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INTRODUCTION AND LITERATURE

REVIEW

 

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1.1 I

ntroduction of Condenser: The Work done in any heat engine is directly proportional to the temp. Range of the working

fluid in the engine, OR For greater amount of expansion of working fluid, greater will be the

work done. In case of steam engines, the lower limit of expansion (or exhaust) may be

decreased below the atmospheric pressure. This is done by exhausting the steam into a

closed vessel called condenser. In condenser exhaust steam is condensed & vacuum is

maintained in it.

Steam condenser is an appliance in which the steam exhausted from a steam engine is

condensed. Condenser is installed such that the exhaust steam from a Steam Engine is

delivered into it. In the condenser, the heat is removed from the exhausted steam in form of

latent heat by means of cooling water which absorbs this latent heat. The exhaust steam after

losing its latent heat changes its state into water, which is termed as Condensate and this

process, is called as condensation.

In effect a Condenser is a heat exchanger wherein the exhaust steam of a Steam Engine is

condensed either in direct or indirect contact with cooling water through a heat transfer

medium separating them.

In short the purpose of the condenser in a vapor compression cycle is to accept the hot, high-

pressure gas from the compressor and cool it to remove first the superheat and then the latent

heat, so that the refrigerant will condense back to a liquid. In addition, the liquid is usually

slightly sub cooled. In nearly all cases, the cooling medium will be air or water.

1.2 Condenser in power plant:

• When the steam has completed its work in the turbine and before it can be returned to the

boiler, it is necessary to change it back into water.

Figure 1.2.1: Inner view of steam condenser used in power plant

• This is the duty the condenser must perform as efficiently as possible and, for this reason, it

 

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is the largest and most important of the heat exchangers in a power station. The heat in the

exhaust steam, which can no longer be converted into mechanical energy, must be

transferred from the steam to the cooling water.

• Steam condenser is a closed space into which steam exits the turbine and is forced to give up

its latent heat of vaporization. It is a necessary component of a steam power plant because of

two reasons. It converts dead steam into live feed water. It lowers the cost of supply of

cleaning and treating of working fluid. It is far easier to pump a liquid than a steam. It

increases the efficiency of the cycle by allowing the plant to operate on largest possible

temperature difference between source and sink.

• The steam’s latent heat of condensation is passed to the water flowing through the tubes of

condenser. After steam condenses, the saturated water continues to transfer heat to cooling

water as it falls to the bottom of the condenser called, hotwell.This is called sub cooling and

certain amount is desirable. The difference between saturation temperature corresponding to

condenser vacuum and temperature of condensate in hot well is called condensate

depression.

Figure 1.2.2: Condenser after manufacturing

Fig 1.2.1 shows the Inner view of steam condenser used in power plant. It is shown the path of

steam comes from the turbine & shown the process how the steam converts in to the water. Fig

1.2.2 shows Condenser after manufacturing. Fig 1.2.3 shows the line diagram of condenser.

 

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Figure 1.2.3: Line diagram of condenser used in power plant

1.3 Functions of a Condenser:

By designing the turbine to exhaust into a condenser which maintains a pressure lower than

atmospheric there are three important advantages to be gained.

Saving in steam:

o There is a big reduction in the amount of steam required to generate each unit of electricity

by using a condenser. In a turbine without a condenser the lowest pressure to which the

steam can be expanded is that of the atmosphere. It can be said that in this case the back

pressure against which the steam is exhausted is atmospheric pressure.Atmospheric pressure

is equivalent to the pressure which would support a column of mercury approximately 760

mm high.

o If the last stages of the turbine were under vacuum, and the back pressure reduced by a

condenser to 68 mbar, then the steam would be able to continue its expansion down to 68

mbar. During this expansion each pound of steam is capable of doing a great deal more

work. For example, in a 62 bar turbine with a back pressure 51mbar, the steam does nearly

30% of its work as it expands below atmospheric pressure. Thus the use of a condenser

brings considerable saving.

Conservation of pure feed water:

o Very large quantities of steam pass though a turbine, for example, a 660 MW machine on

full load uses some 532 kg/sec. It would, of course, be not only very wasteful but almost

impracticable to allow this vast amount of steam to be exhausted to atmosphere. By using a

condenser the exhaust steam is converted back to hot water which is removed from the

condenser for continuous use in the power station heat cycle. This water is known as

condensate. It being free from impurities and non-condensable gases, does not produce

 

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corrosive action and also it being hot (@ 40-50 C), saves a considerable amount of fuel.

Thus the overall efficiency of the plant is increased.

De aeration of make-up water:

o Due to leakage, blowing down, steam soot blowing, etc., some of the feed water in the

boiler/turbine system is lost, and must be made-up.

o Make-up water is usually supplied from Reserve Feed Water (RFW) tanks, where the air in

contact with the water surface introduces oxygen into the RFW. Dissolved oxygen in feed

water must be kept to the lowest practicable minimum, since oxygen causes corrosion of

tubes and turbine internals.

o The most convenient method of removing oxygen form the make-up water is to admit this

water to the condenser, where due to the very low pressure and corresponding low boiling

point, the water flashes off to steam, and dissolved oxygen separates off to be removed with

other air and gases by the air-ejectors.

1.3.1 Based on above discussion here are the some advantages of condenser in power

plant:

o Improved work done & efficiency due to low pressure of condenser.

o Recovery of the condensate to be fed to the boiler as a high quality feed water for reuse.

o Reduce steam consumption for the same power output due to increased work done.

o Economy in water softening plant as only make up water is to be treated instead of full feed

water.

o Reduced thermal stresses due to high temp. of feed water entering to boiler.

1.4 About condensing plant:

Figure1.4.1: Main elements of condensing unit

 

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1.4.1 Elements of a condensing plant: The auxiliaries, which are essentially required for the proper functioning of a condensing plant,

are known as elements of a condensing plant. Figure below shows Condensing plant lay-out.

The main elements of a condenser are:

Condenser where steam is condensed,

Hot well in which the condensate is collected.

