A series of char samples were derived from pyrolysis of two typical low-rank coals in China (Shengli lig- nite and Shenmu bituminous coal) at low, medium and fast heating rates, respectively, to the same pyrol- ysis...A series of char samples were derived from pyrolysis of two typical low-rank coals in China (Shengli lig- nite and Shenmu bituminous coal) at low, medium and fast heating rates, respectively, to the same pyrol- ysis temperature 750℃. Then these chars were characterized by means of thermogravimetric analysis and Fourier transform infrared spectrometer with the aim to investigate the influence of heating rate in pyrolysis process on gasification reactivity and surface chemistry of them. Besides, a homogeneous model was used to quantitatively analyze the activation energy of gasification reaction. The results reveal that Shengli lignite and its derived chars behave higher gasification reactivity and have less content of oxygen functional groups than Shenmu coal and chars. Meanwhile, chars derived from Shengli lignite at 50℃/min and Shenmu coal at 200℃/min have the greatest gasification reactivity, respectively. The oxygen functional groups in Shengli lignite are easily thermo-decomposed, and they are less affected by the heating rate, while that in Shenmu coal have a significant change with the variation of heating rate. In addition, there is no good correlation between the change of oxygen functional groups and that of the gasification reactivity of the derived chars from pyrolysis at different heating rates.展开更多
Two different combustion models,the autoignition(AI)model and flamelet/progress variable(FPV)model,have been applied to study the auto-ignition process of methane/air jet flame in vitiated co-flow.A priori study was c...Two different combustion models,the autoignition(AI)model and flamelet/progress variable(FPV)model,have been applied to study the auto-ignition process of methane/air jet flame in vitiated co-flow.A priori study was conducted to test the validity of the two models.Results show that the different range of predicted reaction rates is mainly responsible for their different performances in large eddy simulation(LES)studies.In this paper,beta PDF was used to model the mixture fraction distribution,while two different shapes of PDF,delta function and beta function,were applied for the reaction progress.Compared to the FPV model,the AI model combined with beta function for reaction progress could capture the auto-ignition process and predict the exact lifted height.Also the results indicate that the variance of reaction progress plays an important role in predicting the flame lifted height.展开更多
The g-C_3N_4 with different structures was prepared by heat treatment using urea(CN-U) and thiourea(CN-T) as precursors under the same conditions. The microstructure and optical properties of the photocatalyst were an...The g-C_3N_4 with different structures was prepared by heat treatment using urea(CN-U) and thiourea(CN-T) as precursors under the same conditions. The microstructure and optical properties of the photocatalyst were analyzed with advanced tools. The results showed that the CN-U has a porous structure, a high specific surface area and a wide band gap in comparison with CN-T. The in situ FT-IR technique was used to monitor the adsorption and reaction process of visible photocatalytic NO oxidation on g-C_3N_4. The corresponding reaction mechanism was proposed based on the results of reaction intermediate observation and electron paramagnetic resonance(EPR) radical scavenging. It was revealed that(1) the presence of defective sites favored the adsorption of gas molecules and electronically compensated it leading to promoted formation of the final products;(2) the high separation efficiency of photogenerated electron-hole pairs enhanced the production of radicals during the photocatalytic reaction;(3) the hydroxyl radicals(-OH) are not selective for the decomposition of pollutants, which are favorable to the complete oxidation of the reaction intermediates. The above three aspects are the main reasons for the CN-U possessing the efficient visible light photocatalytic activity. The present work could provide new insights and methods for understanding the mechanism of photocatalysis.展开更多
According to the principle of thermal activation process, the energy state of a material under the action of stress is a function of local stress. A generalized Butler-Volmer relationship for the electrode reaction on...According to the principle of thermal activation process, the energy state of a material under the action of stress is a function of local stress. A generalized Butler-Volmer relationship for the electrode reaction on the surface of a curved electrode is derived,which takes account of the effects of local stress and the radius of mean curvature. From this relationship, the overpotential is found to be proportional to hydrostatic stress and the activation volume under the condition of open circuit. The conditions for the deposition of the material made solely from solute atoms and the formation of surface pits and porous structures are obtained,using the generalized Butler-Volmer relationship.展开更多
