Experimental study of particle motion and heat transfer in externally heated rotary kiln

doi:10.11949/0438-1157.20250369

Abstract

Abstract:

Externally heated rotary kilns exhibit promising application prospects in the petroleum coke carbonization process, a critical step in the preparation of artificial graphite for lithium-ion battery anodes, due to its advantages of uniform heating, precise temperature control, energy efficiency, and environmental friendliness. The lack of understanding of the heat transfer performance law of the rotary kiln wall bed during the carbonization of petroleum coke restricts the precise design and energy-saving and low-carbon operation of this type of rotary kiln. This study utilized an electrically heated rotary kiln experimental system to investigate the effects of operational parameters on the wall-to-bed heat transfer coefficients of petroleum coke and quartz sand particles. The results indicate that as the filling rate increases, the wall-to-bed heat transfer coefficients of both quartz sand and petroleum coke particles decrease to varying degrees. Increasing the rotational speed significantly enhances the heat transfer coefficient for quartz sand particles, but has limited effect on petroleum coke particles. This is primarily due to quartz sand particles exhibiting rolling motion while petroleum coke particles undergo sliding motion. The heat transfer coefficient under sliding motion is significantly lower than that under rolling motion. Installing strip structures on the inner wall of the kiln can induce regular mixing of the petroleum coke particle bed, thereby enhancing heat transfer by approximately 70%—180%.

Key words: rotary kiln, particle, motion, mixing, operational parameters, heat transfer

摘要：

外热式回转窑因其具有加热均匀、温度控制精准、节能环保等优点，在锂电池负极人造石墨制备关键环节石油焦碳化工艺中具有良好的应用前景。对石油焦碳化过程中回转窑壁床换热性能规律的认识不足，制约了该类回转窑的精准设计及节能低碳运行。利用电加热回转窑实验系统，研究了操作参数对石油焦、石英砂颗粒壁床传热系数的影响。结果表明：随着填充率的增加，石英砂和石油焦颗粒的壁床传热系数出现不同程度的下降；提高转速可以使石英砂颗粒壁床传热系数得到显著提升，但对石油焦颗粒强化传热作用有限，主要原因在于石英砂颗粒呈滚动运动，而石油焦颗粒呈滑动运动；滑动运动的壁床传热系数远低于滚动运动，炉体内壁设置肋带可以使石油焦颗粒床发生规律混合，从而强化传热70%~180%。

关键词: 回转窑, 粒子, 运动, 混合, 操作参数, 传热

CLC Number:

TK 123

Xunxin LI, Huibin XU, Chi MA, Weiyu WANG, Feizi PENG. Experimental study of particle motion and heat transfer in externally heated rotary kiln[J]. CIESC Journal, 2025, 76(10): 5067-5075.

李勋新, 徐惠斌, 马驰, 王威宇, 彭飞子. 外热式回转窑颗粒运动传热实验研究[J]. 化工学报, 2025, 76(10): 5067-5075.

Figures/Tables 11

Fig.1 Experimental system of electrically heated rotary kiln1—stainless steel cylinder; 2—heating cable; 3—temperature measurement board; 4—data acquisition card; 5—Lora wireless transmission module(transmitter module and receiver module); 6—conductive slip ring; 7—angle encoder; 8—temperature controller; 9—heating cable controller; 10—computer; 11—reducer motor; 12—screw feeder; 13—mass sensor

Fig.2 (a) Schematic layout of temperature measuring plate in the furnace; (b) Schematic layout of 12 stainless steel strips

Table 1 Material properties and experimental working condition parameters

物性及工况参数	石英砂	石油焦
颗粒粒径D₁₀/μm	269	2.8
颗粒粒径D₅₀/μm	400	6.1
颗粒粒径D₉₀/μm	584	13.1
20℃物料堆积密度ρ_s/(kg/m³)	1369	535
转速n/(r/min)	1,2,3,4	1,2,3,4
填充率F/%	5,10,15,20	5,10,15,20

Fig.3 (a) Geometrical parameters of rotary kiln; (b) Schematic of area distribution

Fig.4 Image of particle motion in the experiment

Fig.5 Thermocouple temperature measurements of plate A during one rotation cycle

Fig.6 Effect of rotational speed on wall-bed heat transfer coefficient of quartz sand and petroleum coke （F=5%，Ts,m=40℃）

Fig.7 Effect of filling rate on wall-bed heat transfer coefficient of quartz sand and petroleum coke(n=3 r/min，Ts,m=40℃)

Table 2 Wall-bed heat transfer relational model

文献	经验关系式
[23]	$α w s = χ d p λ g + 1 α p e n - 1, χ = 0.085$
[24]	$α w s = χ d p λ g + 1 α p e n - 1, χ = 0.1$
[25]	$α w s = π d * 2 λ s + 1 α p e n - 1; n < 9.5 r / m i n, d * = γ × 1.12 × 10 - 3$
[26]	$α w s = α p e n - b s t 1 h * a s t + 1 h * a s t e x p (h * 2 a s t) e r f c (h * a s t), h * = 3607 1 m$
[27]	$α w s = 11.6 × λ s l γ ω R 2 γ a s 0.3$

Table 2 Wall-bed heat transfer relational model

文献	经验关系式
[23]	$α w s = χ d p λ g + 1 α p e n - 1, χ = 0.085$
[24]	$α w s = χ d p λ g + 1 α p e n - 1, χ = 0.1$
[25]	$α w s = π d * 2 λ s + 1 α p e n - 1; n < 9.5 r / m i n, d * = γ × 1.12 × 10 - 3$
[26]	$α w s = α p e n - b s t 1 h * a s t + 1 h * a s t e x p (h * 2 a s t) e r f c (h * a s t), h * = 3607 1 m$
[27]	$α w s = 11.6 × λ s l γ ω R 2 γ a s 0.3$

Fig.8 Wall-bed heat transfer coefficient of quartz sand and petroleum coke (F=10%, n=2 r/min)

Fig.9 Effect of built-in stripes on wall-bed heat transfer coefficient of petroleum coke (F=10%，n=3 r/min)

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