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Stability and activity maintenance of sol-gel Ni-MxOy (M = Ti, Zr, Ta) catalysts during continuous gasification of glycerol in supercritical water

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JOURNAL OF SUPERCRITICAL FLUIDS 2019年 148卷 137-147页

作者： Li, Sha Savage, Phillip E. Guo, Liejin Nanjing Univ Sci & Technol Sch Energy & Power Engn Nanjing 210094 Jiangsu Peoples R China Univ Michigan Dept Chem Engn Ann Arbor MI 48109 USA Penn State Univ Dept Chem Engn University Pk PA 16802 USA Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

The long-term stability of activities and physicochemical properties for nickel nanoparticles supported on TiO2, ZrO(2 )and Ta2O5 prepared by sol-gel methods, was evaluated for continuous supercritical water gasification (SCWG) of 3 wt.% glycerol at 425 degrees C and 25.2 MPa. The Ni/TiO2 catalyst bed gradually deactivated while the Ni/ZrO2 and Ni/Ta2O5 catalyst beds showed persistent and high carbon gasification efficiency for 80 h operation. Characterization results verified that property stabilization of the sol-gel Ni/ZrO(2 )and Ni/Ta2O5 catalysts occurred in the long-term SCWG flow, indicating a "catalyst in-situ activation" effect that enhanced the activity and coking resistance of the as-prepared sol-gel catalysts for continuous SCWG. Results also indicate that sintering of Ni with the supports to form new phases and metal leaching of the catalyst materials in the SCW flow may be key deactivation factors of the catalyst beds.

关键词： Supercritical water gasification Supercritical water Nickel catalyst Stability Glycerol

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Size effect of one-dimensional nanostructures on bubble nucleation in water splitting

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APPLIED PHYSICS LETTERS 2019年第10期115卷 101602-101602页

作者： Chen, Juanwen Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

One-dimensional (1D) nanostructures have wide applications in photocatalysts for water splitting. Their surfaces may impact the gas bubble nucleation rate, thus influencing the efficiency of gas evolution. However, the effects of the 1D nanostructured surfaces on the bubble nucleation have not been studied to date. Herein, these effects are theoretically analyzed, based on the changes of free energy for a bubble nucleus forming inside/outside a nanotube. The results show that compared to flat surfaces, the inner tube wall favors the bubble nucleation, while the outer wall has an opposite effect. These differences become increasingly significant with tube radius R-t reducing when R-t<10r(*) (r(*)-bubble equilibrium radius). The size effect is further verified experimentally for bubble nucleation on TiO2 nanotube arrays. The sensitivity of bubble nucleation to nanostructure dimensions should be considered in designing high-efficient photocatalysts.

关键词： Nanotubes Nanostructures Supersaturation Water-splitting Bubble dynamics Free energy

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Synergistic effect of nitrogen vacancy on ultrathin graphitic carbon nitride porous nanosheets for highly efficient photocatalytic H2 evolution

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CHEMICAL engineering JOURNAL 2022年第Part2期431卷 134101-134101页

作者： Zhang, Yazhou Huang, Zhenxiong Dong, Chung-Li Shi, Jinwen Cheng, Cheng Guan, Xiangjiu Zong, Shichao Luo, Bing Cheng, Zening Wei, Daixing Huang, Yu-cheng Shen, Shaohua Guo, Liejin Xian Jiaotong Univ XJTU Int Res Ctr Renewable Energy IRCRE State Key Lab Multiphase Flow Power Engn MFPE 28 West Xianning Rd Xian 710049 Peoples R China Xiamen Univ Coll Chem & Chem Engn State Key Lab Phys Chem Solid Surfaces 422 Siming South Rd Xiamen 361005 Peoples R China Tamkang Univ Dept Phys 151 Yingzhuan Rd Tamsui 25137 Taiwan Jiangxi Acad Sci Inst Energy Res 7777 Changdong Ave Nanchang 330096 Jiangxi Peoples R China Xi An Jiao Tong Univ Sch Chem Engn & Technol Xian 710049 Peoples R China Xinjiang Tianchi Energy Co Ltd Zhundong Energy Res Inst 189 Beijing South Rd Changji 831100 Peoples R China

