CONDENSER_AND_COOLING_TOWER_PERFORMANCE.pdf

7/24/2019 CONDENSER_AND_COOLING_TOWER_PERFORMANCE.pdf

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A STUDY ON ROLE OF CONDENSER AND COOLING

TOWER ON THE PERFORMANCE OF THERMAL POWER

PLANT.

A PROJECT REPORT

SUBMITTED IN PARTIAL FULFILLMENT FOR THE

REQUIREMENT OF

POST GRADUATE DI PLOMA COURSE

IN

THERMAL POWER PLANT ENGINEERING

2014-2015.

SUBMITTED BY:-

AMIT KUMAR

ANUBHAV SAHU

ISHAN GURUNG

MANVAR BRIJESHKUMAR CHHAGANBHAI

RAVICHANDRAN.VSUMIT GOPAL

UNDER THE GUIDANCE OF

SHRI.P.MUTHUSAMY

Deputy Director

NPTI (SR)

NATIONAL POWER TRAINING INSTITUTE (SR)

(AN ISO 9001:2000 & 14001 ORGANISATION)

UNDER MINISTRY OF POWER, GOVT. OF INDIA

NEYVELI, TAMILNADU-607 803


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NATIONAL POWER TRAINING INSTITUTE (SR)

(AN ISO 9001:2000 & 14001 ORGANISATION)

UNDER MINISTRY OF POWER, GOVT. OF INDIA

NEYVELI, TAMILNADU-607 803

CERTIFICATE

This is to Certify that the work entitled A STUDY ON ROLE OF

CONDENSER AND COOLING TOWER ON THE PERFORMANCE OF

THERMAL POWER PLANThas been carried out byAmit Kumar, Anubhav

Sahu, Ishan Gurung, Manvar Brijeshkumar Chhaganbhai, Ravichandran.V,

Sumit Gopalunderour supervision in partial fulfillment for the requirement of

Post Graduate Diploma Course in Thermal Power Plant Engineering, during

the session2014-2015 in National Power Training Institute (SR), Neyveli,

Tamilnadu-607 803.

GUIDED BY AND COURSE COORDINATOR

SHRI P. MUTHUSAMY

DEPUTY DIRECTOR


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ACKNOWLEDGEMENT

We are thankful to Shri S.Viswanathan, NPTI (SR), Neyveli, for extending

valuable training reserve unit facilities.

We bring out profound and overwhelming gratitude to our Project Guide

and Program Director Shri P.Muthusamy, Deputy Director, NPTI (SR), Neyveli,

for his relentless guidance, valuable suggestions, constant encouragement

throughout this dissertation work, which were of immense help in successfulcompletion of this project.

We take this opportunity to thank NEYVELI LIGNITE CORPORATION

LIMITED, Neyveli and authorities especially Er.J.Subbiah ACM/MECH for

providing necessary guidance to carry out this project work.

Finally, we also thank all those who have helped directly and indirectly

during this project and also for the successful completion of the same.


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ABSTRACT

In a thermal power plant the efficiency and performance of its individual equipment and

component plays a very vital role in deciding the overall power plant efficiency. As the

overall efficiency of thermal power plant is product of boiler, turbine, generator and

cycle efficiency, where boiler efficiency is around 85-90%, turbine efficiency is around

80-90% and generator efficiency is about 98%. But when cycle efficiency is included

the turbo-generator efficiency is reduced to below 40%, due to which the overall plant

efficiency drops to 32-42 %.

As thermal power plant is based modified Rankine cycle, the most important parameters

of this cycle are pressure and temperature of superheated steam at inlet of high pressure

turbine and pressure and temperature of exhaust steam at outlet of low pressure turbine.

So to increase the cycle efficiency either inlet parameter is to be increased or outlet

parameters to be decreased.

The most of the heat loss in any power plant occurs at the condenser side. This heat

which is lost cannot used for further work done in turbine to rotate the turbo- generatorand produce electricity. So the performance of the condenser plays a very vital role on

deciding the overall performance of power plant. Therefore our aim in this project is to

study, analyse and various factors and parameters which are effecting the condenser

performance and efficiency, calculate its performance and how its optimum

performance can be achieved.

Since the cooling tower is also an important component of power plant, as the

circulating cooling water which coming out of condenser taking the latent heat from

exhaust steam changing its state to water during this heat exchanging process and losses

its heat to the atmosphere .We will also study the how performance of cooling towers

effects the performance of condenser and its impact on plant efficiency.


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TABLE OF CONTENTS

S.NO TITLE OF CHAPTER PAGE NO

1 INTRODUCTION 1-11

1.1 THERMAL POWER PLANT CYCLE 1

1.2 ROLE OF CONDENSER IN THERMAL CYCLE 5

1.3 PRINCIPLE OF CONDENSER 5

1.4 ADVANTAGES OF CONDENSER 6

1.5 PRESSSURE AND ITS MEASUREMENT 8

1.6 VACUUM AND ITS MEASUREMENT 9

1.7 TERMINAL TEMPERATURE DIFFERENCE 10

1.8 INITIAL TEMPERATURE DIFFERENCE 11

1.9 LOG MEAN TEMPERATURE DIFFERENCE 11

1.10 SATURATION TEMPERATURE 11

2. CONSTRUCTIONAL DETAILS OF CONDENSER 13-26

2.1 CLASSIFICATION OF CONDENSER 13

2.2 CONSTRUCTIONAL DETAILS OF UNIT-6/ST-2/TPS -2(NEYVELI) 212.3 TECHNICAL DATA OF UNIT-6/ST-2/TPS-2 26

3. FACOTRS AFFECTING CONDENSER PERFORMANCE 28-35

AND EFFICIENCY

3.1 EFFECT OF VARYING THE BACK PRESSURE 28

3.2 EFFECT OF AIR ON BACK PRESSURE 293.3 SCALE FORMATION 30

3.4 EFFECT ON VACCUM DUE TO VARIOUS FACTORS 31

3.5 CONDENSER EFFICIENCY AND PERFORMANCE 34

4. CALCULATIONS ON THE FACTORS AFFECTING 36-40

CONDENSER PERFORMANCE

4.1 EFFECT IN CONDENSER VACUUM DUE TO CIRCULATING 37

WATER INLET TEMPERATURE

4.2 EFFECT IN CONDENSER VACUUM DUE TO CIRCULATING 38

WATER FLOW4.3 EFFECT IN CONDENSER VACUUM DUE AIR INGRESS 39

/DIRTY TUBES

5 FAULT ANALYSIS IN CONDENSER 41-44

6 INTRODUCTION TO COOLING TOWERS 45-51

6.1 COOLING TOWER IN POWER PLANTS 45

6.2 COMPONENTS IN COOLING TOWER 45

6.3 PRINCIPLE OF OPERATION 47

6.4 TYPES OF COOLING TOWER 48

6.5 TERMINOLOGIES 50


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6.6 DALTONS LAW OF PARTIAL PRESSURE 51

7 COOLING TOWER PERFORMANCE ASSESMENT 52-59

7.1 COOLING TOWER PERFORMANCE 52

7.2 FACTORS AFFECTING COOLING TOWER 53

PERFORMANCE

7.3 PERFORMANCE ASSESMENT OF COOLING TOWERS 57

7.4 DISCRIPTION OF NATURAL DRAFT COOLING TOWER 57

OF STAGE-2/TPS-2 (NEYVELI)

7.5 COOLING TOWER SAMPLE PERFORMANCE 59

CALCULATION

8. BIBILOGRAPHY 61


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LIST OF FIGURES

FIGURE NO. FIGURE NAME PAGE NO.

Fig 1.1 Thermal Power Plant Cycle 1

Fig 1.2 Rankine Cycle With Reheat 2

Fig 1.3 Rankine Cycle With Regeneration 3

Fig 1.4 Modified Rankine Cycle 4

Fig 1.5 Heat Increases Pressure 6

Fig 1.6 Cooling Decreases Pressure 6

Fig 1.7 Pressure Diagram 9

Fig 1.8 Terminal Temperature Difference 10

Fig 2.1 Low Level Jet Condenser 14

Fig 2.2 High Level Jet Condenser 15

Fig 2.3 Ejector Condenser 15

Fig 2.4 Double Flow Type Condenser 17

Fig 2.5 Central Flow Type Condenser 17

Fig 2.6 Evaporative Type Condenser 18

Fig 2.7 Underslug-Axial or Transverse Condenser 18

Fig 2.8 Internal Condenser 19

Fig 2.9 Pennier or Side Mounted Condenser 20

Fig 2.10 Single And Double Pass Condenser 20

Fig 2.11 A Typical 210 MW Condenser 21

Fig 2.12 Condenser Supports 22

Fig 2.13 Steam- Dumping (Throw Off) Device 26

Fig 3.1 Condenser Conditioning Graph 33

Fig 6.1 Schematic Diagram of Cooling Tower 45

Fig 6.2 Cooling Tower Operation 48


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Fig 6.3 (A) Cross Flow Natural Draft Cooling Tower 49

(B) Counter Flow Natural Draft Cooling Tower 49

Fig 6.4 Types of Mechanical Cooling Tower 50

Fig 7.1 Performance of Cooling Tower 54


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CHAPTER - 1

INTRODUCTION

Condenser serves as the closing link in the thermal cycle. The entire heat energy in the steam

entering the turbine cannot be converted into mechanical work. The unutilized heat energy has

to be rejected to a sink. Condenser acts as a heat sink in the thermal cycle in which rejection

of heat energy takes place on condensation of exhaust steam of turbine. With this, the

Herculean task of replenishing the working fluid completely is eliminated.

