Xenobiotic particle emission formation in fixed-bed domestic coal combustion

Abstract : Combustion of solid fuels have been reportedly associated with several cases of cardiovascular, respiratory and neurological diseases. Furthermore, it is suggested that premature deaths and morbidity cases may be prevented by the use of clean energy technologies than coal and wood burning. In South Africa, despite 87% of households being connected to the grid, over 50% and 75% of households in urban and rural areas continue to depend on wood and coal for major household activities respectively. In 2004 the Department of Minerals and Energy advocated for the use of toplit updraft method (TLUD) as an interim clean coal burning technology. The initiative has been associated with the reduction of visible smoke/particulate matter (~80%) and coal consumption. However, studies suggest that there might be other emissions other than PM at household or regional level from such technologies which may be detrimental to health and environmental performances, which requires further investigations. This present study has investigated the emissions of xenobiotic pollutants emitted from small-scale combustion technology currently in use and advocated to be used in South African low-income settlements. The study focused on emission factors from small-scale coal combustion technologies, influence of coal properties on emissions, particle size distribution at different combustion phases, the physicochemical properties of emitted particles, risk assessment of BTEX emissions, toxicity and cellular uptake of particulate matter from coal combustion. All experiments were carried out in a laboratory environment in order to minimize contribution of other environmental contaminants, which were not intended for the scope of the project. The emission factors of CO2, CO, and NOx ranged from 98–102 g MJ-1, 4.1–6.4 g MJ-1, and 75–195 mg MJ-1, respectively. Particulate matter (PM2.5 and PM10) emissions were in the range 1.3–3.3 g MJ- 1 for the BLUD method, and 0.2–0.7 g MJ-1 for the TLUD method, for both field and lab-designed stoves. When employing the TLUD method, emission factors of PM2.5/PM10 reduced by up to 80% compared to the business as usual BLUD method. The fuel moisture content (from 2.4 wt.% to 8.6 wt.%) led to an 18 and 30% decrease in fire-power when using the TLUD and BLUD methods, respectively. Measured carbon monoxide (CO) emission factors (EF) increased with an increase in moisture content, while carbon dioxide (CO2) EF remained unchanged. The use of A-grade coal resulted in 49% increase in PM emissions compared with D-grade coal at high ventilation rates. Particles from the top-lit updraft (TLUD) showed an ultrafine geometric mean diameter centred at approximately 109 ± 18.4 nm for the ignition phase, 54.9 ± 5.9 nm for the pyrolysis/flaming phase, and 31.1 ± 5.1 nm for the coking phase. In studying the physical properties of smoke particles from coal burning three types of shapes were classified, viz., spherical organic particles with similar characteristics to tarballs (ignition), soot particles (flaming), and mineral particles (char-burning). Elemental composition was determined using ICP-MS and it was found that 55%, 28% and 17% of the selected elements (Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu 63, Zn) were emitted during the char burning, flaming and ignition phase, respectively. However, during ignition most emitted element were K and Si, which may be used as markers for the simultaneous combustion of wood and coal. When using near-field breathing zone concentration of BTEX in a simulated exposure scenario applicable for a typical coal burning South African household, the cancer risk for adult males iii iii and females, was found to be 1.1 -1.2 and 110-120 folds higher than the US EPA designated risk severity indicator [1E-6], respectively. All four TEX compounds recorded the Hazard Quotient [HQ] of less than 1, indicating a low risk of developing related non-carcinogenic health effects. Lastly, smoke particles emitted from the TLUD ignition from a high-ventilated stove were used to determine the cytotoxicity and cellular uptake. Particles from three combustion phases showed mild toxicity on the bronchial epithelial cells at highest concentration of 150 μg/ml while lower concentrations (20 μg/ml, 60 μg/ml 100 μg/ml) did not indicate significant toxicity on the cells. The results of this study have shown that the emissions of health and environment damaging may be significantly reduced by the correct selection of stove to fuel combinations. The PM emissions are directly proportional to the stove type, fuel properties and ignition method. Stoves with higher ventilation rate ignited using fuel with low moisture content and lit with the TLUD ignition method, produces optimum performance on the reduction of PM2.5 and PM10. However, the use of fire ignition method and coal with different moisture content did not show a convincing reduction on the gaseous emissions. Therefore, it remains important when promoting clean coal burning technologies to take cognisance on non-conclusive information of emission performance, particularly on gaseous emissions. It was further, established that particles emitted from domestic coal burning are of small diameter with an average mean of less than 100 nm. This is concerning due to the longer residence time of small particles on air spaces and higher deposition rate in the lower respiratory track of the exposed individual. The emitted particles low to medium temperature produced organic enriched spherical particle with similar characteristics to tarballs. The emissions of BTEX remains a worrying subject given the high probability of cancer under a defined exposure scenario defined under this project. Therefore, it remains important not to rule out the potential harm associated with gaseous emissions when promoting the technology (use of TLUD ignition method).Ph.D. (Energy Studies

