Search

The paper presents research on the influence of grain size of selected coals and their structural parameters on the diffusion coefficient and methane sorption isotherms. Two coals from Polish hard coal mines, differing in the coal rank, were tested. Sorption isotherms for methane were determined. An unconventional sequence of pressures 0→0.1→0→0.5→0→1.5 MPa was employed to assess the speed of achieving sorption equilibrium at different pressures. The studies of CH4 accumulation kinetics were performed on various grain classes of the tested coals. Both the sorption capacity of coal and the diffusion coefficient proved to be highly sensitive to the experimental methodology. Critical measurement parameters in terms of determining the diffusion coefficient concerning the assumptions of the Crank model were indicated. The influence of the equivalent radius of coal grain on the process kinetics was demonstrated. The stepwise pressure increase factor was examined in the context of minimising the impact of sorption isotherm non-linearity on the results. The importance of the width of the grain class of coals was determined to reduce their maceral inhomogeneities. These factors are the most common reason that makes it difficult to quantitatively compare diffusion coefficient values. [ABSTRACT FROM AUTHOR]

Rock and gas outburst is a phenomenon in which fragmented rock material is transported deep into a pit. The transport of rock material by gas is a two-phase process. The article deals with the fluidisation of rock material. Considerations on the fluidisation phenomenon were carried out, and experiments were performed to help clarify whether the fluidisation of dolomite is possible. In the last chapter, a discussion was carried out, and the results obtained were analysed regarding the possibility of occurrence in mine conditions. [ABSTRACT FROM AUTHOR]

The authors of the present paper designed and constructed a prototype of an instrument which enables fully automated determination of the desorbable methane content and effective diffusion coefficient in underground conditions. Due to microprocessor analysis of the recorded data and the application of the mathematical model of the diffusion process, it is possible to automatically determine the amount of methane whose release from a coal sample occurred before the sample was placed within a measuring instrument. It is also possible to carry out follow-up extrapolation of the recorded data so the time duration needed to determine reliable results can be reduced. The instrument was tested and optimized, and a number of copies sufficient for performing underground tests were constructed. The concept of the instrument represents a totally new approach to the observation of gas release from a coal sample. Instead of short-period measurements, virtually the whole process of methane release from coal is registered and analysed. This is possibly due to the use of a grain fraction lower than one mm which is presently applied for the sake of evaluating the methane- bearing capacity and desorption intensity.

The goal of this paper is to analyze the phenomenon of gas emission during a methane and coal outburst based on the unipore Crank diffusion model for spherical grains and plane sheets. Two occurrences in the Upper Silesian Coal Basin were analyzed: an outburst in a Zofiówka coal mine in 2005 and an outburst in a Budryk coal mine in 2012. Those two outbursts differed considerably. The first one was connected with an unidentified tectonic disturbance in the form of a triple, interlocking fault, and the other one is an example of an outburst in an area free from tectonic disturbances. The model analysis required laboratory tests in order to determine the sorption properties of coals from post-outburst masses. Sorption isotherms and the values of the effective diffusion coefficient were specified. The post-outburst masses were subjected to sieve analysis and the grain composition curves were plotted. The researchers also used the measurement data provided by proper mine services, such as the methane content, the volume of post-outburst masses, and the time courses of CH4 concentration changes in excavations. They were recorded by methane measurement systems in the mines.

As part of the work the high-pressure sorptomat - a novel apparatus for sorption tests under conditions of high gas pressure was developed. The sorption measurement is carried out using the volumetric method, and the precise gas flow pressure regulator is used in the device to ensure isobaric conditions and regulate the sorption pressure in the range of 0-10 MPa. The uniqueness and high precision of sorption measurements with the constructed apparatus are ensured by the parallel use of many pressure sensors with a wide measurement range as well as high precision of measurement - due to the use of precise pressure sensors. The obtained results showed, i.a. that the time of reaching the isobaric conditions of the measurement is about 6-7 seconds and it is so short that it can be considered a quasi-step initiation of sorption processes. Moreover, the results of the measurement pressure stabilization tests, during the CO2 sorption test on activated carbon, have shown that the built-in pressure regulator works correctly and ensures isobaric sorption measurement conditions with the precision of pressure stabilization of ±1% of the measurement pressure. The maximum range of sorption measurement using the high-pressure sorptomat is 0-86 400 cm3/g, and the maximum measurement uncertainty is ±2% of the measured value. The activated carbon sample used for the tests was characterized by a high sorption capacity, reaching 104.4 cm³/g at a CO2 pressure of 1.0 MPa. [ABSTRACT FROM AUTHOR]

This paper presents results that show the effect of hydrothermal carbonization and subsequent cold plasma jet treatment with helium and argon on the structure and sorption properties of a material—spent brewery grain. Treatment of activated carbon, with a cold atmospheric plasma jet, was used comparatively. The effect of activation on the pore structure of the materials was carried out by the volumetric method at low pressure (N2, 77 K). The specific surface area as well as the total pore volume, average pore size, and pore size distribution were determined using different theoretical models. A high improvement in the sorption capacity parameter was obtained for hydrochars after cold atmospheric plasma jet treatment with an increase of 7.5 times (using He) and 11.6 times (using Ar) compared with hydrochars before cold atmospheric plasma jet treatment. The increase in specific surface area was five-fold (He) and fifteen-fold (Ar). For activated carbon, such a large change was not obtained after plasma activation. Regardless of the gas used, the increase in structural parameter values was 1.1–1.3. [ABSTRACT FROM AUTHOR]

Copyright of Archives of Mining Sciences is the property of Polish Academy of Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)