Impact of coal fired power plant emissions on ambient air quality using a diffusion model

Abstract

Bangladesh government plans to supply uninterrupted electricity to all citizens within 2021 by materializing the Vision-2021. As natural gas reserve is predicted to be exhausted within a decade, strategy has been taken to shift the primary energy focus from gas to coal. A number of coal fired power plant projects have been launched, most of which are located in the Southern region of the country. Payra, in Patuakhali district, is set to be a new energy hub of the country with projects such as Payra Power Plant Phase-I and II in the construction stage, and three other power plants proposed by Rural Power Company Ltd, Ashuganj Power Station Company Ltd, Sena Kalyan Sangstha in the preparation stage. Coal based thermal power plants are cited to be one of the major sources of pollution affecting human health and the environment. It is therefore important to assess the impact of emission of the coal fired power plants in Payra region on ambient air quality. This study involves estimations of emissions of SO2, NOx, PM2.5, PM10 and CO from the Payra power plants and evaluation of air quality impacts associated with the operation of the coal fired power plants under three scenarios: (a) Scenarios I: Operation of Payra Phase I power plant; (b) Scenario II: Operation of Payra Phase I and Phase II power plants: (c) Scenario III: Operation of all 5 power plants. A dispersion model, AERMOD, has been used to investigate the pollutant dispersion and ground-level concentration at receptor grids over a 30 km x 30 km model domain for a one-year period. This study simulates the dispersion behavior of SO2, NOx, PM2.5, PM10, and CO for 1 hour, 24 hour and annual averaging periods in close proximity of the power plants. Compliance evaluation of peak concentrations of the primary pollutants (resulting only from power plant emissions) with Air Quality Standards of Bangladesh and WHO reveals that standards are mostly satisfied only if high efficiency emission control technologies are incorporated in the project. Assessment of seasonal and diurnal variation of pollutants shows that change in pollutant behavior is largely dictated by meteorological parameters (e.g. wind speed, solar radiation and mixing height); over a particular day, peak concentration of pollutants is typically reached in the morning to noon. Sensitivity analysis of predicted pollutant concentrations to chimney height reveals that provision of 165 m height is sufficient to comply with standards and guidelines of most of the pollutants without considering background concentration. Efficiency level of emission control technologies strongly influence ground level concentrations; efficiency drop of Electrostatic Precipitator from 90% to 50% leads to violation of ambient particulate matter standards. Assessment of the coal quality reveals that ash content has moderate impact on ambient particulate concentration, whereas high sulfur content of coal can result in exceedance of the air quality standards of SO2. Hence, stringent emission control measures should be ensured to curb pollutant emission from power plants as well as other air pollution sources in the vicinity (e.g. brick kilns, motor vehicles, etc.).