(156c) Small-Scale Gtl Processes for Utilizing Stranded Gas: Model Identification, Process Synthesis, and Global Optimization
Advances in the shale gas industry have generated abundant and inexpensive sources of natural gas in the United States,  with almost 500,000 active natural wells operating across the nation . There are also many sources of “stranded gas” that are uneconomic to produce due to their low energy content, impurities, small volume of production, or lack of infrastructure. Therefore, this stranded gas is typically vented or flared. Gas-to-Liquids (GTL) processes have been considered as an alternative to monetize the stranded gas [3,4] and mitigate the negative environmental impacts. A recent review outlined that many GTL technologies are commercially and technologically developed . A superstructure based global optimization framework is introduced for a GTL refinery that considers multiple conversion pathways and upgrading technologies . The objective is to find the best processes and topological alternatives across different scales, products, and feedstock compositions .
As a novel natural gas conversion alternative, an annular microchannel reactor (AMR) is designed for the catalytic steam reforming of methane for small-scale applications . Through the use of a rigorous computational fluid dynamics (CFD) model, the AMR is simulated and validated against experimental data . Although the technology is promising for small scales and CFD simulations provide an accurate representation, the model  is computationally too expensive to consider in a superstructure-based approach . Therefore, a grey-box model identification approach is developed to build a surrogate model that will accurately represent AMR behavior. A non-linear non-convex parameter estimation model is built and optimized for this motive to find a mathematical model that predicts the syngas effluent within less than 1% of the CFD simulation results.
The surrogate model is then implemented to a GTL process superstructure  for small-scale GTL applications. A set of case studies along with sensitivity analysis to observe the performance of the AMR at these scales is studied. The results suggest that the break-even oil prices can be as much as $20/bbl lower for technologies that utilize AMR compared to traditional reforming technologies.
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