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.     

Evaluating the overall efficiency of a flameless venting device for dust explosions

Results from cornstarch explosion tests using a flameless venting device (mounted over a burst disc) on an 8 m³ vessel are presented and used to determine the overall efficiency of the device, which is defined as the ratio between its effective vent area and the nominal vent area. Because these devices are comprised of an arrestor element mounted over an impulsively-actuated venting device (such as a burst disc), the functional form of the overall efficiency is taken as the product of the area efficiency (i.e., the ratio between the effective vent area of the entire assembly to that of the venting device without the arrestor element) and the burst efficiency (i.e., the ratio of the effective vent area of the venting device without the arrestor element to the nominal vent area). The effective vent areas are calculated from measured overpressures using three different empirical correlations (FM Global 2001, NFPA 2007, and VDI 2002). Furthermore, due to significant variations in the effective reactivity from test to test, a correction factor proportional to the initial flame speed is applied when determining the area efficiency. In general, it was found that the FM Global and NFPA methodologies yield consistent results with less scatter than VDI 3673.     

Effect of admixture of solid inertant on fire hazard of dust layers oriented at varying degrees of inclination

Unlike metallic dust layers, the layer flammability levels (LFL) of non-metallic dust layers exhibit a wide range from Class 1 (No self-sustained combustion) to Class 6 (explosive combustion). However, determinations of layer flammability have not considered the effect of inclination angle, thereby potentially underestimating fire hazard of combustible dust layers in many industrial situations. In this research, inclined dust layers showed greater fire hazard than did horizontally oriented dust layers. For example, LFL of wood dust jumped from class 3 to class 5 when layers were positioned with an incline. Flame spread rate of PMMA dust layers increased from 1.8 to 3.6 mm/s when the angle of inclination increased from 0 to 40°. Even small amounts of solid inertant significantly decreased surface layer fires. The required amount of inertant to completely inert layer fires was far less than that for smoldering layer fires or dust explosions.     

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.     

Ignition temperatures of dust layers and bulk storages in hot environments

In many industrial installations, particulate solids (cereals, agri-food products, coal, plants, etc.) are stored or processed. Self-heating of these products, which can lead to fires and explosions, can occur in a variety of situations. Examples include large storage at room temperature, formation of a layer on a hot surface, layer deposited on a surface – insulating or conductive – in a hot environment or even storage of product exposed to heating on one side.The main parameters that determine the occurrence of self-heating are the size of the container, the temperature, the residence time and the characteristics of the product. Depending on the type of situation encountered and these implementation conditions, the analysis of self-heating risks must be based on specific models and/or parameters.This paper presents the different variants and combinations of the theoretical model from the theory of thermal runaway to represent self-heating, taking into account in particular the symmetry or asymmetry of heating, reagent consumption and boundary conditions. It also discusses their adaptation to the previous identified industrial situations.Nine products were chosen to be representative of those used in the different considered industrial situations. They were subjected to self-heating basket tests in isothermal ovens in order to determine the parameters for applying the described theoretical models. These results were compared with the results of self-heating tests in layers of different thicknesses in a hot environment, on an insulating or conductive plate, using a specially developed test protocol, as well as with the results of standardized tests of minimum ignition temperature in 5 mm layers.This led to the proposal of the most appropriate theoretical model to represent the self-heating phenomenon for each of the four identified industrial situations.This analysis can promote better design of industrial equipment and production conditions (temperatures, volumes or product flows …) in order to prevent fires and explosions.     

静电除尘在球团竖炉烟尘治理上的应用

介绍了球团竖炉烟尘治理的改造经验,总结了电除尘工程概况及效果。     

韶钢水泥厂的粉尘污染及综合防治措施

韶钢水泥厂在进行干法生产时,会产生大量的粉尘,严重影响生产和厂区周围居民的正常生活,危害严重。通过一些综合防治措施,不仅保护了环境,而且还可回收数量可观的有价原料、成品或半成品。     

化学纤维栅湿式过滤除尘的实验研究

化学纤维栅湿式除尘是一种复合机理的新型湿式过滤除尘技术,其过滤风速为2～10m/s,阻力仅为200～500Pa,除尘效率达到99.62％,能很好解决矿山溜井卸矿产生的粉尘,使溜井含尘气流经净化后达到新鲜风流卫生标准。     

某铁矿胶带运输机移动卸料车的除尘系统

针对该矿胶带运输机移动卸料车定点卸料的作业特点,采用随卸料车移动的抽风罩、水平式风管接口装置及湿式除尘机组,构成简捷的除尘系统,有效地解决了卸料车作业时产生的粉尘污染问题。     

一种用于空气压缩机的空气消声过滤器

介绍了组合式空气消声过滤器的用途、结构、工作原理和使用效果,它是空气压缩机前级的专用理想设备,推广使用后可获得良好的综合效益。