Deaerator

 

                                          DEAERATOR

As discussed in the previous page, boiler feed water form suspended solids, minerals, and other dissolve impurities and gases. DM water is used in a boiler as for steam generation

      Deaerator are commonly used remove oxygen and other dissolve gases in the boiler feed water because oxygen is mainly responsible for corrosion in boiler tube and other equipment forming of oxide like rust.

In case of steam generation in a power plant, the steam is drive turbine , then condensed in a condenser and this condensate steam use again as feed water in a boiler . so the feed water path work as a close loop path . only some make up is required to make up the blow down and leakage losses. Feed water used in the boiler should be free from any dissolved gasses and oxygen. Deaerator is used for this propose. Dissolve carbon dioxide combine with water and make carbonic acid and that may cause of corrosion but mostly deaerator are design to remove oxygen in the feed water. Also, it serves the purpose of a storage tank from where feedwater is pump into the boiler by the BFP( boiler feed pump). L.P( low pressure ) dosing is also done here for removing the dissolved oxygen from the water.

There are many type of deaerator but commonly two type of deaerator are use in a power plant .

·      Tray type , direct contact deaerator

·      Spray type deaerator

Tray type deaerator- In this type of deaerator, water enters from the top of deaerator . water is distributed through a set of nozzles. Water collect into the bottom storage tank from the deareator column through the perforated trays and small droplets are formed. Low pressure steam is supplied to the steam distributor. This steam moves up in the boiling point corresponding to the deaerator pressure. Due to the formation of small water droplets, the contact surface exposed to increase which result in complete removal of dissolved gasses.

by heating the water dissolving capacity of gases in the water decrease. So, dissolved gasses are remove from the water easily.

 Spray type deaerator- Spray Type deaerator is a cylindrical vessel used for the removal of dissolved gases from the feed water. The feed water fed into the deaerator will pass on through the vented section where the water will experience high steam which allows the feed water to remove dissolved gases. The spray type deaerator diagram is shown below