Dusts from dry off-gas cleaning: comparison of flowability determined by angle of repose and with shear cells

The flowability of the dust separated in dry off-gas cleaning systems is an important characteristic for the design of dust storage and conveying equipment. The angle of repose is often used as an indicator for the flowability of granular material. In this study the results for the flowability obtained from the angle of repose and by the ratio of the consolidation stress to the unconfined yield strength were compared for 77 dusts from various dry off-gas cleaning systems. For dust with a Sauter mean diameter of \({>}\)5 \(\upmu \)m the flowability indicated by the angle of repose and the results of a shear test performed at a low pre-shear load correlated reasonably. For dusts with a smaller particle size such a correlation did not exist. The values of the angle of repose were scattered with no relation to the results of the shear test. The dependence of the angle of repose on the \(\hbox {d}_{32}\) described in the literature was confirmed for the coarser dusts only. For dusts with a smaller particle size such a relationship does not exist. For very fine dusts the angle of repose was even smaller. This effect was attributed to the visible small agglomerates formed during the angle of repose measurement. These agglomerates rolling down the slope prevented the formation of a steeper cone which limits the angle of repose.     

Characteristic Analyses of Plasma Air Cleaning Systems for the Removal of Indoor Air Pollutants

Tobacco smoke is one of the most common manmade aerosols. Yellow sand dust and pollen are the particular and regional pollutants generated by natural phenomena. These pollutants have different removal characteristics, respectively, when the air cleaning system is operated. It is well known that tobacco smoke particles are removed effectively with electrostatic precipitators. But it is necessary to evaluate whether the plasma air cleaning system has good performance of removing Yellow sand dusts and pollens simultaneously and also to establish the operation modes for efficient removal of those particular air pollutants by controlling the air flow rates passing the electrostatic precipitator and operating times of air cleaning system. In this study, the performance evaluation of plasma air cleaning systems is investigated with tobacco smoke particles, Yellow sand dusts, and pollens. For the multi-pass test in occupied spaces of 150 m³, the operation time required to reduce dust concentration from the initial concentration of 300 µg/m³ to 150 µg/m³, the criteria of indoor air quality in Korea, are 40 min for tobacco smoke, 28 min for Yellow sand dust, and 5 min for pollen when the flow rate is 17 m³/min. Also, the optimal operation modes for each pollutant are suggested for the efficient removal of indoor air pollutants. At first, most particles are removed by maximum flow operation. Second, the rest of the particles are removed by medium flow operation. Next, the plasma air cleaning systems are maintained by minimum flow for tobacco smoke mode and by repeating minimum flow and medium flow for Yellow sand and pollen modes. Edit to “Because the Yellow sand dust and the pollen flow into the room continuously and settle down … noise reduction.” Because the Yellow sand dust and the pollen flow into the room continuously and settle down. The plasma air cleaning system is suitable for the removal of the tobacco smoke, the Yellow sand dust, and the pollen for maintaining suitable indoor air quality, and, if it is operated through the suitable operation mode, energy efficiency will improve noise reduction.     

Electric arc furnace filter dust: Influence of organic material on the bulk density and flowability

In this study, the influence of condensed organic matter on the flowability and the bulk density of electric arc furnace (EAF) dust was investigated. The properties of the original dust samples containing some organic matter were compared with the properties of these samples after the removal of the condensed organic compounds by a deoiling procedure. The particle size distribution and the density of the three investigated dust samples were quite similar but the content of organic matter (TOC) was different. The values for the bulk density were lower for the original dust compared to the deoiled dust samples. The higher the TOC content, the higher the difference in the bulk density. Thus, the storage capacity of the dust silo was reduced by 9–17%. The flowability of all deoiled dust samples was very similar, whereas the flowability of the original dust was worse. The higher the TOC content, the worse the flowability. The average reduction of ff_c in comparison to the deoiled dust samples was 48, 38, and 17% for EAF dust samples with 0.65, 0.46, and 0.26% TOC, respectively. Evidently, the condensed organic matter on the dust particles reduces the flowability of the material. Therefore, the bulk density for dust with a higher TOC content is also lower.     

