Cooling Tower Jogender

7/28/2019 Cooling Tower Jogender

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Galaxy Surfactants Ltd. Summer Internship 2013

Summer Internship 2013

Date: 11th May, 2013

Under the guidance of

Shrivardhan Nuwal

Sub

mitted byJogender

Dhayal

IIT Kanpur

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Problem Statement 1

Cooling Tower

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INDEXACKNOWLEDGMENTPage no.

1. Theory………………………………………………………………………………….5

1.1. Introduction…………………………………………………………………..5

1.2. Cooling Tower Performance Parameters………………………………...7

1.3. Cooling Tower Internals……………………………………………………8

2. Analysis of Existing System…………………………………………………………11

2.1 Cooling Tower Specifications………………………………………………11

2.2 Existing Network……………………………………………………………12

2.3 Analysis of Cooling Tower Water…………………………………………12

3. Inefficiencies in the Present System ………………………………………………...14

4. Viable Solution………………………………………………………………………..15

5. Calculations……………………………………………………………………………16

6. Cost Analysis………………………………………………………………………….16

7. Energy Saving Opportunities……………………………………………………….17

8. Latest Trends………………………………………………………………………….18

8.1. Chemical treatment programs…………………………………………….18

8.2. Zero Blow Down Technology……………………………………………..198.3. Side Stream Filters………………………………………………………….19

8.4. Fan Control strategies……………………………………………………...21

8.5. Pump Control Strategies…………………………………………………..21

8.6. Special Fills………………………………………………………………….21

8.7. Variable Flow Nozzle……………………………………………………..22

9. Proposed Modification……………………………………………………………….23

9.1 Types of Fills…………………………………………………………………23

9.2 Evaluation of Alternatives…………………………………………………..24

10. References…………………………………………………………………………….27

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ACKNOWLEDGEMENT

My heartfelt thanks to Mahendra Yadav for formulating interesting and intriguing

problem statements which deepened my liking for some aspects of Chemica

Engineering.

I sincerely thank Shrivardhan Nuwal for his guidance throughout the project.

I also thank Jami Shrinu, Siddhart, Vivek, Sachin, Himanshu, Santosh and Vikrant Raut

for providing valuable inputs during various stages.

Ravichandran, Rupali Raut, and Bhoosan Thakur of QA lab for rigorous analysis of various

samples.

Jagdish Boir, Vishal Raut, Vishal Rahul, Vishal Mahatre, Ramchandra Enamdar and other

operators and maintenance staff for providing with the specific information on reactors

cooling towers and chemicals.

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PROBLEM STATEMENT

Study the cooling tower at N-46, evaluate its performance and compare with the actualdata. Optimize the system for energy savings.

1.1. Introduction

• The machines and industrial processes generate tremendous amounts of heat whichmust be continuously dissipated if those machines and processes to operateefficiently.

• Cooling tower is a heat removal device that uses water as the medium to removeheat.

1.1.1. Working Principle:• When warm water is brought into contact with unsaturated air, part of liquid vaporizes

and liquid temperature drops. The cooling takes place by the transfer of sensible heat& by evaporative cooling.

• The driving forces for mass and heat transfer are predicted using a quality called wetbulb temperature. Ideally the wet bulb temperature is the lowest theoreticatemperature to which the air can be cooled.

• Wet bulb temperature is defined as "the steady state, non-equilibrium temperaturereached by a small mass of liquid exposed under adiabatic conditions to a continuousstream of gas”. Water evaporating from the moistened wick on the wet-bulbthermometer bulb cools the thermometer bulb and lowers the temperature reading.

• The reduction in water temperature in the cooling tower comes from evaporation,

although when the air temperature is low, there is some sensible heat transfer to theair.

1.1.2. Types of Cooling Towers:

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1) Mechanical draft is in turn classified into Induced draft and Forced draft based onthe location of the fans.a) Forced draft: In the forced-draft tower the fan is mounted at the base, and it forcesair into the tower, creating high entering and low exiting air velocities. The low exitingvelocity is much more susceptible to recirculation.

b) Induced draft: The fan is located at the top of the tower, induces hot moist air out the discharge.

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2) Natural Draft:Utilizes buoyancy via a tall chimney, usually used in thermal power plants.

Counter Flow Vs Cross Flow

Criteria Counter Flow Cross FlowPrinciple The air is vertically upwards,

with the hot water fallingdownwards. The coldest watercomes in contact with thecoolest and most dry air,

The air flows horizontallyand the water fallingdownwards meets the airat different temperatures. Therefore the heat

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http://en.wikipedia.org/wiki/File:Didcot_power_station_cooling_tower_zootalures




optimizing the heat transferand obtaining the maximumperformance

transfer is not alwaysoptimized

Area The tower area required iscomparatively much smaller.

Larger area due tofeatures like thearrangement and materialof the pack.

Air Flow Since the air-water contacttime is higher, the quantity of air required is lesser

Since the air-watercontact time is lesser,more air is required

Distribution System

The distribution is donethrough channel with lateralpipes, fitted with splash cumspray nozzles.

The distribution is done byopen trough systems onthe fan deck, fitted withnozzles.

