Thermodynamic Simulations of Hydrate-Based Removal of Carbon Dioxide and Hydrogen Sulfide from Low-Quality Natural Gas

Abstract

This paper aims at presenting a computational scheme to thermodynamically simulate a continuous multistage operation for separating, by forming clathrate hydrates, carbon dioxide (CO2) and hydrogen sulfide (H2S) from a low-quality natural gas and at showing the stage-to-stage changes in the gas-phase composition, the crystallographic structure and composition of the formed hydrate, and the gas/aqueous-liquid/hydrate equilibrium temperature (the higher temperature limit for hydrate formation). The paper first describes the fundamental concept and algorithm of the computational scheme and then applies the scheme to the processing of a specific natural gas modeled as a CH4 + C2H6 + C3H8 + N2 + H2S + CO2 mixture. It is demonstrated that the optimum number of stages should be determined by finding a compromise between the improving removal of CO2 and H2S and increasing losses of combustible substances, particularly C2H6 and C3H8, from the residual gas with an increasing number of stages.