Pump for circulating Cooling Water, supply of Circulating Cooling Water,

Air pump (or ejector) to remove air and non-condensing gases from the condenser

Figure 1.4.2: Elements of a condensing plant

Condensate Pump (extraction pump) to remove Condensate from the condenser,

Feed Pump for supplying feed water from De aerator to the boiler.

1.4.2 Features of good condensing plant:

The desirable features of a good condenser are:

• Minimum quantity of circulating cooling water.

• Minimum cooling surface area per kW capacity.

• Minimum auxiliary power.

• Minimum steam condensed per M2 of surface area

As the cooling water temperature entering the condenser increases vacuum decreases. The

following figure shows this:

 

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Figure 1.4.3: Features of a good condenser

 

Heat to be removed: 

• The heat to be removed in the condenser is shown in the p–h diagram and, apart from

comparatively small heat losses and gains through the circuit will be Heat taken in by

evaporator heat of compression.

• This latter, again ignoring small heat gains and losses will be the power input to the

compressor, giving Evaporator load compressor input power condenser load.

• Condenser load is stated as the rate of heat rejection. Some manufacturers give ratings in

terms of the evaporator load, together with a ‘de-rating’ factor, which depends on the

evaporating and condensing temperatures.

• Evaporator load factor condenser load the provision of a separate oil cooler will reduce

condenser load by the amount of heat lost to the oil and removed in the oil cooler.

• This is of special note with oil-injected screw compressors, where a high proportion of the

compressor energy is taken away in the oil. This proportion varies with the exact method of

oil cooling, and figures should be obtained from the compressor manufacturer for a

particular application.

• Here in the figure the condenser load p-h diagram is shown. From the figure it is easily

understand.

 

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Figure 1.4.4: Condenser load p – h diagram

1.5 Operation of condenser:

Before starting up, the system should be checked for correct piping and proper control and

safety devices.

The following procedure is generally applicable to all types of condensers:

Start the moderate temperature fluid and operate vents to remove trapped air.

Gradually start the extreme temperature fluid, allowing the exchanger to adjust its

temperature slowly. Operate the vents.

When shutting down, stop the extreme temperature fluid first, and then operate the vents.

Avoid thermal shock due to rapidly altering the flow of either stream, unless the unit is

specifically designed to withstand this type of service.

Be sure all condensate is drained from the steam units before admitting steam to avoid water

hammer.

When the exchanger has reached operating conditions, check all bolted connections for

tightness.

Record operating pressures and temperature for future reference. Loss of capacity and

increase of pressure drop will indicated the progress of fouling.

 

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Internal leaks will be indicated by contamination of the low pressure stream. External leaks

can usually be seen or heard. To locate leaks, follow the procedure for testing a repaired

exchanger.

1.6 Condenser maintenance: o As with any mechanical equipment, condensers should never be located where they are

difficult of access, since there will then be less chance of routine maintenance being carried

out. Periodic maintenance of a condenser is limited to attention to the moving parts – fans,

motors, belts, pumps – and cleaning of water filters, if fitted.

o The overall performance will be monitored from the plant running log and the heat exchange

surfaces must be kept clean for maximum efficiency – meaning the lowest head pressure and

lowest power.

o Air-cooled surfaces may be cleaned by brushing off the accumulation of dust and fluff where

the air enters the coil, by the combination of a high-pressure air hose and a vacuum cleaner,

or, with the obvious precautions, by a water hose.

o Scale within the tubes of a straight double pipe or shell-and-tube condenser can be

mechanically removed with suitable wire brushes or high-pressure water lances, once the

end covers have been removed. Tubes which cannot be dealt with in this way must be

chemically cleaned.

o It will be appreciated that, where air and water are present, as in a water cooling tower or

evaporative condenser, the apparatus will act as an air washer, removing much of the dust

from the air passing through it.

o Such dirt may be caught in a fine water filter, but is more commonly allowed to settle into

the bottom of the tank and must be flushed out once or twice a year, depending on the

severity of local contamination.

o Where heavy contamination is expected, it is good practice to provide a deeper tank than

usual, the pump suction coming out well clear of the bottom, and tanks 3 m deep are in use.

Where plant security is vital, the tank is divided into two parts, which may be cleaned

alternately.

1.7 Repairs of condenser: Cleaning:

o The method of cleaning will be indicated by the composition of the dirt or scale, its location

and the type of exchanger. Each cleaning job must be considered individually with the help

of cleaning tool manufactures and chemical cleaning contractors.

o Generally, the tube side of exchangers can be cleaned mechanically, except for u-tubes

where the small radius inside bends is usually not cleanable. Removable bundles with tubes

 

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on square pitch can be cleaned mechanically on the shell side. Removable bundles with

triangular pitch can sometimes be cleaned by jetting but generally these and non-removable

bundles must be cleaned chemically on the shell side.

o Mechanical cleaning tools must be applied carefully to avoid cutting or otherwise damaging

the tubes. Sharp, hard cleaning tools should be avoided. Chemical cleaning solutions must be

used with care and completely flushed out to avoid corrosion damage. Never use cleaning

solutions containing hydrochloric acid on galvanized exchangers.

Tube Bundle Removal:

o Before attempting to dismantle a heat exchanger, be sure internal pressure is relieved.

Remote valves should be locked closed.

o Remove channels or cast iron heads. Small bundles can usually be pulled out manually after

starting with jackscrews or a pry. When using a pry, be careful not to damage gasket faces.

o Large bundles may be pulled with a chain fall.

o On single tube sheet exchangers, the bundle may be pried out using a strong-back making

sure that the strong back includes enough tube sheet bolt holes to prevent bending of the tube

sheet.

o Use wide slings or cradles when handling the bundle to prevent damage to individual tubes.

Tube Replacement:

o Where a small portion of the bundle is concerned, it may prove more practical to plug

defective tubes than to replace them.

