Mining Project: Ventilation of Longwall Faces

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Principal Investigator	Steven Schatzel - Request information
Start Date	4/1/2014
End Date	9/30/2018
Objective	To improve the capabilities to detect changing ventilation conditions along a longwall face arising from poor roof caving characteristics and increasing face length.
Topic Areas	Explosion Prevention Ventilation Overview

Research Summary

Longwall mining presents a particularly complex ventilation challenge—not only are large quantities of methane gas liberated during mining, but large methane reservoirs are created concurrently. This necessitates constant vigilance on the part of mine operators to maintain ventilation. Incomplete caving may allow face air to flow behind the shield line resulting in a decrease of airflow on the face. This condition may be magnified in the case of wider faces with increased resistance to airflow reaching the tailgate corner.

To address this problem, this project had two research aims, as follows:

Identify flow paths for ventilation airflow along longwall panels with variations in roof caving characteristics and longwall face lengths.
Specify locations and protocols for implementing continuous ventilation monitoring along the shield line to provide early detection of gas exchanges between face and gob, and thus improve a mine's ability to monitor and control ventilation and methane concentrations around the face.

In this project, various aspects of longwall ventilation research were investigated using multiple research approaches, including field studies, physical and numerical modeling. In addition, an evaluation of a methane monitor using fiber-optic technology was conducted to study the impact of smoke on the monitor’s performance.

Field Studies

NIOSH researchers designed a series of field studies to investigate longwall face airflow and possible exchanges with the gob. With changing face lengths and caving characteristics, these factors are important to consider. As safe concentrations of gas must be maintained and these pathways were not part of the ventilation design, these pathways of movement could be relevant to gas monitoring on the face. Field data show that pathways of movement exist both on the longwall face and in the vicinity of the shield legs. Evidence of alternate pathways of movement and the effects of differing mining and ventilation plans on face air transport and face-gob air exchanges were recently published in the papers listed at the bottom of the page.

Physical Modeling

In order to study longwall ventilation in a controlled environment, researchers built a unique physical model called the Longwall Instrumented Aerodynamic Model (LIAM) in a laboratory at the NIOSH’s Pittsburgh Mining Research Division (PMRD) campus. LIAM was built to maintain critical details of the face and mining machinery. In addition to its research applications, LIAM also serves as a dynamic tool for demonstrating longwall ventilation to mining industry stakeholders and the research community. LIAM’s development and applications are discussed in a paper referenced at the bottom of the page. A virtual tour of LIAM can be accessed below.

LIAM Virtual Tour Navigation Instructions:

When entering the LIAM tour, use your mouse to look around by holding down the left mouse key and dragging.
To move forward, drag to the direction you want to go and the left-click.
To view information tags, double-click. Exit the information tag by clicking the "x" in the top right corner.
For simpler viewing, click the Play button in the bottom left-hand corner.
The upward arrow in the bottom left corner pops up a bar with pre-selected spots in the tour.

Currently, NIOSH researchers are pursuing the development of site-specific simulations with LIAM. The goal is to use the data from field sites to simulate the ventilation of a longwall panel to help address issues related to airflow on the face and gas emissions from the gob.

NIOSH welcomes further collaboration with active longwall mines to help advance this research and to offer mines a better understanding of their site-specific ventilation. We also welcome underground miners, mining students, industry experts, and researchers to visit the PMRD campus for a demonstration of longwall ventilation using LIAM.

Numerical Modeling

NIOSH researchers developed numerical simulations of air movement and pathways to investigate transport characteristics on the longwall face and in the active panel gob. Two numerical models were created. The first uses a discrete fracture network (DFN) model of reservoir transport longwall gobs. This DFN model produces a more accurate representation of gas movement through rock fractures instead of averaged movement throughout gob rubble. The DFN model output was linked to a ventilation model using computational fluid dynamics (CFD) to generate an image of gas movement from the gob, onto the face, and in ventilation air. The second is a CFD model developed to show gob and face air movement in LIAM, which is NIOSH’s physical model for ventilation experiments. This model shows how airflow changes throughout LIAM with different mining and ventilation configurations.

All three tasks (field studies, physical modeling, and numerical modeling) complement each other and show rapid air/gas migration through the front of the gob zone behind the shields with no void space and normal roof caving.

Fiber-optic Methane Monitor

A remote fiber-optic methane monitor developed under a NIOSH contract provides capabilities that may be useful for continued operation after initial fires or explosions. NIOSH researchers conducted experiments to evaluate a prototype fiber-optic methane monitor exposed to smoke using a smoke chamber to simulate atmospheric conditions in an underground coal mine after a fire or explosion. The experiments used test fires of different combustible sources commonly found in mines — Douglas-fir wood, SBR belt, and Pittsburgh seam coal. The potential for using the monitor after an initial fire or explosion and the impact of smoke on optical signal losses and soot accumulation on a protective sensor screen is discussed in an article in the International Journal of Mining Science and Technology, referenced below.

Face Ventilation Suggestions Based on NIOSH Research

Based on this project research, NIOSH researchers have developed suggestions to ensure that alternate airflow pathways near longwall faces were not potential sources of increased methane hazards and did not impact main face airflow levels. These suggestions included the use of a device designed to provide more predictable and consistent airflow pathways and quantities on longwall faces. In-house tests suggest a device on the longwall face that covers part of the shields starting near the headgate corner and extending across a portion of the first fifteen shields. Laboratory tests of a prototype showed an increase in airflow quantity on the longwall face averaging 10 to 20 percent. A second option suggested by NIOSH research is the installation of a static methanometer on the face about 10 shields from the tailgate corner to check potential airflow moving from the back of the shields into the main face air stream.