Aluminum Dust Research Articles

Theoretical analysis of flame propagation velocity in aluminum dust clouds

Theoretical analysis of flame propagation velocity in aluminum dust clouds

Effect of Initial Reactant Temperature on Flame Speeds in Aluminum Dust Suspensions

ABSTRACT Measurements of how the flame speed in suspensions of metal fuels depends on the initial temperature of the unburned mixture are important for understanding the role of mixture preheat by radiation heat transfer. This preheat can be an important stabilization mechanism for metal dust flames in energetic devices. A newly constructed counter-flow flat-flame metal dust burner allows for the measurement of burning velocities in aluminum-air suspensions preheated to temperatures up to 524 K using Particle Image Velocimetry (PIV). The experimental method was verified by measuring and comparing burning velocities in preheated methane-air mixtures at different fuel-oxygen equivalence ratios with previous experimental data and theoretical predictions. Whereas the flame speed in methane-air mixtures increases by 2.75 times with an increase in temperature to about 524 K, the flame speed in aluminum-air mixtures increases by less than 2 times over the same temperature interval. The independence of the adiabatic flame temperature of aluminum-air flames on the initial temperature of the mixture suggests practically constant reaction rates either for kinetically- or diffusion-controlled aluminum combustion. Thus, the observed moderate dependence of the aluminum-air flame speed on mixture initial temperature can be explained by a cumulative effect of the increased heat diffusivity, decrease in the amount of heat required to reach the particle ignition temperature, and increased flame sensitivity to preheat due to discrete source effects discussed in recent flame models.

Suppression effects of ammonium dihydrogen phosphate dry powder and melamine pyrophosphate powder on an aluminium dust cloud explosion

Selecting a suitable flame-retardant powder is essential for preventing or reducing the risk of aluminium dust cloud explosions. Two types of retardant materials were studied, namely ABC powder (a flame-retardant powder mainly composed of ammonium dihydrogen phosphate dry powder) and melamine pyrophosphate powder (MPP). A specially designed rectangular pipe was used to examine the influences and mass fractions of the aforementioned flame retardants and the effects of compounds on maximum explosion pressure and maximum explosion pressure rate of increase. The results showed that the explosion-suppression effects of MPP powder were superior to those of ABC powder. Furthermore, the suppression effects of combining ABC and MPP to form compounds in various ratios were explored. The explosion-suppression effects of the single flame-retardant powders and flame-retardant powder compound were compared, which revealed that the effects of the flame-retardant compound were intermediate to those of ABC and MPP used separately. No synergistic effect was observed in the compound retardant. However, component mass fractions influenced the retardant properties of the compound. The suppression mechanism was investigated through thermal analysis, which revealed that the decomposition of the two flame-retardant powders was an endothermic process that generated inert gas. The addition of flame-retardant powder delayed the time required by aluminium to break through its oxide film. However, the thermal analysis curve of the compound overlapped those of the two single powders, and no new chemical reaction occurred. Thus, no change was observed in the efficacy of the flame-retardant properties.

Acute and Chronic Effects of Aluminum Smelter Dust on Hematology, Metal Bioaccumulation and Oxidant-antioxidant Status in Rat

Background: Aluminum smelting industry is implicated with documented health risks. This study examined toxic effects of aluminum smelting dust as a real-life chemical hazard instead of single aluminum compounds, which seldom exist in real life. Methods: Adult male rats were gavaged acute (3 consecutive days) and chronic (6 weeks) doses of two dust concentrations (10 and 20 mg kg-1). Experimental investigation included toxic metal accumulation and biochemical analysis of blood and liver. Result: Aluminum and iron were highest in dust and respectively accumulated in brain, liver and kidneys. Anemia, inflammation, liver and kidney damage and oxidative stress were established in view of thrombocytopenia (35%), leukocytosis (41%), lymphocytosis (55%) and alterations in aminotransferases, creatinine, malondialdehyde, superoxide dismutase and catalase. Aluminum facilitation of iron-mediated lipid peroxidation is suggested. These findings drew attention to the magnitude (dose-dependent) and persistence (time-dependent) of aluminum dust as health compromising and are of particular significance to workers in aluminum smelting industries.

