The assessment of longwall working stability based on the Mohr-Coulomb stress criterion – numerical analysis

The use of computer techniques at the design stage of industrial facilities is essential in modern times. The ability to shorten the time required to develop a project and assess the safety of the use of assumptions, often enables the reduction of the costs incurred in the future. The possibility to skip expensive prototype tests by using 3D prototyping is why it is currently the prevailing model in the design of industrial facilities, including in the mining industry. In the case of a longwall working, its stability requires the maintenance of the geometric continuity of floor rocks in cooperation with a powered roof support.The paper investigates the problem of longwall working stability under the influence of roof properties, coal properties, shield loading and the roof-floor interaction. The longwall working stability is represented by an index, factor of safety (FOS), and is correlated with a previously proposed roof capacity index ‘g‘. The topic of the paper does address an issue of potential interest. The assessment of the stability of the roof in longwalls was based on the numerical analysis of the factor of safety (FOS), using the Mohr-Coulomb stress criterion. The Mohr-Coulomb stress criterion enables the prediction of the occurrence of failures when the connection of the maximum tensile principal stress σ1 and the minimum compressive principal stress σ3 exceed relevant stress limits. The criterion is used for materials which indicates distinct tensile and compressive characteristics. The numerical method presented in the paper can be utilized in evaluating the mining natural hazards through predicting the parameters, which determine the roof maintenance in the longwall working.One of the purposes of the numerical analysis was to draw attention to the possibilities that are currently created by specialized software as an important element accompanying the modern design process, which forms part of intelligent underground mining 4.0

CFD Simulations of Allothermal Steam Gasification Process for Hydrogen Production

The article presents an experimental laboratory setup used for the empirical determination of the gasification of coal samples in the form of solid rock, cut out in the form of a cylinder. An experimental laboratory set enabled a series of experiments carried out at 700 °C with steam as the gasification agent. The samples were prepared from the coal seam, the use of which can be planned in future underground and ground gasification experiments. The result of the conducted coal gasification process, using steam as the gasification agent, was the syngas, including hydrogen (H2) with a concentration between 46% and 58%, carbon dioxide (CO2) with a concentration between 13% and 17%, carbon monoxide (CO) with a concentration between 7% and 11.5%, and methane(CH4) with a concentration between 9.6% and 20.1%.The results from the ex-situ experiments were compared with the results of numerical simulations using computational fluid dynamics (CFD) methods. A three-dimensional numerical model for the coal gasification process was developed using Ansys-Fluent software to simulate an ex-situ allothermal coal gasification experiment using low-moisture content hard coal under atmospheric conditions. In the numerical model, the mass exchange (flow of the gasification agent), the turbulence description model, heat exchange, the method of simulating the chemical reactions, and the method of mapping the porosity medium were included. Using the construction data of an experimental laboratory set, a numerical model was developed and its discretization (development of a numerical grid, based on which calculations are made) was carried out. Tip on the reactor, supply method, and parameters maintained during the gasification process were used to define the numerical model in the Ansys-Fluent code. A part of the data were supplemented on the basis of literature sources. Where necessary, the literature parameters were converted to the conditions corresponding to the experiment, which were carried out. After performing the calculations, the obtained results were compared with the available experimental data. The experimental and the simulated results were in good agreement, showing a similar tendency

Methodology development and initial results of CFD simulations of methane distribution in the working of a longwall ventilated in a short “Y” manner

The mining in seams with a high methane content by means of a longwall system, under conditions of high extraction concentration, results in exceeding methane concentrations allowed by the regulations at workings of the longwall environment, with the effect of mining machines’ standstill periods. The paper is a part of a study supporting the development of a system for shearing cutting speed control at the longwall, which should substantially reduce the production standstills due to exceeded limits and switching off the supply of electric equipment. Such a control system may be appropriate for longwalls ventilated using “Y” and “short Y” methods. Efficient Computer simulations of the 3D airflow and methane propagation may assist the design and initial evaluation of the control system performance. First chapters present studies that are necessary for a proper formulation of the properties of the longwall model. Synthetic analysis of production during the period of longwall operation allowed one to choose the input assumptions to carry out ventilation-methane computations in a CFD numerical model of longwall Z-11. This study is followed by a description of the model that is used for a case study, considering three variants of the shearer position. Finally, initial simulation results and directions of further studies are discussed

Computational Fluid Dynamics Simulations for Investigation of the Damage Causes in Safety Elements of Powered Roof Supports—A Case Study

The paper describes a case study of the safety hydraulic system damage in the working of a longwall in a Polish coal mine. The safety elements are a component of the powered roof supports which secure the shield against damage during rock burst incidents. The damage event, which occurred in the hydraulic system during the mining process, caused the uncontrolled lowering of the powered roof support height during the mining process. The uncontrolled lowering of a shield may cause the danger of the loss of the stability along the longwall working in the form of a rock burst and collapses and may represent a serious and immediate danger to the safety and health of employees. Based on the results of the computational fluid dynamics methods (CFD) analysis of the safety elements in the hydraulic system of longwall 2-leg shield, the causes of damage were diagnosed and presented. The CFD and the strength analysis by the finite element method (FEM) were used for numerical modeling. The diagrams and maps of changes of parameters having an impact on the damage mechanism in safety elements of the hydraulic leg were developed based on the results of model tests. The forecasted values of stress distributions in the safety system of the hydraulic leg have made it possible to identify the reasons of the damage causes, verified by real observations

Model tests of the rock mass destroying mechanism due to hanging roof in a longwall working

