Browsing by Author "Osman, Khalid."

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Carbon dioxide capture methods for industrial sources.
(2010) Osman, Khalid.; Ramjugernath, Deresh.
In order to reduce the rate of climate change, particularly global warming, it is imperative that industries reduce their carbon dioxide (CO2) emissions. A promising solution of CO2 emission reduction is Carbon dioxide Capture and Storage (CCS) by sequestration, which involves isolating and extracting CO2 from the flue gases of various industrial processes, and thereafter burying the CO2 underground. The capture of CO2 proved to be the most challenging aspect of CCS. Thus, the objective of this research was to identify the most promising solution to capture CO2 from industrial processes. The study focussed on capturing CO2 emitted by coal power plants, coal-to-liquids (CTL) and gas-to-liquids (GTL) industries, which are common CO2 emitters in South Africa. This thesis consists firstly of an extensive literature review detailing the above mentioned processes, the modes of CO2 capture, and the various CO2 capture methods that are currently being investigated around the world, together with their benefits and drawbacks in terms of energy penalty, CO2 loading, absorption rate, capture efficiency, investment costs, and operating costs. Modelling, simulation, and pilot plant efforts are also described. The study reviewed many CO2 capture techniques including solvent absorption, sorbent capture, membrane usage, hydrate formation, and newly emerging capture techniques such as enzyme based systems, ionic liquids, low temperature cryogenics, CO2 anti-sublimation, artificial photosynthesis, integrated gasification steam cycle (IGSC), and chemical looping combustion The technique of solvent absorption was found to be the most promising for South African industries. Vapour-liquid-equilibrium (VLE) measurements of solvent absorption using amine blends were undertaken, using blends of methyl-diethanol amine (MDEA), diethanol amine (DEA) and water (H2O) with composition ratios of 25: 25: 50 wt% and 30: 20: 50 wt% respectively, and with CO2 and N2 gases at CO2 partial pressures of 0.5 to 10.5 bar. Experiments were conducted under system pressures of 5 to 15 bar and temperatures of 363.15 and 413.15 K, using a static analytic apparatus. CO2 liquid loading results were analysed and discussed. The experimental data were regressed in Matlab (R2009b) using the Posey-Tapperson-Rochelle model and the Deshmukh-Mather model. The Matlab programmes are presented along with the regressed binary interaction and model parameters. The accuracy of model predictions are discussed. Thereafter an Electrolyte-NRTL model regression and simulation of the absorption process was conducted using Aspen Plus V 7.1. for flue gas compositions, solvent compositions, temperature, and pressure conditions similar to that of process operating conditions. CO2 loading, design factors, CO2 recovery, and CO2 purity results were analysed and compared where appropriate, with experimental results. Finally a general preliminary energy efficiency and cost analysis was conducted based on the simulation results. The main conclusions reached are that the amine solvent blend containing 25:25:50 wt% of MDEA:DEA:H2O, produced higher CO2 loadings for its respective system conditions than other solvents studied and those found in literature. However, absorption of CO2 was found to be highly dependent on system temperature and pressure. The Deshmukh-Mather model provided higher accuracy than the Posey-Tapperson-Rochelle model, producing CO2 loading predictions with a relative error not exceeding 0.04%, in 1.5 to 3 minutes using a dual core processor. Aspen absorption simulations provided significantly lower CO2 loading results than those experimentally obtained, due to the low contact time achieved and higher temperature dependence in the proposed absorption process. Process improvements were highlighted and implemented to increase CO2 recovery and purity. Energy penalty values were found to be higher than those found in literature, but room for process and design improvement was identified and recommendations were given. Investment cost estimates were found to be justifiable and within reason. Limitations of the simulation were also identified and discussed.
Carbon dioxide removal from coal power plants : a review of current capture techniques and an investigation of carbon dioxide absorption using hybrid solvents.
(2014) Osman, Khalid.; Ramjugernath, Deresh.; Coquelet, Christophe.
