Numerical Simulation of Dispersion of Emissions from Tema Oil Refinery in Ghana

Abstract

The petrochemical industry is a major contributor of industrial air pollutants which are known to have dire consequences on human health and the environment, neccesitating research into their dispersion and transport. The objective of the study, therefore, is to simulate the dispersion and transport of pollutants emitted during the processing of crude oil by the Tema Oil Refinery in the Greater Accra region of Ghana using the California Puff (CALPUFF) modeling system. This thesis couples the Weather Research and forecasting Model (WRF) with the non-steady state California Puff(CALPUFF) modelling system to simulate the dispersion and transport of emissions from the refinery in a coastal urban/industrial area in Ghana. The mass balance approach was employed to estimate the refinery emission rates which were used as input for the dispersion model. Emission rates of five species were estimated - SO2, NO2, PM2:5, CO2 and VOCs. The transport and dispersion of SO2, NO2 and PM2:5 were modelled over the period between 2008 - 2013 and their impact on 38 identifed receptors investigated. Simulation results showed that the radius of impact of the emissions is approximately 10 km. As a result of the prevailing predominant south-westerly winds in the study area, concentrations of emissions at receptors located upwind of the emission source were found to be higher as the winds carried the pollutant clouds in their direction. Conversely, south and south-western receptors, relative to the refinery, on the other hand, were minimally impacted. Concentrations of SO2 and NO2 at 2 out of the 38 receptors exceeded the regulatory limit of the World Health Organisation and Ghana's Environmental Protection Agency. It can be concluded, therefore, that SO2 and NO2 emissions from the refinery do not pose any danger to the larger population and the general environment nearby. PM2:5 levels at 36 receptors however exceeded the WHO guideline value leading to the conclusion that the refinery operations could pose some dangers to the environment regarding PM2:5. The dispersion model results were compared with measurements at the same location in order to validate the model. Similarly, observations from two meteorological stations were compared with results from the meteorological model. The performance evaluation, with the aid of statistical measures revealed that the models' performance were acceptable.