基于静电信号的气固流化床中颗粒运动的表征和颗粒荷质比的测量研究

发布时间：2018-03-12 13:20

  本文选题：气固流化床　切入点：静电　出处：《浙江大学》2016年博士论文　论文类型：学位论文

【摘要】：气固流化床中颗粒的剧烈运动和循环使得气固两相得以充分混合与接触,因而流化床反应器具有良好的热质传递性能,广泛应用于煤燃烧和气化、催化裂化、造粒和干燥、烯烃聚合等工业过程中。烯烃聚合流化床中颗粒之间、颗粒与壁面之间的不断摩擦、碰撞导致静电荷的产生和累积。过量静电荷的累积可能会引起粘壁、结块等现象的发生,甚至造成反应器的紧急停车,为安全稳定生产带来隐患。无论是揭示静电的产生机理,还是对其进行调控甚至消除,准确的静电检测手段必不可少。但现有的颗粒荷质比测量方法仍然存在着诸如无法实现在线检测、侵入流场、信号解析过程复杂等缺点,建立一种结构简单、非侵入式的颗粒荷质比在线测量方法是静电检测领域亟待解决的问题。荷电颗粒流化过程产生的静电信号中蕴含着大量与颗粒运动有关的动态信息,但目前对这些动态信息的挖掘却十分有限。基于静电信号的相关速度测量技术已经在气力输送等稀相体系中有着较为广泛和成功的应用,但目前尚无该方法在气固流化床中应用的研究报道。如果通过互相关计算方法,利用流化床中的静电信号获得与颗粒运动行为有关的参数,则有望建立一种气固流化床中颗粒运动的表征手段,实现流化床中关键流动参数的在线测量,对于保障反应器的安全稳定运行、提高生产效率、实现过程的优化控制,具有十分重要的意义。本论文以烯烃聚合气固流化床反应器为研究对象,利用压力脉动、静电等测量手段,结合频谱分析、互相关计算等信号处理方法,系统对比和分析了多级法拉第筒流化床中静电流与压差信号的相似性,建立了静电流与压差信号的定量模型,并以此为基础提出了基于环形感应电极的流化床中颗粒荷质比的在线测量方法。结合弧形感应电极阵列和互相关计算方法,测量了流化床中的颗粒群相关速度及其分布,建立了基于静电信号的流化床中颗粒运动的表征方法,并基于相关速度测量方法,系统考察了静电对颗粒运动的影响,拟合得到了颗粒平均荷质比预测模型,实现了颗粒运动行为和颗粒荷电量的同步测量。研究结果可用于气固流化床中静电的检测与防控、颗粒流动参数的测量和流化质量的监测,对提升反应器的安全性和稳定性,具有重要的指导意义。论文主要开展了以下四方面的研究工作：1.在自行设计的多级法拉第筒流化床中,利用频谱分析方法系统对比了静电流与压差信号的相似性,发现静电流和压差均受到平均空隙率的影响,建立了静电流与压差信号之间的定量模型。当假设颗粒尺寸均一,荷电量均匀且稳定时,静电流与压差信号对时间的一阶导数成正比,比例系数与颗粒荷质比和流化床尺寸有关。2.以上述定量模型为基础,提出了一种基于环形感应电极的颗粒荷质比在线测量方法。该方法的颗粒平均荷质比测量结果随表观气速的增加而增大,随液体抗静电剂(LAA)含量的增加而减小,与法拉第筒取样法测量结果的变化趋势一致。环形电极宽度为20 mm时,颗粒平均荷质比测量结果的相对误差小于23%。3.建立了基于静电信号的流化床中颗粒群相关速度的测量方法。通过在有机玻璃流化床外壁面设置弧形感应电极阵列,结合互相关计算方法,测量并对比了Geldart B类和D类颗粒流化床中的颗粒群相关速度平均值及其概率密度分布。在流化床密相区内,颗粒群平均相关速度随表观气速和轴向高度的变化趋势与气泡群上升速度理论值一致；在相同过量气速下,D类颗粒平均相关速度小于B类颗粒；提出了一种基于感应电极阵列和颗粒群相关速度分布的流化床动态料位的检测方法,平均料位高度测量结果的相对误差小于10%。4.建立了一种基于感应电极阵列的同步实现颗粒运动行为表征和颗粒荷质比在线测量的方法。通过向流化床中注入微量LAA实现了对颗粒整体荷电水平的调控,系统考察了静电对颗粒群相关速度平均值及其分布的影响,发现随着静电水平的降低,颗粒运动剧烈程度增强。当过量气速为0.35 m/s时,与不带电的情况相比,D类和B类颗粒饱和荷电后的颗粒群平均相关速度分别降低了约26%和50%。基于不同静电水平下的感应静电压、颗粒群平均相关速度和颗粒平均荷质比数据,拟合得到了颗粒平均荷质比预测模型,不同表观气速下,模型预测结果与法拉第筒取样法测量结果变化趋势一致,相对误差低于40%。
[Abstract]:Strenuous exercise and circulation of particles in gas solid fluidized bed makes the gas-solid contact and can be fully mixed, and fluidized bed reactor with good heat transfer performance, widely used in coal combustion and gasification, catalytic cracking, granulation and drying, olefin polymerization in the industrial process. Olefin polymerization of particles in fluidized bed, constant friction between particle wall collision, resulting in the accumulation and accumulation of electrostatic charge. May be excessive static charge will cause wall adhesion, agglomeration phenomenon, and even cause the reactor shutdown, brings the hidden danger for the safe and stable production. It is produced to reveal the mechanism of static electricity, or the control or even eliminate the essential. Electrostatic detection means accurately. But the existing particle charge mass ratio measurement method still exists such as cannot realize online detection, non-invasive, signal analysis process of complex defects, The establishment of a simple structure, non intrusive particle charge mass ratio measurement method is an urgent problem. The electrostatic field of electrostatic detection signal of charged particle fluidization process produced contains a large number of dynamic information related to the motion of the particles, but the mining of these dynamic information is very limited. The speed of electrostatic signal the measurement technology has been in Dilute Pneumatic Conveying has been used widely and successfully in the heterogeneous system based on, but there is no reports on this method in gas solid fluidized bed application. If by calculating the cross-correlation method, obtain the parameters associated with the behavior of particles by electrostatic signals in a fluidized bed, is expected to set up by means of a movement of particles in the gas-solid fluidized bed, measurement of flow parameters in the fluidized bed of the key, to guarantee the safe and stable operation of the reactor, improve production efficiency , to realize process control optimization, it has very important significance. This paper takes olefine polymerization reactor of gas solid fluidized bed as the research object, the use of pressure pulsation, electrostatic measurements, combined with spectral analysis, cross correlation signal processing method, system comparison and analysis of the similarity of static current and differential pressure signals of multistage Faraday tube