Nozzle structure improvement and study of particles agglomeration during liquid injection

doi:10.11949/0438-1157.20190138

Abstract

Abstract:

Reducing the reaction temperature during the raw liquid injection stage will lead to different viscosities of liquid, and result in particles adhesion forming agglomeration in different sizes, this hinders heat transfer to reacting liquid and slows the cracking reactions. Therefore, particles agglomeration is an important and challenging problem for thermal cracking in fluid cokers. In the present study, the gas shroud attachment was used to improve nozzle structure, and the particles agglomeration process during nozzle injection of multi-viscosity liquid was investigated in a fluidized bed operated at different conditions based on a conductance method using a water-sand system to simulate the hot bitumen-coke system at room temperature. The results show that the porous gas shroud attachment can create an ideal dilute phase environment for liquid injection and avoid the droplets accumulation in the injection cavity and particles exchange area. Different stages can be observed during the liquid injection dispersion throughout the bed, i.e., the wetting stage, the agglomerate formation stage, and the agglomerate segregation stage. A higher gas-liquid ratio (GLR) of the nozzle provides a method to prevent particles agglomeration, and the conditions at a high gas velocity allow a higher concentration of sucrose in the liquid injection compared with that at a low fluidizing gas velocity. This study provides a theoretical basis for on-line monitoring of particles agglomeration during liquid injection to guarantee perfect contact between the atomized droplets and the bed particles.

Key words: nozzle structure, viscosity, fluidized bed, liquid injection, particles flow

摘要：

在重质原料液的射流阶段降低反应温度会导致液体呈现不同的黏度，促使颗粒聚集形成不同尺寸的团聚结构，阻碍了原料液的热量传递，减缓了裂化反应的速率，颗粒团聚是流体焦化反应工艺面临的一个重要而又具有挑战性的问题。选用水-沙系统模拟热态沥青-焦炭系统，利用气罩装置改进喷嘴结构，基于电导信号法测量多黏度液体射流过程的电导信号随时间的变化规律，研究不同条件下流化床内颗粒团聚过程。研究结果表明：多孔气罩装置可以为喷嘴射流创造理想的稀相环境，避免了液滴在射流空腔以及交换区域的聚集和压缩；液体射流在床层扩散过程中可以观察到不同的流化阶段，即颗粒润湿阶段、团聚形成阶段、团聚隔离阶段；较高的气液比可以有效地阻止颗粒团聚，相比于较低的流化气速，较高的气速条件允许高黏度糖水溶液参与液体射流。本研究为多黏度液体射流过程颗粒团聚现象的在线监测提供了理论研究基础，确保了流化床内射流液滴与颗粒表面的良好接触。

关键词: 喷嘴结构, 黏度, 流化床, 液体射流, 颗粒流

CLC Number:

TK 121

Ning YANG, Yunlong ZHOU, Shusheng MA. Nozzle structure improvement and study of particles agglomeration during liquid injection[J]. CIESC Journal, 2019, 70(S2): 169-180.

杨宁, 周云龙, 马书生. 喷嘴结构改进及其液体射流过程颗粒团聚研究[J]. 化工学报, 2019, 70(S2): 169-180.

Figures/Tables 14

Fig.1 Experimental device for rectangular fluidized bed

Table 1 Physical properties of experimental particles

颗粒种类	平均粒径/μm	密度/(kg/m³)	临界气速/(m/s)	Geldart颗粒类型
硅砂颗粒	140	2650	0.17	B类

Table 2 Physical properties of experimental liquids

工质种类	质量分数/%	液体黏度/(mPa·s)	表面张力/(N/m)	沸点/℃
糖水溶液	0	1.21	0.0726	101.1
	10	2	0.0758	103.3
	18	3.187	0.0840	107.2

Fig.2 Types of atomization nozzle

Fig.3 Circuit diagram of experimental device

Fig.4 Calibration curve for electrode 1

Table 3 Comparison between solid moistures of samples by Karl Fischer titration and real bed solid moisture contents

采样位置

局部自由水分

(Karl Fischer)

Fig.5 Nozzle gas shroud attachment

Table 4 Effect of nozzle gas shroud attachment on Sauter mean diameter (SMD) of atomized droplets at different liquid concentrations 平均直径的影响

喷嘴形式	液滴Sauter平均直径/μm
喷嘴形式	GLR=1%	GLR=1.5%	GLR=2%	GLR=2.5%	GLR=3%	GLR=3.5%
原始喷嘴	104	87	71	63	52	49
原始喷嘴+SS	69	55	50	47	42	37
原始喷嘴+AS	85	77	60	52	45	40

Fig.6 Variation of bed conductance with time during liquid injection(water)

Fig.7 Sample parameters at GLR = 1% during liquid injection

Fig.8 Variations of values of standard deviation of pressure signals with injection time(water)

Fig.9 Variation of bed conductance with time during liquid injection(sucrose 10%)

Fig.10 Variation of bed conductance with time during liquid injection(sucrose 18%)

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