271280 Optimization-Based Process Synthesis Framework for Thermochemical Conversion of Natural Gas to Liquid Transportation Fuels (GTL) Systems
A significant portion of natural gas resources in the United States is categorized as stranded natural gas since the wells are inaccessible from current pipeline infrastructure. Additionally, the associated gas production from oil operations is either vented, re-injected, or flared. There is a need to monetize these stranded gas resources to channel more fuels to the market as well as mitigate the environmental damage from gas flaring. Natural gas to liquid (GTL) systems can utilize these gas resources to add to the fuel market. A recent review of hybrid and single feedstock energy processes can be found in .
We investigate GTL systems through an optimization-based process synthesis approach to identify an optimal plant design for small-scale GTL systems out of a superstructure of conversion pathways [2-9]. Multiple natural gas conversion technologies are included, namely autothermal reforming, direct conversion to methanol, and direct conversion to ethylene. These processes are followed by the hydrocarbon production section via either a combination of Fischer-Tropsch units operating at multiple temperature levels using iron or cobalt catalysts, a methanol synthesis reactor to produce intermediate methanol from synthesis gas, a combination of methanol to gasoline or methanol to diesel and kerosene units, and an oligomerization unit to convert ethylene to a gasoline product. The upgrading of the fuels take place over ZSM-5 catalyst or a series of hydrocracker, hydrotreater, isomerizer, and alkylation units to produce gasoline, diesel, and kerosene. A hydrogen/oxygen production system that utilizes both carbon and non-carbon sources is included, using a combination of an air separation unit, a pressure-swing absorption unit, and an electrolyzer. The whole process is heat, power, and water integrated to minimize the utility consumption.
Case studies on the different compositions of liquid fuels produced by the GTL system are performed. A range of mixtures for gasoline, diesel, and kerosene products are imposed to elucidate the economic and environmental tradeoffs between technological routes in the superstructure, and identify the topology that will minimize the cost of fuel production.
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