Size distribution of nano particles from residential fixed-bed coal combustion

Abstract: Particle size distribution (PSD) from domestic coal combustion is an important parameter as it affects air quality, climate modelling, and health. There is limited information in the literature on particle size distribution from residential fixed-bed coal combustion processes. This study aimed to investigate the influence of coal combustion phases (ignition, flaming, and coking) on PSD of fine and ultrafine particles. Fine particle emissions from combustion of D-grade type coal (Ø 40 – 60 mm), in a lab-fabricated coal brazier (imbaula), were monitored using a NanoScan Scanning Mobility Particle Sizer (SMPS). Experiments were carried out using the reduced smoke top-lit updraft method, colloquially known as the Basa njengo Magogo (BnM) method. Particles from the top-lit updraft (TLUD) showed an ultrafine geometric mean diameter centred at approximately 110 nm for the ignition phase, 55 nm for the pyrolysis/ flaming phase, and 33 nm for the transition phase. The particle mode diameter rapidly increased during the ignition phase (145 nm) and gradually decreased during the flaming phase (35 nm) and the transition phase (31 nm)

A comprehensive review on small-scale combustion technologies in Southern Africa, what is known, done and emergent knowledge gaps?

Abstract: This is a review paper written with the intention to shed light on continued reliance on high polluting energy sources in the Southern Africa. Tn developing countries the use oflow cost fuels including coal, wood, pellets, charcoal and cow dung remains an obstacle in ensuring the right to clean air. Tn this study, several stove to fuel combustion technologies researches, were reviewed for similarities/ commonalities and differences. The review highlights on critical health and environmental effects associated with burning of solid fuels using inefficient cookstoves. The review deepens the understanding on various clean energy interventions and policy formulation in several countries within the Southern Africa Development Communities (SADC) region. Studies indicated the development of stove alone will not be enough in enhancing or reducing air pollution, but emphasis shall be put on stove to fuel combination. Findings also suggest a lack of clear or practical policy intervention to restore household indoor air quality, while single policy intervention proven inadequate in many studies. In sub-Saharan region, policy intervention focuses on energy switch thus from traditional solid fuels to modern energy resources namely electricity and liquid petroleum gas (LPG). This approach is not feasible given the difficulties in electricity generation and supply system, housing infrastructure and cost implication. Tn conclusion, policies which support energy stacking present a viable solution to improved indoor air quality

Influence of coal properties on the performance of fixed-bed coal-burning braziers

Abstract: Informal fixed-bed coal-burning braziers are used extensively in low-income communities of South Africa for space-heating and cooking needs. An investigation was carried out on the effects of coal moisture content and coal quality on the thermal and emissions performance of domestic coal-burning braziers in three field-procured braziers (with three different air ventilation rates), using the bottom- lit updraft (BLUD) and top-lit updraft (TLUD) ignition methods. Results showed that an increase in coal moisture content (from 2.4 wt.% to 8.6 wt.%) led to 18% and 30% decreases in fire-power when using the TLUD and BLUD methods, respectively. The combustion efficiency increased by 25% with an increase in moisture content. Measured carbon monoxide (CO) emission factors increased with an increase in moisture content, while carbon dioxide (CO2) emission factors remained unchanged. The use of A-grade coal resulted in a 49% increase in PM emissions compared with D-grade coal at high ventilation rates, despite no statistically significant differences (p > 0.05) in CO and CO2 emission factors produced between coal grades

