负压差立管下料过程压力脉动的传递性实验与分析

在高13m大型循环流化床装置上,对φ150 mm×900 mm负压差立管内气固两相流的动态压力进行了轴向多点测量,并用标准偏差进行了分析,主要研究立管下料过程的动态传递特性.实验表明负压差立管内存在明显的压力脉动现象,这种压力脉动具有一定的传递性.颗粒质量流率比较小时是稀密两相共存流态,稀相区的压力脉动主要受进料流量振荡的影响,向下传递;密相区的压力脉动主要受立管的波动性排料影响,向上传递;随着颗粒质量流率的增加达到浓相输送流态时,上部是连续式浓相输送流态,下部是密相波浪式输送流态,立管的压力脉动主要受进口流量振荡和排料过程压缩气体作用,向下传递.对立管的压力脉动进行标准偏差分析表明脉动压力传递沿颗粒的流动方向上具有幅值增大特性.在立管内流态从稀密两相共存流态转变为浓相输送流态时,由于颗粒压缩气体分量最大,压力脉动幅值最大,减小或增加颗粒质量流率,压力脉动幅度均降低.

The Experiment and Analysis of Pressure Fluctuation Transfer in the Standpipe under Negative Pressure Gradient

The transfer characteristics of pressure fluctuation in a 150 mm×900 mm standpipe under negative pressure gradient were investigated based on measuring the dynamic pressure of a gas-solid two-phase flow in the feeding dipleg of a circulating fluidized bed(CFB).Furthermore,the pressure fluctuations measured were analyzed with standard deviation.The results show that the pressure fluctuation exists apparently in the standpipe.When the mass flux of solid is small,the flow pattern in the standpipe is dilute and dense two-phase co-existence;the pressure fluctuation in the dilute phase regime is mainly attributed to the fluctuating feed rate which transfers downward;and in the dense phase regime,the pressure fluctuation is caused by the fluctuating discharge which transfers upward.When the mass flux of solid increases continually,the flow pattern in the standpipe transforms to dense phase conveying which is a continuous dense phase conveying at the top and a wavelike dense phase conveying at the bottom,the pressure fluctuation is mainly attributed to the fluctuating feed rate and the gas compression caused by the discharging solid,which transfers downward.The transfer characteristic of pressure fluctuation along the axial direction of the standpipe is affected by the mass flux and flow pattern mainly.The analysis of the standard deviation of the pressure fluctuation in the standpipe indicates that,at the moment when the dilute and dense two-phase co-existence flow pattern transfers to the dense phase conveying flow pattern,since at that time the component of gas compressed by the solid is maximum,the pressure fluctuation intensity in the standpipe reaches its maximum,and the amplitude of the pressure fluctuation will decrease whenever further the mass flux of the feeding solid is increased or decreased.