CHARACTERISTICS OF PULSING FLOW IN TRICKLE BEDS. IMPROVEMENTS OF A MACROSCOPIC MODEL

A rather simple macroscopic model, originally proposed by Dimenstein and Ng (1986), is examined by comparison with results of experimental work carried out in this laboratory recently. Several improvements are proposed relying either on new correlations or in better physical understanding obtained from the recent experiments. The model, despite its simplicity, is considered quite comprehensive and reliable (for the range of physical properties examined) providing good estimates of essentially all the significant time averaged characteristics of pulsing flow.     

滴流床反应器内脉冲流宏观流体力学的特性参数

引　言在石油化工工业的加氢处理中 ,滴流床反应器常操作在接近脉冲流流型区域[1] .脉冲流下气液流速都比较高 ,所以该操作方式适合催化剂活性高、反应速率快的反应[2 ] ,而且气液流量大有利于强放热反应的反应热从反应器移出。流体力学参数如脉冲速度、脉冲频率、持液量、气液分布、压力降等对于该类反应器的工业设计及操作具有很重要的意义 .Ｓａｔｏ等[3] 较早地对脉冲流的特性进行过定性的实验研究 .Ｂｌｏｋ等[4 ] 以及Ｔｓｏｃｈａｔｚｉｄｉｓ等[5] 通过电导法也对脉冲流宏观特性进行过研究 .本文用不同的实验方法对滴流床反应器内脉…     

滴流床反应器的脉冲特性

滴流床中气液流速较高时会产生脉冲流。脉冲特性可表示为：脉冲频率、脉冲速度、脉冲持液与脉冲间持液。这些参数可用气液流速、填料特性及气液物性来度量。在宏观物料衡算基础上推得脉冲速度的模型。脉冲持液就是反应器的动持液；脉冲持液与脉冲间持液之比近于1．5。发现脉冲频率完全受表观液速与临界液速的差值所控制。获得了三个关联式，涉及不同系统，也包含文献数据。     

EFFECT OF VOLATILE LIQUID PHASE ON TRICKLE BED REACTOR PERFORMANCE

Many experimental trickle-bed reactors are operated at high temperatures and high pressures with volatile feedstocks which undergo partial vaporization of the liquid phase. The effect of this partial vaporization on the rate of reaction is demonstrated. The hydrodesulfurization of benzothiophene was simulated with the feed consisting of 5%, by weight, benzothiophene and 95% solvent. The pressure was held constant at 68 atm and temperature varied between 546 to 606 K employing isothermal simulations. The results show that the choice of solvent can significantly affect the rate of reaction.     

PORE SCALE MODEL FOR FLOW REGIME TRANSITION IN A TRICKLE BED REACTOR

The hydrodynamic modeling of gas-liquid cocurrent downflow through a trickle bed reactor based on pore scale is presented. The pore scale hydrodynamic is related to the macroscopic scale flow parameters. The two-phase flow at pore level channel is modeled similar to annular two-phase flow in tubes. Using the film instability due to shear by the gas at the pore level channel, the transition criterion for the trickle flow to pulse flow regime is obtained. The model predictions agree with the published data. A model for transition from partial wetting to complete wetting in trickling flow is presented. The model predictions are in agreement with previous models. The model indicates better wetting of the smaller size packing for the same liquid mass flux.     

PORE SCALE MODEL FOR FLOW REGIME TRANSITION IN A TRICKLE BED REACTOR

The hydrodynamic modeling of gas-liquid cocurrent downflow through a trickle bed reactor based on pore scale is presented. The pore scale hydrodynamic is related to the macroscopic scale flow parameters. The two-phase flow at pore level channel is modeled similar to annular two-phase flow in tubes. Using the film instability due to shear by the gas at the pore level channel, the transition criterion for the trickle flow to pulse flow regime is obtained. The model predictions agree with the published data. A model for transition from partial wetting to complete wetting in trickling flow is presented. The model predictions are in agreement with previous models. The model indicates better wetting of the smaller size packing for the same liquid mass flux.     

