DEAERATOR CONSTRUCTION

S.Senthil

WHAT IS MEANT BY DEAEARTION?

Deaeration is the process of removal of

oxygen, Carbon di oxide and other non

condensible gases from boiler feed water

thereby reducing the risk of corrosion in the

pressure parts of the boiler.

Deaeration of two types namely Mechanical

Deaeration and Chemical Deaeartion

Mechanical deaeration works on the principle

of Henry’s law of physics

WHAT FOR DEAERATION

In particular, dissolved oxygen in boiler feedwaters

will cause serious corrosion damage in steam

systems by attaching to the walls of metal piping

and other metallic equipment and

forming oxides (rust).

Water also combines with any dissolved carbon

dioxide to form carbonic acid that causes further

corrosion.

WHY DEAERATE BOILER FEEDWATER?

Water is heated during deaeration to near the temperature of the boiler water, thus minimizing the risk of thermal shock.

The deaerating process removes noncondensible gases (oxygen and carbon-dioxide) which tend to act as insulators inhibiting the transfer of heat within the boiler.

Removal of corrosive oxygen and carbon-dioxide controls corrosion within the boiler and piping, extending the life expectancy of the system and reducing maintenance cost.

Higher temperature feed water reduces the drop in boiler operating pressure which can occur when cold water is added.

Mechanical deaeration can reduce the amount of chemical consumables used for water conditioning in turn cost saving.

HENRY’S LAW OF PARTIAL PRESSURE

At a constant temperature, the amount of given gas

dissolved in a given type and volume of liquid is

directly proportional to the partial pressure of that

gas in equilibrium with that liquid. The law further states that the solubility of gas in a

particular temperature is proportional to the

pressure of that gas above the liquid.

HENRY’S LAW OF PARTIAL PRESSURE

An everyday example of Henry's law is

given by carbonated soft drinks. Before the

bottle or can is opened, the gas above the

drink is almost pure carbon dioxide at a

pressure slightly higher than atmospheric

pressure. The drink itself contains dissolved

carbon dioxide. When the bottle or can is

opened, some of this gas escapes and

giving the hiss sound.

HENRY’S LAW OF PARTIAL PRESSURE

Because the pressure above the liquid

is now lower, some of the dissolved

carbon dioxide comes out of solution

as bubbles. If a glass of the drink is left

in the open, the concentration of

carbon dioxide in solution will come

into equilibrium with the carbon dioxide

in the air, and the drink will go "flat".

The easiest way to deaerate the boiler

feed water by forcing the steam into the

feed water, this action is called

SCRUBBING.

The feed water entering the deaerator is

heated to the saturation temperature

corresponding to the steam pressure

maintained in the deaerator. This will

reduce the solubility of dissolved gas in the

water to zero.

TYPES OF DEAERATORS

1. Spray type

2. Spray cum tray type

3. Vacuum type

SPRAY TYE DEAERATOR

SPRAY WITH TRAY TYPE DEAERATOR

DEAERATION PROCESS DESCRIPTION

Deaeration is based on two scientific principles.

The first principle can be described by Henry's

Law. Henry's Law asserts that gas solubility in a

solution decreases as the gas partial pressure

above the solution decreases.

The second scientific principle that governs

deaeration is the relationship between gas

solubility and temperature. Easily explained, gas

solubility in a solution decreases to almost zero

as the temperature of the solution rises and

approaches saturation temperature.

DEAERATION PROCESS DESCRIPTION

A deaerator utilizes both of these

natural processes to remove dissolved

oxygen, carbon dioxide, and other

non-condensable gases from boiler

feed water. The feed water is sprayed

in thin films into a steam atmosphere

allowing it to become quickly heated to

saturation temperature.

DEAERATION PROCESS DESCRIPTION

Spraying feed water in thin films

increases the surface area of the liquid

in contact with the steam, which, in

turn, provides more rapid oxygen

removal and lower gas concentrations.

This process reduces the solubility of

all dissolved gases and removes it

from the feed water. The liberated

gases are then vented from the

deaerator.

OUR PLANT DEAERATOR

It is of spray and trays type deaerator consist of a feed

water storage tank and vapour tank with vent condenser.

Water is sprayed from the top of vapour tank through ten

spray nozzles on set of multi level perforated trays below it

for easy and complete scrubbing with steam .

Steam is fed in storage tank through distribution header

below the water level. Partial scrubbing of steam with

water takes place by raising the water temperature(Since

solubility of gases like oxygen carbon dioxide decreases

with increase in water temperature).

OUR PLANT DEAERATOR

The complete removal of gases taking place in

vapour tank with incoming water spray. Water

sprayed from the top (fixed in two headers with

five nozzles in each to spray the CEP water into

fine particles covering entire cross section of the

tank) and passed through perforated SS trays at

different levels to provide enough scrubbing of

water with upcoming steam from storage tank

through interconnection pipe.

OUR DEAERATOR TECHNICAL DATA

Integral, thermal-mechanical deaerator of spray and

tray type (multi level trays)

Water is sprayed through 10 nozzles arranged in two

rows with 5 nozzles.

Heating and scrubbing action removes all the

dissolved gases.

With mechanical deaeration DO level : 20 to 30ppb

With chemical deaeration DO level :5 to 10ppb

Chemical used : Cortrol-Carbo hydrazide

OVER VIEW OF DEAERTOR

Vent Condenser

Vapour Tank

Storage Tank

Condensate

from CEP

Feed water

to BFP

Condensate outlet from

vent condenser

Steam inlet to vent condenser

VAPOUR TANK

trays

deaerated Water to storage tank Steam Inlet

VAPOUR TANK TRAYS

SS Tray Middle

SS Tray

Outer

VENT CONDENSER CUT SECTION

Vent to atmosphere

DM water

(Condensate)

Outlet DM

Water(condensate)

from CEP

Steam Inlet Condensate

outlet

DEAERATOR TECHNICAL DATA

Design pressure : 6 Ksc

Hydraulic test pressure : 9 Ksc

Working pressure : 2 to 2.5 Ksc

Safety valve Lifting pressure (LHS): 5.57Ksc

Safety valve Lifting pressure (RHS): 5.93Ksc

Thank you