The effects of oxidizing slag on oxygen mass transfer and inclusions in different stages of IF(interstitial-free)steel refining were investigated by several heat simulation experiments.The results of the experiments s...The effects of oxidizing slag on oxygen mass transfer and inclusions in different stages of IF(interstitial-free)steel refining were investigated by several heat simulation experiments.The results of the experiments showed that the oxidizability of slag changed considerably during different refining stages.Keeping the content of FeO in the slag within 1 wt.%would narrow the difference of slag oxidizability,stabilize the content of[Al]s in the steel,avoid secondary oxidation of molten steel by the slag,and reduce the inclusions.When the mass transfer of FeO in the slag phase was a limiting step,the secondary oxidation reaction occurred at the steel–slag interface;when the diffusion of oxygen in the molten steel was a limiting step,the secondary oxidation reaction took place inside the molten steel.The oxygen transfer rate was affected by the mass transfer coefficient of oxygen.For every 0.0001m/s increase in mass transfer coefficient,the oxygen transfer rate increased by about 2.2×10^-6 min^-1.By changing the mass transfer coefficient,the oxygen transfer rate of the slag to the molten steel can be controlled.展开更多
In wastewater treatment plants（WWTPs）using the activated sludge process,two methods are widely used to improve aeration efficiency — use of high-efficiency aeration devices and optimizing the aeration control strat...In wastewater treatment plants（WWTPs）using the activated sludge process,two methods are widely used to improve aeration efficiency — use of high-efficiency aeration devices and optimizing the aeration control strategy. Aeration efficiency is closely linked to sludge characteristics（such as concentrations of mixed liquor suspended solids（MLSS）and microbial communities）and operating conditions（such as air flow rate and operational dissolved oxygen（DO）concentrations）. Moreover,operational DO is closely linked to effluent quality. This study,which is in reference to WWTP discharge class A Chinese standard effluent criteria,determined the growth kinetics parameters of nitrifiers at different DO levels in small-scale tests. Results showed that the activated sludge system could meet effluent criteria when DO was as low as 0.3 mg/L,and that nitrifier communities cultivated under low DO conditions had higher oxygen affinity than those cultivated under high DO conditions,as indicated by the oxygen half-saturation constant and nitrification ability. Based on nitrifier growth kinetics and on the oxygen mass transfer dynamic model（determined using different air flow rate（Q′air）and mixed liquor volatile suspended solids（MLVSS）values）,theoretical analysis indicated limited potential for energy saving by improving aeration diffuser performance when the activated sludge system had low oxygen consumption; however,operating at low DO and low MLVSS could significantly reduce energy consumption. Finally,a control strategy coupling sludge retention time and MLVSS to minimize the DO level was discussed,which is critical to appropriate setting of the oxygen point and to the operation of low DO treatment technology.展开更多
A flexible fibre biofilm reactor was developed for treatment of organic wastewaters.The hydrodynamic characteristics and mass transfer coefficients of oxygen were studied and compared with those of the conventional ac...A flexible fibre biofilm reactor was developed for treatment of organic wastewaters.The hydrodynamic characteristics and mass transfer coefficients of oxygen were studied and compared with those of the conventional activated sludge processes.Tracer experiments were performed to obtain the residence time distributions of the reactors.The results indicated that both reactors could be treated as mixed flow reactors.The effects of flow rates of water and air on the overall mass transfer coefficient of oxygen were investigated,and the correlations between the mass transfer coefficient and the ratio of flow rates were obtained.Compared to the conventional activated sludge reactor,the mass transfer coefficients in the flexible fibre reactor were similar to but slightly lower,and less sensitive to the variation in the ratio of flow rates.It indicated that the fibre packing in the reactor hindered the oxygen transfer to some extent.展开更多
In an internal loop airlift reactor of 55L working volume,the gas-liquid volumetric oxygenmass transfer coefficient k_Lα,gas holdup ε_G and liquid circulation time t_c were measured with the sol-ution of carboxymeth...In an internal loop airlift reactor of 55L working volume,the gas-liquid volumetric oxygenmass transfer coefficient k_Lα,gas holdup ε_G and liquid circulation time t_c were measured with the sol-ution of carboxymethyl cellulose(CMC)to simulate the performance of a reactor with highly viscousbroth.Electric conductivity and oxygen probes were used to measure the local gas holdup,liquidcirculation time and oxygen mass transfer coefficient in the individual sections of the reactor(riser,downcomer and the gas-liquid separating section at the top of the reactor)and the total reactor,respectively.The values of k_Lα for the riser,downcomer and separation sections of the reactor were alsoestimated and compared with that for the total reactor.The results show that,both k_Lα and ε_G in-crease but t_c decreases with increasing gas velocity.Correlations and comparisons with works reportedin the literature are also presented.Data show that the methods developed for k_Lα measurements inthe individual section展开更多
