Full-Chain Air System Upgrade Saves 25.7% at a Machinery Plant in Jiangsu

A large machinery manufacturer in Jiangsu Province relies on one central compressed air station to supply its stamping, welding, painting and assembly workshops. The station had four 55 kW screw compressors (two fixed-speed and two standard variable-speed), conventional dryers and filters, and an ageing distribution network.

After eight years of operation, the system had a range of problems:

• high energy consumption;
• large pressure fluctuations;
• heavy pipeline losses;
• uncoordinated compressor scheduling;
• wasted air at the point of use.

Earlier single-machine VSD retrofits had not changed the overall picture: the average unload rate was 28%, pipeline leakage 22% and network pressure loss 0.12 MPa.

Instead of another single-machine fix, the whole chain from compressors to end use was upgraded in five steps:

1. Compressors. The two fixed-speed units were replaced with SIND SILVERLUBE-VPM series permanent-magnet variable-speed compressors. The two remaining machines were overhauled with new seals and bearings and optimised settings. A SIND heat-recovery system was added to the SIND compressors.
2. Pipework. An ultrasonic leak survey was carried out and leaks repaired, undersized old pipes were replaced, and a ring main was built with fewer bends and valves.
3. End use. Unnecessary consumption at workstations was eliminated, damaged outlets were sealed and inefficient end-use devices replaced.
4. Control. A multi-compressor group controller coordinates and load-balances all four machines.
5. Operations. Standard maintenance, energy-monitoring and air-usage review procedures were introduced.

Measured after three months of stable operation:

• 25.7% energy saving. Daily station consumption fell from about 4,200 to 3,120 kWh, a saving of 1,080 kWh per day.
• Specific energy of 0.083 kWh/m³.
• Unload rate down from 28% to 7%; leakage down from 22% to 6.5%; pressure loss down from 0.12 to 0.04 MPa.
• CN¥310,800 per year saved on electricity (at CN¥0.8/kWh), plus about CN¥42,000 per year saved on heating from recovered heat, for a total of about CN¥352,800 (≈US$49,700 at CN¥7.1/US$).
• 42% fewer equipment failures and 28% lower annual maintenance cost.