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

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

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

Comparison of Single- and Two-Bubble Class Gas-Liquid Recirculation Models - Application to Pilot-Plant Radioactive Tracer Studies during Methanol Synthesis

Radioactive Gas Tracer Measurements Conducted during Liquid-Phase Methanol Synthesis from Syngas in a Pilot-Scale Slurry Bubble Column at the Alternate Fuels Development Unit (AFDU), La Porte Have Been Compared with Simulations from Two Mechanistic Reactor Models - Single-Bubble Class Model (SBCM) and Two-Bubble Class Model (TBCM). the Model Parameters Are Estimated from an Independent Sub-Model Gas and Liquid Recirculation, and the Long-Time-Averaged Slip Velocity between the Gas and Liquid/slurry in the Column Center Can Be as High as 50-60 Cm/s Depending on the Operating Conditions. Comparison of Experimental Data with Simulation Results from the Two Models Indicates that Accurate Description of Interphase Gas-Liquid Mass Transfer is Crucial to the Reliable Prediction of Tracer Responses. Coupled with a Correct Description of Gas and Liquid Recirculation, the Models Presented Here Provides a Simple and Fundamentally based Methodology for Design and Scale-Up of Bubble Column Reactors. © 2001 Published by Elsevier Science Ltd

Evaluation of Trickle Bed Reactor Models for a Liquid Limited Reaction

The Isothermal Decomposition of Hydrogen Peroxide on a CuCr Catalyst in a Laboratory Scale Trickle Bed Reactor Was Used to Test Model Predictions of the Dependence of Liquid Reactant Conversion on Space Time for Different Operating Conditions. It is Assured that the Decomposition of Hydrogen Peroxide is a First Order Liquid-Limited Reaction. Comparison of Model Predictions and Experimental Data Indicates that Both External Mass Transfer Effects and Incomplete External Catalyst Wetting Need to Be Accounted For. Dudukovic\u27s (1977) Approximate Model for the Catalyst Effectiveness Factor Adequately Simulates Both Effects

Using a Fiber-Optic Probe for the Measurement of Volumetric Expansion of Liquids

A Fiber-Optic Probe is Developed for the Fast, In-Situ Measurement of Volumetric Expansion of Multiphase and Multicomponent Systems. an Experiment with the Binary Mixtures of CO2-Toluene and CO2-Ethanol Was Conducted to Demonstrate the Usefulness of the Fiber-Optic Probe in Accurately Tracking the Isothermal Volumetric Expansion as a Function of Pressure. in the 1-L Autoclave that Has Been Used, the Probe Was Shown to Detect the Liquid Level Height within a Precision of 0.35% of the Total Height of the Vessel. the Results for the Volumetric Expansion of Toluene and Ethanol with CO2 Correlate Well with Those Found in the Literature. the Probe itself Can Be Used Up to Pressures of 140 Barg and Temperatures of 120°C. © 2007 American Chemical Society

Hydrodynamics of Churn Turbulent Bubble Columns: Gas-Liquid Recirculation and Mechanistic Modeling

A Phenomenological (Mechanistic) Model Has Been Developed for Describing the Gas and Liquid/slurry Phase Mixing in Churn Turbulent Bubble Columns. the Gas and Liquid Phase Recirculation Rates in the Reactor, Which Are Needed as Inputs to the Mechanistic Reactor Model Are Estimated Via a Sub-Model Which Uses the Two-Fluid Approach in Solving the Navier-Stokes Equations. This Sub-Model Estimates the Effective Bubble Diameter in the Reactor Cross-Section and Provides a Consistent Basis for the Estimation of the Volumetric Mass Transfer Coefficients. the Strategy for the Numerical Solution of the Sub-Model Equations is Presented Along with the Simulation Results for a Few Cases. the overall Reactor Model Has Been Tested Against Experimental Data from Radioactive Gas Tracer Experiments Conducted at the Alternate Fuels Development Unit (AFDU), La Porte, TX under Conditions of Methanol Synthesis

Effect of Operating Pressure on the Extent of Hysteresis in a Trickle Bed Reactor

