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Scuola di Ingegneria

Dipartimento di Ingegneria Civile e Industriale

Master’s Degree in Chemical Engineering

Investigation of fluid behavior in randomly packed

columns using Computed Tomography

Supervisors:

Prof. Elisabetta Brunazzi

Prof. Wolfgang Arlt

Sebastian Schug, M. Sc.

Prof. Roberto Mauri

Candidate:

Domenico Mangiaracina

Academic year 2015/2016

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Gran parte del progresso sta nella volontà del progredire.

Seneca

Il dizionario è l'unico posto dove successo viene prima di sudore.

Vince Lombardi

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Abstract

University of Pisa - Department of Civil and Industrial Engineering

Master Thesis in Chemical Engineering

Investigation of the fluid behavior in randomly packed columns using Computed Tomography

Domenico Mangiaracina

The qualitative investigation of the fluid behavior and the quantitative evaluation of

widespread fluid dynamic parameters like liquid hold-up, wetted area and mass-transfer area

in a randomly packed column are carried out using Computed Tomography CT, a totally non-

invasive measuring technique. Despite the huge effort of different researchers, a lack of

comprehension about the flow field within the packed bed still prevents the development of

completely satisfying models, that are precisely able to predict these fluid dynamic

parameters in order to achieve an economically optimized design of the column.

In the present work, three commercial random packings (Raflux Ring, RMSR and RSR),

belonging to different generations, are scanned in a 0.1 m diameter column in presence of two

different systems: water / air and isopropanol /air. The latter is used for the first time in CT

investigations despite the common industrial applications of these organic compounds. An

algorithm, previously developed by Schug and Arlt. [1], is applied to compute the profile and

the integral values of fluid dynamic parameters along the packed bed, highlighting the effect

of the liquid load (ranged between 2 m3 / m2 h and 70 m3 / m2 h), the gas load (ranged

between 0 Pa0.5 and 2 Pa0.5), the packing type.

The main aims of the present work are summarized in two points: firstly, the investigation of

the effect of the column’s re-packing and on the variance of the fluid dynamic parameters. The

results show an extremely weak effect of the re-packing of the column, with deviation less

than 4 % in terms of coefficient of variation for each fluid dynamic parameter. Secondly, these

parameters are evaluated with an organic liquid (isopropanol) to assess the combined

influence of significantly different physical properties like viscosity and surface tension. A

better wettability of the packing and a higher mass-transfer area is recorded. Furthermore, a

graphical qualitative evaluation of the liquid flow morphology and a successive classification

of the present liquid structures (films and rivulets) are conducted.

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Contents

ABSTRACT ......................................................................................................................................................................... IV

LIST OF FIGURES ................................................................................................................................................................ X

LIST OF TABLES ........................................................................................................................................................... XVIII

SYMBOLS .......................................................................................................................................................................... XX

1. INTRODUCTION ................................................................................................................................................... 1

1.1 OBJECTIVES AND AIMS ....................................................................................................................................... 1

1.2 STRUCTURE OF THE THESIS ............................................................................................................................... 2

2 LITERATURE REVIEW ......................................................................................................................................... 4

2.1 PACKED COLUMNS .............................................................................................................................................. 4

2.1.1 OPERATING PRINCIPLES AND PACKING TYPES .................................................................................... 4

2.1.2 FLUID DYNAMIC PARAMETERS ............................................................................................................. 11

2.1.2.1 Pressure drop estimation ....................................................................................................... 11

2.1.2.2 Liquid hold-up ............................................................................................................................ 14

2.1.2.3 Flow morphology....................................................................................................................... 17

2.1.2.4 Wetted Area ................................................................................................................................. 19

2.1.2.5 Mass-transfer Area .................................................................................................................... 19

2.1.3 MASS-TRANSFER THEORIES AND PACKING HEIGHT DETERMINATION .......................................... 20

2.1.3.1 Mass-transfer theories ............................................................................................................ 20

2.1.3.2 Packing Height determination .............................................................................................. 22

2.1.3.3 Experimental evaluation of wetted and mass-transfer area .................................... 24

2.1.4 LIQUID MALDISTRIBUTION IN RANDOM PACKINGS ........................................................................... 26

2.1.4.1 Effect on HETP ............................................................................................................................ 26

2.1.4.2 Main causes .................................................................................................................................. 27

2.1.4.3 Liquid maldistribution effects .............................................................................................. 28

2.2 COMPUTED TOMOGRAPHY ............................................................................................................................... 30

2.2.1 INTRODUCTION ....................................................................................................................................... 30

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2.2.2 OPERATION PRINCIPLE .......................................................................................................................... 31

2.2.3 X-RAYS - MATTER INTERACTION .......................................................................................................... 32

2.2.4 HARDWARE: DESCRIPTION OF THE MAIN COMPONENTS .................................................................. 34

2.2.4.1 Source of X-rays ......................................................................................................................... 35

2.2.4.2 Detector ......................................................................................................................................... 36

2.2.4.3 Gantry-System and Computer-System .............................................................................. 36

2.2.5 IMAGES RECONSTRUCTION .................................................................................................................... 37

2.3 PREVIOUS INVESTIGATIONS OF PACKED COLUMNS USING CT ...................................................................... 40

3. MATERIALS AND METHODS ............................................................................................................................. 46

3.1 EXPERIMENTAL SET-UP.................................................................................................................................... 46

3.1.1 EXPERIMENTAL SET-UP DESCRIPTION ................................................................................................ 46

3.1.2 SCANNED PACKING TYPES ..................................................................................................................... 47

3.1.2.1 Raflux Ring ................................................................................................................................... 48

3.1.2.2 RSMR (RVT Metal Saddle Ring) ........................................................................................... 48

3.1.2.3 RSR (Raschig SuperRing) ....................................................................................................... 48

3.1.3 CUSTOM-DESIGNED CT SYST