Precise engineering of single-atom catalysts(SACs)with hierarchical porous structures and optimized mass/charge transfer properties is crucial for advancing oxygen reduction reaction(ORR)in proton exchange membrane fu...Precise engineering of single-atom catalysts(SACs)with hierarchical porous structures and optimized mass/charge transfer properties is crucial for advancing oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs).Herein,we present a novel molten salt-assisted pyrolysis strategy that employs a“dimensional reduction and pore creation”approach to exfoliate three-dimensional(3D)-metal-organic frameworks(MOFs)into three-dimensional porous carbon nanosheets doped with single-atom Fe,resulting in Fe SACs supported on hierarchical porous nitrogen-doped carbon(Fe SA@HPNC).The molten salt treatment simultaneously induces exfoliation and etching,resulting in a hierarchical porous structure with both micropores and mesopores,and a remarkably high specific surface area of 919.5 m^(2)·g^(-1).The two-dimensional nanosheet structure enhances the anchoring of Fe by exposing more surface micropores,which reduces Fe being deeply buried in internal micropores and improves oxygen accessibility and mass/charge transfer efficiency.The Fe SA@HPNC demonstrates excellent ORR performance with a half-wave potential of 0.90 V and a kinetic current density of 19.9 mA·cm^(-2).When applied as the cathode in PEMFCs,the Fe SA@HPNC-based cell achieves a remarkable maximum power density of 900 mW·cm^(-2).Distribution of relaxation times analysis further reveals that the exfoliated catalyst exhibits enhanced ORR kinetics and reduced oxygen transport resistance.展开更多
本研究搭建了100 m^(3)/d的膜曝气生物膜反应器(MABR)中试装置,通过对实际市政污水进行处理,探究工艺设计合理性、系统运行效果,分析MABR脱氮贡献、氧传质特性及环境因子的相关性。结果表明:MABR在一个月内可以完成微生物挂膜,并且该工...本研究搭建了100 m^(3)/d的膜曝气生物膜反应器(MABR)中试装置,通过对实际市政污水进行处理,探究工艺设计合理性、系统运行效果,分析MABR脱氮贡献、氧传质特性及环境因子的相关性。结果表明:MABR在一个月内可以完成微生物挂膜,并且该工艺系统内回流点位设置在MABR单元后端,并保持内外回流比均为100%左右,可以避免对进水氨氮的稀释,进而提高MABR硝化速率(NR),强化MABR单元同步硝化反硝化效果;运行期间,MABR硝化速率达(2.75±1.13) g N/(m^(2)·d),MABR单元脱氮贡献占系统总脱氮量的20.42%±7.97%;氧传质效率(OTE)与氧传质速率(OTR)分别达到33.36%±10.75%和(10.85±2.88) g O_(2)/(m^(2)·d),证明MABR具有较强的氧传质特性。本中试系统实现了高效短流程脱氮,在较短生化停留时间(HRT=10.81 h)条件下,出水指标优于江苏省地标《城镇污水处理厂污染物排放标准》(DB 32/4440-2022)的A类标准(其中TN<10 mg/L)。展开更多
基金The authors would like to express their appreciation to the National Natural Science Foundation of China(No.51471002).
文摘The effects of oxidizing slag on oxygen mass transfer and inclusions in different stages of IF(interstitial-free)steel refining were investigated by several heat simulation experiments.The results of the experiments showed that the oxidizability of slag changed considerably during different refining stages.Keeping the content of FeO in the slag within 1 wt.%would narrow the difference of slag oxidizability,stabilize the content of[Al]s in the steel,avoid secondary oxidation of molten steel by the slag,and reduce the inclusions.When the mass transfer of FeO in the slag phase was a limiting step,the secondary oxidation reaction occurred at the steel–slag interface;when the diffusion of oxygen in the molten steel was a limiting step,the secondary oxidation reaction took place inside the molten steel.The oxygen transfer rate was affected by the mass transfer coefficient of oxygen.For every 0.0001m/s increase in mass transfer coefficient,the oxygen transfer rate increased by about 2.2×10^-6 min^-1.By changing the mass transfer coefficient,the oxygen transfer rate of the slag to the molten steel can be controlled.
基金supported by the National Science and Technology Major Project(No.2013ZX07314-001)
文摘In wastewater treatment plants（WWTPs）using the activated sludge process,two methods are widely used to improve aeration efficiency — use of high-efficiency aeration devices and optimizing the aeration control strategy. Aeration efficiency is closely linked to sludge characteristics（such as concentrations of mixed liquor suspended solids（MLSS）and microbial communities）and operating conditions（such as air flow rate and operational dissolved oxygen（DO）concentrations）. Moreover,operational DO is closely linked to effluent quality. This study,which is in reference to WWTP discharge class A Chinese standard effluent criteria,determined the growth kinetics parameters of nitrifiers at different DO levels in small-scale tests. Results showed that the activated sludge system could meet effluent criteria when DO was as low as 0.3 mg/L,and that nitrifier communities cultivated under low DO conditions had higher oxygen affinity than those cultivated under high DO conditions,as indicated by the oxygen half-saturation constant and nitrification ability. Based on nitrifier growth kinetics and on the oxygen mass transfer dynamic model（determined using different air flow rate（Q′air）and mixed liquor volatile suspended solids（MLVSS）values）,theoretical analysis indicated limited potential for energy saving by improving aeration diffuser performance when the activated sludge system had low oxygen consumption; however,operating at low DO and low MLVSS could significantly reduce energy consumption. Finally,a control strategy coupling sludge retention time and MLVSS to minimize the DO level was discussed,which is critical to appropriate setting of the oxygen point and to the operation of low DO treatment technology.
