P.D. Dholabhai

Kinetics of formation of methane and ethane gas hydrates

Abstract An intrinsic kinetic model with only one adjustable parameter is proposed for the formation of methane and ethane gas hydrates. Experimental formation data were obtained in a semi-batch stirred tank reactor. The experiments were conducted at four temperatures from 274 to 282 K and at pressures ranging from 0.636 to 8.903 MPa. The kinetic model is based on the crystallization theory, while the two-film theory model is adopted for the interfacial mass transfer. Experiments were performed at various stirring rates to define the kinetic regime. The study reveals that the formation rate is proportional to the difference in the fugacity of the dissolved gas and the three-phase equilibrium fugacity at the experimental temperature. This difference defines the driving force which incorporates the pressure effects. The gas consumption rate is also proportional to the second moment of the particle size distribution. The rate constants indicate a very weak temperature dependence.

Kinetics of gas hydrate formation from mixtures of methane and ethane

Abstract Experimental data on the kinetics of formation of gas hydrates from three mixtures of gaseous methane and ethane are reported. the experiments were conducted in a semi-batch stirred tank reactor at temperatures from 273 to 284 K and of pressures from 0.68 to 5.60 MPa. An intrinsic kinetic model for the growth of the gas hydrate is proposed. It is extension of the model for pure component hydrate formation. The model is based on the crystallization theory coupled with the two-film theory for the gas absorption into the liquid phase. the model does not contain any adjustable parameters. The kinetic rate constants which appear in the model are those obtained previously from pure component formation data. The results indicate that the formation rate is proportional to a lienar combination of the differences in the fugacities of the dissolved gases and their three-phase equilibrium fugacities at the experimental temperature. The effect of the mixture composition is taken into account indirectly through the computation of the three-phase equilibrium conditions and of the fugacities. the total gas consumption rate is proportional to the second moment of the particle size distribution.

Equilibrium conditions for hydrate formation from binary mixtures of methane and carbon dioxide in the presence of electrolytes, methanol and ethylene glycol

Abstract Ethylene glycol, methanol and electrolytes inhibit hydrate formation. Computation of the inhibition effects of these additives is necessary for the design of industrial operations where it is desired to avoid hydrate formation. Development of thermodynamic methods to calculate the hydrate equilibria conditions requires accurate experimental data. In the present work experimental three phase (aqueous liquid solution, vapor and incipient solid hydrate) equilibrium data for two mixtures of methane and CO 2 in the presence of methanol, ethylene glycol and electrolytes were obtained. The experiments were carried out in the temperature range of 264–282 K and pressure range of 1.5–10.4 MPa. A ‘full view’ fixed volume sapphire cell used earlier to gather data on CO 2 by the authors was converted into a variable volume cell with the help of a movable piston to perform the experiments.

Experimental study on propane hydrate equilibrium conditions in aqueous electrolyte solutions

Abstract Hydrate equilibrium data (aqueous solution - gas - hydrate) on propane hydrates in electrolyte solutions containing NaCl, KCl, CaCl2 and their binary and ternary mixtures, and in a synthetic sea water were experimentally obtained in the temperature range 263 – 276 K using a “pressure search” method. The ionic strengths of the solutions ranged from 0.7 to 4.77 in molality units. The data obtained in 10 wt% NaCl solution in this work were close to one set of published data but were in disagreement with two other sets of published data having their own mutual disagreement. The inconsistency was investigated by employing a “temperature search” method for this solution. The two sets of data obtained in this work by the two different procedures were in close agreement with each other. The predictive method of Englezos and Bishnoi was used to compute the equilibrium pressures at the experimental temperatures for all the electrolyte solutions studied. The computed values matched the experimental data obtained in this work very well, including those for 10 wt% NaCl solution.

Evaluation of Gas Hydrate Formation and Deposition in Condensate Pipelines: Pilot Plant Studies

A recirculation flow loop was designed, constructed, and operated to simulate the flow of light condensate oils in subsea pipelines at hydrate-forming conditions. The primary objective was to evaluate the formation and settling behavior of hydrates around orifice plates, valves, and fittings, as well as in straight sections of a pipe. Pressure drop across any section of the loop and the flow through the section were used to compute a hydrate deposition factor, F[sub H], defined to provide a measure of the hydrate accumulation in that section. The amount of hydrates formed at any instant was calculated from the drop in the total system pressure from its initial value. A horizontal see-through section enabled visual observation.