• Energy Research

Abstract De-pressurization is one approach which has been found to be economically feasible for methane recovery from marine hydrates. Hydrate dissociation being an endothermic process suggests that de-pressurization alone would not be sufficient and some additional stimulation would be required for sustained production from one such reservoir. Thermal stimulation may overcome the challenge posed by the endothermic dissociation process; however, economically it may not be ideal. A possible way out is to use thermal stimulation, but at relatively low temperatures as compared to conventional practice. This would be economical and can be accomplished in the presence of small doses of additives mixed in with the water stream used for thermal stimulation. In the present study, a number of benign additives were identified which when used in low concentrations enhance the kinetics of methane hydrate dissociation compared to pure water. Additives were first shortlisted from a wide potential pool using quantum mechanical calculations. These additives were later tested for their efficacy in stirred tank reactor to quickly identify the best additives for the job and few selected additives were then studied in a larger bench scale setup (fixed bed configuration) where they were injected in the form of an additive-water stream to dissociate already formed hydrates. Factors such as toxicity of the additive, fluidity of additive-water stream, foam formation on mixing of additive with water, etc. were also taken into account. An energy and efficiency analysis revealed that reported additives enhance the energy ratio and thermal efficiency of the process as compared to pure water stimulation.

A fundamental study on hydrate formation from an equimolar CO2–CH4 gas mixture has been carried out with two focal points: accelerating the kinetics of hydrate formation and enhancing the gas separ...

Surfactants such as sodium dodecyl sulfate (SDS), which are used as kinetic hydrate promoters in various hydrate based technological applications, are facing a serious roadblock toward their commercial utilization as a result of the excessive amount of foam generation, particularly during hydrate dissociation. One of the approaches to alleviate this foam formation is the use of various antifoaming agents which may be employed in combination with surfactants. The possibility of using one such antifoaming agent, a silicone based polymeric surfactant, for hydrate based methane storage, has been explored in the current work through a detailed morphological study. Investigations on the morphology of hydrate formation and dissociation reveal the strong antifoaming activity of the silicone based compound and the optimal ratio in which it should be mixed with a surfactant, specifically SDS, in order to effectively alleviate unwanted foam formation. Further, kinetic data reveal that the generally observed kinetic ...

Abstract Solidified Natural Gas (SNG) technology offers an attractive option for compact and safe, large-scale natural gas storage. Gas storage technologies are gaining traction due to the increasing demand for natural gas and the expected transition to hydrogen gas-based economies in the near future. Introduction of thermodynamic promoters like THF into the classical methane-water system enables rapid gas uptake at moderate pressure and temperature due to sII hydrate formation, with highly stable storage characteristics. Herein, we compare the stability of cylindrical mixed methane-THF (sII) and pure methane (sI) hydrate pellets, produced using freshwater. Storage pressure for both types of pellets was 1 atmosphere (atm) whereas the storage temperature was 268 K for sII hydrate and 268 K and 253 K for sI hydrate. While only 7.06% gas evolution occured from a methane-THF (sII) hydrate pellet stored at 1 atm and 268 K over a 10 day period, % gas evolution from two pure methane (sI) hydrate pellets stored at 268 K for similar duration was 41.45% and 37.05% individually. Correspondingly, % gas evolution from an sI pellet stored at 253 K was 51.09%. We also report 2 year uninterrupted stability testing of methane-THF (sII) hydrate pellets produced using both fresh and seawater, stored at atmospheric pressure and temperatures of 271 K and 268 K, respectively. To the best of our knowledge, this is the longest successful storage demonstration of any type of methane hydrates ever reported, showcasing the extraordinary stability of sII hydrates produced using both fresh and seawater. The results obtained in the present study resolve the challenge of hydrate stability in SNG technology and strengthen its commercial viability by reducing downstream complications related to gas hydrate storage.

Abstract The apparent drawbacks of the classical approaches towards dissociation of natural gas hydrates have resulted in a paradigm shift into the development of new hybrid hydrate dissociation practices combining the various basic hydrate dissociation techniques. Another approach that can be followed to maximize the efficiency of gas production from natural gas hydrate reserves is the identification of benign additives which when used even in sparingly small concentrations may enhance the kinetics of hydrate dissociation. In the present work, a class of such additives, never reported before, have been unveiled and christened as Low Dosage Hydrate Dissociation Promoters (LHDPs). The additives were first short listed from a wide potential pool using a lab scale (~250 ml) stirred tank reactor setup and then further studied using a bench scale (~2.35 l) reactor setup where they were injected in the form of a water-additive stream to dissociate hydrates. The dissociation approach followed in the case of the bench scale reactor experiments was a combination of the thermal stimulation and depressurization processes along with the element of injection of additives. For both sets of experiments (lab and bench scale), the newly identified LHDPs were found to enhance the kinetics of methane hydrate dissociation as compared to pure water. It was observed that concentration of additive and its flow rate also affect the kinetics of methane hydrate dissociation. An energy and efficiency analysis for the hydrate dissociation method in the case of bench scale rector revealed that additive presence enhanced the energy ratio and thermal efficiency four fold as compared to pure water.

Abstract In the present study, the effect of the biosurfactant Surfactin on methane hydrate formation kinetics was studied. Initially, several marine derived species were screened for the presence of Surfactin. The polymerase chain reaction technique was used as the preliminary screening step for Surfactin which was then followed up by a couple of different assays to provide conclusive evidence of the same. Based on these tests, the D-9 bacterial strain was identified as a producer of Surfactin. Once the presence of Surfactin had been proven, its effect on methane hydrate formation kinetics was investigated upon by carrying out hydrate formation experiments in a stirred tank reactor. The cell free supernatant containing Surfactin was itself used as the hydrate forming solution without any further processing. It was found that the presence of Surfactin in the system greatly enhances hydrate formation kinetics as compared to pure water. In fact the kinetics in presence of Surfactin also surpassed that obtained with 1 wt% SDS, the most commonly used synthetic kinetic hydrate promoter. This basic study can pave the way for more sophisticated research on the use of biosurfactants as kinetic promoters with a view on rapid methane hydrate formation kinetics for applications such as methane separation, storage and transport.

Abstract We investigate mixed methane-THF hydrate formation at ambient temperature (298.2 K), using natural seawater to make up the hydrate forming solution. The study has been performed with the objective of boosting the economic and operation feasibility of SNG (solidified natural gas) hydrate formation. While high operating temperature and inherently present salts in seawater inhibit rapid hydrate formation with high gas uptake, using amino acids such as L-arginine and L-tryptophan allows a certain level of enhancement in hydrate formation kinetics. A second thermodynamic promoter, 0.3 mol % TBAF (tetra-n-butylammonium fluoride) in the solution facilitates roughly 25% increase in the gas uptake as compared to a counterpart TBAF-free system for the same hydrate formation period. Mapping the hydrate formation morphology reveals subtle details about how the additives employed affect the physical characteristics of hydrates being formed as well as the mechanisms of hydrate growth. This information may be put to good use especially when streamlining the technology for commercial adoption. Finally, the combinatorial hybrid (stirred & unstirred) approach for hydrate formation employed successfully eliminates the stochasticity associated with hydrate nucleation. All systems studied returned induction times of less than or approximately 3 min, with a high degree of reproducibility. Being the first study to investigate SNG hydrate formation at ambient temperature and employing seawater directly, the results obtained in this work set a fundamental benchmark for further research on this economically and operationally inviting prospect, and should be of interest to academic and industry personnel alike.