condenser water and cooling tower in thermal power plant

Adiabatic Expansion in Turbine

Constant Pressure Heat Rejection in Condenser

Pump Work

Sensible heat Addition in Economizer

ENTROPY

TEMPERATURE

Latent Heat Addition in water wall (constt. Pressure) Super Heating

L + V

BASIC RANKINE CYCLE (SUB-CRITICAL)

Effect of CW flow on condenser back pressure

CW Flow, M3/hr

Unit load = 210 MWHeat load = 2.5 x 108 kcal/hrDesign CW flow = 22500 m3/hrTemp. rise = 10.8oCCW inlet temp = 32oC

CW Inlet temperature (oC)

Effect of CW inlet temperature on condenser back pressure

Unit load = 210 MWHeat load = 2.5 x 108 kcal/hrDesign CW flow = 22500 m3/hrLMTD = 7.413oCTemp. rise = 10.8oCCW inlet temp = 32oC

CW (Cooling Water system)CW (Cooling Water system)

CW SYSTEM

• PURPOSE:REJECT THE HEAT FROM CONDENSOR TO ATM IN EFFICIENT MANNER & ALSO CONFIRM THERMAL DICHARGE REGULATION

• QR=(1/n-1)WQR->Rejected heat.W->Work doneN->cycle efficiency

EFFECT OF n ON QRWORK DONE

n QR QR/W

W 0.20 4W 4

W 0.25 3W 3

W 0.33 2W 2

W 0.40 1.5W 1.5

W 0.50 1W 1.0

Open Loop system

Water is abundant…Reduction in the APC..

Condenser

River Flow

Steam from Turbine

PumpHot water

Cold Water

OPEN LOOP SYSTEM-Water is taken from natural body and pump though the condenser, where it heated and discharge back to source

CLOSE LOOP SYSTEM

Condenser

Cooled Water

Cooling Tower AirAir

Make-up Water

Hot Water

Cooling Water Requirement

• Bulk requirement of water is used in thermal plants for the purpose of cooling the steam in condensers. The requirement of water for this purpose is of the order of 1.5-to2.0 cusecs/MW of installation.

• Where sufficient water is available once through system is used.

• Where water supply is not consistent, closed loop cooling system with cooling tower is used.

WATER SUPPLY TO KSTPS

NTPC Korba CW/CT system at a glance

Hasdeo Barrage RBC Darri Gate open

Stage-II3X500 MW

Stage-I3 X 200 MW

Hot pond

CT- I

CT- IIOpen CyclePragati Nagar Regulator

CWPH-I

CWPH-II

Charpara Cross Regulator open

Hasdeo Barrage RBC Darri Gate partially open.

Hot pond

CT- I

CT- IIPartial Closed Cycle

Pragati Nagar Regulator

Stage-II3X500 MW

Stage-I3 X 200 MW

CWPH-I

CWPH-II

Charpara Cross Regulator Partially open

Emergency Exit

Hot pond

CT- I

CT- IITotal Closed CyclePragati Nagar Regulator

Stage-II3X500 MW

Stage-I3 X 200 MW

CWPH-I

CWPH-II

Hasdeo Barrage RBC Darri Gate open for makeup

Charpara Cross Regulator totally closed

CW scheme…

Reservoir/ River Canal Intake

Trash rack

TWS

CW pumps

Condenser

Hot Pond

CT pumps

Cooling tower

RBC

• All water requirement of NTPC korba is met by RBC.• Water to RBC comes from Darri barrage.• Two cross regulator – one at Barrage side other at NTPC side.• Irrigation dept supply water for irrigation thru this RBC.

During this time plant operate on open cycle or semi open cycle.

• If there is no requirement of water for irrigation, only make-up water is released by darri Barrage. During this, CWCT system operates on closed cycle.

• RBC supply water to Raw water p/h, st-1 CW p/h, st-2 CW p/h.

RBC

IRRIGATION X REG

INTAKE (ST-1&2)

Intake• It is RCC open trench from where Raw water/CW is

taken through canal/reservoir. • Metallic grid frame work gate (INTAKE GATE)is

provided to avoid entering wood, tree branches, animal, plastic, floating object. It can be lifted and cleaned when water level difference observed.

