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Geomechanical assessments of longwall working stability – a case study

Nguyen Phu Minh Vuong, Rajwa Sylwester, Płonka Marek, Stachura Waldemar

Archives of Mining Sciences

2022

Vol. 67, no. 2

333--354

The stability of longwall mining is one of the most important and the most difficult aspects of underground coal mining. The loss of longwall stability can threaten lives, disrupt the continuity of the mining operations, and it requires significant materials and labour costs associated with replacing the damages. In fact, longwall mining stability is affected by many factors combined. Each case of longwall mining has its own unique and complex geological and mining conditions. Therefore, any case study of longwall stability requires an individual analysis. In Poland, longwall mining has been applied in underground coal mining for years. The stability of the longwall working is often examined using an empirical method. A regular longwall mining panel (F3) operation was designed and conducted at the Borynia-Zofiówka-Jastrzębie (BZJ) coal mine. During its advancement, roof failures were observed, causing a stoppage. This paper aims to identify and determine the mechanisms of these failures that occurred in the F3 longwall. A numerical model was performed using the finite difference method - code FLAC2D, representing the exact geological and mining conditions of the F3 longwall working. Major factors that influenced the stability of the F3 longwall were taken into account. Based on the obtained results from numerical analysis and the in-situ observations, the stability of the F3 longwall was discussed and evaluated. Consequently, recommended practical actions regarding roof control were put forward for continued operation in the F3 longwall panel.

Investigation and post-mortem analysis of silicon carbide refractory materials used in municipal waste incineration grate furnaces

Pilate Pascal, Abdelouhab Sandra

Materiały Ceramiczne

2020

T. 72, nr 1

16--32

Four municipal waste incineration plants were visited in Belgium. Facilities mainly consist of grate furnaces. During stopping for maintenance, in situ observations were mainly realized in two plants, refractory and slag samples were collected. These samples were observed and analysed in laboratory: ICP chemical analysis, X-ray diffraction, scanning electron microscopy, EDS analysis, thermo-optical analysis. Three mechanisms of degradation were identified. Their appearance mainly depends on the location in the furnace. On site observation and laboratory investigations allow to understand and to model the degradation mechanisms of materials versus composition, temperature, and their locations in the furnaces.

Odwiedzono cztery belgijskie spalarnie odpadów komunalnych. Obiekty składają się głównie z pieców rusztowych. Podczas postoju z powodu konserwacji w dwóch zakładach przeprowadzono głównie obserwacje in situ i pobrano próbki materiałów ogniotrwałych i żużla. Próbki te obserwowano i analizowano w laboratorium: analiza chemiczna ICP, dyfrakcja rentgenowska, skaningowa mikroskopia elektronowa, analiza EDS, analiza termooptyczna. Zidentyfikowano trzy mechanizmy degradacji. Ich występowanie zależy głównie od lokalizacji w piecu. Obserwacje na miejscu i badania laboratoryjne pozwalają zrozumieć i modelować mechanizmy degradacji materiałów w zależności od składu, temperatury i ich lokalizacji w piecach.

Analytical investigation of grain size dependence of microhardness in high nickel-containing reheated weld metal

Mao G., Cao R., Chen J., Guo X., Jiang Y.

Archives of Civil and Mechanical Engineering

2017

Vol. 17, no. 4

935--942

Grain size dependence of microhardness has been addressed in the bainitic reheated weld metals by in situ observation of morphological evolution and characterization of microstructural development. A higher cooling rate promotes the boundary of smaller prior austenite grains to provide more effective sites for primary bainitic ferrite nucleation, yet a lower cooling rate is increasingly beneficial to sympathetic nucleation as well as impingement of secondary bainitic ferrite. The microstructures, obtained by cooling at a higher rate and composed of abundant lath bainite, are closer to the microstructures in the raw weld metal than those cooled at a lower rate, including lath bainite, acicular ferrite and intercritical ferrite. Microhardness is decisive by prior austenite grain size mainly, as well as microstructures. Smaller grains contribute notably to microhardness, and it is worth stressing that the sizes of smaller grains lie on prior austenite grain boundaries rather than the subboundaries generated by intragranular acicular ferrite and intercritical ferrite.