Numerical and experimental study on coke size distribution in bell-type charging in the CDQ shaft

The mechanism of coke size segregation in the radial direction of pre-chamber in coke dry quenching （CDQ） shaft was investigated by experiment and numerical analysis. The experimental apparatus was a cold three-dimensional semicircle model for bell-type charging, which was used to study the influences of different kinds of bells and different stock line levels on the radial distribution of coke size in the radial direction of a pre-chamber. A mathematical model was used, which is capable of estimating the radial average size distribution as well as the radial deposit distribution of each particle size for multiple size coke with a few fixed parameters. The calculated results agree well with the experimental data, which proves the reliability of both experimental study and numerical analysis.

Particle size segregation in hopper at a bell-less top blast furnace with parallel hoppers

Owing to a certain angle existing between a belt conveyor and the parallel hoppers,and the hoppers localizing away from the centerlines of a blast furnace,particles size segregation is likely to happen in a bell-less top blast furnace with parallel hoppers.Mastering the law of particles size segregation in hoppers could help to choose better charging parameters and optimize production and technical indices.As for the previous works on burden segregation at a bell-less top blast furnace with parallel hoppers,more attention was paid to the falling point segregation and the circumferential mass flow segregation while charging from the tilting chute,but ignoring the particle size segregation in burden hoppers as burden falls from a belt conveyor,which is the right basis of analyzing the former,and plays a significant role in controlling the gas distribution in the blast furnace.The present work takes ternary mixtures of coke in three different particle sizes to simulate the size segregation of the coke charged into the hoppers by experiments.The effect of the main striking point on size segregation is also investigated.The research shows that there exists a good linear relation between segregation coefficient k and the dimensionless main striking point when using the equation C = C_0~k to express the degree of size segregation in hoppers.The linear relation is proposed for the first time and provides a new way to predict the size segregation in hoppers,which forms a theoretical basis and technical support for reducing the size segregation degree in hoppers.

Seasonal size-segregated PM10 and PAH concentrations in a rural area of sugarcane agriculture versus a coastal urban area in Southeastern Florida, USA

Airborne particulate matter （PM） is of health and environmental concern not only in highly urbanized areas, but also in rural areas that are used for intensive agricultural purposes, In this study, PM size- segregated samples were collected simultaneously for 12 months in a small town （Belle Glade, Florida）, which is the center of a vast sugarcane growing area and at Delray Beach, a coastal city in Palm Beach County, Florida. During the winter sampling period, when sugarcane foliage is burned just before harvest- ing to reduce the amount of plant matter to be handled, PM10 levels were 50% or higher than otherwise measured, indicating that sugarcane harvesting and processing is a major local source for PM10. For the rest of the year, PM10 levels at both sites are similar, suggesting that ambient PM levels at both sites are impacted by the major urban centers in Southern Florida. During late July and early August, the PM10 levels at both sites were substantially elevated and revealed the typical red-brownish color of Saharan dust. This has been reported to occur frequently with suitable meteorological conditions over the Atlantic Ocean coupled with a Sahara dust storm event. During the sugarcane harvesting season at Belle Glade, the concentrations of PAHs associated with PM10 were up to 15 times higher than those measured during the summer growing season, indicating a substantially higher exposure of the rural population to these often mutagenic and carcinogenic compounds.

Global woodland structure from local interactions:new nearest-neighbour functions for understanding the ontogenesis of global forest structure

Background:A number of hypotheses and theories,such as the Janzen-Connell hypothesis,have been proposed to explain the natural maintenance of biodiversity in tropical and temperate forest ecosystems.However,to date the details of the processes behind this natural maintenance are still unclear.Recently two new nearest-neighbour characteristics were proposed and in this paper we demonstrate how they can contribute to a better understanding of the ontogenesis of global forest structure from localised neighbourhoods.Methods:We applied the new species and size segregation functions together with appropriate test procedures to four example woodland data sets from China at Daqingshan,Jiaohe,Jiulongshan and Xiaolongshan forest regions.In addition we quantified the morphology of the new characteristics and modelled a neighbourhood allometric coefficient linking the two functions.Results:The results revealed quite different species segregation patterns with both conspecific and heterospecific attraction.We found these to be generally matched by equivalent size segregation patterns of attraction of similar and different sizes.It was straightforward to model the size segregation function from the knowledge of the species segregation function by estimating a neighbourhood allometric coefficient.Conclusions:The new characteristics have helped to quantify the extent and rate of decline of neighbourhood interactions in terms of spatial species and size diversity.Through the allometric neighbourhood coefficient the analysis highlighted once more how closely related species and size segregation are,thus supporting the minglingsize hypothesis.Using both a traditional and a restricted random-labelling test has provided a valuable tool for understanding the exact nature of species-mingling and size-inequality relationships.

Enhancing mixing of particles by baffies in a rotating drum mixer

Baffles with shape of ＂-＂ （single baffle）, ＂＋＂ （cross-baffles with four arms） and （baffles with 6 arms） are used to enhance the mixing of particles in a rotating drum mixer. A micro-dynamics study of mixing and segregation ofa bi-disperse system of two particle sizes in the rotating drum with these three kinds of baffles is carried out using the discrete element method （DEM）. The effect of the baffles on mixing, and the mechanisms of mixing enhancement by the baffles are discussed and analyzed. Simulation results show that in an unbaffled drum mixer, particle convection, particle diffusion, and size segregation of hi- disperse particles, all play important roles in the mixing process; whereas size segregation will be largely restrained when the drum mixer has a baffle, regardless of its shape, and the degree of mixing is higher than that in an unbaffled drum mixer. The different mixing characteristics for ＂-＂ shaped baffle, ＂＋＂ baffle, and baffle are revealed by the simulation results. For ＂＋＂ or style baffles, there is an optimal size of baffles for the mixing of particles, and the ootimal mixing efficiency is higher than that for ＂-＂ baffle.

Simulation of particle flow in a bell-less type charging system of a blast furnace using the discrete element method

A three-dimensional model was established by the discrete element method （DEM） to analyze the flow and segregation of particles in a charging process in detail. The simulation results of the burden falling trajectory obtained by the model were compared with the industrial charging measurements to validate the applicability of the model. The flow behavior of particles from the weighing hopper to the top layer of a blast furnace and the heaping behavior were analyzed using this model. A radial segregation index （RSI） was used to evaluate the extent of the size segregation in the charging process. In addition, the influence of the chute inclination angle on the size segregation and burden profile during the charging process was investigated.