Ilmenite particles are readily defluidized when they are reduced in a fluidized bed reactor because nano-micro iron nuclei that precipitate on the particle surface are adhesive and tend to aggregate. We propose herein a novel force balance model with which to predict defluidization phenomena. This model is based on the particle cohesion force comprising the sum of the cohesion forces for surface asperities. As the surface coverage of iron particles increases with the extent of reduction, the cohesion forces of the particles gradually increase and eventually trigger defluidization. The surface coverage predicted by the model agrees well with experimental results for 88.4 - 154.7 mu m particles and the temperature range 700 - 850 degrees C. The new force balance model reveals that particle size, sphericity, and temperature play key roles in defluidization of ilmenite during reduction. Defluidization occurs readily for fine and irregular particles, especially at high temperatures. Our model combines asperity, surface coverage, and particle sphericity to make a more general prediction.

The promotion effect of pre-oxidation on reduction of ilmenite was revealed from the view of pore formation. The result shows that the enhancement of pre-oxidation on reduction of ilmenite ore is attributed to the formation of porous structure during the reduction process. Reduction of ilmenite is inhibited by iron-rutile topology structure formed on the particle surface. By contrast, porous structure ilmenite is regenerated during the ferric-to-ferrous reduction stage of the pre-oxidized ilmenite with dominant reduction rate over diffusion rate of produced ferrous omega & GE; 33.2 mol/m4. The newly formed porous structure ilmenite enlarges particle surface area with facilitated gas-solid contact, thus it is responsible for the enhancement of the reduction of pre-oxidized ilmenite. A novel formation mechanism of porous structure is also proposed based on the competition and coordination between the reduction rate and diffusion rate determined by reduction potential and temperature.

超磁技术是一项先进的水处理技术,其特点是通过磁力替代重力沉降,将污水中的悬浮物快速固液分离.针对有色企业初期雨水水量波动较大、水质成分复杂的特点,提出"中和沉淀法+超磁"工艺对初期雨水进行快速处理.该工艺具有高效、占地小的优点,在项目运行实践中,出水水质可稳定达到行业排放标准中关于重金属指标的要求.

The efficient utilization of manganese dioxide (MnO2) ore is essential for the sustainable development of manganese (Mn) industry. Confronting the great challenge of chemical engineering scale-up, a commercial fluidized reduction project of MnO2 ore with the capacity of 200,000 t a-1 is carried out based on deep experimental investigation, extensive kilogram-scale test and detailed engineering design. Compared with other production technologies and equipment, it is proved that the fluidized process shows distinguished advantages of lower energy consumption, higher production efficiency, larger automation degree and less environmental pollution. The comprehensive studies of experiment, modeling, simulation and optimization are required for a more promising development of fluidization engineering in the future.

The hydrodynamic properties of a dual fluidized bed (DFB) with continuous feeding and discharging of solids were investigated on a pilot-scale plant in cold mode and simulated coupled with the structure-based drag model. We present a deep analysis that focuses directly on the problem of predicting the fluid dynamics behavior of this type of system for which empirical data is limited or unavailable. The fluidization of a DFB shows complex hydrodynamic characteristics because of the intricate interactions between different compartments experimentally. We prove that the simulation based on the structure-based drag model involving different fluidized structures is able to give an accurate prediction of pilot-scale DFB fluidization and capture the correct flow behaviors under different conditions. This work is expected to give thorough analysis and further exploration of the overall fluidization dynamics for DFB optimization and scale-up.

以山东省某赤泥高阶磁选过程中的底流(铁品位31.07％)、粗精(铁品位42.73％)为原料,采用流态化磁化焙烧-弱磁选工艺进行实验研究.结果 表明:该赤泥过细流化困难,但经过高阶磁选工艺“抛细留粗”处理的底流、粗精均可以实现连续、稳定的流态化.底流在采用流态化磁化焙烧-弱磁选工艺后,铁品位可以提高至62.04％,铁回收率可以提高至68.35％;粗精在采用流态化磁化焙烧-弱磁选工艺后,铁品位可以提高至63.88％,铁回收率可以提高至85.47％.

The process of fluidized low-temperature reduction manganese oxide ore developed by the Institute of Process Engineering, Chinese Academy of Sciences was introduced.The results show that compared with the traditional high-temperature reduction process, only 60％unit coal is consumed.The output of unit production line can reach 600 t/d.Manganese oxide ore containing total Fe less than 15％and crystal water less than 18％can be used in this process.The reduction reaction is improved by lower temperature and less side reaction.The leaching reaction is improved by lower impurity leaching rate.The tail gas meets national standards without desulfurization and denitration process.