Application of μRaman Microscopy to the Identification of Individual Airborne Particles: Preliminary Results from Kozani's Area,Northern Greece

In the present study, Raman spectroscopy combined with a con-focal microscope has been applied for the identification of airborne particulate matter collected from Kozani's area, northern Greece. This technique provided a rapid and accurate identification of the molecular composition of micrometer sized (down to 2 µm) airborne particles. Different experimental conditions (laser excitation wavelength of 532 and 780 nm, slit and pinhole aperture, 50× and 100× objectives, number of exposures, and time of each exposure) were employed in order to obtain the optimal analytical parameters. The slit aperture and the 532 nm laser source were preferable. Removal of the background interference caused by the blank Teflon filter was performed for the acquisition of Raman spectra of minute (<10 µm) airborne particles, whereas no background correction was necessary for larger particles (>10 µm). Several distinct mineral phases were determined, such as: the common geogenic minerals calcite, gypsum, anhydrite, titanium oxides and microcline (feldspar); the anthropogenic minerals, black carbon and nitrates; and the lepidolite and smectite (phyllosilicates) attributable to Saharan dust episodes.     

Effect of Particle Size Distribution of Calcined Diatomites on the Extinction Performance

Calcined diatomite was first investigated as matting agent for formulating high-performance coating. Jet milling and sieving or sedimentation methods were employed to obtain rational particle size distributions. It was found that the optimal size distribution of the particles with the diameters of D₁₀ = 2.54 µm, D₂₅ = 5.04 µm, D₅₀ = 9.74 µm, D₇₅ = 18.80 µm, and D₉₀ = 31.66 µm showed the best extinction performance, with the gloss and extinction being 2.9 and 3.3 and 32.6% and 50.7% determined at incidence angles of 60° and 85°, respectively.     

Dust sensor based on luminescent glazing for control of photovoltaic panels cleaning

The installation of photovoltaic panels in dusty areas affects their efficiency by the accumulation of dust on glazing surfaces. The cleaning of the dusty panels allows recovering the maximum efficiency. However, it increases the cost of operating and maintenance for photovoltaic installations, a compromise between the reduction in the annual cleaning cost and the improvement solar energy production is obtained with implementation of a dust sensor. By this study, for a first time a dust sensor is developed by using luminescent glazing material with embedded photocells on borders. The dust deposited on sensor is detected from photogenerated current from the photocell integrated on the edges of a luminescent glass plate of 10 × 10 cm² area. The optical and electrical characterization revealed that the generated photocurrent from the sensor output increases of 9 µA when dusts accumulation shading is widen by 10%. This new principal for dust sensors could be applied to monitor photovoltaic power plant installations for maximizing energy production from solar renewable source in dusty environment as like Saharan regions. In order to start the cleaning cycle of the photovoltaic modules, the signal generated by the dust sensor is amplified by a Darlington analog circuit which assures the relay control for operating of a direct current pump.     

Crystallization kinetics of magnetic glass–ceramics prepared by the processing of waste materials

The objective of the present investigation was to study the feasibility of conversion of an intimate mixture of blast furnace slag and blast furnace flue dust generated by a single industrial company into magnetic glass–ceramic product. Blast furnace slag (BFS) and blast furnace flue dust (BFD) are generated at a rate of 300,000 and 30,000 tons/year, respectively, from iron and steel factory. The crystallization mechanisms of a composition containing BFS and BFD in a 50/50 proportion were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The crystallization temperature was found to vary from 900 to 1100 °C and two phases appeared in the crystallized samples: pyroxene Ca(Mg, Fe, Al)(Si, Al)₂O₆ and magnetite/maghemite. Heating rate and particle sizes effects on crystal growth of powdered samples were studied by DTA. The apparent activation energy of crystal growth using the particle size 180–315 μm was determined to be 355 and 329 kJ/mol for the first and second peak, respectively. The presence of sharp and broad crystallization peaks indicate simultaneous surface and internal crystallization mechanism. Good wear resistance and chemical durability particularly in alkaline environment, combine with good hardness and magnetic properties make this glass–ceramic material potentially useful for various industrial applications.     

Field Electron Emission from Single‐Walled Carbon Nanotube Layers

Abstract

Field emission characteristics of single‐walled carbon nanotube layers have been investigated at room and low temperatures. For these layers the emission current density of 10 mA/cm² was obtained at the average field E _av = 1.6–3.8 V/µm. Current–voltage characteristics in Fowler–Nordheim coordinates have a break at emission current about 10^?8 A. Cooling of samples only insignificantly changed the form of current–voltage characteristics. This indicates, that investigated single‐walled nanotubes have the metal type conductivity.     

