The document defines an HRSG as being composed of an economizer, evaporator, and superheater. As hot exhaust gas passes through these components, its temperature reduces from 550°C to 130°C, heating and converting water into steam. The economizer heats water up to near saturation temperature, while the evaporator heats water into saturated steam. The superheater then heats saturated steam into superheated steam. The deaerator system uses thermal and chemical processes to remove oxygen from water, which is then fed into boiler systems. A preheater is sometimes used to heat condensate water closer to saturation temperature before entering the deaerator.

1. HRSG knowledge
speaker： Deng Yongfu

2. Definition of HRSG
HRSG is composed of economizer, evaporator, superheater
and its accessories.
Hot gas exhaust temperature reduces from about 550 ℃ to
130 ℃ while it passes through superheater, evaporator,
economizer. The released heat boils water supply in pipeline
and vapors it into steam.
Economizer is used to heat water supply up to approaching
saturation temperature.
Evaporator is used to heat water supply into saturation
steam. Its mixture of saturation water and saturation steam in
its inlet.
Superheater is used to heat saturation steam into
superheated steam.

3. Deaerator System
Description of the Deaerator System
Deaerator system purpose : the water will be thermally deaerated
in the deaerator . After deaeration, the water enters into the low
pressure and high pressure systems of three boilers as boiler feed
water.
the method of deaeration：
1.Thermal Deaerating Procedure。
As the temperature increases, the solubility of oxygen in water
decreases.
2.chemical Deaerating Procedure。
NH2.NH2＋O2 = N2+2H2O

4. Preheater
In heavy oil case, the preheater is bypassed. Condensate
water is sent into deaerator directly. Only in natural gas
case, condensate water is heated inside the preheater to a
temperature close to saturated temperature, and is sent into
the deaerator.
Deaerator
During startup , feed water is deaerated by chemicals.
During normal operation, saturated steam from LP drum is
the heating supply for thermal deaerating. After heating and
deaeration, the feed water enters into the deaeration water
tank, and goes to high pressure and low pressure system of
three boilers by high pressure and low pressure pumps.

6. heat exchanger
working substance state
superheater superheated steam
evaporator saturated steam and saturated water
economizer saturated water
preheater unsaturated water，