1.1) THERMAL POWER PLANT CYCLE

A typical 210 MW thermal power plant cycle based on modified Rankine cycle.

Fig 1.1 Thermal Power plant Cycle

Modified Rankine cycle:-

Modified Rankine cycle is based on theory of Rankine cycle. Working of modified Rankine

cycle is similar to that of Rankine cycle with some practical modification in the cycle to make

it more operational.


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The Rankine cycle is a model that is used to predict the performance of steam turbine systems.

The Rankine cycle is an idealized thermodynamic cycle of a heat engine that converts heat into

mechanical work. The heat is supplied externally to a closed loop, which usually uses water as

the working fluid.

The following modifications are done on Rankine cycle to make it practically more operational

and efficient:-

1.Rankine cycle with reheat

FIG. 1.2: - RANKINE CYCLE WITH REHEAT

The purpose of a reheating cycle is to remove the moisture carried by the steam at the final

stages of the expansion process. In this variation, twoturbines work in series. The first accepts

vapour from theboiler at high pressure. After the vapour has passed through the first turbine,

it re-enters the boiler and is reheated before passing through a second, lower-pressure turbine.

The reheat temperatures are very close or equal to the inlet temperatures, whereas the optimum

reheat pressure needed is only one fourth of the original boiler pressure. Among other

advantages, this prevents the vapour from condensing during its expansion and thereby

damaging the turbine blades, and improves the efficiency of the cycle, given that more of the

heat flow into the cycle occurs at higher temperature.
http://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Vaporizationhttp://en.wikipedia.org/wiki/Boilerhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Boilerhttp://en.wikipedia.org/wiki/Vaporizationhttp://en.wikipedia.org/wiki/Turbine


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2. Regenerative Rankine cycle

The regenerative Rankine cycle is so named because after emerging from the condenser

(possibly as asub cooled liquid)the working fluid is heated bysteam tapped from the hot

portion of the cycle. On the diagram shown, the fluid at 2 is mixed with the fluid at 4 (both at

the same pressure) to end up with the saturated liquid at 7. This is called "direct contact

heating". The Regenerative Rankine cycle (with minor variants) is commonly used in real

power stations.

Another variation is where bleed steamfrom between turbine stages is sent tofeed water

heatersto preheat the water on its way from the condenser to the boiler. These heaters do not

mix the input steam and condensate, function as an ordinary tubular heat exchanger, and are

named "closed feed water heaters".

The regenerative features here effectively raise the nominal cycle heat input temperature, by

reducing the addition of heat from the boiler/fuel source at the relatively low feed water

temperatures that would exist without regenerative feed water heating. This improves the

efficiency of the cycle, as more of the heat flow into the cycle occurs at higher temperature.

This process ensures cycle economy.

FIG. 1.3: - RANKINE CYCLE WITH REGENERATION
http://en.wikipedia.org/wiki/Subcooled_liquidhttp://en.wikipedia.org/wiki/Subcooled_liquidhttp://en.wikipedia.org/wiki/Subcooled_liquidhttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Feedwater_heaterhttp://en.wikipedia.org/wiki/Feedwater_heaterhttp://en.wikipedia.org/wiki/Feedwater_heaterhttp://en.wikipedia.org/wiki/Feedwater_heaterhttp://en.wikipedia.org/wiki/Feedwater_heaterhttp://en.wikipedia.org/wiki/Feedwater_heaterhttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Subcooled_liquid


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MODIFIED RAKINE CYCLE PROCESS

The various processes in modified Rankine cycle are as follows

Process 1-2-3-4-5: The working fluid is pumped from low to high pressure. As the

fluid is a liquid at this stage, the pump requires little input energy.

Process 5-6-7: The high pressure liquid enters a boiler where it is heated at constant

pressure by an external heat source to become a dry saturated vapour. After that it

heated in super heater to make it superheated steam.

Process 7-8: The superheated steam expands through a HPturbine,generating power.

This decreases the temperature and pressure of the vapour, and some condensation

may occur.

Process 8-9: The steam coming out of the HP turbine is send back to the furnace

through re-heater again to make it superheated steam.

Process 9-10-11: The superheated steam from re-heater is sent to IP turbine where it

expands isentropically and work is done on turbine blades to produce torque for

rotating of the shaft. The outlet steam from IP turbine is sent to LP turbine, where it

again expands and work is done on the turbine shaft to rotate the shaft which in turn

coupled with the generator to generate electricity.

Process 11-1:The exhaust from the LP turbine is now sent to condenser which isunder vacuum where the steam losses its latent heat to change its to water. During

this process no change of temperature of steam takes place, so temperature of steam

and water remains the same.

FIG. 1.4: - MODIFIED RANKINE CYCLE
http://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Turbine


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1.2) ROLE OF CONDENSER IN THERMAL CYCLE:

Condenser is simply not a closing link, but a vital one in the thermal cycle. Constant

temperature heat rejection is taking place here. It is the only process similar in Carnot and

Rankine cycles. The latent heat of exhaust steam of Turbine is absorbed as sensible heat by the

circulating water.

To extract maximum work from the steam expanding in the Turbine, expansion of steam should

be high. Since the condenser helps in maintaining high vacuum that is practically possible,

maximum work can be expected. If the steam had exhausted at atmospheric pressure, this

would not have become possible.

1.3) PRINCIPLE OF A CONDENSER

1. Volume of Steam:-

If water is put into a closed vessel and heated, a quantity of heat known as sensible heat is

required to bring the water to boiling point and if further heat is added to convert the water into

steam this is known as latent heat.

The volume of the steam formed is far greater than that of the water and consequently the

pressure in the vessel rises. Thus the application of the latent heat has caused an increase in

pressure. (Figure 4 and 5).

2. Removal of Heat:-

Now reverse the process and remove some heat by cooling the vessel. During this cooling the

latent heat is removed from the steam which is reduced to water (or condensed) with a

consequent fall in pressure. (Figure 4)

This removal of latent heat happens on a very large scale in a turbine condenser.


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Fig.1. 5: Heat increases pressure Fig.1 6: Cooling decreases pressure

3. Condenser Pressure:-

The condenser is an airtight vessel where the steam exhausted from the turbine is cooled and

condensed. The condensation is so complete that the pressure inside the condenser is reducedbelow that of the atmosphere and this condition is referred to as the vacuum in the condenser.

To maintain this low pressure condition it is essential that any air or other incondensable gases,

passing in to the condenser with the steam must be continuously removed and, in addition to

condensing the steam, the condenser must separate, these gases from the steam for discharge

by an ejector or air pump.

1.4) ADVANTAGES OF CONDENSER: -

1. Improvement of thermal cycle efficiency:

The minimum absolute pressure, that is practically possible (or the maximum possible

vacuum), which is maintained in the condenser helps to extract maximum work from the steam

expanding in the turbine. This achieves considerable efficiency increase of the turbine. Overall

efficiency of the cycle is raised due to this.


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2. Easy handling of the working fluid, i.e. by condensing and reuse:

Since the condensed steam is reused, make up water requirement is drastically reduced. The

make-up water rate has to be around 3% of steam generation rate in the boiler in normal

working conditions, practically it will be high. After exhaust steam from turbine, which

occupies the first place, the drain condensate (drip) from LP heaters is the major source of

recovery of the working fluid.

3. Hot-well is a water reserve and hence provides flexibility in operation:

Even though the cycle is a closed one, constant water levels are maintained in condenser,

Deaerator and boiler drum. System losses are made up continuously.

During start up, shut down, load raising, load reduction or during any emergency situation, the

water storage in the Hot-well serves as a cushion. This gives flexibility in operation of the

plant. During the situations mentioned above, the incoming fluid rate and outgoing fluid rate

may not exactly match but still the plant can be operated smoothly because the Hot-well serves

as a reservoir.

4. Helping to conserve DM water since the drains are diverted to condenser through flash

boxes:

Many drains are provided in steam and water lines in Turbine area. If these drains are not

properly diverted, wastage of DM water will be there mainly during start up and shut down.

Since condenser is the reserve operating at the lowest pressure in thermal power plant, its serves

as the receiving point. Maximum possible recovery of working fluid is accomplished bydiverting all the drain to the flash boxes, which in turn divert them to the condenser in the form

of steam and water.