• It is approximately 12 meter in depth

• In KSTPS RBC level is 285.3 M

INTAKE CHANNELINTAKE CHANNEL

GRID WALLGRID WALL

Trash Rack

It is near the suction point of CW Pump & made of steel.

Trash rack avoid entering wood, tree branches, animal, plastic, floating object & provides uniform flow/ suction to the CW pump

TRASH RACK

TRASH RACK

CW PUMP SUCTION

Traveling Water Screen

• Traveling Water Screens are Thick wire buckets rides over the structure .

• The whole structure is partially submerged in water before the suction of CW pumps

• It catches small pieces of coal, sand, gravel, wood, plastic, herbs, leaves which can go into the impeller and may choke/damage the pump.

• These foreign material can be removed by jet of water through nozzles over the header inside the TWS.

• Water is supplied by screen wash pump

CW PUMP SUCTION PIT

TWS

TRASH RACK

TWS DRIVEWATER HDR

REVOLVING BASKET

TRAVELLING WATER SCREEN

TWS DRIVE

SHEAR PIN

TWS SECTOR

SCREEN WASH PUMP AND TWS LINE DIAGRAMEMERGENCY LUB WATER SUPPLY

TO ST-I SCREENWASH HDR.

SCREEN WASH PUMP

DPSWITCH

C W PUMP

PG

S

S

TWSA

CW

HDR

JETTING WATER

INLET TO TWS

SCREEN WASH PUMPS

CW Pump Stage#1 Make : M/s. KSB Pumps Limited Model : SEZ 1200-1020 Type : Vertical mixed flow Pump design : Pull out type Speed : 493 rpm Discharge capacity : 15000cub meter/hr Total dynamic head (TDH) : 12.2 m wc Bowl efficiency : 89% Motor : 6.6 KV, 81.5 amp, 685 KW No. of stages : 1 Pump specific speed : 131.6 Critical speed : 625 rpm Spacing between shaft bearing : 4500 mm Impeller shaft dia :150 mm Line shaft Dia : 1.05 mm Impeller weight : 0.45 tonn Impeller Dia :1020 mm

Lube water pumpLube water pump

Pump MotorPump Motor

Motor Foundation Stool Motor Foundation Stool

Discharge Taper PipeDischarge Taper PipeDischarge ElbowDischarge Elbow

Column PipeColumn Pipe

View from (-) minus metre floorView from (-) minus metre floor

Air Vent

MDV

Taper Pipe

View from (-) minus metre floor

efficiency

power

CW PUMP CHARECTRISTIC

clf hdr-6ksc

Flow switch

O/Htank-2

O/HTank-1

x

x

x x

To st-2

Emergency hdr

p/p thrust

motor

Lower guide brg

Upper guide brg motor th-1&2

Pump disch

Swp disch hdrTo st-2

NC

LUB WATER SYSTEM

ROUTINE CHECKS & STARTING PROCEDURE

Checks before Start-up of CW Pump

1. The intake channel level is above 284.75m.2. Oil quality and oil level in the top bearing of the motor is alright. (Oil level

should be halfthe oil pump.)

3. Check the availability of the pump discharge valves by remote full opening and closing.

4. Confirm the proper lubrication of the motor lower bearing.5. Confirm the manually operated discharge valve of the pump is fully

opened.6. Check that permits from all section concerned are clear and pump is free

to rotate.7. Emergency push button is under reset condition.

ROUTINE CKECKS & STARTING PROCEDURE

Starting Procedure of CW pumps1. Start the lube water pump and check that lube water flow to thrust

bearings and rubber bearing is there.2. Start the selected CW pump.3. Check the pressure at the discharge of the pump is about 1.22 ksc.4. Feel the temperature of the glands to be normal (<60oC) of the pump.5. Check that the motor bearing temp. shown in the indicator is normal.

(<60oC)6. Check that the vibrations at the gland housing and motor bearing are

within limit. (<40microns) and no abnormal sound audible from the pump.7. Check oil flow in the motor top bearing by opening drain cock and then

close it.8. Check for any loosening of the lock nut of the pump.9. Check the current absorbed by the motor and the pump discharge

pressure.

