Page 112 - Advances In Productive, Safe, and Responsible Coal Mining

96 Advances in Productive, Safe, and Responsible Coal Mining

6.8 Ventilation network planning for metal
and nonmetal mines

Metal and nonmetal mines often feature dead-ended drifts that are several hundred
meters long. These dead-ended drifts require auxiliary ventilation using ventilation
tubing to pump fresh air to the face or exhaust contaminated air from the face. In metal
and nonmetal mines, ventilation of dead-ended drifts can be reduced to a minimum if
there are no persons working in the face and no equipment is operating in the area.
Often, auxiliary fans can be shut down until the next person or vehicle enters the drift.
Ventilation planning must account for the intermittent operation of these auxiliary
fans. Large mines may operate one hundred or more auxiliary fans, and accounting
for all possible combinations of auxiliary fan operation is not feasible. The ventilation
engineer must design for various peak demand and worst-case scenarios, which
requires close coordination with both mine planning engineers and operators.
Some mines install remotely controlled auxiliary fans that can be turned on, off, or
varied in speed based on current demand. Demand is either triggered by diesel
vehicles passing certain control points prior to entering the drift, or by levels of diesel
particulate, CO, and NO x contamination determined by AMS stations. Some
ventilation-on-demand (VOD) systems are controlled by a central computer system,
while others operate with local control circuits. It should be noted that controls for
auxiliary fans must be capable of turning each fan on in anticipation of the diesel
equipment entering the stope. By the time the equipment enters, ventilation must
be fully developed. Likewise, VOD fans must be kept running until the contaminant
plume from diesel or blasting has been sufficiently diluted.
Proponents of VOD technology often claim savings in power cost, but investment
costs for a VOD system may be substantial, especially when considering that auxiliary
fans may need to be replaced with higher-capacity, variable-speed, controlled models.
Also, the overall mine ventilation system must be designed for sufficient additional
capacity that meets the highest potential demand from the control system, especially
as operating times for VOD fans tend to overlap as contaminants are cleared.
Some metal and nonmetal mines practice controlled recirculation of air that con-
tains contaminants at levels far below designated limits. Controlled recirculation can
reduce the amount of fresh air needed to ventilate the mine, but must be carefully mon-
itored to ensure that all contaminant and dust limits are being met at all times. Con-
trolled recirculation is generally not permitted in coal mines due to the explosion
hazard of accumulating methane.

6.9 Air cooling and refrigeration

In deep metal and nonmetal mines, ventilation air must often be cooled to maintain
acceptable working conditions. A few deep European coal mines also require air
cooling. The human body has evolved to maintain a core temperature below 38.5°
C (101°F). This means that, as a rule of thumb, the dry bulb mine air temperature