About the mass of combustible dust deposited in the room

Темой данной статьи является рассмотрение расчетного метода оценки пыленакопления в помещении с оборудованием, содержащим дисперсные материалы, а задача заключается в его совершенствовании на основании современных представлений. Витающие в воздухе мелкие пылинки постепенно осаждаются на горизонтальных поверхностях, создавая угрозу внезапного перехода в состояние аэровзвеси и взрывообразного сгорания с образованием волны давления. Для определения категории помещения по взрывопожарной и пожарной опасности и разработки профилактических противопожарных мероприятий необходимо иметь математический инструмент, позволяющий оценивать количество пыли, которое может участвовать во взрыве. В статье предлагается определять критический диаметр частиц пыли, исходя из равенства скорости осаждения частиц и скорости распространения пламени. При этом скорость осаждения частиц следует определять по известному соотношению Стокса, а скорость распространения пламени принимать или по данным эксперимента, или среднестатистическую, равную 3 м/с. The dust that settles on the horizontal surfaces of equipment and building structures is inevitably contained in the premises in which technological process is carried out with the presence of combustible dispersed materials. The amount of dust deposited in a room can be determined in several ways. 1. Weighing the dust collected during cleaning. 2. Experimentally by placing dust collectors on different surfaces for a certain period of time. It should be considered the incompleteness of the previous dust collection, which depends on the dust collection method when determining the amount of dust deposited in the room. The amount of the remaining uncollected dust is estimated as 10 % of the detected dust if the cleaning was carried out by a mechanized method (dust extraction coefficient K = 0.9, and insufficient decontamination coefficient n = 0.1). The amount of remaining uncollected dust is estimated as 40% of the detected dust if cleaning was carried out manually using a dry method (dust extraction coefficient K = 0.6 and insufficient decontamination coefficient n = 0.4). The amount of remaining uncollected dust is estimated as 30% of the detected dust if the cleaning is carried out manually with a wet method (K coefficient = 0.7, and insufficient decontamination coefficient n = 0.3). Dust factor is the ratio of amount of dust suspended in the airspace to the total amount of dust in the room. It should be taken equal to 0.5, if the diameter of dust particles is more critical, and equal to 1, if the diameter of dust particles is less than the critical diameter. The diameter of the dust particles is critical, above which the dust ceases to spread the flame. The critical diameter can be determined based on the following considerations. Flame propagation through the air suspension will not occur if the particle deposition rate exceeds the flame propagation rate from bottom to top. The deposition rate is easily determined by the Stokes coefficient. The flame propagation rate can be determined experimentally or estimated as slightly higher than the average for most industrial dusts. The authors obtain a formula for calculating the critical diameter of dust particles equating the terminal velocity to flame propagation rate (3 m/s) and solving the Stokes equations of the particle diameter. The critical particle diameter of air suspension of combustible materials in most cases does not exceed 300 microns at flame propagation speed of 3 m/s. The obtained calculated values of the critical diameters are in satisfactory agreement with the literature data, and also confirm the correctness of the choice of dust formation coefficient K = 1 for dust with dispersion of less than 350 mkm. The air suspension ready for a secondary explosion is formed when combustible particulate material leaves the equipment as a result of an internal explosion. The aerosol with a high concentration of solid phase is formed in case of free precipitation from the device or from damaged packaging located above the floor level of the room. In this case, the amount of fuel capable for explosive combustion is determined by the amount of oxygen in the cloud, since the diffusion supply of oxygen from the outside does not have time to ensure complete combustion of the fuel. When the product spills unhindered, the resulting cloud has the shape of a volumetric cone with a base diameter equal to the height of the cone. It is possible to determine the amount of burned dust knowing the stoichiometric concentration of dust (%) required for its combustion per unit of air volume, as well as the volume of the dust cloud (V). The Pc value can be determined by the combustion reaction if the chemical composition of the dust is known. There are proposed refined equations for determining the critical diameter of combustible dust, the stoichiometric concentration during its combustion in a unit of air volume as well as the mass of dust deposited in the room. It is recommended to estimate the value of the stoichiometric concentration according to the combustion heat of dust for dusts of indeterminate chemical composition.