Nanosheets exfoliation as one of the promising modification strategies for graphitic carbon nitride (g-C3N4) nanosheets has been extensively developed for improving the photocatalytic performance. However, it was commonly found that the enhancement of photocatalytic efficiency by effective nanosheets exfoliation hardly reached the expected satisfactory level, and the corresponding photocatalytic mechanism should be further investigated. Herein, on account of the well-designed thermal exfoliation strategy, the ultrathin and porous nanosheets with the thickness of three layers were elaborately constructed and possessed abundant N vacancies in the in-plane heptazine rings. Surprisingly, the ultrathin nanosheets exhibited superior visible-light-driven photocatalytic H-2-evolution activity, with a H-2-evolution rate (5.74 mmol h(-1) g(-1)) 28.7 times that of the pristine g-C3N4, and with an apparent quantum yield (AQY) of 14.9% (420 nm) much higher than that of the previously reported ultrathin g-C3N4 nanosheets. It was confirmed by systematical characterizations and theoretical calculation that, the ultrathin and porous features in cooperation with local separation of the highest occupied molecular orbital and lowest unoccupied molecular orbital sites by N vacancy-dominated in-plane electronic structure, synergistically strengthened the separation of photo-generated carriers. Meanwhile, the incorporation of the N vacancy-induced midgap state could bring the highly efficient excitation of photo-generated carriers, and abundant photocatalytic reaction sites could be provided by the ultrathin two-dimensional (2D) microstructure. Furthermore, the ultrathin nanosheet-induced quantum confinement effect could enlarge the bandgap and then boost the driving force for water reduction. This work developed one unique synthetic route to g-C3N4 nanosheets exfoliation, and highlighted the synergistic function of nanosheets exfoliation and defect engineering for highly efficient photoc

关键词： Graphitic carbon nitride Ultrathin nanosheet Nitrogen vacancy Photocatalytic hydrogen evolution Synergistic effect

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Ash deposition and sodium migration behaviors during combustion of Zhundong coals in a drop tube furnace

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JOURNAL OF THE ENERGY INSTITUTE 2018年第2期91卷 251-261页

作者： Wang, Chang'an Li, Guangyu Du, Yongbo Yan, Yu Li, Hao Che, Defu Xi An Jiao Tong Univ Sch Energy & Power Engn State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Zhundong coalfield is one super-large coalfield recently discovered in China. However, the utilization of Zhundong coal in power plants has caused serious ash-related issues mainly due to its high-sodium feature. The ash deposition problem on convection heat exchanger surfaces is still particularly difficult to resolve and its mechanism has yet to be fully understood. This study deals with the ash deposition and alkali metal migration behaviors on convection heat exchanger surfaces between 400 and 800 degrees C during combustion of Zhundong coal using a lab-scale drop tube reactor. Experimental results show that the sodium content in ash deposit of Zhundong coals increases obviously as the deposition temperature decreases from 800 to 600 degrees C, while it is almost unchanged below 600 degrees C. The contents of iron and calcium in ash deposits exhibit nonmonotonic variations as the deposit probe temperature varies between 400 and 800 degrees C. Quartz and calcium sulfate are main crystalline phases in ash deposit of Zhundong coals. Calcium is inclined to present as calcite and lime at low deposition temperature, while high temperature facilitates calcium sulfation. Sodium of crystalline phase is found as albite and sodium sulfate at low deposition temperature. Both condensation of gaseous alkali metals and formation of low melting minerals were responsible for the ash deposition phenomenon on convection heat exchanger surfaces involved in combustion of Zhundong coal. The sodium content in ash deposit decreases considerably with the increasing combustion temperature while the case of iron variation is opposite due to its low-volatility. In addition, the Na content in ash deposits increases obviously with the access air ratio reduced from 1.2 to 1.05, but the local weakly reducing atmosphere leads to less iron within ash deposits. Clarification of sodium migration and evaluation of ash deposition behaviors during combustion of Zhundong coal is helpful for a better e

关键词： Zhundong coalfield High-sodium coal Ash deposit Transition behavior Deposition temperature

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Transformation and release of potassium during fixed-bed pyrolysis of biomass

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JOURNAL OF THE ENERGY INSTITUTE 2018年第4期91卷 630-637页

作者： Deng, Lei Ye, Jiaming Jin, Xi Che, Defu Xi An Jiao Tong Univ Sch Energy & Power Engn State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

