Abstract

Methane hydrate (MH) is considered as one of the most promising energy source. It is necessary to understand the characteristics of methane hydrate formation and dissociation in marine sediments. In this study, the marine sediments from the South China Sea were employed to remold sediment core samples containing methane hydrates. Then, the MH-bearing sediment was dissociated by depressurization. The experimental results indicated that with the continuous supply of gas source, it is easier to nucleate and grow for methane hydrate in marine sediments under confining pressure. However, hydrate formation may lead to graincoating or contact-cementing pore, thereby not contributing to the gas flow. Thus, as the continuous gas injection causes the hydrate saturation to increase, the time required for inlet pressure raised to equal outlet pressure becomes longer and longer. In the later stage of depressurization, under the influence of confining pressure and fluid flow driving, water production and gas production in marine sediments are extremely difficult.

Abstract

Methane hydrate is important energy source in the future. The recognition of methane hydrate in marine sediments is a tough task all the time. We employed a mircofocus X-ray CT to investigate the methane hydrate in South China Sea sediments. The CT images indicate that the various components are difficult to be distinguished because of the limitation of CT resolution, but the change of gray distribution can be used to recognize the appearance of methane hydrate. The formation of hydrates caused the density change of sediment sample, which can be reflected on the CT images. The pixel number change of about 13% may correspond to the hydrate saturation formed in the sediments. The results of this study is of significance to the holistic recognition of methane in marine sediments.

Abstract

Due to the vast amount of recoverable natural gas predicated (~3,000 TCM) in natural gas hydrate on earth, natural gas hydrate has the potential to become the next generation of unconventional source of fuel. Recently years, laboratory researches are still underway to advance our understanding of the theory and technology for natural gas hydrate exploitation. The Pilot-Scale Hydrate Simulator (PHS), a three-dimensional 117.8 L pressure vessel, was applied to study the methane hydrate dissociation using depressurization with different depressurization rates in the sandy sediment. The volume of the vessel is big enough to simulate the field-scale gas production from hydrate reservoir. The production behaviors and heat transfer characteristics during hydrate dissociation in sandy sediments with different depressurization rates were compared and investigated. The experimental results indicate the influence of depressurization rate on hydrate dissociation using depressurization method. The lower depressurization rate leads to the larger amount of hydrate dissociation during depressurizing stage, because the fluid flows in this stage enhance the heat convection in the sediment causing a higher heat transfer rate from surroundings. In addition, the lower depressurization rate causes the lower water production rate, which benefits for the gas production from hydrate reservoir. On the other hand, fast pressure dropping may lead to ice formation and secondary hydrate formation in the pipeline. However, the higher depressurizing rate leads to a higher gas production rate in the depressurizing stage. Therefore, an optimized depressurizing rate for hydrate dissociation with the highest energy efficiency is performed.

Abstract

The rack backdoor cooling is an efficient way for server temperature contral and energy saving. In this paper, a coupled model of multiple-heat-sources model of 42U rack and mathematical models of the microchannel vertical evaporator are established and mathematical models are verified by experimental results. Inhomogeneous air temperature and flow velocity data after being heated by servers and before coming in evaporator can be obtained with the rack model. It is discovered that the maximum temperature difference is up to 9.5℃ under uniform load conditions, and 15℃ under non-uniform load conditions. When upper, middle and lower parts of the rack are set to zero load, the overall air-side outlet temperature difference can reach 6.5℃, 8℃ and 8.5℃ separately. Compared with full load working, the air temperature uniformity of evaporator outlet can be improved when some severs are standby, and it improves with the height of inactive servers. These simulation results can provide an effective guidance for the optimization design and application of the micro-channel vertical evaporator in the rack backdoor cooling.

Abstract

The hydrate formation and reformation reduce mining efficiency and safety during natural gas hydrate exploration and natural gas pipeline transportation. In this paper, the methane hydrate formation and reformation in partially water saturated consolidated porous media were studied by low field MRI. The results show that the change of water content was ununiform both in time and space. The water content reduction rate displayed as fast-slow-fast-slow periodic rhythm; Hydrate formed prior in the bigger pores due to the bigger contact area between water and gas and lower pore water saturation; The formed hydrate made the pore structure inside of porous media more complicated; The rate of hydrate reformation was faster than that of hydrate formation because the residual hydrate microcrystalline structure after decomposition provided the place of dendrites nucleated and grew. This research can give some implications for delivering natural gas safely and studying natural gas hydrate reservoirs.

