Abstract

Based on the one-dimensional water transfer model and the lumped parameter model of fuel cell, the relationship between the steady-state output voltage of the fuel cell and the one-dimensional steady-state distribution of multi-state water is constructed in this paper. The optimal humidification strategy of the fuel cell is proposed, which guides the control of the relative humidity of the fuel cell anode and the relative humidity of the cathode and avoids the flooding and dehydration phenomenon inside the fuel cell and realizes the maximize output voltage of the fuel cell.

Abstract

Vapour compression cycle (VCC) is widely used technology of cooling and air-conditioning. Low-qualityindustrial-waste-heat driven ejector refrigeration systems (ERS) are promising solutions but limited by lower efficiency and larger system sizes. This paper presents the analysis of a new system which enhances the electrical-COP of the VCC by incorporating supersonic ejectors driven by heat. This new system, ejector-enhanced-vapour-compression-cycle (EVCC), increases the electrical-COP of the whole system while harnessing low-grade-waste-heat. Engineering Equation Solver (EES) has been used to model the system equations and the system performance is compared with VCC, Enhanced-ERS, and ejection-compression-system. In the analysis, R245fa has been used as the working fluid. The proposed system gives lower global-COP value as compared to conventional-VCC and ejectioncompression-system because this system is designed to be able to extract as much heat as possible from waste stream, therefore, higher electrical-COP is the focus of this proposed system. It is concluded that, for the base case, the proposed EVCC gives higher value of electricalCOP as compared to all the other three systems.

Abstract

Ocean thermal energy has been identified as a good thermal source for electric power generation especially for offshore oil and gas platforms and island energy security. Organic Rankine Cycles (ORCs) are promising systems for conversion ocean thermal energy to electricity; however, the thermal efficiencies still need to be increased. In this work, a dual-pressure ORC is used to improve the thermal efficiency of a closed ocean thermal energy conversion (OTEC) power plant. The evaporation and condensation temperatures of the dual-pressure ORCs are optimized to maximize the net power out. Compared to single-pressure ORCs, the dual-pressure ORCs can reduce the warm seawater temperature drop about 2 °C and generate 28-29% more net power. The working fluid with a higher critical temperature has a lower flow rate for the optimal condition. R600 produces slight high power than the other selected working fluids.

Abstract

This contribution relies on a prospective study of the French power sector up to 2050 using the TIMES model, combined with a reliability operating condition. To consider transient short-term power grid conditions, a reliability indicator related to the reserves of kinetic energy was defined and endogenized in the model to guarantee power system reliability under the implementation of a high share of variable renewable energy sources (VRES). For a declining share of nuclear inducing a high share of VRES, the pace of investments, additional back-up and flexible options to guarantee the grid’s stability anytime were studied.

Abstract

Bifunctional ruthenium and molybdenum oxide nanoparticles supported on activated carbon were designed and empolyed in hydrodeoxygenation (HDO) of lignin-derived aromatics for lignin depolymerization products upgrading. The typical model phenolic monomers and dimers could be efficiently converted to hydrocarbons over RuMoOx/C under mild conditions in decalin, i.e. at 160℃ and 30 bar H2. When HDO reaction was executed with real lignin-derived aromatics at 280℃and 30 bar H2, the total yield of hydrocarbons and cyclohexanol/ether were 56.93% and 18.99%. The main hydrocarbons were cyclohexane and alkyl-substituted cyclohexane. Characterization results revealed that the nanoparticles of ruthenium and molybdenum oxide species highly dispersed on activated carbon, while the presence of Ru active site and MoOx on activated carbon were crucial for the remarkable hydrogenolysis/ hydrodenation and deoxygenation activity, respectively. The hydrodeoxygenation pathway of diphenyl ether as a model compound catalyzed by optimized RuMoOx/C was discussed and the structure-activity relationship in hydrodeoxygenation was proposed.

Abstract

In the past four decades, oil sands production in Canada has increased dramatically. More recently, Canada has developed carbon emission reduction targets to meet its Nationally Determined Contributions and Mid-Century Strategy to reduce GHG emissions. Quantification and assessment of GHG emissions from the oil sands industry – a high emitter – is necessary to track progress toward meeting emissions reduction and technology development. This study uses GCAM, an integrated assessment model, to examine the energy consumption of oil sands extraction and upgrading. Five traditional and cogeneration extraction technologies are compared in model simulations for energy cost and nonenergy (operating) cost. Results show that energy consumed by oil sands production will triple by 2050 because of the expected increase in oil sands production. Cogeneration technologies result in reduced CO2 emissions.

Abstract

With the participating of electric vehicle (EV) aggregators in frequency regulation (FR) services, inevitable time delays are penetrating into power systems due to the open communication infrastructure and scheduling, which may lead to poor performance or even instability. The models of traditional FR system without EVs, FR system including EV aggregators without delay and FR system including EV aggregators consider-ing time delays are deduced and compared. And an effective damping ratio extraction method based on solution operator transformation is then presented for FR systems including EV aggregators with time delays. And by utilizing the proposed method, the dominant oscillation frequency and the minimum damping ratio are obtained. In consideration of time delays, we evaluate the effect of EV aggregators on the performance and stability of the frequency regulation system of the power system. Relationship between time delays, the gains of the PI controller and the dominant oscillation frequency and the minimum damping ratio of the FR scheme are explored. The model differences between time-delay and non-delay systems are revealed. Through comparisons, it is found that the mass utilization of electric vehicles in the frequency control might result in instability due to the aggregation delay, which induces oscillation for the whole system.

Abstract

Natural gas hydrate has currently been recognized as a potential alternative to traditional energy resources. In this study, the layered hydrate, which is a kind of grain-displacing hydrate, was synthetized in sea muds from South China Sea, and its dissociation behaviors by depressurization with different ambient temperature were investigated. The experimental results indicated that the cumulative gas production increases quickly with the pressure decrease. When the pressure reaches the setting production pressure and keeps constant, the gas production rate decreases significantly. The hydrate dissociation rate increases with the increase of the ambient temperature. There are obvious layered hollows in sea muds after hydrate dissociation. The sediment deformation cannot be ignored during the gas recovery from layered hydrate in sea muds.

Abstract

After their wide success in the field of road vehicles, hybrid propulsion technologies are gaining more and more interest for their application also in the marine sector. This interest is mainly justified by the need of reducing pollutant emissions, as required by new strictly standards and legislations for marine transport systems. This paper aims to identify the main hybrid propulsion architectures, also obtained through retrofit operations, to be considered for leisure boats, compared in terms of efficiency and on-board space/weight requirements. On the basis of the above architectures specific energy management strategies are evaluated, reporting their main advantages and disadvantages. The evaluations reported in this paper represents a useful decision support tool, to help ship producers in the design and energy management of an efficient and sustainable maritime mobility.

Abstract

In this paper, the performance of the moving average and moving median load estimation techniques is investigated using aggregated measurements of domestic smart meters. The load estimation techniques were tested using forward and backward walk approaches. Forward walk aims to estimate future load measurements using past measurements while backward walk estimates missing past measurements of the load using more recent measurements. Simulation results show that the moving average combined with forward walk produces load estimates with higher accuracies than the moving median and backward walk.