Modelling of dust lifting process behind propagating shock wave

Dust dispersion from a layer is a complicated problem, which has not been completely solved yet, especially if an Eulerian–Eulerian approach has to be used to model the two-phase dusty flow. In previous investigation, a phenomenological model of the dust dispersion process from a layer was developed, but the evaluation of the model revealed some weaknesses. In the current paper, the model of the dust dispersion process was presented and three improvements of the model were studied: Saffman force, Magnus force and particles collisions. The implementation of Magnus and Saffman forces into the code did not improve the numerical results and it was shown that it had very little influence on the dust lifting process, in case the phenomenological model of the layer is used. Some explanations were proposed in the paper. Besides, an empirical model of particles collisions was also added to the code and its influence on the results was studied. It was shown that the particles collisions model improved the obtained results, but further modifications are to be studied in the future.     

新疆阿拉尔垦区大气降尘中重金属时空分布特征

连续12个月对新疆阿拉尔垦区9个样点的3个不同高度处所采集的大气降尘中的重金属含量进行分析,结果表明:所测大气降尘中的5种重金属元素以铁的含量最高,铬的含量最低,其中铜、铁、锰及锌的含量均在4月份达到最大值,并且与降尘量之间有较好的线性关系。在不同的空间范围内,大气降尘中的重金属含量存在显著差异,其中铜、铁、锰的含量均随着高度的上升而呈现递增的趋势;铬的含量随高度的递增呈现递减趋势。     

Towards an inherently safer bioprocessing industry: A review

The bioprocessing industry is regarded as one of the fastest growing sectors with an estimated compound annual growth rate of 8.6%. The global market for biopharmaceuticals is projected to rise to a market value of USD 727.1 billion by 2025. Due to the unique nature of bioprocessing industries wherein micro-organisms are employed to manufacture the desired products, these processes are prone to additional hazards such as biological hazards and dust explosion amongst others. This necessitates the need to review the existing research in the fields of biotechnology and bioprocessing to reduce/eliminate these hazards and pave the path towards a safer bioprocessing industry. The study involves developing a framework comprising of studying the recent technologies that reduce/eliminate these hazards involved in the bioprocessing industries that include dust explosions, loss of containment of toxic chemicals, loss of containment of biohazard/active product ingredient, fire, and explosion and mapping these technologies with respect to inherent safety principles that include substitution, minimization, moderation and simplification with an overall objective of minimizing the risk associated with bioprocesses and moving towards an inherently safer bioprocessing industry.     

CFD simulations of dust dispersion in the 20 L vessel: Effect of nominal dust concentration

Measurements of flammability and explosion parameters for dust/air mixtures require uniform dispersion of the dust cloud inside the test vessel. In a previous work, we showed that, in the standard 20 L sphere, the dust injection system does not allow generation of a uniform cloud, but rather high gradients of dust concentration are established. In this work, we used a previously validated three-dimensional CFD model to simulate the dust dispersion inside the 20 L sphere at different dust nominal concentrations (and fixed dust diameter). Results of numerical simulations have shown that, as the dust nominal concentration is increased, sedimentation prevails and, thus, when ignition is provided, the dust is mainly concentrated at the vessel walls.     

建筑施工中临边高处坠落危险源影响空间建模

将建筑施工中临边坠落的特性模型化,对于预防建筑施工中伤亡事故具有重要的意义。在分析人或物临边高处坠落事故特点的基础上,给出施工工作面内外2种危险源影响空间范围的定义及其数学表达函数,构建相应的危险源影响空间中危害能量分布的数学模型,提出它对人体不同部位伤害程度的评估分析思路,并在大面积碰撞和小面积碰撞2种情况下,建立该危害能量对人体头枕部伤害程度的评估分析方法。通过上海某个6层框架结构教学楼案例,对上述数学模型和评估分析方法进行验证。这为在进行施工计划安排时,考虑危险源影响空间的影响,降低安全事故发生的可能性创造条件,也为安全事故事前预防提供新思路。     

The effects of relative humidity on the insecticidal properties of a diatomite‐based dust

Abstract

The feasibility of using diatomaceous earth (diatomite) as an insecticidal dust was investigated under conditions of high (80%) and low (10%) relative humidity, using the adult red flour beetle, Tribolium castaneum. Tested were diatomite and two lots of a commercial formulation of the same diatomite, containing 0.2% pyrethrins and 1.0% piperonyl butoxide. For comparison, talcum and a talcum‐based commercial formulation, containing the same concentrations of pyrethrins and piperonyl butoxide, were included in the tests. The insects were exposed to 0.08 mg/cm² of each material tested, equivalent to the label recommendation of 7 lb/acre for the diatomite‐based commercial insecticide. At 10% RH, higher doses of diatomite were also tested. Mortalities were determined at intervals for up to 84 hours.

Diatomite caused no mortalities at the experimental concentration, regardless of RH. At about four times that rate and 10% RH, it caused less than 5% mortality.

At 80% RH, the diatomite‐based product (P. C. P. Act #14074) was significantly more effective than the talcum‐based one (#13074). At 10% RH, however, the latter acted more quickly than the diatomite‐based formulations, but all produced nearly 100% mortality after 68 hours.

