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Abstract The dynamics of CH 4 replacement in the CH 4 hydrate with saturated liquid CO 2 at 273.2 K was measured with a high pressure optical cell. The results showed that CH 4 in the hydrate gradually moved to the liquid CO 2 phase while CO 2 in the liquid phase penetrated into the hydrate from the quantitative analysis. The decomposing process of the CH 4 hydrate during the replacement was analyzed with in situ Raman spectroscopy, which allowed us to distinguish the cage structure of the CH 4 hydrate and discuss the microscopic view of the replacement in the hydrate. It was found that the decomposition of the medium cage (M-cage) in the CH 4 hydrate proceeded faster than that of the small cage (S-cage). The observed rate difference could be related to the stability of the S-cage in the CH 4 hydrate or the re-formation tendency of CH 4 and water molecules in the S-cage after decomposing the hydrate structure, whereas the guest molecule exchange of CH 4 with CO 2 could occur in the M-cage. Based on the experimental data, we developed a kinetic model for calculation of the CH 4 remaining in the hydrate considering the decomposition rate difference between the M-cage and S-cage in the CH 4 hydrate. The results indicate that the driving force could be the fugacity difference between the fluid phase and the hydrate phase for the replacement process.

Abstract The clathrate hydrate formation at the interface between liquefied carbon dioxide (CO 2 ) and liquid water is one of the key processes in the course of direct CO 2 disposal into deep seas—an option to mitigate the emission of CO 2 into the atmosphere. Eight different models have been proposed so far on the formation and metabolic self-preservation of a hydrate film at the interface and also the mass transfer of CO 2 across the hydrate film. This paper reviews those rival models one by one and illustrates how they are discrepant. Each model is critically examined, and if any, its weakness in physical reality or mathematical formulation is pointed out. The state of the art of hydrate-film modeling thus revealed suggests the necessity of more careful consulting of pertinent experimental observations to establish our physical view about hydrate films, which should serve as the base of any further work on hydrate-film modeling.

Abstract In this paper, two robust decentralised proportional integral (PI) control designs are proposed for load frequency control (LFC) with communication delays. In both methodologies, the PI based LFC problem is reduced to a static output feedback (SOF) control synthesis for a multiple delay system. The first one is based on the optimal H ∞ control design using a linear matrix inequalities (LMI) technique. The second control design gives a suboptimal solution using a developed iterative linear matrix inequalities (ILMI) algorithm via the mixed H 2 / H ∞ control technique. The control strategies are suitable for LFC applications that usually employ PI control. The proposed control strategies are applied to a three control area power system with time delays and load disturbance to demonstrate their robustness.

For global survival, we need to launch a rapid regeneration of the nuclear power industry. The replacement of the present fossil fuel industry requires a doubling time for alternative energy sources of 5–7 years and only nuclear energy has the capability to achieve this. The liquid metal cooled fast breeder reactors (LMFBR) have the best breeding criteria but the doubling time exceeds 20 years. Further, the use of plutonium in these systems has the potential of nuclear proliferation. The Thorium Molten-Salt Nuclear Energy Synergetic System [THORIMS-NES], described here is a symbiotic system, based on the thorium–uranium-233 cycle. The production of trans-uranium elements is essentially absent in Th–U system, which simplifies the issue of nuclear waste management. The use of 233 U contaminated with 232 U as fissile material, instead of plutonium/ 235 U makes this system nuclear proliferation resistant. The energy is produced in molten-salt reactors (FUJI) and fissile 233 U is produced by spallation in Accelerator Molten-Salt Breeders (AMSB). This system uses the multi-functional ‘‘single-phase molten-fluoride” circulation system for all operations. There are no difficulties relating to ‘‘radiation-damage”, ‘‘heat-removal” and ‘‘chemical processing” owing to the simple ‘‘idealistic ionic liquid” character of the fuel. FUJI is size-flexible, and can use all kinds of fissile material achieving a nearly fuel self-sustaining condition without continuous chemical processing of fuel salt and without core-graphite replacement for the life of the reactor. The AMSB is based on a single-fluid molten-salt target/blanket concept. Several AMSBs can be accommodated in regional centers for the production of fissile 233 U, with batch chemical processing including radio-waste management. FUJI reactor and the AMSB can also be used for the transmutation of long-lived radioactive elements in the wastes and has a high potential for producing hydrogen-fuel in molten-salt reactors. The development and launching of THORIMS-NES requires the following three programs during the next three decades:

Abstract Recent results of power generation experiments with an improved heat exchanger system in the FUJI-1 facility were described. One of the main purposes was to study the effect of working gas temperature on generator performance. The results with argon working gas showed that the gas temperature of 1850 K is enough to eliminate the effect of inlet relaxation under the present experimental conditions and that gas temperature does not greatly affect the output performance so long as the inlet relaxation is not significant. The radial component of velocity was successfully measured with high time resolution by means of the cross-correlation method. The effect of seed fraction on the measured velocity was discussed. For the case of helium working gas, the voltage drop owing to an inlet relaxation was remarkably decreased, and improvement in both output power and enthalpy extraction can be observed by the increase of gas temperature. The voltage drop still existed at the inlet of the channel, and therefore, higher gas temperature and higher seed fraction are required in order to achieve higher generator performance.

Abstract Photoreduction of CO 2 to formate (HCO 2 − ) can be achieved by the phenazine-catalyzed system consisting of cobalt cyclam complex (Co-cyclam, cyclam = 1,4,8,11-tetraazacyclotetradecane) as an electron mediator and triethylamine as an electron donor. Flash photolysis revealed that the catalytic system should involve electron transfer from the photoformed radical anion of phenazine (P •− to Co III cyclam and hydrogen transfer from phenazinyl radical (P •− ) to intermediary Co II cyclam. The resulting cobalt hydride complex, Co-cyclam(H), provides formate through Co III formate complex formed by CO 2 insertion.

Supercritical cycles for geothermal power generation systems are studied to raise the power output and thermal efficiency by selecting natural fluids and new organic working fluids as the working fluids and optimizing the cyclic parameters, especially the condensing temperature or pressure. For a given liquid dominated geothermal resource, thermodynamic parameters, using propane, R-125 and R-134a as the working fluids, respectively, are calculated to show the features of supercritical power cycles and compare to other design results shown in references. Greater power output shows that propane and R-134a are appropriate working fluids of supercritical cycles for geothermal binary design.

Abstract A robust optimal design method, based on the relative robustness criterion, is proposed to conduct the unit sizing of energy supply systems, so that they are robust economically under uncertain energy demands. The values of design variables or equipment capacities, as well as those of operation variables or utility contract demands and energy flow rates, are determined to minimize the maximum normalized regret or the maximum regret rate in the annual total cost and satisfy all the possible energy demands. This optimization problem is formulated as a multi-level nonlinear programming problem, and its solution is obtained by repeatedly evaluating the upper and lower bounds for the optimal value of the maximum regret rate by means of the fractional, the bi-level and the linear programming. Through a case study on a cogeneration system, features of the robust optimal design, based on the relative robustness criterion, are clarified.