cooling tower presentation

CW /Jaap Hoogland/ 16-10-2007 Seawater Cooling Tower Circuits 1

By: Jaap Hoogland

SPX Cooling Technologies GmbH


SUMMARY

Seawater recooling systems

Technique required for seawater cooling towers– Heat calculation– Construction material

Environment– Drift loss– Salt emission


ONCE THROUGH COOLING

A sea water filtration station, consisting of one bar screen and two travelling basket filters Electro Chlorination station

Cooling water pump

Chiller

100 %

100 %


HELPER or DISCHARGE COOLING TOWER

A sea water filtration station, consisting of one bar screen and two travelling basket filters Electro Chlorination station

Cooling water pump

Chiller

Cooling towers complete with pump pits

98 %

100 %


SEAWATER COOLING TOWER PLANT

A sea water filtration station, consisting of one bar screen and two travelling basket filters

Electro Chlorination stationSuppletion water pump

Chiller

Cooling towers complete with pump pits

4 %

3 %


Technique required for seawater cooling towers


Main Components of a Wet Cooling Tower

fan stack with diffusor

fan with gearbox, shaft and motor

plenum

drift eliminatorwater distribution

spray area

cooling fill

rain area with air inlet

cold water basin with outlet to the main pump(s)


blow- down

evaporation,drift loss

(droplet emission)Drift loss (min. 0.0005 %)

Blow-down

Evaporation

Make-up

Cooling Water Circuit

Principle of Wet Cooling

heat exchanger

CHILLER PLANTCHILLER PLANT

% of Circuit Water Flow

City Water

TSE SEAWATER

Evaporation 1,2 % 1,2 % 1,2 %

Conc. Factor 5 2,5 1,4

Make-up 1,5 % 2,0 % 4,2 %

Blow down 0,3 % 0,8 % 3 %


Salts in the Cooling WaterWhat differentiates seawater cooling towers from fresh water towers is the existence of dissolved minerals (salts) in the cooling water. Therefore, establishing the impact of salts in the cooling water is the single most important technical feasibility concern.

The areas of concern were identified as

• thermal performance• salt concentration• salt emission (Drift) and• environmental impacts as far as• material resistance.

Designing Seawater Cooling Towers Salts in the cooling water

Make-up Circulatingwater water

Brackish Water mg/l mg/l @ 3 -4 cycles Total Dissolved Solids 8000 24 - 32000 Sulfate (SO4) 450 1350 - 1800 Chloride (Cl- ) 4500 13500 - 18000

Sea Water mg/l mg/l @ 1.2 - 1.4 cycles Total Dissolved Solids 35000 42 - 50000 Sulfate (SO4) 2800 3400 - 4000 Chloride (Cl- ) 20 24000 - 28000


Thermal Performance

Salt in the water has four basic effects on its use as a coolant, only one of those is major. Salt lowers the vapor pressure of water, thus the water does not evaporate as readily. This makes it less as a effective coolant and reduces tower performance.

For the above reasons tower performance decreases by approximately 1.1% for every 10,000 ppm of salts in the cooling water.

Designing Seawater Cooling Towers Thermal Performance

Impact of salts in water upon vapor pressure Fresh water Salt water 1)Water Temp. 35 35 [°C]Air Temp. 30,6 30,6 [°C]Air Relative Humidity 60 60 [%]Liquid Vapor Pressure 5,62 5,42 [kPa]Air Vapor Pressure 2,63 2,63 [kPa]Liquid-Air Vapor Pressure Difference 2,99 2,79 [kPa]Liquid-Air Vapor Pressure Difference (of Fresh Water Condition) 100 93,2 [%]Performance loss 2) -- 5,4 [%]

1) At salts concentration of 50,000 ppm2) Performance loss (approximated as 80% of change in VP difference) = 0,8 x (1-0,932)


Designing Seawater Cooling Towers Thermal Performance

Impact on Design / Size of the cooling tower

Rejected Heat = Flow x Density x Spec. Heat x Cooling Range (DT)

fresh water : density = 1000 kg/m³, specific heat = 4.18 kJ/(kg.K)

sea water: density = 1030 kg/m³ specific heat = 3.96 (@ salinity 45000 ppm)

⇒

flow (sea) / flow (fresh) = 1.03 (for the same cooling capacity) !!!

