Air Cooled Condenser —Direct Air Cooled Condensing System
What is an Air Cooled Condenser (ACC)?
In the steam cycle system of a thermal power plant, the Air Cooled Condenser (ACC) serves as an innovative alternative to traditional water-cooled systems.
Characteristics:
- Significant water-saving efficiency
- Environmental benefits
Function: It utilizes ambient air to condense the low-pressure exhaust steam from the steam turbine into water, thereby closing the thermal cycle.
Application – Direct Air Cooled Condensing System
The air cooled condenser (ACC) is the core equipment of the direct air cooled condensing system. Essentially, this system is a complete "air cooling" solution built around the ACC.
Core Principle: The turbine exhaust steam is directed directly into the ACC, where it is condensed by air.
System Characteristics: The system is straightforward, has relatively lower investment costs, and is currently the mainstream technology.
Main Components of a Direct Air Cooled Condensing System
① Air Cooled Condenser (ACC) Unit
The Core Heat Exchange Component
Consists of dozens to hundreds of modularly arranged large-diameter single-row finned tube bundles. These bundles are functionally divided into:
- Main Condensing Zone: Condenses the majority of the steam.
- Counter-flow Zone: Cools non-condensable gases and further subcools the condensate to prevent freezing.
② Forced Draft Ventilation System
Provides Cooling Air
Comprises multiple large-diameter (up to 10 meters or more), variable-frequency controlled axial fans. They are typically installed below the tube bundles, providing either forced draft (air pushed upwards) or induced draft (air pulled downwards).
③ Steam Distribution and Condensate Recovery System
- Exhaust Steam Ducting: Large-diameter piping that transports the exhaust steam from the low-pressure turbine outlet to the ACC platform.
- Steam Distribution Header: A main header located above the tube bundles that ensures even steam distribution to each column.
- Condensate Collection System: Collects condensate from the bottom of all tube bundles, channels it to a hotwell, from where it is pumped back to the boiler feedwater system.
④ Structural Support and Sealing System
- Large Steel Structure Platform: A heavy-duty platform supporting all equipment.
- Windbreak Walls: Enclose the perimeter of the platform to reduce interference from crosswinds on airflow, ensuring cooling efficiency.
Core Heat Exchange Elements of the ACC
① Brazed Single Row Finned Tube
The base tube is a large cross-section rectangular flat tube, with continuous aluminum serpentine fins welded on both sides.
Structural Features: Characteristic single-row tube design with numerous parallel steam passages and large hydraulic diameter.
The large cross-section provides substantial steam volume and short flow paths, resulting in low steam-side pressure drop which is beneficial for maintaining turbine vacuum. However, the rectangular cross-section typically presents higher air-side pressure drop compared to elliptical tubes, necessitating optimized fin design to reduce resistance.
Excellent Freeze Protection: The large steam space and single-row design significantly reduce the risk of internal freezing.
② Hot-Dip Galvanized Elliptical Finned Tube
The tube is formed into an elliptical cross-section, typically sheathed with rectangular steel fins, and the entire assembly undergoes hot-dip galvanizing. Due to environmental considerations, brazed elliptical finned tubes are now more commonly used.
Structural Features: Early designs often used double or triple-row arrangements to form tube bundles.
Superior Aerodynamics: The streamlined elliptical cross-section creates a smaller wake region as air flows over it, leading to lower air-side pressure drop.
Good Freeze Resistance: The shape facilitates drainage of the condensate film by gravity.
Pressure Withstanding: Relatively weaker; the elliptical structure has lower pressure-bearing capacity compared to a round tube.
Strong Corrosion Resistance.
Condenser vs. ACC vs. Air Cooled Heat Exchanger
In the field of industrial heat exchange, the terms Air Cooled Condenser (ACC), Air Cooled Heat Exchanger, and Condenser are often confused due to their similar names and association with "cooling." However, they differ fundamentally in function, design, and application. Clarifying these concepts is crucial for correct selection and system understanding.
| Aspect | Condenser | Air Cooled Condenser (ACC) | Air Cooled Heat Exchanger |
|---|---|---|---|
| Nature & Definition | Functional General Term | A Specific Subset of Condensers | A Category of Independent Industrial Heat Exchangers |
| Core Function | Condenses steam into liquid (water) | Uses air to cool and condense steam into liquid | Uses air to cool process fluids (oil, water, gas, etc.) |
| Phase Change? | Yes (Steam → Water) | Yes (Steam → Water) | Typically No (Sensible heat exchange only) |
| Operating Pressure | High vacuum or negative pressure | High vacuum or negative pressure | Atmospheric or positive pressure |
| System Integration | Core of the thermal cycle, tightly coupled with turbine and boiler | Core of the power plant "Air Cooling Island," large and complex | Independent process auxiliary equipment, modular design |
| Primary Applications | Thermal power plants, nuclear plant thermal cycles | Direct air-cooled thermal or nuclear power plants | Petrochemical, metallurgy, compressed air systems, data centers, etc. |
Application Scenarios for ACCs
- Coal-fired power plants in water-scarce regions.
- Direct air-cooled power stations.