流化床反应器颗粒结块原因与对策分析

流化床反应器在现代工业中的早期应用于粉煤气化的温克勒炉,随着现代流化反应技术的开拓,流化床反应器已在化工、石油、冶金、核工业等部门得到广泛应用。但是流化床反应器的物料结块故障不仅影响产品质量,严重的还会影响生产。本文针对全密度聚乙烯低压气相法流化床层结块的现象,分析了结块的原因,并提出了生产中防止和减少聚乙烯流化床结块的措施。     

基于电-声检测法的整流变压器局部放电故障监测

针对整流变压器局部放电处理不及时会造成变压器击穿、使用寿命缩短的问题，提出了一种基于电-声检测法的整流变压器局部放电故障监测方法。通过加速度传感器和电容传声器分别采集整流变压器振动信号和声纹信号，采用集合经验模态分解（EEMD）和盲源分离相结合的方法提取振动信号和声纹信号特征，包括时域、频域和Mel频谱倒谱系数，以提取的特征作为输入，通过隐马尔科夫模型实现整流变压器局部放电故障识别。以故障类型为绝缘材料内部放电的整流变压器为测试对象进行算例分析，结果表明：绝缘材料内部放电故障类型的观测样本概率最大，说明整流变压器存在局部放电故障，且故障类型为绝缘材料内部放电，与实际情况一致，证明了所研究监测方法的有效性。     

阀门内漏单声波传感器监测方法研究

针对阀门内漏模拟和阀门内漏监测问题,提出了阀门内漏模拟和阀门内漏非介入式单声波传感器监测方法。设计了由法兰、薄纸片和带孔铝片组成的虚拟阀门,可真实地模拟阀门内漏瞬态过程,克服了传统阀门内漏模拟方法中存在的各种缺点。分析、比较了不同条件下阀门上下游声波传感器输出信号的频域特征,验证了阀门上游声波传感器设置的冗余性和基于单声波传感器实现阀门内漏监测的可行性。分析、比较了不同条件下单声波传感器输出信号的时频域特征,提出了基于峰值系数和小波包能量分率的阀门内漏时频域特征提取方法,并以阀门密封良好状态下的声波信号为样本,建立了基于SVDD的阀门内漏诊断模型。测试结果表明:本文提出的单声波传感器阀门内漏监测方法可行、模型诊断准确,且具有较强的抗干扰能力和较高的阀门内漏检测灵敏度。     

阀门内漏单声波传感器监测方法研究

针对阀门内漏模拟和阀门内漏监测问题，提出了阀门内漏模拟和阀门内漏非介入式单声波传感器监测方法。设计了由法兰、薄纸片和带孔铝片组成的虚拟阀门，可真实地模拟阀门内漏瞬态过程，克服了传统阀门内漏模拟方法中存在的各种缺点。分析、比较了不同条件下阀门上下游声波传感器输出信号的频域特征，验证了阀门上游声波传感器设置的冗余性和基于单声波传感器实现阀门内漏监测的可行性。分析、比较了不同条件下单声波传感器输出信号的时频域特征，提出了基于峰值系数和小波包能量分率的阀门内漏时频域特征提取方法，并以阀门密封良好状态下的声波信号为样本，建立了基于SVDD的阀门内漏诊断模型。测试结果表明：本文提出的单声波传感器阀门内漏监测方法可行、模型诊断准确，且具有较强的抗干扰能力和较高的阀门内漏检测灵敏度。     

基于多尺度特征能量-核极限学习机的双循环流化床气流堵塞故障智能诊断

为减轻双循环流化床结块与堵塞故障对生物质气化反应的负面影响,提出基于多尺度特征能量-核极限学习机(kernel extreme learning machine, KELM)的故障诊断模型。首先对故障状态下压力信号采用小波分解获得多尺度信号,然后提取各尺度特征能量作为特征向量,最后将其输入经遗传算法优化的核极限学习智能诊断模型,实现双循环流化床气流堵塞故障的智能诊断。通过对公开的轴承故障数据集和双循环流化床冷态实验系统数据的分类识别分析,并与基于变分模态分解和样本熵特征提取的KELM诊断模型进行比较,结果表明：本模型具有较高的故障诊断精度(82.5%),能够有效提取故障特征,用于双循环流化床气流堵塞的高效分类识别。     

基于多尺度特征能量-核极限学习机的双循环流化床气流堵塞故障智能诊断

为减轻双循环流化床结块与堵塞故障对生物质气化反应的负面影响,提出基于多尺度特征能量-核极限学习机(kernel extreme learning machine, KELM)的故障诊断模型。首先对故障状态下压力信号采用小波分解获得多尺度信号,然后提取各尺度特征能量作为特征向量,最后将其输入经遗传算法优化的核极限学习智能诊断模型,实现双循环流化床气流堵塞故障的智能诊断。通过对公开的轴承故障数据集和双循环流化床冷态实验系统数据的分类识别分析,并与基于变分模态分解和样本熵特征提取的KELM诊断模型进行比较,结果表明:本模型具有较高的故障诊断精度(82.5%),能够有效提取故障特征,用于双循环流化床气流堵塞的高效分类识别。     