To study the release and transformation of fuel K during rapid pyrolysis of biomass, wheat straw, corn stalk and rice hull are pyrolyzed in a fixed-bed reactor system during 400-1000 degrees C, and weight measurement, elemental composition analysis, and chemical fractionation analysis are performed. The effects of fuel type, pyrolysis temperature, co-pyrolysis of different fuels, and water washing pretreatment are discussed. The results show that for all biomass fuels, the released K is far less than the water-soluble K and a sudden increase occurs in the fraction of ion-exchangeable K at 400 degrees C, whereas a significant increase happens in the fraction of insoluble K above 800 degrees C. Wheat straw releases less than 5% of K at 400 and 500 degrees C. As temperature rises, the K release increases abruptly and around 40% of K enters the gas phase at 1000 degrees C. Rice hull has a slow and linear K release with increasing pyrolysis temperature. Corn stalk has the lowest K release during 400-800 degrees C. Co-pyrolysis of wheat straw and rice hull reduce the K release at 1000 degrees C, and the biggest decrement is 0.76 mg g(-1). Water washing removes all the water-soluble K of corn stalk and part of ion-exchangeable K enters the gas phase during pyrolysis of the washed sample. Water washing decreases the K release from 2.77 to 0.18 mg g(-1) at 1000 degrees C. (C) 2017 Energy Institute. Published by Elsevier Ltd. All rights reserved.

关键词： Potassium release Transformation Biomass pyrolysis Co-pyrolysis Water washing

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Effects of silicoaluminate oxide and coal blending on combustion behaviors and kinetics of zhundong coal under oxy-fuel condition

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JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY 2018年第3期134卷 1975-1986页

作者： Wang, Chang'an Zhang, Yuanhang Wang, Pengqian Zhang, Jinping Du, Yongbo Che, Defu Xi An Jiao Tong Univ Sch Energy & Power Engn State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Oxy-fuel combustion of high-alkali coal is beneficial for near-zero emission of pollutants in power plants and has the potential for extensive, efficient, and safe utilization of Zhundong coal in future. The present work was performed on oxy-fuel combustion of Zhundong coal, while the effects of silicoaluminate oxide and coal blending on oxy-fuel combustion characteristics and kinetics of high-alkali coal were further studied using thermogravimetric analysis. The thermogravimetric curves of Zhundong coals present two obvious stages but the contrastive coals are different. The increase in oxygen content weakens the impact of coal property on oxy-fuel combustion behavior of high-alkali coal. The addition of Al2O3 and kaolin results in a slight decline of the peak combustion rate, while the influences of SiO2 and diatomite additives are negligible. The additive fraction of silicoaluminate oxide gives rise to a non-monotonic impact on combustion characteristics of Zhundong coal. The interaction effect within blended coal could cause a reduction in reaction rate during the intense combustion stage, while its influence on kinetics is intensified during the later stage of oxy-fuel combustion. The impact extent of silicoaluminate oxide and coal blending on oxy-fuel combustion kinetics of high-alkali coal is highly associated with additive species and individual coals.

关键词： Zhundong coal High alkali Kinetics Thermogravimetric analysis Additive Blended coal

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The performance of droplet evaporation model in predicting droplet dynamics and thermal characteristics for R134a single isolated droplet and two-phase flashing spray

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AEROSPACE SCIENCE AND TECHNOLOGY 2019年 93卷 105363-000页

作者： Zhou, Zhi-Fu Lu, Guan-Yu Zhu, Dong-Qing Zhang, Lu Wang, Jia-Feng Chen, Bin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Flashing spray with low saturation point and high volatility mediums is of great importance in aerospace field. It involves complex droplet dynamics and heat and mass transfer processes in a turbulent, two phase flow. This paper comparatively evaluates the predictive performance of a selected number of droplet evaporation models that focus on convective and blowing effects. The studies span from a single, isolated R134a droplet that evaporates in a convective environment, to a fully turbulent, flashing spray formed through an accidental release of high pressure R134a liquid. An in-house developed code for single isolated droplet evaporation and a modified sprayFoam solver in OpenFOAM for flashing spray are used to calculate droplet and spray behaviors. The results show droplet evaporation model greatly affects the evolutions of droplet diameter, velocity and temperature for single isolated R134a droplet, that the C-R-S model predicts the lowest droplet diameter and velocity, and highest droplet temperature;the H-N-R model predicts the largest droplet velocity and lowest temperature;the A-S and N-G-R-M models predict almost identical results. In contrast to the great impact on droplet evolution for single isolated droplet modeling, droplet evaporation model has little influence on spray and thermal characteristics for R134a two phase flashing spray simulation. However, the A-S model predicts quite different radial profile of droplet temperature at spray periphery compared with other models, which is much lower than the experimental value. (C) 2019 Elsevier Masson SAS. All rights reserved.

