Linear Attenuation Coefficients and Gas Holdup Distributions in Bubble Column with Vertical Internal for Fischer-Tropsch (FT) Synthesis

Transcription

1 4/26/207 Linear Attenuation Coefficients and Gas Holdup Distributions in Bubble Column with Vertical Internal for Fischer-Tropsch (FT) Synthesis Abbas J. Sultan, Laith S. Sabri, and Muthanna H. Al-Dahhan Department of Chemical and Biochemical Engineering, Missouri University of Science and Technology, Rolla, MO USA

2 Presentation Outline Introduction Motivations Results and Discussion Remarks Acknowledgment 4/26/207 2

3 Introduction & Motivation The conversion of natural and bio gas, coal, and biomass to liquid fuels and chemicals vis synthesis gas is currently of interests to the energy and chemical industries which represents a valuable addition to diversifying in fuels and products resources. X Coal Biomass Natural Gas Gasification G Syngas Processing Fischer- Tropsch Synthesis Syncrude Refining & Upgrading L Fuel & Chemicals The key route for the conversion synthesis gas to liquid fuels and chemicals (GTL) technology is the Fisher-Tropsch (FT) synthesis where the reaction of syngas (H 2 and CO) over catalyst into liquid hydrocarbons takes place. FT synthesis is highly exothermic and hence intense heat exchanging tubes (internals) are needed to control the temperature. H 2 +CO (syngas) F-T waxes (C -C 00+ ) H 2 O Water steam 4/26/207 3

4 Bubble/Slurry bubble column reactor with vertical dense heat exchanging tubes is one of the reactors of choice to conduct the highly exothermic FT reaction. The presence of the dense heat exchange tubes (internals) impacts the hydrodynamics and mixing behavior of the reactor in a very complex way and hence, it will affect the performance, selectivity and the yield. The understanding of such complexity has been completely lacking due to lack of implementing advanced measurement techniques. Gas holdup distribution is the one of the important hydrodynamic parameters governing the dynamic of the bubble/slurry bubble columns where gas holdup drives the liquid circulation, and hence the rate of mixing, mass, and heat transfer. There is a lack of detailed investigation to understand the effect of the intense internals on the gas holdup distribution. Therefore, the focus of this work is to investigate, visualize, and quantify for the first time the influence of the size, and configurations of the intense heat exchanging tubes (internals) at wide range of the superficial gas velocity on the time-averaged cross-sectional gas holdup distribution and their radial/diametrical profiles by implementing non-invasive gamma-ray computed tomography (CT) technique. 4/26/207 Slurry bubble columns with vertical internals Industrial heat exchanging tubes (internals) 4

5 Experimental step up 7.62 cm Dynamic level, L/D=0.3 (58 cm) 4 cm ID The internals was designed to cover 25% of the crosssectional area of the column to mimic the bundle of heat exchanging tubes used in FT synthesis. 83 cm Scan level, L/D=5. (78 cm) 2.54 cm O.D Plexiglas internals Circular configuration (supports) Schematic diagrams and pictures of the circular configurations (spacers/supports) for 0.5, and -inch internals Distributor 30 cm Compressed air in Drain Schematic diagram of 6-inch bubble column equipped with vertical internals Schematic diagram and photo of the stainless steel distributor (perforated plate) 4/26/207 5

6 Gamma ray Computed Tomography (CT) Technique Detectors collimator Top supporter Cs-37 source Lead shield Bubble column with internals Source collimator Bubble column with internals NaI detector Detector collimator Bottom supporter CS-37 source Source collimator 5 NaI detectors CO-60 source Aluminum structure Threaded rods Source collimator Bubble column with internals Detectors collimator (2 mm 5 mm) 5 NaI detectors Photo of dual-source gamma-ray computed tomography (CT) technique with bubble column during CT scan Cs-37 source Circular plate Square plate Steeper motor To the data acquisition system.60 samples at 0 Hz, which took about 8.25 hours for a full scan Flowmeters Motor Chain driver Schematic diagram of single gamma-ray computed tomography (CT) technique with bubble column Scanning a bubble column equipped with dense vertical internals 4/26/207 6