The aim of this project was to identify and assess all possible solutions to reduce carbon dioxide (CO2) emissions from coal power plants in South Africa, identify the most likely solution to be implemented industrially in the short to mid-term future, and contribute towards its development through lab measurement and further research. This thesis thus contains a substantial literature review conducted on the current state of CO2 emissions in South Africa, conventional and novel coal power plant processes, modes of CO2 capture, criteria regarding the implementation of CO2 capture techniques, and the various CO2 capture techniques currently investigated with varying levels of development. The study found gas absorption using solvents to be the most likely mid-term CO2 capture technique to reach industrial implementation. However, certain challenges still need to be overcome, particularly due to numerous limitations of current solvents, to make this technique feasible for CO2 capture. In an attempt to overcome the main challenge of solvent absorption capacity, it was decided to investigate the use of ionic liquids for CO2 absorption. An in-depth review of ionic liquids was conducted, as well as a review of measurement techniques and modelling of gas absorption in alkanolamine and ionic liquid solvents. Four ionic liquids, namely methyl trioctyl ammonium bis(trifluoromethylsulfonyl)imide [MOA][Tf2N], 1-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide [Bmim][Tf2N], 1-butyl-3-methyl imidazolium tetrafluoroborate [Bmim][BF4], and 1-butyl-3-methyl imidazolium methyl sulphate [Bmim][MeSO4] were tested for CO2 and O2 absorption by measuring equilibrium Pressure-Temperature-Liquid mole fraction (P-T-x) data. Measurements were conducted using an Intelligent Gravimetric Analyser (IGA-01) at 303.15, 313.15, and 323.15 K. CO2 partial pressures of 0.05 to 1.5 MPa and O2 partial pressures of 0.05 to 0.7 MPa were investigated. Furthermore, density and refractive index measurements were conducted for all solvents. The ionic liquids were benchmarked against other ionic liquids and conventional alkanolamine solvents for CO2 absorption capacity and selectivity. The study found that ionic liquids achieved higher CO2 absorption capacity at high pressure than conventional alkanolamine solvents, but very low absorption capacity at low pressure. Of the ionic liquids studied, [Bmim][BF4] and [Bmim][Tf2N] achieved high CO2 absorption and high CO2 selectivity over O2. Therefore, these two ionic liquids were selected to be combined with conventional alkanolamine solvents, namely Monoethanolamine (MEA), Diethanolamine (DEA), and Methyl Diethanolamine (MDEA), in order to form hybrid solvents. P-T-x data was obtained for CO2 absorption in alkanolamine-ionic liquid hybrid solvents containing various compositions of the above alkanolamines and ionic liquids, by gravimetric analysis, under temperature and pressure conditions as described above. CO2 absorption in the hybrid solvents was analysed, compared, and benchmarked against absorption in pure ionic liquids and conventional alkanolamine solvents. Absorption data for pure ionic liquid systems was modelled using the Redlich-Kwong equation of state (RK-EOS), while absorption in hybrid solvents was modelled using the RK-EOS for the ionic liquid components and the Posey-Tapperson-Rochelle model for the alkanolamine components of each hybrid solvent. All modelling was programmed using MatlabTM R2012B engineering programming software. Further composition analysis was intended using Fourier transform infrared (FTIR) spectroscopy. The design and development of this apparatus is described herein. The apparatus possessed limitations in achieving the desired measurements. Recommendations are described for future modifications to make the apparatus more applicable for the systems in this work. The most important conclusion was that the hybrid solvents successfully achieved higher equilibrium CO2 absorption than conventional alkanolamine solvents and pure ionic liquids, at low pressure. Absorption increased with higher temperature, lower pressure, and alkanolamine concentrations lower than 40wt%. Modelling of CO2 absorption in hybrid solvents using the above stated model proved inadequate, with deviations nearly as high as 10% of measured data. A process of CO2 capture was simulated using the engineering software Aspen Plus V8.0. CO2 absorption in the hybrid solvent containing MEA:DEA:[Bmim][BF4] at 31.8:12.1:56.1 wt% was benchmarked against CO2 absorption in a conventional alkanolamine solvent. The simulation revealed a significant improvement in CO2 absorption using the hybrid solvent at low system pressure. However CO2 selectivity and solvent recycle heat duty results were undesirable. Finally, recommendations are listed for future research endeavours, simulation and apparatus development.
Co₂ solubility measurements and modelling in amine-NMP solvent blends.
(2022) Dijkman, Rebecca-Lynn.; Naidoo, Paramespri.; Nelson, Wayne Michael.; Osman, Khalid.
