power station report final version

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Cooling Towers ReportList of contents:1.Introduction

1.1.Operation Principle1.2.Cooling towers as a heat exchangers1.3.Assessment of cooling towers

2.Types of Cooling Tower2.1.Usage division2.2.Air drafting system division2.3.Natural drafting cooling tower

2.3.1.Counter.

2.3.2.Cross.2.4.Mechanical draft cooling tower

2.4.1.Forced Draft Cooling Tower2.4.2.Induced Draft Cooling Tower

3.Cooling towers as a heat exchangers3.1.Overview On the components

3.1.1.Frame and casing3.1.2.Ladder splash type polypropylene

cooling tower3.1.3.Fill3.1.4.Cold-water basin3.1.5.Drift Eliminator3.1.6.Air inlet3.1.7.Louvers3.1.8.Nozzles3.1.9.Fans

3.1.10.The Water-Distribution System3.1.11.Fan Thermostats3.1.12.Sound Attenuator Air Discharge3.1.13.Sound Attenuator Air Inlet Side3.1.14.Water Distribution Pipe3.1.15.Fire protection

3.2.Tower materials

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4.Starting Procedure of Cooling Towers &The affecting factors4.1.Before Start-Up4.2.Factors affecting Tower operation

4.2.1.Heat load4.2.2.Air wet-bulb temperature4.2.3.Water flow rate4.2.4.Air flow rate4.2.5.Fan cycling limits4.2.6.Blow down4.2.7.GPM, Range and Approach4.2.8.Tower Sitting and Orientation

5.Inspection component and maintenance ofthe cooling tower5.1.Rotating equipment.

5.1.1.Electric motor5.1.2.Coupling and drive shaft assembly5.1.3.Fan assembly

5.1.4.Cooling tower gear box5.1.5.Coupling and drive shaft assembly5.2.stationery equipment5.3.distribution system inspection5.4.external component inspection5.5.control consideration

6.Deterioration in cooling Towers6.1.Two Sources of Water

6.2.Concentration of Dissolved Solids6.3.Impact of Blow down on ConcentrationRatio

6.4.Corrosion6.4.1.Types of Corrosion

6.4.1.1.Generalized Corrosion6.4.1.2.Galvanic Corrosion6.4.1.3.Localized Pitting Corrosion

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6.4.2.Four Step Corrosion Model6.4.3.Affects of Corrosion6.4.4.Methods To Control Corrosion6.4.5.General Corrosion Inhibitors

6.5.Fouling6.6.Chemical Treatment6.7.Causes of Poor Performance in Cooling

Towers6.8.Poor Water Management

7.Troubleshooting7.1.Troubleshooting Mechanical / Electrical

Components7.1.1.Uneven water distribution7.1.2.Cold water too warm7.1.3.Excessive water drift7.1.4.Noisy gear and bearings in speed

reducer7.1.5.Excessive movement in speed

reducer pinion and low-speed shafts

7.1.6.Vibration In couplings and driveshaft7.1.7.Unusual motor noise7.1.8.Motor, motor-bearing over/heating

7.2.Typical Problems and Trouble ShootingFor Cooling Towers7.2.1.Lowering of cooling capacity7.2.2.Temperature rise

7.2.3.Oil Leaking7.2.4.Air flow low7.2.5.Rise in water temperature7.2.6.Water flow less7.2.7.Noise and Vibration7.2.8.Water carries over

8.Performance testing of cooling Towers8.1.Preparation for test

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8.2.Data required for test8.2.1.Water Flow rate8.2.2.Water Temperatures8.2.3.Air Temperatures8.2.4.Brake horsepower8.2.5.Tower pumping head

8.3.Conducting the test.9.Cooling tower cleaning procedure

9.1.Step 1: Before chemical disinfectionand mechanical cleaning

9.2.Step 2: Chemical disinfection9.3.Step 3: Mechanical cleaning9.4.Step 4: After mechanical cleaning9.5.Scale Inhibition9.6.Ion exchange resin

9.7.Physical Water Treatment Method

9.8.Filtration System and Equipment

9.9.Filtration Equipment

9.10.Bleed-off

9.11.Magnetic devices

9.12.Electronic de-scaling technology

9.13.Water Ionization

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Introduction:A cooling tower is equipment used to reduce thetemperature of a water stream by extracting heatfrom water and emitting it to the atmosphere.Cooling towers make use of evaporation wherebysome of the water is evaporated into a moving airstream and subsequently discharged into theatmosphere. As a result, the remainder of thewater is cooled down significantly.Cooling towers are able to lower the watertemperatures more than devices that use only airto reject heat and are therefore more cost-

effective and energy efficient.

Figure 1. Natural draft wet coolinghyperbolic towers

Operation principles:

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Depending on the entering air and watertemperatures, the water may be cooled bysensible and latent cooling of the air, or simply bylatent cooling of the air. In either case, latent, i.e.evaporative, cooling is dominant.

Figure 2. Schematic diagram of a coolingwater system

For example, consider the case in which the airenters at a lower temperature than the water(Figure 3a). The air will leave completelysaturated and the cooling is part sensible and partlatent. The sensible portion occurs as the airtemperature increases by absorbing heat from thewater. The latent portion occurs as some of thewater evaporates, which draws energy out of the

water.

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A2

A1

W1

W2


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Figure 3.a Psychometric process lines for airthrough a cooling tower when entering air

temperature is less than the entering watertemperature

If the air enters at the same wet bulb temperatureas before, but at a higher dry-bulb temperature

than the water, then the air will cool as it saturates(Figure 3b). Thus, the sensible cooling componentis negative, and the all the cooling is due toevaporation. In general, cooling is dominated bylatent cooling.

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Figure 3.a Psychometric process lines for airthrough a cooling tower when entering airtemperature is greater than the entering

water temperature

The total cooling, ma (ha2 ha1) is the same forboth cases since enthalpy is a function of wet-bulb

temperature alone. However, the dry-bulbtemperature significantly influences theevaporation rate, mwe = ma *(wa2-wa1). The rate ofevaporation increases as the dry-bulb temperatureincreases for a given wet-bulb temperature.

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Cooling towers as heat exchangers:Based on the previous discussion, it is clear thatcooling tower performance is a function of the wet-bulb temperature of the entering air. In an infinitecooling tower, the leaving air wet-bulbtemperature would approach the entering watertemperature, and the leaving water temperaturewould approach the web-bulb temperature of theentering air. The difference between the leavingwater temperature and the entering air wet bulbtemperature is called the approach. Therelationship between air wet bulb and watertemperature is shown in the figure below. In aninfinite cooling tower, the approach would be zero.

Neglecting fan power and assuming steady stateoperation, an energy balance on a cooling towergives:

mw1*Cpw*Tw1 mw2*Cpw*Tw2 + ma *[(ha1 + wa1*hv1) (ha2 + wa2*hv2)] = 0

Assuming steady state operation, a mass balanceon water flow gives:

mw1 mw2 + ma (wa1 wa2) = 0

mw2 = mw1 + ma (wa1-wa2)

Substituting mw2 into the energy balance gives:

mw1*Cpw* (Tw1 Tw2) + ma *(wa2 -wa1) *Cpw*Tw2 = ma*[ (ha2 + wa2*hv2) (ha1 + wa1*hv1)]

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The fraction of incoming water that is evaporated,ma (wa2-wa1) / mw1, is typically less than 1%. Thus,the second term in the energy balance equationcan be neglected with negligible error to give:

mw1*Cpw* (Tw1 Tw2) = ma *(ha2 ha1)

Both sides of this equation represent the totalcooling capacity of the tower, Qct.

The effectiveness, E, of a heat exchanger is theratio of the actual to maximum heat transfer.

E = Qactual / Qmax

For a heat exchanger, Qmax occurs if the airleaves the cooling tower completely saturated atthe temperature of the incoming water. Thus,effectiveness is

E = Qactual / Qmax = [mw1*Cpw* (Tw1 Tw2)] / [ma

*(ha2, sat, tw1 ha1)]

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Assessment of cooling towers: This section describes how the performance ofcooling powers can be assessed. The performanceof cooling towers is evaluated to assess presentlevels of approach and range against their designvalues, identify areas of energy wastage and tosuggest improvements.