5. Thermal cycle water losses are advantageously made up at the Hot-well:

Thermal cycle water losses are made up at the Hot-well. This arrangement has many

advantages over other options.


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Advantages of adding make up water at the Hot-well:

i). Pumping power required is bare minimum since the pressure required is very small. Higher

pressure will be required to inject the make-up water, if it is done at any other point of the

cycle. In fact, without any pumping, the make-up water can be made to be sucked by the

condenser from the CST.

ii). Temperature difference between the make-up water and main condensate water in the

condenser hot-well is the lowest encountered anywhere in the cycle. Hence the problem of

thermal shock (violent heat transfer) is avoided.

iii). As the make-up water undergoes deaeration in the condenser, a portion of the dissolved

oxygen coming along with the make-up water is removed through ejectors.

iv). Since the make-up water is added/injected at the neck of the condenser, i.e., right into the

flow of exhaust steam, condensation of exhaust steam is further improved as the make-up

water directly quenches the exhaust steam

1.5) PRESSURE AND ITS MEASUREMENT:-

Pressure may be defined as the force per unit area applied in a directionperpendicular to the

surface of an object.

Mathematically, pressure may be expressed as:

p = F/A

Where: pis the pressure,Fis the force and Ais the area.

Everyday pressure measurements are usually made relative to ambient air pressure. In other

cases measurements are made relative to a vacuum or to some other specific reference. When

distinguishing between these zero references, the following terms are used:

Absolute pressureis zero-referenced against a perfect vacuum, so it is equal to gauge

pressure plus atmospheric pressure.
http://en.wikipedia.org/wiki/Perpendicularhttp://en.wikipedia.org/wiki/Perpendicular


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Gauge pressure is zero-referenced against ambient air pressure, so it is equal to

absolute pressure minus atmospheric pressure. Negative signs are usually omitted. To

distinguish a negative pressure, the value may be appended with the word "vacuum" or

the gauge may be labelled a "vacuum gauge."

Differential pressureis the difference in pressure between two points.

Fig 1.7 Pressure Diagram

From above figure we can establish the following relations:-

1. Absolute pressure = Gauge pressure + Atmospheric pressure

i.e., Pabs= Pg+ Patm

2. Vacuum pressure = Atmospheric pressureAbsolute pressure

i.e., Pvac= Patm- Pabs

1.6) VACUUM AND ITS MEASUREMENT:-

Vacuum is sub-atmospheric pressure. It is measured as the pressure depression below

atmospheric. The term vacuum in the case of a condenser means pressure below atmospheric

pressure. It is generally expressed in mm of Hg (mercury).The vacuum is measured by means

of a vacuum gauge. Usually for calculation purpose the vacuum gauge reading is corrected to

standard barometric reading 760 mm as follows:


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Corrected vacuum in mm of Hg = (760-absolute pressure in mm of Hg)

= 760- (actual barometric readingactual vacuum)

Also, 760 mm of Hg = 1.010325 bar

Therefore, 1 mm of Hg = 1.01325/760 = 0.0013322368 bar

Vacuum Efficiency: -It is defined as the ratio of the actual vacuum to the maximum obtainable

vacuum

Vacuum Efficiency =Actual vacuum

Maximum obtainable vacuum

Condenser Efficiency: -It is defined as the ratio of the difference between the outlet and inlet

temperatures of cooling water to its difference between the temperature corresponding to the

vacuum in the condenser and inlet temperature of cooling water.

Condenser Efficiency =Rise in temp. of cooling water

Temp corr. to vacuum in condenser-inlet temp. of cooling water

1.7) TERMINAL TEMPERATURE DIFFERENCE (T.T.D.):-

The temperature difference between the exhaust steam and the cooling water is least at the top

of the condenser where the cooling water leaves. Here the cooling water has its highest

temperature. This particular temperature difference is very important and is given a special

name. It is called the terminal temperature difference. The important point is that any increase

in this terminal difference leads directly to increase in the saturation temperature of the exhaust

steam and a higher back pressure.

Fig 1.8 Terminal Temperature Difference

T.T.D. = Condensing Steam saturation temperatureCooling Water outlet temperature


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i.e., 2= t3t2

1.8) INITIAL TEMPERATURE DIFFERENCE (I.T.D.): -

It is defined as the difference between saturation temperature of the condensate water in the

condenser and temperature of cooling water coming into the condenser.

I.T.D. = Condensing Steam saturation temperatureCooling Water inlet temperature

i.e., 1= t3t1

1.9) LOGARITHIMIC MEAN TEMPERATURE DIFFERENCE:-

The logarithmic mean temperature difference (LMTD) is used to determine the temperature

driving force forheat transfer in flow systems, most notably inheat exchangers.The LMTD is

alogarithmic average of the temperature difference between the hot and cold streams at each

end of the exchanger. The larger the LMTD, the more heat is transferred. The use of the LMTD

arises straightforwardly from the analysis of a heat exchanger with constant flow rate and fluid

thermal properties.

Mathematically it can be given as,

LMTD =1 - 2

ln1/2

1.10) SATURATION TEMPERATURE:-

Asaturated liquid contains as much thermal energy as it can without boiling (or conversely a

saturated vapour contains as little thermal energy as it can withoutcondensing).

Saturation temperature means boiling point. The saturation temperature is the temperature for

a corresponding saturation pressure at which a liquid boils into itsvapour phase.The liquid

can be said to be saturated withthermal energy.Any addition of thermal energy results in a

phase transition.
http://en.wikipedia.org/wiki/Heat_transferhttp://en.wikipedia.org/wiki/Heat_exchangerhttp://en.wikipedia.org/wiki/Logarithmic_averagehttp://en.wikipedia.org/wiki/Saturation_%28chemistry%29http://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Thermal_energyhttp://en.wikipedia.org/wiki/Phase_transitionhttp://en.wikipedia.org/wiki/Phase_transitionhttp://en.wikipedia.org/wiki/Thermal_energyhttp://en.wikipedia.org/wiki/Gashttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Saturation_%28chemistry%29http://en.wikipedia.org/wiki/Logarithmic_averagehttp://en.wikipedia.org/wiki/Heat_exchangerhttp://en.wikipedia.org/wiki/Heat_transfer


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If the pressure in a system remains constant (isobaric), a vapour at saturation temperature will

begin to condense into its liquid phase as thermal energy (heat)is removed. Similarly, a

liquid at saturation temperature and pressure will boil into its vapour phase as additional

thermal energy is applied.
http://en.wikipedia.org/wiki/Isobaric_processhttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Isobaric_process


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CHAPTER -2

CONSTRUCTIONAL DETAILS OF CONDENSER

Since the condenser is one of the critical components of a power plant and its also dont have

another backup condenser, so knowledge of its constructional details of every elements

becomes vital before knowing other details on it. Study of its elements will help us to

understand its importance and function in condenser. In this chapter we will deal with each

elements of a condenser in brief to get an idea about it importance.

2.1) CLASSIFICATION OF CONDENSERS

Modern day condensers comes in various types, shapes and arrangements. So it becomes

essential to have classification of these condensers for its easy identification. The condenser

can be classified under various categories which are as follows:

1. According to type of heat rejection of steam to the cooling water.

2. According to the position and arrangement of the condenser itself.

3. According to the flow path of cooling water.

1. According to the heat rejection of steam to the cooling water:-

In condenser steam can be condensed by using either-

a.

Jet condenser (Also known as direct contact type).b. Surface type condenser.

a. Jet condenser: - In jet condenser the exhaust steam and water come in direct contact with

each other and temperature of the condensate is the same as that of cooling water leaving the

condenser. The cooling water is usually sprayed into the exhaust steam in a closed vessel to

cause rapid condensation.

In a power station the condensate is returned to the boiler and must be absolutely pure. If a jet

condenser were used the cooling water, which is mixed with the condensate would have to be


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equally pure. Because very large quantities of cooling water are required, this type of

condenser is not a practical proposition for power plant.

Jet condensers may be further classified as:

i. Low level jet condenser.ii. High level jet condenser.

iii. Ejector condenser.

i. Low level jet condenser: - In this type of condenser the exhaust steam is entering the condenser

from the top and cold water is being sprayed on its way. The baffle plate provide in it ensures the

proper mixing of the steam and cooling water An extraction pump at the bottom discharges to the

hot well from where it may be fed to the boiler if the cooling water being used is free from

impurities. A separate dry pump may be incorporated to maintain proper vacuum.

Fig 2.1 Low level jet condenser

ii. High level jet condenser: - In this type of condenser the shell is placed at a height of about 10.363

metres above hot well and thus the necessity of providing an extraction pump can be avoided

However provision of own injection pump has to be made if water under pressure is not available.

