The document describes the auxiliary PRDS (pressure reducing and desuperheating) system used in thermal power plants. It has two identical systems - the turbine auxiliary steam system (TAS) and boiler auxiliary steam system (BAS). Low and high capacity auxiliary steam is derived from main steam and its pressure and temperature are reduced before supplying it to various locations in the plant for processes like deaeration, soot blowing, oil heating etc. The systems use control valves, isolating valves, desuperheaters and spray water to control pressure and temperature.

1. APRDS SYSTEM
BY
SHARAVAN TRIPATHI
JIPT

2. Auxiliary PRDS System
• Auxiliary PRDS system consists of a Turbine
PRDS control system as well as Boiler PRDS
control system. The controller of these system
are pneumatically controlled. Both the
systems are identical in nature.
• Auxiliary steam is tapped from the main
steam line and its pressure is reduced and de-superheated
to the required temperature and
pressure.

3. Auxiliary PRDS System
• The spray water for de-superheating is
supplied from the CEP discharge header.
• In order to obtain better operational
flexibility and controllability range, both
the system have been split into two
identical PRDS system such as low
capacity PRDS and high capacity PRDS.

6. Auxiliary PRDS System Contd..
• The low capacity is of 30% of that of the high
capacity line.
• Each system comprises of the pressure
controller, one de-superheater and one spray
water flow controller.
• We shall henceforth call the Turbine PRDS
system as TAS and the Boiler PRDS system as
BAS.

7. System Description- High Capacity
• High capacity PRDS comprises of steam pressure
reducing control valve, motorized upstream isolating
valve, downstream manual isolating valve, one spray
water temperature control valve and one de-superheater.
• A motorized regulating globe valve is provided in
bypass line of, which can be operated remote manually
in case of mal-operation of the pressure control valve.
• A motorized bypass globe valve is provided for spray
water control valve , which can be operated remote
manually in case of mal-operation of spray water
control valve.

8. System Description- Low Capacity
• Low capacity PRDS comprises of steam pressure reducing
control valve, motorized upstream isolating valve,
downstream manual isolating valve, one spray water
temperature control valve and one desuperheater.
• A motorized regulating globe valve is provided in bypass
line of, which can be operated remote manually in case of
mal-operation of pressure reducing control valve.
• A motorized bypass globe valve is provided for spray water
control valve, which can be operated remote manually in
case of mal-operation of spray water control valve.

9. TAS/BAS Pressure/ Temperature Control
• The auxiliary steam pressure control valve supplies
steam to TAS/BAS header by maintaining TAS/BAS
line pressure constant at the set point (11 kg/cm2).
Downstream pressure of PRDS valve is taken as
controlled pressure.
• The auxiliary PRDS spray water flow control valve
(CD) maintains the TAS / BAS line temperature
constant at the set point (2600C for TAS & 2200C for
BAS). The downstream temperature of PRDS valve is
taken as controlled temperature.

10. Selection of HT & LT PRDS
• During unit start up auxiliary steam for turbine is supplied
to Deaerator initial heating & pegging, Turbine Gland
Sealing. To meet this high demand of auxiliary steam HT
PRDS should be put into service.
• After unit synchronization and at about 30 to 40% of unit
load deaerator pegging is supplied from CRH / turbine
extraction line (CAP) and pegging from TRDS is cut out. At
about 40% unit load also, turbine gland sealing supply valve
from TPRDS closes as turbine becomes self-sealing
condition.

11. Uses of Aux Steam at various locations of plant
LTPRDS:-
1) VAM
2) FO heating
3) HFO Atomizing
4) Mill Inerting
5) Wet steam washing
HTPRDS:-
1) Turbine Gland Sealing
2) Deaerator Pagging
3) APH soot blowing

12. Vapor Absorber Machine (VAM)

13. Vapor Absorber Machine (VAM)

14. Vapor Absorber Machine (VAM)
• Absorption refrigeration systems replace the
compressor with a generator and an absorber.
Refrigerant enters the evaporator in the form of a
cool, low-pressure mixture of liquid and vapor (4).
• Heat is transferred from the relatively warm water
to the refrigerant, causing the liquid refrigerant to
boil. Using an analogy of the vapor compression
cycle, the absorber acts like the suction side of the
compressor—it draws in the refrigerant vapor (1) to
mix with the absorbent. The pump acts like the
compression process itself—it pushes the mixture
of refrigerant and absorbent up to the high-pressure
side of the system.