Use of Computer Simulation in the Selection of Operating Parameters for the Dust Extractor Built into the Roadheaders

An increase in the rate of mine workings excavation leads to the ingress of large amount of dust into the mine atmosphere. Ensuring the aerological safety of coal mines drifting faces according to the dust factor is an urgent task. To reduce the level of dustiness of a dead mine roadheading during its sinking, the scrubbers built into the roadheader are used. In this case, the joint operation of the ventilation system and the dust extraction system is not considered. This leads to the risk of occurrence of the stagnation zones or air recirculation near the bottom-hole area. At the intensive ventilation with a high air flow, the dust is removed, and the dust extraction system becomes useless. As the analysis showed, currently there are no methods that allow to take into account these two processes simultaneously. The idea of using computer modeling in the Ansys software package is proposed. To correctly solve the problems of optimizing the scrubber operation, a method is given for determining the grid parameters, as well as for setting the initial and boundary conditions. All the data obtained were verified at the coal mines of Russia. To achieve maximum efficiency, it is proposed to use the dust and aerodynamic criteria of the scrubber operation, which will allow to increase the mining operations safety. The dust criterion characterizes the efficiency of the dust extraction systems. The aerodynamic criterion allows to determine the joint operation mode in which there will be no recirculation and not ventilated zones. To take into account the large number of factors that affect the ventilation of a dead mine working and the operation of the dust extraction system, an artificial intelligence was added to computer modeling in system design. It is implemented in the ANSYS DesignXplorer module. In a given range of changing factors during the operation of artificial intelligence, by performing multiple calculations, such a combination of operating parameters of the two systems is obtained, at which the efficiency is maximum.

Reduction of dust extraction from an aspiration shelter due to mechanical shielding

The dust dynamics in an aspiration shelter equipped with various thin mechanical screens is considered. To calculate the trajectories of dust particles, the differential equation of their motion was used, the velocity field of the air flow was calculated by the method of boundary integral equations. The influence of different mechanical screens on the maximum diameter of dust particles is determined. It is shown that when using curved mechanical screens it is possible to significantly reduce dust extraction in the suction network.

Design and implementation of a coal-dust removal device for heavy-haul railway tunnels

The Daqin Railway is China's first electrified double-track heavy-haul railway line dedicated to coal transportation. Over the years of operation, the tunnels have been covered with a thick layer of coal dust, which also pervades in the air. Worse is that the coal dust has even buried the rail joints in some sections, making the repair and maintenance of the line difficult. This paper introduces a coal-dust removal device for railway tunnels that integrates pipeline transportation with dust-collection techniques. The device is mainly composed of a power system, a conveying system, a dust-filtration and collection system, and a control and protection system. The key technical elements of the system, such as the dust-extraction method and dust-filtration and collection parameters, are optimized based on the characteristics of the coal dust in the tunnel (obtained via field trials), which greatly enhances the adaptability of the device. Coal-dust removal efficiency reached over 20 t/h, which improves the working environment, reduces the intensity of manual work required and solves the problem of coal-dust removal from the most polluted area—within 500 m of the tunnel entrance.

Wood coating dust emission in the Malaysian furniture industry: A case study

The objectives of this study were to evaluate the current dust extraction efficiency used in the Malaysian furniture industry and also the effectiveness of using engineered nanoparticle (ENP)-added coatings to reduce dust emission in the wood finishing operation. This study was in response to the enforcement of the Clean Air Regulation (2014), which requires significant improvements in the air quality and the work environment in the wood-based industry in Malaysia. A series of sanding experiments with different abrasive grit sizes and different coating types were conducted to determine the dust emission levels. The results suggested that higher capture velocity of 30 m/s was necessary to effectively capture the wood coating dust emitted. Further, ENP-added wood coatings did not differ markedly from conventional coatings with regard to dust emission characteristics. The study also revealed that total dust concentration had an inverse relationship, while the amount of finer dust particles was linearly related to the coating film hardness. Therefore, to comply with the Clean Air Regulation, the Malaysian furniture industry needs to significantly improve its dust extraction system.

Managing Risks and Exposures to Silica in Training and Assessment Activities in Vocational Education and Training

A number of activities in workplaces, such as such as those including cutting, grinding, sanding, drilling, loading or demolishing products that contain silica, can produce respirable particles of crystalline silica dust that are small enough to inhale. Inhalation of crystalline silica can cause silicosis which is incurable. Work practices are critical to prevent the condition from occurring and safe work practices are as relevant to workplaces as they are to training environments. This study considers methods of risk control and training practices such that silicosis is prevented.Training requirements are profiled in a vocational education and training setting and must include: crystalline silica hazards and health risks, including silicosis; effective use controls; use and maintenance of personal protective equipment, including Respiratory Protective Equipment; safe waste disposal; and, practices for personal decontamination. The training environment must be designed in a manner to allow for engineering controls, such as on-tool water suppression or on-tool dust extraction, to be utilised.