IMPROVED HYDRODYNAMIC MODEL OF TWO-PHASE SLUG FLOW IN VERTICAL TUBES

Merits of the Fernandes model(Fernandes et al.1983)for two-phase slug flow in verticaltubes are reviewed in this paper.While predicting many macroscopic parameters of slug flow in verti-cal tubes,it fails to present correctly the trend that the average voidage in liquid slugs increases asthe rising velocity of Taylor bubbles is increased.It is also desirable to extend its application toelectrolyte systems, and to churn flow conditions.Based on the diagnostic analysis,the model equa-tion for gas entrainment by falling liquid film is reformulated and the influence of surface tension isalso accounted for.Development of the falling liquid film is recognized in the revised model in or-der to suit the case of short Taylor bubbles as well.The modified model predicts the variation of av-erage voidage in liquid slugs in good agreement with available experimental data.     

滴流床反应器中发泡流体的流型转变

滴流床反应器(TBR)广泛用于石油炼制和化工等过程．TBR的流体力学现象十分复杂,因操作条件、床层和流体性质的改变可产生不同的流区．其流型转变行为是TBR反应工程研究的一个重要领域．     

高抗冲聚苯乙烯熔体挤出流动特性的研究

应用毛细管流变仪,分别在低和高的剪切速率范围内考察了两种高抗冲聚苯乙烯熔体的挤出流动行为。研究结果表明:试样的末端压力损大与表观剪切速率γ_a的关系大致上服从指数律;在较高的γ_a下,熔体的剪切流动行为更符合幂律;表观剪切粘度和移动因子对温度的依赖性可用Arrhenius方程描述。     

EFFECT OF EQUATION OF STATE ON PREDICTION OF TRICKLE BED REACTOR MODEL PERFORMANCE

Trickle bed reactors are widely employed in hydrotreating pocesses that operate at conditions where a significant portion of the liquid phase will flash. This partial vaporization of the feed affects the reactor performance. In order to determine the extent of liquid flashing and its effect on reactor performance, an equation of state is needed. In this study we used seven cubic equations of state to determine their effect in predicting reactor performance as well as parameter estimation

Two important variables that are calculated from the equation of state are the vapor liquid equilibrium and the molar density of the liquid phase. It was observed that although the distribution coefficients calculated by each equation of state are significantly different from each other, they do not affect the reactor model appreciably. However, molar density determination has a large effect both on modelling of reactor performance and the parameter estimation.     

喷动床内气固两相流体动力行为的数值模拟

引　言喷动床被广泛应用于不同工业领域中 ,如石油裂解反应 -再生器、煤和农业废弃物气化和燃烧 ,喷动床还被应用于粮食和药品的干燥等[1] .因此 ,喷动床设计应满足不同应用的要求 .喷动床内气相反应物的反应时间和停留时间依赖于床体几何结构和运行参数 .尽管已有许多的实验对喷动床内气固两相流动进行了研究 ,得到了喷射区、环形区和喷泉区内的气固两相流动流体动力特性 ,然而由于喷动床内气固两相流动的复杂性 ,人们对床体几何结构和运行参数对喷动床动力学的影响至今并不清楚 .因此 ,床体几何结构和运行参数等对喷动床动力学的影响成为…     

NR／SBR胎面胶毛细管挤出流动中粘度的压力效应

分析了聚合物熔体于口型挤出流动中粘度的压力效应。提出估算压力系数β的关系式：β＝（Ｃ１－Ｃ２）／（Ｃ１Ｐｍ２－Ｃ２Ｐｍ１）。用毛细管流变仪。研究了ＮＲ／ＳＢＲ共混胎面胶口型挤出流动中粘度对压力的敏感性。结果表明，β值随着挤出速率和温度的提高而减小。     

EFFECTS OF SECONDARY AIR INJECTION ON GAS-SOLID FLOW BEHAVIOR IN CIRCULATING FLUIDIZED BEDS

Effects of secondary air injection on the hydrodynamics such as solid holdup and gas-solid flow behavior were investigated in a circulating fluidized bed. The gas velocity in the riser, the ratio of secondary air velocity to that of primary air, and the solid circulating rate were chosen as operating variables. Fluid cracking catalyst(FCC) with a density of 1840 kg/m³ and a mean diameter of 74 um was employed as the solid phase. The secondary air was fed to the riser radially or tangentially at the wall of the column. Pressure drop fluctuations in the riser were measured and analyzed by adopting the stochastic method to characterize the effects of secondary air injection on the gas-solid flow behavior in the bed.

It has been found that the injection of secondary air into the riser can increase the solid holdup in the riser considerably, and that the tangential injection of secondary air is more effective for the increasing the solid holdup than the radial injection. However, the gas-solid flow behavior has been found to become less persistent with the injection of secondary air; the resultant flow behavior is more complex when the air is injected tangentially than radially. The solid holdups in the primary as well as secondary zones of the riser have been well correlated in terms of not only operating variables but also fractal dimension of the pressure fluctuations.     

