Steam boiler has some systems which running together to produce high quality steam. One of the systems is feedwater system. One of the main parts of feedwater system is deaerator feedwater tank. The mass balance between steam produced by boiler and the feedwater should be maintained in a fluctuating load conditions based on firing rate and steam demand. Furthermore feed water system should be controlled to supply enough water into steam boiler.
The required water must faces water treatment system before supplied into steam boiler, so the water has required parameter contents about silica, scaling, conductivity, PH, dissolved oxygen and so on. The main consideration is how to remove oxygen to prevent corrosion and remove scaling which can isolate heat transfer process in the pressure parts of steam boiler (water wall, header, economizer, etc).
The main functions of deaerator feedwater tank are:
1. Remove oxygen and non condensable gases.
2. As storage tank to maintain and supply enough feedwater into steam boiler
3. Increase temperature feedwater until saturated temperature.
Water which is treated from demineralization process and from condensate is sprayed into through nozzle deaerator. Low pressure steam is injected to deaerator to remove gases content and dissolved oxygen and then discharge them through deaerator venting. In addition to remove oxygen content, low pressure steam is also used to increase temperature up to 130 140 C. The water which gas content and dissolved oxygen had been removed enters to feedwater tank. Moreover chemical contents such as sodium sulfite (Na2SO3) or hydrazine (N2H4) are injected to reduce oxygen content in feedwater.