15. Vapor Absorber Machine (VAM)
• The generator acts like the discharge of the
compressor—it delivers the refrigerant vapor (2) to
the rest of the system.
• The refrigerant vapor (2) leaving the generator
enters the condenser, where heat is transferred to
water at a lower temperature, causing the
refrigerant vapor to condense into a liquid. This
liquid refrigerant (3) then flows to the expansion
device, which creates a pressure drop that reduces
the pressure of the refrigerant to that of the
evaporator. The resulting mixture of liquid and
vapor refrigerant (4) travels to the evaporator to
repeat the cycle.

16. How Absorption Machine Works
• Absorption system employs heat and a
concentrated salt solution (lithium bromide) to
produce chilled water. In its simplest design the
absorption machine consists of 4 basic components:
1. Generator
2. Condenser
3. Evaporator
4. Absorber

18. Function of Components
Generator:
• The purpose of the generator is to deliver the refrigerant
vapor to the rest of the system.
• It accomplishes this by separating the water (refrigerant) from
the lithium bromide-and-water solution.
• In the generator, a high-temperature energy source, typically
steam or hot water, flows through tubes that are immersed in
a dilute solution of refrigerant and absorbent.
• The solution absorbs heat from the warmer steam or water,
causing the refrigerant to boil (vaporize) and separate from
the absorbent solution.
• As the refrigerant is boiled away, the absorbent solution
becomes more concentrated. The concentrated absorbent
solution returns to the absorber and the refrigerant vapor
migrates to the condenser.

21. Condenser:
• The purpose of condenser is to condense the
refrigerant vapors. Inside the condenser, cooling
water flows through tubes and the hot refrigerant
vapor fills the surrounding space.
• As heat transfers from the refrigerant vapor to the
water, refrigerant condenses on the tube surfaces.
The condensed liquid refrigerant collects in the
bottom of the condenser before traveling to the
expansion device.
• The cooling water system is typically connected to
a cooling tower. Generally, the generator and
condenser are contained inside of the same shell.

23. Expansion Device:
• From the condenser, the liquid refrigerant flows
through an expansion device into the evaporator. The
expansion device is used to maintain the pressure
difference between the high-pressure (condenser) and
low-pressure (evaporator) sides of the refrigeration
system by creating a liquid seal that separates the high-pressure
and low pressure sides of the cycle.
• As the high-pressure liquid refrigerant flows through
the expansion device, it causes a pressure drop that
reduces the refrigerant pressure to that of the
evaporator. This pressure reduction causes a small
portion of the liquid
• refrigerant to boil off, cooling the remaining refrigerant
to the desired evaporator temperature. The cooled
mixture of liquid and vapor refrigerant then flows into
the evaporator.

24. Absorber:
• Inside the absorber, the refrigerant vapor is absorbed
by the lithium bromide solution. As the refrigerant
vapor is absorbed, it condenses from a vapor to a
liquid, releasing the heat it acquired in the evaporator.
• The absorption process creates a lower pressure within
the absorber. This lower pressure, along with the
absorbent’s affinity for water, induces a continuous
flow of refrigerant vapor from the evaporator. In
addition, the absorption process condenses the
refrigerant vapors and releases the heat removed from
the evaporator by the refrigerant. The heat released
from the condensation of refrigerant vapors and their
absorption in the solution is removed to the cooling
water that is circulated through the absorber tube
bundle.

26. • As the concentrated solution absorbs more and
more refrigerant; its absorption ability decreases.
The weak absorbent solution is then pumped to the
generator where heat is used to drive off the
refrigerant. The hot refrigerant vapors created in
the generator migrate to the condenser. The cooling
tower water circulating through
• the condenser turns the refrigerant vapors to a
liquid state and picks up the heat of condensation,
which it rejects to the cooling tower. The liquid
refrigerant returns to the evaporator and completes
the cycle.