Experimental study on the overpressure and flame propagation of hybrid hydrogen/aluminum dust explosions in a square closed vessel

The overpressure and flame propagation of hydrogen/aluminum dust hybrid explosions are studied in a 5-L square closed vessel. Aluminum dust was mixed with hydrogen with concentrations of 0%–30%. The results show that there are certain hydrogen concentrations that affected the changing trend of the maximum pressure rise Pex and the maximum rate of pressure rise (dP/dt)ex. When the hydrogen concentration is lower than the certain concentration, the Pex and the (dP/dt)ex are approximately equal to those of pure aluminum dust. When the hydrogen concentration is higher than the certain concentration, the Pex and the (dP/dt)ex increase notably. As the hydrogen concentration increase to more than 20%, the flame front separation can be observed. The addition of hydrogen can significantly affect the ignition delay time and the flame propagation velocity of the hybrid mixtures. There are three stages in the relation of the maximum flame propagation velocity vmax with the hydrogen concentration: in the first stage, the vmax is almost equivalent to that of pure aluminum dust. In the second stage, the vmax increases slightly. In the third stage, the vmax increases significantly, which can exceed more than 50 times the vmax of pure aluminum dust.

Effects of dust dispersibility on the suppressant enhanced explosion parameter (SEEP) in flame propagation of Al dust clouds

This work presents an overview about the suppressant enhanced explosion parameter (SEEP) phenomenon in aluminum dust explosion moderation. The SEEP phenomenon can be attributed to either the flammable gas produced by decomposition of insufficient chemical suppressant so as to form an explosible hybrid mixture, or to the improvement in dust dispersibility caused by small amounts of thermal inhibitor so as to form better dispersed dust clouds. Aluminum (Al) and four particle sizes of alumina (Al2O3) were used to confirm a physically caused SEEP phenomenon by performing flame propagation experiments. Higher flame spread velocities (FSVs) in Al dust clouds were found in the presence of 5 or 10% <150 and <45-µm Al2O3 powder. Adding micro-sized Al2O3 disrupted inter-particle contact in combustible dusts, decreased inter-particle forces, and formed dust clouds with better dispersibility, thereby decreasing the effective particle size distribution (PSD) of Al dust. A strong thermal effect brought about by 2.5 µm Al2O3 overcame the negative effect of improved dispersion, preventing SEEP from occurring. The addition of 50 nm Al2O3 increased cohesion of powder mixtures, and decreased dust dispersibility. With benefits from both dispersion suppression and the thermal effect, Al flame propagation was well quenched.

Respiratory outcomes among refinery workers exposed to inspirable alumina dust: A longitudinal study in Western Australia.

Information is scarce about the occupational health effects of exposure to alumina dust. This study examines the respiratory effects of inspirable alumina dust exposure in alumina refineries. An inception cohort study at three alumina refineries in Western Australia recruited 416 participants (351 males, 65 females) between 1995 and 2000 who were followed up annually until 2008 or until exit from study. At each health interview a respiratory questionnaire and lung function test was undertaken, measuring forced expiratory volume in one second (FEV1 ) and forced vital capacity (FVC). Participants provided job histories which were combined with air monitoring data to calculate cumulative exposure to inspirable alumina dust (mg/m3 -years). Generalized estimating equations with Poisson distribution and mixed effects models were used to examine the effects of alumina exposure. The number of exposed participants was relatively small (n = 82, 19.7%). There was no association between alumina dust exposure and prevalence of cough, wheeze or rhinitis. No associations were found between measures of lung function and tertiles of alumina exposure in the first two follow-ups, or the whole follow-up period, though there was a suggestive dose-response trend across exposed groups for decline in absolute FEV1 (p for trend = .06). For mean annual change in FEV1 and FVC based on the first three follow-ups it was not possible to rule out an effect above a threshold level of exposure. There is no evidence of an association between exposure to alumina and the reporting of respiratory symptoms but some evidence for an effect on lung function.

Experiment on the flammability variation of micron-sized aluminum powder depending on combustion environment for burning of aluminum-diluted oxygen

Experimental research was conducted to study the combustion characteristics of clouds composed of micrometer-sized aluminum particles with an oxidizer blend of oxygen and superheated steam. Both ignition and combustion of an aluminum particle are difficult because it is enveloped by an oxide layer that has a high melting point (above 2300 K). To overcome the problem, we induced a particular shape of the combustor that can keep a stable flame of aluminum dust clouds at a lower feeding-rate. The combustion characteristics were examined using a system applied combustor involving a variety of parameters affecting the burning of the dust clouds. Based on these attempts, the aluminum dust clouds had an upper flammability limit above the equivalence ratio (Ф) 1.9 for oxygen diluted by air. Varying the lower limit of flammability, we found, crucially, that the feeding-rate and velocity of the particles are more effective than the equivalence ratio or combustor length. Furthermore, we could confirm the changing of the lower limit from 0.3 to 0.26 because the steam was additionally fed in the combustion of aluminum-oxygen.

