Theoretical basis for the formation of damaging factors during the coal aerosol explosion

Purpose. Assessing the process of damaging factors formation during the coal aerosol explosion in mine workings on the basis of theoretical research of the explosion of coal dust deposits in order to substantiate promising methods of protecting miners from their impact. Methods. An integrated approach is used, which includes a critical analysis of literature data on the occurrence and development of coal aerosol explosions in mine workings; theoretical research into the state of the gaseous medium at the characteristic points of the development diagram of the coal dust deposits explosion as a result of mining operations based on the laws of classical physics and chemistry. Findings. The main aspects of the explosion mechanism of dust in a powdery state, accumulated on the surfaces along the mine working perimeter, and the formation of such negative factors as the effect of gaseous medium accelerated movement, have been revealed; high temperature formed during coal and methane detonative combustion; increased gas pressure. The revealed aspects of the dust explosion mechanism make it possible to determine the main directions for protection of miners caught in the explosion. The diagram of the development of settled coal dust explosion along the mine working with normal ventilation conditions, taking into account the influence of seismic waves, has been improved. Originality. Analytical dependences, reflecting the value of gas energy at characteristic points of the diagram, have been determined, and the dynamics of the formation of negative factors caused by the explosion have been revealed. Practical implications. Possible ways of protecting miners from the impact of negative factors caused by the coal aerosol explosion and reducing the severe consequences of such accidents are proposed.

The age of dust—A new hydrological indicator in arid environments?

Dust plays important roles in the environment, and there has been much interest in the formation, provenance, and age of the world’s dust deposits. Ongoing debates are concerned with the importance of glacial grinding versus eolian abrasion and fluvial transport in the formation of silt-sized particles. Short-lived uranium-series isotopes afford new insights because they can be used both for provenance fingerprinting and for constraining the integrated age of chemical and physical weathering and subsequent transport and storage of sediments. Here we present trace element and Sr, Nd, and U-series isotope analyses from a number of Australian dusts and suspended river sediments remobilized during floods a year later. The inferred ages of the Australian dust appear to be linked to aridification and the loss of inland megalakes ~30–120 k.y. ago. This provides preliminary evidence that the age of dust may provide a new hydrological indicator in arid environments.

Foliar dust and heavy metal deposit on leaves of urban trees in Budapest (Hungary)

This work considers dust deposition and the heavy metal (HM) content on leaves of urban trees (Acer platanoides L. ‘Globosum,’ Fraxinus excelsior L. ‘Westhof’s Glorie’ and Tilia tomentosa Moench.) in order to estimate the trees’ capacity to remove dust and HM from the air. Leaves were collected from the Buda Arboretum and from different streets of heavy traffic in Budapest, Hungary, during 2015 and 2016. At each site, five trees were sampled by collecting 6 leaves from each tree from the height of 2–3 m. Dust deposits on the leaves were removed by soaking the fresh foliage in distilled water for 20 h and then washed with ultrasound shaking. Afterward, the leaves were dried to constant weight and then they were digested in nitric acid–hydrogen peroxide treatment, and their Pb, Fe, Ni, Zn and Cu contents were measured using an inductively coupled plasma (ICP AS) spectrometer. The removed dust deposit was dried, and after a similar digestion treatment the Pb, Fe, Ni, Zn and Cu contents were measured using an AURORA AI 1200 AAS appliance. The HM deposit was calculated in mg m–2 leaf surface area. In 2015, the amount of foliar dust deposit from spring to autumn increased from 86.3 to 270.2 mg m–2. The most efficient tree species in trapping dust on their leaves was the silver linden (98.5–123.5 mg m−2), followed by the Norway maple (74.2–84.8 mg m−2) and the common ash (62.8–74.6 mg m−2). The deposit of HM elements showed seasonal differences: the quantity of Fe and Pb deposit on autumnal leaves increased five- to tenfold, while other heavy metals did not show accumulation. Silver linden with its pubescent (hairy) leaf surface proved to be most efficient in entrapping and retaining dust and heavy metals. The 60–100% higher Pb and Fe content of autumnal leaves indicate that over the season leaves may absorb Fe and Pb from the foliar dust. Our results confirmed that the foliar dust is a potential indicator for monitoring the HM content in the air. We also show that foliar dust deposits should be considered when estimating the capacity of urban trees to clean the air.

