What is meant by Surface Condenser?
A Surface Condenser is a closed vessel-type heat exchanger where steam is condensed by transferring its latent heat of vaporization to a cooling medium (typically water) flowing through a network of tubes. The key point is that the steam and the cooling water do not mix; they are kept separate by the tube walls.
How It Works (Step-by-Step)
Imagine a large cylindrical shell with many tubes running through it.
- Exhaust Steam Inlet: Low-pressure exhaust steam from a steam turbine enters the main shell of the condenser.
- Cooling Water Circulation: Meanwhile, cold water (called circulating water) is pumped through the thousands of tubes inside the shell.
- Heat Transfer: The hot steam comes into contact with the cold outer surfaces of the tubes. The steam gives up its latent heat to the cooling water and condenses, changing from a vapor into a liquid (water).
- Collection: The condensed water, known as condensate, is collected at the bottom of the condenser (in a section called the hot well).
- Reuse: This high-purity condensate is then pumped back to the boiler to be turned into steam again, creating a closed cycle.
- Non-Condensable Gases Removal: A vacuum pump or ejector continuously removes air and other non-condensable gases that may have leaked into the system. Maintaining this vacuum is crucial for efficiency.
Key Characteristics
- No Direct Contact: The cooling water and steam are physically separated by the tube walls.
- Condensate Recovery: The condensed steam is recovered and reused as boiler feedwater. This is highly economical and saves on water treatment costs.
- Vacuum Creation: By condensing the steam, its volume reduces dramatically, creating a very low pressure (high vacuum) at the turbine’s exhaust. This maximizes the pressure drop across the turbine, which significantly improves its efficiency and power output.
Advantages of Surface Condensers
- High Thermal Efficiency: Enables a high vacuum in the turbine exhaust, leading to more work output from the same amount of steam.
- Reuse of Condensate: The condensate is high-purity hot water, so reusing it as boiler feedwater saves fuel and water treatment chemicals.
- Suitable for Large Plants: Ideal for high-capacity steam power plants like those in thermal and nuclear power stations.
- Cooling Water Flexibility: The same cooling water can be used repeatedly in a cooling tower circuit.