Abstract
Trickle-bed reactors are widely used in industry. These reactors generally are operated at high pressure. In the literature the studies on the design and scale-up parameters have been mainly performed under atmospheric conditions. It is unknown whether the findings of these studies can be extrapolated to much higher pressure. It is noteworthy that such reactors are usually designed and scaled-up based on data obtained in laboratory scale units. 1n such small scale reactors, which use the same catalyst sizes and shapes of the commercial units, wall effect, ax.ial dispersion and liquid maldistribution and hence incomplete catalyst wetting are encountered due to low liquid velocities. Diluting the bed with fines (small, inert and nonporous particles) is recommended to overcome these shortcomings. No study has appeared in the literature which quantifies the effect of fines on liquid-solid contacting efficiency, pressure drop and liquid holdup. In this study_a high pressure trickle-bed reactor facility has been designed and developed. The effects of high pressure and gas flow rate on pressure drop, liquid holdup and liquid-solid contacting efficiency have been investigated. It was found that at high pressure operation and high gas flow rate, pressure drop increases considerably, liquid holdup decreases significantly, and liquid-solid contacting efficiency improves noticeably. A phenomenological analysis has been developed in this study which describes these effects properly. A new model based on phenomenological consideration to predict liquid-solid contacting efficiency at high pressure has been developed. It predicts the measured contacting efficiency at elevated pressure to within± 10% margin. Holub's phenomenological model (I 990) for pressure drop and liquid holdup prediction was found to predict these parameters at high pressure better than the recently reported empirical correlations based on high pressure data. Effects of fines on liquid-solid contacting efficiency, pressure drop and liquid holdup have been investigated. A reproducible procedure to pack the bed with a mixture of catalyst and fines has been developed which is based on filling the bed voidage with fines. lts reproducibility was quantified by pressure drop and liquid holdup measurements. It was found that fines improve liquid-solid contacting efficiency as well as increase pressure drop and liquid holdup. The effect of the degree of the bed dilution on contacting efficiency, pressure drop, and liquid holdup was also investigated . The contacting efficiency in a highly diluted bed was found to be approximately similar to that obtained in a diluted bed packed according to the developed reproducible procedure. TABLEO F CONTENTS Page List of Tables V List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii Dedication Chapter I. Introduction . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Scope ... ... ... ... ... .. . . . . .. ... ... ... ... .. . .. . ... .. . . .. .. . ... ... ... . .. . .. ... 1 Motivation . . . . . . . . . . . . . . . . . . .. . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. . . . . . . . . . 7 Research objectives . . .. . .. . . . . . . . . . . . . ... ... . .. ... ... . .. . .. . . . . ... ... ... .. 10 2. Design of high pressure trickle-bed reactor facility ... ... ... ... ... ... .. 11 High pressure trickle-bed reactors set-up . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Reactor's packed bed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Liquid / gas distributor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Packed bed support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Gas/ liquid separator .. .. .... ...... .... .. ...... ...... .. .. .. .. .. .. .. .. . 21 Liquid delivery system .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . 23 Gas delivery system .. .. .. .. .. . . . . . . . . . .. . . . . . . .. . . .. . . . . . . . .. . . . . . . . . . .. . 24 Tracer technique set-up 26 Data acquisition system 28 3. Effect of high pressure on pressure drop and liquid holdup .. .. .. .. .. . 32 Background . . .. . .. . .. .. . .. . .. . .. . . . . . . .. . .. . . .. . .. . . . . .. . . . . . . . .. . .. . .. . .. . 32 Holub's phenomenologicalm odel ...................................... 39 Phenomenologicala nalysis of the effect of reactor pressure and gas flow rate on pressure drop and liquid holdup .. .. .. . .. .. .. .. 44 II Experimentali nvestigation . .. . .. ... .. . ... ... ... .. . ... ... ... ... . .. . .. . ... . 47 Pressure drop and liquid holdup measurements . . . . . . .. . . .. .. . ... . 47 Operating conditions investigated . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Results and data analysis . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Validity of Holub's model and of other recent correlations . . . . . ... 