Browsing by Author "Li, Qiang"
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Item Andreev Reflection and Klein Tunneling in High-Temperature Superconductor-Graphene Junctions(American Physical Society, 2023-04-12) Jois, Sharadh; Lado, Jose; Gu, Genda; Li, Qiang; Lee, Ji Ung; Department of Applied Physics; Correlated Quantum Materials (CQM); State University of New York Polytechnic Institute; Brookhaven National LaboratoryScattering processes in quantum materials emerge as resonances in electronic transport, including confined modes, Andreev states, and Yu-Shiba-Rusinov states. However, in most instances, these resonances are driven by a single scattering mechanism. Here, we show the appearance of resonances due to the combination of two simultaneous scattering mechanisms, one from superconductivity and the other from graphene p−n junctions. These resonances stem from Andreev reflection and Klein tunneling that occur at two different interfaces of a hole-doped region of graphene formed at the boundary with superconducting graphene due to proximity effects from Bi2Sr2Ca1Cu2O8+δ. The resonances persist with gating from p+−p and p−n configurations. The suppression of the oscillation amplitude above the bias energy which is comparable to the induced superconducting gap indicates the contribution from Andreev reflection. Our experimental measurements are supported by quantum transport calculations in such interfaces, leading to analogous resonances. Our results put forward a hybrid scattering mechanism in graphene–high-temperature superconductor heterojunctions of potential impact for graphene-based Josephson junctions.Item Downhole electric heater with high heating efficiency for oil shale exploitation based on a double-shell structure(PERGAMON-ELSEVIER SCIENCE LTD, 2020-11-15) Wang, Zhendong; Lu-Tervola, Xiaoshu; Li, Qiang; Youhong, Sun; Yuan, Wang; Deng, Sunhua; Guo, Wei; Department of Civil Engineering; Structures – Structural Engineering, Mechanics and Computation; Jilin UniversityTo improve the heating efficiency of the downhole electric heaters used in oil shale exploitation, double-shell downhole electric heaters with continuous helical baffles (DS-DEHs) were developed in this study. These heaters reduce heat loss generated by the shell of single-shell downhole electric heaters with continuous helical baffles (SS-DEHs) and reuse the heat loss by driving air flows through outer and inner shell-passes in sequence. Two types of DS-DEHs with three different helical pitches were experimentally studied, and SS-DEHs were set as the control. The results indicated that the effect of mass flow rate on the heating rate is greater than that of heating power. Forced convection is the major heat transfer mode in heater shell-side, and the contribution of shell-side radiant heat transfer mainly depends on the helical pitch, then on the heating power and mass flow rate. Additionally, the heat loss generated by heater shell is mainly dissipated in the form of radiation. The total heat loss of the DS-DEH is 87.16%–96.41% lower than that of the SS-DEH, and its heating efficiency is 1.06–1.17 times than that of SS-DEH, indicating that the double-shell structure can effectively improve the heating efficiency of downhole electric heaters.Item Effects of composition and pore evolution on thermophysical properties of Huadian oil shale in retorting and oxidizing pyrolysis(Elsevier BV, 2021-12-01) Xu, Shaotao; Sun, Youhong; Lu, Xiaoshu; Yang, Qinchuan; Li, Qiang; Wang, Zhendong; Guo, Mingyi; Jilin University; Structures – Structural Engineering, Mechanics and Computation; Shaanxi Coal Geology Group Co., Ltd.; Department of Civil EngineeringThis chemical composition and pore evolution of oil shale during oxidizing pyrolysis (OP) and their influences on its thermophysical properties were investigated in this study. Various transformations of the minerals in oil shale were detected, among which montmorillonite was noted to transform into illite during anaerobic retorting (AR), and into kaolinite during OP. Variations in the quantities of residual carbon and organic matter during low-temperature AR and OP were noted to be possibly responsible for the difference in pore volumes. Remarkable increases in surface and volumes of mesopores and macropores through OP were observed even at low temperatures. The pore volume was proven to significantly affect the thermophysical properties of semi-cokes at low temperatures during OP. Higher thermal conductivity and thermal diffusivity were observed in semi-cokes obtained via OP at 350 ℃ compared to those obtained via AR at 520 ℃. These phenomena highlight the potential of OP for application in in-situ oil shale exploitation.Item Effects of Packer Locations on Downhole Electric Heater Performance: