Search

An aluminum dust explosion is a major safety hazard that cannot be ignored. It is of great practical significance to investigate explosion flame propagation characteristics and powder inhibition mechanisms of aluminum dust. Based on a self-designed dust explosion experimental system, explosion flame propagation characteristics such as flame shape, temperature and velocity were captured. The effect of aluminum particle size on the flame propagation was explored, and inhibition performances and mechanisms of NaHCO3, CaCO3 and Na2HPO4 on aluminum dust explosion were experimentally and theoretically revealed. The proportion of white bright areas decreased from 17.9% to 7.9%, 8.0% and 8.8% respectively, and the temperature and velocity decreased obviously with powder inhibitors. Especially, NaHCO3 can reduce the maximum flame temperature and maximum flame velocity to 1411°C and 14.27 m/s respectively, and its inhibition performance was optimal. CaCO3 had better performance than Na2HPO4 in suppressing the flame propagation velocity and in delaying the ignition time, and Na2HPO4 was more advantageous in suppressing the explosion flame temperature. It is explained by the mechanism that substances containing Na and P can play an important role in the suppression of gas-phase reactions. The Na cycle (NaO ↔ Na) is effective in scavenging free radicals. [ABSTRACT FROM AUTHOR]

In order to ensure the safe utilization of hydrogen, the flame characteristics and explosion overpressure at lean-burn, stoichiometric and rich-burn conditions are investigated systematically by varying initial pressures. Experiments were conducted in a constant-volume combustion chamber using the Schlieren system to investigate the critical characteristics of hydrogen-air premixed flames at different equivalence ratios (from 0.2 to 6.5) and initial pressures (from 50 kPa to 150 kPa). The cellular instabilities of hydrogen-air premixed flames were interpreted and evaluated from the viewpoint of thermal-diffusive and hydrodynamic instabilities. The influence of initial pressure on the cellular instability and combustion and explosion characteristics were analyzed. The results show that the variation of thermal-diffusive instability dominantly governs the cellular instability at lean-burn conditions (φ = 0.3–1.0). In contrast, the cellular instability at rich-burn conditions (φ > 1.5) is governed by the variation of hydrodynamic instability. The increase of initial pressure promotes the cellular instabilities noticeably caused by the rise of the hydrodynamic instability. With the increase of P 0 , the Lewis number L e and thermal expansion ratio σ almost remain the same while flame thickness δ noticeably decreases. Increasing initial pressure at lean-burn and stoichiometric conditions (φ < 2.0) facilitates cellular instability, making the explosion more intense and resulting in higher explosion overpressure. In contrast, the variation of initial pressure suppresses the laminar combustion at rich-burn conditions (φ > 3.0). • Influence of initial pressure on flame behavior and explosion pressure is obtained. • Flame instability promotes the rise of explosion overpressure. • Thermal-diffusive instability is insensitive to the variation of initial pressure. • Hydrodynamic instability is enhanced by increasing initial pressure. • Increasing initial pressure facilitates laminar combustion and explosion at φ < 2. [ABSTRACT FROM AUTHOR]

[Display omitted] • Inert gases were used to inhibit starch deflagration to avoid powder contamination. • Evolution of starch deflagration flame in the inhibitory atmosphere N 2 or CO 2 was investigated. • Limit inerting ratio of gas for complete inhibition of dust deflagration was studied. • Inerting mechanism was verified by macro flame morphology and micro starch residues. Starch is one type of biomass fuel raw material commonly used, but presents deflagration hazards when suspended in the air. Dust deflagration accidents might be effectively inhibited by creating a gas inerting atmosphere. In this work, the evolution of starch deflagration flame in the inhibitory gas atmosphere N 2 or CO 2 was investigated. Under the action of inerting gas, heterogeneous combustion is strengthened, the flame propagation velocity is reduced and the acceleration trend is smooth. The maximum flame temperature is decreased and fluctuation after reaching the maximum value is weakened. According to the micro characterization of deflagration residues, after injecting inhibitory gas, more amorphous carbon is protected and the carbon layer formed has a smaller crystal size, some easily oxidized functional groups in starch are maintained during the deflagration. Meanwhile, carbon content and the original chemical bond ratio in the residues are also increased. In addition, experimentally measured the maximum limit inerting ratios of CO 2 and N 2 are chosen as 33% and 54%, respectively. On this basis, safety application for gas inerting technology in practical processes was discussed. [ABSTRACT FROM AUTHOR]

