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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 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
Condenser Operation
Typical Steam Surface Condenser
• 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
Condenser Tube arrangement
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
Heat Rejected in Condenser
Rankine Cycle
• 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 Secondary Functions
• 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
Condenser Classification
Types of Condenser
• Shell • Hotwell• Waterbox
• Tubesheet• Tubes • Air-removal equipment
Condenser Components
Condenser Shell Hot well
• The design pressure of the shell is 76.2 cm Hg vacuum and is suitable for an emergency internal pressure of 1 kg/cm²
• Constructed of carbon or stainless steel plates welded together.
• Shell is hydrostatically tested after field assembly.
• Shell might be joined to the turbine exhaust casing by an expansion joint.
• Base of the condenser is a reservoir for the condensate and is called the hotwell.
• Designed to have a minimum available volume sufficient to contain all of the condensate produced in a period of one minute under conditions of maximum steam load.
• Suction is provided from the hot well to the condensate pumps
Components
• 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
• Alloy steel tubes are manufactured by forming alloy steel strips and then welding them with high frequency welding equipment.
• Tubes can be made of titanium, Al-6X, Sea-cure, Al 29-4C, NuMonit, stainless steel, copper nickel, aluminum bronze, and admiralty brass.
• In the air-removal section, the tubes are exposed to an oxygenated, ammonia-rich environment. This promotes corrosion (grooving) in copper-alloy tube , the tube materials is more corrosion resistant alloy such as stainless steel.
• The air-removal section is located toward the bottom of, or deep within, the tube bundles where the condensate and water vapor temperature tends to be lower.
• This region of tubes is surrounded by a shroud (roof and side panels) to protect the tubes from being heated by descending condensate and steam.
Tubes Air Removal Equipment
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.
TYPICAL CONDENSER INSTRUMENTATION
NON-CONDENSABLE OUTLET
STEAM INLET
NON-COND. REMOVAL SYSTEM
CIR
CU
LA
TIN
G
WA
TE
R O
UT
LE
T
CIR
CU
LA
TIN
G
WA
TE
R IN
LE
T
F
T
F
W
PPP
P
T
DO S
T
T
P
F = FLOW MEASUREMENTW = WATER LEVEL MEASUREMENTP = PRESSURE MEASUREMENT
PERF. TEST CONNECTION
SUPPLEMENTAL TEST CONNECTION
T = TEMPERATURE MEASUREMENTDO = DISSOLVED OXYGEN MEASUREMENTS = SALINITY MEASUREMENT
AIR/VAPOR OUTLET
CONDENSATE LEVEL
CONDENSATE LEVEL
( P) ( P)P
WW
4 Nos.
Condenser Performance Monitoring
CW Inlet Temp : 2CW Outlet Temp : 8Condensate Temp: 2
Back Pressure: 2CW Waterbox dP: 2 Air/steam MixtureTemp: 2
S.N Parameter Unit Test
Measured Parameters
Load MW P 2101 Condenser Pressure mm Hg Pc 120.82 CW In Temp Deg.C Ti 34.163 CW Out Temp Deg.C To 45.094 Condensate
TemperatureDeg.C Tcon 55
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 Temperature
mm Hg Ti+dT+TTD 79
11 Back Pressure due to CW Flow mm Hg To+TTD 81
12 Variation due to CW Inlet Temperature
mm Hg 7-10 -6
13 Variation due to CW Flow/Heat Load
mm Hg 11-10 2
14 Variation due to air/Dirty Tubes
mm Hg 1-11 39.8
15 Total variation mm Hg 1-10 41.8
Typical Condenser Calculations
Improvement in Load by 10 MW DO level reduced from 110 ppb to 10-15 ppb
Helium Leak Detection
Infrared Thermography
Air-in-leak identified in LPT gland & parting plane CEP Suction Strainer Flange Bolts
Vacuum Pump Performance
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
Benefits of Testing:1. Improvement in condenser vacuum by 16 mm Hg2. Stoppage of one vacuum pump there by reducing in APC and increased
operational reliability 3. Unit Heat rate improvement : 32 Kcal / KWHr
Temperature difference taken by the IRT Camera around the hole
Condenser : Use of Multiple Technology
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 isharmful for oxide deposits in boiler and turbine blades due to saturationlevel of various oxides at different temperature levels.
• Condensate DO may be increase with small amount of air-ingresswithout impacting the condenser back pressure and withoutoverloading of steam ejector or vacuum pump. Air depressiontemperature 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 criticalunits where separate condenser and CEP is there for TDBFPs) • Any other connections connected to hotwell i.e. below the tube nestarea.
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
