HRSG Components

1. Heat Recovery Steam Generator
(HRSG) Components,
Aux Sys, Supplementary Firing

2. Definition of HRSG
HRSG is composed of economizer,
evaporator, superheater and its accessories.
Hot gas exhaust temperature reduces from
540 ℃ to 150-180 ℃ while it passes through
superheater, evaporator, economizer. The
released heat boils water supply in pipeline
and vapors it into steam.

3. 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.

4. Sorts of HRSG (based on circulation )
Natural Circulation. It uses the density differential between
decline pipelines and endothermic pipelines of heating
surface to generate cycle force power, which drives
working substances cycling inside HRSG naturally.
Forced Circulation. It uses not only the density differential
between steam and water, but also force circulating
pumps to drive working substances cycling inside HRSG.
Direct-through HRSG.
Water supply passes only one circulation and is heated
into superheated steam. No drum.
Compound Circulation HRSG.
Some heating surface follows natural circulation and the
others follows forced circulation.

5. Sorts of HRSG (based on heating surface
structure)
Horizontal HRSG.
Heating surface pipelines are vertical and gas
exhaust passes horizontally.
Vertical HRSG.
Heating surface pipelines are horizontal and
gas exhaust passes vertically.

6. Heating Surface of Forced
Circulation
Steam Header of HP
Economizer I & LP Economizer
Steam Header of
HP Economizer Ⅱ
Steam Header of
LP Superheater
Steam Header of
HP Evaporator
Steam Header of
HP SuperheaterⅠ
Steam Header of HP
Superheater Ⅱ
Steam Header of
LP Evaporator
Steam Header of
preheater
Design:
Evaporator is downstream, others
are upstream.
Analysis:
a) Upstream has efficient heat
exchange, but requires better
pipelines to reduce volume.
b) Downstream gets power from
natural circulation and reduces
output of cycle pumps, according
to its saturation status.
c) If it’s designed upstream, there
may occur vaporization and
damage to hear exchange.

7. Advantages：
1. It’s saving ground acreage to set pipelines
horizontally and heating surface vertically.
2. It’s compact structure based on the small
diameter of pipelines.
3. It’s forced circulation and the circulating rate is
around 3–5.
4.Due to small volume of water, it’s fast to increase
temperature, which means large range of adjustable
load for peak operation. Usually it needs only 20-25
minutes to start up in cold status.

8. Disadvantages：
1.It’s more complicated operation and increase cost
of operation and maintenance.
2.It increases power consumption.
3. It’s lower stability based on the high center of
gravity.
4. The supporting is complicated to support such a
weight.

9. Steam Procedure of Forced Circulation
1.It’s similar with natural circulation, but there are
forced circulating pumps (main/backup) under each
HP/LP downstream pipelines.
2.The circulating power in HP/LP evaporators is
supplied by forced circulating pumps, to insure safe
water circulation.
3.The LP drum can be used as deaerating drum and
mounted on the steel frame of HRSG, which could
simplify pipelines and reduce ground acreage.

10. Design:
It’s bi-pressure (HP/LP), horizontal, staged combusting and natural
circulating HRSG. The heating surface is standard N/E modules and
composed of shun out and staggered spiral fin tube and their
inlet/outlet headers in vertical layout, which will get best heat
exchange and lowest gas exhaust pressure drop.
Heating Surface of Natural Circulation
Module
1
Module
2
Module
3
Module
4
Module
5
Module
6
Gas
Exhaust
HPEconomizer1
LPEvaporator
LPSuperheater
HPEconomizer2B
HPEconomizer3
HPEconomizer2A
HPEvaporator
HPSuperheater1A
HPSuperheater1B
HPSuperheaterII

11. Advantages：
1.It’s good stability, due to low center of gravity.
2.There is large regenerative capacity to adapt various
loads.
3.Pipelines of heating surface are vertical layout.
4.Easy to operate and maintain.
Disadvantages：
1.It’s slow to startup/stop or change load, due to large
water volume.
2.Large ground acreage.