Investigation of the cyanide leaching optimization for ultrafine grinding gold–silver ore

ABSTRACT

In recent years, the ultrafine grinding (UFG) process has become increasingly important for the recovery of precious metals (especially for Au and Ag) from raw ores. It is well known that cyanide leaching of gold–silver ore has been an accepted process in the world. In the current study, UFG was proposed as a pretreatment method prior to cyanide leaching of a gold–silver ore. First, the ore was crushed and ground by jaw, cone crusher, and ring mill, respectively. Particle size of ground product was 75 µm based d₈₀. Second, the fine product was subjected to the grinding process by vertical wet stirred ball mill, and the final ultrafine product was used as leach feed material. The leach feed material had about d₈₀ = 20 µm and d₅₀ = 6.02 µm particle size. Some important leaching parameters were optimized by using the ultrafine powder in the study. The final leach experiments demonstrated that the recoveries of Au and Ag were 91.92% and 82.15% under optimum leaching conditions such as 150 kg/t quicklime dosage, 25% pulp density, 85°C leach temperature, 500 g/t cyanide concentration, and 90 h leaching time.     

Preparation and Properties of Porous Composite of Hematite/Magnetite/Carbon with Eucalyptus Wood Biotemplate

By using eucalyptus wood biotemplate, a novel porous composite material of iron oxides and carbon (PC-Fe/C) was manufactured for adsorption of oxoanion pollutants. The material's microstructure and characteristic were investigated by different characterization techniques. The experimental results show that the PC-Fe/C composite mainly consisted of hematite, magnetite, and carbon, and preserved the porous hierarchical texture of the wood with 70 ～ 120 µm macropores, 4.1 ～ 6.4 µm mesopores, and 0.1 ～ 1.3 µm micropores. Its Brunauer-Emmtee-Teller (BET) surface area was 59.2 m² g^?1. The maximum adsorption capacities were 2.49, 2.96, and 0.69 mg g^?1 for arsenic(V), chromium(VI), and phosphorus(V), respectively. The adsorption capacities of the unpulverized material as a novel filtration adsorbent are comparable to fine particles of the pulverized material, natural, and synthetic iron oxides.     

Acidic leaching both of zinc and iron from basic oxygen furnace sludge

During the steel production in the basic oxygen furnace (BOF), approximately 7-15 kg of dust per tonne of produced steel is generated. This dust contains approximately 1.4-3.2% Zn and 54-70% Fe. Regarding the zinc content, the BOF dust is considered to be highly problematic, and therefore new technological processes for recycling dusts and sludge from metallurgical production are still searched for. In this study the hydrometallurgical processing of BOF sludge in the sulphuric acid solutions under atmospheric pressure and temperatures up to 100 °C is investigated on laboratory scale. The influence of sulphuric acid concentration, temperature, time and liquid to solid ratio (L:S) on the leaching process was studied. The main aim of this study was to determine optimal conditions when the maximum amount of zinc passes into the solution whilst iron remains in a solid residue.     

Development of Venturi negative-pressure secondary dedust device and application of local spray closure technique

In order to enhance the spray for dust suppression performance in a fully-mechanized mining face, based on orthogonal test, comparison test, numerical simulation and field application, the Venturi negative-pressure secondary dedust device was developed. Meanwhile, the local spray closure technique was proposed, which can not only effectively prevent the escape of coal dust from entering the footway space, but also remove coal dust around the respiratory zone from the footway space successfully. The results demonstrated that, under spray pressure of 6?MPa, the Sauter mean droplet size, negative pressure suction flow rate and effective spray distance of the novel dedust device with a throat-to-nozzle distance and throat diameter of 20?mm and 65?mm were 47.37?µm, 11.21?m³/min and 5.4?m respectively. Moreover, the novel dedust device produced droplets to a smaller scale than a single-nozzle. Additionally, the negative pressure and airflow velocity in the negative pressure suction inlet of novel dedust device were within the range from ?0.97?Pa to ?541.04?Pa and from 2.96?m/s to 27.29?m/s respectively. Finally, compared with the original dust suppression measures, the local spray closure technique can enhance the removal ratio of respiratory dust by an average of 44.3%.     

