Use of air dispersion modelling to determine the impact of gas emissions from coal-fired boilers in South African Durban basin

Abstract

The use of fossil fuel due to industrialisation has increased over time and resulted to atmospheric pollution. Industrial facilities utilise fossil fuel as a boiler fuel, pollutants like Sulphur Dioxide, Nitrogen Dioxide, Particulate Matter and Carbon Monoxide are generated from the combustion process. Air pollution has been and continues to be a significant health hazard over the world. Exposure to air pollution is an issue of concern due to human health and the environment. Considering that air pollution is associated with a series of adverse health effects, it is important to predict emissions from boiler stack. The purpose of this study was to analyse the distribution of atmospheric emissions emanating from boilers in the South Durban Industrial Basin. Three boilers i.e. boilers 1, 3 and 4 were considered during this research. The study focuses on the distribution of Sulphur Dioxide, Nitrogen Dioxide, Particulate Matter and Carbon Monoxide concentration emitted from coal fired boilers using Gaussian Dispersion Modelling. In this research, AERMOD, which is the dispersion modelling program approved by the US EPA, was used. The results of these modelling scenario were compared with the National Ambient Air Quality Standards. The results depicted that the concentrations of sulphur dioxide and nitrogen dioxide emissions from coal fired boilers were below the national ambient air quality standard, whereas the concentration of Particulate Matter emission in the vicinity of the receiving environment exceeded the National Ambient Air Quality Standards. Nitrogen Oxide was released at 7.91 g/s whereas sulphur dioxide and particulate matter were released at 40.86 and 18.35 g/s respectively. However, the temperatures at which these gases were released were all the same (450.20 K). Boilers 3 and 4 shared a stack i.e. emission emanating from both boilers are emitted through a single point source. The stack diameters for boilers 3 and 4 (0.8 m and 1.2 m respectively) were lower than that of boiler 1 (2.6 m). Similarly, boilers 3 and 4 had less stack heights (27.5 m and 30.5 m respectively) in comparison with boiler 1 (47.5 m). For boiler 3, the rates at which nitrogen dioxide, sulphur dioxide and particulate matter were released were 2.26, 0.12 and 3.84 g/s respectively. On the hand, for boiler 4, nitrogen oxide was released at 14.5 g/s whereas sulphur dioxide and particulate matter were released at 5.54 and 26.23 g/s respectively. The exit velocities for boilers 1, 3 and 4 were 12.2, 7.1 and 17.5 m/s respectively. These velocities were achieved at temperatures of 450.2, 320 and 504 K respectively.