Experimental Test and Economic Analysis(MDPI AG, 2020-01-13) Guo, Wei; Wang, Zhendong; Sun, Youhong; Lu-Tervola, Xiaoshu; Wang, Yuan; Deng, Sunhua; Li, Qiang; Department of Civil Engineering; Structures – Structural Engineering, Mechanics and Computation; Jilin UniversityA downhole electric heater, which reduces heat loss along a heat insulation pipe, is a key apparatus used to ignite oil shale underground. Downhole heaters working together with packers can improve the heating efficiency of high-temperature gases, while different packer locations will directly affect the external air temperature of the heater shell and, subsequently, the performance and total cost of the downhole heaters. A device was developed to simulate the external conditions of heater shells at different packer locations. Then, the effects of external air temperature on the performance of a downhole heater with pitches of 50, 160, and 210 mm were experimentally studied. In the test, results indicated that the heater with a packer at its outlet had an accelerated heating rate in the initial stage and decreased temperature in the final stage. Additionally, the lowest heating rod surface temperature and highest comprehensive performance were achieved with minimal irreversible loss and lower total cost when using a downhole electric heater with a packer set at its outlet. In addition, the downhole electric heater with a helical pitch of 50 mm and a packer at its outlet was more effective than other schemes in the high Reynolds number region. These findings are beneficial for shortening the oil production time in oil shale in situ pyrolysis and heavy oil thermal recovery.Item Energy consumption and product release characteristics evaluation of oil shale non-isothermal pyrolysis based on TG-DSC(Elsevier, 2020-04) Zhao, Shuai; Sun, Youhong; Lu-Tervola, Xiaoshu; Li, Qiang; Jilin University; Structures – Structural Engineering, Mechanics and Computation; Department of Civil EngineeringThermogravimetric-Differential Scanning Calorimetry Analysis (TG-DSC) was applied to study non-isothermal pyrolysis characteristics of oil shales, such as the starting point, stability, pyrolysis interval and product release using Fuyu and Huadian oil shale samples. Results show that with the increase of heating rate, oil shale pyrolysis moves to higher temperature zone. This trend is more noticeable at higher oil content. The pyrolysis stability of the oil shale is related to oil content and pyrolysis atmosphere. The higher the oil content, the more stable the pyrolysis of the oil shale. Under nitrogen atmosphere, the pyrolysis interval of oil shale is more concentrated, air prolongs the pyrolysis interval, and the pyrolysis stability index decreases. In addition, the increase of heating rate favours the release characteristic index of the product, which is not practically affected by oil content. The release characteristic indices of pyrolysis products from oil shale under nitrogen atmosphere are higher than those under air atmosphere. The optimum heating rate that produces the highest oil product yield for pyrolysis progress of Huadian oil shale is 20 °C/min, and Fuyu oil shale is 40 °C/min.Item Kinetics and thermodynamics evaluation of carbon dioxide enhanced oil shale pyrolysis(Nature Publishing Group, 2021-01-12) Zhao, Shuai; Sun, Youhong; Lü, Xiaoshu; Li, Qiang; Department of Civil Engineering; Structures – Structural Engineering, Mechanics and Computation; China University of Mining and Technology; China University of Geosciences, Beijing; Jilin UniversityThe pyrolysis process of oil shale is significantly affected by atmospheric conditions. In this paper, the pyrolysis experiments of oil shale under non-isothermal conditions are carried out using nitrogen and carbon dioxide as heat-carrying fluids. The results show that the activation energy of the second stage of oil shale pyrolysis under carbon dioxide is less than that under nitrogen. The thermodynamic analysis of the second stage of oil shale pyrolysis shows that Gibbs free energy, activation enthalpy and activation entropy are higher under carbon dioxide than those under nitrogen, which obeys the law of carbon dioxide promoting oil shale pyrolysis. In addition, the volatile release characteristics of oil shale in the second stage of pyrolysis were analyzed, which proves that the volatile release characteristics of oil shale under carbon dioxide are higher than that under nitrogen. Therefore, carbon dioxide is helpful to promote the pyrolysis of oil shale and increases the release of volatile substances during pyrolysis.Item A Novel Energy-Efficient Pyrolysis Process: Self-pyrolysis of Oil Shale Triggered by Topochemical Heat in a Horizontal Fixed