The following procedure is generally acceptable for average exchangers of ordinary

materials.

o For larger units and stronger materials, better tooling will probably be justified and may be

necessary. In these cases, follow the recommendations of the tool manufacture.

o Face off the tube ends flush with the tube sheet with a cut-off tool.

o Loosen one end of the tube with a knock-out tool, and then drive the tube out from the other

end. Some judgment is required here and several tries may be necessary before the tube can

be driven out. If an inner tube of a U-tube bundle is to be removed it will be necessary to

remove some outer tubes to gain access to the faulty one.

o Clean the hole of all tube material and dirt.

o Insert the new tube so that it projects 1 / 16 inch beyond the face of the tube sheet and roll.

The rolling is a skilled job and must be done carefully. Lubricate the roller well and keep it

clean. Do not over expand the tubes. If the maintenance department is not experienced in

tube rolling, it will probably be more satisfactory to return the bundle to the manufacturer for

repairs.

 

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Reassembly and Testing:

o Clean all gasket faces and use new gaskets of the same material, thickness and dimensions as

originally supplied. Pull up bolts only enough to produce a tight seal, alternating between

diametrically opposed bolts to keep flange faces parallel. Do not overstress bolts or flanges.

o When replacing bolts, be sure to use the same alloy and grade as originally supplied. Heat

exchangers are usually tested for tightness with water. Do not pressurize an exchanger with

gas until it has been tested up to the gas pressure with a liquid. Do not exceed the test

pressure stamped on the nameplate of the exchanger.

o To test tube joints, fill and pressurize the shell side with the channels removed to expose the

tube ends. Have the shell side pressure held at the test pressure stamped for tubes and hold

for several minutes. Leaking tube joints can be rolled lightly. Do not over-roll.

o Replace the channels and pressurize both shell and tube side to test flange joints.

o Be careful to protect instruments and fixtures which are not designed for the test pressure.

Routine Inspection:

Exchangers should be painted and inspected periodically for corrosion. Check for corrosion,

particularly around connections and under insulation.

Temperature Shocks:

Exchangers normally should not be subjected to abrupt temperature fluctuations. Hot fluid

must not be suddenly introduced when the unit is cold, nor cold fluid suddenly introduced

when the unit is hot.

Bolted Joints:

Heat exchangers are pressure tested before leaving the manufacturer's shop in accordance

with ASME Code requirements. However, normal relaxing of the gasketed joints may occur

in the interval between testing in the manufacturer's shop and installation at the jobsite.

Therefore, all external bolted joints may require retightening after installation and, if

necessary, after the exchanger has reached operating temperature.

1.8 Condenser fittings: o The inlet pipe bringing high-pressure gas from the compressor must enter at the top of the

condenser, and adjacent piping should slope in the direction of flow so that oil droplets and

any liquid refrigerant which may form will continue in the right direction and not back to the

compressor.

o The outlet pipe must always be from the lowest point, but may have a short internal up stand

so that any dirt such as pipe scale or metal swarf will be trapped and not taken around the

circuit. Condensers for ammonia systems may have an oil trap, usually in the form of a drain

pot, and the liquid outlet will be above this.

 

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o Water connections to a shell-and-tube condenser must always be arranged so that the end

covers can easily be removed for inspection, cleaning, and repair of the tubes.

o Heavy end covers require the use of lifting tackle, and supports above the lifting points

should be provided on installation to facilitate this work.

o Condensers contain pressurized refrigerant and where they exceed certain volumes they will

be subject to the requirements of the Pressure Vessel Directive (PED) and EN378.

Manufacturers will be aware of these requirements, and proprietary products will be

correctly equipped.

1.9 Common Condenser Problems:

Figure 1.9.1: Different parts of condenser

 

Since 1994, Intek has been the leading source of new information on condenser dynamics,

which has been made possible with the RheoVac instrument. The RheoVac instrument measures

the mixture of water vapor and no condensable gases in the vent line. With this information and

other plant measurable, Intek developed a Comprehensive Condenser Model and Theory

(CCMT) based on physical principles. The CCMT has been validated under a variety of

different operating conditions, and has been used to identify deficiencies in condenser design

and problems with condenser operations and maintenance. Intek has established itself as a leader

in solving condenser related problems and improving condenser performance.

► Some of them are given below;

• High Condenser Pressure

• Corrosion

 

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• Dissolved Gases (Oxygen, Carbon Dioxide, Ammonia, etc.)

• Low Cleanliness Factor

• Low Heat Transfer Coefficient

• Air In-Leakage

• Tube Fouling

• Low Pump/Exhaust Capacity

• Other Efficiency/Maintenance/Design/Operations Concerns

1.9.1 High Condenser Pressure:

High condenser back pressure is the most obvious plant measurable that results in lost revenue

or excess operating costs. Simply, back pressure is directly related to the power output from the

turbines and excess back pressure means reduced efficiency and dollars wasted.

How excess back pressure affects the bottom line:

Revenue and profit loss can be significant. As shown in the charts below, even a small excess

back pressure will have a dramatic impact. These results are based on a PEPSE analysis of a

525MW generating unit which shows that each 0.1”HgA rise in back pressure results in an

increase of 0.17% in heat rate. In summary, a 0.3” HgA of excess back pressure, on a base

loaded plant condenser, correlates to a loss of 2.68MW of power and nearly $770,000/year lost

revenue.

Corrosion/Dissolved Gases:

Dissolved Oxygen (DO) and other gases are a major cause of corrosion in the steam cycle.

Corrosion leads to forced outages and increased maintenance costs. A common misconception is

that high DO is concurrent with high air in-leak; this is not always the case. High DO and

condensate ammonia concurrent with low air in-leakage is an indication that the condenser

configuration may be inadequate.

Low Cleanliness Factor/Low Heat Transfer Coefficient: 

Cleanliness Factor (CF) is calculated by measuring the actual heat transfer coefficient as a

percent of the associated HEI specified design heat transfer coefficient. Low CF measurement

could be the result of one or many problems occurring in a plant, and indicates a lower than

desired power generation efficiency; thus, dollars wasted.

