Mine Fans

Fans provide the pressure that drives mine airflow. Learn axial and centrifugal fans, fan characteristic curves, the operating point with the mine resistance curve, fan power and efficiency, fan laws for speed changes, fans in series and parallel, and main vs booster vs auxiliary fans.

Main mine fans can exceed 3 MW each and run 24/7 for decades — so fan selection and efficiency have a major impact on cost and carbon emissions. The fan must deliver the required flow at the mine's resistance, operating in a stable region of its curve.

An analogy

The fan curve is what the fan can push; the mine curve is what the mine demands. Where they cross is where the system settles — like supply meeting demand.

Fan types

Axial fans (air flows parallel to shaft; blade angle adjustable; compact, efficient at high flow) and centrifugal fans (air turned 90°; high pressure, stable). Main fans are usually installed at the top of an upcast shaft, exhausting air (negative pressure system).

Characteristic curves

Fan curves plot pressure, power and efficiency versus flow. The operating point is the intersection with the mine resistance curve p = RQ². Operating near the stall region of axial fans causes instability and vibration.

Changing duty

Variable speed drives, blade-pitch adjustment and inlet vanes change duty. Fan laws: 10 % more speed → 10 % more air, 21 % more pressure, 33 % more power. Fans in series add pressure; fans in parallel add flow.

Booster fans and control

Underground booster fans reduce main fan pressure in large mines but require careful control to avoid recirculation. Ventilation-on-demand systems adjust VSDs automatically based on sensors and schedules.

Formulas

• Fan power: P = p Q / η
• Fan laws (speed): Q ∝ N, p ∝ N², P ∝ N³
• Operating point: p_fan(Q) = R_mine Q²
• Annual energy cost: Cost = P × hours × tariff

Worked example: Fan power and cost

Given: p 2500 Pa, Q 300 m³/s, η 0.75; 8760 h/yr, $0.10/kWh

Find: Power and annual cost.

• P = 2500 × 300/0.75 = 1 000 000 W = 1000 kW
• Cost = 1000 × 8760 × 0.1 = $876 000/yr

Answer: 1 MW, ≈ $0.88M per year

Worked example: Fan laws

Given: Speed increased 10 %

Find: Effect on Q, p, P.

• Q × 1.1, p × 1.21, P × 1.331

Answer: +10 % air costs +33 % power

Common mistakes

• Wrong: Selecting a fan only for today's mine. — Right: Check duty points for future, deeper layouts.
• Wrong: Operating in the stall region. — Right: Keep operating point on the stable, efficient part of the curve.

Applications

• Main fan selection: Duty points over the mine life.
• Energy savings: VSDs and efficient blade designs.
• Emergency reversal: Fan reversal plans for fires.

Key takeaways

• P = pQ/η.
• Operating point = fan ∩ mine curve.
• Q ∝ N, p ∝ N², P ∝ N³.
• Plan for future mine resistance.

Going further

• Booster fan control: Avoiding recirculation underground.
• Fan efficiency audits: Field measurement vs manufacturer curves.
• Controlled recirculation: Reusing air safely with monitoring.