COOLING TOWER

The primary task of cooling tower is to reject the heat of CW into the atmosphere

Training Agenda: Cooling Towers

Introduction

Types of cooling towers

Assessment of cooling towers

Energy efficiency opportunities

Cooling Tower Theory

Water Drop with Interfacial Film

Heat is transferred from water drops to the surrounding air by the transfer of sensible and latent heat

How cooling tower works ?• 1 kg of water on evaporation removes approximately 530

kcals of heat• The heat given up by the water falling inside the tower

equals the heat gained by the air rising through the tower• The hot water entering the tower is distributed within the

structure in a manner that exposes a very large water surface to the air passing through.

• 80% heat removed by evaporation (mass transfer)• 20% heat removed by convection (heat transfer)

Main Features of Cooling Towers

Cooling tower: Types

Natural draftLarge concrete chimneys Generally used for water flow rates above

45,000 m3/hrSuited in cool & humid atmosphereLess mass transferHigh approach

Hot air moves through tower

Fresh cool air is drawn into the tower from bottom

No fan required

Concrete tower <200 m

Used for large heat duties

Natural Draft Cooling Towers

Cooling tower: Types

Mechanical draft Large fans to force or suck air through circulated

water. The water falls downward over fill surfaces, which

help increase the contact time between the water and the air maximizing heat transfer between the two.

Cooling rates of Mechanical draft towers depend upon their fan diameter and speed of operation

Suited in cool & dry atmosphere Low approach

Large fans to force air through circulated water

Water falls over fill surfaces: maximum heat transfer

Cooling rates depend on many parameters

Large range of capacities

Can be grouped, e.g. 8-cell tower

Mechanical Draft Cooling Towers

Three types

• Forced draft

• Induced draft cross flow

• Induced draft counter flow

Mechanical Draft Cooling Towers

60

©© UNP 2006 UNP 2006

• Air blown through tower by centrifugal fan at air inlet

• advantages: less motor power consumption

• Disadvantages: recirculation due to high air-entry and low air-exit velocities

• Poor mass transfer

• More drift losses

Forced Draft Cooling Towers

(GEO4VA)

Types of Cooling Towers

Two types

Counter Flow

Cross Flow

Advantage: less recirculation than forced draft towers

Disadvantage: fans and motor drive mechanism require weather-proofing

Induced Draft Cooling Towers

• Hot water enters at the top

• Air enters at bottom and exits at top

• Uses induced draft fans

Induced Draft Counter Flow CT

65

Induced Draft Cross Flow CT

• Water enters top and passes over fill

• Air enters on one side or opposite sides

• Induced draft fan draws air across fill

Components of Cooling Tower….

Frame & casing : Glass fiber or RCC structures

Fill : It facilitates heat transfer by maximizing water & air contact. Made of PVC, polypropylene, polymers, treated Wood and shaped flat, corrugated, honeycombed.

Cold water basin : have sump/low point for cold water discharge connection

Drift eliminator : Capture water droplets entrapped in air stream

Louver : In cross flow tower to equalize air flow into the fill and retain the water within the tower.

Nozzles : Spray water to wet the fill, made of PVC, aluminum, glass fiber, Galvanized steel

Fan :Axial or centrifugal fan with fixed/variable pitch made of Galvanized steel, aluminum, glass fiber reinforced plastic

CT CELL

CT INTAKE CHANNEL

RISER PIPE

HOT AIR OUT

COLD AIR IN

SPLASH FILLS IN SPLASH FILL, THE HOT WATER

STRIKES OVER THE BARS AND BREAKS UP INTO MANY SMALLER DROPS.

FILM FILLSFILM FILL PROVIDES MORE

SURFACE FOR WATER/AIR CONTACT.

FILM FILLS USED IN NTPC PROJECTS

WATER I/L PIPE TO CELL

NOZZLE HDR FROM INDIVIDUAL CELL

SPLASH BAR

NOZZLE HOLE

SPLASH BARS

SPRAY HEADERNOZZLE

DRIFT ELIMINATOR

FAN

SPRAY OF WATER

CT BASIN

CT SUPPORT STRUCTURE

LOWER HALF OF CT

SUPPORT STR.

