Emission Inventory and Critical Assimilative Carrying Capacity of Petroleum Refinery in India

Petroleum refineries generate hydrocarbons, SO₂, SO₃, VOCs, NO_x, CO, and PM_10/2.5 as air pollutants through fuel combustion for operating process units/stacks, evaporation from tank farms, fugitive emissions, etc., which have been found to be responsible for causing episodic health effects in the population residing nearby the refinery. The stack emissions are one of the lesser studied and a major contributor to air pollution from a petroleum refinery. This paper calculates its emission inventory using the USEPA Methodology based on fuel consumption and simulates ground-level concentration using the dispersion model. Further, the study calculates critical assimilative carrying capacity (ACC) and remaining carrying capacity (RCC) by conducting iterative simulations on CALPUFF View, a Lagrangian approach based Gaussian Puff Dispersion Model. The total emissions of SO₂, NO₂, PM_10, and CO are found to be 2331.57, 1665.34, 213.565, and 800.841 tons/year respectively, the majority of which are contributed by primary and captive process units. The 24-hour average maximum predicted concentration values for SO₂ and NO₂ are 26.8 μg/m³ and 27.9 μg/m³ respectively which occurred in the winter season. The lower ground levelconcentrations are attributed to the use of fuel oil with sulphur content (0.75% by mass), Sulphur Recovery Unit (SRU) which recovers sulphur element from acid gases and low NO_x burners. By iterative simulations, it is found that for SO₂ and NO₂, 65% of the carrying capacity remains at current emissions and the current RCC of NO₂ and SO₂ stands at 4327.6 tons/year and 3091.06 tons/year respectively. The minimum RCC is observed for winters, corresponding to the minimum ventilation coefficient of 1517.15 m²/s, and similarly, the maximum RCC is observed for the summer season at maximum ventilation coefficient of 3413.49 m²/s. The peak values of ACC and RCC can be used for planning possible expansion of the refinery and seasonal variation of the ACC and RCC can be used to bring down the plant capacity in winter and post-monsoon seasons.