29. FO Heating
Viscosity
• The viscosity of a fluid is a measure of its internal
resistance to flow. Viscosity depends on
temperature and decreases as the temperature
increases.
• Any numerical value for viscosity has no meaning
unless the temperature is also specified.
• Viscosity is measured in Stokes / Centistokes.
Sometimes viscosity is also quoted in Engler,
Saybolt or Redwood.

30. • Each type of oil has its own temperature - viscosity
relationship. The measurement of viscosity is made
with an instrument called Viscometer.
• Viscosity is the most important characteristic in the
storage and use of fuel oil. It influences the degree
of pre-heat required for handling, storage and
satisfactory atomization. If the oil is too viscous, it
may become difficult to pump, hard to light the
burner, and tough to operate.
• Poor atomization may result in the formation of
carbon deposits on the burner tips or on the walls.
Therefore pre-heating is necessary for proper
atomization.

31. Pressure Reduce Steam.

34. OIL GUN
HFO NOZZLE
VALVE SCAVENGE
ATOMISING
STEAM VALVE
VALVE
AB ELEVATION
CD ELEVATION
EF ELEVATION
Atomizing Steam Scheme
Oil Gun Connection
HFO Automizing

35. Oil Gun on Elevation AB

36. Oil Gun on Elevation CD & Above

39. Mill Inerting system

40. Wet Steam Washing
• During operation, deposits occur on the turbine
blading to a greater or lesser degree depending on
the steam purity [1] and the pressures and
temperatures of the operating steam. These
deposits cause a reduction of the turbine generator
unit’s efficiency due to:
Changes in the flow profiles
• Thicker boundary layers in the steam
• flow as a result of rough surfaces.

41. • In extreme cases the flow area of turbine may get reduced
with consequent reduction in the maximum possible steam
flow through the turbine, and corresponding output. Choking
of blade flow path can be detected on the basis of internal
efficiency measurement
• If deposit leads to an increase in stage pressures, the
maximum stage pressures shown in the Technical Data should
not be exceeded. If necessary, the output must be reduceds.
• water-insoluble, silicate deposits occur in a temperature
range between 500°C and 350°C. Alkali silicates and silicic acid
are deposited between 350°C and 60°C.
• Salt deposits occur at temperatures ranging from 480°C to the
blading stages where condensation begins. Salt deposits are
water-soluble and can be removed by steam washing with
saturated steam. Depending on their composition, silicate
deposits are either water-soluble (e.g. alkali silicates) or occur
as a hard Water-insoluble coating. In latter case the deposits
can only be removed mechanically during overhauls.

43. Steam Washing of IP Turbine
• All stop and control valves and all valves in the extraction
lines remain closed during steam washing of the IP turbine.
• Any isolating valves present upstream of the feed water
heaters must also be closed.
• The drains from the IP turbine between the reheat control
valves and the IP outlet, the extraction valves or the swing
check valves in the extraction lines must be vented during
steam washing only to the extent required to allow the
condensate arising to drain off whilst preventing excessive
loss of steam.
• All other drains from the turbine generator must be full open.
After the saturated steam line (Fig.1, item 2) has been joined
up at the connection points (3), the washing steam can be
routed into the IP turbine, from there via the cross-around
lines to the IP turbine and then to the condenser.

44. Steam Washing of HP Turbine
• The main control valves must be open during steam washing
of the HP turbine.
• All drains (7, 8) from the HP turbine situated between the
main stop valves and the HP outlet may be vented during
steam washing only to the extent required to allow the
condensate arising to drain off while preventing excessive loss
of steam.
• All other drains particularly those in the cold reheat line, must
be fully open.
• Local drainage may also be provided so that no steam can
enter the Reheater of the Boiler, if at all possible. After the
steam line (6) has been joined up at the connection points (3),
the stream can be routed into the HP turbine.
• The steam leaving the HP turbine is exhausted to the
condenser via the drains (9). The condensate is discharged
and samples are taken to determine the salt content as
described in steam washing of IP turbine, the completion
criteria remaining same.

