Browsing by Author "Minne, Ulrich Ludkin"
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- ItemEffect of liquid and gas physical properties on the hydrodynamics of packed columns(Stellenbosch : Stellenbosch University, 2017-12) Minne, Ulrich Ludkin; Schwarz, C. E.; Burger, A. J.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.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.