Doctoral Degrees (Chemical Engineering)

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Browsing Doctoral Degrees (Chemical Engineering) by browse.metadata.advisor "Burger, Andries Jacobus"

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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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    Contributions to theoretical developments and practical exploitation of mass transfer principles in separation technologies
    (Stellenbosch : Stellenbosch University, 2023-12) Nieuwoudt, Izak; Burger, Andries Jacobus; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering.
    ENGLISH ABSTRACT: Our standard of living and quality of life rely on producing consumer products from chemicals. These chemicals typically have to be purified, and distillation, extraction and absorption are the primary technologies for affecting these separations. Such technologies are energy intensive, and further development and optimization can reduce their impact on greenhouse gas emissions. Furthermore, reduction in the capital consumed by these processes can significantly improve value creation. My contributions to these fields over the past 36 years are covered in detail in this dissertation under the sections highlighted below. It is conservatively estimated that these contributions generated more than two billion dollars of value for the companies who commercialized and use these technologies. In the process of making contributions to this field, I have been blessed to collaborate with brilliant people and their contributions to my endeavors are gratefully acknowledged. Improved separation processes My research into separation processes with reduced energy and capital consumption was focused on solvent-driven separations. Computer Aided Molecular Design (CAMD) methodologies for solventdriven separation processes were developed and, from this, improved extractive distillation, azeotropic distillation and liquid extraction processes were conceived. The energy and capital consumption of these processes were significantly lower than that of competing technologies, which also translates into lower greenhouse gas emissions. These processes were commercialized and create significant value for the chemical producers and the companies who produce consumer products. Improved separation tower internals My research into separation tower internals was focused on creating novel equipment that had higher separation efficiency and higher hydraulic capacity than the best equipment available at the time. The novel INTALOX® ULTRATM random packing exhibited higher efficiency and capacity than other random packing. This allowed chemical companies and refiners to debottleneck towers for capacity and/or separation efficiency. This reduced energy consumption and corresponding greenhouse gas emissions. The size of new towers could also be reduced. The PROFLUX® severe service packing allowed refiners to increase capacity, increase run lengths and increase the product yield in vacuum towers. I developed several tray configurations that improved the capacity and/or efficiency of separation towers. Other developments included improved liquid distributors and droplet separators. These new, improved separation tower products generated significant value for both the companies that commercialized it and the end-users who installed it in their separation towers. Separation technology education Although the separation processes and separation tower internals discussed in this dissertation generated significant revenue for the companies who commercialized and used these technologies, the lasting value lies in the underlying methodologies and knowledge that were developed. It is important that this knowledge be passed on to the next generation of engineers. To this end, I have developed university courses, the Koch-Glitsch Mass Transfer School and the FRI Distillation Academy. Under my guidance 14 Masters and 7 PhD students graduated in the field of separation technology. Almost 1000 students attended these courses and many commented that they have received unique knowledge that equipped them for the future. The details of my non-confidential contributions to the field of separation technology have been summarized in 410 patents (46 patent families), 48 papers and 80 conference contributions. At the 2022 Spring Meeting the Separations Division of the American Institute of Chemical Engineers (AIChE) gave special recognition to my “many outstanding achievements in distillation, extraction, 5 absorption, and troubleshooting” by dedicating an honors session to celebrate my “lifetime of contributions as an engineer, educator, inventor, and R&D leader in separations technology and engineering”.
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    Developing the s-SAFT-γ Mie equation of state toward nonaqueous alkanolamine-based carbon capture systems
    (Stellenbosch : Stellenbosch University, 2024-03) Schulze-Hulbe, Alexander; Cripwell, Jamie Theo; Burger, Andries Jacobus; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering.
    ENGLISH ABSTRACT: Decarbonizing industrial processes is imperative for mitigating the harmful effects of climate change. A promising route to decarbonization lies in developing nonaqueous alkanolamine-based carbon capture processes. However, there is a very wide range of nonaqueous formulations to choose from, and little available thermodynamic data. Accordingly, an apt starting point for assessment of nonaqueous alkanolamine-based carbon capture is the development of a predictive thermodynamic modeling tool which captures the salient phenomena of these systems. The Statistical Associating Fluid Theory (SAFT) equations of state (EoSs) present a fundamental approach to thermodynamic modeling. Combining these EoSs with the group-contribution (GC) approach provides these rigorous models with considerable predictive capabilities. This renders GC-approach SAFT EoSs particularly useful in the data-scarce context of nonaqueous alkanolamine-based carbon capture. Accordingly, the main aim of this work was to develop structural SAFT-γ Mie (“s-SAFT-γ Mie”), a stateof- the-art GC-approach SAFT EoS, toward a description of alkanolamine solvent/CO2/organic cosolvent systems. This presents the first instance in which the predictive capabilities of a GC-approach EoS are extended to nonaqueous alkanolamine-based carbon capture systems. However, myriad approaches can be followed in developing parameters for GC-approach EoSs. This renders parameterization challenging, thus presenting an obstacle to industrial implementation of these models. To facilitate use of GC-approach EoSs, a further aim of this work was to illustrate how GCapproach EoSs can be parameterized for nonaqueous alkanolamine-based carbon capture systems using a systematic and consistent approach. Transferable s-SAFT-γ Mie group interaction parameters were developed from the ground up for primary and secondary alcohols, as well as primary amines. The model exhibited robust capabilities in modelling these components as well as their mixtures with n-alkanes. However, results for linear alkanolamines indicate that s-SAFT-γ Mie’s generalizability comes at the expense of quantitative accuracy. In the process of developing these parameters, a novel and generalizable approach was devised to account for the effect of changing hydroxyl group position in secondary alcohols. This further developed s-SAFT- γ Mie’s capabilities in distinguishing between the properties of isomers, an important characteristic for solvent/cosolvent screening purposes. s-SAFT-γ Mie further provided qualitatively accurate descriptions for a wide range of organic cosolvents with a single parameter set. This broadly generalizable modeling approach can be extended to components for which little or no reliable data are available, highlighting its value to carbon capture process designers. The parameters thus developed were transferred to CO2-containing mixtures. Pertinently, s-SAFT-γ Mie provided qualitatively accurate descriptions of CO2 solubility in polyethylene glycols, which are important components for nonaqueous carbon capture. Regarding alkanolamine solvent/CO2/organic cosolvent systems, s-SAFT-γ Mie was capable of qualitatively reproducing the effects of temperature, liquid-phase composition as well as organic cosolvent chain length on CO2 solubility. This holds for lower pressures, where CO2 solubility is driven by chemical absorption, as well as higher pressures, where CO2 is dissolved by physical absorption. These robust predictive capabilities render s-SAFT-γ Mie well-suited to comparing CO2 solubility in several alkanolamine solvent/organic cosolvent formulations, highlighting its potential future use within the context of a solvent/cosolvent screening tool.