Offshore Gas-to-Liquid Production
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Gas-to-liquid (GTL) production technology is a process by which associated natural gas is chemically converted into liquid products, such as liquefied natural gas (LNG), methanol and liquid transportation fuels. The process is an attractive alternative for the utilization of large amounts of the world?s offshore associated gas which is normally stranded, flared or re-injected. It is well known that the most stranded oil and gas fields are in deep water, and the recovered associated gas cannot be easily transported via a pipeline system. Hence, employing the GTL process on a floating production, storage and offloading (FPSO) vessel is an opportunity of interest for most industrial companies. In this thesis, the GTL FPSO process producing Fischer-Tropsch (FT) synthetic oil is studied. The FT-GTL process is already applied at a massive scale at several onshore locations and is under consideration for application offshore. One of the main objectives of this study is to design the offshore GTL production process with consideration to the size and weight restrictions of the FPSO vessel. The process utilizes the associated gas as a feedstock which is recovered from an offshore oil & gas field. The process has been designed based on the information and data found in available literature sources. The process design has been simulated in HYSYS software at steady-state conditions. Two main units, reforming and the FT synthesis, have been modeled in the GTL FPSO plant. The reforming unit of the GTL process has been designed based on autothermal reforming (ATR) technology that utilizes air. The FT synthesis unit has been simulated with a multi-tubular fixed bed reactor. The FT reactor is based on the Iglesia?s kinetics for cobalt catalyst. In addition, the GTL plant has been integrated with the power generation unit to provide the required energy for the system by utilizing the unconverted syngas produced from the FT synthesis unit. Different process modifications to the simulated GTL design have been implemented. The results from the modifications have been analyzed and compared. After an evaluation of the results, the design case best suited for operation on the FPSO has been selected to be optimized. The optimization parameters of the process are steam/carbon ratio, oxygen/carbon ratio, the inlet ATR temperature, volumes of the FT reactors, and cooling water temperature of the FT reactors. The optimized offshore GTL plant has been evaluated in terms of economics, i.e. the total investment, operating costs and total profit of the plant have been calculated.