Air In-Leakage:

Multiple pathways for air to leak into the steam path are inherent to the sub-atmospheric side of

steam turbine power plants.

Air in the steam path, along with deficiencies in condenser configuration, are major causes for a

number of plant related problems such as excess back pressure, dissolved oxygen, corrosion, and

low cleanliness factor. Quantifying this air in-leakage is essential for maintaining plant

operations.

 

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RheoVac instruments are the solution to measuring air in-leakage. The RheoVac instrument

succeeds where all other air flow monitors fail, because it is the only instrument that is based on

the direct measurement of vent line gas parameters to accurately calculate air in-leakage.

Additionally, RheoVac instruments provide plant operators with other essential data to respond

to common plant maintenance issues, such as monitoring exhaust pump capacity, real-time

verification of leak repairs, vacuum quality, and tube fouling.

1.9.2 Tube Fouling:

Tube fouling occurs when biologic growth or material deposits obstruct the cooling circulating

water flow through condenser tubes. Tube fouling manifests itself in many plant measurable.

Without direct measurement of individual tube flow rates, however, other problems such as poor

condenser configuration can lead to false presumption of tube fouling. Intek offers

instrumentation for monitoring individual tube fouling.

Figure1.9.2: Performance Loss Due to Scaling & Fouling

Fouling factors are best determined from experience with similar units in the same or similar

service. When such information is not available, recourse may be had to publish data. The most

comprehensive tabulation of fouling factors is the one developed by TEMA, which is available

in Refs. The values given below in Table are representative of the data available in the public

domain. It should be realized that there are very significant uncertainties associated with all such

data. Fouling is a complex process that can be influenced by many variables that are not

specifically accounted for in these tabulations. Fouling can occur by a number of mechanisms

operating either alone or in combination. These include:

 

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1.9.3 Corrosion:

Corrosion products such as rust can gradually build up on tube walls, resulting in reduced heat

transmission and eventual tube failure. This type of fouling can be minimized or eliminated by

the proper choice of corrosion-resistant materials of construction in the design process.

► Why does corrosion occur?

o The tubes, the tube sheets and the water boxes are all made up of materials having different

compositions. These materials are always in contact with circulating water. The circulating

water, depending on its chemical composition will act as an electrolyte between the tubes

and water boxes. This will give rise to electrolytic corrosion which will start from more

anodic materials first. The condenser tubes being the lowest in series of anodic materials will

be the first to be effected. This makes the condenser tube ends to get eaten away first.

o Sea water based condensers, in particular when sea water has added chemicals pollutants,

has the worst corrosion characteristics. River water with pollutants also is not desirable for

condenser cooling water.

o However due to large quantity of water flow requirement for large condensers, the corrosive

effect of sea water or river water has to be tolerated and remedial methods have to be

adopted in practice.The concentration of un dissolved gases is high over air zone tubes.

Therefore these tubes are exposed to higher corrosion rates. Sometimes these tubes are

affected by stress corrosion cracking, if originally stress is not fully relieved during

manufacture.

o To overcome these effects of corrosion some manufacturers provide higher corrosive

resistant tubes in this area.

► Effects of corrosion on condenser

• As the tube ends get corroded there is the possibility of cooling water leakage to the steam

side contaminating the condensed steam or condensate, which is harmful to steam

generators. The other parts of water boxes may also get affected in the long run requiring

repairs or replacements involving long duration shut downs.

Crystallization

Crystallization typically occurs with cooling water streams containing dissolved sulfates and

carbonates. Since the solubility of these salts decreases with increasing temperature, they tend to

precipitate on heat-transfer surfaces when the water is heated, forming scale. This type of

fouling can be minimized by restricting the outlet water temperature to a maximum of 110-125F.

Decomposition

Some organic compounds may decompose when they are heated or come in contact with hot

surface, forming carbonaceous deposits such as coke and tar. In cracking furnaces, partial

 

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decomposition of the hydrocarbon feedstock is the objective and coke formation is an undesired

but unavoidable result.

Polymerization

Polymerization reactions can be initiated when certain unsaturated organic compounds are

heated or come in contact with a hot metal tube wall. The resulting reaction products can form a

very tough plastic-like layer that can be extremely difficult to remove from heat-transfer

surfaces.

Sedimentation

Sedimentation fouling results from the deposition of suspended solids entrained in many process

streams such as cooling water and flue gases. High fluid velocities tend to minimize the

accumulation of deposits on heat-transfer surfaces.

1.9.4 Biological activity:

o Biological fouling is most commonly caused by micro-organisms, although macroscopic

marine organisms can sometimes cause problems as well. Cooling water and some other

process streams may contain algae or bacteria that can attach and grow on heat-transfer

surfaces, forming slimes that are very poor heat conductors. Metabolic products of these

organisms can also cause corrosion of metal surfaces. Biocides and copper-nickel alloy

tubing can be used to inhibit the growth of micro-organisms and mitigate this type of

fouling.

o It can be seen from above Table that the range of values of fouling factors spans more than

an order of magnitude. For very clean streams, values of 0.0005 h*ft²*f/BTU. Or less are

appropriate, whereas very dirty streams require values of 0.005-0.01 h*ft²*f/BTU. However,

values in the range 0.001- 0.003 h*ft²*f/BTU are appropriate for the majority of cases.

Figure 1.9.3: The fouling effects

A heat exchanger in a steam power station contaminated with macro fouling. Fouling occurs

 

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when a fluid goes through the heat exchanger, and the impurities in the fluid precipitate onto the

surface of the tubes.

Low Pump/Exhaust Capacity

Exhaust pump capacity must be maintained to ensure proper air removal from the condenser.

Insufficient air removal can lead to increased back pressure, high dissolved oxygen, and low

cleanliness factor. RheoVac instruments provide an accurate and real time measurement of pump

capacity.

Other Efficiency/Maintenance/Design Concerns

For decades, Intek has solved flow and engineering problems for many customers. Intec’s

success is based on a fundamental understanding of physics and engineering backed by a team

of knowledgeable and experienced science and engineering professionals.

