Coupling effects of foam ceramics on the flame and shock wave of gas explosion

The coupling of gas explosion flame and shock wave is analyzed. In the gas explosion process, shock wave is affected by the flame directly, and shock wave also induces the flame. Inhibiting explosion can be achieved by the interference between the flame and shock wave propagation. If the coupling effects can be damaged, the adverse effects caused by the explosion should be mitigated and controlled. According to the structure characteristics of foam ceramics, the coupling effects mechanism of ceramic foam on gas explosion flame and shock wave is researched. When the explosion goes through the structure of foam ceramics, the flame can be quenched and the shock wave be attenuated. After the flame is quenched, the supply of precursor shock wave energy is cut off. Due to lack of energy supply, the destructive effects of blast wave will be reduced effectively. Coupling effects of the flame and shock wave can be damaged by the special structure of foam ceramics. Studies suggest that a certain function to represent the structure characteristics of foam ceramics must exist. For a certain material of foam ceramics, the sure porosity δ and the pore diameter d also can be get, which is the key to research and develop foam ceramic suppression technology of gas explosion.     

Prediction of minimum ignition energy of aerosols using flame kernel modeling combined with flame front propagation theory

Flammable aerosols have created many fire and explosion hazards in the process industry, but the flammability of aerosols has not been fully understood. The minimum ignition energy has been widely used as an indicator for flammability of combustible mixtures, but the amount of experimental data on the minimum ignition energy of aerosols is very limited. In this work, the minimum ignition energy of tetralin aerosols is predicted using an integrated model. The model applies the flame front propagation theory in aerosol systems to the growth of the flame kernel, which was created during the spark discharge in the ignition process. The aerosol minimum ignition energy was defined as the minimum level of energy in the initial flame kernel to maintain the kernel temperature above the minimum ignition temperature of 1073 K specific for tetralin aerosols during the kernel growth. The minimum ignition energy obtained in the model is influenced by the fuel-air equivalence ratio and the size of the aerosol droplets. For tetralin aerosols of 40 μm diameter, E_min decreases significantly from 0.32 mJ to 4.3 × 10 e⁻³ mJ when the equivalence ratio rises from 0.57 to 1.0. For tetralin aerosols of 0.57 equivalence ratio, E_min increases from as 0.09 mJ to 0.32 mJ when the droplet diameter rises from 10 μm to 60 μm. The trends are in agreement with previous experimental observations. The method used in current work has the potential to prediction of the minimum ignition energy of aerosol.     

Flame propagation in lycopodium/air mixtures below atmospheric pressure

Industrial processes are often operated at conditions deviating from atmospheric conditions. Safety relevant parameters normally used for hazard evaluation and classification of combustible dusts are only valid within a very narrow range of pressure, temperature and gas composition. The development of dust explosions and flame propagation under reduced pressure conditions is poorly investigated. Standard laboratory equipment like the 20 l Siwek chamber does not allow investigations at very low pressures. Therefore an experimental device was developed for the investigations on flame propagation and ignition under reduced pressure conditions. Flame propagation was analysed by a video analysis system the actual flame speed was measured by optical sensors. Experiments were carried out with lycopodium at dust concentrations of 100 g/m³, 200 g/m³ and 300 g/m³. It was found that both flame shapes and flame speeds were quite different from those obtained at atmospheric pressure. Effects like buoyancy of hot gases during ignition and flame propagation are less strong than at atmospheric conditions. For the investigated dust concentrations the flame reaches speeds that are nearly an order of a magnitude higher than at ambient conditions.     

Theoretical pressure prediction of confined hydrogen explosion considering flame instabilities

In order to ensure the safe utilization of hydrogen energy, the explosion pressure behavior is extremely important to design chemical equipment and evaluate explosion accident consequence. This paper is aimed at establishing a theoretical method of predicting explosion pressure behavior in the confined chamber by considering flame instabilities. The tendency of flame wrinkling factor in the pressure-buildup stage is firstly evaluated using large eddy simulation and the compensation theory. The limiting value of flame wrinkling factor during entire explosion process is calculated using the fractal theory. Finally, the dynamic model of flame wrinkling factor is implemented into the smooth flame model. The results demonstrated that the flame wrinkling factor in the pressure-buildup stage almost increases linearly with time. The limiting value of flame wrinkling factor is 2.4649. The explosion pressure will be underestimated using the smooth flame model, and the calculated explosion pressure in the isothermal condition is smaller than that in the adiabatic condition. When the fully turbulent flame is considered, the explosion pressure will be overpredicted significantly. By changing the confined chamber size, the explosion pressure could be reproduced relatively satisfactorily when the flame wrinkling factor is assumed to increase exponentially. The explosion pressure prediction must consider the effect of adiabatic compression and flame instabilities on burning rate.     

Law of variation for low density polyethylene dust explosion with different inert gases

To reveal the effects of different inert gases on explosion characteristics during low density polyethylene (LDPE) dust explosion and optimize the explosion-proof process, eight N₂ (CO₂)/air mixed inerting conditions were experimentally studied. Typical inerting conditions with 12 L cylindrical explosive tank were used to study the characteristics on the flame propagation. The thermogravimetric analysis with related theories were used to further explain the mechanism and quantities in low density polyethylene (LDPE) dust explosion with different inert gases. The results showed that the reduction of O₂ concentration could effectively delay the progress of flame growth process and weaken the effect of dust combustion reaction. The flame growth process of condition (N₂/air (18% O₂)) was 2.05 times slower than that of the non-inert condition. The explosion strength was obviously reduced, and the characteristic parameters such as explosion pressure and flame propagation speed were also affected by the decrease of O₂ concentration. For LDPE powder, the smaller the median diameter, the greater the explosion intensity and the lower the limiting oxygen content (LOC). The LOC with CO₂ was usually higher than that with N₂ and the effect of CO₂ was significantly better than N₂ in inerting.     