⇒

cooling tower size or power consumption increases


Computerised DesignOur modern and updated computer design programs are taking into account the salt content depending on density and temperature.Therefore the design of the cooling tower will take place "on point" and no other adds are necessary.Only modern computer design programs, based on huge experience and test results, are able to determinate all parameters correctly to guarantee the most feasable and economical cooling tower design regarding size and type.

Designing Seawater Cooling Towers 3 Computerised Design


Technique required for seawater cooling towers


Materials for• Structural components

• Mechanical part

• Thermo- hydraulic part


Construction materials• Concrete

• Timber

• FRP


The Cooling Tower Environment:

• The warm, saturated, oxygen-rich cooling tower environment promotes rapid corrosion of metallic components.

• Most construction materials are relatively unaffected by salt water

• Temperature level and pH-value has to maintained• Wood and plastic are as good as concrete


Impact on concrete constructions

React with cementMay react with aggregateReaction causes destruction of concrete matrix

Sulfates (SO4 )

Attack steel reinforcementAttack metallic hardwareRapid loss of cross section may occurCorrosion by products result in expansion and cracking of concrete

Chlorides (Cl-)


Desired Properties:

Low absorption/permeability to provide maximumprotection to reinforcement.

High resistance to sulfate attack.

Corrosion resistance

Resistance against biological attack

Temperature resistance


No problems with fill, drift eliminator, spray nozzles and fan if water quality is within the limits

Steel parts made of high grade stainless steel ("Duplex" 1.4462 [316 L], 1.4539) or special coated

Mechanical part should be protected with suitablecoating for salt water application

General Recommendations for thermo- hydraulic & mech. part:


Environment


Cooling Tower DriftCirculating water is distributed as droplets or films to maximise surface area

Exit air from cooling tower contains water vapor, drift dropletsand condensate droplets

Amount of content are mainly regulated by:

Drift eliminator design

Design of water distribution

Ambient psychometric and wind conditions

Water chemistry

Environment


Drift Loss Different Types of Drift Eliminators

0

0,001

0,002

0,003

0,004

0,005

0,006

1 Layer TC 187/44 1 Layer TC 187/33 CDX 0802 layers TC 187/33

Dri

ft L

oss

[% o

f wat

er fl

ow r

ate]

Cooling Tower Drift Loss (Standard Data)

Environment


TC 187/33E2 Layers

Drift Loss as a Function of the Droplet Size(Total Drift Loss = 0.0005% of water flow rate)

0

0,0005

0,001

0,0015

0,002

0,0025

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

Droplet Size [µm]

Drif

t Los

s [%

of w

ater

flow

rate

]

Environment

or 1 Layers


WaterqualityFeature Feature Feature Feature

Make-up system Own intake stationConnection to Grey water system

Connection to Grey water system

Connection to DEWA pipe system

Blow down system (drain) Own outlet station

Connection to sewage water system or irrigation system



Condensor system Titanium Standard material Standard material Standard material

Cooling tower

Titanium/Duplex hardware, special coating, FAND for larger plants

Standard material, low fouling fill Standard material Standard material

Water treatment system

ElectroChlorination, Bromation, hardness stabilizer Biocide, Corrosion inhibitor Biocide, Corrosion inhibitor Biocide, Corrosion inhibitor

Requirements of Cooling Circuit

Seawater Normal Grey water Polished Grey water Potable water


Central unit 125.000 TR 535,1 MW

Cooling tower design dataHot water temparature 105 °F 40,6 °CCold water temparature 95 °F 35,0 °CEntrance Wet bulb temperature 86 °F 30,0 °CEntrance Relative humidity 50% 50%Waterflow 375.000 USGPM 85.125 m³/hSalinity of the seawater 3,50% 3,50%drift loss 0,0005% 0,0005%CF used for seawater 1,4 1,4CF used for Normal Grey Water 2,5 2,5CF used for Polished Grey Water 5 5CF used for Potable water 5 5

Water use based on 80% operation Seawater 4.895.482.415 USGal/year 18.531.416 m³/yearWater use based on 80% operation Normal Grey water 2.331.594.847 USGal/year 8.826.046 m³/yearWater use based on 80% operation Polished Grey water 1.748.893.127 USGal/year 6.620.280 m³/yearWater use based on 80% operation Potable water 1.748.893.127 USGal/year 6.620.280 m³/year

