1. Basic Cooling Water Treatment principles
John Cowpar
Area Manager
GE Water and Process Technologies

2. USING WATER

3. POTENTIAL PROBLEMS
CORROSION
DEPOSITION - Fouling
Biofouling
Scaling

4. Scale Formation Results in loss of heat transfer efficiency
Increased running costs
Danger of under deposit corrosion
Increased maintenance costs
Danger of bacteria
Health implications

5. Corrosion Destruction of plant Fouling Increased Biological Nutrients
increased maintenance costs
Fouling
loss of efficiency due to increased pumping costs
loss of heat transfer efficiency
Increased Biological Nutrients
fouling and health implications

6. Fouling Loss of heat transfer efficiency Under deposit corrosion
increase in running costs
Under deposit corrosion
increase in maintenance requirements
Increased biological nutrients
health implications
Blockages in system
increased operating costs and downtime

7. Objectives of Water Treatment
MINIMISE SCALE
MINIMISE CORROSION
MINIMISE FOULING
MINIMISE BIOFOULING
MAXIMUM SAFETY
MAXIMUM EFFICIENCY
NON-POLLUTING

8. WHAT CAUSES OUR PROBLEMS?

9. DISSOLVED SOLIDS e.g. CALCIUM MAGNESIUM SODIUM CHLORIDE BICARBONATE
SULPHATE
SILICA
IRON

10. DISSOLVED GASES
e.g. OXYGEN
CARBON DIOXIDE
NITROGEN
SULPHUR DIOXIDE

11. SUSPENDED MATTER DUST/DIRT CONTAMINANTS e.g. OIL
BIOLOGICAL e.g. ALGAE, FUNGI, BACTERIA

12. TYPICAL WATER ANALYSIS CHART

13. Water Analysis Result pH 7.7 Colour 3.00 HAZEN Turbidity 9.00 F.T.U.
Solids - Suspended mg/l
Chloride as Cl mg/l
Alkalinity as CaC mg/l
Ammoniacal Nitrogen as N ug/l
Iron (Total) as Fe ug/l
Manganese (Total) as Mn ug/l
Nitrate as N mg/l
Total Hardness as CaC mg/l
Sulphate as S mg/l
Silica - Reactive as Si mg/l
Sulphide as S mg.l
Carbon Dioxide - Free mg.l
Solids - Total Diss. at 180C mg/l
D.O. Concentration (Field Det.) mg/l
Coliforms <10 /100ml
E. Coli <10 /100ml
Faecal Streptococci <1 /100ml
Sulphite Red. Clostridia /20ml

14. Hardness
Hardness is due to calcium and magnesium salts dissolved in water
All hardness salts are less soluble in hot water than in cold water (they show inverse solubility)
Different hardness salts have different levels of solubility
Hardness is normally reported as calcium carbonate

15. EVAPORATION
WINDAGE
MAKE UP
M = E + W + B
BLEED

16. Useful Equations E=R/100 x Temp Drop(degF)/10
W=R x 0.2/100 ( Forced Draught)
W=R x 0.6/ (Natural Draught)
B=E/(C-1) -W
M=E + B + W

17. SCALE FORMATION SCALE CAN BE CONTROLLED BY: PRE-TREATMENT CHEMICALS
CONCENTRATION FACTOR

18. CORROSION
Iron ore is found in nature and requires a large input of energy to convert it into steel.
Steel corrodes in order to get back to its natural (lower energy) state
Corrosion is an electrochemical process

19. CORROSION CAN BE CONTROLLED BY:
REMOVAL OF OXYGEN ?
ADDITION OF CHEMICALS
CONTROL OF pH

20. Biofouling

21. What is Biofouling caused by?
FUNGI
ALGAE
BACTERIA

22. FOULING/BIOFOULING Can be controlled by Filtration
Control of Concentration Factor (bleed)
Dispersants
Biocides

23. Open Cooling
When evaporation occurs, the heat of evaporation is used to drive off the vapour
The loss of this energy results in a cooling effect in the water
Pure water is evaporated (gases may also be lost)
Dissolved solids remain in the water

24. Cooling Water
WATER DROPLET
COOLS BY:
EVAPORATION
RADIATION
CONVECTION

25. Control of Concentration
The number of times the solids build in the system water is termed the concentration factor (CF).
CF is controlled by bleed
to increase CF - decrease bleed
to decrease CF - increase bleed

26. Bleed Control Effect of too much or too little bleed:
Too much bleed :-
low concentration factor
waste of water
waste of treatment
Too little bleed:-
high concentration factor
danger of scale and fouling
increased nutrient in system
danger of biofouling

