World fuel consumption is sharply increasing, especially in Asia and developing countries. Crude oil price has been also on continuously rise. Natural gas is widely used because natural gas hasn’t sulfur producing less sulfur oxides and exhaust fumes than other petroleum products from crude oil. However, natural gas demand is greater than supply, and high-profitability gas wells have been almost developed. For that reason, natural gas price has been on continuous increase. Development of stranded gas wells, neglected because of low economics, is main issue with exploitation of shale gas in U.S., bringing unprecedented decline of natural gas price. Methane which is a main component of natural gas can change into synthetic fuel through Fischer-Tropsch synthesis (FTS) reaction. To satisfy the quantity of demand as well as the preferred form of energy, Gas To Liquid (GTL) process based on natural gas is developed, with strong global interest.

GTL process is usually built in onshore, as it is constructed and operated in South Africa, Qatar, Nigeria, etc. However, transportation of natural gas by liquefaction from stranded gas well is economically infeasible, and converting natural gas to synthetic fuel using Floating Production Storage and Offloading (FPSO) plant becomes a valid option for transportation. FPSO is particularly effective in offshore where seabed pipelines are not cost effective. FPSO eliminates the need to lay expensive long-distance pipelines from the facility to an onshore terminal. This can provide an economically attractive solution for smaller oil field which can be exhausted in a few years and do not justify the expense of installing a pipeline. Furthermore, once the field is depleted, the FPSO can be moved to a new location. As well as considering the strength of Korean ship-building industry, GTL process installed on FPSO ship, called GTL-FPSO, started as part of national top 100 research projects, also contributing to the sustainable energy supply and national energy security.  

The design and operation of the reactor almost decides the economics of a chemical process and it is no exception to the GTL process operated on the FPSO offshore environment. In offshore condition, however, productivity is usually lower than the onshore because of sloshing motion. Sloshing motion is caused by fluctuation of the sea surface, coming from severe weather and ship motion. In this study, a comparison of onshore against offshore multi-tubular fixed bed FTS reactor is performed for the difference of reaction rate, hotspot point and concentration of product using Computational Fluid Dynamics (CFD)-based modeling and simulations. The simulation data are compared with the small-scale experimental data for the verification and the feasibility of scale-up. In addition, reactor length for various internal structures is determined to find the optimal operational condition of FTS. Optimal cooling medium and the temperature are also calculated to prevent the runaway.

This research develops CFD-based models for the evaluation of the sloshing effect to gas-liquid-solid components of the reaction system, coming from the unsteady waves the FPSO endures until it reaches the shutdown and evacuation stage. FTS is exothermic reaction which is occurred with hotspot increase in the reactor tube. To increase the amount of products, finally, scale-up of the FTS reactor is performed based on the developed model considering the catalyst structure and packing effect as well. As part of the scale-up process, enhanced design and flexible operation of the reactor on the FPSO are also investigated. Optimal operating condition and control strategy are proposed using the shell-side cooling temperature and visualizing temperature and concentration profiles.