In this study, solvent blends of monoethanolamine (MEA) or 2-(2-aminoethoxy)ethanol (DGA) with N-methyl-2-pyrrolidone (NMP) or water (H2O) were selected for investigations of carbon dioxide(CO2) solubility due to the high CO2 absorption capacities of the individual solvents. A static synthetic apparatus, consisting of a stirred equilibrium vessel and a gas reservoir, each submerged in their own temperature-controlled environment, was used to measure the CO2 solubility for the systems and conditions stated above. Isothermal solubility measurements were performed at 40 °C over a pressure range of 0.1 – 1.5 MPa for the systems of CO2 in various solvent blends. These included 20% MEA–80% NMP, 30% MEA–70% NMP, 51% DGA–49% H2O, 40% DGA–60% H2O, 30% DGA–70% H2O, 51% DGA–49% NMP, 40% DGA–60% NMP and 30% DGA–70% NMP (by mass). The recorded temperature-pressure-overall composition (T-P-z) data were converted to T-P-mole fraction (T-P-x) data. Results were displayed on pressure vs. CO2 loading (P-𝛼𝐶𝑂2) graphs andcompared to literature data. Further comparisons were made between the various solvent blends. Thermodynamic modelling of the experimental data for the DGA systems was performed using MATLAB®. Due to a solvent blend of a water-lean amine and a physical solvent, two models were fitted to the experimental data by regression of the model parameters, and the results combined and displayed on P-𝛼𝐶𝑂2 graphs with the respective experimental data. The Posey-Tapperson-Rochellemodel was used for DGA, and the Peng-Robinson equation of state (PR-EOS) with modified van der Waals-Berthelot mixing rules was used for NMP in water-lean cases. Only the Posey-Tapperson-Rochelle model was used for amine-water systems. The results indicated that the water-lean blends, MEA-NMP and DGA-NMP, have a higher CO2 loading at the same pressure when compared to the corresponding MEA-H2O and DGA-H2O blends. An increase from 30% DGA–70% H2O to 40% DGA–60% H2O (by mass) resulted in a viscosity increase of 0.65 Pa.s at 40 °C and an increase in CO2 loading of 0.079 molCO2/molamine at 0.63 MPaand 40 °C. Comparing the 30% MEA–70% NMP and 30% DGA–70% NMP (by mass) blends, it was observed that the DGA blend had an increase in CO2 loading of 0.12 molCO2/molamine at 0.24 MPa and40 °C. Thermodynamic modelling for the CO2-51DGA-49H2O system gave a root mean square error of 3.75%, an absolute average deviation (AAD) of 98.24 and an average absolute relative deviation (AARD) of 22.69%, while modelling for the CO2–51 wt% DGA–49 wt% NMP system gave a root mean square error of 0.61%, an AAD of 13.13 and an AARD of 2.94%. Based on the calculated error and AARD, regression for the Posey-Tapperson-Rochelle and PR-EOS model parameters gave the closest results to the CO2–30 wt% DGA–70 wt% NMP measured data. From this work, it was concluded that in terms of the viscosity and CO2 loading at 40 °C, the DGA-NMP blends show promise compared to the DGA-H2O and MEA-NMP blends. The 40 wt% DGA–60 wt% NMP solvent blend was the best-performing DGA-NMP blend. Further experiments to determine the changes in viscosity and CO2 loading of regenerated solvents for a range of DGA-NMP blends are recommended, and further modelling analyses for data prediction are recommended for continuation of this work.
Engineering students and their prospective employers: expectations and reality.
(2019) Osman, Khalid.; Proches, Cecile Naomi Gerwel.
Since the dawn of democracy in South Africa in 1994, numerous changes have occurred at tertiary institutions to enable greater access for people of all backgrounds and increased graduate throughput to fulfil the needs of the labour market for engineers. Widespread changes in the size and composition of successive undergraduate engineering cohorts have occurred. Simultaneously, the needs of industry have undergone significant changes due to the information age, globalisation and the rapid increase in technological advances and access to technology. This study attempted to assess the alignment between the expectations of students who have graduated in engineering, the expectations of engineering employers and reality. A mixed methodology was developed. The study firstly surveyed engineering graduates at the University of KwaZulu-Natal (UKZN) using a questionnaire developed for quantitative analysis. Convenience sampling and a positivist approach were used. Graduates’ needs, study approaches, employment and workplace expectations were determined, analysed and interpreted through the lens of three frameworks, namely Biggs’ study motives and strategies, Bloom’s taxonomy and Boundaryless and Protean careers. Secondly, the study surveyed all engineering discipline academic leaders at UKZN by qualitative, semi-structured interview within an interpretivist paradigm and using deductive thematic semantic analysis. Academic leaders were used as a proxy for obtaining industry opinion and expectations and questioned on a number of themes including graduate and employer expectations, positive or negative trends, graduate training programmes, further training and postgraduate study, exit-level outcomes (ELOs) and graduate attributes, the reality of mis-alignment and what UKZN can do to limit it. Responses were collated and compared quantitatively and qualitatively where appropriate. A number of issues and mis-alignments was identified together with causes of mis-alignment. Mis-alignment was identified in salary, growth and guidance expectations, confidence, software and niche proficiencies and innovation expectations. Key causes included language barriers, lack of engineering hobbyist backgrounds, workload and study strategies, assessment changes and personal responsibility. Findings were discussed within the three theoretical frameworks mentioned above and summarised in light of the objectives of this study. Recommendations for UKZN to play a role in mitigating many of the issues and misalignment were provided, along with recommendations for any possible future research in this area.