12. Steam Procedure of Natural Circulation
The feed water via the inlet header flows into the
pipelines of the HP economizer to be heated and
then goes into the HP drum.
After the feedwater gets into the HP drum, it
goes into the HP evaporater via the decline
pipes at the bottom of HP drum. After the
feedwater is heated into saturated water in the
evaporater, it flows back to the moisture
separator in the HP drum.

13. After the saturated water has been seperated
from the saturated steam, the later one via the
upper of the HP drum goes into the HP
superheater and then be heated up to
supersaturated steam which goes out of the
outlet header of HRSG.
Sprinkler has been set between the first and the
second superheater so as to maintain the normal
temperature of the working supersaturated steam.
Part of the LP steam has been extracted from the
LP drum to the deaerator and deaerate the
desoluable gas.

14. Steam Procedure of Natural Circulation
Inlet Steam Header
of HP Economizer
Pipelines of
Economizer
HP Drum
Pipelines of
HP Evaporator
HP
Superheater II
HP
Superheater I
Water Supply
heated
downstream
heated
Moisture
Separation
Saturated
Steam
de-
superheating
Keep Proper
Temperature
To Steam
Turbine

15. Principe of Deaerator
Gas Hazard
Insoluble gas, such as oxygen and nitrogen,
impedes heat exchange and corrupts pipelines.
Thermal Deaerator Principle
Dalton's Law of Partial Pressure:
The pressure of a mixture of gases is equal to
the sum of the pressures of all of the
constituent gases alone.

16. Henry‘s law:
Several conditions to ensure that effect:
1. Water must be heated to saturation temperature, to
ensure that the water vapor pressure close to the entire
surface of the water pressure.
2. Must be timely escaping the gas emitted in the water,
so that the various gas pressure from surface of water
reduce to zero or minimum.
3. There should be sufficient contact area between water
need deaerated and steam need heated. And reverse flow
is preferred.

17. Deaerator

18. Deaerator structure
(Sprinkler)
1- water supply
2- condensing water
3- water from water tank
4- water from HP heater
5- steam inlet
6- steam room
7- venting

19. Deaerator
Tower
( spray filler)

20. Thermal Deaerating Procedure
Two stages: general deaerating, deeply deaerating.
Deaerating Procedure. Condensing water passes by the
spread tubes of inlet header and 140 pieces of uniform
distributed constant speed (16T/h) nozzle and be ejected
into spray deaerating space as cone-shaped water
membrane.
The condensing water is heated rapidly to saturated
temperature under deaerating pressure since the heating
steam and water membrane are fully mixed in this space.
Most of the non-condensing gas are removed during
spray deaerating stage.

21. Condensing water goes into the lower multi-layer
sprinkler tray and is boiled again by mixing deeply with
steam, to remove the leftover non-condensing gas. The
dissolved oxygen standard could be less than 7ppb,
which is called deeply deaerating procedure.
Deaerated water, meeting the dissolved requirement,
flows into deaerating water tank for water supply system.

22. Other deaerating methods
Vacuum Deaerating.
The dissolved gas will escape automatically
when reduce the gas pressure on the water
surface.
For example: feed demineralized water into
condenser water tank from the annular tube
mounted outside the steam exhaust cylinder.

23. Chemical Deaerating is a supplementary means of
deaerating to remove the residual oxygen.
NH2.NH2＋O2 N2+2H2O
Conditions：
① Water temperature is higher than 100℃ for fast
reaction.
②Water pH value is around 9-11 for fast reaction.
③Surplus capacity of hydrazine in the water.
Caution：
a) Start hydrazine feeding pump when HRSG starts.
b) Water temperature should be higher than 105℃ and
saturated temperature.

24. Adjusting Drum Water Quality
Method: Add NO3PO4 into HP/LP drum.
Function：
a) Adjust the pH value of water.
b) The Ca+, Mg+ and PO4
- react into soft sediment and
drain out of drum, to prevent from generating furring on
the inner side of drum wall, which will be harmful for
heat exchange.

