منتدى الهندسة الكهربية - Open Feed Water Heater (Deaerator)

[LEFT][B][I][U][F**T=&quot]Open Feed Water Heater (Deaerator)[/F**T][/U][/I][/B]
[B]
An open feadwater heater , also called direct-c**tact and deaerating (DA) heater , is **e that heats the feedwater by directly mixing it with bled steam from the turbine. Usually **ly **e DA is used at Power Plant.[/B]
[B]Because the pressure in such a heater can’t exceed the turbine pressure at the point of extracti**, a pump (Main Boiler Feed Water Pump) must follow the heater. The c**fluence of steam and water flows makes possible the efficient removal of n**c**densables as well as the heating of the feedwater.[/B]
[URL="http://3.bp.blogspot.com/_CZnqYQLLQtc/TRyKAUyy-5I/AAAAAAAAAHQ/ViCU3UgrGVg/s1600/dea_1.JPG"][IMG]http://3.bp.blogspot.com/_CZnqYQLLQtc/TRyKAUyy-5I/AAAAAAAAAHQ/ViCU3UgrGVg/s400/dea_1.JPG[/IMG][/URL]

[B]The DA heater is usually positi**ed in the feedwater line at a pressure to prevent air inleakage and at a temperature at which Oxygen retenti** is least likely. Most DA heaters are designed for Oxygen c**centrati** in the outlet feedwater below 0.005Cm3/L[/B]
[B]The DA outlet feedwater is at or near saturati**. Pumping saturated water results in cavitati** because of the pressure drop below saturated pressure, thus causing flashing ** the back side of pump vanes. The DA heater is therefore usually positi**ed in the powerplant steam-generator house high above its pump by perhaps 60 ft. This provides sufficient pump inlet pressure to render the saturated water compressed (or subcooled) and prevents cavitati**s.[/B]
[B][I]There are three types of DA heaters for industrial and utility use.[/I][/B]
[B][U][F**T=&quot]1) Spray-Type deaerators .[/F**T][/U][/B]
[B]In this type the feedwater enters the heater through nozzles that spray it into the extracti**-steam-filled heater space. The water is heated and scrubbed to release the n**c**densables gases. A sec**d agitati** of the now-heated feedwater by another steam flow is provided by an internal baffling system.[/B]
[B][U][F**T=&quot]2) Tray-Type deaerators.[/F**T][/U][/B]
[B]Here the feedwater is directed **to a series of cascading horiz**tal trays. It falls in sheets or tubes from tray to tray and comes into c**tact with rising extracti** steam admitted from the bottom of the tray system. As scrubbing occurs and n**c**densables gases and some steam rise, they come into c**tact with colder water, resulting in a reduced volume of high c**centrati** of n**c**densables to vent into the atmosphere.[/B]
[B][U][F**T=&quot]3) Combinati** spray-tray deaerator [/F**T][/U][/B]
[B]In this type, the feedwater is first sprayed into a steam-filled space, then made to cascade down trays. This combinati** type with horiz**tal stainless steel trays is currently preferred by utilities. [/B]

[URL="http://3.bp.blogspot.com/_CZnqYQLLQtc/TRyKIVO6HoI/AAAAAAAAAHU/FCh3SDiI02k/s1600/dea_2.JPG"][IMG]http://3.bp.blogspot.com/_CZnqYQLLQtc/TRyKIVO6HoI/AAAAAAAAAHU/FCh3SDiI02k/s400/dea_2.JPG[/IMG][/URL]
[URL="http://2.bp.blogspot.com/_CZnqYQLLQtc/TRyKKUfex_I/AAAAAAAAAHY/C0PFoP5WaMM/s1600/dea_3.JPG"][IMG]http://2.bp.blogspot.com/_CZnqYQLLQtc/TRyKKUfex_I/AAAAAAAAAHY/C0PFoP5WaMM/s400/dea_3.JPG[/IMG][/URL]

[B][F**T=&quot]You noticed that just below the heater, is a relatively large feedwater tank (Storage Tank) which allows sufficient water for rapid load variati**s. [/F**T][/B][/LEFT]