The results are discussed in terms of the physical characteristics of diatomite and in terms of the modes of insecticidal actions of diatomite and pyrethrins. It is concluded that diatomite alone, despite its attractiveness to environmental interests, is not likely to become an effective agent for controlling red flour beetles and other pest insects with similar water‐proofing mechanisms.     

红壤丘陵区冬季大气湿沉降化学特征及森林冠层对其截留作用机制

通过对亚热带千烟洲流域的冬季湿沉降化学特征及森林穿透雨进行研究,揭示亚热带流域森林冠层对大气湿沉降中的营养元素(C、N、P、S)及金属元素(K、Ca、Na、Mg、Al、Fe、Mn、Zn)的截留与作用机制.结果表明:1亚热带丘陵区冬季大气湿沉降以酸沉降为主,p H变化范围在3.49~7.0之间,冬季酸沉降离子中以SO_4~(2-)和NO_3~-为主,其月平均沉降通量分别为4.68 kg·hm~(-2)和0.36 kg·hm~(-2),痕量金属元素中以Zn、K、Ca沉降为主,其沉降通量分别为1.72、0.56、0.36 kg·hm~(-2);2森林林冠对溶解性有机碳(DOC)、溶解性总氮(DTN)、总磷(TP)以及痕量元素Ca、Mg、Mn有明显的截留与离释作用,离释百分比达到64.69%、206.75%、301.38%、137.94%、405.25%、1 226.60%;而对Zn、SO2-4具有很好的吸收作用,吸收百分比为73.50%和12.51%,显著降低了亚热带流域冬季酸沉降对土壤生态系统的危害.     

Minimum Ignition Temperature of layer and cloud dust mixtures

The prevention of dust explosions is still a challenge for the process industry. Ignition, in particular, is a phenomenon that is still not completely understood. As a consequence, safety conditions pertaining to ignition suppression are rarely identified to an adequate level. It is well known that, in general, the ignition attitude of a dust depends on several factors, such as the nature of the chemical, the particle size, moisture content, etc., but there is still a lack of knowledge on the effect of the single variables.This paper has the aim of providing data on the Minimum Ignition Temperatures of dust mixtures obtained from a mixing of a combustible dust (flour, lactose, sucrose, sulphur) and an inert dust (limestone, extinguishing powders) as well as from the mixing of two different combustible dusts. Various mixtures with different weight ratios have been tested in a Godbert Greenwald (GG) furnace and on a hot plate in order to measure the effect of mixture composition on the Minimum Ignition Temperature (MIT_L) of the layer and on the Minimum Ignition Temperature (MIT_C) of the cloud. In order to further verify the effects of inert dust particle size, inerts sieved to different size ranges have been tested separately. Generally, both MIT_L and MIT_C increase as the inert content is increased. MIT_C is poorly affected by inert particle size when limestone is used. The MIT_L of pure flour is higher than the MIT_L of mixtures containing up to 40% of 32–75 μm of limestone. This was probably due to the behaviour of pure flour during the test, which demonstrated strong tendency to produce char, cracks in the layer and detachment from the hot plate.     

Biomass explosion testing: Accounting for the post-test residue and implications on the results

This work uses the ISO 1 m³ dust explosion equipment to study the explosion properties and combustion characteristics of pulverized biomass dust clouds. An unreported feature of this apparatus is that in rich concentrations only about half the dust injected is burned in the explosion, while the overpressures remain high. This work was undertaken to try to understand the mechanisms of these phenomena, through the accounting of the debris at the end of the explosion, some of which was found in the form of impacted “cake” against the vessel wall. One possible explanation is that the residue material was biomass dust blown ahead of the flame by the explosion induced wind, impacted on the walls where then the flame side underwent flame impingement pyrolysis and the metal (wall) side material was compacted but largely chemically unchanged. The results also show that the heat transfer insulation provided by the powder wall layer contributes to the higher observed pressures. The risk of explosion with significant overpressures remains at 100% in very rich environments (equivalence ratios of up to 6) although these environments are leaner than thought due to material sequestration within the “cake”. There was little indication that a rich combustion limit was approached, this was determined in standard testing equipment that has been modified and calibrated to handle larger quantities of powder than normal.     

Minimum ignition energy of mixtures of combustible dusts

Most industrial powder processes handle mixtures of various flammable powders. Consequently, hazard evaluation leads to a reduction of the disaster damage that arises from dust explosions. Determining the minimum ignition energy (MIE) of flammable mixtures is critical for identifying possibility of accidental hazard in industry. The aim of this work is to measure the critical ignition energy of different kinds of pure dusts with various particle sizes as well as mixtures thereof.The results show that even the addition of a modest amount of a highly flammable powder to a less combustible powder has a significant impact on the MIE. The MIE varies considerably when the fraction of the highly flammable powder exceeds 20%. For dust mixtures consisting of combustible dusts, the relationship between the ignition energy of the mixture and the minimum ignition energy of the components follows the so-called harmonic model based upon the volume fraction of the pure dusts in the mixture. This correlation provides results which show satisfactory agreement with the experimental values.