Bed(2015) Sun, You-Hong.; Bai, Feng-Tian.; Lü, Xiaoshu; Li, Qiang; Liu, Yu-Min; Guo, Wei; Liu, Bao-Chang; Department of Civil and Structural Engineering; Department of Civil EngineeringThis paper proposes a novel energy-efficient oil shale pyrolysis process triggered by a topochemical reaction that can be applied in horizontal oil shale formations. The process starts by feeding preheated air to oil shale to initiate a topochemical reaction and the onset of self-pyrolysis. As the temperature in the virgin oil shale increases (to 250–300°C), the hot air can be replaced by ambient-temperature air, allowing heat to be released by internal topochemical reactions to complete the pyrolysis. The propagation of fronts formed in this process, the temperature evolution, and the reaction mechanism of oil shale pyrolysis in porous media are discussed and compared with those in a traditional oxygen-free process. The results show that the self-pyrolysis of oil shale can be achieved with the proposed method without any need for external heat. The results also verify that fractured oil shale may be more suitable for underground retorting. Moreover, the gas and liquid products from this method were characterised, and a highly instrumented experimental device designed specifically for this process is described. This study can serve as a reference for new ideas on oil shale in situ pyrolysis processes.Item Optimization of temperature parameters for the autothermic pyrolysis in-situ conversion process of oil shale(Elsevier Ltd, 2023-02-01) Xu, Shaotao; Lü, Xiaoshu; Sun, Youhong; Guo, Wei; Li, Qiang; Liu, Lang; Kang, Shijie; Deng, Sunhua; Department of Civil Engineering; Structures – Structural Engineering, Mechanics and Computation; Jilin University; Xi'an University of Science and Technology; Chinese Academy of SciencesIn this study, a temperature optimization strategy for the Huadian oil shale autothermal pyrolysis in-situ conversion process (ATS) was first proposed by systematically investigating the reaction characteristics of various semi-cokes. As the pyrolysis temperature rised, the semi-coke's calorific value was found to undergo three different stages of increasing, decreasing, and flattening, peaking at around 330 °C. Additionally, the semi-cokes formed at different temperatures exhibited similar combustion characteristics, including combustion activation energy, combustion characteristic parameters, and product release characteristics. Due to the serious pore blockage caused by the substantial generation and the ignition coking of the bitumen, the reaction characteristics of semi-cokes were dramatically decreased at about 330 °C. Finally, the relationship between in-situ heat generation and demand at various stages of ATS process was discussed, and a reasonable strategy for the screening of temperature parameters was proposed. According to this strategy, the optimal control temperature for the preheating stage was determined at 350–370 °C and at Tact (defined in 4.3.2) for the retorting zone in the reaction stage. The results of this study provide a new perspective on the theoretical foundation of the ATS process and have crucial guiding implications for practical engineering applications.Item Productivity analysis of Fuyu oil shale in-situ pyrolysis by injecting hot nitrogen(MDPI AG, 2021-08-02) Zhao, Shuai; Li, Qiang; Lü, Xiaoshu; Sun, Youhong; China University of Mining and Technology; Jilin University; Department of Civil EngineeringIn this paper, the effect of heat injection on productivity of Fuyu oil shale during in-situ pyrolysis was studied by using heat flow coupling analysis method. It is found that fluid conducts heat transmission to the oil shale stratum mainly along the fissure formed by hydraulic fracturing. With the increase of heating time, the oil shale on both sides of fissures were effectively pyrolyzed, and the porosity of the formation increases and the diffusion range of the nitrogen to the oil shale stratum is also improved. After 200 days, the oil shale around the fractures first reaches the pyrolysis temperature, and 700 days later, the average temperature of the oil shale stratum reaches 500◦C; therefore, the whole oil shale can be effectively pyrolyzed. Productivity analysis shows that the best exploitation temperature is 500◦C. When the gas injection rate is in the range of 1.0~11.0 m3/min, different degrees of heat loss will occur, and the output is also different. The pyrolysis time reaches 100~150 days, showing the peak value of daily production, which is between 0.5~3.2 m3/day. The pressure of displacement fluid affects oil shale product recovery in in-situ pyrolysis. High pressure helps to improve the displacement efficiency of oil and gas products and increase the productivity of oil shale in-situ pyrolysis. The best acting pressure is 9.5 MPa.
