Deaerator working principle, Types and Process Control
Deaerator working principle, Types and Process Control
Deaerators is commonly employed in any chemical process industry or in Power Plants wherever boiler is utilized for steam production from boiler feed water. Deaerator solves the aim of removal of unwanted dissolved gases and dissolved oxygen from the boiler feed water before going in boilers. Most of the deaerators are designed in such how that the dissolved oxygen content within the outlet water is regarding7 ppb by WTC.
Principle of Dearators
Dearator commonly
works based on the subsequent principles.
Henry’s Law
According to Henry’s
low is in a liquid the gas solubility is directly proportional to the partial
pressure. thus if we tend to decrease the partial pressure of the dissolved gas
by adding steam in Deaerator, its solubility decreases and also the gas is faraway
from water.
Inverse Solubility of Water
When the temperature
of water is growing, the dissolved oxygen content within the water is
decreases. Thus the water temp. is growing by inserting steam in Deaerator, the
dissolved gas solubility is reduced and also the gases are withdrawal from
water.
Types of Deaerators
1. Tray types
Deaerator
Tray type deaerators
contain perforated trays within the top of the Deaeration section. The bottom portion
volume is high for used as storage for boiler feed water. Feed water to
deaerator enters into the perforated trays wherever the area and residence time
is growing to contact with steam. Then the water goes to the horizontal storage
section wherever steam is pass through sparger pipe to withdrawn the remaining traces
of dissolved gases and keep the stored water at its saturation temperature.
Tray Deaerator
2. Spray type Deaerator
Spray Deaerator type
deaerator contains spray nozzle in feed water entry space. it’s then preheated
and deaerated and sent to storage section. In storage section also steam is
additional to stay the water at its saturation temperature.
Process control system in Deaerator
Deaerator operate in
very low pressure steam about 0.5 to 1.5 kg/cm2 with can produce in process
plant.The low steam sources could also be anyone of the following: Extraction
from back pressure turbines, Flash steam recovered from Boiler blow down or
letdown steam from high pressure steam header through pressure reducing valve. Steam
pressure within the deaerator should be maintained to facilitate the removal of
dissolved gases from water and also to produce adequate NPSH to boiler feed
pump. Deaerators are commonly put in at high elevation so as to produce enough
NPSH within the event of failure in steam pressure control conjointly. Pressure
safety valve is additionally fitted to avoid pressurization of deaerator
because of malfunctioning of pressure control valve.
Water Level control
Main sources of raw
water to deaerator are Treated water from water treatment plant and steam
condensate from the condensing type turbines. During the stable plant operation
the water balance is maintained and through any upset within the higher than
said sources water level fluctuates and control is important. High level and
low level alarms are provided. Low level might lead to starvation of feed water
in pump and High level leads to water entry into steam header. Thus overflow drain
is put in to drain the water if very high level is reached.
Deaerator Water Level control
Other benefits of Deaerator
Dearator acts as an
extra storage that provides reserve amount of boiler feed water throughout
upstream water supply failure for momentary periods commonly for about twenty
minutes.
In some of the Plants, Deaerator is additionally used for dosing oxygen scavenging chemicals like hydrazine or Hydroquinone.
