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In steam generation systems, dissolved oxygen and carbon dioxide in the feedwater are highly corrosive gases that can adversely affect the system’s service life and efficiency. To prevent these gases from entering the steam generator and causing corrosion, they must be separated from the water and removed. Carbon dioxide is completely separated from water at temperatures of 65 °C and above, while oxygen is completely separated at 102 °C and above. The separated gases are discharged from the system through the top of the deaerator dome.
Thermal deaerators operate at 105 °C. To prevent cavitation in the feedwater pump, deaerators operating at this temperature must be installed approximately 5 meters above ground level. This elevation creates positive pressure at the pump inlet, preventing cavitation.
The Importance of Condensate Tank Temperature
If hot condensate from the processes can raise the condensate tank temperature to 80-90 °C, all of the carbon dioxide and most of the oxygen will already have been removed from the water. This reduces the energy and cost required to remove gases from the water. The small amount of oxygen remaining can be captured using a low-cost method by dosing an oxygen scavenger chemical.
However, in plants with insufficient condensate return, if the condensate tank temperature remains below 80 °C, a large amount of oxygen scavenger chemical may be required. In this case, the blowdown rate will need to be increased to prevent the water from exceeding its chemical treatment limit. Since this method can be more costly, using a thermal deaerator offers a more economical and sustainable solution.
How Thermal Deaerators Work
Thermal deaerators heat feedwater by circulating water from the condensate tank over separation trays and bringing it into contact with steam in a tank operating at a pressure of 0.2 barg and a temperature of 105 °C. This process removes dissolved gases from the water, minimizing the feedwater's potential to cause corrosion. Thermal deaerators are especially recommended for plants where the condensate tank temperature is below 80 °C and the boiler room has a height of at least 7-8 meters.
Advantages of Using Thermal Deaerators
Corrosion Prevention: Thermal deaerators remove gases such as oxygen and carbon dioxide from the water, minimizing the risk of corrosion and thereby extending the service life of steam boilers and piping.
Energy Efficiency: Raising the water temperature removes gases from the water, making steam generation more efficient and saving energy.
Reduced Chemical Costs: In systems with adequate condensate return, costs are reduced by using a small amount of oxygen scavenger chemical. In addition, reducing chemical consumption lowers the risk of exceeding the water's chemical treatment limit.
Sustainable Solution: Removing gases and preventing cavitation helps ensure the safe and sustainable operation of the system.
Conclusion
Thermal deaerators effectively remove dissolved gases from water in steam systems at industrial plants, reducing the risk of corrosion and improving system efficiency. Their use stands out as an economical and environmentally friendly solution, especially in plants with insufficient condensate return and a need for high-temperature feedwater.
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