Particle residence time distributions in circulating fluidised beds
Particle residence time distributions in circulating fluidised beds
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DOI：
10.1016/s0009-2509(03)00082-4
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发表时间：
2003-06-01
影响因子：
4.7
通讯作者：
Thorpe, RB
中科院分区：
文献类型：
--
作者：
Harris, AT;Davidson, JF;Thorpe, RB
本文采用Harris等（Chem.Eng.J.89（2002 a）127）开发的快速响应颗粒停留时间分布（RTD）技术，对方形截面冷模循环流化床提升管内的颗粒停留时间分布进行了实验测量。该技术依赖于具有磷光性质的所有颗粒。一小部分颗粒在上升管入口处被闪光激活时成为示踪剂;这些磷光颗粒的浓度随后可以通过光电倍增管检测到。考察了固体循环速率和表观气速对停留时间分布的影响。所提出的结果是新颖的，因为（i）实验是在具有封闭边界的系统中进行的，因此给出了提升管中的真实停留时间分布，以及（ii）示踪剂浓度的测量非常快。大多数以前的研究都是在开边界的情况下测量RTD，给出了一个错误的RTD测量值。结果分析表明，使用提升管中的压力测量来推断固体存量会导致平均停留时间的错误估计。特别是，结果投下的假设，摩擦和加速度的影响可以忽略不计时，推断轴向固体浓度分布从立管的压力measurements.An颗粒RTD模型的评估。将随机颗粒RTD模型耦合到提升管流体动力学模型，该模型包含在快速流化床提升管中观察到的四个主要流体动力学区域，即（i）入口区域，（ii）过渡区域，（iii）芯环区域和（iv）出口区域。该模型成功地预测了实验停留时间分布。(C)2003爱思唯尔科技有限公司版权所有。
This paper gives experimental measurements of the particle residence time distribution (RTD) made in the riser of a square cross section, cold model, circulating fluidised bed, using the fast response particle RTD technique developed by Harris et al. (Chem. Eng. J. 89 (2002a) 127). This technique depends upon all particles having phosphorescent properties. A small proportion of the particles become tracers when activated by a flash of light at the riser entry; the concentration of these phosphorescent particles can subsequently be detected by a photomultiplier. The influence of the solids circulation rate and superficial gas velocity on the RTD were investigated. The results presented are novel because (i) the experiments were performed in a system with closed boundaries and hence give the true residence time distribution in the riser and (ii) the measurement of the tracer concentration is exceedingly fast. The majority of previous studies have measured the RTD in risers with open boundaries, giving an erroneous measure of the RTD.Analysis of the results suggests that using pressure measurements in a riser to infer the solids inventory leads to erroneous estimates of the mean residence time. In particular, the results cast doubt on the assumption that friction and acceleration effects can be neglected when inferring the axial solids concentration profile from riser pressure measurements.An assessment of particle RTD models is also given. A stochastic particle RTD model was coupled to a riser hydrodynamic model incorporating the four main hydrodynamic regions observed in a fast-fluidised bed riser namely (i) the entrance region, (ii) a transition region, (iii) a core-annulus region and (iv) an exit region. This model successfully predicts the experimental residence time distributions. (C) 2003 Elsevier Science Ltd. All rights reserved.