The factors affecting the oxidation degree of vanadium–titanium magnetite (VTM) pellets were analyzed via the isothermal oxidation experiment. Furthermore, the oxidation kinetics of VTM pellets were explored through ...The factors affecting the oxidation degree of vanadium–titanium magnetite (VTM) pellets were analyzed via the isothermal oxidation experiment. Furthermore, the oxidation kinetics of VTM pellets were explored through linear fitting to the kinetic equations based on the shrinking unreacted-core model. The results reveal that VTM pellets undergo oxidation in three distinct phases: pre-oxidation, mid-oxidation, and final stable phase. Notably, the mid-oxidation phase is absent in magnetite oxidation. The shrinking unreacted-core model has been proven to be suitable for modeling the process of oxidizing VTM pellets. In the pre-oxidation stage, the rate-controlling step is determined by both the oxidation temperature and the effective oxygen concentration. The influence of the effective oxygen concentration on the rate of oxidation is more pronounced at temperatures between 1073 and 1273 K, especially when the oxygen content falls below 15 vol.%. For the production of oxidized VTM pellets, it is necessary to maintain a preheating temperature above 1173 K (to accelerate the oxidation reaction) and below 1473 K (to prevent the swift formation of compact Fe2TiO5 at the shell of the pellet) in an oxygen-enriched atmosphere.展开更多
A modified shrinking unreacted-core model,based on thermogravimetric analysis,was developed to investigate CaSO4 decomposition in oxy-fuel combustion,especially under isothermal condition which is difficult to achieve...A modified shrinking unreacted-core model,based on thermogravimetric analysis,was developed to investigate CaSO4 decomposition in oxy-fuel combustion,especially under isothermal condition which is difficult to achieve in actual experiments due to high-temperature corrosion.A method was proposed to calculate the reaction rate constant for CaSO4 decomposition.Meanwhile,the diffusion of SO2 and O2,and the sintering of CaO were fully considered during the development of model.The results indicate that the model can precisely predict the decomposition of CaSO4 under high SO2 concentration（1100×10-6）.Concentrations of SO2 and O2 on the unreacted-core surface were found to increase first and then decrease with increasing temperature,and the average specific surface area and porosity of each CaO sintering layer decreased with increasing time.The increase of SO2 and/or O2 concentration inhibited CaSO4 decomposition.Moreover,the kinetics of CaSO4 decomposition had obvious dependence on temperature and the decomposition rate can be dramatically accelerated with increasing temperature.展开更多
Here, we propose a chemical heat pump chiller with a SrBr<sub>2</sub> hydration reaction system for utilization of waste heat. The SrBr<sub>2</sub> hydration reaction could recover waste heat i...Here, we propose a chemical heat pump chiller with a SrBr<sub>2</sub> hydration reaction system for utilization of waste heat. The SrBr<sub>2</sub> hydration reaction could recover waste heat in low temperatures ranging from 373 K to 353 K, and the system showed good potential in terms of the high cooling thermal-storage density. Previous studies have given little information on the reaction characteristics of the SrBr<sub>2</sub> hydration reaction. In this paper, we developed a measuring method for the hydration reaction equilibrium and reaction rate based on the volumetric method. We analyzed the hydration reaction rate with an unreacted-core shell model. In the experiments, the SrBr<sub>2</sub> equilibrium temperature observed was equal to the theoretical equilibrium temperature obtained from thermodynamic databases. In addition, the hysteresis gap between the hydration and dehydration values was 2.0 K. Thus, the hysteresis effect was negligible for the chemical heat pump cooling operation. The reaction fraction of the SrBr<sub>2</sub> hydration reached 0.7 within 20 s. By analyzing the hydration reaction rate with the unreacted-core shell model, the activation energy value was calculated to be56.6 kJ/mol. The calculation results showed good agreement with those of the experiment as the reaction fraction reached 0.7.展开更多
基金supported by the National Natural Science Foundation of China(No.52204302)Young Elite Scientist Sponsorship Program by CAST(No.YESS20220533)+1 种基金Hunan Provincial Natural Science Foundation of China(No.2022JJ50274)China Baowu Low Carbon Metallurgy Innovation Foundation(No.BWLCF202103).
文摘The factors affecting the oxidation degree of vanadium–titanium magnetite (VTM) pellets were analyzed via the isothermal oxidation experiment. Furthermore, the oxidation kinetics of VTM pellets were explored through linear fitting to the kinetic equations based on the shrinking unreacted-core model. The results reveal that VTM pellets undergo oxidation in three distinct phases: pre-oxidation, mid-oxidation, and final stable phase. Notably, the mid-oxidation phase is absent in magnetite oxidation. The shrinking unreacted-core model has been proven to be suitable for modeling the process of oxidizing VTM pellets. In the pre-oxidation stage, the rate-controlling step is determined by both the oxidation temperature and the effective oxygen concentration. The influence of the effective oxygen concentration on the rate of oxidation is more pronounced at temperatures between 1073 and 1273 K, especially when the oxygen content falls below 15 vol.%. For the production of oxidized VTM pellets, it is necessary to maintain a preheating temperature above 1173 K (to accelerate the oxidation reaction) and below 1473 K (to prevent the swift formation of compact Fe2TiO5 at the shell of the pellet) in an oxygen-enriched atmosphere.
基金Project(51276074)supported by the National Natural Science Foundation of ChinaProject(2014NY008)supported by Innovation Research Foundation of Huazhong University of Science and Technology,China
文摘A modified shrinking unreacted-core model,based on thermogravimetric analysis,was developed to investigate CaSO4 decomposition in oxy-fuel combustion,especially under isothermal condition which is difficult to achieve in actual experiments due to high-temperature corrosion.A method was proposed to calculate the reaction rate constant for CaSO4 decomposition.Meanwhile,the diffusion of SO2 and O2,and the sintering of CaO were fully considered during the development of model.The results indicate that the model can precisely predict the decomposition of CaSO4 under high SO2 concentration（1100×10-6）.Concentrations of SO2 and O2 on the unreacted-core surface were found to increase first and then decrease with increasing temperature,and the average specific surface area and porosity of each CaO sintering layer decreased with increasing time.The increase of SO2 and/or O2 concentration inhibited CaSO4 decomposition.Moreover,the kinetics of CaSO4 decomposition had obvious dependence on temperature and the decomposition rate can be dramatically accelerated with increasing temperature.
文摘Here, we propose a chemical heat pump chiller with a SrBr<sub>2</sub> hydration reaction system for utilization of waste heat. The SrBr<sub>2</sub> hydration reaction could recover waste heat in low temperatures ranging from 373 K to 353 K, and the system showed good potential in terms of the high cooling thermal-storage density. Previous studies have given little information on the reaction characteristics of the SrBr<sub>2</sub> hydration reaction. In this paper, we developed a measuring method for the hydration reaction equilibrium and reaction rate based on the volumetric method. We analyzed the hydration reaction rate with an unreacted-core shell model. In the experiments, the SrBr<sub>2</sub> equilibrium temperature observed was equal to the theoretical equilibrium temperature obtained from thermodynamic databases. In addition, the hysteresis gap between the hydration and dehydration values was 2.0 K. Thus, the hysteresis effect was negligible for the chemical heat pump cooling operation. The reaction fraction of the SrBr<sub>2</sub> hydration reached 0.7 within 20 s. By analyzing the hydration reaction rate with the unreacted-core shell model, the activation energy value was calculated to be56.6 kJ/mol. The calculation results showed good agreement with those of the experiment as the reaction fraction reached 0.7.
