Multi-fluid Eulerian simulation of binary particles mixing and gas–solids contacting in high solids-flux downer reactor equipped with a lateral particle feeding nozzle

Zheng, Qiang; Yang, Jingxuan; Lian, Wenhao; Zhang, Baoping; Pan, Xueer; Zhang, Zhonglin; Hao, Xiaogang; Guan, Guoqing

doi:10.1016/j.cjche.2021.03.009

Cited by 4 publications

(11 citation statements)

References 43 publications

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“…However, the conclusion of the thermal balance analysis seems to contradict the conclusion obtained in section . On the one hand, it is proved that the heat obtained by the coal is mainly contributed by the gas–coal convection . On the other hand, the heat released by gas is far from affording the heat obtained by coal.…”

Section: Resultsmentioning

confidence: 99%

“…It can be observed that the heat transfers of char → gas and gas → coal both decrease at first and then increase to a lower peak value, finally decreasing again. According to our previous work, this specially designed downer with a lateral nozzle to inject coal particles can be divided into three regions, namely, injection mixing region (region I), intermediate transition region (region II), and fully developed region (region III), based on the conditions of gas–solid contacting and solid–solid mixing, as shown in Figure . Regions I, II, and III represent the conditions of the lowest mixing and contact, poor contact but good mixing, and excellence in both mixing and contact, respectively .…”

Section: Resultsmentioning

confidence: 99%

“…More details of simulation method can be found in our previous work. 21 Considering that the grid independence and model have already been validated before, they are not reproduced here for brevity.…”

Section: Heat Radiation Modelmentioning

confidence: 99%

“…On the one hand, it is proved that the heat obtained by the coal is mainly contributed by the gas−coal convection. 21 On the other hand, the heat released by gas is far from affording the heat obtained by coal. Based on the basic understanding of energy conservation, the remaining 99.9% of the heat could be only originated from char particles.…”

Section: Heat Transfer Profile Along the Axial Directionmentioning

confidence: 99%

“…For heat conduction and heat radiation, they do not contribute much in the whole heat transfer process, which is consistent with other researchers' conclusions. 10,21,22 As for the conclusion in section 3.1 obtained by other researchers, 15,21,22 it only focuses on the gas and heat-received particles̀heat convection, but ignores the role played by the heat-carried particles, resulting in this incomplete thought.…”

Section: Heat Transfer Profile Along the Axial Directionmentioning

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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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Heat Radiation Modelmentioning

confidence: 99%

Section: Heat Transfer Profile Along the Axial Directionmentioning

confidence: 99%