SPLASH BAR

SPLASH BAR BARRIER

CT NOZZLE ARRANGEMENT

NOZZLE

REDUCTION GEAR ASSEMBLY

DRIFT ELIMINATOR

GEAR BOX

COUPLING SPOOL

CT FAN FRP BLADES

(FIBRE REINFORCE PLASTIC)

FIXED BLADES

CT Pump Stage#1• Make : M/s. KSB Pumps Limited• Model : SEZ 1200-1155• Type : Vertical mixed flow• Speed : 493 rpm• Discharge capacity : 15000 cub meter/hr• Total dynamic head (TDH) : 18.5 m wc• Bowl efficiency : 81.5%• Motor : 6.6 KV, 130 amp, 1015 KW• No. of stages : 1• Pump specific speed : 98• Critical speed : 625 rpm• Spacing between shaft bearing : 4500 mm• Impeller :Open, pullout type

COOLING TOWER SPECIFICATIONS

Description Stage-I Stage-II

Wet Bulb Temp 27.50 oC 27.50 oC

Approach 5.50oC 6 oC

Tower Pump Head ( Above ground level)

18.5 M 20 M.

Fan Motor Power ( driver out put)

35 KW per fan. 75 KW per fan

Drift loss per Tower 30,000 kgs/hr. 33,000 Kgs/hr.


Number Nozzles /Cell 225 250

Total number of fans 16 x 3 12 x 6

L/G Ratio 1.55 Kg water/ Kg.Air 1.886 Kg water/ Kg. Air

Drift eliminator PVC PVC

Casting Reinforced Concrete Reinforced Concrete

COOLING TOWER SPECIFICATIONS


Type Axial Flow Axial Flow

No. of fans / tower 16 12

Diameter 7315 mm 8530 mm

No. of blade 7 7

Blade angle 13o 13o

Fan speed 151 Rpm 118 Rpm

Absorbed power 35 KW 56 KW

COOLING FAN SPECIFICATIONS


Blade material Al.alloy/FRP , = 80.5%

FRP = 80.5%

Total static pressure 0.4094 inches 0.434 inches

Fan dia. 24ft. 28 ft.

Air delivery per fan 9,97,200 CMH 13,50,000 CMH

COOLING FAN SPECIFICATIONS


Make / Model M/s Elecon / CTU 260 M/s Greaves CT-V 1400

Type / Number Worm gear / 16 x 3 Worm / 12 x 6

Reduction Ratio 9.75:1 12.5 :1

No. of reduction stage 1( One) 1 ( One)

Service factor 2.1 1.5

Weight 765 Kg. 1465 Kg.

Input and output speed 1470 & 151 RPM 1485 & 118 RPM

FAN GEAR BOX SPECIFICATIONS

91

Assessment of Cooling TowersAssessment of Cooling Towers

Measured Parameters

• Wet bulb temperature of air

• Dry bulb temperature of air

• Cooling tower inlet water temperature

• Cooling tower outlet water temperature

• Exhaust air temperature

• Electrical readings of pump and fan motors

• Water flow rate

• Air flow rate

Performance Parameters

1. Range

2. Approach

3. Effectiveness

4. Cooling capacity

5. Evaporation loss

6. Cycles of concentration

7. Blow down losses

8. Liquid / Gas ratio

Assessment of Cooling TowersAssessment of Cooling Towers

93

1. Range

Difference between cooling water inlet and outlet temperature:

Range (°C) = CW inlet temp – CW outlet temp

High range = good performance

Ran

ge

Ap

pro

ach

Hot Water Temperature (In)

Cold Water Temperature (Out)

Wet Bulb Temperature (Ambient)

(In) to the Tower(Out) from the Tower

94

2. Approach

Difference between cooling tower outlet cold water temperature and ambient wet bulb temperature:

Approach (°C) = CW outlet temp – Wet bulb temp

Low approach = good performance

Ran

ge

Ap

pro

ach





95

3. Effectiveness

Effectiveness in %

= Range / (Range + Approach)

= 100 x (CW temp – CW out temp) / (CW in temp – Wet bulb temp)

High effectiveness = good performance

Ran

ge

Ap

pro

ach





96

4. Cooling Capacity

Heat rejected in kCal/hr or tons of refrigeration (TR)

