In order to reduce the amount of pollution that is generated by burning fossil fuels alternative energy sources should be explored. Hydrogen has been identified as the most promising replacement for fossil fuels and can be produced by using the Hybrid Sulphur (HyS) cycle. Currently the SO2/O2 separation step in the HyS process has a large amount of knock out drums. The aim of this study was to investigate new technology to separate the SO2 and O2. The technology that was identified and investigated was to separate the SO2 and O2 by absorbing the SO2 into an ionic liquid. In this study the maximum absorption, absorption rate and desorption rate of SO2 from the ionic liquid [BMIm][MeSO4] with purities of 95% and 98% was investigated. These ionic liquid properties were investigated for pure O2 at pressures ranging from 1.5 to 9 bar(a) and for pure SO2 at pressures from 1.5 to 3 bar(a) at ambient temperature. Experiments were also carried out where the composition of the feed-stream to the ionic liquid was varied with compositions of 0, 25, 50, 75 and 100 mol% SO2 with O2 as the balance. For each of these compositions the temperature of the ionic liquid was changed from 30oC to 60oC, in increments of 10oC. The absorption rate of SO2 in the ionic liquid increased when the mole percentage SO2 in the feed stream was increased. When the temperature of the ionic liquid was decreased the maximum amount of SO2 that the ionic liquid absorbed increased dramatically. However, the absorption rate was not influenced by a change in the absorption temperature. The experimental results for the maximum SO2 absorption were modelled with the Langmuir absorption model. The model fitted the data well, with an average standard deviation of 17.07% over all the experiments. In order to determine if the absorption reaction was endothermic or exothermic the Clausius-Clapeyron equation was used to calculate the heat of desorption for the desorption step. The heat of desorption data indicated that the desorption of SO2 from this ionic liquid was an endothermic reaction because the heat of desorption values was positive. Therefore the absorption reaction was exothermic. From the pressure-change experiments the results showed that the mole percentage of O2 gas that was absorbed into the ionic liquid was independent of the pressure of the O2 feed.On the other hand, there was a clear correlation between the mole percentage SO2 that was absorbed into the ionic liquid and the feed pressure of the SO2. When the feed pressure of the SO2 was increased the amount of SO2 absorbed also increased, this trend was explained with Fick’s law. In the study the effect of the ionic liquid purity on the SO2 absorption capacity was investigated. The experimental results for the pressure experiments showed that the 95% and 98% pure ionic liquid absorbed about the same amount of SO2. During the temperature experiments the 95% pure ionic liquid absorbed more SO2 than the 98% pure ionic liquid for all but two of the experiments. However the 95% pure ionic liquid also absorbed small amounts of O2 at 30 and 40oC which indicated that the 95% pure ionic liquid had a lower selectivity than the 98% pure ionic liquid. Therefore, the 95% pure ionic liquid had better SO2 absorption capabilities than the 98% pure ionic liquid. These result showed that the 98% pure ionic liquid did not absorb more SO2 than the 95% pure ionic liquid, but it did, however, show that the 98% pure ionic liquid had a better selectivity towards the SO2. Hence, it can be concluded that even with the O2 that is absorbed it would be economically more advantageous to use the less expensive 95% pure ionic liquid rather than the expensive 98% pure ionic liquid, because the O2 would not influence the performance of the process negatively in such low quantities. / Thesis (MIng (Chemical Engineering))--North-West University, Potchefstroom Campus, 2013

Graduate / 0485

The utilisation of alternate sources of energy has reached critical levels due to the constantly growing demand for energy and the diminishing of fossil fuels. The production of hydrogen through the Hybrid Sulphur process is a possible alternative that may contribute towards alleviating the pressure on the world's energy resources. The two-step thermochemical cycle for decomposing water into hydrogen and oxygen offers the potential to obtain acceptable thermal efficiencies, while still using common and inexpensive chemicals. The process mainly makes use of two unit process operations: an electrolyser and a chemical decomposition reactor. This research project focuses on the concept design of the decomposition reactor operated adiabatically as a multi-stage reactor system with inter-stage heating, in order to simplify the reactor design. This approach allows for the independent evaluation of the reaction kinetics and the heat transfer mechanism. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.