7 Dual Source Computed Tomography (DSCT) Technique 6-inch Bubble Column without internals Bubble column reactor with 0.5-inch stainless internals 6-inch Bubble Column reactor with 0.5 & Plexiglas Internals Electronics and data acquisition system for CT technique 4/26/207 7

8 CT Scan Validation by Phantom Linear attenuation coefficient,cm Dimensionless radius,r/r(-) Cross-sectional linear attenuation coefficient distribution(cm - ), and diameter profile for phantom Case I for case I (empty phantom) Linear attenuation coefficient,cm Dimensionless radius,r/r (-) Cross-sectional linear attenuation coefficient distribution(cm - ), and diameter profile for phantom case II (the inner cylinder filled with water) Liner attenuation coefficient,cm - Dimensionless,radius,r/R (-) Linear attenuation coefficient,cm Dimensionless radius,r/r (-) Cross-sectional linear attenuation coefficient, distribution (cm - ), and diameter profile of linear for phantom for case IV (the inner and outer cylinders filled with water) Cross-sectional linear attenuation coefficient distribution(cm - ), and diameter profile for phantom for case III (the outer cylinder filled with water) 4/26/207 8

9 Results and Discussion Linear attenuation coefficient distribution (μ, cm - )for a bubble column with and without internals Linear attenuation coefficient distribution for a bubble column without internals: (a) empty column, (b) column filled with water, and (c) column with air-water at superficial gas velocity 45 cm/s Linear attenuation coefficient distribution for a bubble column equipped with 0.5-inch internals: (a) empty column, (b) column filled with water, and (c) column with air-water at superficial gas velocity 45 cm/s The reconstructed linear attenuation images clearly show that the CT technique was able to capture and reproduce the arrangement and location of each of the internals as well as of the column wall. These images confirm the quality of this CT technique and also the image reconstruction algorithm (AM). Hence, the CT is capable of capturing a small maldistribution in the multiphase reactor if it exists and it provides reliable cross-sectional gas holdup distribution to validate CFD simulations and hydrodynamics models. 4/26/207 Linear attenuation coefficient distribution for a bubble column equipped with.0-inch internals: (a) empty column, (b) column filled with water, and (c) column with air-water at superficial gas velocity 45 cm/s 9

10 Gas holdup (-) Gas holdup(-) Gas holdup (-) Effect the size of the internals on the time-averaged cross-sectional gas holdup distributions and their diameter profiles in a 6-inch bubble column with or without internals at different superficial gas velocities (5, 20, and 45 cm/s) calculated based on the free cross-sectional area (FCSA) for the flow at 5 cm/s at 20 cm/s at 45 cm/s 5 cm/s 20 cm/s 45 cm/s Bubble column without internals Dimensionless radius,r/r(-) at 5 cm/s at 20 cm/s at 45 cm/s cm/s 20 cm/s 45 cm/s Bubble column with 0.5-inch internals Dimensionless radius,r/r(-) at 5 cm/s at 20 cm/s at 45 cm/s 5 cm/s 20 cm/s 45 cm/s Dimensional radius,r/r(-) 4/26/207 Bubble column with -inch internals 0

11 Gas holdup,(-) Gas holdup,(-) Gas holdup,(-) Impact of tubes bundle arrangements (hexagonal, circular, circular and one tube at center) on gas holdup distribution and their radial profiles circular circular & tube hexagonal 5 cm/s Hexagonal configuration 20 cm/s Hexagonal configuration 5 cm/s Circular configuration 20 cm/s Circular configuration 5 cm/s Circular & tube at center configuration 20 cm/s Circular & tube at center configuration Dimensionless radius,r/r (-) 5 cm/s circular circular & tube hexagonal Dimensionless radius,r/r (-) 20 cm/s circular circular & tube hexagonal 45 cm/s Hexagonal configuration 4/26/ cm/s Circular configuration 45 cm/s Circular & tube at center configuration Dimensionless radius,r/r (-) 45 cm/s