基金financial support from the Basic Fund for the Scientific Research and Operation of Central Universities of China (No. 2009KH10
文摘A series of char samples were derived from pyrolysis of two typical low-rank coals in China (Shengli lig- nite and Shenmu bituminous coal) at low, medium and fast heating rates, respectively, to the same pyrol- ysis temperature 750℃. Then these chars were characterized by means of thermogravimetric analysis and Fourier transform infrared spectrometer with the aim to investigate the influence of heating rate in pyrolysis process on gasification reactivity and surface chemistry of them. Besides, a homogeneous model was used to quantitatively analyze the activation energy of gasification reaction. The results reveal that Shengli lignite and its derived chars behave higher gasification reactivity and have less content of oxygen functional groups than Shenmu coal and chars. Meanwhile, chars derived from Shengli lignite at 50℃/min and Shenmu coal at 200℃/min have the greatest gasification reactivity, respectively. The oxygen functional groups in Shengli lignite are easily thermo-decomposed, and they are less affected by the heating rate, while that in Shenmu coal have a significant change with the variation of heating rate. In addition, there is no good correlation between the change of oxygen functional groups and that of the gasification reactivity of the derived chars from pyrolysis at different heating rates.
基金supported by the National Natural Science Foundation of China(Grant Nos.51176178 and 50936005)
文摘Two different combustion models,the autoignition(AI)model and flamelet/progress variable(FPV)model,have been applied to study the auto-ignition process of methane/air jet flame in vitiated co-flow.A priori study was conducted to test the validity of the two models.Results show that the different range of predicted reaction rates is mainly responsible for their different performances in large eddy simulation(LES)studies.In this paper,beta PDF was used to model the mixture fraction distribution,while two different shapes of PDF,delta function and beta function,were applied for the reaction progress.Compared to the FPV model,the AI model combined with beta function for reaction progress could capture the auto-ignition process and predict the exact lifted height.Also the results indicate that the variance of reaction progress plays an important role in predicting the flame lifted height.
基金supported by the National Key Research and Development Plan (2016YFC02047)the National Natural Science Foundation of China (51478070, 21777011 and 21501016)+1 种基金the Innovative Research Team of Chongqing (CXTDG201602014)the Natural Science Foundation of Chongqing (cstc2017jcyj BX0052, cstc2016jcyj A0481)
文摘The g-C_3N_4 with different structures was prepared by heat treatment using urea(CN-U) and thiourea(CN-T) as precursors under the same conditions. The microstructure and optical properties of the photocatalyst were analyzed with advanced tools. The results showed that the CN-U has a porous structure, a high specific surface area and a wide band gap in comparison with CN-T. The in situ FT-IR technique was used to monitor the adsorption and reaction process of visible photocatalytic NO oxidation on g-C_3N_4. The corresponding reaction mechanism was proposed based on the results of reaction intermediate observation and electron paramagnetic resonance(EPR) radical scavenging. It was revealed that(1) the presence of defective sites favored the adsorption of gas molecules and electronically compensated it leading to promoted formation of the final products;(2) the high separation efficiency of photogenerated electron-hole pairs enhanced the production of radicals during the photocatalytic reaction;(3) the hydroxyl radicals(-OH) are not selective for the decomposition of pollutants, which are favorable to the complete oxidation of the reaction intermediates. The above three aspects are the main reasons for the CN-U possessing the efficient visible light photocatalytic activity. The present work could provide new insights and methods for understanding the mechanism of photocatalysis.
文摘According to the principle of thermal activation process, the energy state of a material under the action of stress is a function of local stress. A generalized Butler-Volmer relationship for the electrode reaction on the surface of a curved electrode is derived,which takes account of the effects of local stress and the radius of mean curvature. From this relationship, the overpotential is found to be proportional to hydrostatic stress and the activation volume under the condition of open circuit. The conditions for the deposition of the material made solely from solute atoms and the formation of surface pits and porous structures are obtained,using the generalized Butler-Volmer relationship.