Steam Condenser for a Turbine: A Comprehensive Guide
What is a Steam Condenser for a Turbine?
A steam condenser for a turbine is a device that converts the low-pressure exhaust steam from a steam turbine into water by using cooling water. The main function of a steam condenser for a turbine is to maintain a low back pressure on the exhaust side of the steam turbine, which increases the efficiency and output of the power plant.
The exhaust steam from the turbine has to expand to a large extent to convert its available energy into mechanical work. If the steam is not condensed after doing its work, it will not create enough space for the following steam to expand to its required volume. Therefore, condensing the steam in a closed system reduces its volume and creates a vacuum that lowers the pressure at the turbine outlet.
A steam condenser for a turbine consists of several components, such as a condenser chamber, cooling water supply, wet air pumps, and a hot well. The condenser chamber is where the steam is condensed by transferring its heat to the cooling water.
The cooling water supply provides cold water from a cooling tower or another source to circulate inside the condenser. The wet air pumps collect the condensed steam, air, uncondensed water vapor, and other gases from the condenser and discharge them to the atmosphere or a deaerator. The hot well is where the condensed steam is collected and from where it can be pumped back to the steam boiler as feed water.
There are mainly two types of steam condensers for turbines: jet condensers and surface condensers. In jet condensers, the cooling water is sprayed on the exhaust steam and mixed with it. This is a fast process of condensing steam, but it results in contaminated water that cannot be reused as feed water.
In surface condensers, the cooling water and the exhaust steam are separated by a barrier, such as tubes or plates, and condensation occurs by heat exchange through this barrier. This is a slower process of condensing steam, but it produces pure water that can be reused as feed water.
Why Use a Steam Condenser for a Turbine?
Using a steam condenser for a turbine has several advantages for power generation, such as:
It increases the thermal efficiency of the power plant by reducing the specific steam consumption and increasing the work output per unit mass of steam.
It improves the quality of feed water by removing dissolved gases and impurities from the condensed steam.
It reduces corrosion and scaling in the boiler and turbine by preventing direct contact between steam and cooling water.
It reduces environmental pollution by minimizing the discharge of steam and cooling water into the atmosphere or water bodies.
It saves water resources by recycling the condensed steam as feed water.
How Does a Steam Condenser for a Turbine Work?
The working principle of a steam condenser for a turbine is based on heat transfer and phase change. The exhaust steam from the turbine enters the condenser at low pressure and high temperature. The cooling water enters the condenser at low temperature and high pressure. The heat transfer between the two fluids occurs through a barrier that separates them physically. The barrier can be tubes or plates, depending on the type of condenser.
As the heat transfer takes place, the temperature of the exhaust steam decreases, and its latent heat is released. The latent heat is absorbed by the cooling water, which increases its temperature. The exhaust steam changes its phase from vapor to liquid and becomes condensed water. The condensed water collects in the hot well at the bottom of the condenser. The cooling water exits the condenser at high temperature and low pressure.
The condensed water is then pumped by a condensate extraction pump to a deaerator or directly to a boiler feed pump. The deaerator removes any remaining air or gases from the condensed water and heats it up before sending it to the boiler feed pump. The boiler feed pump increases the pressure of the feed water and delivers it to the boiler.
The cooling water is either discharged to a cooling tower or another source or recirculated through a heat exchanger or an economizer. The cooling tower lowers the temperature of the cooling water by evaporating some of it into the air. The heat exchanger or economizer transfers some of the heat from the cooling water to another fluid, such as air or feed water.
What are the Types of Steam Condensers for Turbines?
Depending on the technique of condensation, there are mainly two types of steam condensers for turbines: jet condensers and surface condensers.
Jet Condensers
In jet condensers, the cooling water is sprayed on the exhaust steam and mixed with it. This is a fast process of condensing steam, but it results in contaminated water that cannot be reused as feed water. The mixture of water and steam is then discharged to a hot well, where it is pumped by a wet air pump to a deaerator or a cooling tower.
There are three subtypes of jet condensers: low-level, high-level, and ejector jet condensers. In low-level jet condensers, the hot well is placed at the same level as the condenser, and the mixture flows by gravity. In high-level jet condensers, the hot well is placed above the condenser and the mixture is lifted by a pump. In ejector jet condensers, the cooling water is injected at high velocity into the exhaust steam and creates a vacuum that sucks the mixture into the hot well.
The advantages of jet condensers are:
They are simple, cheap, and easy to install and operate.
They have a high rate of heat transfer and a low-pressure drop.
They do not require a large cooling water supply or a separate air extraction system.
The disadvantages of jet condensers are:
They produce impure water that cannot be reused as feed water and requires treatment before disposal.
They have a high power consumption for pumping the cooling water and the mixture.
They are affected by the quality and temperature of the cooling water.
Surface Condensers
In surface condensers, the cooling water and the exhaust steam are separated by a barrier, such as tubes or plates, and condensation occurs by heat exchange through this barrier. The cooling water passes through an array of tubes or plates, and the exhaust steam flows over their outer surface. The heat of steam is absorbed by the cooling water, which increases its temperature.
The exhaust steam changes its phase from vapor to liquid and becomes condensed water. The condensed water collects in the hot well at the bottom of the condenser. The cooling water exits the condenser at high temperature and low pressure.
There are two subtypes of surface condensers: downflow and counterflow. In downflow surface condensers, the exhaust steam enters from the top and flows downward over the tubes or plates. In counterflow surface condensers, the exhaust steam enters from one end and flows upward over the tubes or plates, while the cooling water enters from the other end and flows downward through them.
The advantages of surface condensers are:
They produce pure water that can be reused as feed water and reduce corrosion and scaling in the boiler and turbine.
They have a low power consumption for pumping the cooling water and the condensed water.
They are not affected by the quality and temperature of the cooling water.
The disadvantages of surface condensers are:
They are complex, costly, and difficult to install and operate.
They have a low rate of heat transfer and a high-pressure drop.
They require a large cooling water supply and a separate air extraction system.
How to Choose a Steam Condenser for a Turbine?
The choice of a steam condenser for a turbine depends on several factors, such as:
The size and capacity of the power plant
The availability and cost of cooling water
The quality and quantity of feed water
The environmental regulations and standards
The operational and maintenance requirements
Generally, surface condensers are preferred for large power plants that require high efficiency, reliability, and purity of feed water. Jet condensers are suitable for small power plants that have limited cooling water supply, low feed water demand, and simple operation.
Conclusion
A steam condenser for a turbine is a device that converts low-pressure exhaust steam from a steam turbine into water by using cooling water. It has several functions and advantages for power generation, such as increasing efficiency, improving feed water quality, reducing corrosion, saving water resources, and minimizing environmental pollution.
There are mainly two types of steam condensers for turbines: jet condensers and surface condensers. Each type has its own features, benefits, drawbacks, and applications.
The selection of a steam condenser for a turbine depends on various factors related to the size and capacity of the power plant, the availability and cost of cooling water, the quality and quantity of feed water, the environmental regulations and standards, and the operational and maintenance requirements. The performance and maintenance of a steam condenser for a turbine are crucial for the overall efficiency and reliability of the power plant.
Therefore, it is important to monitor, analyze, and optimize the performance and maintenance of a steam condenser for a turbine, using various methods and best practices. By doing so, power plant operators and engineers can improve their heat rate awareness and competitiveness in the power generation market.
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