Results 1 - 10 of 12
Results 1 - 10 of 12. Search took: 0.015 seconds
|Sort by: date | relevance|
[en] Highlights: • Three types of hydrate-based air conditioning systems were designed. • Coefficient of performance of the optimized hydrate-base air conditioning system was up to 8.97. • Coefficient of performance of the hydrate-base air conditioning system was 2–4 times of the commercial refrigeration cycle. • The novel hydrate-based air conditioning systems achieved refrigeration at the ambient temperature of 298–308 K. - Abstract: A novel refrigeration system called hydrate-based refrigeration system was proposed, and its performance was analyzed by using Aspen Plus. The system consisted of five parts, compressor/pump, hydrate formation tank, hydrate dissociation tank, expander and gas/liquid separator. Compared with conventional compression refrigeration cycle, hydrate-based refrigeration system uses hydrate formation tank to replace condenser to achieve heat release; hydrate dissociation tank for evaporator of achieve refrigeration. There were three types of the hydrate-based refrigeration system, which refrigeration cycles were analyzed through using Aspen Plus. Methyl fluoride, cyclopentane/monofluoro cyclopentane and water were used to form hydrate as the working fluids. For the system of methyl fluoride, cyclopentane and water, the highest coefficient of performance was 8.01–8.97, For the system of methyl fluoride, monofluoro cyclopentane and water, the best coefficient of performance was 7.58–8.49. Based on it, the relation of temperature and entropy during refrigeration process for hydrate-based refrigeration system was analyzed. It’s coefficient of performance was 2–4 times of the conventional compression refrigeration.
[en] Hydrate technology is being developed for the storage and transport of natural gas. Micellar surfectant solutions were found to increase the gas hydrate formation rate and storage capacity. An anionic surfactant, a nonionic surfactant, their mixtures and cyclopentane were used to improve the hydrate formation of a synthetic natural gas (methane=92.05 mol%, ethane=4.96 mol%, propane=2.99 mol%) in a quiescent system in this work. The effect of an anionic surfactant (sodium dodecyl sulfate) on natural gas storage in hydrates is more pronounced compared to the effect of a nonionic surfactant (dodecyl polysaccharide glycoside). Cyclopentane could reduce hydrate formation induction time but could not improve the hydrate formation rate and storage capacity
[en] Highlights: • Depressurization and thermal co-stimulation using horizontal well were proposed. • 3D stimulation showed that gas release rate was 3 × 105 m3 per day within 450 days. • 2D stimulation showed that Class 3 hydrates could be dissociated within 8500 days. • 2D Simulation showed that heat flow was 1620 W lasting 1500 days, and decreased fast. • 1.1× 105 kg water was collected within 2000 days and then no more water was produced. - Abstract: Class 3 hydrate reservoirs exploiting using horizontal well by depressurization and thermal co-stimulation was simulated using the HydarteResSim code. Results showed that more than 20% of hydrates in the reservoirs had been dissociated within 450 days at the well temperature of 42 °C and well pressure of 0.1P0, 0.2P0 (P0 is the initial pressure of the reservoirs, simplifying 42 °C and 0.1P0, 42 °C and 0.2P0). While the production behavior of 42 °C and 0.5P0, 42 °C and 0.8P0 were not so exciting. In order to understand the production character of the well in long term, the cross section of 1 m length reservoirs was simulated. Simulation results showed that 4.5 × 105 m3 gas would be collected within 4500 days and 1.1 × 106 kg water could be produced within 1500 days in the well at 42 °C and 0.1P0. 3.5 × 105 m3 gas would be collected within 8500 days and 1.1 × 106 kg water could be produced within 1500 days in the well at 42 °C and 0.2P0. The heat flow was 1620 W at the beginning and then decreased rapidly in the two cases. For reservoirs of 1495.2 m in length, about 6.7 × 108 m3 and 5.3 × 108 m3 gas would be collected in the well corresponding to conditions of 42 °C and 0.1P0, and 42 °C and 0.2P0
[en] Within the oil and gas industry, low-dosage hydrate inhibitors (LDHIs) are a proven technology to control hydrates. Besides hydrate inhibitors, wax inhibitors (WIs) are frequently injected to prevent wax buildup in the crude oil pipeline. However, little attention has been focused on the effect of wax inhibitors on the performance of LDHIs. In this study, performance tests of 3 LDHIs in the presence of wax inhibitors were carried out for a 67% CH4/33% CO2 gas hydrate formation. Using the isothermal cooling method at pressures of 9 MPa and temperatures of 4 oC (subcooling is 9 oC), the results showed that the induction time of CH4-CO2 gas hydrate formation with LDHI/WI was shorter than the system with only LDHI. During the growth period, when the concentration of the WIs was 1 mass%, the growth time of the system with LDHI/WI was prolonged. Taking the induction time and the growth time into consideration, it was found that WIs had a more negative impact on the kinetic hydrate inhibitor performance at low dosage. The effect of WIs at high concentration could be negligible. (author)
