Prediction of Axial Liquid Velocity Profile in Bubble Columns

The Liquid Flow and Mixing Behavior in Bubble Columns is Partially Described by Means of Global Liquid Recirculation Velocity Profile. Due to the Complex Character of the Flow in Bubble Columns, the Prediction of the Axial Liquid Circulation is Still a Difficult Task. in This Work, the Following Correlation is Proposed for the Liquid Recirculation Profile: VLO/ VL(R)= 1 - 2.65 * N0.44 * C[R/r] 2.65, N0.442,c , Where N and C Are the Gas Radial Holdup Profile Parameters Evaluated by the Correlations Proposed by Wu, Ong and Al-Dahhan (Chemical Engineering Science, 56 (2001) 1207-1210). N = 2.188 X 103 ReG-0.598 Frg0.146 MoL-0.004, C = 4.32 X 10 -2 ReG0.2492. the Predictions of the Developed Liquid Circulation Correlation Agree Well with the Experimental Data Obtained in Our Laboratory and Reported in Literature. the Model is Simple and is Easy to Use as an Engineering Tool to Assess the Liquid Recirculation in Bubble Columns. © 2001 Elsevier Science Ltd. All Rights Reserved

Assessment of the Effects of High-Pressure Operation on the Liquid-Solid Mass-Transfer Coefficient in Trickle-Bed Reactors

Trickle-Bed Reactors Are Used Widely in Industry and Are Usually Operated at High Pressure. All the Studies on Liquid-Solid Mass Transfer in Such Reactors Were Performed under Atmospheric Pressure And, Hence, the Empirical Correlations for Liquid-Solid Mass-Transfer Coefficients (K1s and K1sa) Were Developed based on Atmospheric Data. However, These Correlations Incorporate One or More of the Parameters Affected by Pressure (E.g., Liquid Holdup, Catalyst Wetting Efficiency, Pressure Drop, Gas Density). in This Work the Effects of High Pressure and High Gas Flow Rates on the Predicted Coefficients using Some of These Correlations Are Evaluated. It is Shown that There Are Discrepancies in the Prediction of These Correlations, and the Use of Them at High Operating Pressure is Unjustified. This Work is an Attempt to Bring to the Attention of the Industrial Practitioners the Fact that the Atmospheric Liquid-Solid Mass-Transfer Correlations Do Not Exhibit the Same Trends with Increased Pressure and Some of Them Do Not Capture the Physics of the System. Thus, Experimental Investigations to Quantify the Effect of Reactor Pressure on K1s and 1sa and a New Correlation for a Wide Range of Operating Pressures Are Needed

Double-Slit Model for Partially Wetted Trickle Flow Hydrodynamics

A Double-Slit Model Developed Can Predict the Frictional Two-Phase Pressure Drop, External Liquid Holdup, Pellet-Scale External Wetting Efficiency, and Gas - Liquid Interfacial Area in Cocurrent Downflow Trickle-Bed Reactors Operated under Partially Wetted Conditions in the Trickle Flow Regime. the Model, an Extension of the Holub Et Al. (1992, 1993) Mechanistic Pore-Scale Phenomenological Approach, Was Designed to Mimic the Actual Bed Void by Two Inclined and Interconnected Slits: Wet and Dry Slit. the External Wetting Efficiency is Linked to Both the Pressure Drop and External Liquid Holdup. the Model Also Predicts Gas - Liquid Interfacial Areas in Partially Wetted Conditions. an Extensive Trickle-Flow Regime Database Including over 1,200 Measurements of Two-Phase Pressure Drop, Liquid Holdup, Gas - Liquid Interfacial Area and Wetting Efficiency, Published in 1974-1998 on the Partial-Wetted Conditions, Was Used to Validate the Modeling Approach. Two New Improved Slip-Factor Functions Were Also Developed using Dimensional Analysis and Artificial Neural Networks. High-Pressure and -Temperature Wetting Efficiency, Liquid Holdup, Pressure Drop, and Gas - Liquid Interfacial Area Data from the Literature on the Trickle-Flow Regime using Conventional Monosized Beds and Catalyst Bed-Dilution Conditions Were Successfully Forecasted by the Model

Digestion of Sand-Laden Manure Slurry in an Upflow Anaerobic Solids Removal (UASR) Digester

