(211f) Natural Gas to Liquid Transportation Fuels Utilizing Chemical Looping Technologies for Syngas Generation: Process Synthesis and Global Optimization
Previous multi-scale engineering  work by Baliban et al.  demonstrated that optimal GTL processes can be economically competitive with petroleum refineries. The primary natural gas conversion technologies investigated were syngas generation via autothermal reforming or stream reforming, partial oxidation to methanol, and direct oxidative coupling to olefins, before further upgrading to liquid fuels via methanol synthesis or Fischer-Tropsch processes. Natural gas conversion is low through partial oxidation and oxidative coupling routes, and while it is greater through traditional reforming, high pressure operation limits the overall conversion.
However, recent developments in chemical looping [5, 6] as an alternative for syngas generation from natural gas have significantly expanded the potential GTL capabilities. Chemical looping can be operated at low pressure and offers close to complete conversion of natural gas in a single pass. A high concentration of syngas can be produced without using pure oxygen, eliminating the need for additional air separation and syngas conditioning units. This could greatly reduce the capital and operational costs associated with generating syngas in GTL processes and improve the overall process efficiency.
In this work, two chemical looping technologies are incorporated into a GTL process superstructure[4, 7, 8, 9] as alternatives to reforming for syngas generation. All process technologies are rigorously modeled and together with other important process components, such as hydrogen and oxygen production, wastewater treatment, and light gas handling, form a large-scale nonconvex mixed-integer nonlinear model (MINLP). A deterministic global optimization branch-and-bound algorithm is used to solve the MINLP . Simultaneous heat and power integration is also performed to minimize utility cost . This process synthesis framework provides an illuminating means to systematically compare chemical looping technologies against other competing technologies in a GTL process.
Several case studies are examined to highlight the prospective benefits of chemical looping technologies over other conversion routes. The effect of plant capacity and production ratios on the overall profit of the GTL process is analyzed. Major topological decisions on process technologies will be discussed. Economic and environmental trade-offs will also be presented.
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