45. Gland Sealing System

47. FUNCTION
• This system ensures the sealing of glands in HP, IP and
LP turbine under various load conditions. The turbine
glands are self seal type (refer gland sealing scheme).
Upto 40% load, steam from an auxiliary source through
valve (MAW10AA001) is taken to seal all the HP,IP and
LP glands.
• During this period the valve (MAW50AA001)
connecting this header to condenser is kept closed.
After 40% load, seal steam valve (MAW10AA001) is
closed and the leak steam valve (MAW50AA001) is
opened.
• Pipings are so sized that the leak off steam from front
and rear ends of HP turbine goes to the condenser
through the valve (MAW50AA001), while steam from
the two IP glands is utilised for sealing the LP glands,
thus avoiding the use of a desuperheater.

48. • The leak off steam and air from the last chambers of
each rotor is sucked into a gland cooler. Building up of
vacuum in the condenser is the first step during start
up. For building up vacuum, it is necessary to seal the
turbine glands by supplying steam to the shaft through
the valve (MAW10AA001).
• The control system opens the gland steam supply valve
(MAW10AA001) until the pressure in the header
acquires a preset value. Subsequently when the set
picks up load, the pressure of steam inside HP and IP
turbine builds up resulting in the leakage of steam from
the turbine into gland steam supply header which in
turn would result in increase of pressure in the header.
• The controller gradually closes the gland steam supply
valve (MAW10AA001) and opens gland leak off valve
(MAW50AA001), if required.

49. 49
Why Deaeration?
Corrosion in boilers is caused by three factors:
1. Feed water temperature
2. Feed water pH value
3. Feed water oxygen content
Temperature and pH value influence the aggressiveness of
corrosion. The higher the temperature, and the lower the pH
value the increased aggressiveness of the feed water. The
dissolved oxygen content of the feed water is a large factor in
determining the amount of corrosion that will take place. The
presence of oxygen, and other non-condensable gases, in the feed
water is a major cause of corrosion in the feed water piping,
boiler, and condensate handling equipment.

50. 50
Why Deaeration?
• Reduce corrosion by dissolved gas: oxygen,
carbon dioxide. Oxygen is the most
aggressive even in small concentrations.
• Sources of oxygen: makeup water,
condensate return system.
• Pitting corrosion. Degree of oxygen attack
depends on concentration of dissolved
oxygen, the pH and the temperature of the
water.

51. Removal of oxygen, carbon dioxide and other
non-condensable gases from feed water.
51
What is Deaeration?

52. 52
Deaerator Principles
Deaeration is the mechanical removal of dissolved gases from the boiler feed
water. There are three principles that must be met in the design of any
deaerator.
1. The incoming feed water must be heated to the full saturation temperature,
corresponding to the steam pressure maintained inside the deaerator. This
will lower the solubility of the dissolved gases to zero.
2. The heated feed water must be mechanically agitated. This is accomplished in
a tray deaerator by first spraying the water in a thin film into a steam
atmosphere. Creating a thin film reduces the distance, the gas bubble has to
travel to be released from the water. Next, the water is cascaded over a bank
of slotted trays, further reducing the surface tension of the water. This allows
for the removal of any gases not liberated by the initial spraying.
3. Adequate steam supply must be passed through the water, in both the spray
section and the tray section to sweep out the gases from the water.

53. The easiest way to de-aerate is to force steam into the feed water,
this action is called scrubbing. Scrubbing raises the water
temperature causing the release of O2 and CO2 gases that are
then vented from the system. In boiling section steam is used to
"scrub" the feed water as
(1)steam is essentially devoid of O2 and CO2,
(2)steam is readily available and
(3)steam adds the heat required to complete the reaction.
53
Deaerator Principles

54. For efficient operation, de-aerating equipment must satisfy the
following requirements:
(1)Heating of the feed water: The operating temperature in the unit
should be saturation temperature. If this temperature and
pressure cannot be economically achieved then it is important to
get as close to it as possible.
(2)Agitation decreases the time and heat energy necessary to
remove dissolved gases from the water.
(3)Maximization of surface area by finely dispersing the water to
expose maximum surface area to the steam. This enables the
water to be heated to saturation temperature quicker and
reduces the distance the gases have to travel to be liberated.
(4)The liberated gases must be vented to allow their escape from the
system as they are released.
54

55. 55

56. 56

57. 57

58. 58
DEAERATION
Oxygen reacts with water ( H20 ) to give ( OH
- ) ION
Fe = Fe+ + e-
O2 + 2H2O + 4e- = 4OH-Fe+
+ 2OH- = Fe(OH)2
2Fe + O2 + 2H2O = Fe(OH)2