During the performance evaluation, portablemonitoring instruments are used to measure thefollowing 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

These measured parameters and then used todetermine the cooling tower performance inseveral ways. These are:

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a) Range.This is the difference between thecooling tower water inlet and outlet temperature.A high CT Range means that the cooling tower hasbeen able to reduce the water temperature

effectively, and is thus performing well. Theformula is:

Cooling Tower Range = Cooling Water inlet tempCooling Water outlet temp

b) Approach . This is the difference between thecooling tower outlet coldwater temperature and

ambient wet bulb temperature. The lower theapproach, the better the cooling towerperformance. Although, both range and approachshould be monitored, the `Approach is a betterindicator of cooling tower performance.

Cooling Tower Approach = Cooling Water outlettemp Wet bulb temp

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c) Effectiveness . This is the ratio between therange and the ideal range (difference betweencooling water inlet temperature and ambient wetbulb temperature), the higher this ratio, the higherthe cooling tower effectiveness.

Effectiveness (%) = (Cooling Water in temp Cooling Water out temp) / (Cooling Water in temp Wet Bulb temp) x100

d) Cooling capacity. This is the heat rejectedfrom water, given as product of mass flow rate ofwater, specific heat and temperature difference.

e) Evaporation loss. This is the water quantityevaporated for cooling duty. The following formulacan be used:

Evaporation loss = ma* (wa1-wa2)

f) Cycles of concentration(C.O.C). This is theratio of dissolved solids in circulating water to thedissolved solids in makeup water.

g) Blow down lossesdepend upon cycles ofconcentration and the evaporation losses and is

given by formula:

Blow down = Evaporation loss / (C.O.C. 1)

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Types of cooling Towers:

Introduction

In a cooling tower, a fan pushes or drawsair from the atmosphere into the tower to

cool recirculating water.

Warm water, that has removed heat from

an air conditioning, refrigeration or

industrial process, enters the top of the

tower. As the water falls through the tower

fresh air is forced through it. This fresh air

cools the water. The cooled water then falls

to a storage basin before being recirculated

through the system again. When the water

is recirculating through the system it

gathers heat from an air conditioner orindustrial process before returning to the

top of the tower.

In general Cooling Towers can be divided

according usage, air drafting system etc

Usage division

According to usage the cooling tower, maybe divided into HVAC cooling towers which

reject heat off the chiller to ambient air.

There can be also industrial towers which

they carry out the heating load of the

machines, water (as in power stations),

..etc

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Air drafting system division

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1. Natural drafting cooling tower

The natural draft or hyperbolic cooling

tower makes use of the difference in

temperature between 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 isrequired 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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Counter flow natural Cross flow natural


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There are two main types of natural draft

towers:

Cross flow tower: air is drawn across the

falling water and the fill is located outside

the tower.

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.

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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 alarge range of capacities. Towers can beeither factory built or field erected forexample concrete towers are only fielderected.

Many towers are constructed so that theycan be grouped together to achieve thedesired capacity. Thus, many cooling towersare assemblies of two or more individualcooling towers or cells. The number ofcells they have, e.g., a eight-cell tower, oftenrefers to such towers.Multiple-cell towers can be lineal, square, orround depending upon the shape of theindividual cells and whether the air inlets arelocated on the sides or bottoms of the cells.

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Forced Draft Cooling Tower

Induced draft counter flow cooling tower

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Induced draft cross flow cooling tower

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Induced Dra f t CounterFlow Cooling Tower :

This type of tower is verycommon. It can be

identified by the fan at

the top of the tower. The

fan pulls air up through

the tower in the opposite

direction to which the

water is falling. The airusually enters the tower

through inlet louvers on the sides of the

tower.

Induced Dra f t Cross Flow Cooling Tower

In an induced draught cross

flow cooling tower, the fanis also mounted on the top.However in this type oftower the fan draws orinduces air across thewater that is falling fromthe top of the tower to the basin.

Forced Dr af t Counter Flow Cooling Tower

In a forced draughtcounter flow coolingtower, the water iscooled by air that isforced through the

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falling water and out through the top of thetower.

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Forced Dra f t Cross Flow Cooling TowerIn a forceddraught cross flowcooling tower thefan is mounted onone side of thetower. The fanforces airhorizontally acrossthe tower throughthe water that is falling from the top of thetower to the basin via the fill.

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Components of the cooling tower:All cooling tower designs have the followingcommon features;

An air circulation system

A water distribution or spray system.

Packing or fill to maximize the contact

between the water and air.

A cooling water collection and discharge

basin.

Mist eliminators that minimize droplet carry-

over and water loss.

The basic components of a cooling tower includethe frame and casing, fill, cold-water basin, drifteliminators, air inlet, louvers, nozzles and fans.

These are described below.1. Frame and casing. Most towers have

structural frames that support the exteriorenclosures (casings), motors, fans, and other

components. With some smaller designs, such

as some glass fiber units, the casing may

essentially be the frame.

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2.Ladder splash type polypropylene

cooling tower

The fill will be used in cross flow cooling towers.The fill will consist of injection moldedpolypropylene in a ladder configuration.

Benefits:

Improved thermal

performance The ladder

configuration provides

highly efficient water

breakup to develop

excellent heat transfer

with low resistance to

airflow. The horizontal

spacing between laddersis variable to meet

thermal performance

requirements.

Corrosion Resistant Injection molded

polypropylene Ladder fills is extremely inert to

chemical reaction.

High Temperature Capability Ladder fill iscapable of 150F operation.

Easy Adaptability to Most Cooling Towers

Ladder fill can be installed in virtually any cross

flow cooling tower regardless of its age or

manufacturer.

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1. Fill. Most towers employ fills (made of plastic

or wood) to facilitate heat transfer by

maximizing water and air contact. The fill, orpacking, is the heart of the cooling tower

should provide both good water-air contact for

high rates of heat transfer and mass transfer

and low resistance to airflow. It should also be

strong, light, and deterioration-resistant.

There are two types of fill:

Splash fill: water falls over successive layersof horizontal splash bars, continuously breakinginto smaller droplets, while also wetting the fillsurface. Plastic splash fills promote better heattransfer than wood splash fills.

Splash packing is made of bars stacked in decksthat break the water into drops as it falls fromdeck to deck. The splash boards serve twofunctions:

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The first is to break the larger water droplets intosmaller ones, thus increasing the air-water contactarea.The second function is to slow the fall of thewater droplets, and increase the water residenttime in the tower. The bars come in differentshapes; narrow, square, or grid, are smooth orrough, and are made of different materials,redwood, high-impact polystyrene, orpolyethylene. Splash till provides excellent heatand mass transfer between water and air.

Film fill: consists of thin, closely spaced plasticsurfaces over which the water spreads, forming athin film in contact with the air. These surfacesmay be flat, corrugated, honeycombed, or otherpatterns. The film type of fill is the more efficientand provides same heat transfer in a

smaller volume than the splash fill.The film type of fill is the more efficientand provides same heat transfer in asmaller volume than the splash fill. Filmfill presents less resistance to airflowand requires less total height thansplash fill.

In general, the film-type packing has a denserconfiguration than do the splash-type fills. Thus,less volume of film-type packing is required toremove a given heat load. However, associatedwith the denser packing arrangements are higherfan power requirement. Therefore, whenconsidering film or splash type fills, it must be

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decided whether it is the fill volume or fan powerthat is to be kept at a minimum.The tower fill performance is affected not only bythe fill arrangement, but also by the water and airloadings. A low water loading results in poor waterdistribution, while a high water loading causes thetower to flood, producing excessive air pressurelosses. In both cases, these conditions cause adeteriorating fill performance. Another factor toconsider in the selection of the tower fill is theactual physical shape. The tower dimensionsshould be kept in mind for the cross. How splash-type fill. For this fill the configuration parametershould be in the range of 0.4 to 1. If theconfiguration parameter

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Different types of fill and configurations used incooling tower:

Trickle Bloc clog-resistant splash fill is comprisedof extruded polypropylene cylinders, heat fused toform blocks of splash media. The open weave ofthe vertical cylinders provides even water flow andpromotes thermal efficiency. The lattice designpromotes splashing to help facilitate self-cleaning.