文摘A flexible fibre biofilm reactor was developed for treatment of organic wastewaters.The hydrodynamic characteristics and mass transfer coefficients of oxygen were studied and compared with those of the conventional activated sludge processes.Tracer experiments were performed to obtain the residence time distributions of the reactors.The results indicated that both reactors could be treated as mixed flow reactors.The effects of flow rates of water and air on the overall mass transfer coefficient of oxygen were investigated,and the correlations between the mass transfer coefficient and the ratio of flow rates were obtained.Compared to the conventional activated sludge reactor,the mass transfer coefficients in the flexible fibre reactor were similar to but slightly lower,and less sensitive to the variation in the ratio of flow rates.It indicated that the fibre packing in the reactor hindered the oxygen transfer to some extent.
基金Supported by the National Natural Science Foundation of China
文摘In an internal loop airlift reactor of 55L working volume,the gas-liquid volumetric oxygenmass transfer coefficient k_Lα,gas holdup ε_G and liquid circulation time t_c were measured with the sol-ution of carboxymethyl cellulose(CMC)to simulate the performance of a reactor with highly viscousbroth.Electric conductivity and oxygen probes were used to measure the local gas holdup,liquidcirculation time and oxygen mass transfer coefficient in the individual sections of the reactor(riser,downcomer and the gas-liquid separating section at the top of the reactor)and the total reactor,respectively.The values of k_Lα for the riser,downcomer and separation sections of the reactor were alsoestimated and compared with that for the total reactor.The results show that,both k_Lα and ε_G in-crease but t_c decreases with increasing gas velocity.Correlations and comparisons with works reportedin the literature are also presented.Data show that the methods developed for k_Lα measurements inthe individual section
基金supported by the National Key Research and Development Program of China(No.2020YFB1506300)the National Natural Science Foundation of China(Nos.21922502,22075018,and 22375017)+5 种基金Young Elite Scientists Sponsorship Program by Beijing Association For Science and Technology(BAST,No.BYESS2023163)China National Petroleum Corporation(CNPC)Innovation Found(No.2022DQ02-0606)Xplorer PrizeInstitute of High Energy Physics,Chinese Academy of Sciences for synchrotron radiation(Beijing Synchrotron Radiation Facility(BSRF))testingBeijing Institute of Technology Research Fund Programand Analysis and Testing Center of Beijing Institute of Technology.
文摘Precise engineering of single-atom catalysts(SACs)with hierarchical porous structures and optimized mass/charge transfer properties is crucial for advancing oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs).Herein,we present a novel molten salt-assisted pyrolysis strategy that employs a“dimensional reduction and pore creation”approach to exfoliate three-dimensional(3D)-metal-organic frameworks(MOFs)into three-dimensional porous carbon nanosheets doped with single-atom Fe,resulting in Fe SACs supported on hierarchical porous nitrogen-doped carbon(Fe SA@HPNC).The molten salt treatment simultaneously induces exfoliation and etching,resulting in a hierarchical porous structure with both micropores and mesopores,and a remarkably high specific surface area of 919.5 m^(2)·g^(-1).The two-dimensional nanosheet structure enhances the anchoring of Fe by exposing more surface micropores,which reduces Fe being deeply buried in internal micropores and improves oxygen accessibility and mass/charge transfer efficiency.The Fe SA@HPNC demonstrates excellent ORR performance with a half-wave potential of 0.90 V and a kinetic current density of 19.9 mA·cm^(-2).When applied as the cathode in PEMFCs,the Fe SA@HPNC-based cell achieves a remarkable maximum power density of 900 mW·cm^(-2).Distribution of relaxation times analysis further reveals that the exfoliated catalyst exhibits enhanced ORR kinetics and reduced oxygen transport resistance.
文摘本研究搭建了100 m^(3)/d的膜曝气生物膜反应器(MABR)中试装置,通过对实际市政污水进行处理,探究工艺设计合理性、系统运行效果,分析MABR脱氮贡献、氧传质特性及环境因子的相关性。结果表明:MABR在一个月内可以完成微生物挂膜,并且该工艺系统内回流点位设置在MABR单元后端,并保持内外回流比均为100%左右,可以避免对进水氨氮的稀释,进而提高MABR硝化速率(NR),强化MABR单元同步硝化反硝化效果;运行期间,MABR硝化速率达(2.75±1.13) g N/(m^(2)·d),MABR单元脱氮贡献占系统总脱氮量的20.42%±7.97%;氧传质效率(OTE)与氧传质速率(OTR)分别达到33.36%±10.75%和(10.85±2.88) g O_(2)/(m^(2)·d),证明MABR具有较强的氧传质特性。本中试系统实现了高效短流程脱氮,在较短生化停留时间(HRT=10.81 h)条件下,出水指标优于江苏省地标《城镇污水处理厂污染物排放标准》(DB 32/4440-2022)的A类标准(其中TN<10 mg/L)。
