Repository logo

College of Agriculture, Engineering and Science

Permanent URI for this communityhttps://hdl.handle.net/10413/6521

Browse

Browsing College of Agriculture, Engineering and Science by SDG "SDG7"

Filter results by typing the first few letters
Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    High temperature production and desulphurisation of syngas.
    (2015) Ali, Johra Said.; Kiambi, Sammy Lewis.; Carsky, Milan.
    Synthetic gas (syngas) produced by the gasification of coal provides a cheap fuel alternative for the production of electricity. However advanced utilization of syngas is limited due to the contaminants which can seriously deactivate the catalysts used in the downstream reactions as well as downstream equipment such as gas turbines. Among the contaminants, sulphur compounds produced in the gasification process, which are mainly H2S with small amounts of COS must be removed. The method presented here is downstream sulphur capture by a metal oxide at high temperatures. In this study, a laboratory scale unit was used to produce and clean synthetic gas (syngas) containing 1.0-1.15 mole % H2S from a liquid hydrocarbon fuel consisting of 86 % methanol, 14 % propanethiol by mass, and 18 mole % oxygen gas as the oxidant. The gasifier operates at 830 0C at atmospheric pressure. Desulphurisation occurs in a fixed bed reactor packed with zinc oxide spherical pellets as the sorbent. Experiments were performed to determine whether the use of the liquid hydrocarbon mixture as fuel in the laboratory could actually produce H2S containing syngas, and eventually compare the composition of the gas produced experimentally to the one predicted by a model. Desulphurisation experiments were performed by varying reaction temperatures (350 0C and 550 0C) and sorbent particle sizes (1.63-2.03 mm) at atmospheric pressure using sorbent with varying surface areas (average of 5 m2/g and 25 m2/g) at high and low gas velocities (average of 3430 h- 1and 610 h-1). These variations were performed in a 2*2 factorial design to determine the effect of these factors on the desulphurisation process and observe whether there is any interaction between them. Statistical analysis was used to determine the significance of each factor on the sorbent sulphur sorption capacity. A packed bed model using shrinking core model was used to describe the desulphurisation process. GC analysis specific to sulphur compound detection showed consistent production of H2S during gasification. In addition to this the composition of the predicted syngas was validated through a GC equipped with a TCD detector and there was a good agreement giving the expected ratio of 2:1 of H2 and CO respectively. Small particle size sorbent with 5.3 m2/g surface area and an average space velocity of 610 h-1 at 350 0C reaction temperature had the highest sulphur sorption capacity of 3.71 Wt. % which was a 20% conversion of zinc oxide to zinc sulphide. There was no effect of increase in temperature on the process. The low surface area sorbents were more effective than the increased surface area sorbents. These results were verified by the statistical analysis performed on the sulphur sorption capacity obtained during experimentation. The packed bed model results were not in agreement with the experimental results.
  • Thumbnail Image
    Item
    Phycoremediation of industrial and municipal domestic wastewaters with concomitant biomass propagation for bioenergy production.
    (2022) Gumbi, S'fiso Thuthukani.; Olaniran, Ademola Olufolahan.
    The utilization of microalgae has been endorsed as a great source of biofuel generation and wastewater reclamation without any adverse effects. Microalgae have high growth rates, efficient photosynthesis process and biomass productivity which serve as an economic advantage. Microalgae can be used for the dual purpose of biodiesel production and wastewater treatment due to their ability to sequester organic pollutants such as nitrogen and phosphorus in wastewater. Thus, the aim of this study was to bioprospect for indigenous hyper lipid producing indigenous microalgal strain for biofuel production and wastewater treatment. Different water samples were collected from diverse aquatic habitats, including freshwater, brackish and marine water in KwaZulu-Natal, South Africa. Eight indigenous microalgal strains were isolated and screened for biomass accumulation and lipid yield using Nile red fluorescence microscopy screening and gravimetric analysis. The strains were identified based on their morphological characteristics and 18S rRNA gene sequence analysis to belong to the genera Chlorella, Neochloris and Chlamydomonas. They showed high lipid yield ranging from 14 ± 6.2 to 38 ± 8.8% dcw, proving to be a good feedstock for biodiesel production. Of the eight isolated microalgae, Chlorella sp. T4 was selected for further analysis based on the growth kinetic, lipid productivity and fatty acid profiles. The strain was subjected to different cultivation conditions to enhance lipid productivity by varying nitrogen and phosphorus concentration. A significant decrease in biomass accumulation and low quantum efficiency of photosystem (Fv/Fm) value was observed under nitrogen and phosphorus limiting conditions. The lowest biomass yield of 0.58 ± 0.03 g L-1 was found in nitrogen limiting medium (0.75 g L-1). High lipid productivity of 15.54 ± 0.7 mg L-1 d-1 was obtained under nitrogen limiting condition which was 1.37- fold higher than phosphorus limiting (0.02 g L-1) condition after 21 days. Nutrient stress caused an increase in the expression of Acetyl-coenzyme A carboxylase carboxyl transferase subunit beta (accD), ketoacylACP synthase-1 (KAS-1), omega-6 desaturase (ω-6 FAD) and omega-3 desaturase (ω-3 FAD) genes responsible for lipid biosynthesis. Whereas a decrease in Ribulose bisphosphate carboxylase large chain (rbcL) gene expression level was noted due to nutrient stress lowering the photosynthetic rate. Fatty acid methyl esters produced - under nutrient limiting conditions were found to be suitable for the production of high-quality biodiesel with enhanced oxidative stability and cold flow properties. The ability of Chlorella sp. T4 to utilize the different nutrient-rich environments and remove nutrients from poultry and dairy wastewater was investigated to ascertain its possible use for the sustainable and low-cost treatment of wastewater. Chlorella sp. T4 showed high nitrogen and