Determination of conditions for spontaneous combustion of combustible dust deposits on equipment, in ventilation systems, and aspiration systems of buildings and structures

Introduction. Determination of the scientifi cally substantiated frequency of cleaning the ducts of local exhausts of industrial buildings and structures is one of the tasks in the fi eld of fi re safety of industrial enterprises. The paper describes design methods, in particular, a method for determination of the induction period during spontaneous combustion of dust deposits in air ducts of ventilation systems and equipment, which can be used in solving problems focused on the development of preventive measures to ensure their fi re and explosion safety.Methods. In order to solve the problem set in this paper and compare the indicators obtained in the calculation and analytical part of the studies with the growth dynamics of deposits in real facilities, fi eld tests have been accomplished in the production facilities of the fl our mill of OJSC MK “Voronezhsky” and JSC Concern “Sozvezdiye”.Results and discussion. The timeframes for cleaning of deposits on ventilation (aspiration) equipment of buildings and structures cannot be universal for various industries and must take into account the dynamics of the growth of deposits depending on the specifi cs of combustible deposits, the workload of the production facilities of the protected object in a given period of time, and the operating conditions of the equipment. As a result of the experiments, it was found that the places of maximum accumulations of deposits are most often formed on the surfaces of joints and on the bends of pipelines of ventilation systems. The conditions of spontaneous combustion of combustible dust are studied by calculation and analytical method, depending on such process characteristics as the speed of the dust-air mixture fl ow in the duct, as well as the diameter of the duct’s cross section.Conclusions. The nomograms built on the basis of the studies performed can be used to determine the multiplicity of cleaning of combustible dusts of equipment and air ducts of industrial ventilation systems. The paper provides a calculation of the period of induction of spontaneous combustion of combustible dust deposits using the example of rye fl our with asymmetric heat transfer. Its signifi cance is due to the process of accumulation of deposits of combustible dust to a critical thickness in terms of spontaneous combustion conditions.

Sand and Dust Storms (SDS): Types, Characteristics, and Indications

Sand and dust storms (SDS) is a common weather phenomenon in the Middle East. Topography and the northern or northwesterly wind are the main control factors for types of SDS trajectories. The main SDS corridors in the Middle East were classified and spotted from March 2000 to March 2017. The SDS can be classified in the region in accordance to shape and magnitude into three main types namely; Small with 3 subtypes (Arrow shape-straight, Arrow shape-curved and Needle like), Intermediate with 3 subtypes (Curved, Hook and Straight), and Extensive with 6 subtypes (Spiral, Agglomerated-Dense, Agglomerated-Dispersed, Wavy, Hook-Single head, and Hook-multiple heads). Most of the trajectories are located within the northeastern parts of the Middle East. Dust properties led us to sort SDS and their indications. Dust deposits in the eastern Mediterranean Sea and the Red Sea and are initiated from Northern Desert of Africa (NDA). On the other hand, dust deposits in the Middle East originate from NDA, Western Desert of Iraq (WD), Mesopotamian Flood Plain (MFP), Ahwaz (HZ), Ahwar (HR) and Baluchistan Desert (BSH). The deposited dust in coastal areas is categorized as trimodal particle size distribution, finer mean size fractions with higher values of particles surface area and contains more carbonates and less quartz percentages compared to fallen dust in inland regions which is dominantly initiated from Western Desert of Iraq (WD), Nafud Desert (NFD) and Empty Quarter (EQ)..