The hydrodynamic characteristics of tapered bubbling/turbulent fluidized beds with/without gas distributor are simulated based on the structure-based drag model. Besides the only parameter of gas voidage (εg) contained in the original drag model, the heterogeneous drag index (Hd) for the tapered fluidized bed (TFB) also includes the parameter of gas velocity (ug) for the axial velocity gradient along bed height. Both the simulations of tapered bubbling and turbulent fluidized beds achieve more accurate predictions than the traditional drag models. There exist dilute center and dense annular regions with solids cycle flow structure in the TFB. The simulation also gives reasonable prediction for TFB without gas distributor, the variation of gas voidage profile reveals gas converging toward bed center with axial location rising.

The gas-solid mass transfer in the downer fluidized bed is analyzed theoretically in this work. Compared to the homogeneous assumption in each calculating grid, a structure-based model was proposed that the process was divided into the mass transfer in the cluster and dispersed phases. Simulations were performed with the cooperation of the Euler-Euler two-fluid method. The model predictions are in good agreement with the previous reported experimental measurements under a wide range of operating conditions. Simulated ozone profiles show a sharp conversion in the acceleration region, and a gentle conversion in the fully developed region. The transition point is well consistent with the boundary measured experimentally. These results show that the consideration of the heterogeneous structure results in a better understanding and prediction of mass transfer in downers.

The influence of reduction conditions on carbon deposition during fluidized-bed pre-reduction of iron ore fines was investigated experimentally. The results showed that reduction temperature and the composition of reducing gases had a significant effect on the rate of carbon deposition and the type of carbon deposits (graphite and Fe3C). Low reduction temperature, high CO content, and addition of H-2 favored the deposition of carbon, especially graphite. The reduction conditions also significantly affected the surface morphology of the as-reduced iron ore fines. As the amount of deposited graphite increased, the formation of fibrous iron disappeared and graphite filaments were observed. The pre-reduced iron ore fines were further fluidized in pure CO at 850 degrees C for final reduction. The results showed that graphite could suppress the formation of fibrous iron and decrease the surface viscosity, thereby inhibiting agglomeration during the final high-temperature reduction stage. Reactions that consume the deposited carbon during the final high-temperature reduction were identified and graphite was shown to be more reactive than Fe3C. To enhance the application of fluidization technology in producing sponge iron, a novel solid-state high-temperature reduction method via deposited carbon was proposed and demonstrated to be feasible. (C) 2018 Published by Elsevier B.V. on behalf of Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences.

The first demonstration plant of fluidizing reduction of pyrolusite with capacity of 200,000 t/a has been set up into production in Wenshan of Yunnan province.A study of thermodynamic and kinetic indicates that the reductions of manganese oxide ores can be completed at a relatively low temperature range of 500～700℃.The influence of temperature on leaching rate of manganese is neglectable if its reduction lasts more than 10 min.With advantages of high production capacity and automation over the conventional technologies, the production line will run smoothly and reliably to reach lead level both in product quality and energy consumption.The plant has contributed a lot to the local economy by utilizing the low-grade manganese ores in the area.

The residence time distribution (RTD) of solids and the fluidized structure of a bubbling fluidized bed were investigated numerically using computational fluid dynamics simulations coupled with the modified structure-based drag model. A general comparison of the simulated results with theoretical values shows reasonable agreement. As the mean residence time is increased, the RTD initial peak intensity decreases and the RTD curve tail extends farther. Numerous small peaks on the RTD curve are induced by the back mixing and aggregation of particles, which attests to the non-uniform flow structure of the bubbling fluidized bed. The low value of t(50) results in poor contact between phases, and the complete exit age of the overflow particles is much longer for back-mixed solids and those caught in dead regions. The formation of a gulf-stream flow and back-mixing for solids induces an even wider spread of RTD. (C) 2016 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

The present work focuses on a numerical investigation of the solids residence time distribution (RTD) and the fluidized structure of a multi-compartment fluidized bed, in which the flow pattern is proved to be close to plug flow by using computational fluid dynamics (CFD) simulations. With the fluidizing gas velocity or the bed outlet height rising, the solids flow out of bed more quickly with a wider spread of residence time and a larger RTD variance (σ2). It is just the heterogeneous fluidized structure that being more prominent with the bed height increasing induces the widely non-uniform RTD. The division of the individual internal circulation into double ones improves the flow pattern to be close to plug flow.

In this work, Pt-SnO2 heteroaggregate nanocatalysts were synthesized by in situ transformation of Pt@Sn core–shell nanoparticles and their catalytic performance for hydrogenation of various substituted nitroaromatics was investigated. The Pt@Sn nanoparticles were prepared by a one-step method, and the alumina-supported Pt@Sn nanoparticles were further transformed in situ into Pt-SnO2 heteroaggregate nanostructures by calcination. The structures of Pt@Sn and Pt-SnO2 nanomaterials were characterized, and FT-IR with CO probes, HRTEM, XRD, and XPS characterizations revealed that the as-synthesized Pt@Sn nanoparticles were core@shell-like structures with Sn-rich shells and Pt-rich cores and the obtained Pt-SnO2 heteroaggregate nanostructures consisted of close-contact pure Pt and SnO2 phases. The Pt-SnO2/Al2O3 nanostructures demonstrated a better catalytic performance for hydrogenation of various substituted nitroaromatics relative to individual Pt/Al2O3 nanocatalysts. Theoretical calculations suggested that P...