Variation of Steam Partial Pressure & Saturation Temperature

Figure 1.9.4: Variation of Steam Partial Pressure & Saturation Temperature

Condensate Depression

• The temperature of condensate is always a few degrees lower than the coincident condensing

steam temperature.

• Sub cooling of condensate is undesirable on two accounts

• It lowers the thermodynamic efficiency of the power cycle.

 

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• It enhances the propensity of the condensate to reabsorb non-condensable.

Power Loss Due to Excess Back Pressure:

Figure 1.9.5: Power Loss Due to Excess Back Pressure

 

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SURFACE CONDENSER HISTORY

 

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2.1 Classification of condenser: Broadly, condensers are classified in to two categories.

► Direct contact type, where the cooling water and steam directly meet and come out as a

single stream.

o They are classified in to three categories.

Spray condenser

Barometric condenser

Jet condenser

► Surface condensers (indirect contact type) where there is no mixing of cooling water and

steam. It is shell and tube type heat exchanger. The heat released upon condensation is

transferred to circulating cooling water through the walls of the tube.

o They are classified in to five categories.

Down flow surface condensers.

Central flow surface condensers.

Inverted type surface condensers.

Regenerative surface condensers.

Evaporative condensers

Our main intension is to design the surface condenser so directly we go to the surface condenser

description.

2.2 Surface condensers:

It is also known as Non-mixing type of condenser as in this type of condenser the exhaust

steam and the cooling water do not come in direct contact with each other. Surface condenser is a shell & tubes type of heat exchanger where normally cooling water is

on the tube side & exhaust steam is on the shell side. It is generally used where large

quantity of inferior quality water is available & condensate formed from exhaust steam is to

be recalculated to be used in boiler. This results in considerable saving in make-up water to

boiler. If we think thermodynamically, in surface condenser, the latent heat of exhaust steam is

being removed there by converting it into hot condensate. The surface condenser requires three (or two) pumps -- one for circulating cooling water one

for extracting the condenser & the third one is for removing air from condenser. In case of

third pump, we can use steam ejector. The surface condensers may be classified according to • No. of water passes: single or multi pass.

• Direction of condensate flow and tube and tube arrangement.

 

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In all surface condensers the cooling water is passed through the tubes & steam surrounds

the tube. the volume occupied by these tubes in the condenser shell is hardly 10% of the

total shell volume due to very large volume of exhaust steam. A good surface condenser

should have a low-pressure drop, maximum effective surface arrangement and should be

economical in first cost.

In modern condensers, a steam bypass line is provided along the side of the shell to pass

steam to the hot well for reheating the condensate; this also helps for de aeration of

condensate before use in boiler.

The rise in temperature of the cooling water passing through the condenser is maximum 10

degree C therefore, quantity of water & surface are condenser causing the heat flow

required are large for calculation purpose, we can write,

Heat given away by steam = Heat gain by cooling water

Following are description for the types of surface condensers:

2.2.1 Down flow type:

Exhaust steam is admitted to the top of the condenser which is tube-and-shell type cross flow

heat exchanger. Cooling water flows through the tubes and extracts heat from the steam

which is on the shell-side.

 

Figure 2.2.1: down flow type surface condenser.

After having condensed on the surface of the water tubes, steam is converted into condensate

which is discharged from the condenser bottom.

2.2.2 Central flow type surface condenser: 

It is also a shell-and-tube type cross flow heat exchanger, at the centre of which is located

the suction of an air extraction pump so that the entire steam moves radially inward and

 

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Figure 2.2.2: Central flow type surface condenser

comes in better contact with the outer surface of the best of tubes through which the cooling

water flows. The steam condensate is extracted from the bottom by the condensate-extraction

pump.

2.2.3 Inverted type surface condenser:

Steam is admitted at the bottom and flows upward in cross-flow with the cooling water

flowing in the tubes.

The air extraction pump draws its suction from the top of the condenser, maintaining a

steady upward current of steam which after having been condensed on the outer surface of

the water tubes is removed by the condensate extraction pump.

2.2.4 Evaporative condenser:

Exhaust steam is condensed inside the finned tubes as cooling water rains down from the to

through the nozzles. Apart of the cooling water in contact with the tube surface evaporates

 

Figure 2.2.3: Evaporative condenser

by drawing enthalpy from the steam which upon losing its latent heat condenses and discharges

out as condensate.

 

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DESIGN CONCEPT

 

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3.1 Design aspects of surface condenser:

• The calculation of heat transfer for determining the tubes and total surface area required by a

surface condenser are rather complex. They required the knowledge of the total heat load on

the condenser, the heat transfer mechanism and co efficient in various parts of condenser.

When the condenser is new, the outside surfaces are usually clean but quickly developed an

oily film that changes condensation from drop wise to film wise condensation. Thus the shell

side heat transfer co efficient is conservatively based on the lower film wise condensation

mechanism.

• The shell side heat transfer co efficient depends upon the difference between the steam

saturation temperature and tube well temperature, the relative position of the tubes steam

velocity and turbulence, the extant of non condensable, and the existence of superheat steam

if any.

• The circulating water side heat transfer co efficient depends upon its velocity, temperature

and cleanliness of the inside surface. Owing to the large number of variables with many

uncertainties, manufacturers have usually based their design in general proposed by the Heat

Exchanger Institutes Standards for Steam Surface Condenser.

