摘要
喷动床技术作为20世纪50年代中期发展起来的一种处理粗颗粒的流态化技术,已经从最初的用于颗粒的干燥过程,逐渐扩展到用于粘性强或粗块状颗粒的表面涂层、涂料、悬浮液以及干燥、粉碎、造粒、煤燃烧和气化、铁矿石还原、焦炭活化、石油热裂化等工艺。喷动床的流动机制与流化床有很大区别。其颗粒的搅动由稳定的轴向射流所致,与流化床中随即复杂的颗粒流动相比,更有规则。
随着该技术的不断推广和研究的深入,又出现了各种各样的改进型喷动床,以适应各种工业应用的需要。本文通过对喷动床机理的深入研究,在前人研究的基础上,以将喷动床技术与煤气化工艺相结合为目的,设计建造了一种新型的喷动床多喷口环形喷动床。采用了统计学分析和频谱分析相结合的手段,系统的研究了该新型喷动床体内的最小喷动速度和压力波动特性。
本课题研究内容主要包括:以采用细颗粒的斜口和直口喷动床型为实验基础,对喷动床主要流体动力学参数:最小喷动速度和最大床层压降进行研究。通过改变颗粒粒径、密度、喷口尺寸、床体直径、静床高等参数所测得的实验数据,对其进行了非线性拟合,拟合结果与实验结果误差在7%以内。还对喷动床内压力波动的生成源进行研究。通过统计与频谱分析,发现了喷动床体内的压力扰动主要来源有三个,分别是气流从压力室进入喷口时产生的脉动、气流在床内轴向输送的间歇性运动、以及多喷口射流之间周向的相互扰动。并对其各自的特性进行了深入的研究。此外,还对斜口喷动床的喷动特性进行了实验研究,比较直向与斜向流动下的颗粒混合机理。
Since invented in 1950s for processing coarse particles, spouted bed technology has been applied initially to dryness of particles, then gradually expand to a wide field of chemical process which includes dryness, comminution, prilling, gasification, combustion, iron ore deoxidization, coke activation, petroleum thermal cracking etc. Although as a branch of fluidization technology, their flow mechanisms are quite different. The particles mixing in spouted bed is induced by a steady axial jet, which is more regular than complicated particles flow in fluidized bed.
With the extension of spouted bed technology, many modified spouted beds have been designed by researchers. These modified spouted beds have been applied to various industrial institutions. Base on the deep research on spouted bed mechanism, a novel annular spouted bed with multi-nozzle has been proposed in this thesis, for combination of spouting and coal gasification. The statistic and power spectrum analysis methods are adopted to research the fluid dynamics and pressure fluctuation characters in that novel spouted bed. The study is expected to provide correct evidence for industrial application.
Based on the angled and vertical nozzles spouted bed using fine particles, present research mainly consists of following sections: (ⅰ) research on the primary fluid dynamic parameters of spouted bed which include the minimum spouting velocity and the maximum pressure drop of bed layer. Through changing the operation parameters, including particles diameter, particles density, nozzles dimension, spouted bed diameter, static bed height, etc, got the experimental dates and calculated the nonlinear recursion. The error between experimental results and calculation results is less than 7%. (ⅱ) research on the origin of pressure fluctuation in spouted bed. By the method of statistics and power spectrum analysis, we considered there are three main sources for the pressure fluctuation in spouted bed, which consist of the impulse from air flow when it entering nozzles, the intermittent movement of air flow’s vertical transmission, the annular interaction between jets from multiple nozzles. (ⅲ) research on the spouting characters of spouted bed with angled nozzles, contrast the particles mixing mechanism in vertical and angled flow.
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