Recirculation

Air intake is at the bottom of the tower and the discharge isat a much higher level. Theproblem of recirculation is less.

Since the air intake areaextends from the bottomto the deck level, itcreates the effect of

recirculation.Fan Power The fan Power consumption is

low as the required airquantities comparatively lower.

The fan powerconsumption is higher asthe airflow required ishigher.

Maintenance

Distribution nozzles difficult toinspect and clean.

Easy maintenance accessto distribution nozzles

1.2.Cooling Tower Performance Parameters

• Range = difference between the cooling tower water inlet and outlet temperature.

• Approach = difference between the cooling tower outlet cold water temperature andambient wet bulb temperature.

• Cooling tower effectiveness = It is the ratio of range, to the ideal range, i.e.,Range / (Range + Approach).

• Cooling capacity = It is the heat rejected in kCal/hr. or TR, given as product of massflow rate of water, specific heat and temperature difference.

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• Evaporation loss = It is the water quantity evaporated for cooling duty andtheoretically, for every 10, 00,000 kCal heat rejected, evaporation quantity works outto 1.8 m3.

An empirical relation used often is:Evaporation Loss (m3/hr) = 0.00085 x 1.8 x circulation rate (m3/hr) x (T1-T2) T1-T2 = Temperature difference between inlet and outlet water.

• Cycles of concentration (C.O.C) = It is the ratio of dissolved solids in circulatingwater to the dissolved solids in makeup water.

• Blow down losses = It depends upon cycles of concentration and the evaporationlosses and is given by relation:

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

1.3.Cooling Tower Internals1) Basin- The cooled water is stored in the basin. Basin can be made from FRP or RCC.Basins can be of various capacities. It is divided into two parts

a) Basin Sump- Lowest portion of the basin to which cold circulating water flowsusually the point of circulating pumps suction connection.b) Basin curb- The top level of the retaining wall of the cold water basin; usually

the datum point from which tower elevation points are measured.A Float valve is used to avoid overflow and to maintain automated makeup water flow.2) Cell - Cooling towers with circulation rate of more than 100 m3/hr are usuallysubdivided into different parts with a common basin. The cell is the smallest towersubdivision which can function as an independent unit with regard to air and water flow;it is bounded by exterior walls or partitions.3) Fills – Fills are installed in cooling tower to increase the surface area of waterexposed to air. Basic types of fills are splash fills and film fills.a) Splash fills

b) Film fills

4) Nozzle-A device for controlled distribution of water in a cooling tower. Nozzles aredesigned to deliver water in a spray pattern.

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5) Louvers-Members installed horizontally in a tower wall to provide openings throughwhich the air enters the tower while also containing the falling water within the tower.

6) Drift eliminators -An assembly constructed of wood, plastic, or other material thatserves to remove entrained moisture from the discharged air. Drift eliminators removeentrained particles from air stream with minimum pressure drop. This helps in reducingthe fan power requirement when the air passes through them.

Drift Eliminators can solve some of the most common problems associated with driftloss:• Corrosion problems on surrounding piping, equipment, and electrical components.

• Short circuiting resulting in failure of electrical systems especially fans.

• Emission of chemicals to the atmosphere.

7) Fan- A device for moving air in a mechanical draft tower. The fan design may beeither an axial flow propeller or centrifugal blower.Fan pitch is the angle that a fan blade makes with the plane of rotation.

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Fan guard is the protective screen installed either at the inlet of a forced draft fan or atthe exit of an induced draft fan.

8) Side stream filter The cascading water in a cooling tower continuously "scrubs" airborne contaminantsfrom the atmosphere. These contaminants, in conjunction with particulate in makeupwater, find their way into the cooling tower sump and ultimately can flow downstreaminto the system, where they accumulate in heat exchangers, condenser tubes and other

critical water-cooled process equipment.In conjunction with corrosion, particles contribute to the following problems:

• Reduced operating efficiency.• Increased downtime for cleaning and repair.• Increased cost of water treatment.• Shortened equipment lifespan.

Side-stream filtration, although popular, does not provide complete protection, but it canbe effective. With side-stream filtration, a portion of the water is filtered continuously This method works on the principle that continuous particle removal will keep the systemclean. For high flow systems, this method is cost-effective.

2. EXISTING SYSTEM

2.1.Cooling Tower Details:

Type Counter flowCapacity 150 TRFills Film fills (PVC)Basin Dimensions 2.5 m X 2.5 m x 0.48 mBasin Water 2.5 m X 2.5 m x 0.48 m

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Capacity

Pump:

Make GRUNDFOSType CR-64-2 A-F-A-E-HQQESr.no. 0003Model A96123530P11019

Rpm 2924Frequency 50 HZQ 64 m3/hr.P2 11.0 KWPmax 16 BARTmax 120 ºcHmax 60.9m

Fan motor:

Voltage 415 V

Rpm 2940

Bearing DE 7309 BE

Bearing NDE 6309 C4

TAmb 400C

Net Weight 89 kg

Grease IOC Servoplex

LC3/Equivalent LI Complex

Type 3~MOT-M6160MB2-

42FF300-F1

KW/HP 11/15

FREQUENCY 50 Hz

SR no. 1569

MAKE GRUNDFOS

2.2.Existing Network:

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2.3.Water Analysis:

Cost savings can result even from one additional cycle if we start at low levels of "Cyclesof concentration". The greater the number of cycles, the lesser will be the cost of waterand chemicals.As cycles increase beyond a certain point, however, the savings become less and lesssignificant. The amount of bleed off and of the make up to replace it declines rapidly atabout 4 cycles and almost levels out at above 6 cycles, resulting in very little furtherreduction in water or chemical consumption. The TRADE OFF - possibility of increased deposition and greater potential for corrosion.