烯烃聚合流化床反应器内动结块的声发射检测

烯烃聚合流化床反应器近分布板区域的动结块是分布板堵塞的诱因,严重影响流化床的正常操作,甚至引发事故。本文在冷模实验装置中,使用声发射技术对近分布板区域的动结块进行检测,分别对比了正常流化、加入丝状结块和加入块状结块时近分布板区域声信号能量和频谱的差异。实验发现,与正常流化时相比,加入结块使得声信号能量下降,且加入块状结块时声信号能量下降更为显著;加入结块后声信号频谱的低频部分（0~20 kHz）和高频部分（70~150 kHz）均出现不同程度的降低,且高频部分下降比低频部分更为显著,块状结块导致的下降比丝状结块更为显著。实验结果表明,声发射技术可以用于流化床反应器内近分布板区域动结块的检测。     

Unipol气相聚乙烯反应器结块问题研究进展

对Unipol工艺气相流化床聚乙烯反应器生产运行过程中生成的块料形态和特征进行了分类与总结;对反应器结块现象、结块原因、结块部位及防结块措施研究进展进行了归纳。结果表明：结块的原因为静电因素、反应器设计因素、工艺条件控制因素和物料性质因素。实际生产运行过程中,严格落实与各种影响因素相对应的防结块措施,能从一定程度上缓解结块现象,但不能彻底消除结块。建议从控制原料质量、优化防结块控制条件和深入研究聚合反应动力学三个方面同时着手,探究结块本质原因和开发抑制结块技术。     

三重环流生物流化床反应器的混合特性

研究了三重环流生物流化床反应器混合特性,通过循环时间与混合时间的测定来比较三重环流五单重环流反应器的混合性能,发现三重环流反应器的混合时间较短。此外,对三重环流反应顺的物料分布测试结果可知正常流态化条件下所有工况其物料分布均接近全混流模型,离散程度随操作液流量的增大而减小,亦随操作气速的增大而变小。     

基于神经网络和宏观动力学模型的流化床反应器离线故障诊断

采用人工神经网络与流化床反应器宏观动力学模型相结合的方法,对丙烯氨氧化流化床反应器的不正常操作进行了故障诊断.经过训练和可靠检验的神经网络能准确辨认故障的发生和类型,流化床反应器宏观动力学模型能根据其知识规则判断引起故障的原因,并提出相应的调节方法,直至反应器操作正常.     

Monitoring the fluidized bed reactor for polyethylene polymerization based on fibre optic acoustic emission sensor

This paper presents applications of a new class of fibre optic acoustic emission (FOAE) sensor to monitor the operation of fluidized bed reactors used in polyethylene production. Specifically, the sensor was implemented to detect undesired, abnormal phenomena related to particle agglomeration, wall sheeting, fine overflow, and variations in the superficial gas velocity. The experiments were executed using a fluidized bed cold model setup for polyethylene powders with average particle sizes of 250, 1000, and 2000 μm. The results demonstrated that the presence of agglomerated particles in the fluidized bed reactor increases the kurtosis of the acoustic emission (AE) signal. Furthermore, the overflow of small particles can be detected by mounting the FOAE sensor below the gas distributor plate and monitoring an increase in the root mean square (RMS) of the AE signal. The AE signal RMS increased with the rising superficial gas velocity. Besides, forming a sheet layer on the reactor wall decreased the AE signal RMS. The proposed sensor's main benefits are its simple design, rapid response to abnormal conditions in the fluidized bed reactor, immunity against electromagnetic noise, high-temperature resistance, and safety in hazardous areas.     

流化床声发射机理及其在故障诊断中的应用

引　言流化床反应器能否长期稳定运行是一个十分严重的挑战 ,如果不彻底掌握流化质量的控制规律 ,对诸如强放热聚合反应过程 ,床层中流化粒子易于聚集、结块 ,甚至导致流化床崩溃而被迫停车 .因此 ,流化床故障诊断一直是工业界和学术界共同面临的难题 .流化系统一旦出现故障就会有反映流动规律本质的特征物理量出现较大变化以至突变 ,只是有些物理量对这些变化存在空间或时间上的不敏感性 .如压力信号就存在时间上的不敏感性 ,即往往压力信号出现显著变化时 ,床层流化质量已无法通过改变操作条件来改善 ;而光纤测量则存在空间上的不敏感性 ,…     

声波的多尺度分解与气固流化床故障检测

引言 在流化床乙烯气相聚合过程中,由于传热速率较低(与淤浆工艺相比),聚合物小颗粒容易聚集在一起形成结块,若不及时采取措施,将影响流化状态.而不良的流化状况经常导致装置不能满负荷、长周期地运转,严重时会"熔床",继而停产.为了保证流化床长期稳定的运行,聚合物颗粒结块的监测就变得十分重要.目前工业生产中主要根据流化松密度、反应温度、床高等参数的突变和γ射线法来检测结块.前者多依赖人为经验的判断,漏报、误报的情况时有发生.而γ射线法则对人体存在致命的伤害.因此,发展一种简单快捷、灵敏准确、安全环保的结块测量技术成为当务之急.     