The constantly growing demand for energy and the consequent depletion of fossil fuels have led to a drive for energy that is environmentally friendly, efficient and sustainable. A viable source with the most potential of adhering to the criteria is nuclear-produced hydrogen. The hybrid sulphur cycle (HyS) is the proposed electrothermochemical process that can produce the energy carrier, hydrogen. The HyS consists of two unit operations, namely the electrolyzer and the decomposition reactor, that decomposes water into hydrogen and oxygen. A techno-economic evaluation of the technology is needed to prove the commercial potential of the cycle. This research project focuses on determining the hybrid sulphur cycle’s recommended operating parameter range that will support economic viability whilst maintaining a high efficiency. This is done by comparing the results of an evaluation of four case studies, all operating under different conditions. The technical evaluation of the research project is executed using the engineering tool Aspen PlusTM. The models used to achieve accurate results were OLI Mixed Solvent Electrolyte, oleum data package for use with Aspen PlusTM, which provides an accurate representation of the H2SO4 properties, and ELECNRTL to provide an accurate representation of H2SO4 at high temperature conditions. This evaluation provides insight into the efficiency of the process as well as the operating conditions that deliver the highest efficiency. The economic evaluation of the research project determines the hydrogen production costs for various operating conditions. These evaluations provide a recommended operating parameter range for the HyS to obtain high efficiency and economic viability. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2010.

The demand for energy is increasing throughout the world, and fossil fuel resources are diminishing. At the same time, the use of fossil fuels is slowly being reduced because it pollutes the environment. Research into alternative energy sources becomes necessary and important. An alternative fuel should not only replace fossil fuels but also address the environmental challenges posed by the use of fossil fuels. Hydrogen is an environmentally friendly substance considering that its product of combustion is water. Hydrogen is perceived to be a major contender to replace fossil fuels. Although hydrogen is not an energy source, it is an energy storage medium and a carrier which can be converted into electrical energy by an electrochemical process such as in fuel cell technology. Current hydrogen production methods, such as steam reforming, derive hydrogen from fossil fuels. As such, these methods still have a negative impact on the environment. Hydrogen can also be produced using thermochemical cycles which avoid the use of fossil fuels. The production of hydrogen through thermochemical cycles is expected to compete with the existing hydrogen production technologies. The sulphur iodine (SI) thermochemical cycle has been identified as a high-efficiency approach to produce hydrogen using either nuclear or solar power. A sound foundation is required to enable future construction and operation of thermochemical cycles. The foundation should consist of laboratory to pilot scale evaluation of the process. The activities involved are experimental verification of reactions, process modelling, conceptual design and pilot plant runs. Based on experimental and pilot plant data presented from previous research, this study presents the simulation of the sulphur iodine thermochemical cycle as applied to the South African context. A conceptual design is presented for the sulphur iodine thermochemical cycle with the aid of a process simulator. The low heating value (LHV) energy efficiency is 18% and an energy efficiency of 24% was achieved. The estimated hydrogen production cost was evaluated at $18/kg. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.

The utilisation of alternate sources of energy has reached critical levels due to the constantly growing demand for energy and the diminishing of fossil fuels. The production of hydrogen through the Hybrid Sulphur process is a possible alternative that may contribute towards alleviating the pressure on the world's energy resources. The two-step thermochemical cycle for decomposing water into hydrogen and oxygen offers the potential to obtain acceptable thermal efficiencies, while still using common and inexpensive chemicals. The process mainly makes use of two unit process operations: an electrolyser and a chemical decomposition reactor. This research project focuses on the concept design of the decomposition reactor operated adiabatically as a multi-stage reactor system with inter-stage heating, in order to simplify the reactor design. This approach allows for the independent evaluation of the reaction kinetics and the heat transfer mechanism. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.

