Formation of the structure-Ⅱgas hydrate from low-concentration propane mixed with methane

It has been recognized that a small amount of propane mixed with methane can change greatly in not only the thermodynamics but also the structural properties of gas hydrate.However,its mechanism is still not well understood yet.In this research,structure-Ⅱ(sⅡ)hydrate is synthesized using a methanepropane gas mixture with an initial mole ratio of 99:1,and it is found that large(5~(12)6~4)cages are cooccupied by multiple gases based on the rigid structure analysis of neutron diffraction data.The first principles calculation and molecular dynamics simulation are conducted to uncover the molecular mechanism for sⅡmethane-propane hydrate formation,revealing that the presence of propane inhibits the formation of structure-Ⅰ(sⅠ)hydrate but promotes sⅡhydrate formation.The results help to understand the accumulation mechanism of natural gas hydrate and benefit to optimize the condition for gas storage and transportation in hydrate form.

Fault Location Method Based on EEMD and Traveling-Wave Speed Characteristics for HVDC Transmission Lines

This paper presents a method of Traveling Wave Fault location based on the improved Hilbert- Huang Transform. First, Intrinsic Mode Functions (IMF) of traveling waves are extracted by Ensemble Empirical Mode Decomposition (EEMD). Then Hilbert Transform is applied to calculate the corresponding instantaneous frequency of the highest frequency component (IMF1), the instantaneous frequency and corresponding time-frequency graph are obtained. Second, the arrival time and speed can be detected by the first instantaneous frequency’s mutational point. Finally, the improved two-terminal traveling wave fault location principle is used to calculate the fault distance. Relevant simulation results are performed to verify the correctness of the method by EMTDC software.

Characterization of extracellular phosphatase activities in periphytic biofilm from paddy field

Periphytic biofilms exist widely in paddy fields, but their influences on the hydrolysis of organic phosphorus(P) have rarely been investigated. In this study,a periphytic biofilm was incubated in a paddy soil solution, and hydrolysis kinetic parameters(half-saturation constant(Km) and maximum catalytic reaction rate(Vmax)), optimal environmental conditions, substrate specificity, and response to different P regimes of the phosphatase activities in the periphytic biofilm were determined, in order to characterize extracellular phosphatase activities in periphytic biofilms from paddy fields. The results indicated that the periphytic biofilm could produce an acid phosphomonoesterase(PMEase), an alkaline PMEases, and a phosphodiesterase(PDEase). These three phosphatases displayed high substrate affinity, with Km values ranging from 141.03 to 212.96 μmol L^(-1). The Vmax/Km ratios for the phosphatases followed the order of alkaline PMEase > acid PMEase > PDEase, which suggested that the PMEases, especially the alkaline PMEase, had higher catalytic efficiency. The optimal pH was 6.0 for the acid PMEase activity and 8.0 for the PDEase activity, and the alkaline PMEase activity increased with a pH increase from 7.0 to 12.0. The optimal temperature was 50℃ for the PMEases and 60℃ for the PDEase. The phosphatases showed high catalytic efficiency for condensed P over a wide pH range and for orthophosphate monoesters at pH 11.0, except for inositol hexakisphosphate at pH 6.0. The inorganic P supply was the main factor in the regulation of phosphatase activities. These findings demonstrated that the periphytic biofilm tested had high hydrolysis capacity for organic and condensed P,especially under P-limited conditions.

