Catalyst Wetting Efficiency in Trickle-Bed Reactors at High Pressure

Trickle-Bed Reactors Are Widely Used in Industrial High Pressure Operations (Up to 30 MPa). the Knowledge of Catalyst Wetting Efficiency as a Function of Operating Conditions is Needed for Relating Laboratory and Pilot Scale Reactor Data to Large Scale Reactor Operation. the Available Predictions of the Wetting Efficiency Rest on Data Collected at Atmospheric Pressure. in This Study a Phenomenological Analysis Has Been Developed to Relate the Wetting Efficiency with Operating Conditions Such as Reactor Pressure, Gas and Liquid Flow Rate. Experimental Data for the Wetting Efficiency at High Pressure Have Been Obtained Via a Tracer Technique. the Data Support the Developed Model Which Can Be Expressed by the Following Correlation: N{Long Right Leg}CE = 1.104 REL1/3 1 + [( ΔP Z)/pLg] GaL1/9 This Correlation is Also in Good Agreement with the Data Correlated Previously at Atmospheric Pressure and Provides the Means for Assessing Liquid-Catalyst Contacting at All Operating Pressures. © 1995

Occupational characteristics of cases with asbestos-related diseases in The Netherlands

OBJECTIVE: To describe the occupational background of cases with an asbestos-related disease and to present overall mesothelioma risks across industries with historical exposure to asbestos. METHODS: For the period 1990-2000, cases were collected from records held by two law firms. Information on jobs held, previous employers, activities performed and specific products used were obtained from patients themselves or next of kin. Branches of industry and occupations were coded and the likelihood of asbestos exposure was assessed. For each branch of industry, the overall risk of mesothelioma was calculated from the ratio of the observed number of mesothelioma cases and the cumulative population-at-risk in the period 1947-1960. In order to compare mesothelioma risks across different industries, risk ratios were calculated for the primary asbestos industry and asbestos user industries relative to all other branches of industry. RESULTS: In total, 710 mesotheliomas and 86 asbestosis cases were available. The average latency period was approximately 40 yr and the average duration of exposure was 22 yr. Ship building and maintenance contributed the largest number of cases (27%), followed by the construction industry (14%), the insulation industry (12%), and the navy and army, primarily related to ship building and maintenance (5%). In the insulation industry, the overall risk of mesothelioma was 5 out of 100 workers, and in the ship building industry, 1 out of 100 workers. The construction industry had an overall risk comparable with many other asbestos-using industries (7 per 10,000 workers), but due to its size claimed many mesothelioma cases. CONCLUSION: The majority of cases with asbestos-related diseases had experienced their first asbestos exposure prior to 1960. For cases with first asbestos exposure after 1960, a shift was observed from the primary asbestos industry towards asbestos-using industries, such as construction, petroleum refining, and train building and maintenance. Due to the long latency period, asbestos exposure from 1960 to 1980 will cause a considerable number of mesothelioma cases in the next two decades

Reproducible Technique for Packing Laboratory-Scale Trickle-Bed Reactors with a Mixture of Catalyst and Fines

A Reproducible Procedure for Packing Small-Diameter Packed Beds with a Mixture of Fines and Catalyst is Reported. Such Beds Are Essential for Process Catalyst Testing in Trickle-Flow Reactors. Packing Uniformity Along the Bed, Reproducibility of Single-Phase Pressure Drop and Reproducibility of Liquid Holdup and Two-Phase Flow Pressure Drop in Repacked Beds Has Been Demonstrated. © 1995, American Chemical Society. All Rights Reserved

