The Deaerator tank is used to store both cold and hot fluid in order to remove dissolved air from the fluid. Deaeration protects the steam system from the effects of corrosive gases. It accomplishes this by reducing the concentration of dissolved oxygen and carbon dioxide to a level where corrosion is minimized.
Principle and working of Deaerator tank
Water or any fluid which is used as a medium for heat transfer generally contains Oxygen and other non-condensable gases in it. These gases dissolved in a fluid acts as an insulation to heat transfer. Due to the presence of these gases in a fluid, heat transfer rates from fuel to fluid is generally reduced which in turn will increase the fuel required for heating, thereby decreasing the efficiency.
Deaerator tank works on a principle
The solubility of gases in a fluid decreases with increase in the temperature of a fluid and the pressure of gas in a fluid is directly proportional to the partial pressure of gas above it, so removing the gas above the fluid decreases the pressure above the fluid and causes the gas dissolved in a fluid to escape the fluid in order to balance the pressure.
Condensate or process fluid returning from the process is generally at high temperature than the ambient temperature and the fluid which needs to be fed is at lower temperature than the ambient. Both the feed and process fluid is kept together in a tank in order to increase the temperature of the feed by taking heat from the process fluid. The level of fluid in a tank is such that, some space above the fluid is kept free for the air to escape the fluid. Air vent is provided at the top of the tank so that all the air could escape the tank leaving behind any vapor formed.
Other advantages of removing non-condensable gases from a feed are:-
- Removing these gases from the feed protects the boiler or heater tubes from getting corroded, thereby increasing the life of equipment.
- Increases the efficiency of a boiler.
- It also acts as a Feed tank which provides Net Positive Suction Head to the feed.