2. RANKINE CYCLE
The Rankine cycle used in modern power plants has
many more components, but the four components
are common to all power plants.
In this cycle, water is heated in the steam generator
to produce high temperature and pressure steam.
This steam is then expanded in a turbine to produce
electricity from a generator that is connected to the
turbine.
The steam from the turbine is then condensed back
into water in the condenser.
The pump then returns the water to the steam
generator.
3. RANKINE CYCLE
1-2:CEP WORK
2-3:LP HEATING
3-4:BFP WORK
4-5:HP HEATING
5-6:ECO,WW
6-7:SUPERHEATING
7-8:HPT WORK
8-9:REHEAT
9-10:IPT WORK
10-11:LPT WORK
11-1: CONDENSATING
4. CONDENSER
The main purposes of the condenser are to condense the
exhaust steam from the turbine for reuse in the cycle and
to maximize turbine efficiency by maintaining proper
vacuum. As the operating pressure of the condenser is
lowered (vacuum is increased), the enthalpy drop of the
expanding steam in the turbine will also increase. This will
increase the amount of available work from the turbine
(electrical output).
By lowering the condenser operating pressure, the
following will occur:
• Increased turbine output
• Increased plant efficiency
• Reduced steam flow (for a given plant output)
It is therefore very advantageous to operate the condenser
at the lowest possible pressure (highest vacuum).
5. FUNCTION OF CONDENSER
Function of the condenser is to create a vacuum by
condensing steam,
Removing dissolved noncondensable gases from the
condensate
Conserving the condensate for re-use as the feedwater
supply to the steam generator
Providing a leak-tight barrier between the high grade
condensate contained within the shell and the untreated
cooling water
Providing a leak-tight barrier against air ingress,
preventing excess back pressure on the turbine
Serving as a drain receptacle, receiving vapor and
condensate from various other plant heat exchangers,
steam dumps, and turbine bleed-offs
receptacle for adding DM makeup
7. CONDENSER OPERATION
The main heat transfer mechanisms in a surface
condenser are the condensing of saturated steam on
the outside of the tubes and the heating of the
circulating water inside the tubes.
Thus for a given circulating water flow rate, the water
inlet temperature to the condenser determines the
operating pressure of the condenser. As this
temperature is decreased, the condenser pressure will
also decrease. As described above, this decrease in
the pressure will increase the plant output and
efficiency.
The noncondensable gases consist of mostly air that
has leaked into the cycle .
These gases must be vented from the condenser .
8. REASON FOR REMOVING AIR/GAS
• The gases will increase the operating pressure of
the condenser. This rise in pressure will decrease the
turbine output and efficiency.
• The gases will blanket the outer surface of the
tubes. This will severely decrease the heat transfer of
the steam to the circulating water. Again, the
pressure in the condenser will increase.
• The corrosiveness of the condensate in the
condenser increases as the oxygen content increases.
Oxygen causes corrosion, mostly in the steam
generator. Thus, these gases must be removed in
order to extend the life of cycle components.
9. CONDENSER TUBE MATERIALS
Copper based alloy(ASTM B 111,B543)
Stainless steel (ASTM A268, B268, A249, A213,
A269)
Titanium( ASTM B 338 Gr 1&2)
Carbon steel (ASTM A 179,A214)
15. Effect of Air Ingress
For maximum thermal efficiency, corresponding to a
minimum back pressure, a vacuum is maintained in the
condenser. However, this vacuum encourages air in-
leakage.
Thus, to keep the concentration of noncondensable gases as
low as possible, the condenser system must be leak tight,
together with any part of the condensate system that is
under vacuum. Failure to prevent or remove the
noncondensable gases may cause serious corrosion in the
system, lower heat transfer properties, and/or increase
plant heat rate due to the back pressure rise associated
with a high in leakage.
The cost of excess back pressure in terms of additional fuel
or increased heat rate .
An adequate air-removal and monitoring system is
essential.
16. SOURCES OF AIR IN LEAKAGE IN A
CONDENSER
• Atmospheric relief valves or vacuum breakers
• Rupture disks
• Drains that pass through the condenser
• Turbine seals
• Turbine/condenser expansion joint
• Tubesheet to shell joints
• Air-removal suction componets
• instrumentation, sight glasses, etc.
• Low-pressure feedwater heaters, associated piping,
• Valve stems, piping flanges, orifice flanges
• Manhole
• Shell welds
• Condensate pump seals
17. CIRCULATING WATER IN LEAKAGE
Circulating water in-leakage into the condenser has
been the major source of impurities introduced into
the condensate and, thus, has been a major factor in
boiler corrosion.
There are a number of possible causes of water in-
leakage, including:
• Use of tube materials, such as admiralty brass, that
are susceptible to erosion/corrosion
• Improperly rolled tube joints
• Poor condenser design leading to tube failures.
• Improperly supported tubes, which can lead to tube
vibration failures
• Tube manufacturing defects.
18. Water In-Leakage Detection Methods
Smoke
Thermography
Ultrasonics
Plastic wrap
Foam
Water Fill Leak Test
Rubber Stoppers
Individual Tube ressure/Vacuum Testing
Tracer Gas Method -HELIUM
19. NDE –EDDY CURRENT TESTING OF
CONDENSER TUBES
In the eddy current testing of condenser tubes, there are at
least four kinds of damage that might be detected:
• Corrosion pitting
• Crevice corrosion
• Fractures caused by tube vibration
• Through wall penetrations
In the first three, the depth of penetration is an important
benchmark, influencing a decision whether to plug the tube
as a precaution against future leaks. The identification of
through-wall leaks will of course call for them to be plugged
when all the testing has been completed.
20. CONDENSER TUBE CLEANING
Macro-fouling (accumulation of debris), not only reduces
the cooling water flow rate through the tubes it can
cause tube corrosion and tube erosion failures.
Micro-fouling (biological growth) and scaling reduces the
heat transfer coefficient and could cause under deposit
corrosion resulting in premature tube failures.
Various tube cleaning options are available to reduce or
eliminate the micro/macro fouling and scaling.
off-line
on-line methods. — (Sponge balls or brushes may be
automatically recirculated through the condenser)
21. Cycle Isolation
Generating plants often suffer from power losses/heat
rate due to leakages through valves to condenser.
Check incoming drain lines, feedwater heater high level
dumps, minimum flow valves, and steam traps for
leakage or improper operation which could add
unexpected heat load to the condenser.
To minimize leakages through valves to condenser ,
Select all control valves (e g emergency drain of
heaters) to condenser with leakage class v and Select
all isolating /drain valve to condenser with leakage class
MSS SP 61.
22. CONDENSER DESIGN CRITERIA
The steam condensing plant shall be designed,
manufactured and tested as per HEI (latest edition).
The condenser(s) shall be designed for heat load
corresponding to unit operation for valves wide open (VWO)
conditions, 3% make-up, design condenser pressure .
The value of design condenser pressure to be measured at
300 mm above the top row of condenser tubes shall be
guaranteed under VWO condition, 3% make-up, design CW
inlet temperature and CW flow.The condenser vacuum shall
be measured with a vacuum grid utilising ASME basket tips.
The condenser hotwell shall be sized for three (3) minute
storage capacity (between normal and low-low level).
Maximum oxygen content of condensate leaving the
condenser shall be 0.015 cc per litre over 50-100% load
range.