12 Gas holdup(-) Gas holdup,(-) Quantification the effect of the size and internals configurations on the gas holdup distribution and their diameter profiles at superficial gas velocity 45 cm/s 0.8 without internals with 0.5-inch internals with.0-inch internals Dimensionless radius,r/r(-) Comparison between the azimuthally averaged gas holdup profiles for bubble columns with (0.5 and -inch) or without internals at superficial gas velocity (45 cm/s) based on the free cross-sectional area (FCSA) for the flow 0.8 circular circular & tube hexagonal Dimensionless radius,r/r (-) Comparison between the azimuthally averaged gas holdup profiles for 4/26/207 bubble columns with different configurations of internals at superficial gas velocity (45 cm/s) based on the free cross-sectional area (FCSA) for the flow 2

13 Remarks For the first time, cross-sectional gas holdup distributions and their diametrical profiles were visualized and quantified at different internal sizes, configurations, and superficial gas velocities to study and assess these parameters. The reconstructed CT images show that the bubble columns equipped with or without internals displayed a symmetric cross-sectional gas holdup distribution for all studied superficial gas velocities. However, the bubble column with -inch internals (sparse arrangement) produced a more symmetric distribution than the bubble column equipped with 0.5-inch internals (dense arrangement). The design of the configurations of internals affect significantly on the gas holdup distribution especially at the core and wall region of the reactor The reconstructed linear attenuation coefficients (μ, cm- ) values are close to the theoretical values. The comparison shows good agreement of these for empty columns and bubble column equipped with internals The gamma-ray computed tomography technique was capable of capturing the wall thickness of a column and the internals. The present work provides, for the first time, benchmarking data to validate reactor models and computational fluid dynamics (CFD) simulations and consequently will facilitate the design and scale-up of bubble column with internals. 4/26/207 3

14 Acknowledgements The authors gratefully acknowledge the financial support in the form of a scholarship provided by the Higher Committee for Education Development in Iraq (HCED), Ministry of Higher Education and Scientific Research (Iraq), and the funds provided by Missouri S&T and Professor Dr. Muthanna Al-Dahhan to develop the CT technique, the experimental set-up, and to perform the present study. Also, the authors would like to thank Dr. Fadha Ahmed,and Mr. Jianbin Shao for his help with the gamma-ray computed tomography (CT) technique. 4/26/207 4

15 Computed Tomography (CT) For Phase Distribution Measurements S0

16 Radioactive Particle Tracking (RPT) δ Sc R R2 Parylene N Sc 46 particle coated with parylene-n, tracking solids Sc 46 particle in polypropylene ball, tracking liquid Picture of RPT In Situ Manual RPT Calibration Tracer particle holding assembly

17 An On-line Technique Using NGD as Gamma Ray Densitometry (GRD) 35 cm cm Source Detector 35 cm For Pinpointing Flow Pattern (Regime), Radial/Diameter Profile of Phases Holdups Mal-distribution identification & Reduced Tomography 3.6

18 Other Selected Sophisticated Techniques at Glance Heat Transfer Coefficients Mass Transfer Probes Gas/Liquid Dynamics Tracer Techniques Optical Probes in Packed bed DC Power PC Amplifier Heat transfer probe DA Q Sol- Gel Overcoat Light going to the probe tip (475 nm) Gas-Solid optical probes Rigs Pressure Transducers Pebble bed unit P F I D A m

19 Radioisotope Laboratory for Advancing Industrial Multiphase Processes

20 Dual Source Computed Tomography (DSCT) Technique

21 Non-Radioisotope Laboratory for Advancing Industrial Multiphase Processes

22 Microalgae Laboratory (Biological Lab)

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