= mass flow rate of water X specific heat X temperature difference

High cooling capacity = good performance

Ran

ge

Ap

pro

ach





97

5. Evaporation Loss

Water quantity (m3/hr) evaporated for cooling duty

= theoretically, 1.8 m3 for every 10,000,000 kCal heat rejected

= 0.00085 x 1.8 x circulation rate (m3/hr) x (T1-T2)

T1-T2 = Temp. difference between inlet and outlet water

Ran

ge

Ap

pro

ach





98

6. Cycles of concentration (C.O.C.)

Ratio of dissolved solids in circulating water to the dissolved solids in make up water

Depend on cycles of concentration and the evaporation losses

Blow Down = Evaporation Loss / (C.O.C. – 1)

7. BLOW DOWN

99

8. Liquid Gas (L/G) Ratio

Ratio between water and air mass flow rates

Heat removed from the water must be equal to the heat absorbed by the surrounding air

L(T1 – T2) = G(h2 – h1)

L/G = (h2 – h1) / (T1 – T2)

T1 = hot water temp (oC)

T2 = cold water temp (oC)

Enthalpy of air water vapor mixture at inlet wet bulb temp (h1) and outlet wet bulb temp (h2)

Tower Size vs Approach

Cause of CT Poor Performance.Common causes are

1. Recirculation of vapors.2. Poor air flow due to less blade angle, algae,

deposition on blade, blade erosion.3. Higher blade tip clearance. In general it should

not be more than 0.3% of the dia of fan blade4. Fan door sealing not proper, other opening in

suction of the fan.5. Damaged Drift Eliminator causes more

makeup and .

Cause of CT Poor Performance

6. Chocking of nozzle by OLTC balls.7. Falling of nozzle.8. Hot water distribution pipe

leaking/braeking/end cover falling.9. Fill clogging10. Damage of fills.11. Lot of trees/plants/bushes growth near

cooling tower 12. Poor quality of water (make-up)

Optimizing C T Performance.• Cleaning of cold water basin during overhauls.• Quarterly cleaning of nozzles.• Visual inspection of pipes, nozzles, fills, etc., for proper water

distribution.• Checking of fan pitch angle, fan blade tip clearance, fan seal

disc cover (at hub).• Annual servicing of gear box.• Regular removal of moisture from G/B oil and oil top up.• Annual cleaning of fills with water jets. And cleaning it

manually by removing from tower when chocking is more.• All around CT proper lawn or brick paving to be done (abut 30

meter from tower)• Fan blade angle to be adjusted to avoid any recirculation of

vapour during mansoon/windy days.• Thickness measurement of hot water duct, inspection,

cleaning/painting if required annualy.

Optimizing CT Performance.

• Cleaning of civil structure annually and removal of algae from DE, Fills.

• Fan door and any other air ingress point to be sealed.• Regular condition monitoring of CT fans.• Continuous chlorine dosing to be done.• Sludge disposal pump to be run once in a day minimum for 15

minutes.• Monthly checking of effectiveness of tower for comparison

purpose and once checking of perf. during mansion as per OGN.• Both side of OAC to be barricaded by railing with wire mesh at

about 1.5 meter height and both side about 2 meter wide brick paving to be done to avoid any plant growth

• At CT outlet screen to be provided to remove any debris, plastic pieces if there is no TWS provided in CW system.

• To protect OLTC balls and any other material going to nozzles; nozzle protector to be provided which is a hollow steel pipe inserted into H.W.D. pipe with wire mesh.

Major Problems faced in CT

• Fill clogging and support structure failure• Sagging of PVC Drift Eliminators in counter flow type:

It has no support in between.• hot water distribution pipe failure.• Growth of trees/bushes/plants near CT after cleaning

again and again.• Civil structure reinforced steel exposed

to atmosphere.• Algae growth in CT structure.

Algae Growth in the Intake Channel

Algae growthAlgae growth

Clogged Fills

Deposited dust particles

Sagged Drift Eliminators

Sagged Drift Eliminators

Clogging Of Fill Packs

Clogged Fills

PVC fill pack saggingExcessive weight initiating bending of SS Supports

Sagging of SS supports of PVC fills at TSTPS-II

SITE FILTRATION SYSTEMTO REDUCE TURBIDITY

C.W Pumps

Site Filt. Pumps

Condenser

Sand Filters

Cooling Tower

Cold Water

Hot Water

5% of C.W Water flow

Chemical Treatment

Drift Eliminators not in position.