The method is based on the usual heat transfer equation for the heat exchanger as given below-

o o mQ U A T= ∆

Where,

Q = heat load on condenser (W)

oU = over all condenser heat transfer co efficient based on outside tube area ( 2W

m K )

oA = total outside tube surface area ( 2m )

mT∆ = log mean temperature difference in condenser ( oC )

mT∆ is expressed by below given equation,

ln

i em

i

e

T TTTT

∆ −∆∆ =

⎛ ⎞∆⎜ ⎟∆⎝ ⎠

iT∆ , eT∆ is define below,

Where,

iT∆ =difference between saturation stem temperature & inlet circulating water ( oC )

eT∆ = difference between saturation stem temperature & outlet circulating water ( oC )

 

25  

3.1.1 Heat Exchanger Institutes (HEI) method:

The overall heat transfer co efficient ( oU ) is expressed empirically by

1 2 3 4o wU C C C C C=

Where,

wC = circulating cold water velocity in tubes inlet ( ms )

1C = dimensionless factor depending upon the tube outer diameter

2C = dimensionless correction factor for circulating water inlet temperature

3C = dimensionless correction factor for tube material and gauge

4C = values of these factors are given in table

Figure 3.1.1: Temperature distribution in a condenser

 

26  

Table 3.1: Standard factors ( 1 2 3 4C C C C ) values

Tube outer

diameter

(mm)

19 22 25 .4

wC 2777 2705 2582

Water

temperature

( oC )

1.66 4.44 7.22 10 12.77 15.55 21.11 26.66 32.22 37.7 - - -

2C 0.57 0.64 0.72 0.79 0.86 0.92 1.00 1.04 1.08 1.10 - - -

Tube

material

304

Stainless

steel

Admiralty

arsenic

copper

Aluminum brass,

muntz metal

Aluminum

bronze 90-10

Cu-Ni

70-30

Cu-Ni

-

3C 0.58 1.00 0.96 0.90 0.83 -

3C 0.56 0.98 0.94 0.87 0.80 -

3C 0.54 0.96 0.91 0.89 0.76 -

4C 0.85 for clean tubes, less for algae covered or sludge tubes

3.1.2 Conventional method:

In conventional method, the usual head transfer equations are used to calculate oU . For film wise

condensation the average heat transfer coefficient on steam side for a horizontal tube is given by

Nusselt;

( )1

3 2 4

0.725 f f fgav oss

f o

k ghh h

N dρµ θ

⎡ ⎤= = ⎢ ⎥

⎢ ⎥⎣ ⎦

Where,

N =no of horizontal tubes in vertical tier

sat wallT Tθ = −

fgh = latent heat of condensation of steam

fµ = viscosity of condensate (fluid)

 

27  

fρ = density of condensate (fluid)

fk = thermal conductivity of condensate (fluid)

od = outside tube diameter

It should be noted that Nusselt’s equation for oh gives a conservative value for the condensing

film coefficient for heat transfer. However this value also be influenced by many factors such as

super heat, vapor velocity, turbulence and the inside released gases and air leaked.

The inside heat transfer co efficient on the water side is given by Mc Adams equation

0.8 0.40.023Re Pri ih dNuk

= =

Where,

Re =Reynolds number due to flow of circulating water through tubes

= iCdµ

Pr = Prandtle number

= pCk

µ

The overall heat transfer co efficient for a condenser is given by

1 1 1 1wall

o o i i scale i wall im o o

xU A h A h A k A h A

= + + +

Where,

scaleh = heat transfer co efficient of scale formed

wallk = thermal conductivity of wall

imA = mean inside area including scale formed

scalex = wall thickness

For simplicity, the tube wall resistance due to thin tube and good thermal conductivity may be

neglected. Hence,

1 1 1 1

o i scale oU h h h= + +

 

28  

It is to be noted that oh is much larger then ih and oU mainly depends on water velocity as

0.8i wh Cα

0.8

1 1

o w

A BU C

= +

Where,

1 1

o scale

Ah h

= + & 0.4

0.2 0.8

1

0.023 f r

i f

Bkd vρ

=

The rate of heat transfer from the condensing vapor to the cooling water is expressed as

( )

( )2 1

o

steam condensate

o

pc c c

o o m

Q h hs

C T TcU A T

m

m

= −

= −

= ∆

Where, o

sm = mass flow rate of steam entering to condenser

o

cm = mass flow rate of coolant

1cT &

2cT = inlet and outlet temperature

Generally ( )2 1c cT T− is around10c C , iT∆ is around 11 to 17 oC and eT∆ =TTD should not

be less than 3 oC . In practice, due to losses in condenser, the under cooling of the condensate

( )satu condensateT T− is around 4 oC

Now the mass flow rate of coolant, i.e. water (o

cm ) is given by

( )( )2 1

oo s steam condensate

cpc c c

m h hm

c T T

−=

−

The outside surface area oA is thus calculated from above equations

 

29  

( )o

steam condensateo o

o m

h hsA n d lU T

mπ

−=

∆

2

4c i w wnm d Cπ ρ⎛ ⎞= ⎜ ⎟

⎝ ⎠

Where,

wρ = density of water (3

310 Kgm )

wC = velocity of water which varies from 1.8 to 2.5 ms

Therefore, the length and number of tubes can be calculated from above equations. Generally

tube length and diameter are selected so the estimation is made for number of tubes. In the case

of large power plant, the number of tubes may be high as 50000 or even more.The pressure drop

in the condenser is composed of the pressure drop in the water box and the friction pressure drop

in the tubes. The pressure drop in terms of head is P gHρ∆ =

Thermal Processes Occurring in Condensers

• The condenser never receives pure seam from the turbine.

• A mixture of steam and non-condensable gases (Air-steam mixture) enters the condenser.

• The ratio of the quantity of gas that enters the condenser to the quantity of steam is called the

relative air content.

• The value of e depends on type, capacity, load and design dimensions of the condenser plant.

Variation of Steam-air Mixture Parameters:

Figure 3.1.2: Variation of Steam-air Mixture Parameters

,

air

c s

m

mε

•

•=

,c s airm m• •

+c steam airp p p= + c steamp p≈

satT

 

30  

• Using Dalon’s Law:

• Gas laws:

• Volumes and temperatures are same:

• At the entry to condenser the relative content of air is very low and partial pressure of steam

is almost equal to condenser pressure.

• As air-steam mixture moves in the condenser, steam is condensed and the relative content of

air increases.

• Accordingly, the partial pressure of steam drops down.

• The pressure in the bottom portion of condenser is lower than that of the top portion.