Advantages: High density counter

flow splash fill.

Most efficient non

fouling counter flow

splash fill.

Drastically improved

thermal performance

in many fouled film fill towers. Structurally superior to withstand foot traffic

resists erosion from water spray.

Significant pump head savings as compared to

other offerings.

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1. Cold-water basin.The cold-water basin is

located at or near the bottom of the tower,

and it receives the cooled water that flowsdown through the tower and fill. The basin

usually has a sump or low point for the cold-

water discharge connection. In many tower

designs, the coldwater basin is beneath the

entire fill. In some forced draft counter flow

design, however, the water at the bottom of

the fill is channeled to a perimeter trough thatfunctions as the coldwater basin. Propeller

fans are mounted beneath the fill to blow the

air up through the tower. With this design, the

tower is mounted on legs, providing easy

access to the fans and their motors.

2. Drift eliminators. These capture waterdroplets entrapped in the air stream

that otherwise would be lost to the

atmosphere.

Drift elimination in a cooling tower is

accomplished using drift eliminators,

or baffles, that change the path of air

flowing through the tower. When airhits a baffle, it changes direction; but

when water droplets hit a baffle, they lose

velocity and fall back into the recirculation

cooling water flow. One method of improving

drift reduction may be to use two passes,

rather than a single pass, of drift eliminators

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in the cooling tower. The amount of additional

drift reduction will be, however, difficult to

verify. And, any reduction of drift below this

range will not be directly proportionate to theamount of additional drift elimination media

that is placed within a cooling tower. A second

pass of drift eliminators may reduce drift

below .001 percent of the recirculation rate;

however, the degree of drift reduction below

this range is verifiable only in controlled

conditions and not in the field. And, becausewater droplets that are still entrained within

the air pathway after one pass will be very

fine, to a large extent, they will remain

entrained in the air pathway and will not be

influenced by a change in the direction of air

flow created by the second pass of drift

eliminators.Types of drift eliminator configurations

include:

1-herringbone (blade-type)

2-wave form

3- cellular (or honeycomb) designs.

The cellular units generally are the most

efficient. Drift eliminators may includevarious materials,such as ceramics,fiber reinforcedcement, fiberglass,metal, plastic, andwood installed or

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formed into closely spaced slats, sheets,honeycomb assemblies, or tiles. Thematerials may include other features, such ascorrugations and water removal channels, toenhance the drift removal further.

3. Air inlet. This is the point of entry for the air

entering a tower. The inlet may take up an

entire side of a tower (cross-flow design) or be

located low on the side or the bottom of the

tower (counter-flow design).

4. Louvers. Generally, cross-flow towers haveinlet louvers. The purpose of louvers is to

equalize air flow into the fill and retain the

water within the tower. Many counter flow

tower designs do not require louvers.

5. Nozzles. These spray water to wet

the fill. Uniform water distribution atthe 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.

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6. Fans. Both axial (propeller type) and

centrifugal fans are used in towers. Generally,

propeller fans are used in induced drafttowers 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 beused 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.

The purpose of a cooling tower fan is to move

a specified quantity of air through the system,

overcoming the system resistance which is

defined as the pressure loss. The product of

air flow and the pressure loss is air power

developed/work done by the fan; this may be

also termed as fan output and input kWdepends on fan efficiency.

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7.The Water-Distribution System

The water-distribution system dispenses hot

condenser water evenly over the fill. There areseveral types, among them are:(1) Gravity distribution, used mainly on cross-flow towers, consists of vertical hot-waterrisers that feed into an open concrete basin,from which the water Hows by gravity throughorifices to the fill below.(2) Spray distribution, used mainly on counter

flow towers, has cross piping with spray-downward nozzles.(3) Rotary distribution consists of two slotteddistributor arms that rotate about a central

8.Fan Thermostats

The fan thermostats serve to switch on or off

the fan drives depending on the cold watertemperature. The sensor is preferably placedin the piping for cooled water and should beprotected by a threaded sensor cartridge. Thesensor may also be placed in the coolingtower basin but it has to be taken into accountthat mechanical stress and vibrations to thesensor are to be avoided. For precise

measurement of the water temperature it isimportant that sensor is completely coveredby the water.

9.Sound Attenuator Air Discharge

The sound attenuator at the air discharge iscarried out with parallel arranged sound

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absorbing elements. In most cases its noiseabsorption factor is sufficient to reach therequired noise level. The casing is made offiberglass reinforced polyester.

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10.Sound Attenuator Air Inlet Side

At the air inlet side, sound attenuator casings of

fiberglass reinforced polyester can be adapted.Sound attenuation is obtained by baffles withmoisture resistant absorption material.

11.Water Distribution Pipe

For cooling towers having multiple water pipeconnectors a pre-distribution device is available to

reduce the number of connectors.

12.Fire protection.

There is the potential for tire on cooling towers,especially when wood or other combustiblematerials are used. Wood towers are susceptibleto fire after they have been out of operation for a

period of time, which would allow (hem to dry out.In order to provide protection, designsincorporating wood have fire-protection systemsas part of their design.

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Tower materialsOriginally, cooling towers were constructedprimarily with wood, including the frame, casing,louvers, fill and cold-water basin. Sometimes thecold-water basin was made of concrete. Today,manufacturers use a variety of materials toconstruct cooling towers. Materials are chosen toenhance corrosion resistance, reducemaintenance, and promote reliability and longservice life. Galvanized steel, various grades ofstainless steel, glass fiber, and concrete are widelyused in tower construction, as well as aluminumand plastics for some components.

1. Frame and casing .

Wooden towers are still available, but manycomponents are made of different materials, suchas the casing around the wooden framework of

glass fiber, the inlet air louvers of glass fiber, thefill of plastic and the cold-water basin of steel.Many towers (casings and basins) are constructedof galvanized steel or, where a corrosiveatmosphere is a problem, the tower and/or thebasis are made of stainless steel. Larger towerssometimes are made of concrete. Glass fiber isalso widely used for cooling tower casings and

basins because they extend the life of the coolingtower and provide protection against harmfulchemicals.

2. FilL

Plastics are widely used for fill, including PVC,polypropylene, and other polymers. When water

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conditions require the use of splash fill, treatedwood splash fill is still used in wooden towers, butplastic splash fill is also widely used. Because ofgreater heat transfer efficiency, film fill is chosenfor applications where the circulating water isgenerally free of debris that could block the fillpassageways.

3. Nozzles.

Plastics are also widely used for nozzles. Manynozzles are made of PVC, ABS, polypropylene, and

glass-filled nylon.

4. Fans

Aluminum, glass fiber and hot-dipped galvanizedsteel are commonly used fan materials.Centrifugal fans are often fabricated fromgalvanized steel. Propeller fans are made from

galvanized steel, aluminum, or molded glass fiberreinforced plastic.

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Starting Procedure of Cooling Towers&

The affecting factors

Before Start-Up1- Inspect the Unit.1.1. Check position of strainer screens and air inletscreens to be sure screens have not shifted during

shutdown1.2. Check fans, bearings, fan motors, and pumpsfor lubrication

1.3. Rotate all fan shafts by hand to make surethey turn freely14. Check fan motors for proper rotation.Directional arrows on fan cowls or housingsindicate correct rotation1.5. Clear fans of any trash or debris that mayhave accumulated during shutdown1.6. Check make-up valve for shut-off ability.

Check float ball for buoyancy1.7. Check spray nozzles for proper distribution1.8. Check surface for scale, sludge or debris andclean if necessary1.9. Check access door gaskets and replace, ifnecessary

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1.10. Check the condition of the cooling tower fill.If it is clogged or deteriorated, replace it withFactory Authorized Replacement Fill.

2- Inspection of Casing.2.1- While the unit is still drained, thoroughlyinspect the unit casing Clean and touch-up anyareas showing signs of deterioration. Forgalvanized steel construction units, any damagedarea should be cleaned to bare metal andrefinished with Zinc-Rich Compound (ZRC). This isalso the time when any casing joint leaks can beeasily repaired2.2- Remove any deposits that have built up andwere not cleared by flushing the basin. Touch upthe area beneath deposits as required.

3- Fill the Cold Water Basin with Fresh Waterto the Overflow level.