Emissions of tar balls from domestic coal burning braziers

Abstract: On the central-plateau of the South African Highveld, domestic coal combustion is associated with the release of carbonaceous aerosols often produced as dendritic carbonaceous particles and tar balls. However, very few studies have been conducted to validate this contribution. Combustion of coal in low-income settlements is done using self-constructed devices (predominantly braziers) known as imbaulas. Combustion characteristics in these devices are influenced by fire ignition methods. The most common ignition method in South African Highveld areas is the bottom-lit updraft (BLUD) relative to the less favoured Top lit-updraft (TLUD) ignition technique. Aerosols samples were collected using Nucleopore filters combustion phases (ignition and pyrolysis). The JSM 5800LV SEM at the University of Pretoria and the Vega3 LM at the University of Johannesburg were used to observe particle morphologies from coal-burning fires. Both instruments were equipped with energy dispersive spectroscopy (EDS), which provides the possibility to analyse particle chemical compositions. Tar balls were identified in both ignition methods (BLUD and TLUD) and in pyrolysis (stage I and II). When sampling close to the fires (at ignition and pyrolysis stage I), the filter material rapidly clogged and a continuous layer of liquid/ tarry substance coalesced and covered the entire filter membrane, with some pores completely closed. At the 5 m exit point, micrographs showed distinct particles morphologies, including giant spherical organic particles that had condensed as the exhaust stream cooled. Perfectly spherical giant tar balls were observed in ageing smoke from smouldering combustion conditions typical of poorly ventilated BLUD fires. The spherical tar ball particles were found as individual spherical particles and as aggregates forming diffusion accretion chains. It is hypothesised that spherical organic particles may have been formed by the ejection of liquid tar droplets (pyrolysis stage I products of coal burning) from the pores of the burning coal, followed by rapid thermal transformation upon passing through the flame or glow zone of the fire

Influence of coal-particle size on emissions using the top-lit updraft ignition method

Abstract: Despite the Government’s intervention of an intensive electrification program in South Africa, which has resulted in more than 87% of households being connected to the grid, a majority of low-income households still depend on coal as a primary source of energy, especially on the central Highveld. In informal settlements, combustion of coal is done in inefficient self-fabricated braziers, colloquially known as imbaulas. Emissions from domestic coal combustion result in elevated household and ambient air pollution levels that often exceed national air quality limits. Continued dependence on coal combustion exposes households to copious amounts of health-damaging pollutants. Despite the health significance of coal-burning emissions from informal braziers, there is still a dearth of emissions data from these devices. Consequently, evaluating the emission characteristics of these devices and to determine the resultant emission factors is needed. The effects of ignition methods and ventilation rates on particulate and gaseous emission from coal-burning braziers are reported in literature. However, to date there are no studies carried out to investigate the influence of the size of coal pieces on brazier emission performance. In this paper, we report on controlled combustion experiments carried out to investigate systematically, influences of coal particle size on gaseous and condensed matter (smoke) emissions from informal residential coal combustion braziers. Results presented are averages of three identical burn-cycles of duration three hours or fuel burn-out, whichever was the soonest

Exposure to wood dust and health effects : a review of epidemiological evidences from developing countries

Abstract: In this paper, biomedical literature assessing the risks of nasal cancer and other wood dust exposure related symptoms and diseases in the developing world were reviewed in detail and contrasted with experiences in the developed world. Pollutants arising from industrial processes, including wood processing plants are amongst the leading causes of morbidity and premature deaths in exposed individuals. Industrial and artisanal wood processes are associated with emissions of varied sizes of wood dust particles, toxic chemicals and biological agents including fungi and endotoxins. To identify studies that assessed the risk of nasal cancer and decreased lung functions in wood industry workers; systematic literature reviews were conducted with scholarly search engines including PubMed, and Scopus. A total of 100 studies published after 1999 were scoped and identified in line with the objectives of the present review. The strongest associations between wood dust exposure and ill-health in developing world are: respiratory symptoms, (100%, n= 33) and an increased risk of nasal cancer (17%, n= 14). While, only 8% of the studies in developed world have associated wood dust exposure with nasal cancer, there is a great debate regarding the validity of such studies as their findings are limited to one sector of wood industries, sawmilling and lack basis of true toxicological studies. To confirm the aetiology of nasal cancer in wood industries, future studies should incorporate dose response relationship and potential implications of fine and ultrafine wood particles as well as endotoxins. This could aid to develop sustainable strategies for interventions and reduction of risk of exposure