W artykule zwrócono szczególną uwagę na zagadnienie związane z trudnością w utrzymaniu stateczności wyrobiska ścianowego w przypadku niekorzystnego zjawiska zawisania stropu wyrobiska ścianowego w warunkach prowadzonej eksploatacji systemem ścianowym na zawał. W tym celu przeprowadzono badania analityczne i numeryczne z zamiarem określenia parametrów, które determinują proces zawisania warstwy stropu wyrobiska ścianowego. Metodą analityczną badano wpływ parametrów fizyko- -mechanicznych oraz geometrycznych górotworu na proces zawisania stropu wyrobiska ścianowego nad zrobami interpretowany wartością jego ugięcia. Przedstawiono schemat obliczeniowy oraz warunki wytrzymałościowe procesu wydłużania belki (wspornika) w stropie wyrobiska. Natomiast za pośrednictwem obliczeń numerycznych badano wpływ wybranych parametrów modelu Coulomba-Mohra na wartości długości wspornika oraz obniżenia stropu dla określonych parametrów geometrycznych i mechanicznych obudowy zmechanizowanej. Otrzymane wyniki badań modelowych pozwoliły na określenie zależności opisujących wpływ wybranych parametrów mechanicznych skał i geometrycznych warstwy stropu wyrobiska ścianowego na proces jego powstawania i zawisania.The article focuses on the problem in maintaining the stability of a longwall working caused by the unfavourable phenomenon of the hanging roof in a longwall working. Model tests were carried out, intended to define the parameters that determine the process of roof hanging, based on the analytical and numerical methods. The analytical method was applied to study the influence of physic-mechanical and geometrical parameters of the rockmass on the process of roof hanging in the longwall working, interpreted the value of its deflection. The calculation scheme as well as the strength and stress conditions of the roof beam lengthening process in the longwall working are presented. Whereas, in the numerical calculations the influence of parameters of the Coulomb-Mohr’s model on the length and the deflection of the roof strata for given geometrical and mechanical parameters of the powered roof support, were investigated. The obtained results allowed to determine parameters describing influence of the selected mechanical and geometric parameters of the roof of the longwall working on the process of its hanging

Numerical Simulation of the Impact of Unmined Longwall Panel on the Working Stability of a Longwall Using UDEC 2D—A Case Study

The main goal of the paper is numerical simulation for investigation of damage causes in the working of a longwall located under the unmined longwall panel. The paper presents the results of model-based research on the stability of the roof of a longwall working in a zone subject to cave-in mining, taking into account the influence of mining conditions in the form of an unmined coal seam located 115 m above the exploited seam. It presents the geometry of the rock mass under study, the discretization area of the solution, and gives an overview of the assumptions used to build the numerical model. The authors discuss the results of numerical simulations of the influence of mining phenomena on the formation of roof falls in the longwall. Based on the results of numerical simulations, the process of identifying the size of roof falls in a longwall working (loss of stability) was carried out through their appropriate classification. The case presented and analyzed in this paper occurred in one of Poland’s coal mines

Modelling of Gas Flow in the Underground Coal Gasification Process and its Interactions with the Rock Environment

The main goal of this study was the analysis of gas flow in the underground coal gasification process and interactions with the surrounding rock mass. The article is a discussion of the assumptions for the geometric model and for the numerical method for its solution as well as assumptions for modelling the geochemical model of the interaction between gas-rock-water, in terms of equilibrium calculations, chemical and gas flow modelling in porous mediums. Ansys-Fluent software was used to describe the underground coal gasification process (UCG). The numerical solution was compared with experimental data. The PHREEQC program was used to describe the chemical reaction between the gaseous products of the UCG process and the rock strata in the presence of reservoir waters

Study on the possibilities of treatment of combustion by-products from fluidized bed boilers into a product devoid of free calcium oxide

AbstractThe purpose of this paper is to examine the possibility of reduction of free calcium oxide content in waste from fluidized bed boilers by treating them with carbon dioxide under various conditions. The primary examination concerning the possibilities of reducing the content of free calcium oxide in waste included carbonation process in a laboratory, taking into account various parameters of the process. The primary examination has been carried out in a fluidized bed reactor, rotary reactor and a ball mill reactor.Depending on the reaction process, the variables in the examined processes included: reaction time, temperature, amount of the catalyst (water), application of an abrasive material. After completion of the process, the treated material was tested with regard to the content of free calcium oxide. Thus, it was possible to determine the most optimal conditions for treatment of combustion products from fluidized bed boilers, that is the conditions which will ensure reduction of the content of free calcium oxide at an appropriate level, under the physical conditions most similar to normal conditions and in the shortest possible time

In-situ experimental study on hydro-borehole technology application to improve the hard coal excavating techniques in coal mine

Abstract The hydro-mining technology is considered as a promising method of bituminous coal excavation. The paper presents the results of the in-situ experimental campaign and modelling of hydro-cutting technology application. The proposed innovative technology was tested in terms of the effects of the distance between the outlet of water from the nozzle and a sidewall, pressure of the water jet, as well as the type of a nozzle on hydro-mining effectiveness. The hydro-cutting tests of coal seam performed in the Experimental Mine “Barbara” in Poland proved that the increase in water pressure in the range 20–40 MPa only slightly affects the coal face structure, while high pressure, of 80–100 MPa, has a significant impact on a coal face structure. The experimental results also showed the major effects of operating time as well as the distance of the water jet on the effectiveness of coal face mining