Feedwater tank and deaeration
The feedwater deaeration system consists of a feedwater tank and deaerator dome. The equipment is intended for the removal of non-condensable gases such as oxygen and carbon dioxide dissolved in the medium.
The boiler feedwater must be free of hardening constituents in order to prevent the formation of scale on the boiler heating surfaces. The presence of dissolved oxygen and carbon dioxide causes severe corrosion of metal boiler parts. The feedwater deaerating plant is custom designed for each application and meets essential thermodynamic requirements to achieve optimal performance.
The make-up water and return condensate enter the tray-type deaerator dome that is fitted with a series of tray compartments to provide maximum spilling. Heating steam is fed into the deaerator dome from below. The make-up water and return condensate are deaerated and flow directly into the feedwater tank, which is flanged to the deaerator dome. The feedwater tank, which is heated by means of a steam injector, heats up the feedwater to 107℃. The solubility of gases in water can be described by Henry Dalton‘s law of absorption which states that gas solubility in a solution decreases as the gas partial pressure above the solution decreases. This means that the gas solubility in a solution decreases as the temperature of the solution rises and approaches saturation temperature. The make-up water and return condensate is distributed over the series of trays and comes in direct contact with the heating steam. This process reduces the solubility of oxygen and carbon dioxide and removes these gases from the feedwater. The released gases work their way to the top of the vessel where they are vented from the deaerator dome via the vent line.
We recommend a temperature-controlled valve for maintaining the water temperature in the feedwater tank and a pressure-controlled valve for maintaining the gas compartment pressure. In the case of liquid media, the net positive suction head (NPSH) available to the pump must be specified to prevent cavitation. The pressure of the liquid inside the pump must continually remain above the predominant boiling point. NPSH is pump-dependent.
The installation reduces the oxygen content down to 0.02 mg/L