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

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Presentation on theme: "Basic Cooling Water Treatment principles John Cowpar Area Manager GE Water and Process Technologies."— Presentation transcript:

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

2 USING WATER

3 POTENTIAL PROBLEMS u CORROSION u DEPOSITION - Fouling Biofouling Scaling

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

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

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

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

8 WHAT CAUSES OUR PROBLEMS?

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

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

11 SUSPENDED MATTER u DUST/DIRT u CONTAMINANTS e.g. OIL u 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 CaC mg/l Ammoniacal Nitrogen as N 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 CaC mg/l Sulphate as S mg/l Silica - Reactive as Si mg/l Sulphide as S 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 u Hardness is due to calcium and magnesium salts dissolved in water u All hardness salts are less soluble in hot water than in cold water (they show inverse solubility) u Different hardness salts have different levels of solubility u Hardness is normally reported as calcium carbonate

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

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: u PRE-TREATMENT u CHEMICALS u CONCENTRATION FACTOR

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

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

20 Biofouling

21 What is Biofouling caused by? FUNGI ALGAE BACTERIA

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

23 Customer Training WT200C Page 23 Open Cooling u When evaporation occurs, the heat of evaporation is used to drive off the vapour u The loss of this energy results in a cooling effect in the water u Pure water is evaporated (gases may also be lost) u Dissolved solids remain in the water

24 Customer Training WT200C Page 24 Cooling Water WATER DROPLET COOLS BY: EVAPORATION RADIATION CONVECTION

25 Customer Training WT200C Page 25 Control of Concentration u The number of times the solids build in the system water is termed the concentration factor (CF). u CF is controlled by bleed u to increase CF - decrease bleed u to decrease CF - increase bleed

26 Customer Training WT200C Page 26 Bleed Control u Effect of too much or too little bleed: u Too much bleed :- u low concentration factor u waste of water u waste of treatment u Too little bleed:- u high concentration factor u danger of scale and fouling u increased nutrient in system u danger of biofouling

27 Customer Training WT200C Page x x x x x Concentration Factor Water Use 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

28 Customer Training WT200C Page 28 Non-biological Fouling u Treated by addition of dispersants u dispersants (antifoulants) coat the particles and so keep them apart u The dispersed particles are then removed from the system water u either with the bleed or via a side stream filter

29 Customer Training WT200C Page 29 Non-biological Foulants u Silt u Rust u Process contamination u all removed by dispersant/bleed u Oil u Grease u a different chemical is required but the principle is the same

30 Customer Training WT200C Page 30 MICROBIOLOGY

31 Customer Training WT200C Page 31 Microbiology in Industrial Cooling Systems Problematic Microorganisms The Biofouling Process Water Treatment Biocides Biocide Programming Monitoring and Control

32 Customer Training WT200C Page 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 Customer Training WT200C Page 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 cellsMulti cellular

34 Customer Training WT200C Page 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 Customer Training WT200C Page 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 Customer Training WT200C Page 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 Customer Training WT200C Page 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 Customer Training WT200C Page 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 Customer Training WT200C Page 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 Customer Training WT200C Page 40 OXIDISING BIOCIDES Sodium Hypochlorite Hypobromous Acid Chlorine dioxide Ozone Hydrogen Peroxide

41 Customer Training WT200C Page 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 SRBs Low residual toxicity Counts approaching potable water standards possible

42 Customer Training WT200C Page 42 Non Oxidising Biocides Screen water Select alternating biocide to prevent resistant strains from developing Effective against SRBs Can protect system long after dosing. Contain biodispersant Higher dosage for kill possible Environmentally some have rapid breakdown e.g. DBNPA

43 Customer Training WT200C Page 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 Customer Training WT200C Page 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 Customer Training WT200C Page 45 Control of Concentration u The number of times the solids build in the system water is termed the concentration factor (CF). u CF is controlled by bleed u to increase CF - decrease bleed u to decrease CF - increase bleed

46 Customer Training WT200C Page 46

47 Customer Training WT200C Page 47


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