Praveen Linga

ABSTRACT A new biodegradable porous medium has been employed in this work for hydrate based gas separation (HBGS) process to capture carbon dioxide in a fixed bed column from pre-combustion stream. 2.5 mol% propane was added as a promoter to reduce the operating pressure of the HBGS process. Experiments were conducted at 6 MPa and 274.2 K at different water saturation levels (50 and 100 %) in cellulose foam bed. It was found that normalized rate of hydrate formation was more than twice for 50 % as compared to 100% water saturated level. Kinetic modelling of hydrate formation in porous media has been carried out using Avrami model by utilizing the experimental gas uptake data from current and literature work. Avrami model was found to capture the hydrate growth kinetics very well up to 40 min of hydrate growth for different porous media like silica sand, polyurethane foam and cellulose foam.

ABSTRACT In a previous study using a single wellbore production system, it was demonstrated that a combination of depressurization and wellbore heating is more efficient than depressurization alone, where the endothermic dissociation process rapidly consumes the formation’s specific heat leading to a sharp decrease in dissociation rate.1 This study extends the work on gas production and explores the feasibility of a novel dual wellbore production scheme; where heating and depressurization are conducted on separate wellbores. The drawback with combining heating and depressurization on a single wellbore is that the produced fluids are flowing in an opposite direction to the heat from the wellbore, and this forced convection may slow down the dissociation process. Gas production tests are carried out using the dual wellbore system with different combinations of pressure and temperature at the depressurization and heating wellbores respectively. The ensuing experimental results showed that both increased depressurization and heating can lead to optimized gas production. A production scheme with a higher depressurization compared to a lower one at the same wellbore heating is generally more energy efficient, while higher wellbore temperature at the same depressurization resulted in more gas produced but no improvement in efficiency. Although a dual wellbore scheme has been an established practice in the petroleum industry, this is likely to be the first employed in the hydrate gas production tests.

ABSTRACT Phase equilibrium (Hydrate+Liquid+Vapour) study on hydrogen/propane mixed gas hydrates was conducted using isochoric pressure search method. Equilibrium studies were conducted using two gas mixtures with varying hydrogen/propane hydrogen/propane (0.905/0.095 mole fraction). For the gas mixture with lower propane concentration (0.095 mole fraction), equilibrium points were determined in a temperature range of 274.2 to 281.2 K and the pressure range of 1.5 MPa to 9.0 MPa. Similarly for the gas mixture with 0.35 mole fraction of propane, equilbrium was determined between 274.2 and 278.2 K and the corresponding pressures were in range of 0.4 to 1.2 MPa. Enthalpy of hydrate dissociation based on Clausius-Clayperon equation was calculated to be 149.3 KJ/mol for gas mixture with hydrogen/propane (0.905/0.095) and 179.0 KJ/mol for gas mixture with hydrogen/propane (0.65/0.35). Kinetic studies were conducted to observe the effect of pressure and temperature on the formation of mixed hydrogen/propane hydrates using hydrogen/propane (0.905/0.095) gas mixture. Dissociation studies were also performed to estimate the composition of hydrogen gas stored in mixed hydrogen/propane hydrates.

ABSTRACT Morphology studies were conducted for the first time on the mixed hydrogen/ tetrabutylammonium bromide (TBAB) semi-clathrates. Morphology study deals with the observation of nucleation of the first hydrate crystal, the growth of hydrates and the characteristic macroscopic appearance of crystals through the microscope. Morphology changes occurring during the formation of mixed hydrogen hydrates using TBAB as a promoter were observed through the microscope. Concentration of TBAB was varied and the influence of concentration on the hydrate crystal morphology was studied. At lower TBAB concentration (1 and 2 mol%) needle like and equi-axial crystals were formed initially which later developed into columnar crystals having high transmittance and retain their individual structure. However, at higher TBAB concentration (2.5 mol% and above), cylinder like crystals were observed which developed into dense irregular shaped crystals with lower transmittance. The individual crystals cannot be distinguished, they become mushy and grow as layers. Characteristic wave formations were observed during crystal formation in all the cases. With the decrease in sub cooling or with the increase in experimental pressure (driving force), the dimensions of the formed crystals was initially same but later increased to around 2-4 times the original size.