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Basic Cooling Water Treatment principles

Basic Cooling Water Treatment principles. John Cowpar Area Manager GE Water and Process Technologies. USING WATER. POTENTIAL PROBLEMS. CORROSION DEPOSITION - Fouling Biofouling Scaling . Scale Formation .

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Basic Cooling Water Treatment principles

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  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 • 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 • 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 5 mg/l • Chloride as Cl 44 mg/l • Alkalinity as CaC03 144 mg/l • Ammoniacal Nitrogen as N 0.140 ug/l • Iron (Total) as Fe 311 ug/l • Manganese (Total) as Mn 65 ug/l • Nitrate as N 4.0 mg/l • Total Hardness as CaC03 207 mg/l • Sulphate as S04 62.3 mg/l • Silica - Reactive as Si02 6.9 mg/l • Sulphide as S 0.015 mg.l • Carbon Dioxide - Free 2.50 mg.l • Solids - Total Diss. at 180C 347 mg/l • D.O. Concentration (Field Det.) 10.7 mg/l • Coliforms <10 /100ml • E. Coli <10 /100ml • Faecal Streptococci <1 /100ml • Sulphite Red. Clostridia 300 /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 0.6/100 (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 1 2 3 4 5 6 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 TOMICROBIAL 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. 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

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