Effects of radial air flow quantity and location of an air curtain generator on dust pollution control at fully mechanized working face

To better understand the effects of radial air flow quantity and the location of air curtain generator on dust pollution control, the 2–109₂ fully mechanized working face in Xinzhi coal mine (Huozhou Coal Electricity Group Co., Ltd., Shanxi, China) was numerically simulated in the present study. A full-scale physical model of the working face was established; then, based on airflow-dust particle two-phase flowing characteristics, the k-ε-Θ-k_p mathematical model was constructed. The comparison between simulation results and field measurements validated the model and the parameter settings. Furthermore, the effects of ventilation parameters on airflow migration and dust diffusion were numerically investigated using FLUENT. The results show that the increase of the radial air flow quantity (denoted as φ) and the distance of the air curtain generator from working face (denoted as d_w) is beneficial to the formation of a dust-control air curtain. At a constant d_w, the dust diffusion distance (denoted as D) decreases with the increase of φ. At a constant φ, D decreases with the increase of d_w when a dust-control air curtain is formed; otherwise, the increase of d_w leads to the increase of D. By analyzing the simulation results, the optimal ventilation parameters for 2–109₂ fully mechanized working face and those working faces under similar production conditions are determined as: φ = 240–270 m³/min and d_w = 20–30 m.     

Refinement of Fe4Al13 in Al–Fe alloys by plasma remelting process

Abstract

Refinement of the Fe₄Al₁₃ phase in Al–Fe (wt-%) alloys has been achieved by a plasma remelting process. The refinement effect is enhanced by increases of discharge current and argon flux. The average size of the Fe₄Al₁₃ is 40 µm in Al–1Fe alloy melted using an electric resistance furnace. This can be reduced to 0.4 µm by a plasma remelting process. Similarly, the average size of the Fe₄Al₁₃ in Al–5Fe alloy can be decreased from 60 to 3 µm by plasma remelting. The refinement is considered to be an effect of the decrease of cluster size retaining genetic information in the Al–Fe alloy melt, the homogenisation of microstructure in the melt, and the increased undercooling during solidification.     

PREDICTION OF PRESSURE DROP IN PNEUMATIC TRANSPORT SYSTEMS AT VARIOUS PIPE ORIENTATIONS USING AN EMPIRICAL CORRELATION FOR THE PARTICLE VELOCITY

ABSTRACT

A new empirical correlation for the particle velocity which incorporates the angle of inclination is proposed here. This correlation coupled with the expression for the solids friction factor obtained from the force balance on the particle was used to predict the pressure drops in the 0.0266 m and 0.0504 m systems held at various angles of inclination. Particles used in these systems included glass particles of 67, 450, and 900 µm weight mean diameter. The existence of minimum points in the predicted pressure drop curves as a function of gas velocity was corroborated by these two expressions.     

A study on the dust control effect of the dust extraction system in TBM construction tunnels based on CFD computer simulation technology

In order to control dust in a tunnel boring machine (TBM) construction tunnels, this paper, in combination with field measurements, applies CFD computer simulation technology to study the dust control effect of TBM construction tunnels under different dust extraction flow rates. Firstly, the dust extraction system is closed, and the result of the simulation show that the dust diffuses to the entire TBM working area within 181 s, indicating the necessity of having a dust extraction system in the tunnel. Secondly, the dust extraction system is open and under the original dust extraction flow rate of Q_e = 8 m³/s, the overall dust diffuses to the entire working area L_o = 130 m, and the full-face dust diffusion distance is L_f = 47.54 m. Then the study was carried out with the setting of 2 m³/s ≤ Q_e ≤ 14 m³/s. The results show that: when Q_e ≤ 8 m³/s, the full-face dust diffuses to 47.54–71.84 m; when Q_e > 8 m³/s, the full-face dust can be controlled at 42.81–46.34 m; and when Q_e = 8 m³/s, the full-face dust control effect is better, and the average dust concentration in the tunnel is as low as 12.25 mg/m³, indicating that the original dust extraction system has a better design. The field measurement results verify that the CFD computer simulation results are accurate.     

Top-down synthesis of mesocrystalline α-Fe2O3 submillimeter-sized rhombohedrons

ABSTRACT

Here, we focus on the obtaining of mesocrystalline submillimeter-sized (150/50 µm) rhombohedral hematite (α-Fe₂O₃) by thermal treatment in air of single crystalline submillimeter-sized (150/50 µm) rhombohedrons of ferrous carbonate (FeCO₃). Mass spectrometer-coupled thermogravimetric analysis and TGA-MS revealed the chemical reactions occurring during the thermal treatment of ferrous carbonate sample. The X-ray Diffraction (XRD) data sustain that the final product is hematite. The XRD line-profile analysis indicates that the resulted hematite is built of individual ordered crystallites with 66 ± 5 nm average sizes, confirmed by scanning electron microscopy and transmission electron microscopy images. Small-angle x-ray scattering investigation of hematite sample was presented. The log-log plot of scattering intensity decay showed the same slope, α = ?3.76, corresponding to both high and low scattering vector regions; the fractal surface is D_s = 2.24. This fractality is extended over a range of sizes and can touch high molecular dimensionality. The internal morphology and the synthesis mechanism of the obtained hierarchical superstructure were described.     