火焰原子吸收法测定苹果中波尔多液的农药残留

通过原子吸收法测定苹果果皮、果肉上波尔多液的农药残留铜的含量,结果表明:喷洒了波尔多液的苹果果皮上铜含量明显大于果肉,在果皮上有一定的农药残留;而未喷洒波尔多液的苹果果皮和果肉中铜的含量的差异很小。     

Experimental study on detonation flame penetrating through flame arrester

In-line detonation flame arresters are important safety apparatus to prevent group tank fires caused by the spreading of fire through vapor connection lines. In this study, a DN50 experimental apparatus aimed at the detonation flame penetration characteristics and failure mechanisms in a flame arrester was set up, and a series of experiments were carried out with 6.6% C2H4 and air mixture. Pressure, and velocity of flame penetrating through flame arrester housing and filters were analyzed. Experimental results showed that the attenuation of pressure and velocity was proportional to the thickness of the filters. Two failure modes of the fire-extinguishing process in the flame arrester were captured directly with a high-speed camera. In Mode I, the detonation flame could go straight through the flame arrester filters when the filters were too thin. In Mode II, when the filters were not sufficiently thick, the remained shock wave pressure of detonation flame was still several times of the initial pressure and could rise sharply at the downstream contraction section, resulting in that the flammable gas at the downstream transition section could be compressed and reignited even the flame had been extinguished by filters. These conclusions are helpful to reveal the nature of failure modes of fire-extinguishing process and design flame arresters with high fire-resisting performance by structure improved.     

Experimental study on the competing effect of ceramic pellets on premixed methane-air flame propagation in a duct

It is urgent to explore effective suppression methods for gas fires and explosions to ensure the safe utilizations of combustible gases in industrial processes. In this work, experiments are performed to study the effect of spherical ceramic pellets on premixed methane-air flame propagation in a closed duct. High-speed schlieren photography and pressure transducers are used to record the flame propagation and pressure transient, respectively. Behaviors of the flame propagating through a section of the duct filled with ceramic pellets in mixtures at different equivalence ratios are scrutinized. Three different diameters of pellets are considered in the experiments. The result shows that the flame can be quenched in the case with a smaller pellet diameter (3 mm) for a wide range of equivalence ratios from fuel-lean to fuel-rich mixture. For larger pellet diameter (5 or 10 mm), flame extinction occurs in fuel-rich mixtures (e.g. Φ = 1.1, 1.2). For the cases of flame surviving through the pellets bed, the pellets show a significant influence on the flame structure and behavior. The flame propagation depends on the porosity and the mean void diameter of the porous media in the pellets bed. Small void diameter is beneficial to flame quenching, while large porosity can accelerate the flame propagation. The pressure dynamics evolution is closely related to the interaction of flame with the pellets, and it depends on whether the flame quenches in the pellets bed. Overall, d = 3 mm ceramic pellets display the best suppression effect on flame propagation and pressure buildup in this study. The results of this study are of great significance to guide the safety design of spherical suppression materials in engineering applications for process safety researchers and engineers.     

PAN dust explosion inhibition mechanisms of NaHCO3 and Al(OH)3

We investigate the PAN dust explosion inhibition behaviors of NaHCO₃ and Al(OH)₃ in a 20 L spherical explosion system and a transparent pipe explosion propagation test system. The results show that, in the standard 20 L spherical explosion system, the highest PAN dust explosion concentration is 500 g/m³, the maximum explosion pressure is 0.661 MPa, and the maximum explosion pressure increase rate is 31.64 MPa/s; adding 50% NaHCO₃ and 60% Al(OH)₃ can totally inhibit PAN dust explosion. In the DN0.15 m transparent pipe explosion propagation test system, for 500 g/m³ PAN dust, the initial explosion flame velocity is 102 m/s, the initial pressure is 0.46 MPa, and the initial temperature is 967 °C; adding 60% NaHCO₃ and 70% Al(OH)₃ can totally inhibit PAN dust explosion flames. Through FTIR and TG analyses, we obtain the explosion products and pyrolysis patterns of the explosion products of PAN dust, NaHCO₃, and Al(OH)₃. On this basis, we also summarize the PAN dust explosion inhibition mechanisms of NaHCO₃ and Al(OH)₃.     

The study of burning behaviors and quantitative risk assessment for 0# diesel oil pool fires

The liquid fuel safety issues on fuel storage, transportation and processing have gained most attention because of the high fire risk. In this paper, some 0# diesel pool fire experiments with different diameters (0.2–1 m) were conducted with initial fuel thicknesses of 2 cm and 4 cm, respectively, to obtain liquid fuel combustion characteristics. Some key parameters including mass burning rate, flame height and the flame radiative heat flux, associated with fire risk, were investigated and determined. Subsequently, a detail quantitative risk assessment framework for 0# diesel pool fire is proposed based on the 0# diesel burning characteristics. In the framework, the probability of personal dead and the facility failure are calculated by the vulnerability models, respectively. In the end, 10 special tank fire scenarios were selected to show the whole risk calculation process. The tank diameter and the distance to pool fires were paid more attention in the cases. The safety distances in the cases are provided for the persons and nearby facilities, respectively. The paper enriches the basic experimental data and the provided framework is useful to the management of 0# diesel tank areas.