Working principle of waste heat recovery of air compressor

The working principle of air compressor waste heat recovery is to recover the waste heat generated during the operation of the air compressor and convert it into usable thermal energy (such as hot water or hot air), thereby improving energy utilization efficiency. Its core process can be divided into the following three parts:

1. Heat Source and Distribution

When an air compressor operates, approximately 80%-95% of the electrical energy is converted into heat, primarily from:

1. Compression Process Heat Generation: When air is compressed, mechanical energy is converted into heat, forming high-temperature compressed air (temperatures can reach 80-100°C).

2. Mechanical Friction Heat Generation: High-speed operation of components such as screws and bearings generates frictional heat, which is dissipated through lubricating oil circulation.

3. Cooling System Heat Discharge: The traditional cooling system (air-cooled/water-cooled) discharges heat into the environment, resulting in energy waste.

2. Working Principle of the Heat Recovery System

1. Heat Exchange Process

• Oil Circuit Heat Recovery: High-temperature lubricating oil is directed through the oil circuit to a plate/shell-and-tube heat exchanger for heat exchange with cold water. The oil temperature is reduced to a suitable range (e.g., 58-80°C), and the cold water is heated to 50-80°C.

• Air Circuit Heat Recovery: Some systems connect an air heat exchanger in series to recover waste heat from the compressed air.

• Temperature Control Mechanism: A mechanical thermostatic valve or bypass system automatically regulates the oil flow to ensure stable operating temperature of the air compressor (typically controlled at 80-90°C), preventing low-temperature condensation or high-temperature oxidation.

2. System Components

• Core Components: Heat exchanger (e.g., Danfoss brand), circulation pump, piping, and insulation materials.

• Control System: Temperature/pressure sensors and a PLC controller for real-time monitoring to ensure safe operation.

• Auxiliary Systems: Water replenishment device, softened water treatment, etc., to prevent scaling from affecting heat exchange efficiency.

3. Advantages and Application Scenarios

1. Energy Saving Advantages

• Reduce Energy Consumption: Replaces traditional heating methods like electric boilers or gas boilers, achieving zero additional energy consumption.

• Improve Air Compressor Efficiency: Stabilizing oil temperature can increase the air output of the compressor (output increases by 0.5% for every 1°C temperature drop).

• Reduce Cooling System Load: Deactivate or reduce the operation of the original cooling fan/cooling tower, saving electricity.

2. Typical Applications

• Domestic Hot Water: Employee showers, canteen water use.

• Industrial Use: Electroplating tank heating, pure water preparation, process hot water (50-70°C).

• Air Conditioning / Heating: Winter space heating or for constant temperature and humidity workshops.

4. Technical Extensions

• Water-Cooled Air Compressor Modification: Directly connect a plate heat exchanger or water-source heat pump in series to utilize the waste heat from the cooling water.

• Centrifugal Air Compressor Recovery: Add an aftercooler for the high-temperature air after three-stage compression.

• Oil-Free Screw Compressor Recovery: Utilize a series compressor heat exchange process, achieving a recovery rate of up to 90%.

The air compressor waste heat recovery system not only achieves efficient energy utilization but also extends equipment life and reduces carbon emissions, offering significant comprehensive economic benefits. Specific technical solutions need to be customized based on the type of air compressor and the heat demand scenario.