The influence of particle size on the thermal performance of coal and its derived char in a Union stove

Abstract

For low-income communities in South Africa, coal is the most common solid fuel which is burnt in a variety of devices, including imbaulas and cast-iron stoves. The present work was conducted with the aim of determining the effect of the fuel particle size on the performance of coal, typically sourced in low-income households in townships in South Africa, and to subsequently compare the performance with a feed char of a common cast iron stove. Four fuel particle sizes of 15, 20, 30, and 40 mm, as well as a composite of the sizes were tested at 550 °C, against their untreated coal analogues to evaluate the thermal performance of each fuel. The thermal performance assessment metrics are ignition time, water boiling time, heat transfer and combustion efficiencies, while CO and CO2 emissions were measured for the calculations of CO/CO2 ratios. Ignition times were found to decrease from coals to chars and to decrease with increasing particle size. The effects of fuel type on the water boiling time were only observed in the later stages of the burn cycle, with the char boiling a 2 L batch of water in an average 24 min, while the coals reported an average boiling time of 20 min. Heat transfer efficiencies showed no significant variation with fuel type or particle size, with the average efficiency for the coals and that of the chars being around 66%. The fuels’ performance was better gauged by the combustion efficiency, which was found to improve marginally from the coal fuels to the chars, and to increase with increasing particle size. Results from this testwork could contribute to the performance inventories from the combustion of domestic coal mined in South Africa in a typical cast iron stove which is used in informal settlements.