Fluidised bed dynamics diagnosis from measurements of low-frequency out-bed passive acoustic emissions

The purpose of this research is to show that measurements of low frequency out-bed passive acoustic emissions are useful for monitoring gas-solid fluidised bed hydrodynamics. A methodology is proposed to develop portable measurement systems (PMS) feasible for both laboratory scale optimisations and, later, for process diagnosis within industrial facilities. The methodology includes a multirate technique where the first sampling frequency used was about 11 kHz that was successfully later reduced to 500 Hz, which is far from the most common used for sampling ultrasonic ranges. The acoustic frequency range of interest (0-200 Hz) allows the use of a commercial jukebox and two low cost condenser microphones to record the out-bed acoustic emissions.The underlying bed dynamic process was studied by monitoring both acoustic and pressure fluctuation signals and by applying time, frequency and state space analysis over the measured time series. The crude acoustic signals exhibit marked random behaviour due to a high content of background noise. This is detected by the mutual information function. The power spectral density of the acoustic time series shows high complexity and claims for reducing the acoustic frequency range to be evaluated (initially 0-5.5 kHz). To decide an optimal frequency range and, consequently, a better sampling frequency, the acoustic pressure was estimated from a numerical simulation based on the well-known particle array model. From the results of the simulations, and in agreement to the literature, it is concluded that the bed dynamic acoustic information mainly lies within the range 0-200 Hz. According to that, the signals were subsequently re-sampled at a sampling frequency of 500 Hz. Finally, by comparing the pressure time series monitoring to the analysis of the mesoscale bed acoustic region (mainly due to bubbles, 0-20 Hz), it is concluded that from out-bed acoustic time series monitoring, only the state space analysis is able to fully characterize the slugging dynamics by means of a correlation dimension in the range 2.5-3.5 for the experimental conditions covered.     

控制气相PE流化床高度对装置运行周期的影响

分析了聚合过程中控制流化床床高对聚合物粒径,催化剂聚合产率和装置运行周期的影响.增加流化床床高,有利于聚合物粉料对反应器上部扩大段的冲刷,有效减少了粉料堵塞循环回路和反应器结块的发生几率,提高了聚合反应器运行周期.     

基于吸引子比较法的卧式搅拌床反应器声发射故障诊断

在卧式搅拌床反应器丙烯聚合工艺中,结块是严重影响装置长期稳定运行和产品质量的隐患之一。本文以时域分析的角度,提出了一种基于吸引子比较法的声发射结块检测技术。该方法通过比较当前状态与正常状态的声发射信号,并借助统计量S值对两个时间序列的分布进行检验,从而判断两者是否由同一机理产生。当S<3时,则表明当前状态为正常;当S>3时,则表明反应器内有95%的可能性发生了结块。冷模实验结果表明,在合理选择传感器位置的前提下,通过对原始声发射信号进行消噪、归一化等预处理后,吸引子比较法能够灵敏地检测出卧式搅拌床反应器内粒径分布的细微变化,继而预警结块的发生。     

声场流化床流动特性研究进展

声场流化床是将声场引入普通流化床,采用颗粒为床层介质的流固相处理系统。声波可以有效降低颗粒聚团尺寸,显著改善超细颗粒的流化质量。本文介绍了声场流化床的基本原理以及近年来在基础研究和应用方面取得的进展及成果,综述了声场流化床在流体力学特性、颗粒特性、声场参数、流态化模型、颗粒团聚以及流化质量机理等方面的研究,并对声场流化床目前存在的问题及发展趋势提出了一些建议。     

Characterization of gas-solid fluidization: A comparative study of acoustic and pressure signals

The hydrodynamics of fluidized beds strongly influence their operation, but are complicated and chaotic. There are many measurement techniques, but none fully characterizes gas-solid fluidized beds. Acoustic signals from fluidized beds cover a wide frequency spectrum and can be correlated to bed characteristics. Experiments were conducted to study the acoustic signals from ultrasonic transducers mounted on the outer wall of a two-dimensional fluidization column. The acoustic signals were related to bubble behavior in 550 μm glass beads. Simultaneous acoustic and pressure measurements allowed direct comparison of these signals for single bubbles, pairs and chains of bubbles. The envelope of acoustic signals, generated by particle collisions and particle-wall impacts, provided information on the behavior of bubbles. Significant peaks appeared as the top portions of the bubble wakes approached the acoustic sensor. Pressure waves propagated considerably in the horizontal direction, whereas acoustic signals propagated little in the lateral direction, but transmitted forward in the wall in the direction of bubble motion, maintaining the wave profile invariant during transmission. The strong lateral localization of acoustic signals is promising for determining the lateral bubble position in the bed. Acoustic signals provide a potential means of determining such bubble properties as velocity, frequency and volume, with some advantages relative to pressure signals.