Simulation study on influence of supplementary gas on dense-phase pneumatic conveying in horizontal pipe under high pressure

doi:10.11949/0438-1157.20191275

Abstract

Abstract:

In view of the defects and deficiencies of the existing mathematical model, a new three-dimensional (3D) unsteady mathematical model for dense-phase pneumatic conveying in horizontal pipe under high pressure was established based on the Euler-Euler model. This mathematical model introduced the modified kinetic theory of granular flows by Savage’s radial distribution function, the frictional stress model established on Berzi’s frictional pressure stress and the modified three-zone drag model to expound the conveying characteristics of all of three flow regimes: dilute regime, intermediate regime and dense regime. Meanwhile, this mathematical model was applied to explore the effects of supplementary gas on dense-phase pneumatic conveying in horizontal pipe under high pressure. The simulation results show that the pressure drop of horizontal pipe and its variation with the supplementary gas flow rates are predicted accurately, and the predicted solids volume fraction distribution at the cross section of horizontal pipe also basically agrees with the electrical capacitance tomography (ECT) diagram, which confirm the reliability and applicability of this mathematical model. The simulation results show that as the supplementary wind increases, the gas-solid two-phase velocity and turbulent kinetic energy and particle pseudo-temperature increase, and the solid phase volume concentration decreases.

Key words: pneumatic conveying, two-phase flow, dense-phase, mesoscale, supplementary gas, numerical simulation

摘要：

针对水平管高压密相气力输送数理模型的缺陷与不足，引入Savage径向分布函数修正的颗粒动理学理论、基于Berzi摩擦压应力模型构建的摩擦应力模型以及修正的三段式曳力模型，在欧拉-欧拉方法的基础上建立了一个能同时兼顾水平管高压密相气力输送中稀相流、过渡流以及密相流输送特性的三维非稳态数理模型。并采用该数理模型考察了补充风对水平管高压密相气力输送的影响，模拟结果精准地预测了水平管压降及其随补充风的变化规律，而且其预测的水平管固相体积浓度分布与ECT图也是相吻合的，从而验证了数理模型的可靠性。模拟结果表明：随着补充风的增加，气固两相速度和湍动能以及颗粒拟温度增大，固相体积浓度减小。

关键词: 气力输送, 两相流, 密相, 介尺度, 补充风, 数值模拟

CLC Number:

TQ 022

Haijun ZHOU, Yuanquan XIONG. Simulation study on influence of supplementary gas on dense-phase pneumatic conveying in horizontal pipe under high pressure[J]. CIESC Journal, 2020, 71(2): 602-613.

周海军, 熊源泉. 补充风对水平管高压密相气力输送影响的模拟研究[J]. 化工学报, 2020, 71(2): 602-613.

Figures/Tables 17

Fig.1 Experimental facility schematic diagram of dense-phase pneumatic conveying under high pressure

Table 1 Conveying experiment parameters

No.	补充风流量，Q_s/(m³/h)	表观气速，U_g/(m/s)	固相质量流量，M_s/(kg/s)	进口固相体积浓度,α_s,in	进口固相平均速度,u_s,inlet/(m/s)	出口气相压力,P_out/MPa
1	0.40	4.71	0.213	0.318	4.43	2.91
2	0.60	5.62	0.206	0.286	5.30	2.91
3	0.80	6.43	0.194	0.245	6.09	2.92
4	1.00	7.24	0.181	0.199	6.79	2.93
5	1.20	8.10	0.168	0.184	7.72	2.93

Table 2 Main physical properties of pulverized lignite

自然堆积固相体积浓度，α_s,b

全水分，

M_c

Fig.2 Solids volume fraction distribution at longitudinal section of horizontal pipe

Table 3 Mathematical model parameters

α_s,max	e_ss	?_i	e_sw	?	μ_w	a
0.60	0.8	32.0°	0.5	1.0×10^-5	0.5	1.8×10^-6

Fig.3 Meshes generation of horizontal pipe

Table 4 Predicted pressure drop of horizontal pipe with different grid scale

网格划分规格	端面格数	轴向网格尺寸/mm	总网格数/万	水平管模拟压降/kPa	水平管试验压降/kPa
Mesh A	180	2	21.60	3.84	4.14
Mesh B	288	1.5	46.08	3.91
Mesh C	420	1.25	80.64	4.07
Mesh D	576	1	138.24	4.08

Fig.4 Predicted gas velocities vs dimensionless height with different grid scale

Fig.5 Comparison of predicted pressure drop of horizontal pipe with its experimental data at different supplementary gas flow rates

Fig.6 Velocities of gas and solids phase vs dimensionless height at different cross sections of horizontal pipe

Fig.7 Solids volume fraction distribution at cross section of horizontal pipe

Fig.8 Particle size distribution of pulverized lignite

Fig.9 Comparison of predicted solids volume fraction distribution with ECT image at different supplementary gas flow rates

Fig.10 Predicted conveying parameters of horizontal pipe vs dimensionless height at different supplementary gas flow rates

Fig.11 Predicted drag forces at cross section of horizontal pipe at different supplementary gas flow rates

Fig.12 Predicted solids frictional shear stress at cross section of horizontal pipe at different supplementary gas flow rates

Fig.13 Predicted frictional shear stresses between gas, solids and wall at different supplementary gas flow rates

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