cooling towers (tna)

8/9/2019 Cooling Towers (TNA)

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COOLING TOWER

Presented By

Anis Abbas

ME-1


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Overview

Cooling Tower

Cooling Tower Principle and

categorization

Types and classifications of

Cooling Towers

Major Components of Cooling

Tower Cooling Tower Maintenance

and troubleshooting


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Heat Transfer Methods

Wet cooling towers or simplycooling towers operate on theprinciple ofevaporation.

Dry coolers operate by heattransferthrough a surface thatseparates the working fluid fromambient air, such as in a heatexchanger, utilizing convective

heat transfer. Fluid coolers are hybrids thatpass the working fluid through atube bundle, upon which cleanwater is sprayed and a fan-

induced draft applied.


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Cooling Tower

A cooling tower is a heat rejectiondevice, which extracts waste heat tothe atmosphere though the cooling

of a water stream to a lowertemperature.

Cooling towers may either use theevaporation of water to remove

process heat and cool the workingfluid to near the wet-bulb airtemperature or rely solely on air tocool the working fluid to near thedry-bulb air temperature.


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Cooling Tower

They represent a relatively inexpensive anddependable means of removing low-grade heatfrom cooling water.


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Cooling Tower Principle

Cooling towers are a

very important part of

many chemical

plants. Theyrepresent a relatively

inexpensive and

dependable means of

removing low gradeheat from cooling

water.


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Cooling Tower Principle

The make-up water source is used to replenishwater lost to evaporation. Hot water from heatexchangers is sent to the cooling tower. The

water exits the cooling tower and is sent backto the exchangers or to other units for furthercooling.


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Categorization by air-to-water flow

Crossflow

Crossflow is a design

in which the air flow

is directed

perpendicular to the

water flow. Air flow

enters one or more

vertical faces of the

cooling tower to meet

the fill material.


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Categorization by air-to-water flow

Counterflow

In a counterflow

design the air flow is

directly opposite to

the water flow. Air

flow first enters an

open area beneath

the fill media and is

then drawn up

vertically.


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Types ofCooling TowersTypes ofCooling Towers

1) Natural Draft

Cooling Towers

Hot air moves

through tower

Fresh cool air is

drawn into the tower

from bottom


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1) Natural Draft Cooling Towers

Cross flow

Air drawn across

falling water

Fill locatedoutside tower

Counter flow

Air drawn up

through falling

water

Fill located

inside tower


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2) Mechanical Draft CoolingTowers

Large fans to force air throughcirculated water

Water falls over fill surfacesmaximum heat transfer

Cooling rates depend on manyparameters

Large range of capacities Can be grouped, e.g. 8-cell

tower


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2) Mechanical Draft Cooling Towers

Three types

Forced draft

Induced draft cross flow

Induced draft counter flow


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Air blown through tower by

centrifugal fan at air inlet

Advantages: suited for high

air resistance & fans are

relatively quiet

Disadvantages: recirculationdue to high air-entry and low

air-exit velocities

Forced Draft Cooling Towers


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Induced Draft Counter Flow CT

Hot water enters at the top

Air enters at bottom and exits at top

Uses forced and induced draft fans


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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


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Classification of Cooling Tower

1) Open (Direct) CoolingTowers

Open cooling towers

expose the condenserwater coming from thechiller plant directly to theatmosphere. This warmwater is sprayed over a fillin the cooling tower toincrease the contact area,and air passes through thefill.


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Classification of Cooling Tower

2) Closed (Indirect)

Cooling Towers

A closed cooling tower

circulates warm waterfrom the chiller plant

through tubes located in

the tower. In a closed

tower, the cooling water

does not come in contact

with the outside air.


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Cooling Tower Treatment

The three potential problems associated withcooling water are:

Corrosion

Scale/deposits Microbiological activity

Corrosion will shorten the life of the equipment.Scale/deposits will decrease heat transfer and

increase energy usage. Microbiological activitywill cause system blockages and potential healthhazards.


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Major Components

WaterDistribution

Hot water from the chilled-watersystem is delivered to the top of thecooling tower by the condenser pumpthrough distribution piping.

Heat Transfer Medium (Fill)

Cooling towers use evaporation torelease waste heat from an HVAC

system. In an open tower, hot waterfrom the condenser is slowed downand spread out over the fill. Some ofthe hot water is evaporated in the fillarea which cools the water.


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Major Components

Drift Eliminator

As air moves through the fill, smalldroplets of cooling water becomeentrained and can exit the coolingtower as carry-over or drift. Devicescalled drift eliminators remove carry-over water droplets.

Frame and casing

Most towers have structural framesthat support the exterior enclosures(casings), motors, fans, and othercomponents.


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Major Components

Cold-water basin

The cold-water basin is located ator near the bottom of the tower,

and it receives the cooled waterthat flows down through the towerand fill.

Nozzles

These spray water to wet the fill.Uniform water distribution at thetop of the fill is essential toachieve proper wetting of the

entire fill surface.


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Major Components

Fans

Both axial (propellertype) and centrifugalfans are used intowers. Generally,propeller fans areused in induceddraft towers andboth propeller andcentrifugal fans arefound in forced drafttowers.


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Types ofCooling tower fan

Metallic blades, which aremanufactured by extrusion orcasting processes and therefore it

is difficult to produce idealaerodynamic profiles

Fiber reinforced plastic (FRP)blades are normally hand moldedwhich makes it easier to producean optimum aerodynamic profile.FRP fans are light, low startingtorque, long lives of the gear box,motor and bearing is increased.


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Steps to Cooling Tower Efficiency

Follow manufacturers recommended clearancesaround cooling towers and relocate or modifystructures that interfere with the air intake or

exhaust. Optimize cooling tower fan blade angle on a

seasonal and/or load basis.

Correct excessive and/or uneven fan blade tip

clearance and poor fan balance. Check cooling water pumps regularly to

maximize their efficiency.


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Steps to Cooling Tower Efficiency

In old counter-flow cooling towers, replace old

spray type nozzles with new square spray

nozzles that do not clog. Install nozzles that

spray in a more uniform water pattern. Balance flow to cooling tower hot water basins.

Optimize the blow down flow rate.

Consider energy efficient fiber reinforced plasticblade adoption for fan energy savings.


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Hazards

Cooling towers which are constructed in wholeor in part of combustible materials can supportpropagating internal fires.

Cooling-tower water must be regularly treated,generally with chemicals, to prevent the growthof harmful bacteria, minimize corrosion, andinhibit the buildup of scale (mineral deposits) onthe fill.


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Cooling Tower Maintenance


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Troubleshooting


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Troubleshooting

cooling towers (tna)

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