Department of Chemical Engineering

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https://scholar.sun.ac.za/handle/10019.1/321
Department Process Engineering now has a new name, and will be known from March 2023, as Department of Chemical Engineering.

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Browsing Department of Chemical Engineering by browse.metadata.advisor "Carrier, Marion"

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    Pyrolysis of Eucalyptus grandis
    (Stellenbosch : Stellenbosch University, 2013-03) Joubert, Jan-Erns; Knoetze, J. H.; Carrier, Marion; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: In recent times, governments around the world have placed increasing focus on cleaner technologies and sustainable methods of power generation in an attempt to move away from fossil fuel derived power, which is deemed unsustainable and unfriendly to the environment. This trend has also been supported by the South African government, with clear intentions to diversify the country’s power generation by including, among others, biomass as a renewable resource for electricity generation. Woody biomass and associated forestry residues in particular, could potentially be used as such a renewable resource when considering the large amount of fast growing hardwood species cultivated in South Africa. Approximately 6.3 million ton of Eucalyptus grandis is sold annually for pulp production while a further 7 million ton of Eucalyptus species are sold as round wood. With these tree species reaching commercial maturity within 7 – 9 years in the South African climate, there is real potential in harnessing woody biomass as a renewable energy source. In this study, pyrolysis was investigated as a method to condense and upgrade E.grandis into energy and chemical rich products. The pyrolysis of E.grandis is the study of the thermal degradation of the biomass, in the absence of oxygen, to produce char and bio-oil. The thermal degradation behaviour of E.grandis was studied using thermo-gravimetric analysis (TGA) at the Karlsruhe Institute of Technology (KIT) in Germany and subsequently used to determine the isoconversional kinetic constants for E.grandis and its main lignocellulosic components. Slow, Vacuum and Fast Pyrolysis were investigated and optimised to maximise product yields and to identify the key process variables affecting product quality. The Fast Pyrolysis of E.grandis was investigated and compared on bench (KIT0.1 kg/h), laboratory (SU1 kg/h) and pilot plant scale (KIT10 kg/h), using Fast Pyrolysis reactors at Stellenbosch University (SU) in South Africa and at KIT in Germany. The Slow and Vacuum Pyrolysis of E.grandis was investigated and compared using a packed bed reactor at Stellenbosch University. The TGA revealed that biomass particle size had a negligible effect on the thermal degradation behaviour of E.grandis at a heating rate set point of 50 °C/min. It was also shown that increasing the furnace heating rates shifted the thermo-gravimetric (TG) and differential thermo-gravimetric (DTG) curves towards higher temperatures while also increasing the maximum rate of volatilisation. Lignin resulted in the largest specific char yield and also reacted across the widest temperature range of all the samples investigated. The average activation energies found for the samples investigated were 177.8, 141.0, 106.2 and 170.4 kJ/mol for holocellulose, alpha-cellulose, Klason lignin and raw E.grandis, respectively. Bio-oil yield was optimised at 76 wt. % (daf) for the SU1 kg/h Fast Pyrolysis plant using an average biomass particle size of 570 μm and a reactor temperature of 470 °C. Differences in the respective condensation chains of the various Fast Pyrolysis reactor configurations investigated resulted in higher gas and char yields for the KIT reactor configurations compared to the SU1 kg/h Fast Pyrolysis plant. Differences in the vapour residence time between Slow (>400 s) and Vacuum Pyrolysis (< 2 s) resulted in a higher liquid and lower char yield for Vacuum Pyrolysis. Local liquid yield maxima of 41.1 and 64.4 wt. % daf were found for Slow and Vacuum Pyrolysis, respectively (achieved at a reactor temperature of 450 °C and a heating rate of 17 °C/min). Even though char yields were favoured at low reactor temperatures (269 – 300 °C), the higher heating values of the char were favoured at high reactor temperatures (29 – 34 MJ/kg for 375 – 481 °C). Reactor temperature had the most significant effects on product yield and quality for the respective Slow and Vacuum Pyrolysis experimental runs. The bio-oils yielded for SP and VP were found to be rich in furfural and acetic acid.
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    Valorisation of paper waste sludge using pyrolysis processing