74 4. Effect of high pressure on external liquid-solid contacting efficiency 82 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Phenomenologicalm odel and analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Experimentali nvestigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 External liquid-solidc ontacting efficiency determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Operating conditions investigated ... . . . .. . . .. ... ... ... ... ... ... ... .. 106 Results and data analysis . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .. . I 08 The effect of high pressure and gas flow rate on contacting efficiency . . . ... ... . .. ... . . . .. . . . . . .. . ... ... . 112 The developed model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 5. Effect of fines on external liquid-solidc ontacting efficiency, pressure drop, and liquid holdup .. .. . . . . . . . .. . .. . . . . .. . .. . ... .. . .. . ... . .. . 122 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 A reproducible procedure for packing a laboratory trickle-bed reactor with a mixture of catalyst and fines .. .. . . . . . . . . 125 The developed procedure .. . .. .. . .. . ... ... ... .. . ... ... . . . . . . . . . . ... .. . 127 Portion of catalyst by portion of fines packing procedure .. ... ... ... ... ... ... ... ... ... . .. . .. .. .. ... .. . 127 Whole bed packing procedure . . .. . .. ... . . . . . . . .. . . .. ... ... . .. 129 Quantificationo f reproducibilityo f the developed procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . .. . .. . . . I 30 iii Experimental investigation .. ... ... .. . .. . .. .. . ... ... . .. . ... ... ... ... ... ... 137 Parameter determination . ... ... ... .. . .. ... ... . . .. .. . ... ... ... ... . .. ... 137 Pressure drop and liquid holdup measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Liquid-solid contacting efficiency determination . . . . . . . . . . . . .. . .. . . . . .. . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . I 37 Operating conditions investigated ... ... ... ... ... ... ... ... ... . .. . .. .. 142 Results and data analysis . .. . . .. ... ... .. . . .. ... ... ... . . . . . . . . .. . .. ... . 144 Effect of fines on pressure drop and liquid holdup ... ... .. . .. . .. . .. ... ... ... ... . .. . .. . ... ... ... ... ... . 144 Effect of fines on liquid-solidc ontacting efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 6. Conclusionsa nd recommendations ......................................... 157 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 7. Appendices .................................................................... 162 Sample of a data acquisition program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 Getting started . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 DPT.BAS program .................................................... 164 Trickle-bed reactor operating procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 8. Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 9. References .................................................................... 174 10. Acknowledgments ............................................................ 184 I I. Vita 186 iv LIST OF TABLES Page I. I Characteristic parameters of a trickle-bed reactors 2 1.2 The main advantages and disadvantageso f trickle-bed reactors . .. . .. . . 3 I. 3 Macroscale and microscale design parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. I Hardware for the data acquisition system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 2.2 Instruments connected to the data acquisition system .................... 31 3.1 Recent correlations for pressure drop and liquid holdup based on data obtained at high pressure and Holub's (1990) model ............... 37 3.2 Experimental methods used to measure liquid holdup in packed-beds .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 3.3 Range of covered operating conditions . .. . ... . . . . .. ... ... . .. .. . .. . . . . . . . . .. 52 3.4 Physical properties of liquid-gas systems at 298 K and 1 atm . . . . . . . . . . 53 3.5 Packed bed characeteristics 53 3.6 Measured Ergun constants 74 3. 7 Comparison of Holub's model (1990) prediction and high pressure data for pressure drop and liquid holdup .......................... 75 3.8 Comparison of models to data ............................................... 77 4.1 External contacting efficiency review . ... .. . ... .. . . . . .. . .. . . .. ... ... ... . .. . 84 4.2 Methods used to evaluate the external contacting efficiency 94 4.3 Expressions for the moments of infinite cylinder catalyst for a nonvolatile and nonadsorbingt racer (EI-Hisnawi, 1981) ........ 100 V
Committee Chair
M. P. Dudukovic
Committee Members
P.A. Ramachandran
Degree
Doctor of Science (DSc)
Author's Department
Chemical Engineering
Document Type
Restricted Dissertation (Restricted to WashU only)
Date of Award
12-1-1993
Language
English (en)
Recommended Citation
AL-Dahhan, Muthanna H., "Effects Of High Pressure And Fines Onthe Hydrodynamics Of Trickle - Bed Reactors" (1993). Chemical Engineering Theses and Dissertations. 2.
https://repository.library.washu.edu/chemeng_etds/2
Comments
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