Deaerator: Definition, Function, Working Principle, and Types
A deaerator is a crucial piece of equipment in boiler systems, particularly in industries like power generation, chemicals, and oil refineries. Its primary function is to remove dissolved gases from the boiler feedwater, especially oxygen (O₂) and carbon dioxide (CO₂), which can cause corrosion in the boiler system if not eliminated. In this article, we will explain in detail what a deaerator is, how it works, and the different types of deaerators commonly used in the industry.
What Is a Deaerator?
A deaerator is a device used to remove dissolved gases from the boiler feedwater by heating the water to near its boiling point. This process is essential to prevent corrosion damage to the metal components of the boiler system caused by dissolved oxygen and carbon dioxide in the water.
The Function of a Deaerator
The primary function of a deaerator is to remove dissolved oxygen and carbon dioxide from the boiler feedwater. If these gases are not removed, they can cause corrosion in pipes, boilers, turbines, and other metal components. Additionally, the deaerator heats the feedwater to near its boiling point, improving energy efficiency in the boiler heating process.
How a Deaerator Works
The process of removing dissolved gases in a deaerator follows basic physical principles related to the solubility of gases in liquids, where gas solubility decreases as temperature increases. By heating the water to near its boiling point, gases like oxygen and carbon dioxide are released from the water and vented out through the deaerator.
- Boiler Feedwater Inlet: The boiler feedwater containing dissolved gases is introduced into the deaerator.
- Steam Inlet: Pressurized steam is supplied into the deaerator to heat the feedwater to near its boiling point.
- Dissolved Gas Removal: The dissolved gases are released from the water as their solubility decreases at high temperatures and are vented out.
- Water Storage: The deaerated water is stored in a tank before being pumped to the boiler.
Types of Deaerators
In general, there are two main types of deaerators used in industry: Tray-Type Deaerators and Spray-Type Deaerators. Both work on the same principle but differ in how they spread water for contact with steam.
1. Tray-Type Deaerator
This type of deaerator uses a series of trays inside the tank to increase the contact surface between water and steam. Water flows through the trays, while steam flows upward through them, causing the dissolved gases to be released from the water.
- Advantages: Stable operation.
- Disadvantages: Slightly less efficient than spray types due to a smaller contact surface.
2. Spray-Type Deaerator
This type of deaerator uses nozzles to spray water into small droplets, which increases the surface area for contact with the steam. This process is more efficient at removing dissolved gases.
- Advantages: Higher efficiency due to the larger contact surface.
- Disadvantages: The nozzle system is more complex and requires more frequent maintenance.
The Importance of Removing Dissolved Gases
Why is it important to remove gases like oxygen and carbon dioxide? Because these gases can trigger pitting corrosion, which can damage the walls of pipes and other metal components in the boiler system. Oxygen is the main cause of corrosion, while carbon dioxide, when dissolved in water, forms carbonic acid (H₂CO₃), which lowers the water’s pH and accelerates corrosion. Using a deaerator helps to minimize corrosion, thus extending the lifespan of boiler equipment.
Deaerator Efficiency
The efficiency of a deaerator is influenced by several factors, including steam temperature and pressure, feedwater quality, deaerator design, and maintenance practices. A well-designed and properly operated deaerator can reduce the oxygen content in water to less than 0.005 cc/liter, which is the industry standard.
Deaerator Maintenance
To ensure optimal operation of a deaerator, regular maintenance is crucial. Some important steps include:
- Temperature and Pressure Monitoring: Steam temperature and pressure should be monitored to ensure efficient deaeration.
- Nozzle and Tray Inspection: The nozzles in spray-type deaerators and the trays in tray-type deaerators should be regularly inspected to prevent clogging, which can reduce efficiency.
- Ventilation Monitoring: The ventilation system must be functioning properly to remove dissolved gases without excessive steam loss.
Benefits of Using a Deaerator
Using a deaerator offers many benefits to the boiler system, including:
- Reducing Corrosion: By removing dissolved gases, a deaerator prevents corrosion that can damage equipment.
- Increasing Energy Efficiency: Boiler feedwater that has been preheated by the deaerator requires less energy to be heated by the boiler, thus increasing overall system efficiency.
- Lower Maintenance Costs: Deaerators help to extend the lifespan of equipment, reducing the frequency of maintenance and replacement due to corrosion.
Conclusion
A deaerator is a crucial piece of equipment in boiler systems used to remove dissolved gases like oxygen and carbon dioxide from boiler feedwater. By using a deaerator, the risk of corrosion in the boiler system is significantly reduced, which in turn extends the lifespan of the equipment and improves energy efficiency.
FAQ:
What is the main function of a deaerator?
- A deaerator’s main function is to remove dissolved gases, primarily oxygen and carbon dioxide, from boiler feedwater to prevent corrosion.
What is the difference between a Tray-Type Deaerator and a Spray-Type Deaerator?
- Tray-type deaerators use trays to expand the contact surface between water and steam, while spray-type deaerators use nozzles to spray water into the steam.
Why must oxygen and carbon dioxide be removed from feedwater?
- Oxygen causes pitting corrosion, which damages metal components, while carbon dioxide forms carbonic acid that can accelerate corrosion.
