Condensers
Sankar Bandyopadhyay
Email : sankarbando1956@gmail.com
Effect of Condenser Vacuum
10 mmHg Improvement in Condenser Vacuum
Leads to 20 Kcal/kwh Improvement in Heat Rate
for a 210 MW Unit
Annual Impact for one 210 mw Unit
Saving in Coal Consumption 9400 Tons
Saving in Coal Cost (for rail fed) 2.1 Cr
Condenser Operation
Condenser is a large heat exchanger of the shell and tube type.
Cooling water enters through the waterbox, through the tubesheet and into the
tubes.
The steam is cooled to a liquid by passing over the tubes where the cooling water
is circulated.
Heat is transferred from the steam to the cooling water. For the steam to be
condensed to water, the amount of heat removed must at least be equal to the
latent heat of vaporization.
Latent heat will depend on the pressure in the condenser and the quality of
exhaust steam.
A vacuum is produced in the condenser by the condensation process and the
specific volume change from steam to a liquid.
The tube pattern and shell volume is designed to minimize the steam side
pressure drop
Typical Steam Surface Condenser
Condenser Tube arrangement
Condensers handle large quantities of
steam at low pressure, the volumetric
flow is high.
The condenser tube arrangement
must be opened, in order to allow
steam flow into the inner region of the
tube bundle
Removal of Non-Condensable Gas
Condensers must continually vent non
-condensable gases to prevent air
binding and the loss of heat transfer capability.
Noncondensable gas has a tendency to flow to the coldest area.
This area is typically the circulating water inlet region of the condenser
Steam jet air ejectors and/or vacuum pumps establish a vacuum in the
condenser before start-up & operation and pull non-condensable gas
Rankine Cycle
Heat Rejected
in Condenser
Condenser Secondary Functions
Removing dissolved non-condensable gases from the condensate
Conserving the condensate for re-use as feed water.
Providing a leak-tight barrier between the high-grade condensate and
untreated cooling water.
Providing a leak-tight barrier against air ingress and preventing excess
backpressure on the turbine.
Serving as a drain receptacle for condensate.
Providing a convenient place for feed water makeup.
Maintains vacuum for the discharge of the turbine blades.
Condenser Classification
The number of compartments, usually one compartment for each
set of turbine two-flow exhausts
The number of tube passes, one or two
Orientation of the condenser tubes, transverse or parallel to the
axis of the turbine
Whether the circulating water flows in parallel through each
condenser shell or in series through each shell
Types of Condenser
Condenser Components
Shell
Hotwell
Waterbox
Tubesheet
Tubes
Air-removal equipment
Components
Condenser Shell Hot well
Base of the condenser is a reservoir for
The design pressure of the shell is 76.2
the condensate and is called the
cm Hg vacuum and is suitable for an
hotwell.
emergency internal pressure of 1
kg/cm Designed to have a minimum available
volume sufficient to contain all of the
Constructed of carbon or stainless
condensate produced in a period of
steel plates welded together.
one minute under conditions of
Shell is hydrostatically tested after maximum steam load.
field assembly.
Suction is provided from the hot well to
Shell might be joined to the turbine the condensate pumps
exhaust casing by an expansion joint.
Waterbox :
Constructed of carbon steel or cast iron or stainless steel, copper nickel, or titanium.
Internals are generally coated or cathodically protected to minimize corrosion.
Designed to the pressure of the circulating water system.
There should be one manway at the bottom of the box and one at the top. Two manways at the top are
preferable.
Tubesheet
Non-rigid structural member of the condenser.
Does not support the total load of waterbox pressure, the waterbox, or water in the waterbox.
Primary function is to prevent leakage of cooling water into the condensate.
Constructed of copper nickel, Muntz metal, aluminum bronze, carbon steel, stainless steel, titanium, or
carbon steel clad with stainless steel or titanium.
Condenser Classification
Tubes Air Removal Equipment
Alloy steel tubes are manufactured by The air-removal section is located
forming alloy steel strips and then welding toward the bottom of, or deep within,
them with high frequency welding the tube bundles where the
equipment.
condensate and water vapor
Tubes can be made of titanium, Al-6X, Sea- temperature tends to be lower.
cure, Al 29-4C, NuMonit, stainless steel,
copper nickel, aluminum bronze, and This region of tubes is surrounded by a
admiralty brass. shroud (roof and side panels) to
In the air-removal section, the tubes protect the tubes from being heated by
are exposed to an oxygenated, descending condensate and steam.
ammonia-rich environment. This
promotes corrosion (grooving) in
copper-alloy tube , the tube materials
is more corrosion resistant alloy such
as stainless steel.
Steam Jet Air Ejector
Vacuum Pump
Condenser Problems
Increased Condenser Pressure
Air Binding Problems
Air-Removal Equipment Problems
Condenser Cleaning
Before After
Offline Line Cleaning
Use of brushes, scrapers and hydro blasting.
These systems are relatively inexpensive.
The unit must be derated or off-line in order to clean the tubes.
Can be scheduled during boiler outages or during a scheduled load reduction.
The cleaning process requires an operator and the air and water pressures used
can impose a safety concern.
Tube cleanliness might begin to deteriorate as soon as tube cleaning is complete.
Fouling can take on different characteristics so the scraper or highpressure water
might have to deal with a hardened, tightly adherent material that is difficult to
remove.
Lances, rotating scrapers, and brushes can gouge and damage tube walls if they
are used aggressively and/or incorrectly.