27. x
While increasing concentration factor reduces water use, it also increases nutrients in the system water, encouraging growth of bacteria and slimes. Therefore, we normally run most cooling systems between 2 and 5
Water
Use x x x x x
Concentration Factor

28. Non-biological Fouling
Treated by addition of dispersants
dispersants (antifoulants) coat the particles and so keep them apart
The dispersed particles are then removed from the system water
either with the bleed or via a side stream filter

29. Non-biological Foulants
Silt
Rust
Process contamination
all removed by dispersant/bleed
Oil
Grease
a different chemical is required but the principle is the same

30. MICROBIOLOGY

31. Microbiology in Industrial Cooling Systems
Problematic Microorganisms
The Biofouling Process
Water Treatment Biocides
Biocide Programming
Monitoring and Control

32. FUNGI
Although yeast and some aquatic fungi are normally unicellular, most fungi are filamentous organisms
Fungi form solid structures which can reach a considerable size
Some wood destroying fungi exist, associated with deterioration of tower timber
Fungi require presence of organic energy source
Exist at between 5 to 38 C and pH 2 to 9 with an optimum of 5 to 6

33. ALGAE Classified as plants as they grow by photosynthesis
Range in size from unicellular microscopic organisms to plants that can be up tp 50m in length
Single cells
Multi cellular

34. ALGAE Algae cannot survive in the absence of air, water or sunlight
Basic difference is that algae utilise CO2 and water using sunlight as the energy source to assimilate food
Large quantities of polysaccharides (slime) can be produced during algal metabolism
Plug screens, restrict flow and accelerate corrosion
Provide excellent food source
Exist between 5 to 65 C and pH 4 to 9

35. BACTERIA Universally distributed in nature
Great variety of micro organisms
Multiply by cell division
Slime formation
Pseudomonas (utilise hydrocarbon contaminants)
Sulphur bacteria - anaerobic sulphate reducing bacteria
Nitrogen cycle bacteria

36. FACTORS CONTRIBUTING TO MICROBIAL GROWTH
Rate of incoming contamination
Amount of nutrient present pH
Temperature
Sunlight
Availability of oxygen/carbon dioxide
Water velocities

37. THE BIOFOULING PROCESS
Bacteria prefer to colonise surfaces
enables production of biofilm which acts to protect and entrap food sources
Planktonic bacteria
free swimming in bulk water
Sessile bacteria
attached to surfaces

38. EFFECTS OF BIOFOULING
Fouling of: tower, distribution pipework, heat exchangers
Reduction in heat transfer efficiency
Lost production
Under deposit corrosion
Inactivation/interference with inhibitors

39. WATER TREATMENT BIOCIDES
Oxidising Biocides
Have the ability to oxidise organic matter eg. protein groups
Non-Oxidising Biocides
Prevent normal cell metabolism in any of the following ways :
Alter permeability of cell wall
Destroy protein groups
Precipitate protein
Block metabolic enzyme reactions

40. OXIDISING BIOCIDES Sodium Hypochlorite Hypobromous Acid
Chlorine dioxide
Ozone
Hydrogen Peroxide

41. Oxidising Biocides Rapid kill Cost effective Tolerant of contamination
e.g. Bromine, Chlorine Dioxide
Minimal environmental impact
e.g. Bromine, Ozone, Peroxide, Chlorine Dioxide
Ineffective against SRB’s
Low residual toxicity
Counts approaching potable water standards possible

42. Non Oxidising Biocides
Screen water
Select alternating biocide to prevent resistant strains from developing
Effective against SRB’s
Can protect system long after dosing.
Contain biodispersant
Higher dosage for kill possible
Environmentally some have rapid breakdown e.g. DBNPA

43. BIODISPERSANTS Improves penetration of biocide within bacterial slime
Disperse released bacteria and biofilm into bulk water for removal by blowdown
Reduces ability for bacteria to attach to system surface
Improves performance of both non oxidising and particularly oxidising biocides

44. Ultra Violet and Ultra Filtration
Physical Methods
Ultra Violet and Ultra Filtration
Only Effective At Point Of Use
Cannot Kill Sessile Organisms
Offer No Protection To Isolated Parts Of System (Static Areas)
Environmentally Acceptable.

45. Control of Concentration
The number of times the solids build in the system water is termed the concentration factor (CF).
CF is controlled by bleed
to increase CF - decrease bleed
to decrease CF - increase bleed