2.3.1. Tests:Most commonly, chloride tests are used since chlorides are highly soluble, remain in

solution, and are easy to measure at low levels.

Conductivity readings were used in the QA Lab to calculate TDS in water samples.

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Conductivity Meter in the QA lab, probes for TDS and Temperature measurement

2.3.2. Terms used:1. Bleed Off or Blow Down (BD) (m3/h)

2. Evaporation Rate (ER) in (m3/h). Includes "windage" and "drift".

3. Makeup (MU) in (m3/h).

4. Circulation Rate (CR) in (m3/h).

5. Delta T (∆T) in °C. Differential between incoming water and outgoing water.

6. Cycles of Concentration (C)

7. TDS - Total Dissolved Solids (in ppm)

2.3.3. Calculations:Cooling Tower Make Up

TDS*

Blow Down

TDS*

Cycles of

Concentration150 TR 93.6 1112 11.88

*All the measurements for hardness, TDS and pH were done in the QA lab.

Treatment/Operating procedure being followed:Chemical Amount Effect Frequency Cost per

kg(Rs)

MAX Treat2521

500ml Controls precipitation of Calcium phosphate,carbonate, sulfate.

Daily 151

MAX Treat 606 300ml Control build-up of biological

slimes formed by algaeand bacteria

Alternate Weeks 214

MAX Treat 608 300ml Biocide / Slimicide forbacterial and fungal

Slime control

Alternate Weeks 214

MAX Treat2001

300ml Cleaning Action For higherEfficiency

Weekly 337

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3. INEFFICIENCIES IN THE PRESENT SYSTEM

Some pressing issues:1. Blow Down done on arbitrary basis rather than analyzing the outlet water samples andrequired cycles of concentration.

2. No arrangement is made to measure blow down water quantity.

3. No flow measuring equipments near the outlets of the tower and at the main header.

Proper estimate of overall TR required cannot be calculated.

4. Continuous operation of the towers despite very low heat load, no controlsimplemented over the CT pump.

5. Insufficient basin cleaning. Huge amounts of algae formation.

All these situations lead to the inter related cooling tower problems.

What Causes Poor Performance? The performance of a cooling tower degrades when the efficiency of the heat transferprocess declines. Some of the common causes of this degradation include:Scale DepositsWhen water evaporates from the cooling tower, it leaves scale deposits on the surface ofthe fill from the minerals that were dissolved in the water. Scale build-up acts as abarrier to heat transfer from the water to the air.

Clogged Spray ControllersAlgae and sediment that collect in the water basin as well as excessive solids get intothe cooling water and can clog the spray nozzles. This causes uneven water distribution

over the fill, resulting in uneven air flow through the fill and reduced heat transfersurface area.

Poor Air FlowPoor air flow through the tower reduces the amount of heat transfer from the water tothe air. Some causes of poor air flow are buildings or walls adjacent to the towerheating equipments like compressors located nearby, poor motor and fan alignment,improper fan pitch, damage to fan blades, or excessive vibration. Reduced air flow dueto poor fan performance can ultimately lead to motor or fan failure.

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Extreme cases of clogging in fills and Scale deposit in pipes

4. VIABLE SOLUTION The principal objective of a good cooling water treatment programme is to:

• Prevent corrosion to extend equipment life,

• Inhibit scale and deposit build up and

• Control the growth of micro-organisms which can both-corrode and foul thesystem.

Proposed Scheme of Audit: The intent of cooling water treatment audit is three fold:

• Measure the Effectiveness• Improve upon the practices

• Standardize Improvements and Practices

In order to carry out the audit the following procedure is suggested:A. Review the current conditions and service standards This is the starting point and forms the baseline data. The following data should becollected:• Details of the treatment programme currently used.• Overall treatment performance currently achieved and history.• History of critical equipment and parameters.• Critical process data relevant to water treatment.

B. Gather records, data and statistics The data for screening should include:• Daily log sheets at operating levels• Daily water analysis data• Monitoring data and records• Data on microbial analysis• Data on corrosion rates measured• Consumption of chemicals• Specific observations - Nearby equipments, Leaks, etc• Seasonal variations

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C. Evaluate performance The performance evaluation is based on:• Corrosion control

• Microbial control

• Scaling & deposition control

• General water chemistry

D. Measure costs: Actual Vs. capability This data will allow for optimization of the feed rates of various chemicals and fine tunetheir frequency of addition to bring in direct benefits to the plant. Variations in theregular maintenance level can be reduced and the chemicals can be maintained in anarrower band of operation to avoid wide fluctuations and overfeed of chemicals.

