What is the function of a condenser in a power plant?

Short Answer:

The function of a condenser in a power plant is to convert exhaust steam from the turbine back into water by removing its heat and turning it into liquid. This process takes place at low pressure to help improve the efficiency of the steam cycle. The condensed water is then pumped back to the boiler to be reused, saving both water and energy.

By maintaining low pressure at the turbine exit, the condenser allows more expansion of steam, resulting in higher power output from the turbine. It also ensures a continuous flow of water and steam within the Rankine cycle.

Detailed Explanation:

Function of a condenser in a power plant

In steam-based power plants, the Rankine cycle is commonly used for electricity generation. This cycle involves heating water to produce steam, using that steam to rotate a turbine, and then cooling the steam back into water before returning it to the boiler. The device responsible for this cooling process is called a condenser.

A condenser is placed after the steam turbine in the power plant. Its job is to remove the remaining heat from the exhaust steam coming out of the turbine and convert it into liquid water (condensate). This process is essential for both the efficiency of the power plant and the recycling of water.

How a Condenser Works

  1. Steam Entry from Turbine
    After steam expands and does work in the turbine, it exits at low pressure and temperature. This exhaust steam enters the condenser chamber.
  2. Heat Removal by Cooling Water
    The condenser contains tubes through which cold water flows (usually from a cooling tower or natural source). The steam surrounds these tubes and gives off its heat to the cold water inside.
  3. Condensation Process
    As the steam loses heat, it changes its phase from vapor to liquid (condensate). This liquid is collected at the bottom of the condenser.
  4. Water Pumping to Boiler
    The condensed water is then sent back to the boiler using feedwater pumps, completing the closed cycle.

Importance of the Condenser in Power Plants

  1. Improves Thermal Efficiency

Condensers maintain low pressure at the turbine exit. This allows more expansion of steam in the turbine, extracting more energy, which increases the overall efficiency of the power plant.

  1. Condensate Recovery

The steam is converted back into pure water, which is then reused in the boiler. This reduces the need for fresh water and saves resources.

  1. Maintains Cycle Continuity

Without a condenser, the Rankine cycle would be open, and new water would need to be added continuously. The condenser makes it a closed-loop system.

  1. Reduces Back Pressure on Turbine

Lowering the pressure at the turbine exhaust increases the pressure difference across the turbine, leading to greater work output.

  1. Environmental Benefit

Recycling steam into water reduces thermal pollution and water wastage, making the plant more sustainable.

Types of Condensers

  1. Surface Condenser
    Steam and cooling water do not mix. Heat is transferred through metal tubes. Most common in power plants.
  2. Jet Condenser
    Steam and cooling water mix directly. Simple in design but not suitable for reuse of water due to contamination.

Common Cooling Methods

  • Cooling Towers: Reuse water by evaporative cooling.
  • Rivers or Lakes: Natural water bodies used for cooling.
  • Air-Cooled Condensers: Use ambient air to cool steam, useful where water is scarce.

Real-Life Example

In a 500 MW thermal power plant, the condenser maintains a vacuum of about 0.1 bar at the turbine exit. This allows the steam to expand more, giving higher turbine efficiency. The condensed water is pumped back to the feedwater heater and then to the boiler, reducing water usage and improving cycle performance.

Conclusion

The function of a condenser in a power plant is to condense the exhaust steam from the turbine back into water, allowing it to be reused in the cycle. This process improves the efficiency of the power plant, helps maintain continuous operation, and saves water. By creating a low-pressure environment, the condenser allows the turbine to produce more work, making it an essential part of modern thermal power systems.