25. Adjusting Drum Water Level
Tri-parameter: water level, water flow and steam flow.
Adjusting Water Level：
1、Adjust single-parameter if steam flow is less than
20% rated flow.
2、Adjust tri-parameter if steam flow is more than 20%
rated flow.
Dynamic Equilibrium of Water Level：
Condensing Flow + Fill Water = Supply Flow = Steam
Flow

26. Principe of Water Level Gauge
1、Glass Water Level
Gauge
Principle: Connectivity
Principle
Differential: Due to heat
loss, gauge’s value is a
little bit lower than real
level.

27. Electronic Pressure Difference
Gauge
 The static pressure of the point A
 Pa=Pg+Hs* ρ’’g+Hw* ρ’*g
standard water column
 The static pressure of the point A’
 Pa’=Pg+Hr* ρr*g
 The differential pressure between
the point A and the point A’ is the
differential pressure of the
electronic differential pressure
water gauge
 ΔP= Pa’- Pa=[Hr* ρr-(Hw* ρ’+Hs* ρ’’)]*g
 由Hs= Hr- Hw带入上式：
 Hw＝ [Hr* (ρr- ρ’’)- ΔP/ g]/（ ρ’－ ρ’’）
 Hr,pr is the design value of the
gauge.Generally, the temperature
of the standard water column is
38 degree
汽包Drum
凝液罐Condensing Tank
Hr

28. Relationship of difference and level L
Nearly Reverse
Caution：
It’s a must to calibrate the electronic
pressure difference gauge before use.
Usually use glass level gauge as
reference.
O
ΔP

29. Pinch, Less Enthalpy and Hot-side
Temperature Difference
Pinch Δtx: It’s also called as node temperature
difference. It is the temperature difference between
saturated vaporizing water and exhaust from output of
evaporator.
Less Enthalpy Δtw: It’s also called close to points
temperature difference. It’s the temperature difference
between water from outlet of economizer and saturated
temperature under matched pressure. Economizer is
designed into less saturated status to prevent from
being vaporized when economizer absorbs too much
heat under partial load of gas turbine.

30. If close to point temperature difference is over range, it
will reduce heat absorption, which means less heat
absorption in evaporator. In order to ensure the same
evaporation, the surface of heat absorption should be
increased. So it’s usually set close to point temperature
difference as 5-20 ℃.
Hot-side temperature difference. It’s difference between
exhaust temperature from superheater inlet and steam
temperature from superheater outlet. If reducing this
difference, it can obtain higher superheat and enlarge
surface of heat exchange in superheater. Usually it’s
set around 30-60 ℃.

32. Influence of exhaust resistance
Increase of exhaust resistance means increase of
pressure difference between HRSG inlet and venting
chimney.
The faster flow or larger heat transfer factor it is, the
less surface of heat exchange it needs.
But it will cause the increase of exhaust pressure to
gas turbine and decrease of power output.
Every 1kPa resistance it increases, the output reduces
0.8%.

33. Exhaust Venting Temperature
It depends on node temperature difference. In order to
prevent from low temperature corrosion, it’s better 10 ℃
higher than acid dew point.
The exhaust venting temperature is usually 110-130 ℃.
The acid corrosion’s range is 100-130 ℃, and tube wall’s
temperature is a little bit higher than water inside, so the
water supply temperature could be 5-10 ℃ lower than
acid dew point when burning sulf-fuel.
The exhaust dew point is due to the acid volume in
exhaust, SO3 volume converted from SO2 and
overfeeding air factor of HRSG.

34. Relationship of Venting Temperature and
Corrosion Strength
Sulfuric Acid
Concentration
Temperature/ ℃
MaterialLoss

35. Legend & Abbrev. of HRSG
Refer to PDF file.

36. Chapter 2
Structure and Accessory of HRSG

37. Structure of Natural Circulation
1- expansion joint
2- inlet flue
3- heat preservation
4- drum
5- chimney
6- outlet flue
7- expansion joint
8- economizer
9- downstream pipeline
10- evaporator
11- superheater
12- manhole
13- steel frame
14- upstream pipeline

38. #7 HRSG in
Nanshan Power
Plant (natural
circulation)

39. #7 HRSG in Nanshan Power Plant
(natural circulation)

