• Energy Research

Abstract CO 2 capture has become an important part in building a sustainable energy system featuring the clean use of fossil fuels with low carbon footprint. Hydrate-based gas separation (HBGS) is one of the potential technologies to capture carbon dioxide from pre-combustion (fuel gas) stream. Promoters are often employed to moderate the formation conditions of hydrates. Tetra- n -butylammonium fluoride (TBAF) exhibits great thermodynamic promotion on hydrate formation. In this study the kinetic performance of the formation process of CO 2 -H 2 -TBAF semiclathrate hydrate was evaluated under different experimental pressures (6 MPa, 4 MPa and 2 MPa) and temperatures (298 K, 292 K and 286 K), with the stoichiometric TBAF concentration (3.38 mol%). Gas uptake measurement and visual observations showed that at a given pressure, the total gas uptake decreased with the decrease of experimental temperature due to high mass transfer resistance caused by rapid growth of TBAF hydrate. The highest gas uptake was achieved by experiments conducted at 6.0 MPa and 298.0 K. It was the highest among semiclathrate promoters with stoichiometric concentration, but lower compared with THF. The major advantage of the use of TBAF is that the HBGS process can be operated at near ambient temperatures compared to other promoters. The CO 2 composition in the hydrate phase was between 65.2 and 93.1 mol%, highly dependent on the experimental conditions. Variance analysis was employed to evaluate the impact of pressure and temperature on gas uptake. Gas solubility measurements were conducted to provide further insights into the kinetic performance of CO 2 -H 2 -TBAF semiclathrate hydrate formation.

Abstract Being a promising potential source for natural gas, methane hydrate (MH) is attracting increasing interest due to its great amount and diverse geographic distribution. The formation of MH is significantly influenced by the properties of sediment media such as porosity and permeability. In this study, in order to have a better understanding on the relationship between MH formation behavior and sediment properties, as well as to synthesize representative hydrate samples, MH was formed in six different sets of mixed-size porous media composed of clay, silt and fine sand, with saline water and circulating methane gas to reflect MH formation with free methane flux in marine sediment. The sediment composition, experimental pressure (15 MPa) and temperature (286.2 K) were chosen based on the SH2 drilling site in the Shenhu area in South China Sea. A two-stage growing behavior was observed for all systems. The gas consumption and hydrate formation rate exhibited positive relations with the permeability and porosity of the sediments. Furthermore, hydrates were found to be preferably formed in the bottom layer of the sediment, which could be attributed to the drastic drop of permeability at the early stage of hydrate formation. Lastly, the hydrate formation rate constant was calculated based on the intrinsic kinetic model and found to be a good reflection of the mass transfer properties of different porous media.

In order to mitigate global warming with growing demands on fossil fuels, it is essential to reduce CO2 emissions from the energy sector. Hydrate-based CO2 capture from fuel gas mixture (40% CO2/60...

Abstract Hydrate based gas separation (HBGS) process is a promising technology for carbon capture from pre-combustion streams of power generation. Recently, fixed bed reactor (FBR) configuration has been reported to significantly enhance the kinetics of hydrate formation for the HBGS process. In this work, silica sand bed reactor was employed along with 5.56 mol% THF solution to capture CO2 from fuel gas mixture (CO2/H2) at 6.0 MPa, to investigate the effects of reactor orientation (vertical, horizontal), liquid saturations in the bed (50%, 75%, 100%), and fixed bed volume. Horizontal configuration showed a major improvement in terms of gas uptake and normalized rate of hydrate formation than vertical configuration, due to the larger cross sectional area in the horizontal configuration. 50% liquid saturation performed better than the other saturations from water utilization perspective, whereas 100% saturation was better from space utilization perspective. While bed volume did not influence the kinetics of hydrate formation much, smaller bed volume showed better dissociation kinetics. In addition, the effect of operating temperatures (279.2 K, 282.2 K and 285.2 K) were evaluated for a chosen configuration. Operating temperature of 282.2 K presented slightly lower performance compared with 279.2 K, but had the advantage of energy saving. The short induction time and high CO2 composition in hydrate phase (more than 91%) further enhanced the potential and feasibility of employing this horizontal FBR configuration for pre-combustion CO2 capture with the use of THF.

