(573b) Nationwide, Regional, and Statewide Natural Gas to Liquid Fuels (GTL) Supply Chain
Recent discoveries of shale gas in the United States coupled with the technologies that enable the increase of horizontal drilling and fracking have driven the cost of natural gas down, making it an attractive feedstock for fuels and energy production. Recently, a comprehensive thermochemical superstructure of natural gas to liquids (GTL) processes has been proposed and optimized using mathematical modeling and process synthesis approach . The superstructure includes steam reforming, auto thermal reforming, partial oxidation of methane, and direct conversion to olefins as natural gas conversion options, following by conversion to liquid fuels via the Fischer-Tropsch process, methanol synthesis and conversion to hydrocarbons, and upgrading [1-3]. The selected topology is optimized to produce fuels commensurate with the United States demand, maximized diesel production, maximized kerosene production, or unrestricted fuel composition.
An optimization-based supply chain framework is proposed for the nationwide, regional, and statewide analyses based on the optimized GTL refineries for different capacities (i.e., 1, 5, 10, 50, and 200 thousand barrels per day) and fuel product ratios . The optimal nationwide, regional, and statewide supply chains for the United States are obtained by solving a large-scale mixed-integer linear optimization (MILP) model that minimizes the total cost of fuel production [4-6]. The mathematical formulation includes the locations of natural gas in the United States discretized by county, the delivery locations of fuel products, the transportation costs of every input and output of the refinery, the material balances of each GTL refinery, water resources, electricity requirement/production of the supply chain, and the CO2 sequestration capacities in the United States. Solutions of the proposed MILP optimization model provide useful information for the strategic locations of GTL refineries, the allocations of feedstocks and products in the supply chain, as well as a quantitative basis in evaluating each cost contributing factor.
Results on the nationwide supply chain, six United States regions, and the state of Texas are presented, and the economic performances of the GTL supply chains are compared. Results suggest that GTL supply chains can product highly competitive liquid fuels in the United States, and the Southwest and Central regions are the most profitable areas for GTL systems.
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