Two-Stage Compressors Cut Specific Power 28% at a Coal Mine in Ningxia

At a coal mine in Ningxia, compressed air powers underground tools and equipment. Its efficiency therefore has a direct effect on production cost. The mine’s main supply was a 250 kW single-stage screw compressor that had been running at high load since 2011.

Testing showed how far its performance had fallen:

• Specific power of 7.2 kW/(m³/min) — well above current benchmarks for its size.
• Air delivery down from the rated 42 m³/min to 30.8 m³/min.
• Rising maintenance costs, high energy use and insufficient output.

Wear in the single-stage airend had increased rotor clearances and internal leakage. Meanwhile, the underground roadways were being extended and air demand was rising, so the old equipment could no longer guarantee a stable supply.

After an on-site inspection of the operating environment, equipment condition and air demand, the mine chose a targeted, cost-effective upgrade rather than replacing everything. It installed two SIND DUALLUBE-VPM series two-stage, permanent-magnet variable-speed screw compressors.

Two-stage compression with interstage cooling reduces the work needed per cubic metre of air. Variable-speed drive matches output to fluctuating underground demand. Installation and system commissioning were completed within 15 days.

The two-stage machines place the station in the national Grade-1 energy-efficiency category.

After testing, the new units delivered:

• Specific power reduced to 5.15 kW/(m³/min), 28.47% lower than the old unit.
• About 426,400 kWh of electricity saved per year, based on about 6,750 operating hours.
• About CN¥238,700 (≈US$33,600 at CN¥7.1/US$) lower electricity cost per year, at CN¥0.56/kWh.
• About 243 t lower CO₂ emissions per year.
• Sufficient, stable air supply for the extended underground workings.

The project shows that two-stage compression can deliver fast, measurable savings in mining applications.