CFD Modeling of Ventilation and Dust Flow Behavior in Polishing and the Design of an Innovative Wet Dust Removal System.

Fine aluminum dust pollution in the polishing process was detected during a field survey. To obtain a fundamental understanding of the airflow patterns and the fine dust dispersion characteristics during a polishing process, computational fluid dynamics simulations were first performed to analyze the data collected in field measurements. The inappropriate ventilation arrangement and lack of effective dust control measures were identified as the main reasons for the high dust exposure levels (in excess of 1000 μg/m3). Simulation results showed that inhalable dust particles (PM10) could be significantly diluted at the operator’s breathing level by adding a supply air inlet above the operating area. Moreover, dry dust collection systems create a risk of aluminum dust explosion accidents. An innovative design of wet dust removal system which could mitigate the occurrence of dust explosions was proposed and then implemented on site. An independent field dust assessment showed that a reduction of fine dust particles up to 95% in the worker’s breathing area and the fine dust in the vents was reduced to 80%. Therefore, the proposed strategies are implemented immediately to address the combustible dust in the polishing working environment and can provide guidance for operators.

Using soybean isoflavone to prevent hydrogen production reaction of aluminium dust and water in wet dust removal systems

Using a dry dust removal system used for aluminium dust collection presents a dust explosion risk, whereas a wet dust removal system presents a risk of hydrogen fire and explosion. Neither system can attain a sufficient level of safety for use at aluminium processing sites. In this paper, soybean isoflavone, a non-toxic and environmentally sustainable flavonoid, was investigated to inhibit hydrogen production from aluminium dust and water. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR) were used to characterize aluminium particles before and after the reaction. Soybean isoflavone was found to inhibit hydrogen production from aluminium dust and water. At a soybean isoflavone solution concentration of 2.1 g L−1, a dense protective film resulting from chemical adsorption on the surfaces of the aluminium particles isolated the aluminium particles from water molecules. This film blocked the reaction pathway between the aluminium particles and water to suppress hydrogen generation. This fundamental study addresses the problems of hydrogen fires and explosions in wet dust removal systems for aluminium dust collection and provides a novel, safe and effective method for aluminium dust removal.

Visualization of aluminum dust flame propagation in a square-section tube: comparison of schlieren, shadowgraphy and direct visualization techniques

This paper presents the results of aluminum dust flame propagation inside a vertical prototype of 700 mm height and 150 × 150 mm square cross section. The study considers three visualization techniques. At first, direct visualization is employed to record the flame light with high speed camera. Special attention is given to collect images without saturation. This is especially important with aluminum flames as they are very luminous. To ensure that the exact delimitation of the flame is well defined, two additional optical techniques have been implemented: schlieren and shadowgraphy. For each explosion test, these three techniques were used simultaneously to compare the flame propagation and the burning velocity. The first one corresponds to the flame speed in the laboratory referential, determined from the obtained images, while the burning velocity corresponds to the consumption rate of the reactants by the flame front. The method used for the determination of burning velocity from the images obtained is exposed. A pulsating behavior of the light emitted by the flame is observed with the direct visualization technique. This behavior confused the determination of the flame front. This contour is easier to define with shadowgraphy images. Nevertheless, results of flame front propagation velocity are close for each technique. Burning velocity is then determined only from direct visualization and shadowgraphy images, to avoid uncertainties due to flame contour detection from schlieren images. Again, results of burning velocity are fairly close for both techniques.

An investigation on the aluminum dustexplosion suppression efficiency and mechanism of a NaHCO3/DE composite powder

A NaHCO3/diatomaceous earth (DE) composite powder suppressant with unique clustered structures is prepared by high-pressure impact method, using DE as the carrier and NaHCO3 as the loaded chemical suppressant. The purpose is to obtain affordable, environmentally friendly, high-efficiency power explosion suppression materials. The suppression efficiencies of the NaHCO3/DE composite powder suppressant on aluminum dust propagation and explosion pressure are tested. The results show that as the content of the NaHCO3/DE composite powder suppressant increases, the maximum flame length gradually reduces and the suppression efficiency gradually increases. Addition of 60 wt% of the NaHCO3/DE composite powder suppressant suppress aluminum dust flame propagation and addition of 100 wt% of the NaHCO3/DE composite powder suppressant can fully suppress aluminum dust explosion. Comparison with pure NaHCO3 and pure DE reveals that NaHCO3/DE composite powder suppressant is more effective in suppressing aluminum dust flame propagation and aluminum dust explosion pressure than either of the two powders alone. The suppression mechanism of the NaHCO3/DE composite powder suppressant is established: On the one hand, reaction is suppressed by the decomposition of NaHCO3 and the product of this decomposition; on the other hand, as DE is rich in porous structures, when the loaded NaHCO3 powder separates from DE, the porous structures will not only limit flame propagation, but will also well adsorb the substances generated from explosion reaction.