3.1- At initial start-up or before restart-up wherethe basin was completely drained; the initialbiocide treatment should be applied at this time.

3.2- Following a shut-down period, where the basinwas not completely drained: It is recommendedthat an initial shock treatment of appropriatebiocides be administered at restart-up to eliminate

accumulated biological contaminants.

4- Fill Basin with Water and Check FloatValve Level.After the unit has been in operation under load forseveral days, operating water level should bechecked.

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5- Adjust Belt Tension of Fan Motors.Proper belt tension is determined by pressingagainst a single belt midway between sheaveswith one finger, which should deflect the belt 1/2"with moderate pressure. To adjust belts, loosenlocknut on the motor base and rotate the exteriornut as necessary. Re-tighten locknut and rechecktension.

Start CleanDuring storage of cooling tower systems, a varietyof debris, rust, and airborne dirt or silt willaccumulate in the cooling tower. Unless athorough cleaning is done before starting regulartreatment, you will circulate this debris and causeplugging up of strainers, heat exchangers, andcondensers and disrupt cooling tower water flow.

This will also provide food for microbial growth,

potentially increasing health risks. This procedureshould be performed ideally on a semi-annualbasis, in order to minimize the risk of disease.1- Physically remove accessible sludge and debrissuch as leaves and twigs2- Fill with water, flush, and refill with fresh water

Finish CleanMany cooling tower systems are not operated yearround. Prior to shutting down, inspect the towersystem for algae, slime, scale, corrosion products,or other foulants such as mud and silt.If biogrowth is present (even in small quantities)perform a cleanup with prior to shutdown. This will

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help alleviate the corrosion and health hazardsassociated with stagnant water in the piping.

Factors affecting Tower operationThe cold water temperature obtained from anoperating cooling tower will vary with the followinginfluences:1-Heat load; With the fan in full operation, if theheat load increases, thecold water temperature will rise. If the heat loadreduces, the cold watertemperature will reduce.

2- Air wet-bulb temperature; Cold watertemperature will also vary withthe wet-bulb temperature of the air entering thelouvered faces of the tower.Reduced wet-bulb temperatures will result in

colder water temperatures.However, the cold water temperature will not varyto the same extent as thewet-bulb. For example, a 20F reduction in wetbulb may result in only a 15F reduction in coldwater temperature.

3- Water flow rate: Increasing the water flowrate (GPM) will cause a slight elevation in coldwater temperature, while reducing the water flowrate will cause the cold water temperature todecrease slightly. However, at a given heat loadwater flow reductions also cause an increase inthe incoming hot water temperature. Use care toprevent the hot water from exceeding 125F in

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order to prevent damage to the towercomponents.

4- Air flow rate: Reducing air flow through thetower causes the cold water temperature to rise.

This is the approved method by which to controlleaving water temperatureIf your tower is equipped with a single-speedmotor, the motor may be shut off when the watertemperature becomes too cold. This will cause thewater temperature to rise. When the watertemperature then becomes too warm for yourprocess, the motor can be restarted.

5-Fan cycling limits: A cooling tower equippedwith a two-speed motor, has a greater opportunityfor temperature control. When the watertemperature becomes too cold, switching the fanto half-speed will cause the cold water

temperature to rise stabilizing at a temperature afew degrees higher than before. With a furtherreduction in water temperature, the fan may becycled alternately from half-speed to off subject tothe same constraint of 30 seconds of allowableacceleration time per hour as outlined above. Ifyour tower consists of two or more cells, cycling ofmotors may be shared between cells, increasing

your steps of operation accordingly. Multicelltowers equipped with two-speed motors willmaximize energy savings and minimize soundlevels if fans are staged so that all fans arebrought up to low speed before any fan goes tohigh speed.

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Control of tower air flow can be done by varyingmethods: starting and stopping (On-off) of fans,use of two- or three-speed fan motors, use ofautomatically adjustable pitch fans, and use ofvariable speed fans.

On-off fan operation of single speed fans providesthe least effective control. Two-speed fans providebetter control with further improvement shownwith three speed fans.

6- BlowdownA cooling tower cools water by continuouslycausing a portion of it to evaporate. Although thewater lost by evaporation is replenished by themakeup system, it exits the tower as pure waterleaving behind its burden of dissolved solids toconcentrate in the remaining water. Given nomeans of control, this increasing concentration of

contaminants can reach a very high levelIn order to achieve water quality which isacceptable to the cooling tower (as well as theremainder of your circulating water system), theselected water treatment company must workfrom a relatively constant level of concentrations.

This stabilization of contaminant concentrations isusually accomplished by blowdown, which is the

constant discharge of a portion of the circulatingwater to waste. As a rule, acceptable levels onwhich to base a treatment schedule will be in therange of 2-4 concentrations. The following tableshows the minimum amount of blowdown (percentof flow) required to maintain differentconcentrations with various cooling ranges

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7- GPM, Range and ApproachAlthough the combination of range and gpm isfixed by the heat load , approach is fixed by the

size and efficiency of the cooling tower. A largetower of average efficiency will deliver cold waterat a temperature which "approaches" a given wet-bulb temperature no closer than a somewhatsmaller tower having significantly betterefficiency.Given two towers of reasonably equal efficiencies,operating with proportionate fill configurations and

air rates, the larger tower will produce colderwater. Important to note, from a tower coststandpoint, is the fact that the "base" tower (15Tapproach) would have had to be twice as large toproduce a 7 F approach (8F colder water),whereas it could have produced a 25 F approach(10 F warmer water) at only 60% of its size

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Effect of chosen approach on tower size at fixedheat load, gpm, and wet-bulb temperature

Note also that the deceasing approach curve isbeginning its asymptotic movement toward zeroapproach. For this reason it is not customary in thecooling tower industry to guarantee any approachof less than 5F.Where some variations by the process isacceptable, a smaller, less costly tower will be

required when the range is increased and the GPMdecreased.. Although practical designresponsibility places flow and temperaturerestrictions on cooling towers as well, their latitudeusually exceeds that of the typical processes theyare designed to serve.

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Effect of varying range on tower size when heatload, wet-bulb temperature and cold watertemperature are constant

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8- Recirculation and interference

Local heat sources upwind of the cooling tower

can elevate the wet bulb temperature of the airentering the tower, thereby affecting itsperformance. One such heat source might be apreviously installed cooling tower on site, or in theimmediate vicinity. A phenomenon called"interference", wherein a portion of the saturatedeffluent of an upwind tower contaminates theambient of a downwind tower. Although proper

cooling tower placement and orientation canminimize the effect of interference, many existinginstallations reflect some lack of long rangeplanning, requiring that design adjustments bemade in preparation for the installation of a newtower, cannot accept all of the blame forrecirculation. At any given wind condition, thevelocity ratio will decrease if the plume velocity is

decreased, resulting in an increase in therecirculation ratio. This is what makes forced drafttowers so susceptible to recirculation. The normaldischarge velocity from an induced draft tower isabout 20 mph, whereas the plume velocity leavinga forced draft tower is approximately 5-6 mph.

This 4:1 difference in velocity ratios results in

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considerably greater recirculation in a forced drafttower

Recirculation potential in a forced draft coolingtower

For that reason, accepted codes under whichcooling towers are tested for thermal performancelimit wind velocity during the test to 10 mph.Without this, and similar limitations, cooling towertesting and design would become infinitely moreuncertain and difficult.

9- Tower Sitting and OrientationEvery effort should be made to provide the leastpossible restriction to the free flow of air to thetower. In addition to this primary consideration,the Owner must give attention to the distance ofthe tower from the heat load, and the effect ofthat distance on piping and wiring costs; noise orvibration may create a problem, which can be

expensive to correct; drift or fogging may beobjectionable if the tower is located too close to anarea that is sensitive to dampness or spotting;also easy access and adequate working spaceshould be provided on all sides of the tower tofacilitate repair and maintenance work

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The performance of every cooling tower, large orsmall, is dependent upon the quantity and thermalquality of the entering air. External influenceswhich raise the entering wet-bulb temperature, orrestrict air flow to the tower, reduce its effectivecapacity. Air restrictions, recirculation andinterferences can be minimized, possiblyeliminated, by careful planning of towerplacement using the following guidelines:

a- Air Restrictions:In residential, commercial,and small industrial installations, towers arefrequently shielded from view with barriers orenclosures. Quite often, these barriers restrict airflow, resulting in low pressure areas and poor airdistribution to the air inlets. Sensible constructionand placement of screening barriers will help tominimize any negative effect upon thermalperformance.

