Zinc Smelter Retrofit | BOSAN LDPMII VSD Air Compressors
Two 355kW BOSAN LDPMII VSD screw air compressors support continuous production with stable air delivery and approximately 30% overall energy savings.
Two 355kW BOSAN LDPMII VSD screw air compressors support continuous production with stable air delivery and approximately 30% overall energy savings.
- ≈30% — Overall System Energy Savings
- 2 × 355 kW — BOSAN LDPMII VSD Compressor Units
- ≈1,700,000 kWh — Estimated Annual Electricity Savings
- ≈1,020,000 CNY — Estimated Annual Electricity Cost Savings
Project Background
The customer, a zinc smelting and processing company that requested anonymity, operates zinc ingot refining, plate manufacturing and by-product recovery lines. Compressed air powers instrumentation, pneumatic valves, process purging, baghouse filter cleaning and maintenance tools. Air demand is substantial, with continuous production 24 hours a day.
Three Challenges Before the Retrofit
High Unloaded-running Losses
Multiple aging fixed-speed screw compressors used load/unload control. Unloaded running at part load caused significant losses and high electricity consumption per unit of air delivered.
Poor Demand Matching
Air demand fluctuated with production processes, while fixed-speed units struggled to track changing loads, creating a mismatch between supply capacity and actual demand.
Growing Maintenance Burden
Rising failure rates and spare-parts costs for aging equipment threatened the reliable air supply required for continuous smelting operations.
Retrofit Solution: Efficient Compressors and Coordinated System Control
Based on measured air demand and load profiles, the retrofit uses two BOSAN LDPMII 355kW VSD screw air compressors, each with a discharge pressure of 0.7–0.8MPa, to meet the zinc smelter's continuous, high-volume central air supply requirements.
High-efficiency Screw Air End
Optimized rotor profiles and high-efficiency motors reduce electricity consumption per unit of air delivered under rated operating conditions.
Demand-based VSD Air Delivery
Compressor speed adjusts to actual air demand, improving part-load efficiency and reducing unnecessary unloaded operation.
Intelligent Multi-compressor Control
Automatic load-based compressor sequencing handles demand peaks and troughs smoothly, improving overall system efficiency.
Stable Discharge Pressure
Reduced discharge pressure fluctuations provide a more stable air supply for downstream pneumatic equipment and continuous production.
Before and After the Retrofit
| Before · Aging Fixed-speed Compressors | After · BOSAN LDPMII VSD Compressors | |
|---|---|---|
| Operating Mode | Fixed-speed operation with load/unload control | Permanent-magnet VSD with intelligent coordinated control |
| Load-following Capability | Limited, with unloaded-running losses | Responsive, with demand-based speed adjustment |
| Overall Energy Savings | Pre-retrofit baseline | Approximately 30% |
| Air Supply Stability | Moderate | Smaller pressure fluctuations and steadier air delivery |
Energy Savings and Calculation Basis
After commissioning, the customer compared compressed-air electricity consumption per unit of product before and after the retrofit, recording approximately 30% overall energy savings. At approximately 8000 operating hours per year and an electricity tariff of approximately CNY 0.6/kWh, estimated annual savings are approximately 1.7 million kWh and CNY 1.02 million.
Note: approximately 30% is the overall saving reported in the original case. Annual electricity and cost savings are estimates: 1.7 million kWh × CNY 0.6/kWh ≈ CNY 1.02 million. The new compressors' rated power and the saving percentage alone cannot establish the old system's consumption. Verification requires before-and-after metering at equivalent production and air pressure. These figures are not guarantees for other projects.
“Since the BOSAN VSD air compressors went into operation, electricity consumption for compressed air has noticeably decreased and the air supply is steadier. For a smelter operating continuously, reliable air and energy savings bring tangible benefits.”Equipment Manager · Anonymous Zinc Smelting Company
Why Is This Relevant to Metal Smelters?
Non-ferrous metal smelting is energy-intensive and continuous, with compressed-air systems operating at high loads throughout the year. Replacing aging fixed-speed units with efficient VSD compressors enables demand-based air delivery without changing production lines and reduces unloaded-running losses. Processes with fluctuating air demand particularly merit an on-site energy assessment.
Project Questions and Answers
How Much Electricity Can a Zinc Smelter Save Through a Compressor Retrofit?
This case uses two BOSAN LDPMII 355kW VSD screw air compressors and achieved approximately 30% overall energy savings. Actual savings depend on existing equipment efficiency, operating hours and air demand fluctuations, and must be verified on site.
Which Applications Suit a 355kW Screw Air Compressor?
Applications include high-volume central air supply for continuous production, such as instrumentation, pneumatic valves, purging and process air in non-ferrous metal smelting. Selection must account for required pressure and flow.
What Enables BOSAN VSD Compressors to Save Energy?
An efficient air end, permanent-magnet VSD and intelligent coordinated control work together to adjust speed and compressor operating states to demand, reducing unloaded-running losses and improving variable-load efficiency.
What Is the Typical Payback Period for an Energy-saving Retrofit?
The case estimates a typical payback of 1–2 years at approximately 30% energy savings, 8000 annual operating hours and CNY 0.6/kWh. Actual payback also depends on equipment and installation costs and requires a site-specific assessment; the savings percentage alone is insufficient.