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Numerical simulation of CO emission in a sintering pot under flue gas recirculation
No full textA transient two-dimensional sintering model coupling porous medium flow, interphase heat mass transfer and reactions was established through computational fluid dynamics (CFD) method by Comsol Multiphysics 6.0 for a sintering pot under sintering flue gas recirculation (SFGR). The ignition was considered and CO was the carbon combustion intermediate and experienced catalytic oxidation in the ferric oxide bed. The model was verified by sintering pot experimental data of flue gas temperature and components fractions with maximum deviation less than 10 %. The bed temperature, CO emission and solid fuel consumption were focused under different SFGR parameters by the verified model. Ignition was important for the beginning flue gas component fractions, especially when the bed height was less than 700 mm. The effect of SFGR parameters on the maximum bed temperature (MBT) was sequenced: inlet gas velocity > inlet CO fraction > inlet O2 fraction > inlet gas temperature. MBT grew up when each of the four parameters increased. The impact on the CO emission was different: inlet CO fraction > inlet O2 fraction > inlet gas velocity > inlet gas temperature. CO emission declined when each of the parameters increased. The total reaction rate of CO was studied for explanation. The reduction of solid fuel consumption was studied by energy conservation to evaluate the influence of inlet CO, inlet gas temperature and flue gas recirculation fraction. The three factors had positive linear correlation with solid fuel consumption reduction. The reduction maximally reached 16.6 % at flue gas recirculation fraction of 50 %, inlet 2 % CO and 473.15 K temperature, providing theoretical support for SFGR application
Cooperation project on transformation of major scientific and technological achievements of CAS
No full textControlled alcoholysis of PET to obtain oligomers for the preparation of PET-PLA copolymer
No full textControlled degradation of macromolecules or natural macromolecules is important for their subsequent utilization. Normally, it is easier to degrade them to monomers than to oligomers in designated molecular weight range, the controlled degradation is much difficult to achieve and has been challenge for the utilization of macromolecules. Here, we proposed a strategy for simultaneous degradation of the inner and outer layers of PET, which avoid the degradation of polymers from the outside to the inside and achieved the controlled degradation. Under high temperature and micro-pressure conditions, PET is transformed from dense to flocculent structure by the swelling effect, which satisfies the need for simultaneous degradation of the inner and outer layers. In addition, a stable "Dawson" type Polyoxometalates (POMs) alpha(2)-K8P2W17O61X(H2O)center dot 16H(2)O (X = Zn, Mn, Co, Ni, Cu) with limited number of catalytic activity center was synthesized and applied to PET alcoholysis to obtain oligomer with given molecular weight range. Under the optimal conditions, PET: EG: POM catalyst = 1.0: 4.0: 0.02 (wt%), 240 degrees C, 10 min, PET was completely degraded and obtained the oligomer products (Mn < 2000 g/mol) with 72.1 % yield. By investigating the mechanism of the controlled alcoholysis, the formation of flocculent PET was be the key factor in achieving controlled degradation; hydrogen bonding and coordination of POMs are the key interactions to achieve rapid alcoholysis. Finally, oligomers were applied in the preparation of PET-PLA copolymers to follow sustainable route. The incorporation of bio-based polymers demonstrates better inclusiveness to the environment and contributes to harmonious development
State Key Laboratory of Multiphase Complex Systems Institute of Process Engineering, Chinese Academy of Sciences
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Fabrication of Ti-6Al-4V alloy powder by a novel sintering-deoxygenation process
No full textGiven the high cost of fabricating the Ti-6Al-4V alloy powder by the traditional hydriding-dehydriding and atomization methods, a novel sintering-deoxygenation process was proposed and studied in this research. With the help of the developed deoxygenation treatment, value-added raw materials such as Ti sponge can be substituted by low-cost and low-grade materials with high oxygen content. In addition, sintering in a solid state saves a significant amount of processing energy compared to alloying above the melting point of Ti in the conventional alloy production process. This paper prepared six sintering precursors with different initial compositions and oxygen contents using the low-valued raw materials of crude titanium, crude vanadium, V2O3, Al powder, and Al2O3 powder. These precursors' sintering performances on shrinkage, phase composition, microstructure, and porosity were investigated. The results show that the sintering shrinkage is positively correlated with the sintering temperature and holding time and is also affected by the raw materials. The pellet made by mixed crude titanium and AlV master alloy showed the largest shrinkage and the densest bulk. The various combinations of the raw materials led to the changes in the oxygen contents in the precursors, the alpha-beta phase ratio, and the shift of the diffraction peaks of the alpha-phase. The dissolving of the AlV master alloy and the formation of the Ti3Al intermediate phase took place during sintering due to diffusion. Sintering at 900-1000 degrees C is critical for elemental diffusion and densifi-cation, and sintering at higher temperatures is decisive for microstructure homogenization and further densification. Using the hydrogen-assisted Mg deoxygenation method, all the sintered samples could be treated to an oxygen level of around 0.4 wt% regardless of oxygen content in precursors. The contents of Ti, Al, V, and Fe in the obtained Ti-6Al-4V powders met the requirements of GB/T 34486-2017. This research has demonstrated the feasibility of fabricating Ti-6Al-4V alloy powder by the novel sintering-deoxygenation process.(c) 2022 Elsevier B.V. All rights reserved