Screening in the form of bushes, fences, orlouvered walls should be placed several feet fromthe air inlet to allow normal air entry into thetower. When an induced draft tower is enclosed, itis desirable for the enclosure to have a net freearea opposite each louvered face which is at leastequal to the gross louver area of that tower face.

Screening barriers or enclosures should not beinstalled without obtaining some input concerningtheir design and placement from the cooling towermanufacturer.

b- Recirculation:Except in the case of singleflow towers , the proper placement to minimizerecirculation is to orient the tower such that the

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primary louvered faces are situated parallel notbroadside to the prevailing wind coincident withthe highest ambient wet bulb temperature. Ontowers of relatively shorter length, this allows thesaturated effluent to be carried beyond the airinlets. Longer multiple-fan towers in thisorientation benefit from the wind havingconcentrated the separate-cell plumes into one ofgreater buoyancyBecause of the restricted sitting areas available insome plants, the Owner may have no choice but toorient towers broadside to a prevailing wind, andto adjust his design wet-bulb temperatureaccordingly. The amount of adjustment necessarycan be reduced by recognizing that recirculationpotential increases with the length of the towerand by splitting the tower into multiple units oflesser individual length with a significant air spacein between.

c- Air Discharge Velocity: At any givenatmospheric condition, the velocity at which thedischarge plume from a tower will rise dependsupon the kinetic energy imparted by the fan, andthe buoyant energy decrease in density) impartedto the effluent plume by the tower heat load, bothof which are changed to potential energy by virtue

of ultimate elevation of the plume.The direction that a plume will travel dependsupon the speed, direction, and psychrometriccharacteristics of the wind it encounters uponleaving the fan cylinder. Low wind velocities, willpermit an almost vertical plume rise, barringretardation of that rise by unusual atmosphericconditions. For an induced draft tower operating

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under calm conditions, with a vertically risingplume, entering and ambient wet-bulbtemperatures can be considered to be equal.Higher wind velocities will bend the plume towardthe horizontal, where a portion of it can becomeentrapped in the aforementioned lee-side lowpressure zone for re-entry into the tower

Effect of wind velocity and discharge velocity onplume behavior

The velocity ratio is the result of dividing theplume discharge velocity (V)) by the velocity of theambient wind (Va). For all intents and purposes,the recirculation ratio is the percent of totaleffluent air that is reintroduced into the tower airinlets by virtue of recirculation. As can be seen,lower velocity ratios (higher wind velocities) resultin greater recirculation. The values for the

rectangular tower represent those anticipated foran industrial tower of moderate size operatingbroadside to the prevailing wind. The recirculationratio for that tower would reach minimum valuewith a 90 degree directional change. Since thevelocity ratio is also a function of plume dischargevelocity, ambient wind force

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d- Tower shape:The wind flows in a much morecivilized fashion around a round cylindrical shapethan the rectangular, creating an almost negligiblezone of reduced pressure on the downwind side;the air requirements of which are easily satisfiedby streamlined flow around the shape.

Comparative recirculation potential of round andrectangular towers

The Round Mechanical Draft tower is, of course,unaffected by wind direction, and the centralizedclustering of the fans produces a concentrated,buoyant plume.

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Inspection component and maintenanceof the cooling tower

The cooling tower contain

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rotating equipment1. Electric motor

(a)Electric motor overload

(b)Vibration and noise

(c) Motor temperature

(d)Torque output control

1. Coupling and drive shaftassembly

A. Bearing conditions

The surface of the bearing should be smooth to be

sure of the oil lubrication pressure.

B. Lubrication efficiency

The oil temperature and viscosity and the oil pump

discharge.

1. Fan assembly(a)Tip clearance

(b)Vibration or pulsating

(c) Leading edge inspection

(d)Pitch setting

(e)Foil surface inspection due to contamination will

form unbalance for the fan

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(f) Hub shaft connection hardware

Note:A. The connections of the fan should be checked

every 6 months for tightness and corrosion

and erosion and to prevent vibration andunbalance due to high inertia and high speed.

B. The blades surface should checked periodically

due to contamination formation and vibration

monitoring and if the vibration or the

contamination increases, the fan blades

should cleaned or changed immediately to

have good vibration limit and the best

performance.

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1. Cooling tower gear box

A. The oil level in the gear box should be checked

every week and the proper oil level maintained

B. Over filling with the oil will cause oil seal premature.C. Low level oil in the gear box will damage the teeth

of the gears and the surface of the bearing.

1. Coupling and drive shaft assembly

A. The shaft alignment should be kept in the

manufacturers limit; else the vibration and the

fatigue will increase.

B. Input bearing and output bearing backlash should

be in the safe region.

stationery equipment1) Cold water basin.2) Basin sump.

A. The cooling tower collects the dust and other

solids from the scrubbed air and collects them in

the basin.

B. Basin sump can contain concrete cracks that will

cause side leakage.

C. The method of cleaning the basin is the vacuum

pump (pump out).

1) Basin piping.

Deterioration in the piping system will cause side

leakage.

2) Fill area component inspection.

3) Basin walls.

4) Sump screen

The screen could reduce the flow rate due to

contamination accumulation

1) Basin base.

2) Welding component.

3) Fan stack assembly

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A. Vibration and the flow rate speed (if chocked or

at high pressures and over expanded) in Exit top

area And Deck support area and Throat area of

the stack.

B. Stack material should withstand thermal

stresses.

C. Tip clearance.

distribution system inspectionA. Supply pump should be checked and to be sure

of its performance and discharge and the oil

level for lubrication and strainer pressure dropdue to contamination.

B. Entrance flange and elbows leakage.

C. The pump header corrosion and erosion.

D. Valves and fitting

external component inspectionNozzles and orifices that will make us able to

calculate the discharge.

control considerationA. The speed of the fan and the power consumed

should increase for other reduction in the output

temperature.

B. The pump discharge should increase.

C. The maintenance and shutdown occurs for the

successive conditions:

A. The higher temperature output.

B. High leakage from piping system, header, basin,

valves and fittings

C. Lager pressure drops on the strainer or the

orifices or the valves.

D. Higher rate of vibration and noise in the stack or

the fan due to unbalance in the fan because of

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contamination accumulation on the blades or

erosion or corrosion.

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Deterioration in cooling Towers :

The majority of the cooling tower deteriorationproblems are due to poor water management. Bio-

fouling, corrosion and scale forms the triangle of

industrial water problems.

The high temperature and relative humidity forms

a favorable environment for bacterial growth

which causes tube fouling and forms a hazard for

human health. Evaporating water leaves its saltsin the circulating water. At certain point, salts will

precipitate causing formation of scales on cooling

tower parts. Scale reduces heat transfer and

hence reduces the cooling tower efficiency.

Corrosion can result from water vapor, from water

additives or even the construction materials.

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Corrosion may attack several parts in the cooling

towers such as concrete, shell and water

distribution elements.

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Two Sources of WaterSurface Water Low in dissolved solids High in suspended solids Quality changes quickly with seasons & weather

Ground Water High in dissolved solids Low in suspended solids High in iron & manganese Low in oxygen, may contain sulfide gas Relatively constant quality & temperature

What Chemical Properties of Water Are Important?

Important Properties of Water1. Conductivity2. Hardness3. Alkalinity4. pH5. Silica6.0ther impurities, Iron, Manganese, Chlorides,Phosphate etc.

Note: PH: a scale for expressing acidity oralkalinity of the circulating or make up water .a PHbelow 7 indicates acidity, and above 7 indicatesalkalinity, a PH of 7 indicates neutral water.