E. Overall reviewOnce all the information is collated a detailed study of the data is necessary to suggestany improvements with regard to the system, and to bring in value addition and costbenefit.

5. CALCULATIONS

S. No. Properties Theoretical

Actual

1 Dry-Bulb Temperature 35°C 35°C

2 Wet-Bulb Temperature 29°C 29°C3 Cold water outlet

Temperature32°C 32°C

4 Hot water Inlet Temperature

42°C 42°C

5 Range 10°C 10°C6 Approach 3°C 3°C7 Effectiveness 0.76 0.768 Cooling Tower TR 144 1509 Circulation water flow

rate58 m3/hr. 64 m3/hr.

10 Head Loss 52 m 60 m11 Pump power 10.88 kW 11kW12 Fills cross-section area 6.49 m2 6.25 m2

13 Fills height 2.93 m 2 m14 C.O.C. 11.88 11.8815 Evaporation and drift

losses0.98 m3/hr. 0.5 m3/hr.

16 Blow down losses 0.08 m3/hr. 0.009m3/hr.

17 Total water losses 1.06 m3/hr. 0.51 m3/hr.

6. COST ANALYSIS

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Pump running cost:Volt 420 V

Current 17.6 Amp.Power consumed 12.54 KW

Cost of electricity Rs7.5/kWh Total cost of operation

Rs2954/day

Fan running cost:Volt 420 V

Current 9.3 Amp.Power consumed 6.6 kWCost of electricity Rs7.5/kWh Total cost of operation

Rs696/day

Chemical cost:Chemical Amou

nt

Frequency Cost per kg

(Rs)

Cost per

monthMAX Treat2521

500ml Daily 151 2265

MAX Treat 606 300ml AlternateWeeks

214 128.4

MAX Treat 608 300ml AlternateWeeks

214 128.4

MAX Treat2001

300ml Weekly 337 404.4

Total Chemical cost per month = Rs2926.2

Total Chemical cost per day = Rs97.54

Make up water cost:Water consumed perday

25.85 m3

Water cost Rs15/m3

Water cost per day Rs387

Maintenance and labor cost = Rs600/month= Rs20/day

Total cost per day = Rs3460

Cost of per m3 cooling water = Rs2.5

7. ENERGY SAVING OPORTUNITIES

i. Follow manufacturer's recommended clearances around cooling towers and

relocate or modify structures that interfere with the air intake or exhaust.

ii. Optimize cooling tower fan blade angle on a seasonal and/or load basis.

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iii. Correct excessive and/or uneven fan blade tip clearance and poor fan balance.

iv. Automatic adjustable pitch fans and variable-speed fans can provide closer contro

of tower cold water temperature than the on/off control strategy.

v. On old counter-flow cooling towers, replace old spray type nozzles with new square

spray, variable flow, and practically non-clogging nozzles.

vi. Periodically clean plugged cooling tower distribution nozzles.

vii. Optimize blow down flow rate, as per COC limit.

viii. Replace slat type drift eliminators with low pressure drop, self-extinguishing PVCcellular units.

ix. Monitor L/G ratio, CW flow rates w.r.t. design as well as seasonal variations. It

would help to increase water load during summer and times when approach is high

and increase air flow during monsoon times and when approach is narrow.

x. Monitor approach, effectiveness and cooling capacity for continuous optimization

efforts, as per seasonal variations as well as load side variations.

xi. Consider energy efficient FRP blade adoption for fan energy savings.

xii. Control cooling tower fans based on leaving water temperatures especially in case

of small units.xiii. Use of side stream filters for continuous filtration of circulating water. This wil

increase the C.O.C and thus decrease Blow Down.

8. LATEST TRENDS

8.1.Chemical Treatment Programs : The most commonly adopted methods include zinc and orthophosphate as the maincorrosion inhibitors along with organo-phosphonates and polymers for scale and deposit

control. Microbial control is done by addition of specific biodispersants.Corrosion Inhibition:

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With aromatic azoles it is possible to operate cooling water system at alkaline pH (8-9)with all organic water treatment formulations. It becomes especially useful in preventingthe usage of base for the control of pH. At higher pH the corrosion potential is lower andthe all organic composition provides adequate corrosion protection without the fear ofdeposition usually faced with inorganic salts used. The most widely used polymers are low molecular weight (2000 to 20,000) and usuallyuse acrylic acid as one of the monomers.Polymers are designed for specific functions like:• Calcium carbonate inhibition• Metal ion and their foulant control• Suspended matter dispersionMicrobial Control:It is important to control the formation of Biofilm very efficiently because they can causethe:• Reduction in plant performance by the growth of Biofilm.• Reduction in plant integrity due to microbial corrosion• Reduction in plant safety due to the growth of legionella.Biodispersants preferably should be non foaming or low foaming

Biodispersants are specific surfactants that target microbiological slime and biofilm anddislodge them from metal surfaces. Once brought into circulation, regular biocides(oxidizing or non-oxidizing) can then control these organisms by killing them.Some of the future trends in microbial control that are being worked on are:• Enzyme control of Biofilm• Ultrasound control of biofouling

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than clean water because a buildup of solid contaminants provides a buffer thatreduces the effects of treatment chemicals. A side stream filtration system canremove suspended particles, reducing the need for additional chemical treatmentssuch as dispersants and biocides.