BÜCHI nano spray dryer B-90: a promising technology for the production of metformin hydrochloride-loaded alginate–gelatin nanoparticles

Abstract

The current study aimed to formulate gelatin/sodium alginate nanoparticles utilizing BÜCHI nano spray dryer B-90. Nanoparticles possess many of the advantages including new routes of drug administrations and sustained release properties. Utilizing B-90 technology, metformin hydrochloride (MET) nanoparticles were successfully developed. Preformulation studies such as atomization head mesh size, flow rate, head temperature, polymer viscosity, and surface tension, were adjusted. Additionally, post-formulation characters such as particle size, flowability, surface scan, and dissolution profiles, were evaluated. Spray head (7 µm hole), flow rate (3.5?ml/min) and head temperature (120?°C) were optimized. Polymer viscosity was less than 11.2 cP with a surface tension less than 70.1?dyne/cm. Moreover, anti-diabetic effects of MET formulations were evaluated in streptozotocin-induced diabetic rats. Here, discrete, non-aggregated free-flowing nanoparticle powders with a particle size less than 850?nm were generated. Gelatin/sodium-alginate (1:3) produced nanoparticles were successfully sustained by the in vitro release profile of the drug. In vivo evaluations of the previous formula showed a significant reduction of blood glucose level over 24?h. In conclusion, Nano Spray Dryer B-90 (Büchi Labortechnik AG, Flawil, Switzerland) offers a promising technology for nanoparticles formulation as controlled drug delivery systems enhancing compliance of type-II diabetic patients.     

Modeling Dense-Phase Pneumatic Conveying of Powders Using Suspension Density

This article presents results of an investigation into the modeling of pressure drop in horizontal straight pipe section for fluidized dense-phase pneumatic conveying of powders. Suspension density and superficial air velocity have been used to model pressure drop for two-phase solids-gas flow. Two applicable models formats (developed by other researchers using two different definitions of suspension density) were used to represent the pressure drop due to solids-gas flow through straight pipe sections. Models were generated based on the test data of conveying power-station fly ash and electrostatic precipitator (ESP) dust (median particle diameter: 30 and 7 µm; particle density: 2300 and 3637 kg m^?3; loose-poured bulk density: 700 and 610 kg m^?3, respectively) through a relatively short length of a smaller diameter pipeline. The developed models were evaluated for their scale-up accuracy and stability by using them to predict the total pipeline pressure drop (with appropriate bend model) for 69 mm I.D. × 168 m; 105 mm I.D. × 168 m and 69 mm I.D. × 554 m pipes and comparing the predicted versus with experimental data. Results show that both the models with suspension density and air velocity generally provide relatively better prediction compared to the conventional use of solids loading ratio and Froude number. For fly ash, the two formats result in considerable different predictions, whereas they provide relatively similar results for ESP dust.     

Recycling of an electric arc furnace flue dust to obtain high grade ZnO

The production of steel in electric arc furnace (EAF) generates a by-product called EAF dusts. These steelmaking flue dusts are classified in most industrialized countries as hazardous residues because the heavy metals contained in them, tend to leach under slightly acidic rainfall conditions. However, and at the same time they contain zinc species which can be used as a source to obtain valuable by-products. The present investigation shows results on the processing of an EAF flue dust using ammonium carbonate solutions. Once zinc is dissolved: ZnO + 4NH3 + H2O --> Zn(NH3)4(2+) + 2OH- with other impurities (i.e. cadmium and copper), these are eliminated from the zinc solution via cementation with metallic zinc. The purified zinc solution was evaporated (distilled) until precipitation of a zinc carbonate species, which then was calcined to yield a zinc oxide of a high grade. For the unattacked dust residue from the leaching operation, mainly composed of zinc ferrite, several options can be considered: back-recycling to the furnace, further treatment by sodium hydroxide processing or a more safely dumping due to its relatively inertness.