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Concentration of Dissolved Solids

Only pure water can evaporate, no dissolvedsolids leave the liquid water. If there are noother water losses from the system, theevaporation process causes an increase in theconcentration of dissolved solids in therecalculating cooling water. Mineral scale willform if the dissolved solids concentration in thecooling water becomes too high

Impact of Blow down on Concentration Ratio

Blow down: Deliberate discharge of water toprevent the dissolved solids from getting tohigh

Makeup Water: Amount of water required toreplace water lost by evaporation andblowdown

Makeup = Evaporation + Blowdown

Corrosion

Corrosion is the condition wherein metal starts todissolve because of high oxidation level. When asystem that makes use of such metal starts toshow some signs of corrosion, it wouldn't be longbefore you realize that your cooling tower won't

last that long.This is because the strength as well as thethickness of your metal is has greatly decreased.Moreover, the metal cannot withstand thepressure.

When it comes to cooling tower water treatment,ensure, too, that you can protect the device from

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corrosion. One of the best ways is to make use ofozone treatment.

Cooling Systems are exposed to many types of

corrosion, from general electrochemical corrosion,to pitting caused by deposits, electrolysis, or microorganisms. Corrosion can reduce the life-span ofequipment by years, requiring expensivereplacement. It can lead' to costly equipmentrepairs and production downtime. Corrosionrelated deposits lead to reduced capacity andwasted energy because of heat transfer efficiencylosses.

Types of Corrosion

All cooling system metallurgy experiencessome degree of corrosion. The objective is tocontrol the corrosion well enough to maximizethe life expectancy of the system...

1. General Corrosion2. Localized Pitting Corrosion3. Galvanic Corrosion

General Corrosion Preferred situation

Take a small amount of metal evenly throughoutthe system Anode very large

A. Generalized Corrosion - This 40 year old

sample of 8 in, while clearly containing deposits

of iron oxide, shows very even wall loss and long

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remaining service life.

The pipe was cleaned using high pressure water

jet and returned to service with approximately

schedule 40 thickness remaining

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B. Galvanic Corrosion

Occurs when two different metals are in thesame system, more reactive metal will corrode in

presence of less reactive metal.

Potential for galvanic corrosion increases withincreasing distance on chart.

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Active End

MagnesiumGalvanized SteelMild SteelCast Iron18-8 Stainless Steel Type 304 (Active)18-12-3 Stainless Type 316 (Active)Lead TinMuntz SteelNickel (Active)76-NM6 Cr-7 Fe Alloy (Active)

BrassCopper70:30 Cupro Nickel67-Ni-33 Cu Alloy (Monel)

Titanium18-8 Stainless Steel Typ 304

(Passive)18-12-3 Stainless Steel Type 316(Passive)

GraphiteGoldPlatinum

Passive End

C. Localized Pitting Corrosion

Pitting corrosion, or pitting, is a form ofextremely localized corrosion that leads to thecreation of small holes in the metal. The drivingpower for pitting corrosion is the lack of oxygenaround a small area. This area becomes anodicwhile the area with excess of oxygen becomescathodic, leading to very localized galvaniccorrosion. The corrosion penetrates the mass ofthe metal, with limited diffusion of ions, further

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pronouncing the localized lack of oxygen. Themechanism of pitting corrosion is probably thesame as crevice corrosion.

Diagram showing a mechanism of localized

corrosion developing on metal in a solutioncontaining oxygen

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Four Step Corrosion Model

Step 1: At the anode, pure iron begins to breakdown in contact with

the cooling water. This stepleaves behind electrons.Step 2: Electrons travel throughthe metal to the cathode.Step 3: At the cathode, achemical reaction occursbetween the

electrons and oxygen carried bythe cooling water. This reactionforms hydroxide.

Step 4: Dissolved minerals in the coolingwater complete theelectrochemical circuit back to the anode.

Affects of Corrosion Destroys cooling system metal Corrosion product deposits in heat exchangers Heat transfer efficiency is reduced by deposits Leaks in equipment develop Process side and water side contamination

occurs Water usage increases Maintenance and cleaning frequency increases

Equipment must be repaired Unscheduled shutdown of plantMethods To Control Corrosion Use corrosion resistant alloys Adjust (increase) system pH: Scale Apply protective coatings: Integrity Use "sacrificial anodes": Zn/Mg Apply chemical corrosion inhibitors

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General Corrosion InhibitorsProtect metal by filming all surfaces whether they

are anodic or cathodic, General Inhibitors: SolubleOils, Tolyltriazoles, Benzotriazoles

Anodic Corrosion Inhibitors: Stop corrosion cell byblocking the anodic site. Severe localized pittingattack can occur at an unprotected anodic sites ifinsufficient inhibitor is present

Anodic Inhibitors : Chromates, Nitrites,Orthophosphates, Silicates, Molybdates

Cathodic Corrosion Inhibitors: Stop corrosion cellby blocking the electrochemical reaction at thecathode .Corrosion rate is reduced in directproportion to the reduction in the size of thecathodic area.

Cathodic Inhibitors: Bicarbonates, Polyphosphates,Polysilicates, Zinc, PSO

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FoulingFouling occurs when solid materials form or

contribute to the formation of deposit onequipment surfaces. They are introduced to thesystem as suspended solids and may enter by themakeup water, from corrosion by products, or asairborne materials. Examples include mud, sand,silt, clay oils, debris, organics, microbes, etc.

These materials adhere to eat transfer surfacesand reduce heat transfer and water flow

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Factors Influencing Fouling Water Characteristics Water Temperature Water Flow Velocity Microbio Growth Corrosion Process Leaks

Economic Impact of Fouling Decreased plant efficiency Reduction in productivity Production schedule delays Increased downtime for maintenance Cost of equipment repair or replacement Reduced effectiveness of chemical inhibitors.

Affects of Fouling Foulants form deposits in hot and/or low flow

areas of cooling systems Shell-side heat exchangers are the most

vulnerable to fouling Deposits ideal for localized pitting corrosion Corrosive bacteria thrive under deposits Metal failure results

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Three Levels of Attack Can Be Employed toAddress The Effects of Fouling.

A. Prevention

Good control of makeup quality.Good control of corrosion, scale, & microbio.High Efficiency Multimedia Filters Capable of 80%removal of 0.5 micron Typical multimedia depthfilters capable of 80% removal only down to 10micron Most (greater than 90%) of particles found

in a cooling tower are less than 10 micron. Do notoverlook sidestream filtration and choose wisely

B. Reduction Increase blowdown Sidestream filter

A. Ongoing Control Backflushing, Air rumbling, Clean tower.

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Chemical TreatmentCharge Reinforces Anionic polymers increase strength of charge

already present on suspended solids Keep particles small enough so they do not settle

out

Wetting Agents: Surfactants, Penetrate existingdeposits, Wash away from metal surfaces

Microorganisms

Bacteria and other pathogenic microorganisms arepresent everywhere throughout the environment.

They can often be found in cooling tower water.When cooling towers contain an open recirculationsystem, microorganisms can spread from air towater. Microorganisms can rapidly multiply, when

a substrate is present and a number of conditionsare ideal for microbial growth. Examples are pH,temperature, oxygen concentration and nutrients.

The nutrient content in water increases, becauseof water evaporation. Process leaks and water usecan also cause the nutrient content in the water toincrease. This can cause problems.

If you will not be able to use it, microorganisms

will start to grow and multiply, which will thenproduce a biological film. This film shall thenappear on the water's surface.

And if the problems weren't enough, you'll soonrealize that it will be very hard for you to removethem, especially if you're only applying basic

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cooling tower water treatments.

The process is commonly known as biologicalfouling.

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Microbiological Contamination

Water treatment is about managing three foulingprocesses... Corrosion Scale Microbiological

The microbial fouling process is... The most complex The least understood The hardest to measure and monitor

Controlled using the least desirable, mostexpensive, & potentially hazardous products

Cooling systems provide the idealenvironment for microbiological growth

Nutrients: Ammonia, oil, organiccontaminants Temperature: 70-140F acceptable pH: 6.0 - 9.0 ideal Location: Light/No Light Atmosphere: Aerobic/Anaerobic

Three Kinds of Troublesome Microorganisms InCooling Water : Bacteria, Algae andFungi/Mold/Yeast. They cause plugging, fouling,corrosion, and destruction of wooden coolingtower components. Many different bacteriaspecies may exist in cooling water systems. Someof the problems caused include severe bacterialslimes and fouling, sulphuric acid, under depositcorrosion and health hazards

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BacteriaBacteria extremely small compared to a human, a

bacteria is like a grain of sand to the Sears Tower.Size allows many (millions) to fit into a smallvolume of water.