Flame behaviours and deflagration severities of aluminium powder–air mixture in a 20-L sphere: Computational fluid dynamics modelling and experimental validation

Flame behaviours and explosion severities are vital for conducting risk evaluations, obtaining a dynamic control, and determining propagation mechanisms of aluminium dust explosions. In this study, a three-dimensional (3D) mathematical framework and a computational fluid dynamics (CFD) model were established to numerically reveal the dynamic evolution of flame morphology, deflagration severities, and heterogeneous combustion properties of an explosion due to an aluminium dust–air mixture by using a standard 20-L spherical chamber. Moreover, the validity of the numerical model was precisely verified using an experiment. Furthermore, the flame propagation and explosion process of the aluminium dust–air mixture were reproduced using the 3D CFD model. The dynamic behaviour of flame in the initial explosion stage and explosion parameters pertaining to three dust concentrations were qualitatively and quantitatively investigated using numerical calculation and experimental comparison. Results revealed that the flame morphology and explosion pressure obtained by conducting numerical simulation demonstrates a favourable agreement with those obtained using experimental observation. This indicates that the 3D CFD model presented in this study is appropriate for conducting numerical predictions on other dust explosions. Finally, the flame propagation mechanism and feedback of the aluminium dust–air mixture explosion were proposed on the basis of the obtained experimental and numerical information. This preliminary study can be conducive to hazard assessment and disaster-causing mechanism determination of dust-based explosions.

A study on the influencing factors and trends of the falling extra-fine aluminium flake dust generation rate

In order to provide a theoretical basis for reducing dust dusting, study the dusting characteristics of flake dust in production sites. Prediction calculation method of flake aluminium powder dust generation rate through research. Measure the mass loss of powder during different falling heights, different wind speeds and different solid flow diameters. The dust generation rate of the dust fall is calculated by mass loss of aluminium powder. Analyse the dust generation rate affected by falling heights, wind speeds and solid flow diameters. This study shows that the dust generation rate increases exponentially with the falling height, increases linearly with the wind speed, and decreases with the solid flow diameter. By combining these results with the dust generation theory by Marc, we obtained a calculation model of the flake aluminium dust generation rate, and this model has good accuracy with an average error of only 11.71% compared with the experimental values.

Study of a Hydrogen Inhibition Method with Sodium Tungstate for Wet Aluminum Dust Removal Systems

Hydrogen, which can be produced due to the accumulation of aluminum dust that reacts with water in wet dust removal systems, is a fire and explosion hazard. To reduce hydrogen production, sodium tungstate is used in hydrogen inhibition experiments to inhibit the reaction between aluminum dust and water. The purity of the aluminum powder was 95.15%, analyzed with X-ray fluorescence spectrometry (XRF). Each of the hydrogen inhibition experiments lasted for 12 h. In addition, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface morphology and composition of particles before and after the experiments. There was nearly no hydrogen produced when the concentration of the sodium tungstate solution reached 100 g/L. The results show that a protective coating containing W element was formed on the surface of the aluminum particles after the reaction with sodium tungstate, and the coating prevented the aluminum particles from contacting with water.

Using sodium D-gluconate to suppress hydrogen production in wet aluminium waste dust collection systems

The reaction of aluminium dust and water generated in the production of aluminium products generates hydrogen, which poses a risk to wet collection systems for hydrogen explosions. In this paper, non-toxic and environmentally friendly sodium D-gluconate is used to suppress the hydrogen production reaction of aluminium waste dust and water. The results of the hydrogen evolution curves and chemical kinetics of 7 different concentrations of sodium D-gluconate showed that when the sodium D-gluconate concentration reached 0.25 g L−1, there was almost no hydrogen generation, and the rate constant was almost zero. The scanning electron microscopy (SEM) results showed that the surface of the reaction product became smoother with increasing solution concentration. The energy dispersive spectroscopy (EDS) results showed that increasing the solution concentration slowed the formation of aluminium oxide in the product, confirming the effectiveness of sodium D-gluconate in inhibiting the reaction of aluminium waste dust particles with water. The Fourier transform infrared (FTIR) results showed that sodium D-gluconate formed a chemical adsorption film on the surface of aluminium waste dust particles to prevent the dust from contacting water, thus suppressing hydrogen production. This method provides a new approach to design safe wet collection systems by suppressing hydrogen production.