Fig 2.2 High level jet condenser


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iii. Ejector condenser: -Here the exhaust steam and cooling water mix in hollow truncated

cones. Due to this decreased pressure exhaust steam along with associated air is drawn

through the truncated cones and finally lead to diverging cone. In the diverging cone, a

portion of kinetic energy gets converted into pressure energy which is more than the

atmospheric so that condensate consisting of condensed steam, cooling water and air is

discharged into the hot well. The exhaust steam inlet is provided with a non-return valve

which does not allow the water from hot well to rush back to the engine in case a failure

of cooling water supply to condenser.

Fig.2.3- Ejector condenser

c. Surface condensers: - In surface condensers, the exhaust steam and water do not come

into direct contact. The steam passes over the outer surface of the tubes thorough which a

supply of cooling water is maintained. This type of condenser is useful where water is

available in large quantities it is usually very impure, for example, sea water and river

water, but such impurities have little effect upon its cooling properties. . In this case the

purity of the cooling water does not matter because apart from any leakages which may

occur it is never in contact with the condensate.


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Types of surface condensers: -

i. Down-flow type.

ii. Central-flow type.

iii. Invertedflow type.

iv. Regenerative-flow type.

v. Evaporative type.

i. Down-flow type: The cooling water enters the shell at the lower half section and after

traveling through the upper half section comes out through the outlet. The exhaust steam

entering shell from the top flows down over the tubes and gets condensed and is finally

removed by an extraction pump. Due to the fact that steam flows in a direction right angleto the direction of flow of water, it is also called cross-surface condenser.

Fig 2.4: Down-flow type condenser

ii. Central flow type: In this type of condenser, the suction pipe of the air extraction pump

is located in the centre of the tubes which results in radial flow of the steam. The better

contact between the outer surface of the tubes and steam is ensured, due to large

passages the pressure drop of steam is reduced.
http://engineering.myindialist.com/wp-content/uploads/2009/10/clip_image012.gif


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Fig 2.5: Central-flow type condenser

iii. Inverted-flow type: This type of condenser has the air suction at the top, the steam

after entering at the bottom rises up and then again flows down to the bottom of the

condenser, by following a path near the outer surface of the condenser. The condensate

extraction pump is at the bottom.

iv. Regenerative type: This type is applied to condensers adopting a regenerative method

of heating of the condensate. After leaving the tube nest, the condensate is passed

through the entering exhaust steam from the steam engine or turbine thus raising the

temperature of the condensate, for use as feed water for the boiler.

v. Evaporative type: The principle of this condenser is that when a limited quantity of

water is available, its quantity needed to condense the steam can be reduced by causing

the circulating water to evaporate under a small partial pressure.

The exhaust steam enters at the top through gilled pipes. The water pump sprays water

on the pipes and descending water condenses the steam. The water which is not

evaporated falls into the open tank (cooling pond) under the condenser from which it

can be drawn by circulating water pump and used over again. The evaporative

condenser is placed in open air and finds its application in small size plants.
http://engineering.myindialist.com/wp-content/uploads/2009/10/clip_image014.gif


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Fig 2.6: Evaporative type condenser

2.According to the Positions or Arrangement of the condenser itself:

According to the position condenser are classified as :

i.Underslug Axial or Transverse condenser.

ii. Integral condenser

iii.Pannier or side mounted condenser.

i. Underslug -Axial or Transverse Condenser:In this condensers are mounted below the L.P.

Turbine. The condenser may be located axially w.r.t turbine shaft. In some machines

condenses are mounted under the turbine at right angles to the turbine shafts.

Fig. 2.7 Underslug -Axial or Transverse Condenser


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ii.Integral Condenser: In this condensers are arranged around the L.P. Turbine cylinders as

shown in fig. 2.8

Fig. 2.8 Integral condenser.

iii.Pannier Condenser: In this condenser are arranged at each side of the L.P. turbine

cylinder, known as Pannier condenser.

Fig. 2.9 Pannier or side Mounted condenser.

3.According to the flow path of the cooling water:-

According to the cooling water flow the condenser can be classified as

i. Single flow (Single Pass).

ii. Double flow (Double Pass).

iii. Three pass condenser.


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When the cooling water makes only one journey across, this is known as a single pass

condenser. If the cooling water makes two journeys then it is known as a double pass

condenser. In this case the water in the bottom half of the tubes will be flowing from front to

back and in the top half from back to front. Fig.2.10 (b) shows a method of venting for a 2

pass condenser. A 3" air vent is fitted to each shell from the highest point on the return water

box. The air is vented to the cooling water outlet main and prevents air bubbles in the second

pass. The inlet pass is protected by drilling say 4 one inch holes in the inlet water box divisional

wall between passes 'x'. More emphasis is given on single pass and double pass condenses in

the next chapter.

Similarly with a three pass condenser the water makes three journeys across. A single

pass design which gives a long narrow condenser, suits the large modern turbines and can be

mounted axially under the machine in line with the turbine shifts. The steam distribution is line

with the turbine shafts. The steam distribution is not as good in a single pass as in two pass

condenser.

Fig 2.10 Single and Double Pass Condenser.


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2.2) CONSTRUCTION DETAIL OF CONDENSER-- 210 MW -UNIT-6/STAGE-

2/TPS-II

The condenser of 210 MW units 4 to 7/Stage-II/TPS-II is a rectangular shell of surface type.

The exhaust steam flow pattern in the condenser is down flow. The circulating water flow is of

double pass type and the lower tubes are in series with the upper tubes. The condenser is with

divided water boxes to have the tube nest in two parts in order to have 50% operation during

on load leak testing and maintenance. The circulating water system is of closed circuit type

with a cooling tower. The condenser primarily comprises of

Condenser supports

Hot well

Condensing chamber

Condenser neck

End tube plates

Tube nest

Water boxes

Air removal system

Steam dumping device.

The condenser is rated to handle 442 t/hr. of exhaust steam at the parameters of 0.1033

ata and 46.1 deg. C

Fig 2.11 A typical 210 MW condenser


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1. Condenser Supports

The condenser is supported on 24 springs in the two rows (2 x 12) in order to have flexible

connection with the turbine. It is rigidly connected to the base (Bottom half) of the LP cylinder of

the turbine. This kind of support for condenser ensures effective dampening of vibration and shockand also gives provision for thermal expansion of the LP cylinder of the turbine, condenser neck

and condenser itself.

Since the condenser has been floated over the springs, empty weight of the condenser is taken

by the springs along with partial operating weight. The remaining operating weight is taken by

the turbine foundation. While conducting hydraulic test in the shell side of the condenser water

is to be filled up into steam space up to one meter above the top tube row. Prior to filling water

into condenser steam space for testing, jacking screws provided with spring support should beused for ensuring water weight being passed on to them, to avoid over stressing of springs.

Prior to putting the system back in operation, condenser must be floated over springs to avoid

excessive upward thrust being passed on to the turbine foundation.

Fig. 2.12 Condenser supports

2. Hot-well:

The Hot well is in the lower part of the condenser to form a storage tank for main condensate.

It also collects the drains entering through flash boxes. It is a water reserve in the thermal cycle

along with deaerator and boiler drum. Hot well is divided in the middle through a partition.

The purpose is to separate the condensate condensed in each half of the condenser nest for

better identification of tube leaking zone. Conductivity measurements are to be done in each


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condensate outlet from the hot well to give a warning of any leakage of circulating water into

the condenser.

Two lines from the bottom of the hot well will take the main condensate to the suction of the

condensate extraction pumps. The hot well is provided with 2 level columns having level

glasses, level switches and level transmitters. It is also provided with 3 nos o f drains at its

bottom. Normal water level in the hot well is 750mm and its capacity is designed to be for 3

minutes of pumping by a CEP.

3. Condensing Chamber

The condensing chamber is a shell where the exhaust steam of turbine comes into contact with

the tube nest and gets condensed. It is floated on spring supports and welded to the condenser

neck and its top. The end tube plates secured to the shell provide support for the tube nest.

4. Condenser Neck:

This is the part of the condenser to form an interconnection between the condensing chamber

and LP turbine. It is designed such that the exhaust steam of turbine reaches the condensing

chamber with a relatively low velocity and very low-pressure drop. The make-up water line

and LP bypass steam lines join the condenser at the neck.

5. End Tube Plates

The end tube plates are perforated plates, which separate the water boxes from the condensing

chamber. There are 4 end tube plates, two on each side of the condenser, to have divided water box

construction. The circulating water tubes have been roller expanded into end tube plates. These tube

plates ensure a perfect sealing so that the purity of the main condensate is not affected. They are also

designed for withstanding against the difference in pressure between the condensing chamber and the

water box. The end tubes are cladded with stainless steel plates on C.W side for corrosion protection.

6. Tube Nest:

1. The thickness of the tubes should be as small as possible to have high rate of heat transfer.

The tubes are of outer diameter 25.4 mm and thickness of 0.7112 mm.

2. 16418 Nos. of tubes are provided in the condensing zone and 1240 Nos. of tubes in air

cooling zone.


