Three strategies for ventilation control in underground mines

An underground mine is a busy environment with lots of drilling, blasting, crushing, conveying, hauling and hoisting, all in an effort to get the ore to surface. Typically, fresh air is delivered to the main backbone of the mine via intake raises or a fresh air portal by using large intake or exhaust fans. The contaminated air is exhausted to the surface via raises or an exhaust portal. Auxiliary fans are then used to deliver fresh air, when required, to the remote working faces attached to this backbone.

Three possible strategies

There are three main strategies for controlling fresh and exhaust air fans:

1. Scheduling: During normal daily mine operations, fresh air requirements are generally based on mobile diesel equipment airflow requirements. However, when blasting, more contaminants are added to the airflow. Prior to any blasting, all personnel are sent back to the surface for two hours or more, which cuts into effective underground production time. However, by scheduling and increasing your main fan airflow using variable speed drives (VFD) on the main surface fans and remotely controlled starters on auxiliary fans, you can effectively decrease the blast clearing period by 50%. This allows personnel to return to the faces more quickly and resume normal mine operations.
2. Telemetry: Personnel and mobile equipment can be equipped with radio-frequency identification (RFID) tags, allowing control room operators to view the activity underground by location. Since the RFID tags communicate via wireless signals, additional underground network infrastructure would be required to communicate with the tags and send the data back to the surface. Telemetry or asset tracking software would also be required to provide the exact or general area of the tag location. Using telemetry allows auxiliary fans, when equipped with either normal starters, two speed starters or, in some cases, VFDs, to control the required airflow based on the type of equipment entering or the activity taking place in the heading.
3. Environmental: Instrumentation can be installed throughout the underground mine to monitor airflow, temperature and parts per million concentrations of the various contaminants produced by diesel or other equipment. Regulations exist for determining the amount of airflow required based on the brake horsepower of typical diesel equipment, as well as for contaminants such as carbon monoxide (CO), diesel particulate matter (DPM), nitrogen oxides (NO_x) and other hazardous gases. By monitoring these gases, fans could be programmed to increase fresh air flow if these gases are detected.

Investments that pay off

Whichever option is chosen, implementing any type of ventilation system control or automation means investing in worker health and safety as well as in new infrastructure and equipment. The capital cost will need to be weighed against potential energy savings, the fresh air required in the various areas of the mine, any impacts on production and the projected end-of-mine life.

Depending on the strategies selected to control the ventilation system, additional ventilation or automation experts may be required to support the new system. This will also affect underground personnel who will be wearing RFID tags for tracking purposes.

Assessment is an essential step

The first step is to perform an assessment of mining operations and current infrastructure to determine whether the mine is a good candidate to implement various strategies to automate ventilation system control.

Many factors would be examined in the assessment, including:

• Estimate of current energy consumption of the ventilation system based on the total horsepower of all ventilation fans
• Mining plan, leading to the end-of-mine life
• Shift changes and blasting schedules
• Ventilation model to ensure adequate fresh air is available when and where it is required

Then, a comprehensive report would provide the following:

• Capital cost estimate for any required infrastructure
• Updated energy consumption estimate based on selected control strategies
• Return on investment (ROI) calculation
• Change management strategy to implement the solution

In conclusion

Adding control strategies to an underground mine ventilation system is a viable solution for reducing operating costs, providing additional insight into the system and increasing health and safety benefits by eliminating hazardous contaminants and knowing where personnel are located using telemetry. A comprehensive audit and assessment by BBA experts can help determine whether it makes sense for your mine!