59. 59
DEAERATION
Carbon dioxide is an acidic gas and
could form carbonic acid with water,
carbonic acid liberates H+ ions that
attacks on metal.
CO2 + H20  H2CO3
 H+ + HCO
2H+ + 2e- = H2
-
3

60. 60
TYPES OF DEAERATION
1. Physical deaeration.
2. Chemical deaeration.
PRINCIPAL FOR PHYSICAL DEAERATION
The principle of deaeration is based on the following laws
• HENERY’S LAW
• DALTON’S LAW OF PARTIAL PRESSURE

61. 61
Dalton’s Law of Partial Pressure
It states that the pressure in a container having a
mixture of a gas and vapour, is the sum of partial
pressure of the vapour at the common
temperature and the partial pressure of the gas,
at any point inside.

62. 62
HENERY’S LAW
• The mass of gas with a definite mass of liquid,
which will dissolve at a given temperature, is
directly proportional to the partial pressure of
the gas in contact with the liquid.
• This hold with in the close limit for gases which
don’t unite chemically with water.

63. Decreasing the partial pressure of the gas in water
may be achieved by following methods:
63
Use of another gas to remove the undesirable
gases e.g. Nitrogen can be used to remove
oxygen.
Decreasing the total pressure so as to
approach the vapour pressure of the water.
Increasing the vapour pressure by heating
the water

64. (A) According to working pressure under which they
operate:
 Vacuum deaerator
 Atmospheric deaerator
 High pressure deaerator
64
Classification of Deaerator

65. 65
Vacuum Deaerator

66. 66
Classification of Deaerator
(B) Also deaerator can be classified in accordance with the
mode of steam-water distribution:
Atomizing ( spray ) type
Tray type
Film type ( combination of both spray and tray
type)

67. 67
Tray Type Deaerator

68. 68
Tray Type Deaerators
These are composed of a deaerating section and a feed water storage
section. Incoming water is sprayed through a perforated distribution pipe into
a steam atmosphere where it is atomized. There it is heated to within a few
degrees of the saturation temperature of the steam. Most of the non-condensable
gases are released to the steam as the water enters the unit. The
water then cascades through the tray section, breaking into fine droplets,
which immediately contact incoming steam. The steam heats the water to the
saturation temperature of the steam and removes all but a trace of
oxygen. Deaerated water falls to the feed water storage section below and is
protected from recontamination by a blanket of steam. As the non-condensable
gases are liberated, they as well as a small amount of steam are
vented to atmosphere. It is essential that sufficient venting is provided at all
times or deaeration will be incomplete.

69. 69
Tray Type Deaerator

70. 70
Trays

71. 71
Spray Type Deaerators

72. 72
Spray Type Deaerators
The spray-type deaerators do not use trays for dispersion of the water. In this
case, spring loaded nozzles located in the top of the unit spray water into a steam
atmosphere which is heated to within a few degrees of the saturation temperature
of the steam. Most of the non-condensable gases are released to the steam, and
the heated water falls to a water seal and drains to the lowest section of the steam
scrubber. The water is scrubbed by large quantities of steam and heated to the
saturation temperature prevailing at this point. The intimate steam to water
contact achieved in the scrubber efficiently strips the water of dissolved gases. As
the steam-water mixture rises in the scrubber, a slight pressure loss causes the
deaerated water temperature to remain a few degrees below the inlet steam
saturation temperature. The deaerated water overflows from the steam scrubber
to the storage section below. The steam, after flowing through the scrubber,
passes up into the spray heater section to heat the incoming water. Most of the
steam condenses in the spray section to become part of the deaerated water. A
small portion of the steam, vented to atmosphere, removes non-condensable
gases from the system.