40. #7 Gas Turbine in Nanshan Power Plant

41. Forced Circulation HRSG
Upper Transition
Section
Economizer
Evaporator/Superheater
Venting Chimney
Drum
Steel Frame
L-type Flue
Inlet Flue

42. #10 HRSG in
Nanshan Power
Plant

43. Design Parameters of #10 HRSG
Steam Pressure of HP Outlet
Steam Temp. of HP Outlet
Max. Continuous Evaporation Vol. of HP Outlet
Steam Pressure of LP Outlet
Steam Temp. of LP Outlet
Max. Continuous Evaporation Vol. of LP Outlet
Steam Pressure of Deaerator
Steam Temp. of Deaerator
Evaporation Vol. of Deaerator
Temp. of Water Supply
Inlet Temp. of Condensing Heater
30 ℃ circumstance temp. / 180CST heavy oil

44. #10 HRSG in
Nanshan Power
Plant

45. #10 Gas Turbine in Nanshan Power Plant

46. #3 HRSG in
Nanshan Power
Plant (bypass flue)

47. Directly-through
HRSG
When the steam pressure is
over 16MPa and even
reaches supercritical
parameters, choose directly-
through HRSG
to improve circulation
efficiency.

48. Steam Header
Each steam header is an integrated module, which is
composed of tubes of heat exchange surface, steam box,
tube plate, side plate and sealing box. Tubes of heat
exchange surface is composed of horizontally staggered
spiral fin tubes. It’s node length is 6.25-8.0mm. There are
2 piece of tube plate and 8 pieces of side plate to
support all the tubes inside steam header.

49. Structure of
Steam Header

50. Steam Header of HP Superheater

51. Steam Header of LP Superheater

52. Steam Header

53. Assembly of Steam Header

54. Structure of CMI Steam Header

55. CMI heat exchanger is designed to allow free
expansion of tubes.
Expansion:
Forward
Backward
Downward

56. Combined Header
Combined header is the last assembly after tubes and
frames.
The combined header of economizer and superheater
are the same.
The combined header of evaporator is different usually.
The diameter of inlet is smaller than the one of outlet,
because inlet is water while outlet is mixture of steam
and water.

57. Flue
It’s composed of Inlet L-type flue, outlet flue and
chimney.
In order to support the pressure and impact of gas
exhaust in normal operation, it use steel sealing frame
and different steel outside to strengthen structure.
There is 100mm thick inner temperature preservation in
L-type flue to mitigate thermal impact during startup.
There are temperature preservation outside outlet flue
and chimney to prevent low temperature.

58. Exhaust Venting System
The chimney is 60m tall and there are water-resistance
device inside. Lightening protection measure and anti-
aircraft collision warning lights are also mounted on
the outlet of chimney.
Chimney is mounted on the backstop and connected
with outlet flue by metal expansion joint.

59. The temperature preservation structure ensures that it
isn’t higher than 50 ℃ when circumstance temperature
is 25 ℃. The material of temperature preservation is
aluminosilicate fiber and the temperature drop is no
more than 4 ℃ from gas turbine exhaust to inlet
(superheater) of HRSG.
It’s full-TIG welded structure for the heating surface
and the connectors of steam headers.

60. Expansion Joint
There is flexible expansion joint before L-type flue to
absorb horizontal and vertical expansion of L-type flue.
Non-metal expansion joint absorbs downward and
forward displacement generated by HRSG in hot
operation status.
It’s universal compensation, isolation and noise
reduction.

61. Tube Material of HRSG
20G, carbon steel. The tube and pipe production
process strictly, and it can be used as a high-pressure
tubes ≤ 480 ℃ heating surface tubes and ≤ 430 ℃
header pipes, without pressure limitation.
12Cr2Mo1G, Austenitic alloy steel. It has a good overall
performance, but the high temperature strength and
technological properties such as 12Cr1MoVG Steel ≤
580 ℃ of the superheater, reheater, ≤ 565 ℃'s header,
pipeline.

