CFD simulation of solids residence time distribution in a multi-compartment fluidized bed

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.

Histological Study of the Liver Pigmentation of Chinese Fire-bellied Newt (Cynops orientalis) During Activity and Hibernation Periods

The pigmentation in the liver of Chinese fire-bellied newt(Cynops orientalis) was described during two periods of the annual cycle(summer activity and winter hibernation). A large number of melanin granules were gathered into clusters and distributed unevenly inside the pigment cells. Liver pigmentation(melanin content) was found unstable,varying during the annual cycle. During the hibernation period,pigmentation accumulation was shown to increase in the liver of the Chinese fire-bellied newt. Hepatocytes during the active period are approximately 14.64% larger than those in the hibernation period,while the nucleus is approximately 7.43% bigger during the active period when compared with that during the hibernation period. These findings indicate that variation in pigment distribution and hepatocyte morphology in Chinese fire-bellied newt liver may be an ecologically adaptive strategy to the adverse physiological conditions during hibernation.

Numerical analysis of residence time distribution of solids in a bubbling fluidized bed based on the modified structure-based drag model

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 t50 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.

From laboratory research to industrial application:a green technology of fluidized mineral processing for manganese dioxide ore reduction

The efficient utilization of manganese dioxide(MnO_(2))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 MnO_(2)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.

Evolution of deposited carbon during multi-stage fluidized-bed reduction of iron ore fines

The influence of reduction conditions on carbon deposition during fiuidized-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 H2favored 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 fiuidized in pure CO at 850℃ 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.