非均匀布风流化床内大颗粒停留时间特性

doi:10.11949/0438-1157.20191359

摘要/Abstract

摘要：

试验考察了非均匀布风配置对大颗粒在倾斜布风板流化床内停留时间分布的影响规律。结果表明，排渣管风速增加，E(t)曲线变平、波动增加，平均停留时间(MRT)呈指数增长；高风速区风速升高，先是分离过程占优，后转变为返混能力占优，MRT先减后增，存在一个适宜于分离的运行风速窗口；低风速区风速加快，混合能力增强，MRT变长。此外，还探讨了物性参数的影响。示踪物球形度越高、表面越光滑，越有利于分离，MRT变短。而尺寸的影响则与密度相关，对于重质示踪物，尺寸增加，MRT变短；而对于轻质示踪物，尺寸变大，MRT变长。试验所得停留时间分布(RTD)曲线形状、波峰时刻、峰值、波动等信息能够充分反映床内的颗粒流动与混合过程；对于内循环流动机理的探索、多组分流化床的工程应用具有一定的参考意义。

关键词: 流化床, 非均匀布风, 粒子, 停留时间分布, 试验研究

Abstract:

The experiment investigated the influence of non-uniform air distribution configuration on the residence time distribution(RTD) of large particles in a fluidized bed with an inclined air distribution plate. The results indicate that, an increase in the discharging velocity makes the E(t) curve more flat and fluctuating, with the mean residence time (MRT) growing exponentially. With an increasing air velocity in the high-gas-flow-rate-zone (HGFRZ), the segregation of tracers is initially dominant and gives way to the mixing process at the late stage. There is an optimal range of the HGFRZ gas velocity for separation. A high air velocity in the low-gas-flow-rate-zone (LGFRZ) induces an intensive mixing and a longer MRT. Additionally, the effects of tracers property are studied, as well. Regarding the particle shape, a spherical and smooth surface is good for the separating and results in a short MRT. As far as the size concerned, its impact couples with that of the density. For the dense particles, a large size causes a short MRT. However, for the light ones, a large size brings about a long MRT. Many characteristics of RTD curves from current works, such as the shape, fluctuation, peak time and value, properly reveal the particle flow and mixing behaviors in fluidized beds. These achievements are supposed to provide tangible references to the mechanism exploring of the internally circulating stream, and the engineering applications of fluidized beds with multiple components.

Key words: fluidized bed, uneven air supply, particle, residence time distribution, experimental investigation

中图分类号:

TK 224

田凤国, 朱田, 孔德正, 雷鸣. 非均匀布风流化床内大颗粒停留时间特性[J]. 化工学报, 2020, 71(4): 1520-1527.

Fengguo TIAN, Tian ZHU, Dezheng KONG, Ming LEI. Residence time of large particles in fluidized beds with non-uniform gas introducing[J]. CIESC Journal, 2020, 71(4): 1520-1527.

图/表 10

图1 内循环流化床RTD试验台

Fig.1 RTD test rig of internally circulating fluidized bed1—fluidized bed; 2—feeding port; 3—flowmeter; 4—bypass; 5—valve; 6—gas header; 7—wind box for low-gas-flow-rate-zone; 8—wind box for high-gas-flow-rate-zone; 9—discharging tube; 10—electronic balance

表1 床料物性参数

Table 1 Physical parameters of bed material

床料

平均粒径/mm

堆积密度/

(kg/m³)

真实密度/

(kg/m³)

临界流化

风速/(m/s)

表2 大颗粒物性参数

Table 2 Physical parameters of large particles

种类	颗粒密度/(kg/m³)	颗粒尺寸/mm	临界排出风速/(m/s)
煤粒	1860	4.5	8.78
绿豆	1360	3.8	9.51
黄豆	1280	6.5	10.24
玻璃	2500	5×5×5	12.32
灰渣	2200	12	15.77

图2 示踪物注入量对RTD的影响

Fig.2 Effect of tracer amount on RTD

图3 排渣管风速对RTD的影响

Fig.3 Effect of discharging velocity on RTD

图4 高风速区风速对RTD的影响

Fig.4 Effect of gas velocity in high-flow-velocity-zone on RTD

图5 低风速区风速对RTD的影响

Fig.5 Effect of gas velocity in low-flow-velocity-zone on RTD

图6 绿豆与煤粒 E(t)曲线的比较

Fig.6 Comparison of E(t) curves between green bean and coal particle

图7 停留时间分布累积函数F(t)

Fig.7 Accumulated function of RTD

图8 示踪物尺寸对RTD的影响

Fig.8 Effects of tracer size on RTD

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