A review paper on traditional fuel use, indoor air pollution, and respiratory diseases : lessons for South Africa

Abstract: About 90% of the South African population have got access to electricity, yet it is believed that several households continue to rely on traditional fuels such as coal, charcoal, firewood, animal dung as their primary cooking fuels. The combustion of traditional fuels in an inefficient cookstoves results in increased Indoor Air Pollution (IAP), ill respiratory health and several cases of premature deaths. This paper summarizes studies providing evidence of an association between household energy patterns, IAP and of acute or chronic lower and upper respiratory infections in South African households. It is believed that IAP has contributed to about 1400 premature deaths and current interventions programmes to increase access to modern energy services including electricity for poor households could be failing as reports of diseases and deaths continue to be documented. Based on existing evidence, it is that recommended energy practitioners should target achievable, yet health-saving interventions targets for the poor

Influence of fire-ignition methods and stove ventilation rates on gaseous and particle emissions from residential coal braziers

Despite extensive electrification of low-income residential areas on the South African Highveld, extensive use is still made of wood and coal as domestic fuels, particularly for winter space heating. In informal settlements characterised by poverty and lacking electrification, coal is combusted in non-standardised, inefficient and polluting metal braziers, colloquially known as imbaulas. Copious emissions from domestic coal fires result in elevated household and ambient air pollution levels well above national air quality limits. Despite the severity of this pollution as a public health issue, emissions data from residential coal-burning braziers are still scarce. Consequently, there is a need to evaluate the emission characteristics of these devices. In this paper, we report on controlled combustion experiments carried out to investigate systematically influences of fire-ignition methods and stove ventilation rates on gaseous and condensed matter (smoke) emissions from informal residential coal combustion braziers. Two methods of stove ignition—conventional bottom-lit updraft (BLUD) and the top-lit updraft (TLUD) (colloquially known as the Basa njengo Magogo) were investigated. Emission factors (EFs) were found to be dependent on fire ignition method and stove ventilation rates. The top-lit ignition method reduces PM10/PM2.5 by 76% to 80% compared to the BLUD method. Carbon monoxide emissions do not change significantly with the ignition method. Pollutant emissions from normal combustion in high ventilation conditions were low compared to pollutants emitted when an oxygen deficient atmosphere was created under low ventilation conditions. High stove ventilation rates resulted in a 50% reduction in PM10/PM2.5 emissions compared to the low ventilation rates. Emissions of gaseous and particulate matter from incomplete combustion can be minimised by design optimisation of the braziers. Ideally, the emissions of condensed matter particles (which form the bulk of emitted particles in residential coal fires) can be reduced through good mixing of emitted gases and air, and by ensuring a long residence time in the high temperature oxygen rich post combustion zone, to allow for complete oxidation. This study is significant in that it presents the first systematic and comprehensive study of factors affecting emissions from coal braziers

Dissemination of free basic electricity in rural settlements

Abstract: This paper evaluates the implementation of the Free Basic Electricity (FBE) programme in the needy South African households. A total of 5 governmental sites were used to assess the implementation of the FBE program; while 165 households were surveyed from 2016-2017 to determine the dissemination and use of FBE. The desktop survey revealed that approximately 1.8 million poor South Africans have access to FBE. Furthermore, tariff relief sets at 50 kWh based on 2001 household energy survey was found to differ per implementing agency, ranging from 20 kWh - 100 kWh. However, no data was available regarding the total number of South African who are energy poor. The survey found that 18% of households are employed, while 82% is unemployed and mainly depend on social grants. Majority of the households cannot afford electricity for cooking and heating, consequently spend over 14% of their income on energy budget which include a mixture of clean and dirty fuels such as wood, coal and paraffin. A total of 15 (9%) households are beneficiaries of FBE; while 91% indicated that they do not know about the tariff relief. Findings from this study suggest the need for an improved public communication strategy, especially in rural areas. It can be recommended that the 50-kWh tariff relief be reviewed to qualify the current household energy needs. Furthermore, enhanced community engagement is recommended in rural settlements to improve clean energy adoption strategies, either energy efficiency or FBE utilization