Types of Bacteria1. Slime Forming2. Anaerobic Corrosive3. Iron Depositing4. Nitrifying

5. Denitrifying

Two Classifications of BacteriaPlanktonic: Free-floating bacteria in bulk water

Sessile: Bacteria attached to surfaces. Over 95%

of bacteria in a cooling system are sessile and live

in BIOFILMS

Bio film

When a significant microbial growth takes place, aslime layer is formed. This contains both organicand inorganic matter. Some microorganismsexcrete polymers, which can form a gel-likenetwork around cells after hydrolysis takes place.

This is called a bio film. As a result of bio film

formation, microorganisms can attach themselvesto surface layers. This causes microorganisms tono longer be flushed away by cooling tower water.Bio films protect microorganisms from othermicroorganisms and from toxic disinfectants. Thiscauses water disinfection to be much moredifficult when a bio film is present.

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Bio film partly consists of microbiological cells andcomponents. Bio film, which is very sticky, alsocontains organic and inorganic matter that ispresent in the water and is absorbed by the film.

This concerns chemical precipitation, organicflakes and dead cell mass. Bio film consists of 90%water.

Bio film causes a number of problems, knowing:Within the protected slime layer microorganismscan cause a speedy corrosion, causing the walls ofcooling towers and heat exchange systems to becorroded. The bio film prevents materials thatcause corrosion protection from reaching thesurface. Furthermore, microbiological reactionscan accelerate corrosion reactions and microbialproducts can corrode materials.Bio film creates an isolation layer on heat-exchange systems, causing them to no longerfunction properly. Microorganisms present in thebio film accelerate oxygen uptake. This can causean oxygen deficiency in the system. Somemicroorganisms switch to fermentativemetabolisms and produce a number of organicacids, which causes a decrease in pH. Anaerobicbacteria form sulphide byproducts, which arecorrosive

Foulant Thermalconducti

CaC03 1.3-1.7CaS04 1.3CaP04 1.5M P04 1.3Fe oxide 1.7

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Biofilm 0.4

Algae Require sunlight to grow Found on tower decks & exposed areas Form "algae mats" Plug distribution holes on tower decks Plug screens/foul equipment Consume oxidants Provide food for other organisms

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FungiUse carbon in wood fibers for food . Destroy

tower lumber by either surface or internalrotting (deep rot) . Loss of structural integrity oftower

Controlling Microbiological Growth Water Quality Eliminate organic contaminants (food) No food =No bugs System DesignConsiderations Clean tower andsumps, cover decks Chemical Treatmentwith Biocide Oxidizing Biocides Non-oxidizing Biocides Biodispersants

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Causes of Poor Performance in CoolingTowers

The performance of a cooling tower degradeswhen the efficiency of the heat transfer processdeclines.Some of the common causes of thisdegradation include:

A. Scale DepositsWhen water evaporates from the coolingtower, it leaves scale deposits on the surface

of the fill from the minerals that weredissolved in the water. The most commonscales are calcium carbonate, calciumsulphate and silica or silicates. Scale build-upacts as a barrier to heat transfer from thewater to the air. Excessive scale build-up is asign of water treatment problems.

B. Clogged Spray NozzlesAlgae and sediment that collect in the waterbasin as well as excessive solids get into thecooling water and can clog the spray nozzles.

This causes uneven water distribution overthe fill, resulting in uneven air flow throughthe fill and reduced heat transfer surfacearea. This problem is a sign of watertreatment problems and clogged strainers.

C. Poor Air Flow

Poor air flow through the tower reduces theamount of heat transfer from the water to theair. Poor air flow can be caused by debris atthe inlets or outlets of the tower or in the fill.Other causes of poor air flow are loose fanand motor mountings, poor motor and fanalignment, poor gear box maintenance,improper fan pitch, damage to fan blades, orexcessive vibration. Reduced air flow due to

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poor fan performance can ultimately lead tomotor or fan failure.

D. Poor Pump PerformanceAn indirect cooling tower uses a cooling tower

pump. Proper water flow is important to achieveoptimum heat transfer. Loose connections,failing bearings, cavitations, clogged strainers,excessive vibration, and non-design operatingconditions result in reduced water flow, reducedefficiency, and premature equipment failure.

Poor Water ManagementPoor water management causes the following

problems:

1. Algae, Slime, and BacteriaWarm temperatures increase theMicrobiological growth which substantiallyreduces evaporation performance, increasesBio-Slime on the condenser tubes and is aserious threat to life and health as a result ofincreased Legionnaires Disease potential.

Airborne bacteria & algae grow rapidly in thewarm water cooling tower condenser loopsystem. The customary treatment process is touse algaecides & biocides such as chlorine orother oxidizing biocides as a preventativemeasure.

2. Corrosion

Historically, corrosion reduces the equipment lifespan by 50%. Replacement time accelerates 2fold. Corrosion is typically controlled by theaddition of corrosion inhibitor chemicals suchsodium or molibdate compounds. Rarely does thisprocedure result in corrosion.

3. Lime Scale Build Up on Condenser Tubes

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NBS statistics show 1/4" scale thickness reducesheat transfer by 38%. In hard water areas scalecontrol is normally accomplished by the addition ofacid which unfortunately counteracts corrosioncontrol chemical inhibitors. This becomes a dominobalancing game where the customer rarely wins.

4.Sediment and SludgeDirty cooling tower sumps create toxic wastedisposal problem as well as a hiding place for theacid producing bacteria. This is another source ofcorrosion. When solids precipitate, those drop to

bottom of the sump and low flow areas in thepiping. The customary method of treatment is todo nothing, then muck out the sump once or twicea year. Some opt to install sand or centrifugalfilters on the sump. The sand filters will be rapidlybecome obsolete without continuousmaintenance.How to limit deterioration in cooling towers? Blow down Scale Prevention

Corrosion Control

Erosion control

Control of Biological Growth

Foaming and Discoloration

Control of Foreign Matter

PH control Conductivity check

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Troubleshooting

TROUBLESHOOTING MECHANICAL /ELECTRICAL COMPONENTS

1. Uneven waterdistribution

Causes Broken or plugged nozzles distribution piping broken fill distribution pan out of level excessive or uneven water flow

Remedy

Replace or repair defective parts

clean distribution system and pump suctionscreen

adjust water flow to design conditions

1.Cold water too warm

Causes

Over pumping, fill improperly installed not enough air

Remedy

Adjust water flow to Design conditions

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make sure all till sections are intact andproperly installed

make certain motor Hp is correct see if fill or eliminators need cleaning See if anything obstructing inlets or discharge.1.Excessive water drift

Causes

Broken or plugged distribution system broken or missing drift eliminators fan pitched above design over pumping

Remedy

Replace or clean nozzles see that all fill and eliminator sections are in

place and intact

pitch fan to design conditions reduce water flow to tower design

1.Noisy gear and bearings in speedreducer

Causes

Worn bearings or gear set warped gearing low oil level contaminated oil protective shield rubbing gear case bearing fatigue

Remedy

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Check oil Tor level and contamination adjust oil shield replace worn bearings oil seal or gear sets check tooth contact of gears Add oil if necessary.

1.Excessive movement in speed reducerpinion and low-speed shafts

Causes

Worn high-speed and low-speed bearings.

Remedy

Replace wont bearings and oil seats check tooth contact or gears after replacing

gears and/or bearings.

1. Vibration In couplings and drive shaft

Causes

Misalignment of Coupling Foreign matter adhering to coupling

shaft out of balance, bent or off-centre worn bearing or bent shaft in motor or gearunit.

Remedy

Realign coupling and recheck alignment after30 days

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tighten motor and speed-reducer hold-downbolts.

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1.Unusual motor noise

Causes

Motor running single-phased electrical unbalance worn bearings.

Remedy

Stop motor, try to restart (unit won't start ifsingle-phased)

check wiring, controls, motor and all threelines-correct if required

check lubrication replace bad bearings.

