Assessing the Methods of Spent Caustic Effluent Treatment from Liquid Petroleum Gas (LPG) Sulphur Purification Process

Abstract

Abstract Sweetening natural gas is extremely important to remove contaminants that affect the quality of the final product and could cause serious safety, environmental, health and/or process problems. Sweetening processes varies from single-simple step to multiple-complex steps depending on the type and the quantity of the contaminants. Bahrain’s old gas treatment plant utilizes a caustic treatment method that produces an unpleasant smell caused by the presence of hydrogen sulfide and other organic sulfur compounds. This research aimed to find the best treatment method for the generated spent caustic solution produced upon Liquefied Petroleum Gas (LPG) sulfur purification process. A third-party laboratory was asked to conduct American Public HealthAssociation (APHA) analysis to measure the wastewater content concentrations. A questionnaire was conducted, and the results were analyzed using Analytical Hierarchy Process (AHP) to find the best treatment option. Among the five AHP model criteria (initial investment cost, operational costs, environmental impact and safety concerns, materials availability, and treatment benefits), the costs (initial investment and operational costs) were the leading criteria, followed by the environmental impact and safety concerns. The leading alternative for the top three criteria was biological treatment. The biological treatment was proven economically with efficiency to remove sulfur compounds. GRAMM/GRAL software was used for hydrogen sulfide emission dispersions. Hydrogen sulfide concentrations were 30.86 μg/m3 and 16.09 μg/m3 at 1.8m height above the ground and a distance of 21 to 27 meters from weathering pits and 6.4 to 7 meters from the desulfurization unit, respectively, which is above the Bahrain legal standard of 15 μg/m3. From an occupational health point of view, the computed concentrations were well below the hazardous limits for occupational health impacts, i.e. the impact was limited to the bad odor smell. The main drawn recommendations from this study were: to adopt the biological treatment method for the wastewater and to assess the impact of other odours of organic sulfur compounds.