Total drain amount 80% operation Seawater 3.496.210.320 USGal/year 13.234.595 m³/yearTotal drain amount 80% operation Normal Grey water 932.322.752 USGal/year 3.529.225 m³/yearTotal drain amount 80% operation Polished Grey water 349.621.032 USGal/year 1.323.459 m³/yearTotal drain amount 80% operation Potable water 349.621.032 USGal/year 1.323.459 m³/year

This is the amount produced by a city of around 180.000 peopleThis is the amount produced by a city of around 130.000 people


Environment


Critical Zone

Cooling Tower

Dispersion AreaPrevailing Wind

UseUse ofofWindroseWindrose

Environment


Relative Immission as a Function of the Distance from CTComparison between Round Type and Cell Type

0%

10%

20%

30%

40%

50%

60%

70%

0 100 200 300 400 500 600 700 800 900 1000Distance from CT [m]

C/C

max

cell 20 m acrossround 20 mcell 20 m averagecell 20 m alonground 60 m

wind

Environment


Salt Immission at Ground Level (Relative Concentration)as a Function of the Cooling Tower Heightand the Distance from the Cooling Tower

0102030405060708090

100

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000Distance from the Cooling Tower [m]

15 m (cell)40 m60 m80 m

Environment


0

10

20

30

40

50

60

70

80

90

0,1 1 10 100

Distance from the coast [km] measured in Newport USA

Tota

l mas

s AS

SP

[µg/

m³]

source: AM S Journals Online, study Rossknecht , Elliot and Ramsey 1972

Environment

Cooling tower outlet will be arround 470-550 µg/m³


Objects of the Investigation

which will be referred to as:

Cooling tower conceptscell type cooling towers

case 1~50.000 TR

case 2~ 90.000 TR

Environment

circular cooling tower with forced draught fans

case 3~ 125.000 TR


Methods of the Investigation

Simulation of the flow in the surroundings of the cooling towers

calculated magnitudes:• velocity• pressure• temperature• mass ratio between wet air and dry air• relative humidity• flight path of salt water droplets

Environment


Boundary conditions of the calculationscell type cooling towers

Methods of the Investigation

windspeed

=

6 m/s

(at 10m height)profile

=

atmospheric boundary layerdirection

=

0°

and 90°temperature

=

5

°Cabs. humidity

=

0,43 % massratio

Environment


Salt emission

case 1, 50.000 TR winddirection = 0°

figure explaination:

colours

=

ratio local

salt

concentration

to salt

concentration

at the

outlet

of the

tower

[ unit

= % massratio](values

lower

than

100% represents

dillution)colourrange

=

red ≥

80%, blue

≤

20%

case 1, winddirection = 90°

increased

salt

concentration

close

to the

ground

50 storied bld

Results

Environment

Building needs to be at at least 400 m


case 2, 90.000 TR winddirection = 0° case 2, winddirection = 90°

increased

salt

concentration

close

to the

ground

Salt emissionfigure explaination:

colours

=

ratio local

salt

concentration

to salt

concentration

at the

outlet

of the

tower

[ unit


lower

than

100% represents


=

red ≥

80%, blue

≤

20%

Results

Environment

50 storied bld

Building needs to be at at least 500 m


downwash

Case 3 ~ 125.000 TR

Salt emissionfigure explaination:

colours

=

ratio local

salt

concentration

to salt

concentration

at the

outlet

of the

tower

[ unit


lower

than

100% represents


=

red ≥

80%, blue

≤

20%

Results

Environment

Nearest 50 Storied bld should be in approx. 400 m

50 storied bld


cold air

warm air

Cooling Fills

Water Distribution

Drift Eliminator

Arrangement of a Round Wet Cooling TowerArrangement of a Round Wet Cooling Tower

hot water inlet

cold water outlet


BuildingBuilding 75 m x 75 m x 38 m 75 m x 75 m x 38 m talltall ((aboveabove groundground))

125.000 TR central plant


Shell Shell couldcould bebe mademade of of frameworkframework structurestructure withwith claddingcladding



FloorsFloors forfor pumpspumps, , chillerschillers, , fansfans, and , and miscellaneousmiscellaneous



TheThe towertower cancan bebe divideddivided intointo 4 4 oror 8 8 sectorssectors



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