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3. Method for making tube to end plate expansion joint on at both ends of the tube is by roller

expansion. Quality of expansion joints determine whether there is any seepage of cooling

water into steam space which has a bearing on the scaling of the water wall tubes of the

boiler, steam purity and silica deposition on last stage turbine blades. To ensure very high

quality of the expansion joints the expansion is carried out by torque controlled expander

tools. The holes should have good finish and minimum ovality. The expanders should be set

to achieve 7 to 10 % wall thinning

The intermediate tube plates at twelve places on each side provide the support for the tubes.

These intermediate support plates serve the following purposes:

To support the weight of the tubes thereby preventing sagging of these tubes

To provide increased strength to withstand the force of direct impingement of

the exhaust steam.

To curb flow induced vibration.

4. The tubes are placed horizontally with an inclination of 0.5 degree towards the front water

box side for self-draining during circulating water pump tripping or plant shutdown.

5. The principal factors to be taken into consideration when determining the tube spacing are

low steam velocity between condenser tubes, uniform distribution of the steam over the

whole condensing surface and equal pressure at the top and bottom rows of tubes. A

computerized design is used to optimize tube spacing, tube cross section and condensing

surface of the condenser. The tube spacing is broken up to a large extent by the arrangement

of the condenser tubes in bundles. Wide lanes from top to bottom are left between the tube

bundles so that the steam can also reach the lower rows of the tubes without incurring

appreciable pressure loss. The steam then flows sideways from these lanes into the tubes

7. Water Boxes:

Since the condenser is constructed with divided water boxes, there are totally 4 water boxes.

Two front water boxes are divided horizontally to have 2 passes of the circulating water. The

water makes its entry at the bottom and leaves at the top of the front water box. The reversing

chamber at the rear acts as an interconnecting chamber for bottom and top passes. All the water

boxes are provided with vents and drains. The inlet and outlet circulating water pipes join the

front water boxes through expansion joints. Water box inside surfaces have been protected

against corrosion by application of protective coating over the surfaces in contact with the


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circulating water. Water boxes incorporate hinge arrangement to facilitate the removal of cover

for enabling leak detection, re-tubing and cleaning of tubes etc.,

8. Air off Take System:

Although the condenser is theoretically expected to condense the entire quantity of exhaust

steam, practically a small quantity of steam will remain in the vapour state along with the air

ingresses into the system and non-condensing gases. This uncondensed vapour and the air will

have to be removed by means of ejectors in order to sustain the vacuum inside the condenser.

The system, which collects the uncondensed vapour and the air from the condenser, so as to

enable ejection is known as AIR OFF TAKE SYSTEM.

As explained earlier, the pattern of exhaust steam flow is Down Flow and the exhaust steam

gets condensed before reaching the bottom. Hence the air and the uncondensed vapour will

reach the bottom space of the tube nest in each side.

At the bottom space of the tube nest of each side, a horizontal pipe with perforations at its

bottom surface only is provided for collecting the air and the uncondensed vapour. A zone

called as air cooling zone is formed below these 2 pipes. The air and the uncondensed vapours

existing at the bottom space (above the hot well water level) gets sucked (through the air

cooling zone) into these horizontal pipes are in communication with the ejectors through twovertical pipes, there is vacuum inside these pipes.

Since the air and uncondensed vapour flow over the surfaces of 1240 Nos. of circulating water

tubes separately provided in air cooling zone, the reduction in specific volume of the air and

the uncondensed vapour takes place (due to temperature reduction) resulting in reduction of

the volumetric load on the ejectors.

9. Steam Dumping Device:

Two numbers of Steam Dumping devices are provided for the condenser for dumping bypassed steam

(from LP bypass system) directly into the condenser during start-up, load throw-off etc., Each device

is provided with an orifice plate which reduces the bypassed steam pressure to approximately

condenser pressure. The pressure of bypassed steam has already been reduced partially due to

throttling in LP bypass control valve. Moreover, injection of main condensate into the bypassed steam

is done here to reduce the temperature.


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100% steam dumping can be carried out in condenser for a maximum duration of 10 minutes,

and within this time, Unit operation is required to be brought down to 60% and then the Unit

may be operated continuously.

Fig. 2.13 Steam dumping (throw-off) device

2.3) TECHNICAL DATA OF 210 MW UNIT 6/STAGE -2/TPS-II

CONDENSER:-

Design Features:

1. Number of condenser per unit : One

2. Type: Rectangular down flow type surface condenserDivided water box with two waterpasses in each section

3. Overall length of the condenser : 14000 mm

4. Method of support for condenser : Floated over the springs

5. Number spring elements : 24 Nos. (In 2 rows)

6. Loading data

a. Dry weight of condenser : 361 Tonnes

b. Operating weight of Condenser : 555 Tonnes

c. Weight transferred to LP cylinder

from stability consideration : 190 Tonnes

d. Operating weight on springs : 365 Tonnes

e. Hydraulic Test weight : 693 Tonnes

f. Water to be filled in the

hot-well during spring adjustment : 4 Tonnes


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7. Hot well Storage capacity : 3 minutes of pumping by CEP

8. Number of end tube plates : 4 (2 on each side)

9. Length between end tube plates : 10,000 mm

10. C.W.Tubes:

a. Length of the tube : 10, 1 0 mm

b. Tube OD and thickness : 25.4 x 0.7112 mm

c. Tube material : Stainless steel (SS TP 316)

d. Percentage tube thinning : 7.5 % (average)

e. Number of tubes:

i) Condensing zone : 16148 nos.

ii) Air cooling zone : 1240 nos.

TOTAL : 17658

f. Total heat transfer surface area : 14090 m2

11. Number of support tube plates : 2 x 12

12. Design Data: Water side Steam side

i) Condenser pressure : 5.0 ksc full vacuum

ii) Condenser temperature : 50 deg C 100 deg C

15. Circulating water Data

i) Design inlet temperature : 34 deg C.

ii) Temperature rise in tubes : 8.6 deg C.

iii) Flow quantity : 29000 m3/ hr.

iv) Pressure drop across the tubes : 5.5 mm W.C.

2. Thermal Cycle Data (at 100 % MCR ):

Rate of steam flow from main turbine : 441.96 T/Hr.

Enthalpy of steam from turbine : 579.5 Kcal / kg.

Temperature of exhaust steam from turbine : 46.1 deg C

Condenser pressure : 0.1033 ata.


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CHAPTER-3

FACTORS AFFECTING CONDENSER PERFORMANCE AND

EFFICIENCY

3.1) EFFECT OF VARYING THE BACK PRESSURE

A large amount of the extra work is done by the steam, when the back pressure is reduced.

However, the trouble is that as the back pressure improves certain losses increase.

Those are mainly:

1) CW Pumping Power.

2) Leaving losses.

3) Reduced condensate Temperature.

4) Wetness of the steam.

1. Increased CW Pumping Power

Assuming that the CW inlet temperature is low enough, the back pressure can be reduced by

putting more and more CW through condenser tubes. However, this will require more CW

pumping power and the gain from improved back pressure must be offset against extra power

absorbed by the pumps. So the CW pumps should be run only when the cost of running the

pump is equal to, or less than the gain in output from the machine.

2. Increasing leaving loss

The steam leaves the last row at a velocity which depends upon the conditions prevailing at the

point. As this velocity is not utilized usefully, it is represents a loss of possible work known

as the leaving loss. So velocity steam through fixed annulus is must also double. But leaving

losses varies as square of the velocity. So it will increase four times.

Leaving Loss = mvo2/ 2

Where, m= Mass steam flow,

V0= Absolute velocity at the outlet of last row of blade


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3. Reduced condensate temperature / increased bled steam

The condensate in the condenser is at saturation temperature corresponding to the back

pressure. It back pressure is reduced, saturation temperature will drop. When it enters first LP

heaters it will be cooler than before consequently more steam will automatically be bled to the

heater. The extra steam is no longer available to do work in the turbine will be deprived of

some work.

4. Increase wetness of the steam

The lower the back pressure, the greater the wetness of steam. The extra moisture could result

in damage to the moving blade. Also with increased wetness, volume of steam is reduced water

droplets being heavier than steam moves slowly. So the front edge of moving blades have to

push the droplets out of the way. This can cause damage to blades. Therefore, it is usual to fit

satellite erosion shields to the leading edge to reduce this damage. As a rough guide, it can be

assumed that every 1% wetness will reduce efficiency of associated stage by 1%.

The reduction in back pressure will result in net improvement in heat consumption until a pointis reached beyond which benefit due to improve back pressure is outweighed by the losses and

heat consumption increase.

3.2) EFFECT OF AIR ON BACK PRESSURE

The reason why air has such an adverse effect on vacuum is often misunderstood, so a few

words on the subject will not be out of place.

The 100 percent capacity of the air pumps is often of the order to 1/2000 of the weight of steam

entering the condenser per hour.

Now, it is frequently (but wrongly) assumed that the back pressure suffers because of the extra

partial pressure of the air. That this is not so can be easily shown by calculation. Maxing even

the maximum weight of the air, the air pumps can handle with the steam in the condenser would

do very little to increase the back pressure because of the partial pressure alone.


