Abnormal release of toxic gases from natural gas processing plants

Abstract

Qatar, one of the Arabian Gulf States, possesses one of the world's largest non-associated gas fields. Most of the country's development plans are based on the preparation of natural gas for export and local use. Under normal operation of gas processing plants, the residual, H2S-rich Acid Gas is treated in a sulfur recovery unit to produce pure sulfur. However, under abnormal situations, the acid gas is burned in incinerators or flares releasing SO2-rich combustion products. Under severe weather conditions, such a flare may get extinguished and the acid gas is released unignited into the atmosphere. This paper studies the environmental hazards due to the release of such dangerous gases. Dispersion models developed by the US EPA have been used to determine the size and map location of the dangerous zones. For ignited acid gas, the results indicated the possible formation of SO2-toxic clouds extending to 110 km from the flare location in the downwind direction and 210 m above ground level. For the less common case of releasing unignited acid gas, the H2S-toxic cloud may extend to 20 km and 110 m in the downwind and vertical directions, respectively. A parametric study has been conducted to consider the effects of some meteorological conditions (wind speed and atmospheric stability) as well as the number of operating trains in a typical gas processing plant.