DEAERATION IN PRINCIPLE Henry's law of partial pressures allows that the solubility of any gas dissolved in a liquid is directly proportional to the partial pressure of that gas above the liquid. Thus, a dissolved gas can be removed by reducing the partial pressure of that gas in the atmosphere surrounding the liquid. This is accomplished by passing the liquid containing the dissolved gases into a countercurrent flow of steam. This method also takes advantage of the fact that, within typical deaerator operating ranges, the solubility of a gas in a liquid decreases with an increase in the temperature of that liquid is sprayed in thin flims and droplets and then vigorously scrubbed by the incoming steam.

OPERATION ONE-STAGE Incoming water flows through spray valve and enters the steam-filled vent condensing chamber as a thin-walled, hollow cone spray pattern. Latent heat transfer is instantaneous because of the intimate water-to-steam exposure. As the water reaches the tray stack, at which point stage one is complete, its temperature is within 1.1 °C of the counterflowing saturated steam tempersture, and virtually all dissolved.Nearly all of the steam has now condensed, permitting the non-condensable gases to be carried through the vent by the remaining steam, exiting as a plume.

OPERATION TWO-STAGE The water enters the tray stack, which comprises stage two, and immediately reaches saturation(operation)temperature. With the water so preheated, the remainders of the tray stack and counter-flowing steam are now available to scrub and remove the final traces of oxygen and carbon dioxide without additional condensation of steam. The preheated water flows down over the trays, zig-zagging its way through a countercurrent of pure steam. The water leaving the bottom layer of trays is "stripped" by the purest steam entering the DEAERATOR and flows into storage completely deaerated and heated.

****DEAERATOR DESIGN CHECK ITEM*******

A. DEAERATOR DESIGN FEATURES

1. Process calculation

1.1 Heat and Mass Balance

1.1.1 At design condition(Normal, VWO, Heaters bypassed, etc.)

1.1.2 At start-up condition

1.1.3 During transient condition(Turbin Trip)

1.2 Storage Vessel Sizing

1.2.1 Capacity requirements and calculation of vessel dimensions

1.2.2 Definition of reference levels

1.2.2.1 Normal water leve

l1.2.2.2 Overflow level

1.2.2.3 Mim. water level

1.2.2.4 Alarm levels(High level, low level, low low level)

1.3 Nozzle Sizing 1.3.1 Cold water connection(Condensate, Make-up)

1.3.1.1 Sizing basis and tolerances

1.3.1.2 Nozzle locations

1.3.2 High Pressure(Flashing) Condensate

1.3.2.1 Sizing Basis and Tolerance

1.3.2.2 Nozzle locations

1.3.2.3 Internal treatments-Baffle &Distributors

1.3.3 Steam

1.3.3.1 Sizing Basis and tolerances

1.3.3.2 Location and Effects of superheat in steam

1.3.3.3 Effects of Moisture in steam

1.3.4 Pressure Safety/Relief valves

1.3.4.1 ASME Requirements

1.3.4.2 HEI Requirements

1.3.4.3 Locating and Sizing Nozzles

1.3.4.4 Effects of relief valves blowing during operation

1.3.5 Vacuum""s relief devices

1.3.5.1 Need for

1.3.5.2 Types

1.3.5.3 Sizing and locating

1.3.5.4 Effects of vacuum breaker operation on DA performance

1.3.6 Vents

1.3.6.1 Determining vent rates

1.3.6.2 Vent rate calculation and control

1.3.6.3 Vent Condenser Sizing

1.3.7 Equalizers

1.3.7.1 Operation during normal and transient conditions

1.3.7.2 Sizing basis and location

1.3.7.3 Internal projections and Flash/Impingement baffle

1.3.8 Downcomers

1.3.8.1 Operation during normal and transient conditions

1.3.8.2 Internal projection/Flash baffles(Drip Pan(Shield)/Screen and Bortes Breaker/Distribution devices

1.3.9 Crossover pipes

1.3.9.1 Sizing and location

1.3.10 Pump Suction

1.3.10.1 Sizing basis and location

1.3.10.2 Vortex breakers/Screen/Sludge Lip

1.3.11 Pump Recirculation Lines

1.3.11.1 Sizing basis and location

1.3.11.2 Baffles and Distributtors

1.3.12 Overflow

1.3.12.1 Sizing basis Location

1.3.12.2 Interal standpipes location

1.3.13 Miscellaneous

1.3.13.1 Instruments(Pressure and Temperature) connection

1.3.13.2 Level instrument connection

1.3.13.3 Sample/Chemical feed connection