62. Structure of HP Drum
In order to meet the quick-start and various load needs,
HP drum uses large-diameter cylinder, bi-layer structure
both inside and outside; liner for the isolation shell,
shell casings for the pressure.
First stage separation is a large space jet gravity
separation. The mixture of steam and water goes from
the bottom of the drum to the mezzanine, spray from the
top down, and separate by gravity.
Second stage separation uses waving plate separator
and uniform steam orifice in front of the steam outlet at
the top of drum.
In the largest continuous evaporation, water in drum can
maintain 3-4 minutes.

63. Structure of CMI HP Drum
Whirlpool Destroyer
Downstream Pipeline
Feed Water Distributing Header
Mist Eliminator
Water Supply from Economizer
Mixture of Steam and Water
from Evaporator
Saturated Steam to Superheater
Multi-aperture Separating Plate

64. Structure of HMI Drum

65. Structure of Drum
Separator
Downstream Pipeline with
Whirlpool Destroyer
16 pieces of Whirlpool
Separator
Connecting Tube
Scrubber
Steam
Outlet
Mist
Eliminator
Centerline of
Drum Diameter of
Drum
Inner Feed Water
Pipeline

66. Steam Header of
Desuperheater/Superheater
Desuperheater is mounted before HP/LP superheater
outlet to adjust and control the temperature
superheated steam.
Desuperheating manner is water spray desuperheating.
The desuperheater is composed by flute-shaped tube
and mixed-lined tubes. Its diameter and thickness are:
HP(325*20mm), LP(325*10mm). The length of mixed-
tubes are: HP(4m), LP(3.95m), to ensure water and
steam will be fully mixed to prevent steam header from
being superheated or damaged.

67. HGC4-8 Multi-stage Centrifugal Electric
Pumps

68. HP Feedwater Pump
Manufacturer Germany KSB
Model multistage centrifugal pump)
Quantity 2×100%
Rated Flow 230 M3/H
Net Positive Suction Head 5.3 M
Head 930 M
Rotating Speed 2983 RPM
Model of Motor AMA400L2L BAH
Power of Motor 750 KW
Rated Current 85 A
Voltage/Frequency 6000 V/ 50 HZ
Rotating Speed 2977 RPM
Power Factor 0.88
Manufacturer of Motor ABB

69. Mechanical Seal
Pump’s joint is vertical, which is easy to take out rotor
for maintenance. It’s mechanical seal between pump
body and shaft. The sealing surface of HP feedwater
pump is mutual meshed by static and rotating ring
made by graphite and tungsten carbide. (Mechanical
seal picture is shown next page.) Sleeve(7) is
connected to rotating sealing ring(2) on shaft. Sealing
gland(8) press static sealing ring(5) and rotating
sealing ring(2) together.
In order to long-time work, cooling water is used to
take out the friction heat generated by the relative
movement between static ring(5) and rotating ring(2).

70. Cooling
Water
Cooling
Water
Mechanical Seal

71. Wash and Steam Sootblowers of
Heating Surface
Washing spray pipes are mounted upon the parallel
tubes of feedwater heater and HP evaporator to spray
water to 100% cross section of steam pipelines to
wash pipeline fouling regularly.
Washing water could be HP feedwater or LP
feedwater.

72. The rotating telescopic steam sootblowers are
mounted along the fin tubes. The steam sootblowers’
working pressure and temperature are 2.5MPa and 350
℃. The layout of steam sootblowers is suitable for the
moving stroke of sootblower tubes.
It is designed to continuously work half a year. At the
same working condition, the reduction of HP/LP
superheated steam should not be more than 1T/h as
well as the reduction of venting temperature should
not be more than 2 ℃.
There are three steam sootblowers each floor and
totally 9 floors. Overhaul platforms are mounted each
two floors.

73. HP Feedwater Pump

74. Seal of HP Feedwater Pump

75. LP Feedwater Pump

76. Seal of LP Feedwater Pump

77. LP Circulating Pump

78. HP Circulating Pump

79. Deaerating Circulating Pump

80. Spring-loaded
Safety Valve

81. Pneumatic
Control Valve

82. Electric
Valve /
Motor

83. HP Drum

84. LP Drum

85. Deaerator

86. Electric Switch
Valve

87. Drainage
Expansion
Tank

88. The end.
Thanks!