Optimization of Mg Production by Pidgeon Process Based on Heat Transfer in the Bed

doi:10.12068/j.issn.1005-3026.2024.04.009

Abstract

Abstract:

The temperature gradient in pellets bed caused by heat transfer is a key factor which limits the reduction reaction in the Pidgeon process. In this paper， the effects of some factors， such as pellet size， charging pattern， temperature of the outer wall of the retort on the temperature distribution and reduction ratio distribution in the bed are studied with numerical method. The results show that the maximum reduction rate can be obtained when the pellet diameter is 22.3 mm and the reduction time is the same. The temperature of the outer wall of the retort should be increased as much as possible in the production process. The closer to the central area of the bed， the lower is the temperature， and the lower is the reduction ratio， and reduction reaction lage.The method by making an empty central region can effectively shorten the reduction cycle and improve the utilization ratio of raw materials. The optimal size of the empty central region is less than 27 mm diameter based on Mg yield per unit volume and unit time by taking operation time and reduction time into consideration for the retort with inner diameter 270 mm.

Key words: Mg, Pidgeon process, vacuum silicothermic reduction, numerical simulation, heat transfer

CLC Number:

TF 822

Da-xue FU, Yue-zhong DI, Yao-wu WANG. Optimization of Mg Production by Pidgeon Process Based on Heat Transfer in the Bed[J]. Journal of Northeastern University(Natural Science), 2024, 45(4): 523-529.

Figures/Tables 14

Fig.1 Flow chart of Pidgeon process

Fig.2 Industrial retort and schematic diagramof geometric model

Table 1 Physical parameters

相关参数	数值
球团密度ρ/（kg·m^-3）	2 100-420α
球团比定压热容c_p /（J·kg^-1·K^-1）	955.02+0.1T
球团导热系数λ_s/（W·m^-1·K^-1）	0.14+0.000 288T
反应（1）焓变ΔH/（J·mol^-1）	249 023.4-21.2T
球团中镁的初始浓度c/（mol·m^-3）	17 500

Table 2 Reaction rate equations and related kinetic parameters

参数	时间/min
参数	≤15	≤12	≤10	≤8	>15	>12	>10	>8
温度/℃	1 050	1 100	1 150	1 200	1 050	1 100	1 150	1 200
动力学常数k/min^-1	0.025 13	0.051 74	0.079 42	0.110 55	9.98×10^-4	3.03×10^-3	5.32×10^-3	9.65×10^-3
还原反应速率/min^-1	$d α (t, T) d t = k (1 - α)$				$d α (t, T) d t = 3 k (1 - α) 2 / 3 2 [1 - (1 - α) 1 / 3]$

Table 2 Reaction rate equations and related kinetic parameters

参数	时间/min
参数	≤15	≤12	≤10	≤8	>15	>12	>10	>8
温度/℃	1 050	1 100	1 150	1 200	1 050	1 100	1 150	1 200
动力学常数k/min^-1	0.025 13	0.051 74	0.079 42	0.110 55	9.98×10^-4	3.03×10^-3	5.32×10^-3	9.65×10^-3
还原反应速率/min^-1	$d α (t, T) d t = k (1 - α)$				$d α (t, T) d t = 3 k (1 - α) 2 / 3 2 [1 - (1 - α) 1 / 3]$

Fig.3 Comparison between numerical results and industrial data

Fig.4 Effect of pellet diameter on average reduction ratio in the pellets bed

Fig.5 Effect of retort outer wall temperature on average reduction ratio in the pellets bed

Fig.6 Relationship between temperature and heating time at inner radius midpoint and center point of the retort at different heating temperatures

Fig.7 Temperature distribution in the pellets bed （pellet diameter 22.3 mm，heating temperature of retort T=1 473 K）

Fig.8 Reduction ratio distribution in the pellets bed （pellet diameter 22.3 mm，heating temperature of retort T=1 473 K）

Fig.9 Variation of reduction ratio with time in different bed volumes

Fig.10 Variation of Mg productivity with reduction time in different bed volumes

Table 3 Maximum production efficiency of different bed volumes

体积	还原时间/h	还原率/%		最大生产效率
体积	还原时间/h	还原率/%		kg·m^-3·h^-1
V10⁺	2	73.53	5.42
V9⁺	2.69	71.88	16.47
V8⁺	2.94	66.29	23.72
V7⁺	3.32	65.23	28.39
V6⁺	3.74	65.00	31.91
V5⁺	4.09	64.74	34.23
V4⁺	4.36	64.61	35.73
V3⁺	4.55	64.59	36.51
V2⁺	4.68	64.45	37.15
V1⁺	4.72	64.45	37.14

Fig.11 Relationship between Mg productivity and reduction ratio in different bed volumes

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