Multi-scale approaches for gas-to-liquids process intensification: CFD modeling, process synthesis, and global optimization

This paper presents a multi-scale framework for the intensification of small scale gas-to-liquids (GTL) processes. As the process intensification tool, a radial microchannel reactor is used to facilitate the catalytic steam reforming of methane. Due to the endothermicity of this reaction, a microchannel reactor serves as a promising alternative because of its enhanced heat transfer characteristics. However, the underlying mathematical model for the microchannel reforming process is complex. Since our aim is to elucidate the optimal process topology from a plethora of alternatives through a global optimization framework, we built a surrogate mathematical model to bridge this gap. Through a rigorous model identification, parameter estimation, and cross-validation analysis we have developed an accurate mathematical model that can predict the microchannel reactor output within 0.43%. We then implemented this mathematical model into a process superstructure that considers several novel and competing process alternatives for the production of liquid fuels from natural gas. Across different case studies ranging from 500 to 5000 barrels per day of total production, we have observed that the microchannel process can improve break-even oil prices (BEOP) by as much as $10/bbl. Since the small scale GTL process aims to utilize stranded natural gas with almost zero value, a parametric analysis is performed to evaluate the BEOP at different feedstock prices. We have observed that the microchannel reforming alternative is the superior process at all the scales investigated when a natural gas price of $1/TSCF is considered. The topological findings suggest that process intensification through microchannel steam reforming is a viable approach to monetize stranded natural gas. (C) 2017 Published by Elsevier Ltd.