【作者】 刘明辉；

【导师】 丁忠伟；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2011， 硕士

【摘要】 气-固流化床广泛应用于许多工业过程,如催化裂化、S-zorb脱硫工艺等,了解并改善其流动行为有助于装置的平稳运行及目标产物收率的提高,对气-固流化床特别是气-固加压流化床压力脉动信号进行深入分析有助于更好地了解其流动行为。为了研究压力脉动信号与加压气-固流化床内流动行为的关系,以FCC催化剂为实验物料,采用密相段内径300mm、高度3800mm、扩大段内径600mm、高度800mm的加压流化床,改变系统压力,测量不同气速时各轴向位置处FCC催化剂的体积分率,考察压力对流态化行为的影响,并对压力脉动信号进行统计分析、快速傅里叶变换(FFT)和小波分析。压力升高,气相密度增大,气体对FCC颗粒曳力增加,使得流化床内颗粒浓度分布更加均匀,得到更加“平滑”的流态化。使用无量纲气速Frp表征不同气速和压力下的流态化,发现相同Frp时流态化状态相近。因此,可以在较高气速、较低压力和较低气速、较高压力下的得到相同的流态化。采用统计分析的方法得到流型转变速度u。,发现不同轴向位置的变化对于流型转变速度没有明显的影响。应用功率谱方法得出了气泡运动的特征频率为0.5-1.75Hz。压力升高,气泡的运动频率向高频区移动(1.5Hz-2.5Hz)。通过小波分析获得了代表气泡行为的特征频率(D5-D7)；分析此频段能量特征值随表观气速的变化规律,得出了流型转变速度uc,并考察压力对uc的影响。结果表明：压力波动能量集中在低频,随着气速的增加能量特征值先增加后减小,压力升高uc减小。通过流体力学计算(CFD)软件,对三维流化床进行模拟,采用双流体模型,模拟了不同压力下流化床内FCC催化剂颗粒体积分率的分布,通过模拟发现：随着压力的增加,轴向分布更加均匀。高压能改变气-固流化系统中颗粒与颗粒之间、颗粒与气体之间的作用力,抑制气泡的生长,产生更加均匀的流态化行为。更多还原

【Abstract】 Gas-solid fluidized bed is widely used in many industrial processes such as catalytic cracking, S-zorb desulfurization process, etc. Understanding and improving the flow behavior is helpful to operate the fluidized bed smoothly and increase the yield of target products. It is necessary to find out the flow behaviors in the reactor by analysis the pressure fluctuation in the gas-solid fluidized bed, especially the gas-solid pressurized fluidized bed. In order to investigate the relationship between the pressure fluctuation and the flow behavior in the pressured gas-solid fluidized bed. Experiments were conducted in pressurized fluidized bed of 300mm-i.d.×3800mm in high(with an expanded top section of 600mm-i.d.×800mm in high) with FCC materials. FCC catalyst volume fraction distribution at different axial positions under diffeerent air velocity and pressure were measured. Statistical analysis, fast Fourier transform (FFT), and wavelet analysis were also used to investigate the pressure fluctuations in the fluidized bed.With the increase of pressure, gas density increase, the drag force on the FCC particles increased, Making more uniform particle distribution in fluidized bed, a "smooth" the fluidization were found. The fluidization at different pressure and gas velocity can be characterized by a dimensionless parameters Frp. So, the same fluidization can be obtained at higher gas velocity,lower pressure or lower gas velocity,higher pressure.Through statistical analysis,flow regime transition velocity uc was determined, Axial position had no significant effect on uc. By analysis of power spectrum, characteristic frequency of bubbles(0.5Hz～1.75Hz) was obtained. By wavelet analysis, characteristic frequency of bubbles(D5-D7) was found.uc can be determined by analysising the energy distribution of this band changed with superficial gas velocity. The influence of pressure on uc was also discussed. The results showed that:power energy mainly concentrated in the low-frequency, With the increase of gas velocity, energy eigenvalue of the pressure fluctuation increased first and then decreased, When pressure increased uc decreased.By computational fluid dynamics (CFD) software, two-dimensional and three-dimensional fluidized bed were simulated. Two-fluid model was adopted to simulate FCC catalyst particle distribution under different pressure in the fluidizedbed. Through simulation:With the pressure increased, more uniform axial distribution was found.Pressure can change the force between gas-particles and particles- articles, inhibit the growth of the bubble, resulting in a more uniform fluidization更多还原