Liquid holdup in packed columns

122 Pages·04.508 MB·English

by  Melrose, Richard E

LIQUID HOLDUP IN PACKED COLUMNS
A Thesis
Presented to
the Faculty of the School of Engineering
The U niversity of Southern California
In P a rtia l Fulfillm ent
of the'Requirements for the Degree
Master of Science in Chemical Engineering
by
Richard E. Melrose
June 1950
UMI Number: EP41731
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This thesis, written by
Richard E. Melrose
under the guidance of hi.s.... Faculty Committee,
and approved by all its members, has been
presented to and accepted by the Council on
Graduate Study and Research in partial fulfill­
ment of the requirements for the degree of
Master of Science in
Chemical Engineering
Date
Faculty Committee
I Chairman
'jgL&aMe*L
SUMMARY
The liquid holdup in packed columns was inves­
tigated using four different packings, three liquids,
and two sizes of columns. The investigation was di­
vided into a study of the liquid which wets the pack­
ing (static holdup) and the liquid which is in the
voids of the packing under operating conditions (oper­
ating holdup).
Static holdup was found to be dependent on the
packing m aterial to a large extent. With packing which
is non-absorbent and is completely wet by the liquid,
static holdup for liquids and packings used in th is in­
vestigation may be expressed by the equation:
Hs r 0.029( /i2 S/ r yo g0)*°74
With absorbent packing, most of the sta tic hold­
up may be liquid absorbed in the packing m aterial and
w ill depend on the porosity of the m aterial. If the
packing surface is liquid repellent, drops w ill collect
on the surface and in the crevices, and the above equa­
tion does not apply.
Operating holdup was found to follow the equation:
H0 r KL’f
where K and f are functions of the packing and liquid
being used. Operating holdup is independent of the
liquid disperser, and is not affected by repacking the
column. Increasing the size of the packing or re ­
ducing the column diameter reduces operating holdup.
When foaming occurs, operating holdup increases and
does not follow the above equation.
TABLE OF CONTENTS
CHAPTER! PAGE
I. INTRODUCTION.......................................................... 1
The problem ........................................ . . 1
Statement of the problem . . . . • 1
Importance of the s tu d y ......................... 2
Definitions of terms u s e d ........................ 4
II. REVIEW OF THE LITERATURE............................. 7
General r e v i e w ................................................ 7
Relation to absorption rate .................... 8
Effect of gas v e l o c i t y ............................. 11
Effect of column d ia m e te r........................ 11
S tatic holdup ..................................................... 12
Holdup in packed d istilla tio n columns 12
Theoretical considerations .................... 13
I II. EXPERIMENTAL WORK ........................................... 14
Apparatus .............................. 14
Operating holdup .................................. 14
Static holdup ............................................ 18
M aterials . . . . . .................................. 19
Liquids . . . ....................................... 19
Packings ..................................................... 22
Measuring devices .................................. 22
Experimental procedure ............................. 28
V
CHAPTER PAGE
Static h old u p .................................................... 29
Absorption of liquid by the
packing .......................................................... 30
IV. EXPERIMENTAL RESULTS................................... 31
Effect of liquid d isp ersers.................. y £
E ffect of operating time on
steady-state operation ........................ 33
Effect of column d iam eter.......... 33
Effect of repacking the column . . . 33
D istinguishing between operating
and static h old u p ....................................... 33
Static holdup . ....................................... 49
Discussion of experimental
methods .......................................................... 52
Static holdup results .................................. 33
Operating holdup ........................................... 59
Variables considered .................................. 59
Operating holdup resu lts ........................ 6l
Effect of foam ing............................. 69
Effect of packing size and shape . . 72
V. SUMMARY AND CONCLUSIONS................................ 73
NOMENCLATURE............................................................................. 73
CHAPTER PAGE
BIBLIOGRAPHY.................................................... 81
APPENDIX A. Sample c a lc u la tio n s ....................... 83
APPENDIX B. Experimental data and
LIST OF TABLES
TABLE PAGE
I. Liquid Physical P r o p e r t i e s .......................... 23
II. A. S. T. M. D istillatio n of the
K e ro s e n e .................................................... 24
III. Packing Properties ............................................. 25
IV. Effect of Operating Time on
stead y-state...................................... 34
V. Effect of Viscosity on T0 .............................. 48
VI. Static Holdup Summary .................................... 56
VII. Operating Holdup Equation
Constants .......................................................... 68
VIII. Operating Holdup Sum m ary............................. 73
LIST OF FIGURES
FIGURE PAGE
1. Results of Other I n v e s t i g a t o r s .............................. 10
2. Schematic Diagram of Operating Holdup
Equipment ......................................................................... 1.5
5* Photograph of Operating Holdup
Equipment ......................................................................... 17
4. Schematic Diagram of S tatic Holdup
Equipment ......................................................................... 20
5* Photograph of S tatic Holdup Equipment . . . . 21
6. Photograph of the Packings U s e d .............................. 26
7. Effect of Liquid Dispersers on
Operating H o ld u p .......................................................... 22
8. Drainage Rate of Water from l/2"
Raschig Rings ............................................................... 37
9. Drainage Rate vs. Adjusted Time ......................... 27
10. Drainage Rate of Water from 1”
Raschig Rings ............................................................... 39
11. Drainage Rate vs. Adjusted T im e.............................. 39
12. Drainage Rate of water from 1-1/2”
Raschig Rings ............................................................... 40
12. Drainage Rate vs. Adjusted Time ......................... 40
14. Drainage Rate of Water from 1”
Berl Saddles . . . . . . . . . . . . . . . 41