The simulation of bubbling fluidized beds (BFB) residence time distribution (RTD) based on the structure-based drag model are conducted for the single and binary gas-solid phases systems, a comparison of computed results with experimental data proves that our model is applicable to both systems with better accuracy. The revised drag coefficient (Hd) increases with decreasing the gas velocity or increasing the particle diameter. The increase of the feed rate could improve the solids flow pattern to be close to the plug flow, while increasing gas velocity or bed height would lead to a wider RTD. The particles in the binary mixture are in more diffusion-oriented movement so as to have less MRT (mean residence time) than that of the single system. The coarse particles with longer MRT are simulated to accumulate into the bed bottom with a slower vertical velocity.

Brazilian iron ore fines were reduced in a laboratory fluidized bed with different Ca-based additives at 800°C using 0.5L/min H2–0.5L/min N2. The fluidization results show that pure CaO and Ca(NO3)2·4H2O only slightly prolong the fluidization time, with defluidization occurring eventually. However, mixtures of Ca(NO3)2·4H2O and Fe(NO3)3·9H2O could effectively inhibit defluidization. Reduction results of CaO/Fe2O3 suggest that Ca-based additives mainly inhibit defluidization through the physical spacer effect. Microstructure observations indicate that 2CaO·Fe2O3 could suppress the growth of sharp-pointed whisker, and the introduction of Fe2O3 allows the Ca species to adhere tightly to the surface of the sticky iron, thereby decreasing its adhesiveness. Moreover, Fe2O3 is demonstrated to be a general binder capable of enhancing the ability of ineffective additives to prevent defluidization.

The PdAu and PdAg bimetallic nanoparticles were synthesized by one-step reduction with sodium borohydrid and characterized by XRD,TEM and UV-visible spectroscopy.The results show that Pd and Ag,or Pd and Au can both form alloy structure,the nanoparticles are monodisperse.PdAg/Al2O3 and PdAu/Al2O3 bimetallic nanocatalysts were successfully prepared by homogeneous loading of bimetallic nanoparticles on Al2O3 by colloid deposition.The catalyst was probe-tested in the selective hydrogenation of o-chloronitrobenzene,compared with the Pd/Al2O3 catalyst,the PdAg/Al2O3 catalyst showed 95.5 ％ selectivity and PdAu/Al2O3 catalysts showed higher selectivity up to 98.7％,which could be attributed to the synergistic effect of Pd and Ag or Pd and Au.

The fine iron ores from Chile are reduced in a laboratory fluidized bed at 973–1173 K with CO–H 2 –CO 2 mixtures to investigate the influence of reduction condition on the morphology of newly formed metallic iron and its corresponding agglomeration behavior. The results reveal that the addition of H 2 in CO accelerates the moving rate of the Fe/Fe 1– x O interface and increases the amount of the iron nucleus formed during the initial reduction period, which induce the transformation of iron morphology from fibrous to dense. The presence of CO 2 in CO makes the fibrous iron shorter and sparser, especially when the content of CO 2 is 30% (by volume), the iron appears as “cactus‐like.” The increase of reduction temperature makes the fibrous iron stronger and more active. The sticking index indicates that the long and strong iron whiskers are prone to form stable agglomerates even at a low metallization degree, but the dense iron trends to behave separate. Furthermore, based on the precipitation mechanism of iron proposed by the authors, it is manifested that the agglomeration behavior of the fine iron ores could be controlled by pre‐reduction in H 2 ‐rich reducing gas (H 2 /(H 2 + CO) ≥ 30%, by volume).

Coating carbon on the iron ore powder is a quite promising way to prevent defluidization during its high-temperature direct reduction in the fluidized bed reactor, but usually causes excessive carbon content of the DRI production, thus the present study focuses on decreasing the critical carbon content (Ccritical value) needed for defluidization prevention by the optimization of the pre-reduction process. It was for the first time found that increasing the metallization ratio of the pre-reduced iron ore significantly could reduce the Ccritical value, since it inhibited the carbon consumption and formation of metallic iron during the early stage of high temperature reduction. Based on this result, optimization principle to reduce the Ccritical value was further proposed, i.e. increasing the pre-reduction rate (Rpre-reduction) and reducing the carbon deposition rate (Rcarbon deposition) during the pre-reduction, such as by increasing the temperature and the H2 mole fraction in CO–H2 mixture gas. And such principle was verified by the experiment results, where for the iron ore pre-reduced in CO–H2 mixture gas with the xH2≥0.9 at 600°C, its corresponding Ccritical value was less than 3.5wt.%, much lower than that of other conditions or the reported value in the literature.