Gas hydrate formation and dissociation numerical modelling with nitrogen and carbon dioxide

Abstract

This work aims at providing experimental data for various methane-based hydrates, namely nitrogen and carbon dioxide gas mixtures with varying concentrations to provide an empirically based hydrate equilibrium model. Acquired using a sapphire pressurevolumetemperature (PVT) cell, this data is used as the foundation for the derivation of a model able to calculate the equilibrium temperature of a nitrogen and/or carbon dioxide diluted methane gas is accomplished. There are several theoretical predictive models used in software which can provide hydrate formation and equilibrium data, however theoretical models appear to outnumber experimental data and empirical models for which a comparison can be made.The effect of nitrogen and carbon dioxide, an inhibitor and promotor respectively, on methane hydrate formation and dissociation and their associated pressure and temperature conditions are explored. The hydrate profiles for various gas mixtures containing the gases mentioned are presented at pressures ranging between 40-180 bara. These hydrate profiles and the model presented were compared to those predicted by hydrate computational software and experimental data from other studies for verification. The derived model proved to be reliable when applied to various gas mixtures at different pressure conditions and was consistent when compared to computational software based on theoretical models.Consistency of methane hydrate formation data was compared to dissociation data proved that the formation temperature is not an accurate representation of the equilibrium temperature. A simple statistical measure revealed the dissociation temperature measurements to be more precise and agreed to a much larger degree with literature.

Hydrate Phase Equilibria for Methyldiethanolamine and Empirical Modeling for Prediction

“…A vacuum pump was then utilized for drying the cell and to remove any remaining contaminants, and finally purged with nitrogen. The cell was equipped with a magnetic stirrer (up to 500 rpm stir rate) to promote mixing between the phases to facilitate hydrate formation and the prevention of a hydrate film to simply form at the gas–liquid surface. , Pressure sensors for measuring pressure and K-type thermocouples were installed for measuring the air bath, vapor, and liquid temperatures within the sapphire cell. The cell was mounted firmly within an air bath operated by a cooling/heating system.…”

Effect of Dissolved Oxygen, Sodium Bisulfite, and Oxygen Scavengers on Methane Hydrate Inhibition

“…The preliminary experiments were conducted three times to test repeatability. Details of the procedure and test apparatus for hydrate testing were explained in our previous research studies. − …”

Propane, n -butane and i-butane stabilization effects on methane gas hydrates

“…Its simplicity makes handling and control of the flow loop a safe and non-demanding process. (Smith, et al, 2015) The PVT cell is cylindrical and constitutes 1 inch thick glass for enduring pressures up to 500 bar. The volume of the cell is 80 cm 3 and 106 cm 3 inclusive of internal tubing.…”

“…This therefore implies that the equilibrium conditions are altered to a varying extent throughout the vapour-liquid-hydrate (V-Lw-H) phase region when a fixed amount of sII promoting gas is introduced to C1. For example, it has been previously determined (Smith et al 2015) that the change in equilibrium temperature is not fixed throughout the V-Lw-H region, but varies when at different points on the equilibrium phase boundary. This effect is explored by experimenting with various binary C1 gas compositions diluted with C3, iC4 and in some cases nC4 using a sapphire microcell and comparing these results to pure C1 hydrate equilibrium data.…”