Effect of liquid and gas physical properties on the hydrodynamics of packed columns

Minne, Ulrich Ludkin (2017-12)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH SUMMARY: To fully utilise the higher capacity and separation efficiency of modern random packings, models are required that are capable of accurately predicting the capacity and separation efficiency of these packings. Since the capacity and separation efficiency in packed columns are influenced by the physical properties of liquids and gases, experimental data with varied liquid and gas physical properties are required for both the development and validation of these models. The aim of this project was to investigate the effect of liquid and gas physical properties on the hydrodynamic behaviour of Intalox Ultra A and O random packing with nominal sizes of 1.5” and 2.5”, respectively. This was achieved experimentally by measuring the pressure drop, liquid hold-up and liquid entrainment for four liquids with different viscosities, densities and surface tensions, and two gasses with different densities, at different liquid flow rates over the entire hydrodynamic range. The pilot plant in which the experimental work was performed had a column diameter of 400 mm and a packed bed height of 3 m. Liquid flow rates of 6, 37, 73, 98 and 122 m3/(m2.h) were investigated. The small open area of the existing pan type distributor restricted the accurate measurement of liquid entrainment. Therefore, it was replaced with a channel-type distributor, doubling the available open area for gas flow to 60 %. A method was developed to identify the loading and flooding points when presented with the experimental pressure drop data, based on the statistical approach of prediction intervals of regressed curves. Overall, this method provides relatively accurate identification of the loading and flooding points at high liquid flow rates, while the use of entrainment data in identifying the flooding point was found to over-predict the flooding point at high liquid flow rates. The high viscosity of silicone oil and ethylene glycol resulted in these liquids having higher pre-loading liquid hold-up compared to that of water and Isopar G. For silicone oil and ethylene glycol, the ratio of viscous forces over the gravitational forces is much larger than for water and Isopar G. Despite the difference in their physical properties, Isopar G and silicone oil produced very similar flooding velocities, which were lower than that of water and ethylene glycol. While the high viscosity of silicone oil resists the flow of liquid down the column, resulting in low capacity, the low density of Isopar G allows the upward drag force of the gas to counteract the gravitational force on the liquid at a lower gas flow rate than the other liquids with higher densities. At the same superficial gas velocity, carbon dioxide, with a higher gas density, produced a higher pressure drop than air/nitrogen, as well as a higher liquid hold-up above the loading point. This is a result of the higher gas kinetic energy of carbon dioxide compared to air/nitrogen at the same superficial gas velocity. The general effect of increasing the packing size from 1.5” Intalox Ultra A to 2.5” Intalox Ultra O is a reduction in both pressure drop and liquid hold-up, as well as an increase in capacity of approximately 11 % at a liquid flow rate of 6 m3/(m2.h), increasing to approximately 37 % at a liquid flow rate of 122 m3/(m2.h). A comparison of the Billet and Schultes, Maćkowiak and Stichlmair model predictions for the experimental data showed that in general all three models predict the pre-loading pressure drop for both packings with all four liquids poorly. Overall, the Maćkowiak model predicts flooding points better than the other two models. The Maćkowiak model is the only model based on the droplet entrainment modelling approach, whereas the Billet and Schultes and Stichlmair models are based on the liquid film modelling approach. The Maćkowiak model is the only model that takes into account the surface tension of the liquid. The experimental pressure drop was also compared to the pressure drop predicted with KG-Tower. The predicted and experimental pressure drop were in good agreement in the pre-loading region, with some deviation at higher gas flow rates. Overall, KG-Tower predicted the pressure drop better than the Billet and Schultes, Maćkowiak and Stichlmair models. The project created an extensive data set of experimental hydrodynamic data, for a range of physical fluid properties, which can be used in both the verification of existing hydrodynamic models and the development of new models.