Climate change is known to be dominantly caused by the increased concentration of greenhouse gases in the atmosphere, in particular CO2. To prevent excessive accumulation of CO2 in the atmosphere a...

Abstract Liquefied natural gas (LNG) is widely used in many countries around the world primarily as a mode of transport for natural gas. However, massive amount of energy (around 830 kJ/kg of LNG) is wasted during the regasification process in the LNG regasification terminals. Therefore, the technologies to utilize the LNG cold energy have received significant attention over recent decades. In this paper, we review various studies on the current LNG cold energy utilization systems, including power generation, air separation, desalination, cryogenic carbon dioxide capture, and NGL recovery. Utilizing LNG cold energy on such systems can improve the energetic and exergetic efficiencies significantly. Furthermore, several potential applications to utilize LNG cold energy in the future are proposed and discussed to broaden the perspectives of the researchers in the community. Among these potential applications, recovering LNG cold energy on cold chain for food transportation, data center cooling and hydrate based desalination are very promising. Finally, the limitations and challenges to be addressed for LNG cold energy utilization are discussed in detail.

Abstract In this study, tetra-n-butylammonium fluoride (TBAF) is investigated as a promoter for pre-combustion CO2 capture via hydrate formation process. Hydrate phase equilibrium data for fuel gas mixture at 6.0 MPa with TBAF of various concentrations (0.80, 1.50, 2.00, 2.50, 2.96 and 3.38 mol%) were first determined. The kinetic performance with different TBAF concentrations was studied at 6.0 MPa given the same temperature driving force (ΔT = 4.1 K) in a stirred tank reactor. 3.38 mol% TBAF performed the best in terms of normalized gas uptake based on unit amount of water, while 1.50 mol% TBAF solution could capture the most amount of gas in terms of unit volume of solution. Solution with a higher TBAF concentration resulted in a higher CO2 composition in the non-gaseous phase after hydrate formation, and 97.7 mol% CO2 composition was achieved by 0.80 mol% TBAF solution. The effect of three kinetic additives, namely sodium dodecyl sulfate (SDS), leucine and tryptophan, were also evaluated. All kinetic additives studied were able to significantly reduce the induction time. However, the short induction time and block of stirring caused by drastic hydrate formation leaded to low gas uptakes.

The energy demand for space cooling has more than tripled for the past thirty years and was responsible for emissions of about 1 Gt CO2 annually. The ever-increasing energy demand for cooling has posed a demanding question on improving the energy efficiency of cooling processes. On the other hand, with the growing global demand on LNG, cold energy released from LNG terminals has been growing to a historical high at 6.6 × 1014 kJ in 2017. Thus, there is a strong need to search for a suitable phase change material (PCM) best utilizing the cold energy released from the production sectors for storage and transport to the needed sectors. Among all the PCMs, semiclathrate hydrates (SCHs) with a suitable phase change temperature (5–27 °C) and high latent heat (190–220 kJ/kg) stand out as one promising candidate (a) to store and transport the cold energy and (b) to improve the energy efficiency of the cooling processes synergistically. In this review, we focus on reviewing SCHs as a cold energy storage and transport PCM covering both its fundamental properties (thermophysical properties, kinetics of formation and dissociation, rheological and transport properties, and safety and economic aspects) and its novel applications in several cooling processes. Prospects and challenges are also delineated on commercializing SCHs as a key technology enabler for the cold energy industry. There is strong confidence that possible disruptive SCH-based cooling technologies could be developed in the near future for energy efficiency improvement and environmental sustainability.