• Lower maintenance cost: Traditionally, cooling towers are cleaned by draining thetower and having the sediment removed mechanically or manually from the sump.Costs associated with the cleaning process include downtime, labor, lost water, andadditional chemicals. Cooling systems that are cleaned via side stream filtrationroutinely provide longer periods of continuous operation before being taken off-linefor required maintenance.

• Improvement in productivity and reduction in downtime: When a coolingsystem is fouled or has scale buildup, production may be slowed due to inefficientheat exchange equipment. In some cases, the cooling system and heat exchangeequipment may need to be taken offline for repairs, decreasing production.

• Control of biological growth: Biological growth control and reduction can mitigate

potential health problems, such as those caused by Legionella. ASHRAE Guideline 12-2000 has basic treatment recommendations for control and prevention, stating thatthe key to success is system cleanliness. Legionella thrives where there are nutrientsto aid its growth and surfaces on which to live. Use of side stream filtration canminimize habitat surfaces and nutrients by maintaining lower particle levels in thewater stream.

8.4.Fan Control Strategies :Control of tower air flow can be done by varying methods: starting and stopping (On-off)of fans, use of two- or three-speed fan motors, use of automatically adjustable pitch fans,and use of variable speed fans.

On-off fan operation of single speed fans provides the least effective control. Two-speedfans provide better control with further improvement shown with three speed fansAutomatic adjustable pitch fans and variable-speed fans can provide even closer controof tower cold water temperature. In multi-cell towers, fans in adjacent cells may berunning at different speeds or some may be on and others off depending upon the towerload and required water temperature. Depending upon the method of air volume controselected, control strategies can be determined to minimize fan energy while achievingthe desired control of the Cold water temperature.

8.5.Pump Control Strategies: Typically, the water pump is connected to the different processes with a system of pipe

work. Instead of running at constant speed, the speed of the pump is adjusted byVariable Speed Drive (VSD) according to the temperature of process water leavingtemperature could be good indicator for the adequacy of condensing water flow rate.

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8.6.Special Fills

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From these data we can say that C6 is the best fill.

8.7.Variable Flow Nozzles:Cooling tower do not always have a constant heat load, so depending upon the loadpump needs to change its flow rate accordingly for energy saving. But Cooling Towermanufacturer do not allow reducing water flow rate below 80% because fills may get dryand becomes more prone to scaling. But now with the variable flow nozzles you can varythe water flow rate to save pump energy.Following are the advantages of variable flow nozzle:

• The Variable Flow nozzle has variable flow capability with an 8 to 1 turn down ratioallowing pumps to be cycle off during cool climatic conditions or when loadsdemands are down.

• The Variable Flow nozzle produces a square water distribution pattern, which willincrease thermal performance by 10% to 12%.

• The Variable Flow nozzle operates only 3” above the fill media reducing structuralheight requirements in new tower construction. Also this feature reduces towerpump head by approximately (2) ft.

• The Variable Flow nozzle operates at a sweet spot of only (1) lb of pressure ascompared to 2lbs or more for other nozzles.

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http://www.curtistech.com/spinfree-nozzle/variable-flow.shtml

http://www.curtistech.com/spinfree-nozzle/square-pattern.shtml

http://www.curtistech.com/spinfree-nozzle/close-operation.shtml

http://www.curtistech.com/spinfree-nozzle/low-pressure.shtml

http://www.curtistech.com/spinfree-nozzle/variable-flow.shtml

http://www.curtistech.com/spinfree-nozzle/square-pattern.shtml

http://www.curtistech.com/spinfree-nozzle/close-operation.shtml

http://www.curtistech.com/spinfree-nozzle/low-pressure.shtml




9. PROPOSED MODIFICATIONS

9.1.Type of Cooling Tower - Cross Flow and Counter FlowWhat is Common to both designs?1. Both are induced flow arrangements.

2. The interaction of the air and water flow allows for evaporation of water.

3. Both are draw-thru arrangement where a fan induces hot moist air out the discharge.

What is different in Cross-flow and Counter-flow designs? The comparative analysis is on the distinctive parameters:1. Fill MediaCounter-flow cooling towers utilize a plastic film fill heat exchange media and cross-flowtowers typically utilize a splash-type heat exchange media.

2. Space and Size ConstraintsCounter flow towers are compact and have a smaller footprint, but these tend to be tallerthan cross flow models .Cross Flow Cooling Towers are large because of the cavity leftbetween the fan and the fills.

3. Spray Pattern (Water Distribution)Counter flow towers use pressurized spray systems that are considered to be the mostefficient method of water distribution in a cooling tower. No sprinkler distribution ispossible in a cross flow cooling tower.4. Operating WeightCounter flow towers have low operating weight and thus find greater acceptability at rooflocations. Cross-flow operating weight is higher than the counter-flow tower.