[en] This paper is intended to determine the appropriate conditions for replacing CH4 from NGH with CO2. By analyzing the hydration equilibrium graphs and geotherms, the HSZs of NGH and CO2 hydrate, both in permafrost and under deep sea, were determined. Based on the above analysis and experimental results, it is found that to replace CH4 from NGH with gaseous CO2, the appropriate experimental condition should be in the area surrounded by four curves: the geotherm, (H-V)CO2, (L-V)CO2 and (H-V)CH4, and to replace CH4 from NGH with liquid CO2, the condition should be in the area surrounded by three curves: (L-V)CO2, (H-L)CO2 and (H-V)CH4. For conditions in other areas, either CO2 can not form a hydrate or CH4 can release little from its hydrate, which are not desirable results
[en] The major technical issue in gas hydrates energy storage systems is how to increase the refrigerants-water mass and heat transfer and how to realize a rapid formation of clathrate hydrate. Borrowing ideas from heat transfer enhancement of the fluid with the addition of nano-sized particles, the formation and dissociation of HFC134a (CH2FCF3) hydrate were studied in nano-copper suspensions of different mass fractions. The experimental results indicate that the addition of nano-copper enhances the heat and mass transfer process of HFC134a hydrate formation, which was shortened with the increasing mass fraction of nano-copper. Compared with the dissociation pressure at a given temperature below the critical dissociation point, a significant upward shift of the dissociation pressure of the HFC134a hydrate formed in the nano-fluid was observed. The critical dissociation point shifts from the former point (283.15 K, 414.86 kPa) to the latter one (282.65 K, 401.35 kPa), and the dissociation curve does not shift with the change of mass fraction of the nano-copper
[en] In this work, we investigate the dissociation behavior of natural gas hydrate in a closed system with microwave (MW) heating and hot water heating. The hydrate was formed at temperatures of 1-4 deg. C and pressures of 4.5-5.5 MPa. It was found that the gas hydrate dissociated more rapidly with microwave than with hot water heating. The rate of hydrate dissociation increased with increasing microwave power, and it was a function of microwave power. Furthermore, the temperature of the hydrate increased linearly with time during the microwave radiation
[en] This study reports on the modification of the anode and the cathode in a dual-chamber microbial fuel cell (MFC) with a polypyrrole (PPy)/anthraquinone-2,6-disulfonate (AQDS) conductive film to boost its performance and the application of the MFC to drive neutral electron-Fenton reactions occurring in the cathode chamber. The MFC equipped with the conductive film-coated anode and cathode delivered the maximum power density of 823 mW cm-2 that was one order of magnitude larger than that obtained in the MFC with the unmodified electrodes. This was resulted from the enhanced activities of microbial metabolism in the anode and oxygen reduction in the cathode owing to the decoration of both electrodes with the PPy/AQDS composite. The MFC with the modified electrodes resulted in the largest rate of H2O2 generation in the cathode chamber by the two-electron reduction of O2. The increase in the concentration of H2O2 was beneficial for the enhancement in the amount of hydroxyl radicals produced by the reaction of H2O2 with Fe2+, thus allowing an increased oxidative ability of the electro-Fenton process towards the decolorization and mineralization of an azo dye (i.e., Orange II) at pH 7.0.
[en] The methane hydration process is investigated in a semi-continuous stirred tank reactor. Liquid temperatures and reaction rates without stirrer are compared with those occurring with stirrer, while at the same time better stirring conditions of the methane hydration process are given by the experiments. Some basic data of fluid mechanics, for example, stirring Reynolds number, Froude number and stirrer power, are calculated during the methane hydration process, which can be applied to evaluate stirrer capacity and provide some basic data for a scaled up reactor. Based on experiment and calculations in this work, some conclusions are drawn. First, the stirrer has great influence on the methane hydration process. Batch stirring is helpful to improve the mass transfer and heat transfer performances of the methane hydration process. Second, induction time can be shortened effectively by use of the stirrer. Third, in this paper, the appropriate stirring velocity and stirring time were 320 rpm and 30 min, respectively, at 5.0 MPa, for which the storage capacity and reaction time were 159.1 V/V and 370 min, respectively. Under the condition of the on-flow state, the initial stirring Reynolds number of the fluid and the stirring power were 12,150 and 0.54 W, respectively. Fourth, some suggestions, for example, the use of another type of stirrer or some baffles, are proposed to accelerate the methane hydration process. Comparing with literature data, higher storage capacity and hydration rate are achieved in this work. Moreover, some fluid mechanics parameters are calculated, which can provide some references to engineering application
[en] A new method, a molecular thermodynamic model based on statistical mechanics, is employed to predict the hydrate dissociation conditions for binary gas mixtures with carbon dioxide, hydrogen, hydrogen sulfide, nitrogen, and hydrocarbons in the presence of aqueous solutions. The statistical associating fluid theory (SAFT) equation of state is employed to characterize the vapor and liquid phases and the statistical model of van der Waals and Platteeuw for the hydrate phase. The predictions of the proposed model were found to be in satisfactory to excellent agreement with the experimental data