Abstract

This paper studies CO2 emission structure of China from 1957 to 2012 by using newly compiled environmentally-extended historical input-output tables of China. These tables are the first environmentallyextended input-output tables covering the years in the early stage of People’s Republic of China. The result shows that China’s emission structure was stable for almost six decades. Heavy industries contributed about 80% of CO2 emission in 1950s and 1960s, although China was a poor country at that time. Although after economic reform the share of CO2 emitted directly from heavy industries has decreased and that from electricity has increased, a network analysis shows that a significant part of CO2 emitted directly by electricity sector was induced by heavy industries. Therefore heavy industries are still the main contributor of CO2 emission after economic reform. The independent and self-reliance ideology of China leads to stability of emission structure. Because the independent ideology will continue in the future, the only option for China is to increase energy efficiency for the current existing industries.

Abstract

Pyrolysis is widely used to convert biomass to liquid biofuel. It is also an interesting technology at an industrial scale, which is a motivation to seek an increase in process efficiency. The pyrolysis of large biomass particles differs from the pyrolysis of fine particles because they do not heat and decompose homogeneously. In this work, experimental data for the pyrolysis of a wheat straw pellet and a single particle model are presented. Furthermore, the key parameters controlling the internal temperature distribution are discussed.

Abstract

Solar irradiance prediction is an emerging area of research for various applications in renewable energy domain. So far, numerous physical models, statistical models and machine learning based techniques have been utilized to accomplish solar irradiance prediction. However, existing models are not good at learning long-term historical dependencies, lead to compromise in modeling non-linear solar irradiance patterns. In this paper, a novel prediction model (i.e. Long Short Term Memory, LSTM) from deep neural network family is used to predict hourly solar irradiance with enhanced prediction accuracy by considering long-term historical data dependencies. To provide an extensive and strong assessment of proposed model, present study employs National Solar Radiation Database (NSRDB) data for evaluating prediction accuracy at 7 locations of India having different climatic conditions. The proposed model is compared with Feed Forward Neural Network (FFNN), Extreme Gradient Boost (XGBoost) and Persistence model at broader coverage of geographical regions. Empirical outcomes suggest that proposed LSTM model outperforms different models with an average forecast skill of 50.72% over persistence model.

Abstract

Aiming at the problems of high moisture content of semi-coke products, high water consumption in the production process and severe environmental pollution in the production process of coal pyrolysis, the paper proposes the process of using semi-coke dry quenching coke waste heat recovery by using inert gas as quenching medium. The simulation calculation of the pyrolysis semi-coke dry quenching waste heat recovery process was carried out. The initial temperature, water vapor content, and gas flow rate of different medium circulating gases were studied. The relationship between the preheating outlet temperature and the drying temperature of the coal was analyzed, and the energy saving effect of the process was analyzed and verified by experiments. The results show that the pyrolysis semicoke dry quenching coke waste heat recovery process is feasible; the quenching temperature and the coal drying waste heat outlet temperature have no significant relationship with the medium drying type, which is closely related to the specific heat of the gas; Compared with water-saving and energy-saving effect, it does not consume water, avoiding a series of problems caused by it. While meeting the process requirements, it can reuse 65-75% of the sensible heat of hot semi-coke. Theoretical analysis and experimental verification prove the good application prospect of this technology.

Abstract

Although there is abundant geothermal energy in deep reservoirs, to effectively extract the heat rather than the geofluid is still a challenge. This study investigated the heat extraction performance of a coaxial double-pipe heat exchanger in a deep geothermal well with particular reference to geothermal heating. A numerical simulation model is established and the heat extraction rates (geothermal energy production rates) and their changes with the time of production are analyzed in detail. As a result, either the heat-carrier mass flowrate of 1.5 kg/s for direct heating utilization or 4 kg/s for heating with use of heat pump system has shown a sound performance. Results obtained are useful for better understanding of such geothermal heat extraction technology.