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For example, if the back pressure is 34.474 mbar (vacuum) without any air presently would

only rise to 34.3485 mbar. The real trouble with air is that as the steam condenses on the

condenser on the condenser tubes the air (which is incondensable) is left behind. If the quantity

of air is mall the scouring action of the steam and condensate will sweep the air is small the

scouring action of the steam and condensate will sweep the air off the tubes. However, if the

air quantity is significant things are different. Air is such an excellent heat insulator that it only

requires a film a few molecules thick to seriously interfere with the heat transfer to the cooling

water from the steam. Accordingly the vacuum suffers.

Fortunately, it is easy to determine whether air is present in a condenser by merely measuring

the temperature of the contents of the air suction pipe to the air pumps. With no air present

this temperature is approximately the same as that of the saturated steam in the condenser.

When air is present this temperature falls-the more air present the lower is the temperature.

3.3) SCALE FORMATION

Scaling is the precipitation of hare and adherent salts of calcium and magnesium on metal

surface. These scales have very poor thermal conductivity and heat transfer in condenser is

affected very seriously. It is therefore essential to control the scale formation on one hand and

remove the deposited scale on the other hand for good condenser performance. Some of the

common scale are calcium and magnesium carbonates and sulphates, silicatesand iron salts. Most

commonly encountered scale in normal cooling water system is calcium carbonate, which is

moderately soluble in water is present in almost all cooling waters and get decomposed into

calcium carbonate at higher temperature and ph.

Calcium carbonate is soluble in water and gets precipitated on the tubes. Calcium sulfate has

higher solubility and hence less precipitation scale. Magnesium salts have less scaling

potential, asthey are more soluble than calcium salts and their concentration in water is usually

slow. Process of scale formation gets accelerated with increase in water temperature and pH

or alkalinity. Limiting cycle of concentration, using softening water for CW makeup, reducing

CW water pH to about 8.5, and using on-line tube cleaning system with sponge balls - these

are some of the measures that can be taken for controlling scale formation.


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3.4) EFFECT ON VACUUM DUE TO VARIOUS PARAMETERS:-

1) Losses due to high CW temperature.

Provided that the cooling towers are performing satisfactorily this loss must be accepted to

some extent. It is possible, of course, to minimize the loss by having an abnormal quantity of

cooling water flowing through the condenser; this gives a smaller cooling water temperature

rise across the condenser then optimum. However, the gain which results from this is almost

cancelled out by the additional pumping power required. Therefore, the increased turbine

output caused by improving the vacuum must be greater thanthe increased circulating pump

hour by required tojustifythese means of reducing the loss.

2) Variation of CW temperature rise:

This is due to CW Flow. If the cooling water temperature rise across the condenser is less

then optimum, then the opening of the condenser cooling water outlet valve should be

reduced. This condition may also be shown up when the condensate temperature is lower

than the saturated steam temperature. If the cooling water temperature rise is hardly effected

by opening (even abnormally wide) of the cooling water valves then the condenser tube

plates are probably fouled-assuming that there is no shortage of cooling water.

3) Dirty tubes.

The effect of the dirty tubes on the heat transfer is to increase the TTD above optimum .

Operationally little can be done to eliminate the cause of this loss, as the tubes must normally

be cleaned when the unit is off - load. However, as soon as loss due to dirty tubes is determined,

it should be ascertained that chlorine injection to the affected condenser satisfactory.

The effect of this loss on vacuum can be minimized by increasing the flow of cooling water

through the condenser on account of increase pumping power. So that we have to observe that

this should be less than the gain in output from the machine.

4) Effect of air in condenser.

Practically all the air entering the condenser does so through leakages into the turbine spaces

which are under vacuum and can have one or more of the following ill effects on operation:-


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a) Air entering to the outside to the condenser tubes adds considerable resistance

to the heat flow. To overcome this, in order to maintain the flow of heat the

exhaust temperature must rise. This is known as air blanketing.

b) The corresponding backpressure will rise as a result of increased exhaust

temperature.

c) The condensate temperature in relation to that of the exhaust temperature in a

similar manner to the pressure drop.

In the case of a) the increasing heat transfer resistance will increase the amount of heat that

must be transferred and as the steam consumption is increaser attempts to hold the turbine

output constant would further aggravate the situation.

Possible areas of air ingress:

LP Turbine Glands.

LP Turbine Diaphragms.

LP Turbine Parting Plane.

CEP Glands (Standby Pump)

Hot well

Valve Glands, Flange Joints etc.

5) Partial Pressure.

The reason for a) and b) are clear but some explanation is necessary for c). Here the reason lies

in a scientific law known as Dalton's law of partial pressure, which states that if a mixture of

gases of vapour is contained in a closed vessel each gas exerts a pressure equal to that which it

would normally exert if alone in the vessel. In other words each exerts a partial pressure and

the total pressure in the vessel is the sum of the partial pressures.

Consider these laws in relation to the condenser. At the top, the weight of air present is very

small compared with the weight of steam and the air partial pressure can be neglected. The

total pressure can be regarded as that due to the steam alone. The steam temperature actually

corresponds to the partial steam pressure. At the top of the condenser, steam temperature will

therefore correspond to total pressure.


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At the bottom of the condenser, however, most of the steam will have been condensed and

there is a much bigger ratio by weight of air to steam. So, now the air partial pressure is not

negligible, hence, at the bottom of the condenser the total pressure is greater than the steam

partial pressure by an amount equal to the partial pressure.

The condensate temperature corresponds to the steam partial pressure at the bottom of the

condenser. It will therefore, be lower than if calculated from the total pressure.

This is shown numerically in the following examples:

Pressure (mm of Hg ) Temperature (0C)

At the top of the condenser, due to

steam alone.38 33

Pressure drop through condenser. Say 5 --

Total pressure at the bottom of the

condenser made up of partial

pressure of steam & air.

33 30.5

Partial air pressure at bottom Say 2.5

Partial steam pressure at bottom 30 29

Thus the total losses in temperature are now 70C and there are due to air in the example shown

is 20C. These emphases the importance of prevention of the air leaks and the removal of them

condenser.

Fig 3.1 Condenser conditioning graph


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6) Velocity of steam.

The velocity of incoming steam is the main factor in the forcing the air towards the bottom of

the condenser. Because of these velocities, the steam sweeps over tubes and drives the air away

before it. In this way the tubes are kept free of air, which is kept. Moving towards the air outlet.

It must not be allowed to recalculate or find a stagnant corner. During this tine the steam has

been condensing so the air concentration increased towards the bottom of the condenser.

When the air and the any uncondensed steam mixed with it reach the bottom of the condenser

they come within the range of powerful effect of ejector draws this mixture under a baffle

which encloses a nest of the tubes in the lowest temperature cooling water zone. In fact the

water temperature at the outlet from this section might be only 50F higher than the water inlettemperature.

In this air cooler section any steam remaining in the mixture is condensed and the air cooled.

The reason for cooling the air is to reduce the volume and enable the ejector, which operates

by volume, to remove a greater weight of air.

The actual take off from the air cooler is usually placed about three tubes drawn the top of the

air cooler section. This is to prevent air being reheated through contact with the baffle plate

which has relics much hotter steam on the side.

3..5) CONDENSER EFFICIENCY AND PERFORMANCE

The condenser efficiency may be defined as ''the ratio of the difference between the outlet and

inlet temperature of cooling water to the difference between the temperature corresponding to

the vacuum in the condenser and the inlet temperature of the cooling water."

Because of the considerable effect that condenser performance can have upon heat rate there is

a need to apply a strict control upon its operation. Though the main control parameter is the

back pressure measured at the turbine exhaust flange, since any deviation in this directly affects

the heat of the machine, the following parameter also have to be measured and recorded

periodically.


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1) C. W. inlet temperature

2) C. W. outlet temperature

3) C. W. pump amperage and bus voltage

4) Loss of pressure across the condenser

5) Megawatt load on unit.

6) Main steam temperature and pressure.

7) Reheat heat temperature and pressure.

8) FW final temperature.

9) Whether all feed water heaters are in service, if not , which are not

10)Condenser exhaust temperature

11)Condensate temperature

Generally, condensers are designed to operate at 85% cleanliness factor. It is possible to

draw curves for different C.W. inlet temperature designed exhaust pressure at different

cleanliness factors at a different MW loads. The steam flows can be read out from heat balance

chart or in case of any basic departure (like a particular heater remaining out of service) a fresh

heat balance can be drawn. Once these curves are available, the performance of the condenser

can be easily estimated any time. The C.W. pump current and pressure drop across condenser

would give fair estimate of the quantity of C.W. flow to the condenser in practice checking of

condenser tubes can be apprehended by people, but loss due to scaling/deposition is not easily

seen and need shut down inspection.


