In the classical bottom-up fire ignition approach, the order of laying the fire is paper, wood then coal. In the "Basa Njengo Magogo" or top-down ignition approach, the order of laying the fire is coal, paper then wood, and few lumps of coal on top at an appropriate time after the fire has been lit. The principle is as follows: smoke is generated at the hot/cold boundary. In the normal bottom-up coal fire ignition process, the smoke rises through the cold coals and thus escapes. In the top-down ignition process, the smoke rises through the hot zone and is consequently burnt.

Particulate emission is a major problem in industrial processes, mainly power plants that make use of coal as a primary source of energy. Stringent emissions limits, set by government organisations requires industries to conform to these limits to ensure that air quality is sustained and with minimum pollutant present. Electrostatic precipitators are typically used to filter and collect these particulate emissions. Fly ash resistivity is a primary parameter in the collection of particulate emissions, and there is a resistivity range at which electrostatic precipitator collection is most efficient and anything outside this range limits, their operation. High resistivity ash results in back-corona discharge, whilst low resistivity results in particle re-entrainment into the flue gas stream. The purpose of this paper is to investigate and obtain a fly ash resistivity profile for existing power plants in South Africa. Ash samples obtained from power plants are, tested making use of an ash-resistivity test oven, in accordance with IEEE Standard 548-1984. This paper discusses obtained experimental results, to determine the resistivity profile at which South African power plant electrostatic precipitators operate. The electrical efficiency of the electrostatic precipitator system is evaluated based on the obtained resistivity profiles.