Swapping of Hydrated Natural Gas with CO2/N-2 Guest: Physical Modeling, Validation, and Genetic Algorithm-Based Optimization

Replacing methane (CH4) imprisoned in naturallyoccurringhydrates by pure or mixed carbon dioxide (CO2) gas is anemergent technique to recover the clean fossil energy as well as tosequestrate the primary global warming-responsible gas. Having deeperinsights into the fundamentals of hydrate swapping is the foremoststep for advancing this gas replacement technology at a commerciallevel. This work aims at formulating a rigorous thermo-kinetic modelto analyze the guest gas swapping phenomena. Apart from introducingthe nth order phase transformation kinetics, a globaloptimization technique based on the technique for order of preferenceby similarity to ideal solution (TOPSIS) embedded non-dominated sortinggenetic algorithm-II (NSGA-II) is developed for the first time toidentify the model parameters and operating conditions of the transientswapping process. To assess the proposed formulation, it is validatedwith the experimental data of CH4-CO2 and CH4-CO2/N-2 gas swappingunder diverse geographic conditions. Moreover, to evaluate its rigorand versatility, the model is employed in predicting the Ignik Sikumifield data collected from the North Slope of Alaska in 2011-2012for (CH4-CO2/N-2) swapping.Furthermore, the developed optimization strategy is used to identifythe parameters of the existing swapping models as well and it is shownthat these models with proposed optimal parameter sets provide betterpredictions than those with their original parameter values. Finally,it is investigated that the proposed formulation secures a promisingperformance and consistently outperforms the existing models.

Automated summary

Replacing methane in naturally occurring hydrates with carbon dioxide is a promising technique for recovering clean fossil energy and sequestering the primary global warming gas. This study develops a thermo-kinetic model and a global optimization technique to analyze and optimize the gas swapping process. The proposed formulation is validated with experimental data and outperforms existing models in predicting gas swapping performance.