The constantly growing demand for energy and the consequent depletion of fossil fuels have led to a drive for energy that is environmentally friendly, efficient and sustainable. A viable source with the most potential of adhering to the criteria is nuclear-produced hydrogen. The hybrid sulphur cycle (HyS) is the proposed electrothermochemical process that can produce the energy carrier, hydrogen. The HyS consists of two unit operations, namely the electrolyzer and the decomposition reactor, that decomposes water into hydrogen and oxygen. A techno-economic evaluation of the technology is needed to prove the commercial potential of the cycle. This research project focuses on determining the hybrid sulphur cycle’s recommended operating parameter range that will support economic viability whilst maintaining a high efficiency. This is done by comparing the results of an evaluation of four case studies, all operating under different conditions. The technical evaluation of the research project is executed using the engineering tool Aspen PlusTM. The models used to achieve accurate results were OLI Mixed Solvent Electrolyte, oleum data package for use with Aspen PlusTM, which provides an accurate representation of the H2SO4 properties, and ELECNRTL to provide an accurate representation of H2SO4 at high temperature conditions. This evaluation provides insight into the efficiency of the process as well as the operating conditions that deliver the highest efficiency. The economic evaluation of the research project determines the hydrogen production costs for various operating conditions. These evaluations provide a recommended operating parameter range for the HyS to obtain high efficiency and economic viability. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2010.

The demand for energy is increasing throughout the world, and fossil fuel resources are diminishing. At the same time, the use of fossil fuels is slowly being reduced because it pollutes the environment. Research into alternative energy sources becomes necessary and important. An alternative fuel should not only replace fossil fuels but also address the environmental challenges posed by the use of fossil fuels. Hydrogen is an environmentally friendly substance considering that its product of combustion is water. Hydrogen is perceived to be a major contender to replace fossil fuels. Although hydrogen is not an energy source, it is an energy storage medium and a carrier which can be converted into electrical energy by an electrochemical process such as in fuel cell technology. Current hydrogen production methods, such as steam reforming, derive hydrogen from fossil fuels. As such, these methods still have a negative impact on the environment. Hydrogen can also be produced using thermochemical cycles which avoid the use of fossil fuels. The production of hydrogen through thermochemical cycles is expected to compete with the existing hydrogen production technologies. The sulphur iodine (SI) thermochemical cycle has been identified as a high-efficiency approach to produce hydrogen using either nuclear or solar power. A sound foundation is required to enable future construction and operation of thermochemical cycles. The foundation should consist of laboratory to pilot scale evaluation of the process. The activities involved are experimental verification of reactions, process modelling, conceptual design and pilot plant runs. Based on experimental and pilot plant data presented from previous research, this study presents the simulation of the sulphur iodine thermochemical cycle as applied to the South African context. A conceptual design is presented for the sulphur iodine thermochemical cycle with the aid of a process simulator. The low heating value (LHV) energy efficiency is 18% and an energy efficiency of 24% was achieved. The estimated hydrogen production cost was evaluated at $18/kg. / Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.

Graduate / 0485

Small quantities of reduced sulphur compounds (RSCs) emitted from Kraft pulp mills can affect air quality due to low odour thresholds. Chromatographic methods were developed for individual RSCs at ppt to ppb concentrations. Analyses of ambient air samples showed that while H2S, CH3SH, DMS and DMDS were linked to the pulp mill, the majority of COS and CS2 was due to other sources unrelated to the mill. The fluxes of individual RSCs from kraft wastewater clarifiers were quantified for the first time. DMDS and DMS were the major RSCs emitted from the primary and secondary clarifiers, respectively. RSC fluxes were one to three orders of magnitude higher at the primary clarifier than at the secondary one. Clarifier emissions were, however, insignificant compared to point sources in the mill. Statistically significant correlations were found between the DMS emission and BOD, COD, as well as TSS in the secondary treatment system.