oa An energy integration approach for gas-to-liquid process

Gas-to-liquid (GTL) products have increasingly become a promising energy resources over the past two decades. Qatar possesses the third largest proven reserve of natural gas in the world, with a net capacity approaching 900 tcf (trillion cubic foot). This has motivated Qatar to develop a long term vision, involving the investment of huge expenditures into world-class commercial plants that convert natural gas into value-added liquid hydrocarbon products. This vision was translated into the Oryx GTL plant in late 2006 and the Shell Pearl GTL plant reported to be the largest in the world, which began operations officially at the end of 2011, leading Qatar to be described as the world capital of GTL. The substantial usage of energy in Fischer-Tropsch (FT) GTL processes and the complexity of energy distribution throughout the process offer opportunities for heat integration and waste heat recovery. The objective of this paper is to carry out an energy integration analysis for a typical GTL process. The approach was started with process simulation to develop the base-case data for the process. Next, energy integration tools were used to optimize energy distribution, heat exchange, and waste heat recovery. Finally, simulation and techno-economic analysis were utilized to assess the performance of the proposed design changes and their economic viability. The resultant pinch diagram showed that a single pinch case was faced with a fixed driving force of 10 oC, in which both external cooling and heating utilities were required to satisfy energy needs. Meanwhile, the Grand Composite Curve (GCC) showed that flue gases cover most of the heating utility while cooling water covers all the required cooling utility. Moreover, the waste heat recovery study supported by HYSYS software illustrated considerable recoveries in steam qualities from discharged flue gases within the FT reactor section. In conclusion, energy integration on a GTL process was realized to be a promising one as the targets for net energy savings were found to be close to 40%. Additionally, generation of various qualities of steam can be obtained in a cost-effective manner. At the top of it, most of the recommended projects have attractive payback periods, below six years.