5. Fill ArrangementFor the counter flow tower, the wet deck (fill media) is encased on all four sides. Theentire working system is guarded from the sun's rays and helps reduce algae growth. Air

inlet louvers serve as screens to prevent debris from entering the system. Cross-flow wetdeck (fill) is encased on two sides only. A cross-flow cooling tower where two opposed filbanks are served by a common air plenum is termed double flow arrangement.6. Fill SupportIn counter flow design, the wet deck (fill) is supported from structural supportsunderneath. This prevents sagging and creates a working platform on top of the fill forservice. In cross-flow design, the fill media is generally supported by rods. Wearing maydeteriorate the fill making it sag, which may affect performance.

7. Operating Efficiency

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Counter flow cooling towers are 25% more efficient than cross flow type. The reasonbeing that as the air is being sucked from the lower part of the cooling tower, it risesupwards, gets warmer and when it reaches the top, it is hottest at that point. Since thewater is flowing in the downward, it is the hottest at the top. Thus, the hottest of aimeets the hottest of water and evaporation is more and thus the cooling is more. In thecase of a cross-flow tower, air that passes the water is not capable of passing water atdifferent temperatures. Thus the level of cooling in this case is less.

8. MaintenanceCounter-flow towers are easy to maintain at cold-water basin level because they areopen on all sides with no restrictions from the wet deck. Cross flow towers are difficult toclean at the cold water basin under the wet deck because of limited access. Howeverwhile considering the cleaning of the nozzles, due to accessibility cross flow towers areeasier to maintain.

9. Initial CostCounter-flow towers are typically expensive to build and have higher initial cost v/scross flow towers as the cross flow towers usually use low cost fills.

ConclusionBased on the above mentioned parameters, counter flow seems to address all theexisting issues in the plant despite the higher initial cost.

9.2.Types of fills: There are two broad categories of fills - splash and film.

Splash fills: The lower thermal performance is due to the splash fill's inability to equalthe surface area of film fills coupled with the higher pressure drop of splash fills.

The designs can be grouped into two categories.• First category includes extruded "V" bars, flat bars, convex profiles and net shapes.

• Second category is grid packs

Splash Fills

Film fills - Allow water to flow on film, thereby exposing more area to heat transfer.

• Cross-fluted fills for counter flow or cross flow towers.

• Vertical-offset fills for counter flow towers.

• Vertical-flow fills for counter flow towers.

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Cross-fluted designs• Provide high thermal performance

• Have alternating fill sheets at 60o angles to one other, creating redistribution of waterat each sheet interface. They also offer improved water distribution in the direction ofthe fill pack. For optimum water distribution the fill installation be done in alternating

layers, each at a 90

o

angle to the adjacent layer .

Vertical-offset fills are a newer design• The majority of the water film travels in a vertical path.

• The larger flute openings and the higher water-film velocity makes the vertical-offsetfills less prone to fouling.

Vertical-flow fills• Address poor water-quality applications.

• The design directs the water in a vertical path, and microstructure and capillaryfeatures allow for water mixing and lateral water distribution. The higher watervelocity through the fill reduces fouling potential.

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Conclusion:No single type of fill is absolutely better than the other hence combining a vertical-flowfill with a high performance fill such as cross-fluted or vertical-offset on the top 1' (0.30m) will improve overall performance. The immediate layer of fill should be at 90o to thetop and bottom layer. This arrangement increases water mixing and helps ensure evendistribution of air and water, optimizing tower performance.At present only cross fluted fills are being used.Material Thickness. The most commonly used material thickness is 0.010" (0.25 mm).For applications where there is excessive wear due to maintenance conditions or uniquespray impingement, the material thickness of 0.015" (0.38 mm) should be considered

Non-glued Fill. Consider using non-glued, mechanically assembled fill, which has twoimportant advantages.First, if the fill packs are to be assembled at the site, the environmental and safety issuesof gluing packs may prohibit field assembly.Second, unglued mechanically assembled systems address long-term environmentaproblems. ISO14001 directs the use of best available technology to protect theenvironment.Temperature - CTI Standard 136 specifies a heat-deflection temperature of 160oF(71oC) for PVC, which is adequate for most applications.

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10.REFERENCE• Unit Operations McCabe and Smith

• Separation Process Principles Seader and Henley

• Mass Transfer Operations Robert E. Treybal

• http://www.energy.ca.gov/title24/2013standards/prerulemaking/documents/current/Reports/Nonresidential/HVAC/2013_CASE_WS4-CTWS_10.5.2011.pdf

• http://www.sanjoseca.gov/esd/PDFs/cooling.pdf

• http://www.waterworld.com/articles/iww/print/volume-10/issue-1/feature/-sidestream-filtration.html

• https://en.wikipedia.org/wiki/Cooling_tower

• http://www.cti.org/whatis/coolingtowerdetail.shtml

• http://che.sharif.edu/~heatlab/Lab/Benefit%20Book%20&%20Journal/Benefit%20book/Cooling%20Tower%20Thermal%20Design%20Manual.pdf

• http://www.waterworld.com/articles/iww/print/volume-10/issue-1/feature/-sidestream-filtration.html

