Numerical simulation of ventilation air flow in underground mine workings

S.M. Aminossadati

The University of Queensland, CRCMining, Brisbane, Australia

K. Hooman

The University of Queensland, Brisbane, Australia

Источник: http://www.smenet.org/uvc/mineventpapers/pdf/038.pdf

1ABSTRACT: In recent years, Computational Fluid Dynamics, CFD, has been commonly utilized in the mining industry to model the fluid flow behavior in underground mine workings. This paper uses CFD modeling to simulate the airflow behavior in underground crosscut regions, where brattice sails are used to direct the airflow into these regions. Brattice sails are cost effective ventilation control devices for temporary or permanent use in underground mining. They can be used to deflect air into the unventilated areas such as crosscut regions. Their design and installation is a fundamental issue for maintaining a sufficient supply of fresh air and achieving effective air circulation and contaminant removal. At the same time, they should have little impact on the mine ventilation system. This paper presents the results of a two-dimensional CFD model, which examines the effects of brattice length on fluid flow behavior in the crosscut regions. The results of this study will assist in understanding the ventilation air behavior and in determining the optimum size of brattice curtain (sails), which provide a highly effective contaminant removal from the unventilated mine areas. This, in turn, helps the mine ventilation designers to meet the mine safety requirements.

1 Introduction

In underground mining, it is often necessary to provide fresh and cool airflow in unventilated areas such as crosscut regions. Ventilating air is employed to dilute and remove undesirable or dangerous gases such as methane and to reduce the air temperature in these areas. Crosscut regions are frequently used as crib rooms when their one end is sealed and the other end is open to the mine airways. They are also used for accommodating the mining equipment, electrical transformers, or drilling machineries. In many underground mining operations, it is common practice to direct and control the airflow into the unventilated areas such as crosscut regions by means of hanging a thin, lightweight, and fire resistant cloth known as brattice curtains (or sails). Brattice sails are hung against the ceiling across tunnel openings and are extended in the crosscut regions, so that the airflow can be diverted away from the tunnels and flow into the crosscut regions. Companies are continuously attempting to provide innovative products and solutions for a range of ventilation related applications of brattice, to be cost effective, flexible, durable, and tear and fire resistant. The structure of brattice sails and the influence of various arrangements and qualities of ventilation brattices on the distribution of air through various areas of underground mines has been extensively studied and well documented in the literature. Louw (1974) found a wide variety of airflow patterns for different brattice locations and qualities. Kissell and Matta (1979) described a proper ventilation system by means of a conventional brattice. Standish (1983) investigated the effects of different brattice types on the ventilation characteristics.

In a notable study, Taylor et al. (1992) evaluated the face ventilation for two face ventilation techniques that utilize either blowing brattice or a jet fan. The influence of brattice sails on the reduction of methane concentration in face ventilation was investigated by Smith and Stoltz (1991) and Thimons et al. (1999). They evaluated the effectiveness of a blowing face ventilation system in controlling methane liberation in the face area while ventilation was carried out with brattice sails with different configurations, qualities, and distances from the face. They argued that the methane concentration is affected by the quantity and quality of fresh air reaching the face, as expected. Moreover, it was shown that the selection of the brattice setback distance could significantly improve ventilation to the end of box cut.

Lee et al. (1996) investigated the effects of brattice characteristics on the effectiveness of ventilation on reductions in concentration of diesel particulate matter. They developed computer models to study the generation, transfer, and distribution of diesel particulate matter in coal mine sections. They found that the reduction of diesel particulate matter is significantly influenced by ventilation schemes using vent tubing and brattice, exhaust locations and direction of ventilation.

Literature indicates a number of studies on the effectiveness of brattice sails in controlling respirable dust. Tien (1988) and Potts and Jankowski (1988) studied the airflow pattern in the working face and showed that the usage of a brattice is essential in order to avoid recirculation and control respirable dust in the face area. They argued that the heading airflow was maximized by properly installing the brattice curtain.

Recently, researchers have studied the effects of brattice setback distance on the flow-field behavior in underground workings. Goodman and Pollock (2004) studied the effects of line brattice setback distance and showed that changes in setback distance affected return airway dust levels and untransformed gas levels around the cutting drum. They concluded that changes in the brattice flow quantity and setback distance impacted effectiveness of the face ventilation. Taylor et al. (2005) developed a test system to measure the airflow profiles at locations between the face and the end of the brattice for different brattice setback distances, intake flow quantities, and entry widths. They found that the entry geometry had a significant effect on airflow patterns. Goodman et al. (2006) used a line brattice for a series of laboratory evaluations to examine the impact of brattice setback distance. They showed that increasing brattice setback distance often elevated dust levels, likely due to the reduction of the amount of airflow reaching the face.

Along with the development in experimental studies (some of them have been mentioned above), there have been a growing number of numerical studies addressing the problem. One of the important reasons for using a computational model is the superlative illustrative presentation of the results, which allows designers to have an increased understanding of the problem. A good understanding of the fluid-flow behavior results in improving the accuracy and, consequently, safety of designs with minimum cost of the investigation. However, comprehensive validation process of CFD modeling against actual mining experiments is an important issue in the application of the CFD results in appropriate designing of mine ventilation systems. Simulation of airflow in underground mine workings is one example of the application of CFD modeling in mining industry. For instance, Van Heerden and Sullivan (1993) applied CFD in evaluating and improving environmental conditions in continuous miner and road header sections. Even though, they did not validate their model, the results presented a good understanding of the movement of dust and methane in the predicted flow fields. Srinivasa et al. (1993), however, validated their numerical results, from commercial software, using field trail measurements and obtained a good degree of agreement. Of particular interest were air velocities and the effect of dust control techniques on dust concentrations at a typical longwall face. Comparing their results with analytical predictions, Brunner et al. (1995) used CFD to evaluate the effects of varying the airflow rate in a ventilated airway on the layering along the roof of smoke and hot gases due to a vehicle fire. In an interesting study, Wala et al. (2003) reported that the proper development of the computer code, the application of software, and selection of the grid size and turbulence modeling are crucial when CFD is considered as a tool to evaluate the mine face ventilation. Silvester et al. (2004) used a k-Ε model to account for turbulence in their three dimensional model for the ventilation system within an underground crushing installation.

Absent in the above studies; however, is a numerical analysis of the airflow behavior within a crosscut region of an underground mine. The problem is of particular interest not only for providing the ventilation air to those hard-toventilate regions but also for washing the contaminants out of these regions. This paper aims to address the importance of this crucial safety issue in underground mine environment.