On Line Cleaning
Newer Design Ball Strainer System
Advantages of the sponge ball cleaning system
Continuous cleaning of the tubes
Reduction or elimination of the need for biofouling chemical addition
Reduction or elimination of shutdown for manual cleaning
Operation is automatic
System can prevent under-deposit pit corrosion
Start-up costs are lower than for brush and cage systems
Different balls are available for different foulants
Condenser efficiency can be greatly improved
Disadvantages
Labor required for frequent ball inspection and replacement.
Adjustments to mechanized system components and controls are required.
There is tube abrasion of soft metals.
Operating costs are higher due to increased maintenance, auxiliary power consumption, and
ball replacement.
System is susceptible to the introduction of debris.
Capturing balls can be problematic. A major escape of balls into a body of water can cause
problems.
An uneven distribution of balls might not clean tubes uniformly.
Space and outlet piping configurations can influence retrofit.
Balls can become lodged in tubes, causing blockage.
Collection screens might experience fouling that increases water side pressure.
Factors affecting Condenser Performance
Condensate Subcooling
Air In-Leakage
Condensate Oxygen
Hotwell and Condensate Temperature
Circulating Water Flow
Circulating Water Temperature
Pressure Drop
As a rule of thumb, each 5 degrees of condensate subcooling results in a 0.05% increase in heat rate.
Condenser Performance Monitoring
STEAM INLET NON-CONDENSABLE
OUTLET T
CW Inlet Temp : 2 F
CW Outlet Temp : 8 NON-COND.
P
AIR/VAPOR REMOVAL
Condensate Temp: 2 OUTLET SYSTEM
P P P Back Pressure: 2
W W CW Waterbox dP: 2
Air/steam Mixture
Temp: 2
CONDENSATE W T
LEVEL
P
P
WATER OUTLET
( P)
CIRCULATING
WATER INLET
CIRCULATING
( P) T
DO S
CONDENSATE
LEVEL F PERF. TEST
4 Nos. T CONNECTION
F = FLOW MEASUREMENT T = TEMPERATURE MEASUREMENT SUPPLEMENTAL
W = WATER LEVEL MEASUREMENT DO = DISSOLVED OXYGEN MEASUREMENT TEST CONNECTION
P = PRESSURE MEASUREMENT S = SALINITY MEASUREMENT
TYPICAL CONDENSER INSTRUMENTATION
Typical Condenser Calculations
S.N Parameter Unit Test
Measured Parameters
Load MW P 210
1 Condenser Pressure mm Hg Pc 120.8
2 CW In Temp Deg.C Ti 34.16
3 CW Out Temp Deg.C To 45.09
4 Condensate Deg.C Tcon 55
Temperature
5 Air suction Temp Deg.C Ta 48.9/50.04
Calculated Parameters
6 Saturation Temp Deg.C Tsat 55.56
7 Expected Back Pressure * mm Hg Pxp 85
* Expected BP to be derived from design BP after applying corrections for Load
and CW inlet temperature during test
Typical Condenser Calculations
S.N Parameter Unit Test
8 Design CW Temp Rise Deg.C dT 10
9 Design TTD Deg.C TTD 2.5
10 Back Pressure due to CW Inlet mm Hg Ti+dT+TTD 79
Temperature
11 Back Pressure due to CW Flow mm Hg To+TTD 81
12 Variation due to CW Inlet mm Hg 7-10 -6
Temperature
13 Variation due to CW mm Hg 11-10 2
Flow/Heat Load
14 Variation due to air/Dirty mm Hg 1-11 39.8
Tubes
15 Total variation mm Hg 1-10 41.8
Condenser : Use of Multiple Technology
Helium Leak Detection Vacuum Pump Performance
Air-in-leak identified in LPT gland & parting plane CEP Suction Strainer Flange Bolts
Infrared Thermography
Improvement in Load by 10 MW DO level reduced from 110 ppb to 10-15 ppb
Complement the strength of one technology with another technology
Condenser : Use of Multiple Technology
Hole in the CRH strainer drain line Hole fixed up using clamp
Temperature difference taken by the IRT Camera around the hole
Benefits of Testing:
1. Improvement in condenser vacuum by 16 mm Hg
2. Stoppage of one vacuum pump there by reducing in APC and increased
operational reliability
3. Unit Heat rate improvement : 32 Kcal / KWHr
Condensate Dissolved Oxygen (DO) high maintaining
due to air-ingress in condenser
Condensate DO value is to maintained < 10-15 ppb if there is no air-
ingress in condenser. It should not increase the FW DO value which is
harmful for oxide deposits in boiler and turbine blades due to saturation
level of various oxides at different temperature levels.
Condensate DO may be increase with small amount of air-ingress
without impacting the condenser back pressure and without
overloading of steam ejector or vacuum pump. Air depression
temperature may not change while condensate DO is increased.
Followings are the probable area of air-ingress in condenser which is
vulnerable for increase in condensate DO.
High DO in makeup water itself by air-ingress in makeup pump.
Make up line connection and flanges near hotwell
Hotwell drain line
Hotwell manhole
Hotwell stand pipe connections for all level transmitters and switches
All flash tank drain connections to hotwell
CEP suction lines and suction strainers
CEP glands
All HP & LP heaters alternate drain lines connected to condenser
All MAL drain line valves
TDBFP condenser connections and CEPs (Typically for super critical
units where separate condenser and CEP is there for TDBFPs)
Any other connections connected to hotwell i.e. below the tube nest
area.
Followings are the probable reasons for vacuum deterioration
High energy drain passing
Low CW flow due to dust, debris , fills
CW treatment not proper
High dp across travelling water screen in the CW water,
CW pump problem
Dirty Tube
Air ingress in the system
Normal drip operation
Cleanliness Factor Calculation
