Exergy analysis of waste emissions from gas flaring in Nigeria

Nigeria is one of the top ten countries responsible for the largest percentage of gas flaring in the world. It is still practised due to the unwillingness of oil and gas companies to put a stop to it. Other reasons are due to over-pressure or failure of plant equipment. Gas flaring releases substantial amounts of greenhouse gases into the environment and causes potential economic loss for the nation. In this study, the exergy of natural gas and waste emissions from flaring were estimated and the analysis was compared with other methods used to assess the environmental impact potential of emissions. This was done by characterising the gas components in gas flaring, quantifying the exergy of the various components in gas flaring, analysing the unconstrained exergy of the flue gases and comparing the analysis with environmental impact potential assessment methods. The analysis was performed using MATLAB R2021a software to model the exergy analysis, global warming potential, acidification potential and removal pollution cost while ANSYS Chemkin 2021R2 was used to estimate the adiabatic flame temperature. The emitted exergy of the flue gas ranged from 2.56 X 1012 kJ to 7.00 X 1012 kJ and it was about 5% of the total exergy of the natural gas flared. It was discovered that natural gas with a higher proportion of heavier hydrocarbons leads to higher exergy values for both the natural gas and the consequent flue gas. This also correlates positively with a higher global warming and acidification potential for the flue gases and correlates negatively with the pollution removal cost. The adiabatic flame temperature was also observed to have a low positive correlation with the exergy values of the flue gas. These findings show that heavier hydrocarbons have a greater environmental impact compared to methane-rich natural gas. This study highlights the adverse effect of gas flaring in our environment apart from the potential economic losses as a result of the exergy destroyed, the exergy emitted also cause damage in the environment.