phosphorus removal efficiency of 85 to 95% and 35 to 93%, respectively. This was followed by a high biomass yield of 1.28 g L-1 and 0.85 g L1 obtained using raw poultry and dairy sludge wastewater, respectively. The biomass contained significant iv amounts of lipids (16.2–25.7 % dry wt.), carbohydrates (20.7–33.1 % dry wt.), and proteins (24.5–34.6 % dry wt.), regardless of the wastewater type. Biodiesel properties of lipids extracted from the cell grown in poultry and dairy wastewater complied with most of the international standards by ASTM D6751 and EN 14,214. Based on the lipid productivity and fatty acid profile, sludge dairy wastewater was used for biomass propagation for simultaneous bioethanol and biodiesel production. Optimization of cell disruption and extraction techniques resulted into high lipid and sugar recovery efficiency. Through acid hydrolysis using sulphuric acid, 2.14 g L-1 of sugar was recover from Chlorella sp. T4 biomass and fermented to ethanol (0.81 g L-1) using Saccharomyces cerevisiae. High lipid content of 21.7 ± 0.5% was recovered from the residual biomass after hydrolysis and converted into biodiesel via transesterification. The biodiesel produced from the residual biomass meets most of the standards specified by ASTM D6751 and EN 14214. In conclusion, hyper lipid producing microalgal strain Chlorella sp. T4 isolated from KwaZulu-Natal, South Africa showed potential for biofuel production after proper optimization of growth conditions. The potential of Chlorella sp. T4 to utilize different wastewater high in nutrient concentration confirm potential application during large scale cultivation for biofuel production to address energy crisis and water shortage.
  • Thumbnail Image
    Item
    Sustainable energy efficiency and energy security in developing countries: a case study of airports in South Africa.
    (2022) Joseph, Jerusha Sarah.; Inambao, Freddie Liswaniso.
    When looking at the penetration of energy efficiency into the built environment and progress in the decrease in reliance on fossil fuel sources for energy generation, there is a definite challenge in obtaining the priority it requires to arrest the exponential increase in carbon emissions. Energy being key to economic development and improvement of the human way of life, developing countries face unique challenges to secure and sustain low carbon energy sources and effectively inculcate energy efficiency. This study aimed to present a solution in the form of an engineering approach entrenched in the three dimensions of business sustainability, i.e., environmental, social, and economic, to ensure that efforts towards energy efficiency and energy security in developing countries are effective and sustained in reducing carbon emissions. This solution was implemented in a live environment for nine airports in South Africa, and the results are presented in the form of case studies. The thesis investigated the global context of the climate change challenge and the global trends regarding carbon emissions from energy generation. The barriers that developing countries face with respect to achieving energy efficiency and energy security are presented together with the focuses required to overcome the barriers. Energy efficiency is investigated from the point of resource extraction to the point of energy end use, investigating energy conversion efficiencies, showing its best-matched end-use, resulting in the determination of principles for energy efficiency from component to system to infrastructure ecosystem. The principles developed were used to write an energy efficiency policy for all new infrastructure adopted at Airport Company South Africa’s (ACSA’s) nine airports in South Africa. An approach to interpreting onsite low carbon energy sources and their generation potential using available commercial technologies is proposed. Principles are created to determine an optimum low carbon energy mix that is suitable to available resources, business focus, operating environment and efficiently matching the site energy demand. The resulting energy mix based on these principles is presented as a case study for ACSA’s airports. The technologies identified for implementation to reduce energy consumption of the airports as well as their carbon footprint through the energy mix are tested for their financial viability using an economic model run via Microsoft Excel. These initiatives are SMART (specific, measurable, achievable, relevant, timed) in that they are specifically chosen for an organisation in a developing country, measurable in economic return and environmental benefit, achievable for the business, relevant to the airports’ geographical location and timed to map a pathway to carbon neutrality in electricity consumption for the airports by 2030. To ensure that the principles defined are sustained through the necessary changes in legislation, personnel and technologies, a set of key factors that underpin energy efficiency and energy security were determined and are presented. A case study of the implementation of these factors for airports in South Africa are presented. The thesis concludes with leveraging the fourth industrial revolution for innovative engineering solutions, presenting smart solutions to close the large development time gaps required for building human capacity, engineering capability and costly storage technologies to mature due to inherent intermittency of renewable energies. The results of the study and its implementation show that the solutions presented for energy efficiency and a low carbon energy mix are realistic and successful, while being grounded in sound scientific and engineering principles and sustained through inevitable changes. This is evident in the various strategies, company policies, technical guidelines and other programmes being approved and implemented by the senior management of the organisation that owns and operates the nine South African airports presented in this case study. The findings of the implementation show that a low carbon energy mix makes business sense, provides energy security and that achieving carbon neutrality is possible through the adoption of carbon offsetting. The “acid test” showing the solution presented in this thesis is being implemented for the nine airports in South Africa is that it still remains as a valid and a business focus even in the financial crisis faced by the aviation industry since the COVID-19 pandemic.