73. 73
Spray Type Deaerators

74. Spray Valve
74

75. 75
Counter & Parallel Flow Deaerator

76. 1. In this design, the inlet water is sprayed into a steam atmosphere
spray nozzles.
2. This action heats the water to liberate most of the dissolved gases.
3. This flows down through water seals for distribution over the tray
bank, which serve two functions.
4. First they prevent gases liberated in the initiate heating, from
entering the tray bank.
5. Second they direct the steam to flow down through the trays,
before entering the upper heating section.
6. The main function of the tray bank is to remove the remaining
amounts of dissolved gases, not liberated in the initial heating.
76
Parallel Down Flow

77. 7. Since very little, or no heating takes place in the trays, the entire
volume of steam is used to scrub out the remaining gases.
8. The trays are slotted, and provide a great amount of spilling
edge.
9. This allows for a great amount of water surface area to be
exposed to the steam.
10.Water and steam flow downward through the trays.
11.The steam, after exiting the tray bank, steam is condensed by
the colder inlet water, and a small amount is vented to
atmosphere, along with the dissolved gases.
77
Parallel Down Flow

78. 78
Packed Column Type

79. 1. Inlet water is sprayed into a steam atmosphere through a
variable orifice & spring loaded spray nozzle.
2. water heating liberate dissolved gases & heated water
flows down onto a distribution plate, which evenly
distributes the water over the entire cross-sectional area
of the tower packing.
3. As the water flows down through the distribution plate it
enters a steam chest area, where it is further heated by
up flowing steam and more of the dissolved gases are
liberated.
79
Packed Tower

80. 1. Remaining dissolved gases are removed when the water
flows down from the steam chest and then down through
the packing tower.
2. The packing tower exposes a greater surface area of the
water; while up flowing steam completes the deaeration
process. The water leaving the bottom of the packing
tower is given a final scrubbing of steam.
3. The steam, entering the deaerator from below the packing
tower, is introduced through a fixed orifice steam
distributor. This steam distributor directs high velocity
steam through the down flowing water leaving the bottom
of the packing tower.
80
Packed Tower

81. 81
Deaerator Functions
Deaerator has to meet following needs.
 It does deaeration
 Acts as a feed water heater.
 Acts as a storage tank (reservoir)
 Accept the leak-off flows from the BFP.
 Accept the H.P. Heater drains.
 Heat the tank content from cold to provide
hot deaerated water for unit start-up.
 Ensure NPSH for BFP

82. 82
DEAERATING RATIO
O2 Content in Condensate at
inlet to deaerator
= 6
O2 Content in feed water at outlet S.T.

83. TECHNICAL PARTICULARS OF DEAERATOR
1. Type Tray with external vent condenser
2. Design Pressure Kg/cm2 7.4
3. Design Temperature OC 250
4. Hydraulic Test Pressure Kg/cm2 11.1
5. Storage capacity M3 90
6. No. of perforated trays 5
83

84. 84
Operating Conditions of Deaerator
 Temperature of deaerated water must be equal to
saturation temp. of water corresponding to the
pressure at which deaerator operates.
 Sufficient heating steam must be delivered to the
deaerator to ensure continuous boiling of water
undergoing deaeration.
 The feed water charge to deaerator must be
disintegrated into fine droplets to ensure better heat –
transfer
 Deaerator must be provided with sufficient venting to
purge all the non-condensing gases out of the system
and to ensure minimum partial Pressure of these gases
in the upper part of the deaerator.

85. Causes of High O2/CO2 Concentration
 Inadequate deaerator vent leading to accumulation of
non-condensing gases and increase in their partial
pressure.
 High feed-water flow rate.
 Delivery of O2 - containing condensate directly into
85
the storage tank.
 Frequent pressure drop in the deaerator.
 Faulty deaerator internals.
 Delivery of relatively “cold” flows with higher O2 -
content to deaerator.

86. While the most efficient mechanical deaerators
reduce oxygen to very low levels (.005cc/l or 5
ppb), even trace amounts of oxygen may cause
corrosion damage to a system. Consequently,
good operating practice requires removal of that
trace oxygen with a chemical oxygen scavenger
such as sodium sulfite or hydrazine.
86

87. 87
Chemical Deaeration
The addition of an oxygen scavenging chemical (Sodium Sulphite or Hydrazine) will
remove the remaining oxygen and prevent corrosion.
Na2SO3 + O2 = Na2SO4
Sodium Sulphite Oxygen Sodium Sulphate
Now obsolete, as it increases the total dissolved solids.
Modern Practice: Hydrazine is used for chemical Deaeration.
N2H4 + O2 = N2 + 2H2O
3N2H4 = 4NH3 + N2
Additional ammonia reacts with
2NH3 + CO2 + H2O = (NH4)2CO3
(acidic) Ammonium Carbonate (Neutral)

