热爆炸理论在粉尘爆炸机理研究中的应用

笔者对粉尘爆炸的几种机理进行了简要分析 ,认为粉尘爆炸是由热爆炸引起的。在对粉尘燃烧过程作了较为合理的假设后 ,将热爆炸理论中均温系统的热爆炸判据 ,应用于粉尘爆炸中 ,得出了爆炸下限与粉尘粒径呈线性关系的结论 ,且与实验符合 ,并推导出粉尘的热爆炸判据。结果表明 :用热爆炸理论来解释粉尘爆炸机理是可行的。     

Post-explosion observations of experimental mine and laboratory coal dust explosions

The Pittsburgh Research Laboratory (PRL) of the National Institute for Occupational Safety and Health (NIOSH) and the Mine Safety and Health Administration (MSHA) conducted joint research on dust explosions by studying post-explosion dust samples. The samples were collected after full-scale explosions at the PRL Lake Lynn Experimental Mine (LLEM), and after laboratory explosions in the PRL 20-L chamber and the Fike 1 m³ chamber. The dusts studied included both high- and low-volatile bituminous coals. Low temperature ashing for 24 h at 515 °C was used to measure the incombustible content of the dust before and after the explosions. The data showed that the post-explosion incombustible content was always as high as, or higher than the initial incombustible content. The MSHA alcohol coking test was used to determine the amount of coked dust in the post-explosion samples. The results showed that almost all coal dust that was suspended within the explosion flame produced significant amounts of coke. Measurements of floor dust concentrations after LLEM explosions were compared with the initial dust loadings to determine the transport distance of dust during an explosion. All these data will be useful in future forensic investigations of accidental dust explosions in coal mines, or elsewhere.     

Determination of turbulent burning velocities of dust air mixtures with the open tube method

Correlating turbulent burning velocity to turbulence intensity and basic flame parameters-like laminar burning velocity for dust air mixtures is not only a scientific challenge but also of practical importance for the modelling of dust flame propagation in industrial facilities and choice of adequate safety strategy. The open tube method has been implemented to measure laminar and turbulent burning velocities at laboratory scale for turbulence intensities in the range of a few m/s. Special care has been given to the experimental technique so that a direct access to the desired parameters was possible minimising interpretation difficulties. In particular, the flame is propagating freely, the flame velocity is directly accessible by visualisation and the turbulence intensity is measured at the flame front during flame propagation with special aerodynamic probes. In the present paper, those achievements are briefly recalled. In addition, a complete set of experiments for diametrically opposed dusts, starch and aluminium, has been performed and is presented hereafter. The experimental data, measured for potato dust air mixtures seem to be in accordance with the Bray Gülder model in the range of 1.5 m/s<u′<3.5 m/s. For a further confirmation, the measurement range has been extended to lower levels of turbulence of u′<1.5 m/s. This could be achieved by changing the mode of preparation of the dust air mixture. In former tests, the particles have been injected into the tube from a pressurised dust reservoir; for the lower turbulence range, the particles have been inserted into the tube from above by means of a sieve–riddler system, and the turbulence generated from the pressurised gas reservoir as before. For higher levels of turbulence, aluminium air mixtures have been investigated using the particle injection mode with pressurised dust reservoir. Due to high burning rates much higher flame speeds than for potato dusts of up to 23 m/s have been obtained.     

Influence of the oxide content on the ignition energies of aluminium powders

Some results of determination of ignition energies for an aluminium powder with various oxide contents are presented. Common use of processes like high-speed cutting produce explosive dust clouds, so that we focused this study on hazard of metallic powders. An industrial aluminium powder has been used for this work. An original process, based on the principle of electrochemical anodisation, has been developed to increase, under control, the oxide coating of particles.

The sensitivity study to spark ignition was performed in an Hartmann explosion tube of 1.3L. The Langlie test method was applied to evaluate the energies leading to a probability of ignition of 50% (E₅₀) of the selected samples. The results confirm that the ignition energies increase with the oxide content of the powder.     

Moderation of dust explosions

Inherent safety is a proactive approach to process safety in which hazards are removed or minimized so as to reduce risk without engineered (add-on) or procedural intervention. Four basic principles are available to attain an inherently safer design—minimization, substitution, moderation, and simplification. The subject of the current paper is the principle of moderation as it applies to the prevention and mitigation of dust explosions.

Moderation can be achieved by processing a material under less severe operating conditions or by processing the material in a less hazardous form. With respect to the latter approach, it may be possible to alter the composition of a dust by admixture of solid inertants, or to increase the dust particle size so as to decrease its reactivity. Additionally, avoidance of the formation of hybrid mixtures of explosible dusts and flammable gases is an application of moderation of the material hazard.

Several examples are given for each of the above three forms of moderation. The discussion on admixture of solid inertants includes examples from the following industrial applications: (i) refractory materials manufacturing, (ii) food processing, (iii) power generation, (iv) industrial recycling, and (v) foundry shell mold fabrication. The importance of particle size consideration is explained first from the perspective of engineering tools such as the Dow Fire & Explosion Index, and professional guidance on the definition of a dust and suitable particle sizes for explosibility testing. Industrial examples are then drawn from the following areas: (i) rubber recycling and textile manufacturing, (ii) industrial recycling, (iii) wood processing, (iv) dry additive handling (polyethylene facility), (v) polyethylene production, (vi) carbon block recycling, and (vii) coal mining. The concluding discussion on hybrid mixtures includes brief cases from the process safety literature.     

Ignitability characteristics of aluminium and magnesium dusts that are generated during the shredding of post-consumer wastes

The authors investigated the ignitability of aluminium and magnesium dusts that are generated during the shredding of post-consumer waste. The relations between particle size and the minimum explosive concentration, the minimum ignition energy, the ignition temperature of the dust clouds, etc. the relation between of oxygen concentration and dust explosion, the effect of inert substances on dust explosion, etc. were studied experimentally.

The minimum explosive concentration increased exponentially with particle size. The minimum explosive concentrations of the sample dusts were about 170 g/m³ (aluminium: 0–8 μm) and 90 g/m³ (magnesium: 0–20 μm). The minimum ignition energy tended to increase with particle size. It was about 6 mJ for the aluminium samples and 4 mJ for the magnesium samples. The ignition temperature of dust clouds was about 750 °C for aluminium and about 520 °C for magnesium. The lowest concentrations of oxygen to produce a dust explosion were about 10% for aluminium and about 8% for magnesium. A large mixing ratio (more than about 50%) of calcium oxide or calcium carbonate was necessary to decrease the explosibility of magnesium dust. The experimental data obtained in the present investigation will be useful for evaluating the explosibility of aluminium and magnesium dusts generated in metal recycling operations and thus for enhancing the safety of recycling plants.     

卧式电除尘器电晕极优化实验研究

运用粉尘粒子荷电原理,对四种电晕极的主要技术性能进行了试验研究,探讨了卧式电除尘器的最佳极配形式。     

地矿部门坑道作业尘毒危害情况

对坑道中的尘毒进行了测试,并根据测试结果提出了一些建议。     

胶带输送机防尘治理综合改进措施

叙述了胶带输送机现有防尘罩的不足及改进措施。     

磨细粉煤灰自动装车除尘系统的研制

针对磨细粉煤灰由储料仓向罐式汽车内装料的作业特点,研制了自动化装车除尘系统,解决了装车过程中的粉尘污染问题,并实现了装车过程的自动化。