ECISGROUP - Cooling Tower Water Treatment - Rev1

TRAINING

COOLING TOWERS WATER TREATMENTS

1Dr. Ing. Carlo Lebrun 1Dr.Ing. Carlo LebrunCooling Tower Water Treatments

COOLING TOWERS

Source: Wikipedia

Cooling Tower Water Treatments 2Dr.Ing. Carlo Lebrun

PROCESS DIAGRAM & WATER MATERIAL BALANCE


Drawing source: Wikipedia

KEY OPERATING PARAMETERS

- Cooling tower inlet water temperature- Cooling tower outlet water temperature

Water flow rate- Water flow rate

- Inlet air temperatureInlet air temperature- Air Humidity (higher humidity reduce cooling)- Air flow rate- Exhaust air temperature

Electrical readings of pumps and fans motors- Electrical readings of pumps and fans motors

- Cycles of Concentration (COC)


Cycles of Concentration (COC)

CYCLES OF CONCENTRATION (COC)

A measure of cooling tower operation efficiency also referred to as “cycles”

Compares 1 TDS (total dissolved solids mg/l)1 - TDS (total dissolved solids – mg/l)or2 - conductivity (microSiemens – uS) y ( )in the makeup water and in the blowdown water.

C l t TDS / k TDSCycles = system TDS / makeup TDSe.g. TDS 2,150 mg/l / 390 mg/l = 5.5 COC

5Dr.Ing. Carlo LebrunCooling Tower Water Treatments

COMMON WATER COOLERS TERMINOLOGY

-Drift: Water droplets that are carried out of the cooling tower with theDrift: Water droplets that are carried out of the cooling tower with the exhaust air. Drift droplets have the same concentration of impurities as the water entering the tower.

-Plume: The stream of saturated exhaust air leaving the cooling tower. The plume is visible when water vapor it contains condenses in contact with cooler ambient aircooler ambient air.

- Blow-down: portion of circulating water flow that is removed. N Hi h TDS ( l di l d lid ) i i l i l iNote: Higher TDS (total dissolved solids) concentration in solution results in greater potential cooling tower efficiency. However the higher the TDS concentration, the greater the risk of scale, biological growth and corrosion.


WHAT IS IN THE WATER?

- Suspended Solids

- Dissolved Solids (= dissolved salts)

Od i d- Odour causing compounds

- Biological ContaminantsBiological ContaminantsAlgaeFungiProtozoansBacteriaVirus


Virus

COOLING TOWER WATER TREATMENT

C l d C li T t t t t h i lCommonly used Cooling Towers water treatment chemicals are:

- Sodium Hypochlorite

- Biocide

Bi di t- Biodispersant

- Scale/Corrosion inhibitorScale/Corrosion inhibitor

- Sulphuric acid


EXAMPLE OF PROJECT DATA


TYPICAL INJECTION VALUES

-Sodium Hypochlorite keep total free chloride in system/blowdown waterSodium Hypochlorite keep total free chloride in system/blowdown water between 0.5 and 1.0 ppm (practically = mg/L)

-Biocide as per vendor recommendation,Biocide as per vendor recommendation, and change periodically

- Biodispersant as per vendor recommendationp pand change periodically

- Scale/Corrosion inhibitor as per vendor recommendation

- Sulphuric acid keep pH in system/blowdown water between 7 and 7.5



Commonly used Cooling Towers water treatment chemicals are:


- Biocide

- Biodispersantp

- Scale/Corrosion inhibitor

- Sulphuric acid


USE OF SODIUM HYPOCLORITE

- disinfection of stagnant water (biocide)

- limit fouling of pipes & equipment due to biological factors

NOTENOTE: it is an “oxidising” biocide which promotes corrosion, and environmental contamination (air & water)environmental contamination (air & water). Quantity should be limited.





Biocide- Biocide

- Biodispersantp


- Sulphuric acid


USE OF BIOCIDE

A id f li f i & i t d t bi l i l- Avoid fouling of pipes & equipment due to biological factors

NOTE 1: same purpose of sodium hypchlorite, but less corrosive and contaminant. Normally a non-oxidising biocide.