Inhibition evaluation of gas inhibitors in micron-sized aluminum dust explosion

The inhibition effects of gas inhibitors (nitrogen, carbon dioxide, and heptafluoropropane) on aluminum dust explosion were investigated experimentally and numerically. The results showed that as the inhibition volume fraction increased, the flame propagation characteristics parameters and explosion severity parameters were inhibited by inert gases accordingly. The inhibition performance of carbon dioxide was superior to that of nitrogen, and the minimum inhibition volume fractions of nitrogen and carbon dioxide were determined. XRD results indicated that the crystal form of major condensed product of aluminum dust explosion using two kinds of inert gas as inhibitors was different due to the distinct inhibition effect. Moreover, the XPS analysis revealed that the nitrogen oxide of aluminum adsorbed on the surface of aluminum particles blocked gasification process of aluminum particles. To explore the inhibition mechanism microscopically, a kinetic model concerning gas phase combustion was established. The above discussion indicated that the inhibition effect was the combination of multiple factors. In addition, due to the strong reactions between aluminum particles and heptafluoropropane, it cannot be regarded as gas inhibitor in aluminum dust explosion.

Suppression of aluminum dust explosions by expandable graphite

The suppression effect of expandable graphites (EGs) on 5 μm aluminum dust explosions was systematically studied in an open-space dust apparatus. Flame propagation behaviors showed that flame structures became more discrete and more irregular after the addition of EGs. The flame propagation velocities declined variously owing to the suppression effect of EGs. Meanwhile, the optimum suppression concentration for each EG was determined. It was proved that the suppression effect was improved remarkably by increasing the expandable ratios of EGs. Moreover, expandable ratios of EGs had a preferable influence on the suppression effect in comparison with size distributions. Scanning electron microscopy demonstrated that the volumes of EGs increased by several hundred times when encountered with high temperature and the surface got fluffy and multihole. Based on above results, the suppression mechanism of EG for aluminum dust explosions was summarized in this paper in detail.

DESIGN ANALYSIS OF A LOW-COST PARABOLIC ANTENNA FOR DEVELOPING NATION

&lt;p&gt;This paper is aimed at designing a locally fabricated fiberglass parabolic antenna as a replacement for a metallic fabricated parabolic antenna. They are coated with a thin film of aluminum dust to enhance reflectivity since electromagnetic radiations do not travel deep in a conductor. This reduces the thick mass of metal usually used for constructing metallic parabolic antenna leading to a reduced cost of production. It incorporates a Low Noise Block (LNB) Converter comprising of amplifiers and frequency down converter. Metallic parabolic antenna contributes more to signal loss by reflecting radio waves. The Parabolic antenna is designed to receive microwave signals in the K-band with the down converter converting it to very high frequency (VHF) and ultra-high frequency (UHF) employing the super-heterodyning principle. The study shows the design and installation of a low-cost parabolic antenna in the rural community in Nigeria. The designed parabolic antenna is used to receive a signal with the center frequency of 11.3GHz and signal strength of 60%. The economic viability is that fiber-glass Parabolic antenna can replace the metallic fabricated ones.&lt;/p&gt;

Minimum ignition temperatures and explosion characteristics of micron-sized aluminium powder

To forestall, control, and mitigate the detrimental effects of aluminium dust, a 20-L near-spherical dust explosion experimental system and an HY16429 type dust-cloud ignition temperature test device were employed to explore the explosion characteristics of micron-sized aluminium powder under different ignition energies, dust particle sizes, and dust cloud concentration (Cdust) values; the minimum ignition temperature (MIT) values of aluminium powder under different dust particle sizes and Cdust were also examined. Flame images at different times were photographed by a high-speed camera. Results revealed that under similar dust-cloud concentrations and with dust particle size increasing from 42.89 to 141.70 μm, the MIT of aluminium powder increased. Under various Cdust values, the MIT of aluminium dust clouds attained peak value when concentrations enhanced. Furthermore, the increase of ignition energy contributed to the increase of the explosion pressure (Pex) and the rate of explosion pressure rise [(dP/dt)ex]. When dust particle size was augmented gradually, the Pex and (dP/dt)ex attenuated. Decreasing particle size lowered both the most violent explosion concentration and explosive limits.