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Date submitted2024-06-17
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Date accepted2024-07-17
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Date published2024-10-03
Justification on the safe exploitation of closed coal warehouse by gas factor
The annual increase of coal production and its demand lead to the necessity in temporary storage places (warehouses) organization to accommodate raw coal materials before the shipment. It is noted that at the open method of coal storing the dust emission from loading/unloading operations and from the pile surface effects negatively the health of the warehouse workers and adjacent territories. An alternative solution is closed-type warehouses . One of the main hazards of such coal storage can be the release of residual methane from coal segregates into the air after degassing processes during mining and extraction to the surface, as well as transportation to the place of temporary storage. The study carries the analysis of methane content change in coal during the processes of extraction, transportation and storage. Physical and chemical bases of mass transfer during the interaction between gas-saturated coal mass and air are studied. It is determined that the intensity of methane emission depends on: the coal seam natural gas content, parameters of mass transfer between coal, and air and the ambient temperature. The dynamics of coal mass gas exchange with atmospheric air is evaluated by approximate approach, which is based on two interrelated iterations. The first one considers the formation of methane concentration fields in the air space of the bulk volume and the second accounts the methane emission from the pile surface to the outside air. It is determined that safety of closed coal warehouses exploitation by gas factor can be ensured by means of artificial ventilation providing volumetric methane concentration in the air less than 1 %. The flow rate sufficient to achieve this methane concentration was obtained as a result of computer modeling of methane concentration fields formation in the air medium at theoretically calculated methane emission from the pile surface.
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Date submitted2019-04-04
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Date accepted2019-08-04
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Date published2020-04-24
Chemical heterogeneity as a factor of improving the strength of steels manufactured by selective laser melting technology
The aim of this paper was to establish the causes of the heterogeneity of the chemical composition of the metal obtained by the LC technology. The powdered raw material was made from a monolithic alloy, which was fused by the SLM, the initial raw material was a laboratory melting metal of a low-carbon chromium-manganese-nickel composition based on iron. To determine the distribution pattern of alloying chemical elements in the resulting powder, electron-microscopic images of thin sections were combined with X-ray analysis data on the cross-sections of the powder particles. As a result, it was found that transition (Mn, Ni) and heavy (Mo) metals are uniformly distributed over the powder particle cross-sections, and the mass fraction of silicon (Si) is uneven: in the center of the particles, it is several times larger in some cases. The revealed feature in the distribution of silicon is supposedly due to the formation of various forms of SiO 4 upon the cooling of the formed particles. The internal structure of the manufactured powder is represented by the martensitic structure of stack morphology. After laser fusion, etched thin sections revealed traces of segregation heterogeneity in the form of a grid with cells of ~ 200 μm.
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Date submitted2017-10-26
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Date accepted2017-12-25
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Date published2018-04-24
Conditions of austenite diffusional transformation in steel of Cr–3Ni–Mo–V-composition with high austenite stability
- Authors:
- V. V. Tsukanov
- N. V. Lebedeva
- Yu. M. Markova
The paper investigated the bainitic steel of 10KHN3MFA grade, which is characterized by the increased tendency to display structural heredity in the forgings with large cross-sections. The samples have been studied for kinetics of diffusional transformation process both under continuous cooling and isothermal conditions, as well as its microstructure. It is determined that in the range of subcritical temperatures with cooling from 900 °C in the studied steel, the initial stage of separation of the ferrite phase takes place. It is shown for the first time that the diffusional ferrite-pearlite transformation fades. Previously it was believed that the beginning of transformation under isothermal conditions proceeds to the end. It was found out that the transformation begins immediately after the beginning of isothermal holding, without the generally accepted incubation period.
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Date submitted2016-08-30
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Date accepted2016-10-30
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Date published2017-02-22
Gas-dynamic processes affecting coal mine radon hazard
- Authors:
- V. I. Efimov
- A. B. Zhabin
- G. V. Stas
The paper focuses on vertical migration of radon in surrounding rocks described by Fick's first law as well as by the continuity equation for diffusion flow, with allowance for sorption and radioactive decay processes. Taking into account special characteristics of vertical radon diffusion, the process can be considered stable. It is demonstrated that for productive areas it is feasible to consider one-dimensional convective diffusion, as diffusive transport of radon by the air of productive areas occurs at steady-state conditions. Normally the factor of radon emissions prevails if atmospheric pressure is constant. Amount of air, calculated using this factor, by 20-30 % exceeds the one needed to dilute carbon dioxide to maximum allowed concentration (MAC).