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CHAPTER4

CALCULATION ON FACTORS AFFECTING CONDENSER

PERFORMANCE

The following tabulation of various condenser parameters including values of both actual and

design are taken from UNIT No -6 (210 MW), NLC Thermal Power Station (TPS) 2 Stage -

2, Neyvelion 16/01/2015during full load operation of the unit.

Where, LMTD =1 - 2

ln 1/ 2

PARAMETERS UNITS ACTUAL DESIGN/OPTIMUM

Circulating water inlet

temperature (T1)

C A32.38 A - 34

B - 32.06 B - 34

Circulating water outlet

temperature (T2)

C A37.40 A42.1

B36.75 B42.1

Circulating water

temperature rise ( T =

T2T1)

C A - 5.02 A - 8.6

B - 4.69 B - 8.6

Vacuum in condenser mm of

Hg

689.95 684

Saturation temperature

(T3)

C 41.5 46.1

Terminal Temperature

Difference (2= T3T2)

C A - 4.1 A - 3.5

B - 4.75 B3.5

Initial Temperature

Difference (1= T3T1)

C A9.12 A12.1

B9.44 B12.1

LPT exhaust hoodtemperature

C 44.89 44

Air Temperature Main

Ejector

C A39.62 A45.7

B45.7 B45.7

LMTD C A6.26 A6.93

B6.83 B6.93


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4.2) Effect in condenser vacuum due to variation in circulating water flow:-

In this situation for calculating actual value condenser vacuum we have to take the effect of

circulating water flow variation also apart from the effect of variation in circulating water inlet

temperature.

As we know that the direct effect of change in circulating water flow is change in circulating

water temperature rise.

So our equation no.-1 becomes like this,

Saturation temperature (TS)=Actual value circulating water inlet temperature (Avg.)(T1)+

Actual value of change in circulating water temperature rise ( T )+ Optimum value Terminal

Temperature Difference(T.T.D.)

Data from our observations are as follows

T1(actual) = 32.22 C,

T (actual) = 4.86 C

T.T.D (optimum) = 3.5 C

By putting these values into the equation no.-1, we get

Saturation temperature (TS) = 32.22 C + 4.86 C + 3.5 C

= 40.58 C

So back pressure in the condenser corresponding to saturation temperature 40.58 C is (by using

steam table)

Pb= 0.0758 bar (abs.)

So, deviation in back pressure due variation in circulating water inlet temperature is

= Actual back pressureOptimum back pressure

= (0.07580.0881) bar

= -0.0123 bar

= -0.0123 750.061 mm of Hg

= - 9.22 mm of Hg

Here negative sign indicates that back pressure is decreased by 9.22 mm of Hg due to variation

in circulating water inlet temperature & circulating water temperature rise.

Therefore increase in vacuum = 9.22 mm of Hg

Actual value of vacuum

Pv2 = 684 + 9.22

= 693.22 mm of Hg

So rise in vacuum due to circulating water temperature rise due variation in circulating water

flow only is,


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= Pv2Pv1

= (693.22 - 680.10) mm of Hg

= 13.12 mm of Hg.

4.3) Effect in condenser vacuum due to air ingress & dirty tubes:-

As the effect of air ingress and dirty tubes is hindrance to heat transfer process between steam

and circulating water by acting like an insulation layer between condenser tubes surface (both

inside and outside of the tubes) effecting heat transfer between steam and circulating water.

This effect of air ingress and dirty tubes will have a direct impact on terminal temperature

difference (T.T.D.)

So our equation no.-1 becomes like this,

Saturation temperature (TS)=Actual value circulating water inlet temperature (Avg.)(T1)+Actual value of change in circulating water temperature rise( T)+ Actual value Terminal

Temperature Difference (T.T.D.)

Data from our observations are as follows

T1(actual) = 32.22 C

T (actual) = 4.86 C

T.T.D (actual) = 4.43 C

By putting these values into the equation no.-1, we get

Saturation temperature (TS) = 32.22 C + 4.86 C + 4.43 C

= 41.51 C

So back pressure in the condenser corresponding to saturation temperature 41.51 C is (by using

steam table)

Pb= 0.0802 bar (abs.)

So, deviation in back pressure due variation in circulating water inlet temperature is

= Actual back pressureOptimum back pressure= (0.08020.0881) bar

= -0.0079 bar

= -0.0079 750.061 mm of Hg

= - 5.925 mm of Hg

Here negative sign indicates that back pressure is decreased by 5.925 mm of Hg due to air

ingress and dirty tubes.

Therefore increase in vacuum = 5.925mm of Hg

Actual value of vacuum


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Pv3 = 684 + 5.925

= 689.925 mm of Hg

So vacuum fall due to terminal temperature difference rise due air ingress and dirty tubes only

is,

= Pv2Pv3

= (693.22 - 689.925) mm of Hg

= 3.295 mm of Hg

S.NO EFFECT VACUUM RISE OR

FALL

1. Drop in Circulating water inlet temperature only -3.9 mm of hg(Fall in vacuum)

2. Drop in circulating water temperature rise only +13.12 mm of Hg(Rise in

vacuum)

3. Air ingress and dirty tubes only -3.925 mm of Hg(Fall in

vacuum)

Total rise in vacuum +5.925 mm of Hg

Therefore the actual vacuum created in the condenser

= Optimum value of vacuum + deviation due to circulating water inlet temp only + deviation

due to circulating water temperature rise only + deviation due to air ingress and dirty tubes

only.

= [684 + (-3.9) + (13.12) + (-3.925)] mm of Hg

= 689.925 mm of Hg

So we can conclude that the vacuum of the condenser is increased by 5.295 mm of Hg due variation in

1. Circulating water inlet temperature2. Circulating water flow

3. Air ingress/Dirty tubes.


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CHAPTER -5

FAULT ANALYSIS IN CONDENSER

During normal operation of the condenser any fault can occur which will directly affect the

condenser working and its performance decreases drastically, so we have to find the fault,

observe its nature and cause of the of and how we can attend it so that the plant will operate

smoothly without any fault occur in the condenser.

The various faults occur in the condenser during its normal operation are as follows:-

S.No Fault Symptoms Cause Remedy

1

Low

vacuum in

the

condenser

a.) 't' is high CW flow is less Attend the

pumpPerformance of

one CWP is poor

b.) 't' is higher

corresponding to

turbine loading & 'P'

Condenser tubes

chokedClean the tubes

c.) tg& tg1excessive

1.)Excessive airingress

Locate and plug

the points of air

ingress

2.) Poor

performance of the

air ejectors

Attend the

ejectors

3.) Gland seal

steam pressure

Low

Correct seal

steam supply

pressure

d.tgis high and tg1is

normal and flooding

of condenser

1.) Fault in hot

well level controlAttend the fault

2.) Poor

performance of

CEP

Attend the

pump


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2

Rapid fall in

condenser

Vacuum

a.) C.W

supply,air

venting &

CEP are

normal

Failure of Gland

sealing steam

and its control

Attend the fault in

control system

b.) C.W

supply, gland

seal system,

air venting &

condensate

pumping are

normal

1.) Severe air

ingress

Locate and plug the

points of air ingress

2.) Leakage inpiping/valves

connected to

vacuum system

Locate and plug the

leakage points

3

Leak test

reveals high

h/t

a.) Ejector

operation is

normal

Excessive air

leakage

Locate and plug the

leakage points

b.) Turbine

gland seal

steam pressure

low

Defective gland

seal systemRectify the defect

c.) No water

supply to

glands of

valves

Leakage through

the valve glands

connected with

vacuum system

Establish sealing water

supply

d.) Rate ofvacuum drop

is high at

lower turbine

loads than at

higher turbine

loads

Leakage throughpiping/equipment

(connected to

turbine vacuum

system) which

remain under

pressure at high,

normal load.

Locate and repair the

leakage points


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4

Higher

tg& tg1

than at

reference

Power

a.) t1, t

(corresponding

to the power

output &h

/t are higher

Air leakage into

vacuum system

Plug the air leakage

points

b.) t1, t, P

&h /t are

normal

Poor

performance of

Air ejector

Switch over to stand-

by

c.) t1&h /t

are normal. 't'

and P are

high

Condenser tubes

fouled on water

side

Clean the tubes

d.) t1&h /t

are normal. P

is low and 't' is

high

Circulating water

flow is lessIncrease the CW flow

e.) t1,t,P &h

/t are normal.

