Browsing by Author "Lamprecht, Johannes Hendrik"

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    Characterisation of liquid distribution and behaviour within randomly packed columns using electric impedance tomography
    (Stellenbosch : Stellenbosch University, 2022-04) Lamprecht, Johannes Hendrik; Burger, Andries Jacobus; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH SUMMARY: The optimum design of column internals plays a prominent role in the economic viability of distillation setups, due to such internals’ notable contribution to both operating and capital costs. Progression in both our understanding and characterisation of column internals is therefore paramount. Both hydrodynamic and kinetic characterisation methodologies consider the influence of the vapour-liquid interface, whether directly (effective interfacial area) or indirectly (pressure drop and liquid hold-up). Most of the random packing literature, however, focuses on the evaluation of macro parameters (e.g. pressure drop, holdup, flow rates, packing dimensions and fluid physical properties), with notably less attention to the fluid behaviour at a micro level (e.g. droplet formation, distribution and rivulet formation). This limits the fundamental basis of the available models, introducing numerous regressed empirical constants. In other words, while modern random packing designs are strongly influenced by the optimisation of inter-packing droplet and rivulet formation, the available mathematical models lack predictive capabilities of such micro-behaviour. Against this background, and in pursuit of a better understanding of fluid behaviour and distribution in random packing, an Electrical Impedance Tomography (EIT) measurement system was designed and constructed to visualize and quantify liquid distribution behaviour inside randomly packed columns. The EIT system was preferred to conventional X-Ray tomography, due to a) safety, b) cost-effectiveness, and c) simplicity, while it can be utilised for both conducting and non-conducting liquids. The sensor of the EIT system consisted of a stainless-steel wire matrix, installed at a horizontal plane directly below 3m random packing in a 400mm diameter column. It provided 1369 measuring points, with measuring frequencies of 207 Hz and 21 Hz for conductive and non-conductive liquids, respectively. The data were processed using 2-D and 3-D image processing algorithms to enable quantification of individual liquid elements. The individual elements were evaluated based on their reconstructed volume, surface area and sphericity. The experimental characterisations were used to evaluate the liquid distributions inside two types of industrial random packing, FlexiRing® and Intalox® Ultra, at sizes ranges between 1.5” to 2.5”. The evaluations considered various liquid- and vapour loadings using both water and ethylene glycol to vary the liquid physical properties; water being electrically conductive and ethylene glycol being predominantly non-conductive. The presented results show increased element uniformity in favour of the Intalox® Ultra throughout and illustrated the presence of a force-balance transition in the mechanism of liquid hold-up creation. This indicated the transition from conglomerating inter-packing liquid (IPL) streams, towards droplet-creation. The onset of this transition was found distinctly related to the relative velocity profiles and vapour - liquid shear forces of the respective packings. The contribution of droplets in the inter-packing space to the total vapour-liquid interfacial area was also evaluated. The Intalox® Ultra presented ca 17% and 9.4% increase in total reconstructed surface area for the respective 2” and 1.5” equivalent comparisons with FlexiRing® (for the air-water system). This confirmed the applicability of the EIT characterisation system for both hydrodynamic and kinetic prototyping. Several novel contributions were developed in this work. These are: [1] The development of a characterisation methodology based on EIT for better understanding of inter-packing liquid distributions. [2] Novel experimental inter-packing distribution data for IPL element-volumes and -areas and their relation to: i. packing type, ii. liquid and vapour loadings, and iii. liquid physical properties. [3] Presenting the existence of a packing-specific transitional point, based on liquid and vapour loadings, where the mechanism of liquid hold-up changes. This point marks the cross-over between the conglomeration of inter-packing liquid elements into streams, and their break-up/ redistribution into smaller elements. This alludes to a possible increase in interfacial turbulence (decreasing liquid phase resistance to mass transfer) while adding to the understanding of the pressure drop mechanisms in packed columns. [4] Presenting the total IPL element-surface area as a comparative kinetic characterisation parameter for use in prototyping. This is posed to assist in the design of future packings, in finding the optimum packing area and structure to minimize entrainment and maximize efficiency.
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    The development of simplistic and cost-effective methods for the evaluation of tray and packed column efficiencies
    (Stellenbosch : Stellenbosch University, 2017-03) Lamprecht, Johannes Hendrik; Burger, A. J.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH SUMMARY: Phase contacting column internals are manufactured through a series of punching, die moulding and bending. Although cost-effective on a large scale, this process is considered unfavourable for prototyping, as it is both time-consuming and expensive. This limits designer creativity and introduces extended waiting periods between the design, fabrication and evaluation phases. This translates into development timelines in excess of two years. During the evaluation stage, efficiencies are conventionally measured using hydrocarbons system at total reflux. This introduces notable constraints on the prototype packing and tray material, due to the high temperatures and pressures required for these tests. Therefore, this research project focused on the development and experimental validation of two simplistic and cost effective methods that can be used to quantify column internal efficiency. The ADIBAA (aqueous desorption of isobutyl acetate in air) and HA (Humidification of air) methods are hereby proposed for efficiency measurements in packed and tray columns respectively. For validation of both methods, two separate pilot plant facilities were designed and constructed, one at Stellenbosch University and one at an industrial research laboratory. The ADIBAA-method involved using a liquid phase limiting system to isolate the performance parameters in the liquid phase. The combination of the method and experimental setup offered rapid quantification, while remaining cost-effective and environmentally friendly. The ADIBBA-method was experimentally validated in a 400mm diameter stainless steel packed column, with a bed height of 1.1 metre. Such validation entailed (a) experimental measurement of isobutyl acetate concentrations, (b) calculation of volumetric liquid phase mass transfer coefficients and (c) comparison of these calculated coefficients with predictions by four independent correlations from literature. Agreement between the literature correlations and the newly-determined experimental data was found to be within 10%. The applicability of the ADIBAA-method, in evaluating column internal efficiencies, was confirmed through comparison of 1.5’ FlexiRings® and the equivalent Intalox® Ultra™. A quantifiable improvement of 15% was recorded in the preloading regime, in favour of the Intalox® Ultra™. Further justification of the ADIBAA-method was presented in the evaluation of 2.5’ Intalox® Ultra™ packing. The HA-method, proposed to use for tray columns, focused on the evaluation of Murphree tray efficiencies. This method offered large improvements over the constant reflux method in terms of environmental and safety considerations, while also reducing the experimental time by an order of magnitude. A rectangular tray column with respective weir and flow path lengths of 762mm and 870mm was used in the experimental evaluation. The HA-method was found to adequately quantify hydrodynamic variations in both weeping and vapour bypass. The comparative ability of the method was experimentally verified by relating a 12% open area sieve tray with two separate prototypes. The method enabled rapid evaluation and quantitatively illustrated difference in efficiencies between the prototypes. From this research, it follows that the ADIBAA- and HA- methods can indeed be used as cost-effective, simple and time-efficient methods to evaluate prospective designs of random packing and trays.