Effect of drum rotational speed on flow field characteristics of decanter centrifuge for solid-liquid separation of salt sludge

doi:10.16085/j.issn.1000-6613.2018-1793

Abstract

Abstract:

The salt sludge produced by the mine brine production process uses a decanter centrifuge for solid-liquid separation. Based on the Eulerian multiphase flow model and RNG k-ε turbulence model in a multiple coordinate reference system, the three-dimensional fluid domain of decanter centrifuge was numerically simulated with a computational fluid dynamics software Fluent. The relationship between the rotating speed of the drum and the separation characteristics was studied by the combination of simulation and experiments. The results showed that the tangential speed hysteresis coefficient of the decanter centrifuge is obviously improved when considering the spiral blade than when neglecting the spiral blade. The concept of correcting centrifugal hydraulic pressure was proposed. It was numerically proved that the error between the static pressure value and the theoretical value of the separation liquid was due to the lag of the tangential speed. When the drum rotation speed reaches 3000r/min or more and continues to increase, the sediment solid phase mass fraction will not continue to increase. The sedimentation velocity of the solid phase particles in the separation liquid increases slightly with the increase of the rotational speed. Experiments showed that the decanter centrifuge will produce a certain degree of NaCl concentration gradient in the radial direction when the high concentration brine is centrifuged at high speed. The solute concentration is higher in the outer layer of the separation liquid and lower in the inner layer.

Key words: decanter centrifuge, salt sludge, drum rotational speed, flow field simulation, centrifugation

摘要：

对矿井采卤制盐工艺产生的盐泥使用卧螺离心机进行固液分离，应用计算流体力学软件Fluent，基于多相流Eulerian模型、RNG k-ε湍流模型及多重参考系（MRF）方法，对卧螺离心机流体域进行三维数值模拟，采用仿真与实验相结合的方式，研究了转鼓转速与分离特性的关系，结果表明：卧螺离心机在考虑螺旋叶片情况下比忽略螺旋叶片时切向速度滞后系数有明显提升；提出修正离心液压的概念，通过该理论数值证明分离液静压值与理论值的误差源于切向速度的滞后；当转鼓转速达3000r/min以上继续提高时，沉渣固相质量分数不会随之继续增大；分离液中固相微粒的沉降速度随转速增大会小幅均匀增大；实验表明卧螺离心机用于高浓度卤水高速离心时，将在径向产生一定程度的NaCl浓度梯度，溶质浓度在分离液外层较高，内层较低。

关键词: 卧螺离心机, 盐泥, 转鼓转速, 流场模拟, 离心分离

CLC Number:

TK-9

Guihua ZHU, Aolin ZHANG, Nanhui PENG, Sai BA, Weize HE, Zhikun HU. Effect of drum rotational speed on flow field characteristics of decanter centrifuge for solid-liquid separation of salt sludge[J]. Chemical Industry and Engineering Progress, 2019, 38(06): 2590-2599.

朱桂华, 张傲林, 彭南辉, 巴赛, 何伟泽, 胡志坤. 卧螺离心机用于盐泥固液分离时转鼓转速对流场特性的影响[J]. 化工进展, 2019, 38(06): 2590-2599.

Figures/Tables 22

物性参数	数值
密度ρ/kg·m^-3	1378
液相密度ρ ₁/kg·m^-3	1189
固相密度ρ _s/kg·m^-3	2238
液体黏度φ/Pa·s	0.0098
固相体积分数/%	18
液相体积分数/%	82
固相粉末粒径d/mm	0.046
pH	9.5
液相（卤水）NaCl浓度/g·L^-1	296

成分	质量分数/％
CaCO₃	37.40
Mg(OH)₂	25.43
NaCl	20.70
其他微量元素	16.47

名称	数值
转鼓直径 D/mm	520
螺旋内筒直径 d/mm	340
转鼓柱段长度 L ₁/mm	870
转鼓锥段长度 L ₂/mm	690
全长 L/mm	1560
液池深度 ΔH/mm	90
转鼓锥角 α/(°)	9.0
螺旋导程 S/mm	130
长径比 L/D	3.0
进料口直径 a/mm	50

实验编号	流量/L·s^-1	理论速度 /rad·s^-1	ΔH/mm	实验速度 /rad·s^-1	实验滞后系数	模拟速度 /rad·s^-1	模拟滞后系数	误差/%
1	0.125	36.65	40	23.09	0.63	22.1835	0.6053	3.93
2	0.125	42.95	40	22.34	0.52	21.3679	0.4975	4.35
3	0.125	47.12	40	32.04	0.68	30.1337	0.6395	5.95
4	0.125	52.36	40	36.65	0.70	34.1384	0.6520	6.85
5	0.198	41.89	34	22.20	0.53	20.9573	0.5003	5.60

转速/r·min^-1 $μ α ˉ$		转速/r·min^-1 $μ α ˉ$
500	0.9364	3000	0.9247
1000	0.9306	3500	0.9252
1500	0.9245	4000	0.9223
2000	0.9288	4500	0.9201
2500	0.9306	5000	0.9231

转速/r·min^-1 $μ α ˉ$		转速/r·min^-1 $μ α ˉ$
500	0.9364	3000	0.9247
1000	0.9306	3500	0.9252
1500	0.9245	4000	0.9223
2000	0.9288	4500	0.9201
2500	0.9306	5000	0.9231

实验编号	转鼓转速 /r·min^-1	差速/r·min^-1	固相质量分数/%
1	520.0	9.0	46.00
2	1007.0	13.0	57.27
3	1495.0	12.0	60.71
4	2015.0	12.0	61.40
5	2502.0	14.5	66.80
6	2990.0	13.0	69.53
7	3217.5	13.0	69.60

实验编号	转鼓转速 /r·min^-1	差速 /r·min^-1	样品A NaCl浓度 /g·L^-1	样品B滤液NaCl浓度 /g·L^-1	样品C NaCl浓度 /g·L^-1
1	1007.0	13.0	230.0	310.0	—
2	1495.0	12.0	191.0	311.0	—
3	2015.0	12.0	185.0	310.7	—
4	2502.0	14.5	166.5	313.5	—
5	2990.0	13.0	158.0	313.0	—
6	3217.5	13.0	157.0	312.6	—
7	原盐泥清液1	—	—	—	298
8	原盐泥清液2	—	—	—	284
9	原盐泥清液2	—	—	—	306

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