Abstract

In the current work, the analysis of regenerative organic Rankine cycle (ORC) using wet fluids is performed. For the purpose to convert waste energy to useful work from three different heat sources, eleven wet organic fluids were selected divided into three groups according to their critical temperatures ranging from 66°C to 132°C. Results show that the working fluids with the lowest critical temperature to heat source inlet temperature ratio will generate the maximal net power output, namely R125, R1270 and R152a. Superheating affects the system performance negatively, since the net power output decreases as the superheat increases.

Abstract

This paper covers the thermodynamic and techno-economic optimization of ORCs for low-to-medium temperature heat source applications, when ammonia, propylene, R152a and R32 are used as cycle working fluids. Results were obtained for a varying hot source inlet temperature, from 120°C to 250°C, and different capacity power plants, showing that the most efficient ORC power plants always had a higher Specific Investment Costs (SIC) for the studied cases. Large capacity power plant (power output between 1 and 2.5 MW) are more expensive than the small-capacity ones (power output below 1 MW) but the SIC of large capacity systems can be half of that of small-capacity systems. Minimizing the SIC of ORCs tends to higher evaporating and condensing temperatures than the ones that result from the thermodynamic optimization.

Abstract

Energy conversion, energy efficiency and the study of producing liquid fuels from other carbon resources are getting an increasing attention, as the continue depletion of oil. In this paper, SiO2-encapsulated Fe@Mn catalysts were prepared by Stöber method and applied for the production of olefins-riched liquid fuels from syngas. With the thickening of SiO2 shell, the selectivity for liquid hydrocarbons (C5+) presents a volcanic trend, which is the result of the balancing effect between hydrogen enrichment and spatial restriction of SiO2 shell. The promotional effect of SiO2 shell on the formation of C5+ can be attributed to the confinement effect of SiO2 shell, which prolongs the residence time of light hydrocarbons formed on Fe@Mn, enhancing the polymerization reaction for producing more C5+ hydrocarbons. The C5+ selectivity can reach 72% with 78% olefins in it, at CO conversion of 67%. However, the continued increase in the thickness of SiO2 shell may lead to the enrichment of H2 and increase the local H2/CO ratio in the vicinity of the active metal, enhancing the hydrogenation reaction and suppressing the formation of C5+ hydrocarbons.

Abstract

Gas hydrate is usually regarded as a huge potential energy resource as well as its promising industrial application for gas separation, storage and transportation. Previous researches have shown that gas hydrate phase transition is mainly controlled by heat and mass transfer, while limited work concerns the mass transfer effects of gas micro-bubbles on the hydrate crystallization. In this study, variations in microscopic morphology of hydrate crystals growth in a liquid-gas phase have been observed using a microscope imaging system. The results indicate that the nucleation of hydrate firstly tends to occur at a bubble interface. And the cooling rates increase exponentially with the crystal growth rates and play an important role in the morphology of hydrate crystal growth. In addition, the hydrate crystals tend to grow in the direction of the bubbles affected by the Ostwald ripening effects, which suggests that the bubbling is an efficient measure to promote the application of hydrate-based technologies.

Abstract

For downhole coaxial heat exchanger (DCHE), the working fluid is injected from the annulus and produced from the central insulated tubing. There have been many studies on the heat extraction performance of DCHE. However, to the best of our knowledge, most previous numerical models did not consider the fluid flow in the reservoir, which has a significant effect on DCHE performance. Thus, an unsteady-state heat transfer model considering flow in reservoir is presented. The effects of the key factors are studied. The field test is conducted to verify the feasibility of DCHE system. The simulation results depict that the increase of flow velocity in reservoir will increase the outlet temperature and thermal power. As the mass flow increases, the thermal power increases. As the inlet temperature decrease, the outlet temperature decreases and the thermal power increases. The simulation data are in good agreement with the test data, and the error is less than 12%. The findings can offer guidance for optimal design of DCHE.

Abstract

Aiming at the failure with large scale and long lasting time of distribution network(DN) under extreme natural disaster, a strategy of micro-energy grid(MG) and DN improving resilience in coordination in the process of dealing with surface nature disaster is proposed. First, combining the system function curve of DN under extreme disasters, a framework of resilience enhancing strategy during the overall process is proposed. Second, during the stage of DN defending and adapting to disasters, rolling outage management scheme when MG is in islanding state is raised, which considers the relevance among cool, heat and electric load as well as the influence of the remaining capacity in ESS on the next stage. Third, during the stage of fault recovery, robust DN fault recovery model which considers MG’s supporting role is established, including raising the master-problem of fault repair plan and the sub-problem of restoration plan of some repair plan; through iteration of the masterproblem and sub-problem, the optimal fault recovery strategy is worked out. Finally, the effectiveness of the method proposed in this paper is verified.

Abstract

With rapid depletion of conventional energy resources and the promotion of low-carbon energy development, natural gas hydrate (methane hydrate) has been attracting increasing attention over the governments, scientists, and industries, for its huge reserves and less environmental pollution after combustion. Japan and China have successfully conducted trail production and harvested natural gas from marine hydrate reservoir, which ignites the hope of commercial natural gas production by natural gas hydrate exploitation. However, natural gas was buried in the sediment under the deep ocean sea floor, and gas hydrate serves as effective cementing agent among the sediment particles. Drilling production well and gas production from hydrate reservoir may result in a series of natural geological hazards. Methane leakage from the hydrate reservoir and the migration of methane into the overlying water column can cause ocean acidification. Furthermore, once abundant methane bubbles escaped into the atmosphere will influence the carbon cycle and global climate change. Quantitative research of environmental and ecosystem impact of methane leakage from natural gas hydrate exploitation is indispensable for promoting the commercial exploitation process of natural gas hydrate. This paper outlines the potential environmental impact of natural gas exploitation in detail, which provides references for future natural gas hydrate exploitation and utilization.

Abstract

In the non-horizontal pipeline flow, the fluid will accelerate (or decelerate) and contact with the heat exchange surface due to the influence of gravity. In this paper, the effects of different vane angles and Reynolds numbers on the heat transfer and pressure drop characteristics in the non-horizontal swirling tube are investigated by numerical simulation. It shows that the component force of gravity in the axial direction plays a key role in the heat transfer intensity and pressure drop. Compared with the horizontal flow, the cross-section temperature distribution of the non-horizontal flow changes significantly, and the pressure distribution changes moderately. These findings provide some theoretical guidance for the optimization of the structure of the swirler in a non-horizontal pipeline.

Abstract

In this work, the maize straw based hydrochars were produced under various conditions by the hydrothermal carbonization (HTC) process. The properties of prepared hydrochar were analyzed experimentally in order to evaluate the feasibility for the blast furnace injection. It was found out that the carbonization temperature of 280 °C with a holding time of 60 minutes was the optimal operating condition to produce the hydrochar. The evaluation results show that the produced hydrochar has the required fuel properties and combustion performance.

Abstract

Solar energy is a sustainable source that is favored in tropical areas where the resource intensity is high. However, developing accurate forecasting models, which is crucial in the optimal design and operation of tropical solar energy systems, has been challenging due to the high-dimensional nature of the system. This study presents a novel forecasting model for such systems using support vector machines. The proposed model was developed using a data-driven methodology. Model optimization and feature selection were applied to improve predicting accuracy. Modeling results show that the medium Gaussian function provided the most desirable balance between the accuracy and speed of the training functions. The previous hour observation was found to be the most significant input, while some variables considered in the initial model caused overfitting. The final model had superior accuracy over the initial models and those developed in the literature, thereby validating the effectiveness of the presented methodology.