Extraction and Removal of Molten Sulphur from Sour Gas at Offshore Facility Using Amine and Sulphur Recovery Unit

Abstract

Abstract Husky CNOOC Madura Ltd (HCML) is monetising the Madura Strait Block BD gas reserves to produce sweet sales gas for buyers on Java Island, Indonesia. This field is located offshore in the Madura Strait East Java, about 65 km east of Surabaya and about 16 km south of Madura Island. The project includes development of a Well Head Platform (WHP) and an offshore spread moored converted tanker based Floating, Production, Storage and Offloading (FPSO) vessel by Bumi Armada Berhad and its partner Shapoorji Pallonji Oil & Gas called as "Karapan Armada Sterling III," or KAS3 with gas/condensate/produced water processing facilities and self-sufficient utility systems. Gas Metering Station (GMS) is at onshore; 10" multiphase flexible riser connecting WHP to FPSO, 16" gas export flexible riser connecting FPSO to WHP and 16" export gas pipeline from WHP to GMS. Gas Treatment Unit (GTU) and Sulphur Recovery Unit (SRU) designed for this floating gas processing facility are unique in their project design requirements. Most gas treatment facilities fall into some common and basic configurations. The differences between them are usually found in some specific design details and particular process licenses utilised. However, all Gas treatment and Sulphur recovery facilities do not fall in the similar design pattern and can present unusual challenges. In such cases, traditional design concepts / process technology may need to be properly evaluated and reassessed from the generic ones. The result can be equally distinctive designs to handle the project specific challenges. This paper discusses the uniqueness of design in the removal of Hydrogen Sulphide (H2S) from sour gas and extraction of sulphur in elemental molten liquid form from the acid gas processing facility using amine (MDEA) in GTU that is part of a gas/condensate treating complex installed on the FPSO vessel moored off the coast of Indonesia. The sour gas contains approximately 4500 ppm of H2S and needs to be sweetened to less than 10 ppm of H2S in the export sales gas. The acid gas exiting the GTU is very lean (3-16 mol% H2S) along with heavy hydrocarbons (including BTEX), but local environmental regulations required high sulphur recovery efficiency (99%). Pretreatment with regenerable activated carbon is required to prevent fouling of the direct oxidation catalyst bed in the Recycle Selectox™ front-end of the SRU, while conventional and sub-dewpoint Claus catalyst beds are required to achieve the high recovery efficiency. The plant design also addresses the unique issues caused by the motion inherent in any floating processing facility, which affects the design of the equipment and instrumentation in a number of ways, some of which are rather distinct. It is unique to have catalyst based high temperature reaction unit processes on an offshore asset and even more ambitious in a floating facility That makes this project a novel, frontier development providing confidence and assurance to the industry in making sour fields economically worthwhile. The processing facility flowed first gas in June 2017. This paper gives insight into the interesting and in some cases unique design and features of the field development strategy. Due to this being the first time such technology has been deployed on an FPSO, the intricicies of the project are also discussed.