Simulation of gas-solid flow behavior in downers using a new drag model based on the spatial superposition assumption

Pan, Xueer; Lian, Wenhao; Yang, Jingxuan; Zhang, Zhonglin; Hao, Xiaogang; Fushimi, Chihiro; Guan, Guoqing

doi:10.1016/j.powtec.2020.06.090

Cited by 7 publications

(2 citation statements)

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“…The presence of mesoscale clusters is confirmed in the downer; however, the conventional homogeneous drag model cannot capture the effect of mesoscale structure on the flow behavior. Herein, our developed drag model based on the spatial superposition assumption was adopted in this work to consider the effect of heterogeneous structure. The gas–solid momentum exchange coefficient can be expressed as follows: β g i = H d i 3 4 false( 1 − ε normalg false) ε g d i ρ g false| v normalg − v i false| C D 0 ε normalg − 2.7 H d i = a italicRe i b a = 3.1128 ε normalg 2 − 4.8113 ε g + 1.8697 b = − 2.064 ε normalg 2 + 2.9949 ε …”

Section: Model and Methodsmentioning

confidence: 99%

Section: Model and Methodsmentioning

confidence: 99%

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Simulation of Heat Transfer in a Downer-Type Pyrolyzer with Binary Particles by Considering Carrying Gas Role in the Coal Heating Process

Lian,

Zhang,

Pan

et al. 2024

Ind. Eng. Chem. Res.

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Heat transfer between binary particles in an internally heated downer pyrolyzer was carefully studied because it is an important element for the reactor design, but a consensus on the heat transfer process has not been achieved. Compared with the experimental, numerical simulation can provide more details for understanding the heat transfer process. In this work, the widely used multifluid model (MFM) was adopted with considering the multiscale heat convection, conduction, and radiation behaviors inside the downer pyrolyzer. To clearly recognize the exact route of how heat transfers from high-temperature char to low-temperature coal, herein, the rate of each heat transfer way was calculated and counted separately. It is found that the heat radiation and conduction directly transferred from char to coal are all relatively small, and the gas–coal convection is the main factor in the coal heating process. However, the heat carried by the gas into the pyrolyzer only accounts for less than 0.1% of the heat received by the coal, implying that the gas phase is only the heat source by direct contact while the char is the indirect but main heat source. This was confirmed by the thermal balance analysis. Therefore, a conclusion of two-stage heat convection processes was proposed, in which the heat first transfers from char to gas, then from gas to coal, and these two stages belong to heat convection. Hence, the gas phase plays an intermediate medium role in the heat transfer process. Furthermore, the final temperature of the coal increases with the decrease in heat carrier diameter but is not sensitive to the gas velocity. This work is expected to provide guidance for the optimization of an efficient downer-type pyrolyzer.

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