Stage-I CT

Asbestos Drift Eliminators in

C.T.

Drift Eliminators that are not

properly laid only serve to block the air

passage

Shaft hole of fan not sealed

Inspection door not sealed

To be sealed properly

Energy Efficiency Opportunities

1. Selecting a cooling tower

2. Fills

3. Pumps and water distribution

4. Fans and motors


Capacity

• Heat dissipation (kCal/hour)

• Circulated flow rate (m3/hr)

• Other factors


Range

• Range determined by process, not by system

Approach

• Closer to the wet bulb temperature

= Bigger size cooling tower

= More expensive



Heat Load

• Determined by process

• Required cooling is controlled by the desired operating temperature

• High heat load = large size and cost of cooling tower



Wet bulb temperature – considerations: Water is cooled to temp higher than wet bulb

temp

Conditions at tower site

Not to exceed 5% of design wet bulb temp

Is wet bulb temp specified as ambient (preferred) or inlet

Can tower deal with increased wet bulb temp



Relationship range, flow and heat loadRange increases with increased

Heat load

Causes of range increase

Inlet water temperature increases

Exit water temperature decreases

Consequence = larger tower



Hot water distributed over fill media and cools down through evaporation

Fill media impacts electricity useEfficiently designed fill media reduces pumping

costs

Fill media influences heat exchange: surface area, duration of contact, turbulence

2. Fill media


123

Comparing 3 fill media: film fill more efficient

Splash Fill Film Fill Low Clog Film Fill

Possible L/G Ratio 1.1 – 1.5 1.5 – 2.0 1.4 – 1.8

Effective Heat Exchange Area

30 – 45 m2/m3 150 m2/m3 85 - 100 m2/m3

Fill Height Required 5 – 10 m 1.2 – 1.5 m 1.5 – 1.8 m

Pumping Head Requirement

9 – 12 m 5 – 8 m 6 – 9 m

Quantity of Air Required High Much Low Low

2. Fill media


Fill Media Effects

Heat exchange between air and water is influenced by surface area of heat exchange, time of heat exchange (interaction) and turbulence in water effecting thoroughness of intermixing. Fill media in a cooling tower is responsible to achieve all of above.

3. Pumps and water distribution Pumps: ?

Optimize cooling water treatmentIncrease cycles of concentration (COC) by

cooling water treatment helps reduce make up water

Indirect electricity savings

Install drift eliminatorsReduce drift loss from 0.02% to only 0.003 –

0.001%


4. Cooling Tower Fans

Fans must overcome system resistance, pressure loss: impacts electricity use

Fan efficiency depends on blade profile Replace metallic fans with FBR blades (20-

30% savings)

Use blades with aerodynamic profile (85-92% fan efficiency)


Stage I

3 x 200 MW3 cooling towers16 fans per tower Induced draft multi fill

counter flow30,000 mtr cube per

hour per towerNozzles per cell-225

Stage II

3 x 500 MW6 cooling towers12 fans per tower Induced draft multi fill

counter flow33,000 mtr cube per

hour per towerNozzles per cell-250

Specifications

Specifications…

Stage-1 Hot CW inlet temp.- 43°C

Cold CW outlet temp.- 33°C

Range- 10 °C

Wet bulb Temp.- 27.5°C

Approach- 5.50°C

Stage-2 Hot CW inlet temp.- 43°C

Cold CW outlet temp.-33 °C

Range- 10°C

Wet bulb Temp.-27.5°C

Approach-6°C

• Drift loss-30,000 kg/hr• Evaporation loss per

tower-4,35,000 kg/hr• L/G Ratio-1.55 kg

water/kg air• Absorbed power-35 kw

• Drift loss-33,000 kg/hr• Evaporation loss per

tower-4,79,156 kg/hr• L/G Ratio-1.886 kg

water/kg air• Absorbed power-56 kw

Specifications…

condenser water and cooling tower in thermal power plant

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