in a fluidized bed, a static pressure difference and the quantitative model of current signal, and proposes the measurement method of particle fluidized bed induction electrode in charge mass ratio based on inductive electrode array. The combination of arc and cross-correlation calculation method in a fluidized bed of particles relative velocity and its distribution measurement, set up characterization method of moving particle fluidized bed based on the electrostatic signal, and based on the cross-correlation velocity measurement method, investigated the effects of electrostatic on particle motion, fitting to flat particles Both charge mass ratio prediction model, realizes the synchronous measurement of particle movement and particle charge. The results can be used for detection and prevention of electrostatic in gas solid fluidized bed, flow parameters measurement and monitoring of particulate fluidization quality, to enhance the safety and stability of the reactor, which has important guiding significance. This paper the research work has been carried out in the following four aspects: 1. in the multi-stage Faraday cylinder self-designed fluidized bed, system analysis method compares the similarity of static current and differential pressure signal spectrum, found that the static current and differential pressure are affected by the average air gap ratio, established the static current and differential pressure signal between the quantitative model when the assumption of the homogeneous particle size, charge uniform and stable, the electrostatic current is proportional to the pressure difference signal is a derivative of time, ratio and particle charge mass ratio and the size of the.2. in the fluidized bed The quantitative model, proposed a particle charge induction electrode based on on-line measurement method. The method of average particle charge mass ratio measurement results with the increase of apparent gas velocity increases with the liquid antistatic agent (LAA) content decreases with the increase of the trend and the Faraday tube sampling method the measurement result. The ring electrode width is 20 mm, the relative error of the average particle charge mass ratio measurement results is less than 23%.3. to establish the measurement method of electrostatic signal in particle fluidized bed. By setting the related speed based on arc induction electrode array in organic glass wall with cross-correlation fluidized bed, calculation method, the average measurement and comparison the Geldart B class and D class of particles in fluidized bed of particle velocity and its associated probability density distribution in circulating fluidized bed, particle average velocity associated with the superficial gas velocity and axial height The changing trend of the bubbles rising speed of the theoretical value; at the same excess air velocity, the average velocity is less than D particles related to B particles; a sensing electrode array and particle velocity distribution in fluidized bed dynamic related material level detection method based on the material level, the average relative error of the measuring result is less than 10%.4. a sensing electrode array to realize the synchronization of particle movement behavior and characterization of particle charge mass ratio method of on-line measurement. Based on the injection of LAA to realize the control of particles in the fluidized bed overall charge level, investigated the electrostatic effect on the average value and distribution of particles was found to decrease with increasing speed, static level the particle motion intensity is enhanced. When the excess gas velocity is 0.35 m/s, compared with uncharged, D and B particles of charged particles saturated average phase Clearance rates were reduced by about 26% and 50%. levels under different electrostatic induction based on static voltage, particle velocity and particle average average relative charge mass ratio data obtained by fitting average particle charge mass ratio prediction model, different superficial gas velocities, the model prediction results measured with Faraday tube sampling method the results are consistent. The relative error is less than 40%.

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ051.13
，

本文编号：1601731