【作者】 马丽萍；

【导师】 石炎福；

【作者基本信息】 四川大学 ， 化学工程， 2002， 博士

【摘要】 循环流化床气-固两相复杂的流动系统使其过程控制、预测和放大相当困难，至今仍有许多问题未能很好地理解和掌握。本文利用混沌、分形这一新的非线性分析方法，结合新兴的数学工具-小波分析对循环流化床压力、颗粒浓度波动信号进行分析，从局部和整体不同的侧面来研究循环流化床气-固两相流动系统，以一个新的视角来认识循环流化床复杂的流体流动规律。 运用小波变换对信号具有时频局部化的特点，以及混沌信号与噪声小波变换模极大值变化趋势的不同，提出了基于分形理论的小波变换噪声去除方法，首次对循环流化床波动信号的噪声问题提出了客观、有效的除噪方法，克服了以往对未知动力系统信号除噪的盲目性。 对波动信号进行了系统的功率谱分析和相关性分析，首次指出信号的频带随操作条件的不同而略有差异，压力波动信号在低固体循环量下主要由低幅、周期信号的气体波动引起，随固体循环量的增加则以颗粒运动贡献为主，主要频带集中在5Hz以内，信号表现出混沌特征。 在混沌理论运用研究方面，探讨了用C-C算法来确定相空间重构滞时和时间窗，指出固定时间窗计算关联维比固定滞时计算关联维的优越性，首次将用此方法得到的时间窗用于循环流化床波动信号的混沌分析，确定关联维和Kolmogorov熵，并对循环流化床颗粒浓度波动信号径向、压力波动信号轴向混沌特性进行了系统的分析，混沌特征参数的变化在一定程度上反应了床层内气-固流体的运动状况。 引入多重分形测度分析理论，首次用小波变换模极大值的方法，对压力波动、 四川大学博士学位论文颗粒浓度波动信号进行多重分形分析，得到相关奇异谱，为揭示循环流化床非线性、非均匀性的流动机制提供了一种新的方法。提出以多重分形理论为依据的压力波动信号的间歇性指数的计算方法，并对压力波动信号进行了间歇性分析，提出了由快速流态化向密相气力输送的新的判据，并指出循环流化床提升管流型的转变沿轴向并不是同时一致转变的，而是床层顶部要先于床层底部。上述研究结果对深入了解循环流化床中气固两相流动机制具有重要意义。更多还原

【Abstract】 The hydrodynamics in circulating fluidized bed (CFB) are complex. In spite of increasing interest in CFB fundamental research in the past decades, the knowledge on the hydrodynamics is still not sufficient for straightforward design control and scale-up of CFB . In this work the non-linear analysis technique (chaos and fractal theory) combining with the new mathematics tool (wavelet transform) is applied to analyze the solid hold-up and pressure fluctuation signals in CFB riser for understanding the complex non-linear dynamic behavior in CFB from a new point of view.Based on the wavelet transform and fractal theory, a new noise-reduction algorithm is put forward and successful used in noise reducing of solid hold-up and pressure fluctuation signal of CFB riser. This method does not require information on the properties of noise and equation of dynamic system and is practicable and effective. The true fluctuation signal can be extracted through this method and used for chaotic analysis .The frequency characteristic of fluctuation signals is dissected through power spectral analysis. The frequency range of signals changes with the operation conditions. Gas movement fluctuation is the predominant source for pressure fluctuation in CFB riser at the low solid circulating rate, and the solid movement is the predominant source for pressure fluctuation at the high solid circulating rate. The main frequency range of pressure fluctuation signal is smaller than 5Hz.Based on the C-C method (correlation integral),the Td(time delay) and rw(time window) used for reconstructing chaotic attractors from experimental time series have been estimated simultaneously. Results show that fixing TW is better than fixing rd in calculating correlation dimension .The correlation dimension and Kolmogorov entropy are first obtained with this method. In addition, the chaotic characteristics of fluctuation signal in both axial and radial direction are also analyzed quantitatively. The change of the chaotic characteristic can be used to characterize the flow dynamic behavior in CFB riser.In order to understand the heterogeneity non-linearity and chaotic behavior of particle-fluid system in CFB, based on wavelet transform modulus maxima(WTMM) method ,we perform multifractal measure analysis on solid hold-up and pressure fluctuation signals of CFB riser and get the multifractal singularity spectrum . The method to calculate intermittent index is also proposed according to the WTMM method. With this method, we propose a new judgement to determine the transition of flow regimes from fast fluidization to dense pneumatic conveying. Results show that the transition of flow regimes in CFB riser does not change at the same time along the axial direction. The transition on the upper region is more early than on the bottom region.更多还原