While screw air compressors are widely used, their energy consumption has become a key concern. Electricity accounts for 77% of total costs, followed by maintenance (18%), and equipment investment (only 5%). Thus, optimizing energy use through waste heat recovery is critical.
1. Common Heat Recovery Methods & Applications
Waste heat from air compression can be recycled via heat exchangers to warm water or air, used for heating, process needs, or preheating boiler feedwater. Systems include oil-injected and oil-free screw compressor heat recovery, based on cooling methods:
• Cooling Methods: Air-cooled and water-cooled. Water cooling is preferred for better efficiency (higher specific heat) and lower temperatures, suited for most industrial settings.
• Heat Recovery Systems: Classified as air-cooled or water-cooled. Water-cooled systems dominate retrofits due to stable heat output and versatile hot water applications.
Advantages of Heat Recovery:
• Eco-friendly: No emissions, reduces energy waste.• Cost-saving: Free hot water for daily use or heating.
• Enhances compressor performance: Lowers operating temperature, increases output, and extends oil life.
• Aligns with energy-saving policies, generating economic and social benefits.
2. Air-Cooled Heat Recovery Systems
These use heat exchangers to warm outdoor air for heating offices or workshops in winter (via adjustable dampers). In summer, hot air is exhausted. Simple, low-cost, and ideal for nearby heat users.
3. Water-Cooled Heat Recovery Systems
• Oil-injected Compressors: Recover heat from 80–100°C oil-air mixtures. Retrofits replace cooling towers with heat exchangers, producing hot water. Pros: Stable oil temperature, high efficiency. Cons: Prone to scale, limited auto-control.• Oil-free Compressors: Handle 170–190°C compressed air.
o Primary Heat Exchange: Directly cools hot air for hot water. Pros: Stable air outlet temperature. Cons: Severe scaling, high maintenance.
o Secondary Heat Exchange: Adds a softened water loop to reduce scaling, improving efficiency and stability.