EFFECTS OF SECONDARY AIR INJECTION ON GAS-SOLID FLOW BEHAVIOR IN CIRCULATING FLUIDIZED BEDS

Effects of secondary air injection on the hydrodynamics such as solid holdup and gas-solid flow behavior were investigated in a circulating fluidized bed. The gas velocity in the riser, the ratio of secondary air velocity to that of primary air, and the solid circulating rate were chosen as operating variables. Fluid cracking catalyst(FCC) with a density of 1840 kg/m³ and a mean diameter of 74 um was employed as the solid phase. The secondary air was fed to the riser radially or tangentially at the wall of the column. Pressure drop fluctuations in the riser were measured and analyzed by adopting the stochastic method to characterize the effects of secondary air injection on the gas-solid flow behavior in the bed.

It has been found that the injection of secondary air into the riser can increase the solid holdup in the riser considerably, and that the tangential injection of secondary air is more effective for the increasing the solid holdup than the radial injection. However, the gas-solid flow behavior has been found to become less persistent with the injection of secondary air; the resultant flow behavior is more complex when the air is injected tangentially than radially. The solid holdups in the primary as well as secondary zones of the riser have been well correlated in terms of not only operating variables but also fractal dimension of the pressure fluctuations.     

低、高压滴流床中压降和持液量计算的统一关系式

基于对滴流床中气液两相流动特征尺度的分析,提出以修正的相摩擦系数对相Reynolds数进行关联,获取低、高压滴流床中压降和持液量计算的统一关联式的方法.对于滴流床中单相不饱和流（液体流动,气体静止）情形,以及低压和高压滴流床中两相流、高气液作用情形,收集了文献报道的不同大小颗粒、不同物系的大量实验数据,以相摩擦系数对相Reynolds数进行关联,得到新的压降和持液量计算式,其物理意义明确,计算精度得以提高.     

HPVC／ABS共混物加工流动性能的研究

通过分析HPVC/ABS共混物溶液的粘度 -组成关系 ,证实了HPVC与ABS具有相容性。ABS在HPVC/ABS共混物中含量超过某一临界值 ,才能改进HPVC的加工流动性能 ,此临界值为 10 %～ 14 %。ABS含量为 60 %时 ,HPVC/ABS共混物的流动性能最好。     

径向流固定床数学模型研究进展

简要阐述了径向流固定床反应器在化学工程中的重要性及研究该类流动问题的迫切性，回顾了文献中描述该反应器中流体流动的六类数学模型，提出了设计准则及均布措施，指出了存在的问题及解决的途径．     

添加ATH的UPR树脂粘度特性研究

本文采用数字粘度仪对不同温度和促进剂下添加氢氧化铝(ATH)的不饱和聚酯树脂(UPR)的粘度和凝胶时间进行测试,然后对粘度和凝胶时间进行分析。分析结果表明,对于所选定的树脂,温度是影响树脂粘度的决定性因素;对凝胶时间的影响,温度的作用要大于促进剂的作用。     

THE EFFECT OF PARTICLE DILUTION ON WETTING EFFICIENCY AND LIQUID FILM THICKNESS IN SMALL TRICKLE BEDS

Partial wetting in small scale trickle bed reactors results in incorrect determination of intra-particle apparent kinetic parameters as well as in erroneous reactor scale-up. Although a dilution of catalyst particles with inert fines improves the catalyst wetting efficiency, it does not guarantee full external catalyst wetting at all superficial liquid mass velocities. In this work, a method is presented to relate the wetting efficiency obtained at different operating conditions and at different laboratories for diluted and non-diluted beds. Liquid film thickness in diluted and non-diluted beds is estimated. The effect of the operating conditions on partial wetting and liquid film thickness is discussed.     

液相物性对壳侧不互溶双组分两相流截面含气率及两相压降的影响

在用空气-水、空气-0号柴油研究的基础上,用空气和质量浓度为30％的甘油水溶液研究了理想管壳式换热器壳侧平均截面含气率和两相压降,以期进一步考察不同液相物性的影响.研究表明,液相物性对两者均有一定影响.提出了不同液相物性时截面含气率的通用关联式.根据流型整理了两相摩擦因子.并提出了一种新的两相摩擦压降关联式,它能较好地预测不同液相物性时两相压降的实验数据.