Solid flow rate prediction in hoppers with complicated flow channels

doi:10.11949/0438-1157.20190867

Abstract

Abstract:

By means of perspex hopper platform built in the laboratory, the flow behaviors of powders were investigated under the action of various flow channel structures in hoppers without insert (No-In), with confined insert (Con-In) and with unconfined insert (Ucon-In). Discharge experiments of free-flowing glass beads and adhesive pulverized coal and polyvinyl chloride were carried out and a model was established to predict the solid flow rate. The effects of inserts contributing to increasing the flow rate were analyzed quantitatively and the flow characteristics of glass beads, pulverized coal and polyvinyl chloride were compared considering distinct flow channel structures. The research shows that the introduction of the modified fluid is beneficial to increase the flow rate of the silo. Con-In promotes the most obvious flow effect. For the weak coal powder, the flow rate of the lower flow rate reaches the maximum of 58%. Based on the evolution of shear flow zone, a correction factorF was proposed to modify the minimum energy theory equation, and the model for ideal hoppers was extended to take effect under actual situations. Furthermore, regarding Con-In, according to the structural characteristics of the flow channels and the force analysis on powders, the term relating to conical angle in the model was modified. In terms of Ucon-In, based on the competition mechanism, a specific flow sequence during discharge was proposed and the relationship between flow rate of inner layer and that of interlayer was obtained. Finally, a model to predict the solid flow rate in hopper with complicated flow channel structures was established. The model took into account the effects of powder properties, flow patterns and structural parameters, which can effectively predict the discharge rate of free-flowing and adhesive powders flowing through traditional hoppers (No-In) and hoppers with insert (including Con-In and Ucon-In) with the deviation less than 10%.

Key words: powders, hoppers, discharge rate, flow channel structure, inserts

摘要：

在实验室搭建的有机玻璃料仓下料平台上，分别以自由流动粉体玻璃微珠和黏附性粉体煤粉和聚氯乙烯为实验介质，针对无改流体(No-In)、封闭改流体(Con-In)和开放改流体(Ucon-In)三种情况所形成的不同流道结构，开展了粉体料仓下料及其流率建模研究，定量分析了改流体对粉体下料流率的促进作用，对比给出了玻璃微珠、煤粉和聚氯乙烯在不同流道结构料仓内的下料特性。研究表明，改流体的引入有利于提高料仓下料流率，Con-In促进流动效果最明显，对于流动性弱的煤粉，下料流率提升幅度达到最大的58%。基于剪切摩擦区的概念，提出流率校正因子F对最小能量理论方程进行了修正，将理想的料仓下料模型拓展至实际下料过程。进一步，对于Con-In，根据流道结构特征结合对粉体的受力分析，修正了模型中的锥角项；对于Ucon-In，基于粉体下料流动竞争机制，提出分阶段下料模式并关联了内层和夹层的下料流率，最终建立了复杂流道结构料仓的下料流率预测模型。该模型综合考虑了粉体物性、下料流型和流道结构的影响，可有效预测自由流动粉体和黏附性粉体流经传统料仓(No-In)和改流体料仓(包括Con-In和Ucon-In)的粉体下料流率，且预测偏差<10%。

关键词: 粉体, 料仓, 下料流率, 流道结构, 改流体

CLC Number:

TQ 536

Dong SUN, Haifeng LU, Jiakun CAO, Yuting WU, Xiaolei GUO, Xin GONG. Solid flow rate prediction in hoppers with complicated flow channels[J]. CIESC Journal, 2020, 71(3): 974-982.

孙栋, 陆海峰, 曹嘉琨, 吴雨婷, 郭晓镭, 龚欣. 复杂流道结构料仓的下料流率预测[J]. 化工学报, 2020, 71(3): 974-982.

Figures/Tables 19

Fig.1 Accumulative particle size distribution

Table 1 Physical properties of experimental materials

Material	d₃₂/μm	d₄₃/μm	Span	ρ_b/(kg·m^-3)	AOR/(°)	AIF/(°)
glass bead-a	47.22	49.43	0.56	1410	28.8	19.8
glass bead-b	62.76	65.13	0.51	1404	28.3	21.2
glass bead-c	75.84	120.14	0.90	1353	34.6	32.7
lignite	115.63	134.12	0.88	621	36.7	28.7
pvc	116.36	128.61	0.73	567	34.0	26.5

Fig.2 Diagram of discharge device

Fig.3 Device parameters

Fig.4 Discharge operation modes (hatched domain is not available for flow)

Fig.5 Diagram of sequential flow order during discharge

Table 2 Experimental value of discharge rate

Material	No-In /(g·s^-1)	Con-In/ (g·s^-1)	Ucon-In /(g·s^-1)
glass bead-a	45.0	53.2	52.1
glass bead-b	46.7	54.2	48.4
glass bead-c	38.8	48.7	43.0
lignite	13.8	21.7	18.1
pvc	13.7	16.7	15.1

Fig.6 Relationship between increase of discharge rate and flow channel structure

Fig.7 Schematic diagram of coordinate system

Table 3 Deviation between experimental value and theoretical value under No-In mode

Material	Experiments/(g·s^-1)	Eq. (1)/(g·s^-1)	Eq. (3)/(g·s^-1)	\|RE\| of Eq. (1)/%	\|RE\| of Eq. (3)/%
glass bead-a	45.0	52.9	45.3	14.9	0.7
glass bead-b	46.7	52.6	44.3	11.2	5.4
glass bead-c	38.8	49.7	34.7	21.9	11.7
lignite	13.8	22.9	17.3	39.7	20.6
pvc	13.7	20.9	16.4	34.4	16.5

Fig.8 Free surface during powder discharge process[6]

Fig.9 Diagram of discharge of glass bead

Fig.10 Comparison of experiment and model values of discharge rate

Fig.11 Schematic diagram of flow zones transition

Fig.12 Schematic diagram of force analysis of powders under Con-In

Table 4 Deviation between experimental value and theoretical value under Con-In mode

Material	Experiments/(g·s^-1)	Eq. (10)/(g·s^-1)	\|RE\| of Eq. (10)
glass bead-a	53.2	61	12.80%
glass bead-b	54.2	59.6	9.10%
glass bead-c	48.7	46.7	4.20%
lignite	21.7	23.3	6.80%
pvc	16.7	22	24.10%

Fig.13 Diagram of variation of sample instantaneous discharge rate with time in silo with unconfined insert

Fig.14 Relationship of discharge rate between two stages

Fig.15 Comparison of experiment and model values of discharge rate

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