• The pressure drop from inlet to exit of condenser is called steam exhaust resistance of a

condenser.

• The partial pressure of air at the bottom of the condenser cannot be neglected.

• The temperature of steam is a function of condenser pressure.

• This is due to increase in relative content of air in the mixture.

• The pressure also decreases due to resistance to flow of steam.

c s ap p p= +

&a a s sa a a s s sp v m R T p v m R T• • • •

= =

0.622aa a

s s s

p R mp R m

ε•

•

⎛ ⎞⎛ ⎞ ⎜ ⎟= × =⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

1 0.622c

spp

ε=

+

ec c cp p p∆ = −

 

31  

Figure 3.1.3: Variation of Steam-air Mixture Parameters

Cooling Water Outlet Temperature Calculation:

The outlet temperature for the fluid flowing through the tube is

The surface area of the heat exchanger for the fouled condition is:

Condensate Loading

This can be used to calculate a Reynolds number

• Flow is considered laminar if this Reynolds number is less than 1800.

• The driving force for condensation is the temperature difference between the cold wall

surface and the bulk temperature of the saturated vapor

c steamp p≈

esp

eap

satT

ec sT T=

ε

'ε

sT

cT

( ), ,

,

steamcw out cw in

cw p cw

m hT T

m c∆

= +&

&

[ ]transfer surface fQ A U F LMTD m h= = ∆& &

Mass flor of condensatePerimeter

Γ =

0

for vertical tubes.condensatemdπ

Γ =&

for horizontal tubes.condensate

tube

mL

Γ =&

4RecondensationfilmµΓ

=

driving sat wall vapour surfaceT T T T T∆ = − ≈ −

 

32  

• The viscosity and most other properties used in the condensing correlations are evaluated at

the film temperature, a weighted mean of the cold surface (wall) temperature and the (hot)

vapor saturation temperature

Wall Temperatures

• It is often necessary to calculate the wall temperature by an iterative approach.

• The summarized procedure is:

Assume a film temperature, Tf

Evaluate the fluid properties (viscosity, density, etc.) at this temperature

Use the properties to calculate a condensing heat transfer coefficient (using the correlations

to be presented)

Calculate the wall temperature. The relationship will typically be something like

Use the wall temperature to calculate a film temperature

Compare the calculated film temperature to that from the initial step. If not equal, reevaluate

the properties and repeat.

Laminar Flow outside Vertical Tubes

If condensation is occurring on the outside surface of vertical tubes, with a condensate loading

such that the condensate Reynolds Number is less than 1800, the recommended correlation is:

• Since the vapor density is usually much smaller than that of the condensate film, some

authors neglect it and use the film density squared in the denominator.

• The presence of ripples (slight turbulence) improves heat transfer, so some authors advocate

increasing the value of the coefficient by about 20%.

Another form of writing h is:

This may also be compensated for rippling (0.925*1.2=1.11).

Turbulent Flow outside Vertical Tubes:

( )33

4 4driving

film sat saturation wall sat

TT T T T T

∆= − − = −

( )1

1wall sat sat coolant

o o

UAT T T Th A

⎧ ⎫⎪ ⎪= − −⎨ ⎬⎪ ⎪⎩ ⎭

( )1

33

23

1.47Re

f f f vcond

fcondensation

k gh

ρ ρ ρ

µ

⎧ ⎫−⎪ ⎪= ⎨ ⎬⎪ ⎪⎩ ⎭

( )1

33

0.925 f f f vcond

f

k gh

ρ ρ ρµ

⎧ ⎫−⎪ ⎪= ⎨ ⎬Γ⎪ ⎪⎩ ⎭

 

33  

When the condensate Reynolds Number is greater than 1800, the recommended correlation is:

 

Laminar Flow outside Horizontal Tubes:

• When vapor condenses on the surface of horizontal tubes, the flow is almost always laminar.

• The flow path is too short for turbulence to develop. Again, there are two forms of the same

relationship:

• The constant in the second form varies from 0.725 to 0.729.

• The rippling condition (add 20%) is suggested for condensate Reynolds Numbers greater

than 40.

• Condenser tubes are typically arranged in banks, so that the condensate which falls off one

tube will typically fall onto a tube below.

• The bottom tubes in a stack thus have thicker liquid films and consequently poorer heat

transfer.

• The correlation is adjusted by a factor for the number of tubes, becoming for the nth tube in

the stack.

• Splashing of the falling fluid further reduces heat transfer, so some authors recommend a

different adjustment.

► Performance of Condensers:-

• The following needs to be computed:

• Condenser heat load = Q x T x Cp

( )1

330.4

20.0076 Re f f f vcond

f

k gh

ρ ρ ρ

µ

⎧ ⎫−⎪ ⎪= ⎨ ⎬⎪ ⎪⎩ ⎭

( )1

33

23

1.51Re

f f f vcond

fcondensation

k gh

ρ ρ ρ

µ

⎧ ⎫−⎪ ⎪= ⎨ ⎬⎪ ⎪⎩ ⎭

( )1

43

0

0.725 f f f v fgcond

f driving

k ghh

T dρ ρ ρ

µ

⎧ ⎫−⎪ ⎪= ⎨ ⎬∆⎪ ⎪⎩ ⎭

( )1

43

40

0.725 f f f v fg topcond

f driving

k gh hh

N T d N

ρ ρ ρ

µ

⎧ ⎫−⎪ ⎪= =⎨ ⎬∆⎪ ⎪⎩ ⎭

 

34  

Table 3.2: Parameter Details for Performance of Condensers

Parameter Details Unit

Q Water flow rate Kg/h

T Average CW temperature rise oC

Cp Specific heat kcal/kg oC

• Calculated condenser vacuum =Atmospheric pressure – Condenser back-pressure

• Deviation in condenser vacuum =Expected condenser vacuum - Measured condenser vacuu

• Condenser TTD = Saturation temperature – Cooling water outlet temperature

• Condenser Effectiveness = Rise incooling water temperature Saturation temperature Cooling water inlet temperature−