• Thermokinetic suppression of APP powder on sucrose dust deflagration is researched. • Decomposition products of APP have a composite weakening effect on reaction exotherm. • Crosslinking reaction of PPA catalyzes the formation of more and dense carbon layer. • Suppression mechanisms of sucrose dust deflagration by APP powder is investigated. In this investigation, ammonium polyphosphate (APP) is applied to suppress the deflagration of sucrose dust. Through the systematic research on flame propagation images and temperature, decomposition behavior of powder samples and the compositions of deflagration residue, the suppression performance and mechanism of APP on sucrose deflagration are profoundly summarized. Timing diagrams show that APP contributes to reduce deflagration flame brightness, increases ignition delay time and flame fault area. The minimum inerting concentration of APP for sucrose deflagration is determined to be 8 %. From the collected deflagration flame temperature curves, it is confirmed that APP can delay peak temperature arrival time, weaken temperature fluctuation, and decrease peak values of flame temperature and temperature rising rate. Through the analysis on thermal decomposition of samples and deflagration residue, it is reflected that APP has superior composite suppression effect. It can not only absorb reaction heat, but also decrease deflagration exotherm to improve thermal stability of sucrose particles. Thus, the easily oxidized components in sucrose are protected, and deflagration intensity is effectively weakened. This work provides a new solution for prevention and suppression deflagration of dust waste in sugar industry. [ABSTRACT FROM AUTHOR]

Minimum ignition energy (MIE) is a crucial parameter for identifying the hazards of combustible gases. To rapidly obtain accurate MIE values for various gases, the shape of the ignition source was simplified to cylindrical. Based on theories of heat conduction and chemical reaction kinetics, a physical model of the ignition process was established. The spatial and temporal evolution of temperature was used as a basis for judging the success of ignition. A numerical algorithm was developed and maximum flame temperatures and MIE were calculated for several combustible gases (H 2 , CH 4 , C 2 H 6 , C 3 H 8 , C 4 H 10 , C 2 H 4 , C 2 H 2). This model accurately predicted the U-shaped trend of MIE values with concentration for CH 4 /air and H 2 /air mixtures. It found that the MIE was minimal at the stoichiometric concentration, at 0.37 mJ and 0.017 mJ, closely aligning with experimental data. This numerical model has been validated for its accuracy and promises to make relatively precise theoretical predictions for the MIE values of uncommon combustible gases or mixtures of various gases. [Display omitted] • New prediction model for the minimum ignition energy of gases. • Full consideration of ignition details and comparison with experimental values. • Maximum temperature and minimum ignition energy for multiple gases. • Trends in minimum ignition energy with concentration for H 2 and CH 4. [ABSTRACT FROM AUTHOR]

Drug powder explosions pose a potential threat to the process safety of pharmaceutical companies in the processing and storage of products. To explore a reasonable and efficient technology to prevent and mitigate the explosion of combustible drug dust, an experimental system of vertical combustion pipeline equipped with a partial suppression device was built, and the performance of N 2 and CO 2 loaded with hydrophobic SiO 2 encapsulated SiO 2 gel (HSESG) respectively to synergistically suppress the explosion of acetaminophen powder was investigated. The results demonstrated that N 2 /HSESG and CO 2 /HSESG were effective in reducing the flame average velocity (V avg), maximum velocity (V max), velocity to the top of the pipe (V top), and maximum flame temperature (T max). N 2 loaded with 60 wt% HSESG reduced the V max , V avg , and V top of the explosion flame by 68.1%, 66.7%, and 81.3%, respectively, and T max by 58.7%. Acetaminophen dust explosion could be completely suppressed by CO 2 /40 wt% HSESG with 83.7%, 73.0%, and 85.7% decrease in V max , V avg, and V top values, respectively, and 80.7% decline in T max. The results of thermal decomposition tests and residues characterization indicated that the partial suppression of N 2 /HSESG and CO 2 /HSESG was mainly accomplished through the synergistic interaction among thermodynamic, kinetic, and non-homogeneous chemical effects. Subsequently, the reason for the more pronounced suppression effect under the impact of CO 2 /HSESG was further explained. [ABSTRACT FROM AUTHOR]

