Numerical studies of solid–solid mixing behaviors in a downer reactor for coal pyrolysis
Numerical studies of solid–solid mixing behaviors in a downer reactor for coal pyrolysis
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DOI：
10.1016/j.powtec.2013.11.042
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发表时间：
2014-02
影响因子：
5.2
通讯作者：
Yongpan Cheng;Wenbiao Zhang;G. Guan;C. Fushimi;A. Tsutsumi;Chi‐Hwa Wang
中科院分区：
文献类型：
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作者：
Yongpan Cheng;Wenbiao Zhang;G. Guan;C. Fushimi;A. Tsutsumi;Chi‐Hwa Wang
下行床反应器是一种理想的煤气化快速热解反应器，因为它的固含率分布和停留时间分布比较均匀，停留时间短。由于热解是一个快速反应，下行床固-固混合对促进热解反应至关重要。因此，本研究通过数值模拟研究下行床内的固-固混合。应用欧拉-拉格朗日方法，并结合计算流体力学和离散元方法（CFD-DEM）实现。模拟了硅砂载热介质从下行床顶部流出，煤粒通过两个垂直和切向布置的侧向喷嘴引入的情况。结果表明，切向排列比常规排列具有更低的固含率和更高的颗粒速度。在下行床入口处，二元固体颗粒之间的混合较差。混合的程度迅速增加，并在下行床的下游区域接近一个几乎恒定的值。高的空气速度和小的固体颗粒尺寸可以导致更好的混合，无论是正常的和切向布置。但切向布置比常规布置更有利于二元固体颗粒的混合，当颗粒尺寸从2 mm减小到1 mm时，喷嘴布置的影响减小。
A downer reactor is ideal for fast pyrolysis during coal gasification as solids holdup distributions and residence time distribution in the reactor are fairly uniform and residence time is short. Because pyrolysis is a rapid reaction, in the downer solid–solid mixing is critical to promote pyrolysis reaction. Thus, solid–solid mixing in the downer was studied through numerical modeling in this study. An Eulerian–Lagrangian method was applied and implemented by combining Computational Fluid Dynamics and Discrete Element Method (CFD–DEM). The heat carrying media of silica sand was modeled to flow from the top of the downer while coal particles were introduced through two lateral nozzles in normal and tangential arrangements. Numerical results showed that tangential arrangement had lower solids holdups while higher particle velocities than normal arrangement. Mixing among binary solid particles was poor at the entrance of downer. The extent of mixing increased rapidly and approached an almost constant value in the downstream regions of the downer. High air velocity and small solid particle size could lead to better mixing for both normal and tangential arrangements. But tangential arrangement had better mixing of binary solid particles than normal arrangement, and when the particle sizes were reduced from 2 to 1 mm, the influence of nozzle arrangement was reduced.