•

http://spxcooling.com/en/green/leed/water-usage-calculator

• http://www.cheresources.com

• http://www.starcoolingtowers.com

• http://www.oceaniccooling.com/Frp-Induced-Draft-Cooling-Towers.aspx

• http://wextech.co.in/cooling-water-systems-%E2%80%93-audit-and-future-trends/

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http://www.energy.ca.gov/title24/2013standards/prerulemaking/documents/current/Reports/Nonresidential/HVAC/2013_CASE_WS4-CTWS_10.5.2011.pdf


http://www.sanjoseca.gov/esd/PDFs/cooling.pdf

http://www.waterworld.com/articles/iww/print/volume-10/issue-1/feature/-sidestream-filtration.html


https://en.wikipedia.org/wiki/Cooling_tower

http://www.cti.org/whatis/coolingtowerdetail.shtml


http://che.sharif.edu/~heatlab/Lab/Benefit%20Book%20&%20Journal/Benefit%20book/Cooling%20Tower%20Thermal%20Design%20Manual.pdf





http://www.cheresources.com/

http://www.starcoolingtowers.com/

http://www.oceaniccooling.com/Frp-Induced-Draft-Cooling-Towers.aspx

http://wextech.co.in/cooling-water-systems-%E2%80%93-audit-and-future-trends/



http://www.sanjoseca.gov/esd/PDFs/cooling.pdf



https://en.wikipedia.org/wiki/Cooling_tower







http://www.cheresources.com/

http://www.starcoolingtowers.com/

http://www.oceaniccooling.com/Frp-Induced-Draft-Cooling-Towers.aspx

http://wextech.co.in/cooling-water-systems-%E2%80%93-audit-and-future-trends/




• http://www.curtistech.com/variable-flow-nozzle/

• The most used link http://www.engineeringtoolbox.com

APPENDIX

Sample calculation:1. Reactor details and heat load calculation:

Organic solvent properties

density 1000 kg/m3

ΔHvap 125 kCal/kg

Cp 0.55 kCal/kg*K

waterproperties

density 995 Kg/m3

Cp 0.9 kCal/kg*K

Reactorproperties

Cp_steel 0.47 kCal/kg*K

Density 7.9 g/cm3

Heat load of:SSR I3 reactormass Condenser

Reactorbody

Product Rx OCN

Reactor capacity 6 kl Time of operation 48 hr

11.1419704

kCal/hr

Temperature_Initial 86 °C mass collected 2800 kg

Temperature_Final 55 °C Heat of vap. 125 kCal/kg

Cooling Time 0.8 hr

Batch Mass 5500 kg

Cp 0.55kCal/kg*K

Total heat117218

.8 kCal/hr7291.666

67 kCal/hr11.141970

4kCal/hr

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http://www.curtistech.com/variable-flow-nozzle/

http://www.engineeringtoolbox.com/

http://www.curtistech.com/variable-flow-nozzle/

http://www.engineeringtoolbox.com/




Inlet Outlet Inlet Outlet

Pipe length 10 6 Pipe length 2 2

Valves 1 1 Valves 1 1

Pipe Diameter 2" 2" Pipe Diameter 2" 2"

Bends 6 6 Bends 3 3

Total heat load for SSR13 = 124521.5586 kCal/hr.

Similarly, Total heat load for SSR12 = 124521.5586 kCal/hr.

Total heat load for SSR10 = 162229.5 kCal/hr.

Total heat load for oil vacuum pump = 5040 kCal/hr. Total heat load for dry vacuum pump = 44100 kCal/hr. Total heat load for Thin Film Evaporator = 10787.5 kCal/hr.

Therefore, total heat load on cooling tower = 471166.7 kCal/hr.

Cooling Tower TR = 124.58With 15% extra cooling tower TR will be = 144

Pump flow rate by energy balance: Total heat load = Cooling water flow rate*Cp*Range

Range = 10°C Therefore, Cooling water flow rate = 52.35 m3/hrWith 10% extra pump flow rate will be = 58 m3/hr

2. Head loss calculation:

Sample head loss calculation in pipes and fittings:Pipe losses = f*L*V2

D*2gFriction factor (f) can be calculated by calculating Reynolds number.Fluid velocity (V) in pipes can be calculated by corresponding flow rates.

Fitting losses = K*V2/2g

Given Data

Flow Rate (Q)m3/hr 0.062 0.00002 m3/s

Pipe Inside Diameter (D) mm 15 0.015 m

Kinematic Viscosity (ν) cSt 11.000E-

06 m2/s

Specific Roughness (Є) m1.50E-

06

Pipe Length (L) m 3

Calculated Data

Average Velocity - V (m/s) 0.10

Reynolds Number 1462Darcy Friction Factor 0.044 TOTAL 0.01

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HEADLOSS, hf (m)

Head Loss - Pipe (m) 0.00

Calculated Head Loss in Fittings, Valves,Entrances & Exits

K Qty

Sub

Total K Ball Valve, Full Port 0.05 2 0.1

Butterfly Valve 0.6 0 0Elbow 90 Degrees, LongRadius 0.6 0 0

Elbow 90 Degrees, Standard 0.9 23 20.7

Gate Valve 0.2 0 0

Globe Valve 10 0 0Pipe Entrance, InwardProjected Pipe 1 0 0

Pipe Entrance, Sharp Edge 0.5 0 0

Pipe Exit 1 0 0Tee, Standard, Flow ThroughBranch 1.8 0 0Tee, Standard, Flow ThroughRun 0.6 0 0

20.8 Head Loss - Valves & Fittings(m) 0.01

Head loss in reactors, condensers, etc:Sample calculation:Reactor coil head

loss:Length 104 mDiameter 80 mmflowrate

18.60792

m3/hr

0.005168866 m3/s

Velocity 2.06 m/sHeadloss 5.3 m

Total head loss

= 9.57 m

Similarly for others also head loss is calculated.