• Ceramic foam damages the spread of wheat dust flame and the flow field in pipeline. • Temperature of upper end is proportional to aperture, but inversely to layers. • The pressure increases and then decreases with the increasing PPI and layers. • The effect of ceramic foam on combustion pressure is more manifested as incentive. A vertical dust combustion pipeline with high-speed photography, micro-thermocouple and pressure sensor was built to investigate the influence of ceramic foam on the wheat dust explosion flame. Ceramic foams with different parameters were adopted in this paper, and compared with metal mesh. The chemical structures of dust explosion residue were characterized by X-ray photoelectron spectroscopy. Results indicate that the wheat dust flame propagation and structure were significantly destroyed by ceramic foam. With the decreasing aperture or increasing layer, the blocking effect of ceramic foam was aggravated on the dust flame. The flame cannot pass through the ceramic foam with 20 PPI and 3 layers. On the upper end of ceramic foam, the flame temperature is positively proportional to the aperture but inversely proportional to the layers. With the PPI and layers of ceramic foam increases, the combustion pressure firstly increases and then decreases when the dust combustion intensity is strong. Ceramic foam shows the incentive effect to some extent on the combustion pressure, but the continuous inhibition effect is found for the metal mesh. [ABSTRACT FROM AUTHOR]

[Display omitted] • A core–shell composite (FA-2@Mg(OH) 2) is synthesized by the heterogeneous nucleation method. • The modified fly ash greatly improves the interfacial compatibility with Mg(OH) 2 substrate. • The suppression effects of FA-2@Mg(OH) 2 on the explosion flame and pressure of Al-Mg alloy dust is explored. • FA-2@Mg(OH) 2 shows excellent capability owing to the multiple suppression effect embodied in the unique structure. Dust explosions caused by energetic metals pose a significant risk to process industries, making it crucial to develop high-performance explosion inhibitors. In this study, the modified power plant solid waste fly ash (FA) was confirmed as a raw material for the preparation of core–shell inhibitors to efficiently suppress dust explosion of Al-Mg alloy. The interfacial compatibility of FA was dramatically improved by using alkali hydrothermal modification and organic modification. It formed a well-coated nano-Mg(OH) 2 cladding layer on the surface of modified FA by the heterogeneous nucleation method. In a vertical combustion pipe and a 20 L spherical explosion device, the suppression effect of this novel core–shell inhibitor (FA-2@Mg(OH) 2) was investigated. The experimental results showed that the addition of 60 wt% of FA-2@Mg(OH) 2 reduced the maximum flame velocity (V max), velocity to the top of the pipe (V top), and average pulsation degree (V ap) by 87.9 %, 92.5 %, and 87.7 %, respectively, and the peak flame temperature (T p) declined to 298 °C. The maximum explosion pressure (P max) and the maximum explosion pressure rise rate ((dp / dt) max) were reduced by 86.1 % and 92.9 %, respectively. Combining the analysis results of SEM, EDS, XRD, and TG-DSC, the suppression mechanism of FA-2@Mg(OH) 2 was explained in depth, mainly from the heat absorption, coating effect, gas dilution, and radical adsorption. This work not only sheds new light on the design of dust explosion suppression functional materials but also broadens the application of industrial solid waste FA. [ABSTRACT FROM AUTHOR]

A series of explosion suppression experiments on aluminum powder with diverse morphologies were carried out in vertical pipelines. By combining the flame propagation images and flame temperatures, the physical and chemical effects of inhibitors on the flame propagation of spherical aluminum powder (S Al) and flaky aluminum powder (F Al) were explored. The results demonstrated that the amount of inhibitor required for F Al was greater than S Al , and the chemical effects of piperazine pyrophosphate (PPAP) were more effective in inhibiting S Al , whereas the physical effects of nano-SiO 2 were more significant in suppressing F Al. PPAP dramatically reduced the flame propagation velocity, flame temperature, and flame propagation maximum height of S Al as the inhibitor mass fraction increased. The flame temperature, ignition delay time, and flame illumination of F Al could even be considerably changed by nano-SiO 2. The microscopic and macroscopic suppression mechanisms of PPAP and nano-SiO 2 on different morphology of aluminum powder were proposed. [Display omitted] • PPAP displays superior performance in inhibiting spherical aluminum powder. • Flake aluminum powder explosion suppression is more difficult than spherical powder. • Nano-SiO 2 can significantly affects the explosion of flake aluminum powder. • Microscopic and macroscopic suppression mechanisms of PPAP and nano-SiO 2 are studied. [ABSTRACT FROM AUTHOR]