat transfer coefficient increases with the increase of pressure and bed temperature.In addition,with the increase of fluidization velocity,the average heat transfer coefficient increases first and then decreases.Moreover,the average heat transfer coefficient of immersed tubes reaches the maximum at 4-6 times of fluidization number.The circumferential distribution of heat transfer coefficient with ilmenite as bed materials is consistent with that with silica sand as bed materials.Furthermore,the heat transfer coefficient on both sides of horizontal tubes is higher than that at the bottom and top of immersed tubes.By considering the effect of bed material thermal conductivity,an empirical correlation for heat transfer of immersed tubes in the dense zone of pressurized fluidized bed is proposed.It is validated by experimental data in this study and published literatures.The empirical correlation for heat transfer has higher accuracy in the existing models.