NOTE 2: effectiveness may vary in time as some bacteria may develop resistance (periodical checks required)

NOTE 3: effectiveness may be increased by correct water operating temperature:pcold water below 25°C and hot water above 55°C do not allow Legionella to grow


USE OF BIOCIDE (Legionella)

A very important reason for using biocides in cooling towers is to prevent the growth of Legionella, including species that cause legionellosis or Legionnaires' disease most notably L pneumophilaLegionnaires disease, most notably L. pneumophila.Various Legionella species are the cause of Legionnaires' disease in humans and transmission is via inhalation of mist droplets containing the bacteria.

Legionella can spread through the air up to 6 kilometres from a large contaminated cooling tower.

Periodical inspection of cooling tower are necessary to early detect any infection.


BIOLOGICAL AGENTS

AlgaeAlgae• food for bacteria• deposits may induce corrosion• deposits can reduce heat exchange deposits can reduce heat exchange• deposits can foul piping

FungiFungi• deposits can reduce heat exchange

BacteriaBacteria• some bacteria may cause health hazards (legionella)• sulphate reducing bacteria can produce hydrogen sulphide (corrosive!)





- Biocide- Biocide

- Biodispersantp


- Sulphuric acid


USE OF BIODISPERSANT

- cooperate with biocide to avoidcooperate with biocide, to avoid accumulations/concentrations of biological residues

- limit fouling of pipes & equipment due to biological factors


…





- Biocide- Biocide

- Biodispersant


- Sulphuric acid


USE OF SCALE/CORROSION INHIBITOR

- Scale & Deposit On Heat Transfer Surface

- Corrosion in pipes & equipment


SCALING


POSSIBLE SCALE CAUSING SALTS

Calcium Carbonate Magnesium SilicateCalcium Sulphate pZinc PhosphateCalcium Phosphate Calcium FluorideIron Oxide Iron CarbonateSilica Aluminium Hydroxide

Example reaction: C ++ + 2(HCO ) ¯ > C CO ( i it t ) + H O + COCa++ + 2(HCO3) ---> CaCO3 (precipitate) + H2O + CO2

Reaction is helped by concentration, high pH, high temperature


COST INCREASES DUE TO SCALING & FOULING

Reduced heat transfer efficiency and/or greater energy y g gylosses

Production losses

Reduced pipe diameters (greater pumping energy)

Increased maintenance cost


COST INCREASES DUE TO CORROSION

Loss of Metal and alloys

Replacement of product time and energyReplacement of product, time and energy

Loss of manpower due to shutdowns.AccidentsAccidents

Loss of Efficiency





- Biocide- Biocide

- Biodispersant


- Sulphuric acid


USE OF SULPHURIC ACID

- adjust pH level before discharge to effluent

- reduce scaling: acid treatment reduces [CO3] ions


HOW TO VERIFY THE COORECT RESULT OF CHEMICALS INJECTION?OF CHEMICALS INJECTION?


FEEDBACK ON WATER QUALITY

1 - feedback through lab analysis 2 - corrosion and scaling probes g p3 - equipment inspection are essential to evaluate the effectiveness ofare essential to evaluate the effectiveness of treatment and adjust chemicals injection to the correct quality and quantitythe correct quality and quantity.

F (d il kl t ) t b t dFrequency (daily, weekly, etc.) to be tuned on site real needs.


PERIODICAL TESTS OF WATER QUALITY

- Chemicals Residual Analysis- Corrosion Coupon Monitor

Fouling Depositor- Fouling Depositor- Microbiological Count Test- Hardness (both total and Calcium )Hardness (both total and Calcium )- Total Dissolved solids (TDS) - Total Suspended Solids (TSS)- pH- Chloride

Silica- Silica- Iron- Other …


Other …

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ECISGROUP - Cooling Tower Water Treatment - Rev1