    (Stellenbosch : Stellenbosch University, 2016-03) Ridout, Angelo Mark Christopher Juan Johan; Gorgens, Johann F.; Carrier, Marion; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Due to depleting fossil fuel reserves and environmental concerns over global warming, alternate sources such as renewable energy are required. One such renewable energy source is biomass which includes plant matter, agricultural residues and industrial wastes. Of interest in this study is the industrial waste paper waste sludge (PWS) which is generated in large quantities by the pulp and paper industry. PWS is mainly landfilled which is costly and environmentally unfriendly, and thus alternative methods of valorisation such as thermochemical and/or biochemical conversion needs to be considered. The thermochemical process of pyrolysis thermally decomposes biomass, in the absence of oxygen, into products of bio-oil, char and non-condensable gas which have various beneficial applications. Alternatively, biochemical conversion of PWS into bioethanol using fermentation can be used as an initial step, followed by pyrolytic conversion of its fermentation residues (FR). The global objective of this PhD project was to assess the full potential of alternative pyrolysis processes, at varying key operating conditions, as part of a biorefinery to maximise the conversion of PWS and its FR, containing variable amount of organic material, into energy, chemical and biomaterial resources. In addition, statistical analysis of the product yields and quality were performed to reveal new mechanistic insights. The first part of the study considered the maximisation of the bio-oil yield from low and high ash PWS (8.5 and 46.7 wt.%) using fast pyrolysis (FP) processing. To do this, both reactor temperature and pellet size were optimised using a 2-way linear and quadratic model. Maximum bio-oil yields of 44.5 and 50.0 daf, wt.% were obtained at an intermediate pellet size of ~5 mm and optimum reactor temperatures of 400 and 340 oC for the low and high ash PWS, respectively. In addition to the above, a thermogravimetric study was implemented to gain insights in the thermodynamic mechanisms behind the increase in bio-oil yield with larger pellet sizes. Results indicated that fewer secondary tar cracking reactions were prevalent due to lower mass transfer limitations leading to greater yields of bio-oil. Vacuum, slow and fast pyrolysis processes were assessed and compared, at varying reactor temperatures and pellet sizes, for their ability to maximize the gross energy conversion (EC) from the raw PWS to the liquid and solid products. A 2-way linear and quadratic model was used for the statistical approach. Comparison of the overall EC, as a combination of the solid and liquid products, revealed that FP was between 18.5 and 20.1 % higher for low ash PWS (LAPWS), and 18.4 to 36.5 % higher for high ash PWS (HAPWS) when compared to slow and vacuum pyrolysis. This finding was mainly attributed to the higher production of organic condensable compounds during FP for both PWS. The calorific values displayed by the vacuum pyrolysis (VP) tarry phase and FP bio-oil for both PWSs, as well as the LAPWS char, were high (~18 to 23 MJ.kg-1) highlighting their potential for industrial energy applications. The capability of vacuum, slow and fast pyrolysis to selectively drive the conversion of raw PWS into chemicals (primarily glycolaldehyde and levoglucosan) and biomaterials (sorption medium or biochar) was assessed. Product yields were optimised according to reactor temperature and pellet size (2-way linear and quadratic model) and their variability quantified using principal component analysis (PCA). Results indicated that the high heating applied by FP significantly promoted depolymerisation and/or fragmentation reactions leading to higher yields of most organic compounds, particularly levoglucosan for both LAPWS (1.5 daf, wt.%) and HAPWS (3.7 daf, wt.%). The char biomaterial displayed by both PWSs were ultra-microporous, and the application of VP significantly enhanced the sorptive properties of the LAPWS char. Sequential PWS fermentation for bioethanol production (separate study), followed by pyrolytic conversion of the FR using alternative processes at varying reactor temperatures, was performed to maximise the recovery of energy, of which the performance was compared to stand-alone pyrolysis. The recovery of energy was maximised by coupling PWS fermentation and FR fast pyrolysis, resulting in gross ECs of between ~75 and 88% for the LAPWS, and ~41 and 48 % for the HAPWS. These gross ECs were up to ~10 % higher in comparison to those attained for stand-alone pyrolysis of PWS. The greater availability of lignin in FR, after fermentation, led to bio-oil products that were phenols-rich. In summary, the present study pointed out the promising potential of pyrolysis processing of PWS/FR as part of a biorefinery for production of fuels, chemicals and biomaterials resources. FP maximised the organic liquid and levoglucosan yields as well as the gross EC from PWS. Sequential fermentation of PWS coupled with FP of FR maximised the gross ECs, which were higher in comparison to stand-alone PWS pyrolysis ECs. To confirm which process option is best in terms of overall energy efficiency and economics additional modelling and economic feasibility studies are recommended.