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: Candidate: Prof. Elisabetta Brunazzi Domenico Mangiaracina Prof. Wolfgang Arlt Sebastian Schug, M. Sc. Prof. Roberto Mauri Academic year 2015/2016 i Gran parte del progresso sta nella volontà del progredire. Seneca Il dizionario è l'unico posto dove successo viene prima di sudore. Vince Lombardi ii iii 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. iv v 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 vi 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 SYSTEM .......................................................................................................... 49 3.2 EXPERIMENTAL PROCEDURE ........................................................................................................................... 51 3.3 EXPERIMENTAL CAMPAIGN .............................................................................................................................. 52 3.4 IMAGE PROCESSING ........................................................................................................................................... 53 3.4.1 IMAGE PROCESSING WITH IMAGEJ ......................................................................................................