Resistance approach to head loss calculation:All components’ head loss is converted into corresponding resistance by followingformula:

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R =hL/F(1.75)




Resistance diagram:

R1+R2114522

.3

R3280806

7

R4

362321

8

R5114045

7

R6+R75873.0

28

R896043.

98

R9244246

4R10+R11

59629.75

R12

94052.

13

R13946999

.3

R14289901

.2

R15145872

7R16+R17

842.8413

R18179286

.9

R19244246

4

3. Tower height calculation:

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Overallresistance 43431.16

Head loss34.67731

13 mwith 15% extra,

hL

52.01596695 m




Design flow rate 52355 Kg/hrHot water temp.(T1) 42 °CCold water temp.(T2) 32 °CWet bulb temp.(Twb) 29 °CDry bulb temp.

(Tdb) 35 °C

Range 10 °C

Approach 3 °C

Effectiveness0.7692

31

Equilibrium line

T H

32 110

33 115

34 121

35 128

36 135

37 141

38 150

39 156

40 163

42.5 185

43.5 200

45 21646.5 230

50 258

For minimum gas flow rate a tangent line is drawn to equilibrium line.Minimum gas flow rate = 6.84184626Kg/sActual gas flow rate = 1.5*Minimum gasflow rate

= 10.26 Kg/s

H2 Enthalpy = 154333.3 J/Kg dry air

For liquid rate = 2.7 Kg/m2.s

Tower cross section area = 5.386375m2

For gas flow rate = 1.58 Kg/m2.s

Tower cross section area=

6.495424 m2 (This one is to be used.)

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TL H* (eq.)H

(op.)10^5/(H*-H)

area*105

32 111000 95000 6.2536397.

06

33 118000

10100

0

5.882352

94

34313.

73

34 12500010700

05.555555

5634313.

73

35 13000011300

05.882352

9421288.

52

36 13800011700

04.761904

7627922.

08

37 14500012300

04.545454

5529370.

63

38 15600013000

03.846153

8529370.

63

39 159000

13700

0

4.545454

55

12175.

32

40 16800014000

03.571428

5727619.

05

41 17800014800

03.333333

3325833.

33

42 18800015600

0 3.125278604

.1

Area under the curve=

2.786041

K y

*a*Z/G =2.786041K ya = 1.5

Therefore, Z = 2.93 mNtOG

=2.7860

41HtOG

=1.0533

33

4. Water analysis and losses:

CoolingTower

MakeupwaterTDS

BlowdownwaterTDS

COC

150 TR 93.6 1112 11.88034

Evaporation losses = 0.00153*Range*Circulation

= 0.88 m3/hr.Drift losses = 0.2% of circulation rate

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= 0.115 m3/hr.Blow down losses = Evaporation loss/ (COC – 1)

= 0.1 m3/hr

Total water loss = 1.08 m3/hr

5. Pump power calculation:Hydraulic power = Flow rate*ρ*g*hL/(3.6*106)

Shaft power = Hydraulic power/ηFlow rate 57.59

112m^3/hr

density 1000 Kg/m^3

g 9.81 m/s^2

head 52.01597

m

efficiency 0.75

Hydraulicpower

8.163168

kW

Shaft power 10.88422

kW

6. Cost analysis:

Pump and Fan Operating cost:

Pump 1 Pump 2* Fan

Actual amp. 17.6 8.4 9.3

Power 12547.25 5988.466630.0

8Operationtime 24 (optional) 14

Cost per day 2258.50 696.15 Total electricitycost/day = Rs 2954.66

*Only one pump is used at a time.

Make up water cost:MW perday

25.8554733 m^3

Cost of MW 15 /m^3

Total water cost perday = Rs

387.8321001

Chemicalcost:

Chemical Amount

Frequency

Costperkg

(Rs)

Costper

month

MAX Treat2521

500ml Daily 151 2265

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MAX Treat606

300ml AlternateWeeks

214 128.4

MAX Treat608

300ml AlternateWeeks

214 128.4

MAX Treat2001

300ml Weekly 337 404.4

Total chemical cost per month = Rs2926.2 Total Chemical cost per day = Rs97.54

Maintenance and labor cost per day = Rs20

Total cost per day = Rs3460

Total cost per hr = Rs144

Cooling water flow rate = 57.59m3/hr

Cost of water per m

3

= Rs2.5

Cooling Tower Jogender

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