AFRIKAANS OPSOMMING: Om die verhoogde kapasiteit en skeidingsdoeltreffendheid van moderne ongeordende pakking ten volle te benut, word modelle benodig wat in staat is om die kapasiteit en skeidingsdoeltreffendheid van hierdie pakking akkuraat te voorspel. Aangesien die kapasiteit en skeidingsdoeltreffendheid in gepakte kolomme beïnvloed word deur die fisiese eienskappe van vloeistowwe en gasse, word eksperimentele data met gevarieerde vloeistof en gas fisiese eienskappe benodig vir beide die ontwikkeling en validering van hierdie modelle. Die doel van hierdie projek was om die effek van vloeistof en gas se fisiese eienskappe op die hidrodinamiese gedrag van Intalox Ultra A en O ongeordende pakking, met nominale groottes van onderskeidelik 1.5” en 2.5”, te ondersoek. Dit is behaal deur eksperimenteel die drukval, vloeistof inhoud en vloeistof meesleuring van vier vloeistowwe met verskillende viskositeite, digthede en oppervlaktespannings, en twee gasse met verskillende digthede, by verskillende vloeistof vloeitempo’s, oor die hele hidrodinamiese gebied te meet. Die lootsaanleg waarin die eksperimentele werk uitgevoer is, het 'n kolom deursnee van 400 mm en 'n gepakte bedhoogte van 3 m. Vloeistof vloeitempo’s van 6, 37, 73, 98 en 122 m3/(m2.h) is ondersoek. Die klein oop area van die bestaande pan-tipe verspreider het die akkurate meting van vloeistof meesleuring beperk. Daarom is dit vervang met 'n kanaal-tipe verspreider, wat die beskikbare oop area vir gasvloei verdubbel het tot 60 %. 'n Metode is ontwikkel om die ladingspunte en vloedpunte te identifiseer. Die metode maak gebruik van die eksperimentele drukvaldata en is gebaseer op die statistiese benadering van voorspellingsintervalle van regresseerde kurwes. Oor die algemeen bied hierdie metode relatief akkurate identifisering van die ladingspunte en vloedpunte by hoë vloeistof vloeitempo's, terwyl die gebruik van vloeistof meesleuring data vir die identifisering van die vloedpunt, die vloedpunt oorvoorspel by hoë vloeistof vloeitempo's. Die hoë viskositeit van silikoonolie en etileenglikol het daartoe gelei dat hierdie vloeistowwe hoër vloeistof inhoud in die ladingsgebied het in vergelyking met die van water en Isopar G. Vir silikoonolie en etileenglikol is die verhouding van viskosekragte oor die gravitasiekragte veel groter as vir water en Isopar G. Ten spyte van die verskil in hul fisiese eienskappe het Isopar G en silikoonolie baie soortgelyke vloedpunt snelhede opgelewer, wat laer is as die van water en etileenglikol. Terwyl die hoë viskositeit van silikoonolie die afwaartse vloei van vloeistof in die kolom weerstaan, en gevolglik lae kapasiteit veroorsaak, veroorsaak die lae digtheid van Isopar G dat die opwaartse sleurkrag van die gas die gravitasiekrag op die vloeistof by ‘n laer gasvloeitempo teen werk as vir die ander vloeistowwe met hoër digthede. By dieselfde oppervlakte-gassnelheid het koolstofdioksied, met 'n hoër gasdigtheid, 'n hoër drukval as lug/stikstof ervaar, as ook 'n hoër vloeistof inhoud bo die ladingspunt veroorsaak. Dit is as gevolg van die hoër gaskinetiese energie van koolstofdioksied in vergelyking met lug/stikstof by dieselfde oppervlakte-gassnelheid. Die algemene effek van die verhoging van die pakkingsgrootte van 1.5" Intalox Ultra A tot 2.5" Intalox Ultra O is 'n afname in beide drukval en vloeistof inhoud, sowel as 'n toename in kapasiteit van ongeveer 11 % teen 'n vloeistof vloeitempo van 6 m3/(m2.h), wat verhoog na ongeveer 37 % teen 'n vloeistof vloeitempo van 122 m3/(m2.h). 'n Vergelyking van die Billet en Schultes, Maćkowiak en Stichlmair modelvoorspellings vir die eksperimentele data het getoon dat in die algemeen al drie modelle die voor-ladings-drukval, vir beide van die pakking, met al vier vloeistowwe, swak voorspel. Oor die algemeen voorspel die Maćkowiak model die vloedpunte beter as die ander twee modelle. Die Maćkowiak model is die enigste model wat gebaseer is op die drupel-meesleuring-modellerings-benadering, terwyl die Billet en Schultes en Stichlmair modelle gebaseer is op die vloeistoffilm-modellerings-benadering. Die Maćkowiak model is ook die enigste model wat die oppervlakspanning van die vloeistof in ag neem. Die eksperimentele drukval is ook vergelyk met die drukval wat deur KG-Tower voorspel is. Die voorspelde en eksperimentele drukval het goed vergelyk in die voor-ladingsgebied, met 'n mate van afwyking by hoër gasvloeitempo’s. Oor die algemeen het KG-Tower die drukval beter as die Billet en Schultes, Maćkowiak en Stichlmair modelle voorspel. Die projek het 'n omvattende datastel van eksperimentele hidrodinamiese data, vir ‘n uitgebreide omvang van fisiese vloeistof eienskappe, geskep, wat gebruik kan word in beide die verifikasie van bestaande hidrodinamiese modelle en die ontwikkeling van nuwe modelle.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102978
This item appears in the following collections: