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DISSERTATION O Attribution COPYRIGHT AND CITATION CONSIDERATIONS FOR THIS THESIS/ DISSERTATION o Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. o NonCommercial — You may not use the material for commercial purposes. o ShareAlike — If you remix, transform, or build upon the material, you must distribute your contributions under the same license as the original. How to cite this thesis Surname, Initial(s). (2012) Title of the thesis or dissertation. PhD. (Chemistry)/ M.Sc. (Physics)/ M.A. (Philosophy)/M.Com. (Finance) etc. [Unpublished]: University of Johannesburg. Retrieved from: https://ujdigispace.uj.ac.za (Accessed: Date). SYSTEMATIC INVESTIGATION OF SMOKE EMISSIONS FROM PACKED-BED RESIDENTIAL COAL COMBUSTION DEVICES Tafadzwa Makonese Student Number: 200946372 Department of Geography, Environmental Management and Energy Studies Supervisor: Professor H. J. Annegarn Department of Geography, Environmental Management and Energy Studies University of Johannesburg Co-supervisor: Dr Patricia Forbes Department of Chemistry, University of Pretoria A thesis submitted in partial fulfilment of the requirements for the degree Doctor of Philosophy (PhD) (Energy Studies) in the Faculty of Science at the University of Johannesburg 21 April 2015 ii Abstract A review of health effects of emissions from solid fuel combustion shows clear links between morbidity and mortality, and residential combustion smoke exposure. On the interior plateau of the South African Highveld, use of coal fuel in informal domestic braziers – imbaulas – constitutes a major source of local ambient and household air pollution. This thesis aimed to develop an improved understanding of the complex processes of packed-bed combustion in small domestic devices studying smoke emissions from informal domestic stoves. A robust dilution sampling system for testing emissions from residential coal-burning appliances was developed and used in the emission studies. Systematic experiments were carried out to evaluate thermal performance and emissions of coal braziers, varying fire ignition method, ventilation rate, fuel moisture and fuel quality. Three field-collected and three laboratory constructed braziers were tested, with a range of ventilation hole-densities. The variables measured are particle mass (PM2.5 and PM10), gases (CO, CO2, NOx), and particle composition and morphology. Emission factors, referenced to zero excess oxygen are reported. Two fire-ignition methods are evaluated namely: the conventional bottom-lit updraft (BLUD) method, and the top-lit updraft (TLUD)–the so-called Basa njengo Magogo method. PM2.5 and PM10 emissions reduced by 80% on average when using the TLUD in contrast to the business-as-usual BLUD method. High smoke emissions from the BLUD method during pyrolysis are found to be associated with an oxygen deficit, allowing products of incomplete combustion to be emitted. Influences of ventilation rates on the stove emissions are reported – products of incomplete combustion (PM2.5 and CO) are higher for low ventilation rates. For a given device, PM2.5 and PM10 emission factors reduce by ~50% from low to high ventilation rates (an advantage offset by firepower too high for convenient cooking). Emissions from A-grade (low ash-14%) and D-grade (high ash-24%) coal are compared. There are no significant differences in particle emissions between the two fuel qualities when using the BLUD method. For the TLUD method, PM emissions increase (~2-fold) with a switch from D-grade to A- grade coal. Comparisons of CO, CO2 and NOx are reported. The influences of coal moisture content (fresh coal 8.6% and air-dried 2.4%) on emissions and efficiencies of the braziers are reported. Emissions of PM10, CO increase with increasing coal moisture. Higher moisture content reduces the combustion efficiency and firepower (heat delivery), while increasing the cooking efficiency. Polycyclic aromatic hydrocarbons (PAHs) are sampled using multi-channel rubber traps, applied as pre-concentrators of PAH emissions from real-world combustion of coal fuel. PAHs detected by chromatographic analysis are primarily naphthalene, fluorene and phenanthrene. Changes in combustion conditions have a marked effect in the ratios of various PAH emissions–relative concentrations of phenanthrene and fluorene, normalized to naphthalene, are higher in BLUD than in the TLUD ignition method. The morphology and chemical composition of the particles are investigated by SEM/EDS analysis. We classify the pyrolysis phase of a coal brazier fire into two stages: stage I and stage II. Filter samples collected during pyrolysis stage I reveal continuous layers of merged tar-like deposits with no discrete particles visible. During pyrolysis stage II, filters collect particles that retain their morphology on impact, presenting on the electron micrographs as discrete particles with a range of morphologies. Increasing combustion temperature yields decreasing emissions of coarse particles (>10 µm). Giant carbonaceous conglomerates are observed in abundance from BLUD fires but are sparse from TLUD fires. Morphological differences are observed between particles sampled directly above the fire (<1 m) and aged by ~2 s by passing through a 5 m chimney. This thesis presents the first comprehensive, systematic study of condensed matter (smoke) emissions and emission factors from informal packed-bed coal stoves in use in South Africa. The thesis has generated new insights into the factors influencing combustion behaviour and emissions. An original contribution is dividing the pyrolysis phase into two stages, and presenting evidence on how the different combustion conditions during these two stages affect the morphology of condensed matter emissions, and explain previous failures of attempts to sample such emissions. A comprehensive set of emission factors in units [g s-1] is presented per hour and three-hour full burn cycle. These contributions lay the groundwork for improvements in the design of existing coal braziers and development of novel low-emission combustion technologies, and understanding potential health impacts of condensed matter emissions. The insights gained will assist in selecting appropriate strategies and technologies to mitigate health, indoor and local air pollution associated with domestic coal combustion. The reported emission factors from coal braziers provides the first comprehensive, systematic set of emission factors for this source category, and fills a major gap in the previous efforts to conduct dispersion modelling of South African Highveld air quality. ii Affidavit To whom it may concern This serves to confirm that I, Tafadzwa Makonese, Passport Number DN888449, Student number 200946372, enrolled for the qualification PhD (Energy Studies) in the Faculty of Science, herewith declare that my academic work is in line with the Plagiarism Policy of the University of Johannesburg, with which I am familiar. I further declare that the work presented in the thesis: SYSTEMATIC INVESTIGATION OF SMOKE EMISSIONS FROM PACKED-BED RESIDENTIAL COAL COMBUSTION DEVICES is authentic and original unless clearly indicated otherwise, and in such instances full reference to the source is acknowledged, and I do not pretend to receive any credit for such acknowledged quotations, and that there is no copyright infringement in my work. I declare that no unethical research practices were used or material gained through dishonesty. I understand that plagiarism is a serious offence and that, should I contravene the Plagiarism Policy notwithstanding signing this affidavit, I may be found guilty of a serious criminal offence (perjury) that would amongst other consequences compel the UJ to inform all other tertiary institutions of the offence and to issue a corresponding certificate of reprehensible academic conduct to whomever request such a certificate from the institution. Signed at Johannesburg on this _______ day of _______________ 2015 ________________________ Tafadzwa Makonese STAMP COMMISSIONER OF OATHS Affidavit certified by a Commissioner of Oaths This affidavit conforms with the requirements of the JUSTICES OF THE PEACE AND COMMISSIONERS OF OATHS ACT 16 OF 1963 and the applicable Regulations published in the GG GNR 1258 of 21 July 1972; GN 903 of 10 July 1998; GN 109 of 2 February 2001 as mended. iii Declaration The work contained in this thesis is my own, unless otherwise acknowledged. This thesis has not been presented for examination at any other university. Parts of this thesis have been presented at various national and international conferences, or published in journals during the course of the research, as follows: Makonese, T., Forbes, P., Mudau, L., Annegarn, H. J. (2014), Aerosol particle morphology of residential coal combustion smoke, The Clean Air Journal, 24(2): 24–28. Makonese, T., Annegarn, H. J, Masekameni, D., Forbes, P. (2015), Influence of fuel-bed temperatures on CO and condensed matter emissions from packed-bed residential coal combustion, Proceedings of the Domestic Use of Energy (DUE) Conference, 31 March–2 April, 2015, Cape Town. Makonese, T., Forbes, P., Annegarn, H. J. (2015), Spherical organic particle (SOP) emissions from fixed-bed residential coal-burning devices, International Conference on Environmental, Biological and Ecological Sciences and Engineering (ICEBESE), 14–15 March, London, United Kingdom, 1(3):832; ISSN no. 1307- 6892.
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