Studies on the Performance of a Laboratory Scale Up flow Anaerobic Solids Removal (UASR) Digester Were Carried Out using Sand-Laden Cow Manure Slurries Having Total Solids (TS) Concentration as 50 and 100 G/l. Hydraulic Retention Time (HRT) Was Maintained as 32.4 Days, Which Resulted in the Volatile Solids (VS) Loading Rates of 1 and 1.64 G/l D. the UASR System Was Designed to Remove Sand from the Manure Slurry, While Anaerobically Digesting Biodegradable Solids Inside a Single Reactor. to Enhance the Contact of Microorganisms and Substrate, the Liquor from the Top of the Digester Was Recirculated through the Bed of Settled Solids at its Bottom. Volatile Solids Reduction through This Process Was Observed to Be 62% and 68% in the Case of Feed Slurries Having TS Concentration as 50 and 100 G/l (Referred in the Text as 5% and 10% Feed Slurries), Respectively. the Methane Production Rates Were Observed to Be 0.22 and 0.38 L/l D, While Methane Yield Was 0.21 and 0.27 L CH4/g vs. Loaded, for 5% and 10% Feed Slurries, respectively. This Indicates that the Increase in the vs. Loading Had a Positive Impact on Methane Production Rate and Methane Yield. It Would Be of Interest to Study the Performance of a UASR Digester at Higher Solids Loadings and with Longer Solids Retention Times. Nonetheless, the Presented Study Showed that Sand-Laden Manure Slurries Can Be Successfully Digested in a UASR Digester Producing Methane Energy Equivalent to 4 KW H Per M3 of Digester Volume Per Day. © 2007 Springer Science+Business Media B.V

Statistical Characterization of Macroscale Multiphase Flow Textures in Trickle Beds

Experimental Studies (Lutran Et Al., Ind. Engng Chem. Res. 30 (1991) 1270; Ravindra Et Al., Ind. Engng Chem. Res. 36 (1997) 5133) and Numerical Simulation (Jiang Et Al., Chem. Engng Sci. 54 (1999) 2409-2419) Lead to the Conclusion that Fluid Flow Distribution in Trickle Beds is a Function of Bed Structure (I.e. Porosity Distribution), Particle External Wetting and Inlet Superficial Velocities of the Two Fluids. in This Study, Quantitative Relationships among the above Parameters Are Developed in a Statistical Manner through a Series of Computational Fluid Dynamics Simulations. the Contribution of Capillary Forces to Liquid Maldistribution is Significant in the Case of Partial Particle External Wetting; However, It is Shown that the Effect of Porosity Non-Uniformity in Packed Beds Can Be Reduced If the Particles Are Prewetted Well. © 2001 Elsevier Science Ltd. All Rights Reserved

Predictions of Radial Gas Holdup Profiles in Bubble Column Reactors

Gas Holdup and its Profile Are Important Parameters to Be Characterized in Bubble Column Reactors. Proper Prediction of the Radial Gas Holdup Profiles is Necessary for Determining Liquid Mixing, Flow Regime Transition, Heat and Mass Transfer. in This Study, the Following Gas Holdup Profile Form, Which Can Be Fitted to the Observed Holdup Profiles, is Proposed: EG = EG (N + 2/n + 2 - 2c) [1 - C(R/R)n]. the Parameters N and C Needed to Describe the Gas Holdup Profile Are Correlated with Appropriate Dimensionless Groups. N = 2.188 X 103 ReG-0.598 Frg0.146 MoL-0.004, C = 4.32 X 10-2 ReG0.2492. However, the Cross-Sectional Average Gas Holdup, EG, Can Be Estimated using the Available Correlations for overall Gas Holdup. the Agreement between the Correlation Predictions and Experimental Data is Reasonable over Wide Range of Operating Conditions. © 2001 Elsevier Science Ltd. All Rights Reserved

Multicomponent Flow-Transport-Reaction Modeling of Trickle Bed Reactors: Application to Unsteady State Liquid Flow Modulation