Hot-well level

is high

Failure of hot

well Level

Controller

Attend the defect

5 tg> tg1Hot well level

is high" "

6 Conductivity

of

Condensate

is high

---- Circulating water

leakage into the

condenser

Locate the failed tube

and plug its ends

7 Dissolved

oxygen in

condensate

is high

---- 1.) Excessive air

ingress

Locate and plug the

leaking points

2.) Excessive

make-up water

Improve the system

tightness to reduce

make-up


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Symbols used:

P : Reference Power output

t1 : Circulating water inlet temperature

t2 : Circulating water outlet temperature

t : t2-t1

P : Circulating water pressure drop across condenser tubes

t3 : Hot well (Main condensate) temperature

t4 : Exhaust steam temperature

h/t : Rate of Vacuum drop in condenser

h : Vacuum drop in mmHg

t : Time in minutes

tg : Terminal Temperature Difference (TTD) Steam/C.W

tg : t4t2

tg1 : Terminal Temperature Difference (TTD) Condensate/C.W

: t3t2


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CHAPTER6

INTRODUCTION TO COOLING TOWER

6.1) COOLING TOWERS IN POWER PLANTS

Cooled water is needed for, for example, air conditioners, manufacturing processes or power

generation. A cooling tower is an equipment used to reduce the temperature of a water stream by

extracting heat from water and emitting it to the atmosphere. Cooling towers make use of

evaporation whereby some of the water is evaporated into a moving air stream and

subsequently discharged into the atmosphere. As a result, the remainder of the water is cooled

down significantly. Cooling towers are able to lower the water temperatures more than devices

that use only air to reject heat, like the radiator in a car, and are therefore more cost-effective

and energy efficient.

Fig 6.1 Schematic diagram of cooling tower

6.2) COMPONENTS IN COOLING TOWER: -

The basic components of a cooling tower include the frame and casing, fill, cold-water basin,

drift eliminators, air inlet, louvers, nozzles and fans. These are described below.

1. Frame and casing: -Most towers have structural frames that support the exterior enclosures

(casings), motors, fans, and other components. With some smaller designs, such as some


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and spray in a round or square patterns, or they can be part of a rotating assembly as

found in some circular cross-section towers.

8. Fans: -Both axial (propeller type) and centrifugal fans are used in towers. Generally,

propeller fans are used in induced draft towers and both propeller and centrifugal fans

are found in forced draft towers. Depending upon their size, the type of propeller fans

used is either fixed or variable pitch. A fan with non-automatic adjustable pitch blades

can be used over a wide kW range because the fan can be adjusted to deliver the desired

air flow at the lowest power consumption. Automatic variable pitch blades can vary air

flow in response to changing load conditions.

9. Nozzles: - These spray water to wet the fill. Uniform water distribution at the top of the fill

is essential to achieve proper wetting of the entire fill surface. Nozzles can either be fixed

and spray in a round or square patterns, or they can be part of a rotating assembly as

found in some circular cross-section towers.

6.3 PRINCIPLES OF OPERATION: -

Cooling water is pumped from the turbine condenser by the tower pump to the cooling tower.

Inside the tower the water passes through sprinklers, and sprays out in find drops. The water

then falls as droplets, passing over pickings where it is made to present a greater surface area

to the cooling air. The water then falls into the cooling tower pond.

Air is drawn in near the bottom of the tower, either by natural draught or by a fan. The air

passes up the tower and cools the water is it does so. Any water droplets which have been

carried up by the air are removed by the water droplet eliminator screen.

The theory of cooling: -As a water droplet falls through the tower, air flows past it and cooling takes

place in three ways:

(a) A small proportion of heat is lost from the droplet by radiation of heat from its surface.

(b) Approximately a quarter to one-third of the heat transferred is by conduction and convection

between the water and the air the amount of heat transferred depends on the temperature of

water and air.


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Fig. 6.3: Cooling Tower Operation.

(c) The remainder of the heat transfer is by evaporation. As the air evaporates some of the water

into water vapour, the vapour takes with it the latent heat of evaporation. The remaining water

therefore has a lower heat content than it had originally, and is also at a lower temperature.

The amount of evaporation which takes place depends on a number of factors; these include

the total surface area the water presents to the air (the reason the packing design is so important),

and the amount of air flowing. The greater the air flow, the greater the cooling achieved.

6.4) TYPES OF COOLING TOWERS

This section describes the two main types of cooling towers: the natural draft and mechanical

draft cooling towers.

1. Natural draft cooling tower:-The natural draft or hyperbolic cooling tower makes use of

the difference in temperaturebetween the ambient air and the hotter air inside the tower. As

hot air moves upwards through the tower (because hot air rises), fresh cool air is drawn into

the tower through an air inlet at the bottom. Due to the layout of the tower, no fan is

required and there is almost no circulation of hot air that could affect the performance.

Concrete is used for the tower shell with a height of up to 200 m. These cooling towers are

mostly only for large heat duties because large concrete structures are expensive.


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Fig6.4 a) Cross flow natural draft cooling tower b) Counter flow natural draft cooling tower

There are two main types of natural draft towers:

a. Cross flow tower: - Air is drawn across the falling water and the fill is located

outside the tower

b. Counter flow tower: - Air is drawn up through the falling water and the fill is

therefore located inside the tower, although design depends on specific site conditions

2. Mechanical draft cooling tower:-Mechanical draft towers have large fans to force or draw

air through circulated water. The water falls downwards over fill surfaces, which help

increase the contact time between the water and the air - this helps maximize heat transfer

between the two. Cooling rates of mechanical draft towers depend upon various parameters

such as fan diameter and speed of operation, fills for system resistance etc.

Mechanical draft towers are available in the following airflow arrangements:

a. Counter flows induced draft.

b. Counter flow forced draft.

c. Cross flow induced draft.

In the counter flow induced draft design, hot water enters at the top, while the air is introduced

at the bottom and exits at the top. Both forced and induced draft fans are used.

In cross flow induced draft towers, the water enters at the top and passes over the fill. The air,

however, is introduced at the side either on one side (single-flow tower) or opposite sides

(Double-flow tower).


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is exposed to atmosphere, it indicates the dry bulb temperature, which is nothing but

atmospheric temperature.

4. Wet-bulb temperature: -It is the temperature measured by the thermometer when the bulb

of the thermometer is covered by a wetted cloth and is exposed to a current of rapidly moving

air (twb), commonly referred as WBT. When the air comes in contact with the wet cloth it

absorbs some moisture and gives up some heat, sue to which the temperature of the air reduces.

This reduced temperature measured by the thermometer is called the wet bulb temperature.

If the moisture content of the air is very low, it will give up more heat to the cloth and wet bulb

temperature of air will also be comparatively low. On the other hand, if the moisture content

of air is high it will lose lesser heat to the air and the wet bulb temperature will be higher. Thus

the wet bulb temperature indirectly indicates the moisture content present in the air.

The wet bulb temperature of the air is always less than the dry bulb temperature of the air,

i.e., twb< tdb

5. Wet bulb depression: - It is the difference between dry-bulb and wet bulb temperatures

(tdb-twb).

6. Relative humidity (RH): -The amount of water vapour in the air at any given time is usually

less than that required to saturate the air. The relative humidity is the percentage of saturation

humidity, generally calculated in relation to saturated vapour density.

RH () =Mass of water vapour in a given volume

Mass of water vapour in the same volume if saturated at the same temperature

6.6) DALTONS LAW OF PARTIAL PRESSURE: -

Daltons law of partial pressure state that

In a container in which gas and a vapour are enclosed, the total pressure exerted is the sum of

partial pressure of the gas and partial pressure of the vapour at the common temperature.

Let t = Temperature of mixture of air and water vapour in the container in oC

pa= Partial pressure of air at temperature t,

ps= Saturation pressure of water vapour at temperature t

p = Total pressure in the container.

Therefore, p=pa+ ps


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CHAPTER -7

COOLING TOWER PERFORMANCE ASSESSMENT

7.1) COOLING TOWER PERFORMANCE

The important parameters, from the point of determining the performance of cooling towers,

are:

1. Cooling range:The extent by which the hot water is cooled in the tower is known as cooling

range

2. Approach: The difference between the cold water leaving the tower and the wet bulb temperature

of air entering is called Approach. Presumably the wet bulb temperature is the ambient minimum

temperature.

3. Heat Load:It is the amount of heat exchanged in a cooling tower between the hot water and

the cold air in calories/minute.

4. Drift:The windage loss or carry over is otherwise known as drift and this indicates the

amount of water that is carried from cooling towers in the form of fine droplets entrained in

the circulation air.

5. Evaporation Rate:The rate at which the water is being evaporated to cool the hot water is

called evaporation rate and circulating air carries this evaporated water vapour away.

6. Capacity:The average volume of circulating water that is cooled in the tower at any time isthe capacity of the tower.

7. Sprinkling density:The rate at which the water is falling through unit fill area of the tower

is known as sprinkling density

8. Draught factor= P / 1.64(10-8 h).

Where P is the density difference in air at inlet and exit of the tower in kg/m3and

h is the total enthalpy difference of air at inlet and exit of the tower KJ/kg

9. Performance Coefficient C = L X / (L/GN1/3

)

Where L is the cooling water flow or sprinkling density

X is Markels factor

N is the resistance of tower to air flow through it in velocity head

G is the Dry airflow

10. Duty coefficient D = AH/C .C1/2

A is the Pond area at sill level

H is the height of tower above sill


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11. Cycles of concentration (C.O.C) is the ratio of dissolved solids in circulating water to the

dissolved solids in make-up water.

12. Blow down los

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