NOVEL DESIGN OF MULTIPHASE REACTORS FOR BIOMASS-TO-LIQUID SYNTHESIS

Generation of liquid fuels from renewable sources such as biomass has been practiced since early 1900’s. In view of the skyrocketing oil prices and the depleting reserves of natural gas, it has gained further interest. The Fischer-Tropsch synthesis is one of the main processes considered. It involves the reaction of syngas in presence of a catalyst to produce liquid fuels. Syngas sources are numerous ranging from waste gasification, anaerobic digestion to clean coal. The reactor of choice for gas to liquid conversion is a slurry bubble column. Although, these multiphase reactors offer several advantages including good heat and mass transfer, ease of construction and operation, the absence of moving parts, one of their main disadvantages is the difficulties associated with the scale-up. The latter is due to complex phases’ interactions and significant backmixing of phases. In general, the scaling rules are derived from mass and momentum balances resulting in dimensionless hydrodynamic numbers. For a proper scaling these numbers should be kept constant, together with dimensionless geometric numbers in order to ensure both dynamic and geometrical similarity. With the complex nature of the flow in these systems, this becomes very hard to achieve since it may result in the need for matching a large numbers of dimensionless quantities. Hence, different routes to provide a firm scale-up methodology are needed. Controlling the effect of scale using heat exchanging internals by means of reactor compartmentalization is proposed in this study. The details of this methodology can be summarized as follows: a) The large reactor diameter is subdivided into similar, vertical compartments by means of the cooling tubes; b)The compartments are to have a diameter similar to that of a small scale column on which investigations can be (have been) performed; and c) The various hydrodynamic parameters within each compartment are to be compared with those measured in a bubble column of the same diameter. Preliminary results show that radial gas holdup profiles inside the compartments exhibited similar behavior as inside a solid wall column, with a close agreement between resulting gas holdup profile inside the single tube bundle compartment and data obtained in 6 inches steel bubble column

3D CFD Simulation of a Bubble Column with Internals: Validation of Interfacial Forces and Internal Effects for Local Gas Holdup Predictions

CFD Models (Turbulent Models and Interfacial Forces) Incorporated with the Population Balance Model (PBM) Have Been Validated, Azimuthally, with the Gamma-Ray-Computed Tomography (CT) Results to Address the Effect of the Presence of Internals with Different Arrangements and Diameters. the Superficial Gas Velocity Applied Was Varied from 0.05 to 0.45 M/s. the Results Exhibit the Capability to Predict the Hydrodynamics of the Bubble Column, Further Incorporating the Population Balance Model and Promoting the Prediction of Simulation in High Superficial Gas Velocity. the Effect of Internals Revealed that the Gas Holdup Was Significantly Enhanced in the Bubble Column\u27s Wall Region, While the Gas Holdup Was Increased Remarkably in the Center and the Wall Regions of the Bubble Column Equipped by Internals of 1 In. Diameter More Than in Internals of 0.5 In. However, Internals with a Hexagonal Arrangement Increase the Gas Holdup in the Central Region and Less in the Wall Than in the Circular Arrangement

Quantification of Solids Flow in a Gas-Solid Riser: Single Radioactive Particle Tracking

Solids in Risers of Circulating Fluidized Beds (CFB) Exhibit Local Backflow and Recirculation. Measurement of the Concentration-Time Response to an Impulse Injection of Tracer, Even at Two Elevations Cannot Determine the Residence Time Distribution (RTD) of Solids Uniquely. Hence, Evaluation of RTD in Risers from Conventional Tracer Responses is Difficult and Often Not Possible. in Addition, Estimating the Solids Circulation Rate in These Closed Loop Systems, is a Non-Trivial Problem. in This Work, a Single Radioactive Particle in the CFB Loop is Tracked during its Multiple Visits to the Riser And, by Invoking Ergodicity, Solids Circulation Rate, Accurate Solids RTD and Additional Information on the Solids Flow Pattern in the Riser Are Estimated. a Calibration Curve Was Established for the overall Solids Mass Flux as a Function of Superficial Gas Velocity. a Second Peak in the Probability Density Function (PDF) of the Solids RTD Curve in the Riser Was Observed for Operating Conditions in the Fast-Fluidization Regime. © 2004 Elsevier Ltd. All Rights Reserved

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

High-Pressure Trickle-Bed Reactors: A Review

A Concise Review of Relevant Experimental Observations and Modeling of High-Pressure Trickle-Bed Reactors, based on Recent Studies, is Presented. the Following Topics Are Considered: Flow Regime Transitions, Pressure Drop, Liquid Holdup, Gas-Liquid Interfacial Area and Mass-Transfer Coefficient, Catalyst Wetting Efficiency, Catalyst Dilution with Inert Fines, and Evaluation of Trickle-Bed Models for Liquid-Limited and Gas-Limited Reactions. the Effects of High-Pressure Operation, Which is of Industrial Relevance, on the Physicochemical and Fluid Dynamic Parameters Are Discussed. Empirical and Theoretical Models Developed to Account for the Effect of High Pressure on the Various Parameters and Phenomena Pertinent to the Topics Discussed Are Briefly Described

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