• Condenser heat duty in kcal/h =Heat added by main steam + heat added by reheater + heat

added by SH attemperation + heat added by RH attemperation + heat added by BFP - 860 x

(Pgen + Pgen losses + heat loss due to radiation)

• Condenser tube velocity (m/s) =

( )( ) ( )

3 6

2

Cooling water flow rate *10

3600 x tube area * no. of tubes per pass no. of tubes plugged per pass

mhr

mm −

Determination of actual LMTD

ln

out in

sat in

sat out

T TLMTD T TT T

−=

−−

LMTD expected = LMTD test x tf x wf x qf

tf =Correction for cooling water inlet temperature

wf =correction for water flow rate

0.25SaturationTemperature during test – LMTD during test

SaturationTemperature design – LMTD designtf⎛ ⎞

= ⎜ ⎟⎝ ⎠

 

35  

0.50Tube velocityduring test

Tube velocitydesignwf⎛ ⎞

= ⎜ ⎟⎝ ⎠

qf =correction for cooling water heat load

Condenser designdutyCondenser dutyduring testqf

⎛ ⎞= ⎜ ⎟⎝ ⎠

• Observations during Condenser Energy Audit

Tubes in operation Vs total installed.

Cleaning system operation.

Filtering system for cooling water.

Regular monitoring system for performance.

Comparison of LMTD, TTD, heat load, condenser vacuum, flow, temperatures, pressures.

with design / PG test- arriving the factors causing deviation.

Modifications carried out in the recent past.

Cooling water flow.

Pressure drop on water side and choking.

Affect of present performance of cooling tower.

Accurate metering of vacuum.

Absolute back pressure deviation from expected value.

 

36  

PROBLEM FORMULATION

 

37  

4.1 Data for designing the surface condenser for 60 MW capacity power plant:

Table 4.1: Input design data for condenser

Steam inlet temp. 180 ˚C to 30˚C

Steam outlet temp. 55˚C to 90˚C

Pressure within condenser 0.1 bar

Mass flow rate of steam 30 tone

Mass flow rate of water 165.5 tone

Cooling water inlet temp. 25˚C to 40˚C

No. of pass 4 as well as 2

Inner and outer dia. Of tube 10 mm & 12 mm

Velocity of water 1 m/s

From above given data we have to design the surface condenser for steam power plant and we

have to find;

Out let temperature of cooling water

Numbers of tubes

Tube length

Condenser area

Over all heat transfer co efficient

Mass flow rate of condensation

Condenser efficiency

 

38  

NOMENCLATURE:

: Area,

: Specific heat, : Inner diameter, m : Outer diameter, m : Thermal conductivity, : Length, m : Mass flow rate, : Pressure, bar : Heat transfer rate per unit time, watt : Temperature, : Over all heat transfer coefficient,

: log mine temperature,

: Heat transfer rate at inner surface, : Heat transfer rate at outer surface, : No. of tubes : Inlet temperature of cooling water, : Outlet temperature of cooling water, : Inlet temperature of steam,

: Outlet temperature of steam,

These nomenclatures are used when we designing the steam condenser which we are used in power plant.

A2m

pCKj

Kg K

iD

oD

KW

m K

L

MKg

sp

Q

T oC

U 2W

m KoC

iH

oH

N

1wT

2wT

1sT

2sT

oC

oC

oCoC

2W

m K

2W

m K

LMTD

 

39  

DESIGN OF CONDENSER

 

40  

5.1 Steps taken under consideration when designing the condenser: Effective steam condenser design of necessity must take many performance variables into

consideration.

Some of them are given below:-

The configuration of the exhaust flow pattern entering the condenser.

The moisture content of incoming steam.

The design of the transition piece to achieve the most uniform distribution of incoming

steam over the tube bundle.

Shell design parameters that provide maximum supports to the tube bundle without

impacting pressure drop.

De-aeration and reheat requirements for the steam condensate.

Tube sheet design consideration that will enhance the steam flow over and through the tube

bundle to achieve maximum performance efficiencies.

Plus many more design variables that impact condenser performance.

5.2 Design calculation for condenser: Mass of steam:-

3

30

30 103600

8.33

stonem hrs

Kgs

=

×=

=

Heat lost by steam = Heat gain by water

……… (Answer)

Rate of heat transfer is given by;

( ) ( )1 2 1 2s ws p s s w p w wm C T T m C T T∴ − = −

( ) ( )2

30,000 2.1 150 40 46 4.186 303600 wT∴ ∗ ∗ − = ∗ ∗ −

239.99 o

wT C∴ =

( )2 1ww p w wQ m C T T∴ = −

( )46 4.186 39.99 30= ∗ ∗ −

1925560 Q W∴ =

 

41  

Mass flow rate of water;

No of passes = 4

No of tubes

……… (Answer)

Figure 5.1.1: Tubing process

2

4w im d V Nπ ρ∴ = ∗ ∗

( )246 0.010 1000 14

Nπ∴ = ∗ ∗

585.98N∴ =

585.98 4= ∗2345=

 

42  

Property of water at

Now from all these data we calculate Rey. & Prant. Nos.

Reynolds number:

 

Prenatal number:

Nusset number:

Heat transfer co efficient of inside boundary of tube:-

And also, 

35o C

3993.95 Kgm

ρ =

4.176pKjC

KgK=

262.5343 10k = ∗

4 215. 3* /04 m hrα =

2262.73*10 /Kg hr mµ =

6 20.752*10v m=

4.86rP =

R eVdρµ

=

6

2

993.95 0.752 10 0.010262.73 10∗ ∗ ∗

=∗

284.49=

pr

CP

kµ

=

2

262.73 4.17662.53 10

∗=

∗

17.53=

0.8 0.40.023 e rNu R P=

0.8 0.40.023 (284.49) (17.53)= ∗ ∗ 6.64=

id hNuk∗

∴ =

2

0.0106.64 62.53 10

ih ∗∴ =

∗

2