CFD-DEM simulation of the force acting on immersed baffles during the start-up stage of a gas-solid fluidized bed

doi:10.11949/0438-1157.20211701

Abstract

Abstract:

In the start-up stage of a fluidized bed, the internal components will be impacted by a large destructive load. In order to ensure the long-term reliability of the internal components of the fluidized bed, it is necessary to master the force characteristics of the internal components in the fluidized bed at this stage. To this end, a method for statistically calculating the stress exerted on the internals from CFD-DEM simulation was proposed, and the simulation results were validated. It was found that the experimentally measured dynamic load impact can be reproduced semi-quantitatively, the effects of superficial gas velocity and particle properties on the load impact can also be predicted. Present study proved not only the correctness of the proposed statistical method, but also the feasibility of extracting the stress exerted on the internals using CFD-DEM method.

Key words: baffle, mesoscale structure, fluidized bed, CFD-DEM method, multiphase flow, numerical simulation

摘要：

流化床启动阶段内构件会受到较大的破坏性载荷冲击，为了保障流化床内构件的长周期可靠性，需要掌握这个阶段内构件在流化床内的受力特性。首先提出了一种统计内构件表面受力的方法，将微观颗粒-挡板作用信息转换为宏观挡板受力载荷信息。在此基础上采用CFD-DEM方法，统计分析了流化床启动阶段床层中水平挡板内构件的受力载荷特性。研究结果表明：CFD-DEM方法可半定量复现实验中启动阶段内构件表面受到的动态载荷信号，并复现了表观气速和颗粒粒径对挡板峰值载荷强度的影响规律。本研究证明了内构件表面受力载荷强度统计方法的正确性和CFD-DEM统计分析受力载荷的可行性。

关键词: 内构件, 介尺度结构, 流化床, CFD-DEM方法, 多相流, 数值模拟

CLC Number:

TQ 021.1

Tienan LI, Bidan ZHAO, Peng ZHAO, Yongmin ZHANG, Junwu WANG. CFD-DEM simulation of the force acting on immersed baffles during the start-up stage of a gas-solid fluidized bed[J]. CIESC Journal, 2022, 73(6): 2649-2661.

李铁男, 赵碧丹, 赵鹏, 张永民, 王军武. 气固流化床启动阶段挡板内构件受力特性的CFD-DEM模拟[J]. 化工学报, 2022, 73(6): 2649-2661.

Figures/Tables 11

Fig.1 Schematic diagram of contact between the baffle and particles in dense bed(a) and contact between an imaginary plane and particles in a dense bed(b)

Fig.2 Schematic diagram of the cold three-dimensional fluidized bed with a square cross-section[11]

Fig.3 The geometry of fluidized bed for simulation

Table 1 Simulation parameters for the baffled and free fluidized bed

Parameter		Value
bed size	L_x ×L_y ×L_z /mm	300×300×2200
baffle size	l_x ×l_y ×l_z /mm	60×300×10
particle	mean Sauter particle diameter/μm	595
	density/(kg/m³)	2906
	voidage at the minimum fluidization condition	0.47
	minimum fluidization velocity/(m/s)	0.33
	sphericity	0.86
	coarse-graining ratio	5
	coarse-grained particle number	3459863
	restitution coefficient	0.90
	friction coefficient	0.30
	rolling friction coefficient	0.01
	characteristic velocity/(m/s)	0.5
	Young’s modulus/Pa	1×10⁸
	Poisson’s ratio	0.3
	time step/s	1×10^-5
gas	density/(kg/m³)	1.2
	viscosity/(Pa·s)	1.8×10^-5
	superficial gas velocity/(m/s)	0.4, 0.6, 0.9
	operating pressure/Pa	101325
	gas grid size/mm	10
	time step/s	1×10^-4

Fig.4 Comparison of the experimental and simulation results of the stress exerted on the baffle during start-up of the fluidized bed

Table 2 Simulation parameters for the baffled fluidized bed

Parameter	Value
Young’s modulus/Pa	1×10⁸	5×10⁸	1×10⁹	2×10⁹	3×10⁹	5×10⁹	1×10¹⁰
DEM-time step/s	1×10^-5	1×10^-5	1×10^-6	1×10^-6	1×10^-6	1×10^-6	1×10^-6
CFD-time step/s	1×10^-4	1×10^-4	1×10^-5	1×10^-5	1×10^-5	1×10^-5	1×10^-5

Fig.5 Effect of particle Young's modulus on the stress exerted on the baffle immersed in the fluidized bed

Fig.6 Variation of the ratio of the maximum particle-particle overlap to particle size with time under different Young's modulus

Fig.7 Effect of particle restitution coefficient (a), particle sliding friction coefficient (b), and particle rolling friction coefficient (c) on the stress exerted on the baffle immersed in the fluidized bed

Fig.8 Effect of superficial gas velocity on the stress exerted on the baffle immersed in the fluidized bed

Fig.9 The variation of stress on the baffle immersed in the fluidized bed with time using different particle sizes

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