Five Two-Stage VSD Compressors Cut Energy 31% at a Steel-Pipe Plant in Chengdu

The client is a large steel-pipe manufacturer in Chengdu, Sichuan Province. It produces straight-seam welded pipe, square and rectangular hollow sections and hot-dip galvanised products for domestic and export markets. Compressed air is a key utility across its forming, welding and galvanising lines.

The existing station ran eight older fixed-speed screw compressors, five of 132 kW and three of 55 kW. Energy monitoring showed that the station’s overall efficiency was well below current standards. Air demand varies with shift patterns, product mix and line speed, and fixed-speed machines cannot follow those swings without unload losses. As part of a green-production programme, the company decided to rebuild the station.

After the energy consumption of the old equipment was monitored and analysed, the station was rebuilt around five 175 kW SIND DUALLUBE-VPM series two-stage, permanent-magnet variable-speed screw compressors. These replace the eight old machines.

The design took into account the plant’s different working hours, consumption patterns and flow fluctuations. A station master control system coordinates all five compressors and the auxiliary equipment:

• sequencing and load balancing based on real-time supply and demand;
• timed and pressure-based control for unattended operation;
• data collection through IoT gateways and edge devices, with dashboards in the compressor room, the control room and on mobile devices;
• equipment-health and supply models for the whole station, with operating reports uploaded to the cloud.

The station was tested and certified to meet the national Grade-1 energy-efficiency standard.

After commissioning, the station’s overall transmission efficiency was measured on site:

• 64.9% overall transmission efficiency.
• 31.3% energy saving compared with the previous station.
• About 900,000 kWh saved per year.
• 124.6 m³/min average air supply delivered by the new station.
• Automated, unattended operation with full remote visibility.

Replacing eight fixed-speed machines with five two-stage variable-speed units under system-level control turned the station into one of the plant’s most efficient utilities.