1. Motor, motor-bearing over/heating

Causes

Overload (measure load, compare withnameplate rating)

Misalignment excessive end thrust too much grease (ball or roller bearing)

insufficient lubricant

Remedy

Check for excessive friction in motor drive orunit

check for over voltage, improper connections realign set

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reduce thrust from drive or machine relieve grease supply and boost oil to points

set by manufacturer.

Typical Problems and Trouble Shooting ForCooling Towers

1. Lowering of cooling capacity

Causesa. Motor stoppage Electric blackout Fuse burnout due to damaged Contacts Insufficient switch capacity Bad switch contact

Remedy Contact power company Get proper fuse Change to proper switch Adjust / Clean Contacts.

a. Sudden lowering of motor speed (rotations perminute)

Defective starter Too heavy load Low supply voltage

Remedy Check starter for defects Reduce the load by checking motor

current Consult power company

a. Cannot rev up motor speed (rotations perminute)

Defective starter / starter connections Connection of rotary and fixed section

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Motor winding damaged Remedy

correct connection according to nameplate

Check supply voltage across all 3 Check current in all 3 phases Send out to repair shop Send out to repair shop

1. Temperature riseCauses

Motor getting over heated Too heavy load Lowering of voltage supply Unbalanced voltage supply High surrounding temp

Remedy Lighten load proper level Consult power company

Consult power company

1. Oil LeakingCauses

In case of gear speed reducer oil leakage Too much oil Loose bolt

Remedy Lower the oil face to proper level Tighten properly

1. Air flow low

Cause fan speed low

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Fan blade angle incorrect

Inlet jali chocked

Remedy Check bearings/motor Correct blade angle to required setting Clean air path

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1. Rise in water temperatureCauses

Water flow above specified flow Air flow below specified flow Load higher than design Fill checked or coated Fresh air intake not sufficient or area

sufficient or area around tower not asspecified.

WBT high Water bypassing fills Sprinkler jammed/water not being sprinkled

and distributed

Remedy Regulate to correct flow rate. Adjust blade angle check and clean jail

Adjust load to correct level. Clean / replace fills. Use proper water (Makeup) quality

Improve ventilation and ensure exhaust airdoes not get recycled.

Check design condition and ensure norecycling of exhaust air.

Check sprinkler head and pipe leakages.

Repair sprinkler and distribution system.

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1. Water flow lessCauses

Filter chocked

Sprinkler pipes chocked

Level of water low in pump

Pump small

Remedy Clean water filter. Clean pipes and holes Adjust float/inlet flow ensure proper make-up Replace for correct flow volume

1. Noise and Vibration:

Causes

Fan mounting loose Fan blocks loose Fan unbalanced Motor bearing faulty Hub mounting on motor shaft loose Many parts rubbing against tower components

Remedy Tighten mounting bolt and correct/ replace if

needed. Tighten blade in hub Rebalance and adjust Check and grease or replace bearing on

motor.

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Tighten and use end plate and shims ifrequired.

Give proper clearances and adjust/ aligncomponents

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1. Water carries over:

Causes

Sprinkler rotation too faster Blocking of filter Defective eliminator Sprinkler too high above filter

Remedy Adjust sprinkler angle as to match the

specified rotation Clean up any blocked part Replace eliminator Adjust as specified: 25mm-DMA 2116

toDMB4116 / 50mm-DMA 6616 toDMB8416

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Problem/Difficulty

Possible Causes Remedies/Rectifying Action

Excessive

absorbedcurrent/electricalload

1. Voltage

Reduction

Check the voltage

2a. Incorrect angleof axial fan blades

Adjust the bladeangle

2b. Loose belts oncentrifugal fans (or

speed reducers)

Check belttightness

3. Overloadingowing to excessiveair flow-fill hasminimum waterloading per m" oftower section

Regulate thewater flow bymeans of thevalve

4. Low ambient airtemperature

The motor iscooledproportionatelyand hencedelivers morethan name platepower

Drift/carry-over of wateroutside theunit

1. Unevenoperation of spraynozzles

Adjust the nozzleorientation andeliminate any dirt

2. Blockage of thefill pack

Eliminate any dirtin the top of thefill

3. Defective or Replace or realign

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displaced dropleteliminators

the eliminators

4. Excessivecirculating waterflow (possiblyowing to too highpumping head)

Adjust the waterflow-rate bymeans of theregulating valves.Check forabsence of damage to the fill

Loss of water from

basins/pans

1. Float-valve notat correct level

Adjust the make-up valve

2. Lack of equalizingconnections

Equalize thebasins of towersoperating inparallel

Lack ofcoohug andhence

increase intemperatures owing toincreasedtemperaturerange

1. Water flowbelow the designvalve

Regulated theflow by means ofthe valves

2. Irregular airflowor lack of air

Check thedirection of

rotation of thefans and/or belttension (brokenbelt possible)

3a. Recycling ofhumid dischargeair

Check the airdescent velocity

3b. Intake of hot Install deflectors

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air from othersources4a. Blocked spraynozzles (or evenblocked sprayrubes)

Clean the nozzlesand/or the tubes

4b. Scaling of joints

Wash or replacedie item

5. Scaling of thefill pack

Clean or replacethe material(washing with

inhibited aqueoussulphuric acid ispossible but long,complex andexpensive)

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Performance testing of coolingTowers

Preparation for test

1. The water distribution system must beempty of strange materials2. Fill must be level and free of strangematerial.3. Drift eliminators must be clean.

4. Positioning of instruments for obtainingtemperature and water flow measurements mustbe so established so as to reflect the true tower

capability.

Data required for testWater quantities and temperatures, as well as any

miscellaneous water sources, may need to be

measured, depending upon their effect upon the

aforementioned primary variables.

1. Water Flow rateWater flow rate to the cooling tower can bedetermined by several means.

the pitot tube traverse method.( Most commonlyused)It is both practical and accurate providedlaboratory calibration has been made.Other acceptable means include the orifice plate,venturi tube, and flow nozzle, all of which alsorequire laboratory calibration. Tracer methods, as

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well as acoustic methods, have been developed(usually dilution techniques) and are beingrefined.Occasionally,pump curves are used toapproximate the flow. Distribution basin nozzlecurves (gpm vs depth of water over nozzle) arefrequently used as a check method and, in theabsence of other methods, may be used tomeasure flow directly.

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2. Water Temperatures

Water temperatures should be obtained withcalibrated mercury-in-glass thermometers orresistance-type sensors (RTD's, thermostats, etc.),either used in direct contact with the flowingwater or inserted in thermometer wells. Theseinstruments must reflect the true averagetemperature to and from the tower. The returnwater temperature to the tower is usually well

mixed, and a single paint of measurement willnormally suffice., However, cold watertemperatures from the tower can varyconsiderably throughout the collection basin.

Therefore, care must be taken to select a point ofmeasurement where thorough mixing hasoccurred. The pump discharge is geneyconsidered to be a satisfactory location.

3. Air Temperatures

Air temperatures include both the wet-bulb anddry-bulbtemperatures. Wet-bulb temperatures should bemeasured with mechanically-aspirated

psychrometers whenever feasible, although slingpsychrometers are occasionally used and do affordan alternate and accurate means of measuringthis variable. The location of wet-bulb temperaturemeasurement stations will depend on the contractguarantee. That is, whether the guarantee basis isambient or entering wet-bulb temperature. (Sect.

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1-E-l) Reference should be made to theappropriate test code for exact locations ofinstruments. Any effect on wet-bulb thermometersfrom extraneous. sources of heat must be takeninto account when data evaluation is made.Dry-bulb temperatures must also be measuredwith laboratory-calibrated instruments at locationscalled out by the appropriate test code. Themeasurement of dry-bulb temperature is confinedprimarily to natural draft towers.4. Brake horsepower

Brake horsepower refers to the output of the fanprime mover, which is usually an electric motor.

Thermal performance guarantees are based on aspecific brake horsepower at the design thermalconditions, which establish a design air density.Fans should be adjusted prior to a scheduled testso that the horsepower is within 10% of the designvalue, after corrections to design air density have

been made. Since input electric power is usuallymeasured, the brake or output power must becomputed by multiplying the input power by themotor efficiency. The efficiency and power factorare obtained

power station report final version

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