88. 88
FST - Deaerator

89. 89

90. Disadvantages of Counter Flow Deaerators
• Inability to deliver 0.007 ppb outlet quality in applications with a
low inlet water temperature, or when 100% make-up is
required.
• Low tray loading. This reduces the flow rating for a given
diameter deaerator vs. a parallel down flow unit.
• High vent rate. This reduces operating efficiency
Advantages of Counter Flow Deaerators
• The counter flow deaerator is cheaper to manufacture.
• The higher capacity and the ability to perform under varying steam
and water conditions make the parallel down flow (and packed
tower for smaller applications) design competitive, and the only
logical choice.
90

91. Disadvantages of Atomizer Deaerators
• Inability to deliver 7 ppb outlet quality when plant conditions
vary from design specifications. Requires constant plant
conditions.
• Failure rate of the atomizer valve, and maintenance required to
keep it operating properly.
Advantages of Atomizer Deaerators
• 1. Low cost
• 2. Low overall height
The atomizer type deaerator is only effective when applied to an application with no plant or
process swings. Along with the maintenance required, this type deaerator, while inexpensive,
has only limited applications.
91

92. Disadvantages of Parallel Down Flow
• More complicated design, resulting in slightly higher cost.
Advantages of Parallel Down Flow
• Time proven design
• Thousands of installations worldwide
• Design suitable for small to medium size plants
• Can meet outlet guarantees at varying plant conditions.
• High tray loading, resulting in higher outlet capacity for any
given diameter.
• Large tray spilling edge, resulting in high deaerating efficiency
• Low vent rate, resulting in increased operating efficiency.
92

93. 93
Disadvantages of Packed tower
• Height requirement
• Typically considered for small size plants.
Advantages of Packed tower
• Low cost
• Low maintenance
• Ability to handle varying plant conditions
• This design can meet the requirements for a reliable
deaerator capable of producing completely deaerated
water for small plants. Packed tower design includes
multi-stage deaeration, to deliver top performance.

94. CORROSION is defined as the destruction of a metal by chemical or
electromechanical reaction with its environment. Corrosion dramatically
increases maintenance costs and can cause unnecessary safety risks. It will
occur when levels of oxygen or carbon dioxide are high, where pH values are
low, where contact occurs between dissimilar metals and in corrosive
atmospheres. Corrosion is an electrochemical process in which electricity flows
through a solution of ions between areas of metal. Deterioration occurs when
the current leaves the negatively charged metal or anode and travels through
the solution to the positively charged metal or cathode, completing an
electrical circuit in much the same manner as a battery cell. The anode and the
cathode can be different metals or areas of the same metal. Corrosion occurs
when there is a difference in the electrical potential between them.
SCALE is a very hard substance that adheres directly to heating surfaces
forming a layer of insulation. This layer of insulation will decrease heat transfer
efficiency. Scale also results in metal fatigue/failure from overheating, energy
waste, high maintenance costs and unnecessary safety risks. A one-sixteenth
inch thickness of scale in a fire tube boiler can result in a 12.5% increase in fuel
consumption.
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95. FOULING occurs when a restriction develops in piping and equipment
passageways and results in inefficient water flow. The fouling of boiler room
equipment directly impacts energy efficiencies and cost of operations.
FOAMING is a condition in which concentrations of soluble salts, aggravated
by grease, suspended solids or organic matter, create frothy bubbles or foam
in the steam space of a boiler. When these bubbles collapse it creates a
liquid that is carried over into the steam system. Foaming degrades steam
quality and in some cases can create a water slug that is discharged into the
steam lines.
CAUSTIC GAUGING will occur when there is a high concentration of alkaline
salts (a pH value of 11 or greater) that will liberate hydrogen absorbed by
the iron in the steel. It will be more evident in high temperature areas of the
boiler's waterside and manifests itself in the form of hairline cracks.
HYDROGEN EMBRITTLEMENT occurs in the event of lower pH value of the
water in evaporator
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96. Thank you