A One-Dimensional Reactor and Catalyst Pellet Scale Flow-Transport-Reaction Model Utilizing the Multicomponent Stefan-Maxwell Formulation for Inter- and Intraphase Transport is Developed to Simulate Unsteady State Operation in Trickle Bed Reactors. the Governing Equations and Method of Solution Are Discussed. Results Are Presented for a Model Reaction System (Hydrogenation of A-Methylstyrene) under Gas Reactant Limiting Conditions, for Liquid Flow Modulation as a Test Case of Unsteady State Operation. Model Simulations Predict that Periodic Liquid Flow Modulation Can Alter the Supply of Liquid and Gaseous Reactants to the Catalyst and Result in Reactor Performance Enhancement above that Achieved in Steady State Operation. the Effects of Key Modulation Parameters Such as the Total Cycle Period, Cycle Split, and Liquid Mass Velocity Are Simulated, and Model Predictions Are Found to Be in Agreement with Experimentally Observed Trends in the Literature. © 2005 American Chemical Society

Parametric Study of Unsteady-State Flow Modulation in Trickle-Bed Reactors

Unsteady-State Liquid Flow Modulation (Periodic Operation) Was Investigated for Hydrogenation of Alpha-Methylstyrene to Cumene in a Hexane Solvent over 0.5% Pd on Alumina Spheres. This Test Reaction Was Run under Both Gas and Liquid Reactant-Limited Conditions. It is Shown that Periodic Liquid Flow Modulation Can Alter the Supply of Liquid and Gaseous Reactants to the Catalyst and Result in Reactor Performance Different from that Obtained under Steady-State Conditions. the Effect of Key Parameters Such as Extent of Gas/liquid Limitation, Total Cycle Period, Cycle Split, and Liquid Mass Velocity Were Investigated Experimentally to Demonstrate the Cause-Effect Relationships in Periodic Operation. Performance Enhancement Was Observed for a Wide Range of Operating Conditions under Gas Reactant Limitation. It Was Strongly Dependent Upon the Extent of Catalyst Wetting under Liquid-Limited Conditions. the Feasibility of Achieving Improved Reactor Performance is Shown to Depend on the Extent of Reactant Limitation, the Cycle Period and Split, Mean Liquid Mass Velocity, and the Improvement of Liquid Maldistribution by Periodic Operation. Moreover, Performance Enhancement is Dependent Upon the Induced Flow Modulation Frequency and This is Discussed in Relation to the Natural Frequency of the Governing Process

Phase Distribution in an Upflow Monolith Reactor using Computed Tomography

Computed Tomography (CT) is Known to Be a Viable Technique for Determining Flow Maldistribution in Two-Phase Flow through Packed Beds. in This Study, Gamma Ray Computed Tomography Has Been Used to Quantify the Flow Distribution in a Monolith Catalytic Bed, with Water as the Liquid Phase and Air as the Gas Phase, Flowing Co-Currently Upward. the Flow Conditions Were Selected to Bracket Some Commercially Viable Operating Conditions for Such Reactors. in the Monolith Core Region, Fairly Uniform Flow Distribution Has Been Obtained for All the Flow Conditions Used. This Distribution is Quantified using the Standard Deviation of the Holdup Distribution. However, Maldistribution of Air and Water in the Monolith Bed Wall Region Due to Wall Effects at the Monolith Entrance Has Been Observed and Quantified by CT. the Obtained Results Confirm that the Entrance and Exit Regions of the Monolith Bed Need to Be Carefully Designed and to Be Free of Obstacles and Vortex Creating Devices. © 2005 American Institute of Chemical Engineers

Assessment of the Dimensionless Groups-Based Scale-Up of Gas–Solid Fluidized Beds

The most common scale-up approach for gas–solids fluidized beds is based on matching the governing dimensionless parameters. In the literature, this approach has been validated only by means of measuring global parameters between different sizes of fluidized beds. However, such global measurements are not sufficient to depict all the interplaying hydrodynamic phenomena and hence verify the scale-up relationships. Therefore, to assess this approach, an advanced gas–solids optical probe and pressure transducer measurement techniques have been applied to quantify local hydrodynamic parameters in two different sized fluidized beds. Four different sets of experimental conditions were designed and conducted to examine the assessment of the scaling approach with matched and mismatched dimensionless groups between the two beds. The results indicated that the reported dimensionless groups are not adequate for achieving similarity between the two gas–solids fluidized beds in terms of solids holdup, gas holdup, particle velocity, mass flux, and pressure fluctuation. This finding demonstrates the importance of local measurements of the hydrodynamic parameters of fluidized beds in order to evaluate scale-up relationships. Finally, the results further advance the understanding of the gas–solids fluidized beds and present deeper insight into their solids dynamics