Semi-clathrate hydrate based carbon dioxide capture and separation techniques

CO_(2)is considered as the main contributor to global warming,and hydrate enclathration is an efficient way for carbon capture and separation(CCS).Semi-clathrate hydrate(SCH)is a type of clathrate hydrate capable of encaging CO_(2)molecules under mild temperature and pressure conditions.SCH has numerous unique advantages,including high thermal stability,selective absorption of gas molecules with proper size and recyclable,making it a promising candidate for CCS.While SCH based CCS technology is in the developing stage and great efforts have to be conducted to improve the performance that is determined by their thermodynamical and structural properties.This review summarizes and compares the thermodynamic and structural properties of SCH and quaternary salt hydrates with gas mixtures to be captured and separated.Based on the description of the physical properties of SCH and hydrate of quaternary salts with gas mixture,the CO_(2)capture and separation from fuel gas,flue gas and biogas with SCH are reviewed.The review focuses on the use of tetra-nbutyl ammonium halide and tetra-n-butyl phosphonium halide,which are the current application hotspots.This review aims to provide guidance for the future applications of SCH.

Frontier science and challenges on offshore carbon storage

Carbon capture and storage(CCS)technology is an imperative,strategic,and constitutive method to considerably reduce anthropogenic CO_(2)emissions and alleviate climate change issues.The ocean is the largest active carbon bank and an essential energy source on the Earth's surface.Compared to oceanic nature-based carbon dioxide removal(CDR),carbon capture from point sources with ocean storage is more appropriate for solving short-term climate change problems.This review focuses on the recent state-of-the-art developments in offshore carbon storage.It first discusses the current status and development prospects of CCS,associated with the chailenges and uncertainties of oceanic nature-based CDR.The second section outlines the mechanisms,sites,advantages,and ecologic hazards of direct offshore CO_(2)injection.The third section emphasizes the mechanisms,schemes,influencing factors,and recovery efficiency of ocean-based CO-CH_(4)replacement and CO_(2)-enhanced oil recovery are reviewed.In addition,this review discusses the economic aspects of offshore CCS and the preponderance of offshore CCs hubs.Finally,the upsides,limitations,and prospects for further investigation of offshore CO_(2)storage are presented.

油气储层长石矿物表面水滴接触角

润湿性是油气储层岩石的一个重要特性,但由于组成储层孔隙的矿物成分多样且颗粒多在微米尺度,准确评价某一矿物的润湿性是一个难题.长石是砂岩储层的重要组成矿物,然而关于长石润湿性的研究却很少.本文利用原子力显微镜测量了微米级水滴在储层岩石钾长石和钠长石表面的接触角.结果表明,水-钾/钠长石接触角并不是一个定值,而是分布一定范围,这可能与晶体表面粗糙与非均质、晶面不同有关.相比于以前研究中用间接方法计算得出的水-长石接触角,本研究在实际储层长石矿物表面直接测量的接触角具有更好的代表性.就平均接触角而言,水-钾/钠长石的接触角均小于相同条件下测得的水-石英接触角,从而说明在用接触角法评价人造砂岩岩心的润湿性时,应综合考虑长石、石英对润湿性的影响.

A statistical-based online cross-system fault detection method for building chillers

Practical applications of data-driven fault detection(FD)are limited by their portability.The costs of model training and validation are extremely high when each system requires a model retrained on its own fault and fault-free data.Therefore,this paper proposes a statistical-based online cross-system FD method to address the problem of model portability.The proposed FD model can be cross-utilized between building chillers with various specifications while it only needs to update the original fault detection model by the normal operation data of the new chiller system,thus saving huge fault experimental costs for the fault detection of new chiller.First,a theoretical basis for the proposed cross-system fault detection method is presented.Then,experiments were conducted on three building chillers with different specifications.Both fault and fault-free data were collected from the three chillers.The development and validation of the proposed cross-system fault detection method are then conducted.Results show that the cross-system fault detection models perform well when used with different chillers.For instance,when the fault detection model of system#1 was cross-utilized to system#2,the detection accuracies of refrigerant leakage,refrigerant overcharge,and reduced evaporator water flow were 99.73%,90.17%,and 96.94%,respectively.Compared with original models,the detection accuracies were improved by 33.78%,84.07%,and 65.56%,respectively.Therefore,the proposed cross-system fault detection method has potential for online application to practical engineering FD.