The Dependence of Hydrodynamic Parameters, Such as Pressure Drop, on the Flow History of the Bed is Called Hysteresis. This Phenomenon is Most Commonly Associated with Changes of Flow Distribution and Flow Patterns with the Flow History. Many Studies Have Shown that Increased Operating Pressure Will Affect Flow Distribution and Wetting Efficiency; However, There Seems to Be No Study of the Effect of the Elevated Operating Pressure on the Extent of Hysteresis. in This Study, an Experimental Investigation of the Hysteresis in a High-Pressure Trickle Bed Has Been Performed. a Hysteresis Factor Has Been Introduced to Quantify the Extent of Hysteresis and Was Found to Be a Strong Function of Gas and Liquid Operating Flow Rates as Well as the Operating Pressure. in the Region of Lower Liquid Velocities, Hysteresis is Present Regardless of the Operating Pressure or Gas Velocity. in the Region of Higher Liquid Velocities, Increases in Both Pressure and Gas Velocity Will Lower the Extent of Hysteresis. for the Range of Conditions Considered in This Study, the Extent of Hysteresis Was Uniquely Determined by the Pressure Drop in the Levee Mode, Regardless of the Operating Pressure or Velocities. the Results Are Interpreted in Terms of the Phenomenological Analysis of Al-Dahhan and Dudukovic (Al-Dahhan, M. H.; Dudukovic, M. P. Chem. Eng. Sci. 1994, 49, 5681-98), Which Relates Operating Pressure and Gas Velocity to the Flow Distribution and Wetting Efficiency in a Trickle Bed Reactor. © 2008 American Chemical Society

On the Measurement of Gas Holdup Distribution Near the Region of Impeller in a Gas-Liquid Stirred Rushton Tank by Means of Γ-CT

Three Flow Patterns of Flooding, Loading and Complete Recirculation in a Gas-Liquid Stirred Rushton Tank Were Identified based on Experimental Observation. the Gas-Liquid System Was Composed of Air and Water. under Different Operating Conditions of Gas Flow Rate and Impeller Rotating Speed, the Distribution of Gas Holdup Near the Region of Impeller Was Measured using a Γ-CT Scan Method. Both Quantitative Digital Distribution Curves of Gas Holdup and their Qualitative Color CT Images Were Obtained. at the Region of Impeller, There Was a Convex Characteristic Peak of Gas Holdup Distribution Both in Radial and in Axial Directions, and with the Region Being Gradually Away from the Impeller, the Distribution of Gas Holdup Became Flatter. the Values of Gas Holdup in S33 Regime Were a Little Higher Than Those in L33 Regime. Higher Impeller Rotating Speed Had Some Effect on the Increasing of Gas Holdup at the Region of Higher Axial Height. the Experimental Measurement Results Were Basically Consistent with Those Previously Published by Bombač. the Hole Number and Diameter of Sparger Had Little Influence on the Distribution of Gas Holdup, While the Sparger\u27s Installed Height Had Significant Influence on Them. When the Sparger Was Installed Close to the Bottom of Rushton Tank, a Comparatively Smoother Distribution of Gas Holdup above the Space of Impeller Could Be Obtained. the Research Results in This Paper Were Useful for Better Understanding of Gas Holdup Distribution Near the Region of Impeller of Rushton Tank and Could Also Provide Experimental Data for CFD Simulation. © 2012 Elsevier B.V

Modeling of the Fischer-Tropsch Synthesis in Slurry Bubble Column Reactors

A Multicomponent One-Dimensional Dynamic Mathematical Model for the Reacting Slurry Systems with a Change in Gas Flow Rate Due to the Chemical Reaction is Developed. a Change in Gas Flow Rate Caused by the Chemical Reaction is Modeled using the overall Gas Mass Balance. Thus, All Relevant Chemical Species Are Included in the Model. Linear First-Order Reaction Kinetics is Considered. the Gas Phase is Modeled using the Two-Bubble Class Hydrodynamic Model. the Interaction between Small and Large Bubbles is Included as the Cross-Flow. Suspension of Liquid and Solids is Assumed to Form a Pseudo Slurry Phase. Back-Mixing in All of the Three Considered Phases, Small Bubbles, Large Bubbles and Slurry, is Accounted for using the Axial Dispersion Model (ADM). Energy Balance of the Slurry Phase is Also Included in the Model. the Developed General Reacting Slurry System Model is Used to Simulate the Performance of the Fischer-Tropsch (FT) Slurry Bubble Column (SBC) Reactor. Performance of the Developed ADM based Model is Compared with the Reactor Scale Models in Which the Reactor Back-Mixing is Represented using Some Combination of the Two Limiting Ideal Reactor Models Of, Complete Stirred or Plug Flow. © 2003 Elsevier Science B.V. All Rights Reserved