Abstract
PhD. (Energy Studies)
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).