关键词： Evaporation Single isolated droplet Flashing spray R134a OpenFOAM

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Rapid pyrolysis and CO₂ gasification of anthracite at high temperature

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JOURNAL OF THE ENERGY INSTITUTE 2018年第6期91卷 1143-1152页

作者： Zha, Qiongliang Zhao, Jing Wang, Chang'an Che, Defu Xi An Jiao Tong Univ Sch Energy & Power Engn State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Anthracite could be burnt efficiently at high temperature utilizing oxy-coal technology. To clarify the effects of temperature and atmosphere on char porosity characteristics, char morphology, fuel-N conversion, and reducing products release, rapid pyrolysis and CO2 gasification of anthracite was carried out in a high temperature entrained-flow reactor to simulate the condition in a pulverized coal furnace. Developed pore structure was formed in the gasification chars, which could be contributed to char-CO2 reaction at high temperatures. More mesopores were formed in internal carbon skeleton and retained against collapse and coalescent for gasification chars than pyrolysis chars. Compared with pyrolysis char, smoother and denser surface was observed in gasification char with the irregular bulges disappeared due to the destruction of external carbon skeleton. Char-N could be oxidized to NO in CO2 atmosphere and then reduced to N-2 by (-CN) on the char surface. Char-N release was greatly promoted due to gasification reaction along with poly-condensation at high temperature;and the preact release of char-N would result in a larger portion of NOx reduction in the following reduction zone with the oxygen-staging combustion technology compared with that in air-staging combustion. Complementally, homogeneous reduction in NOx emission would play a minor effect for anthracite in oxy-coal combustion because of the deficiency of CH4 and HCN, especially at high temperature. (C) 2017 Energy Institute. Published by Elsevier Ltd. All rights reserved.

关键词： Anthracite High temperature CO2 Char porosity Fuel-N conversion

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Experimental study on energy conversion in static flash evaporation of aqueous NaCl solution

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DESALINATION 2018年 430卷 56-63页

作者： Yang, Qingzhong Zhang, Dan Yan, Junjie Liang, Ting Xi An Jiao Tong Univ Sch Energy & Power Engn State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Energy conversion during static flash of aqueous NaCl solution was analyzed on the basis of experiments with an initial waterfilm concentration ranging from 0 to 0.26 (saturated at room temperature), initial height from 0.1 m to 0.4 m, and superheat from 1.8 K to 55.9 K. In the energy released from superheated waterfilm, the present study focused on the portion that transformed into the latent heat of flash steam;this fraction of the total released energy was defined as energy conversion efficiency (ECE). Results suggested that ECE highly depended on both evaporation and steam-carrying effect. Second, ECE decreased monotonically with rising initial height of waterfilm in both non-crystallization and crystallization regions. Finally, with rising superheat or initial concentration of waterfilm, ECE decreased within the non-crystallization region but increased within the crystallization region.

关键词： Static flash evaporation Crystallization Aqueous NaCl solution Steam-carrying effect Energy conversion efficiency

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Experimental and numerical study on laminar burning velocity of gasoline and gasoline surrogates

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FUEL 2019年 256卷 115933-000页

作者： Hu, Erjiang Xu, Zhaohua Gao, Zhenhua Xu, Jiawei Huang, Zuohua Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

The outwardly propagating spherical flame method was used to measure the laminar burning velocity of a Chinese commercial gasoline and gasoline surrogates. Measurements were conducted at different equivalence ratios of 0.8 to 1.5, initial temperatures of 358 K, 403 K, and 448 K and initial pressures of 1 atm, 2 atm and 5 atm in a constant volume bomb. The primary reference fuel (PRF-92, vol. %: 92% iso-octane + 8% n-heptane) and toluene reference fuel (TRF-92, vol. %: 16.69% iso-octane + 22.65% n-heptane + 60.66% toluene) surrogates were proposed to predict the laminar burning velocity of commercial gasoline. It was found that the TRF-92 was able to successfully reproduce the laminar burning velocity of commercial gasoline under various experimental conditions. The chemical kinetic model of Park et al. was validated and used to simulate the laminar burning velocity. The simulated laminar flame speeds showed good agreement with the experimental values.

关键词： Laminar burning velocity Gasoline Gasoline surrogate Experimental measurement Numerical simulation

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