Transcript USING WATER - SEAI - Welcome to the Sustainable Energy
Basic Cooling Water Treatment principles
John Cowpar Area Manager GE Water and Process Technologies
USING WATER
POTENTIAL PROBLEMS
CORROSION
DEPOSITION
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Fouling Biofouling Scaling
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
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
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
Objectives of Water Treatment
MINIMISE SCALE MINIMISE CORROSION MINIMISE FOULING MINIMISE BIOFOULING MAXIMUM SAFETY MAXIMUM EFFICIENCY NON-POLLUTING
WHAT CAUSES OUR PROBLEMS?
DISSOLVED SOLIDS
e.g. CALCIUM MAGNESIUM SODIUM CHLORIDE BICARBONATE SULPHATE SILICA IRON
DISSOLVED GASES
e.g. OXYGEN CARBON DIOXIDE NITROGEN SULPHUR DIOXIDE
SUSPENDED MATTER
DUST/DIRT
CONTAMINANTS e.g. OIL
BIOLOGICAL e.g. ALGAE, FUNGI, BACTERIA
TYPICAL WATER ANALYSIS CHART
Water Analysis Result pH 7.7
Colour Turbidity Solids - Suspended Chloride as Cl Alkalinity as CaC03 Ammoniacal Nitrogen as N Iron (Total) as Fe Manganese (Total) as Mn Nitrate as N Total Hardness as CaC03 3.00 HAZEN 9.00 F.T.U.
5 mg/l 44 mg/l 144 mg/l 0.140 ug/l 311 ug/l 65 ug/l 4.0 mg/l 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 Solids - Total Diss. at 180C 2.50 mg.l
347 mg/l D.O. Concentration (Field Det.) Coliforms E. Coli Faecal Streptococci Sulphite Red. Clostridia 10.7 mg/l <10 /100ml <10 /100ml <1 /100ml 300 /20ml
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
MAKE UP M = E + W + B EVAPORATION WINDAGE BLEED
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
SCALE FORMATION
SCALE CAN BE CONTROLLED BY: PRE-TREATMENT CHEMICALS CONCENTRATION FACTOR
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
CORROSION CAN BE CONTROLLED BY:
REMOVAL OF OXYGEN ?
ADDITION OF CHEMICALS CONTROL OF pH
Biofouling
What is Biofouling caused by?
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FUNGI
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ALGAE
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BACTERIA
FOULING/BIOFOULING
Can be controlled by Filtration Control of Concentration Factor (bleed) Dispersants Biocides
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 Customer Training WT200C Page 23
Cooling Water
WATER DROPLET COOLS BY: EVAPORATION RADIATION CONVECTION Customer Training WT200C Page 24
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 Customer Training WT200C Page 25
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 Customer Training WT200C Page 26
Water Use x
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
x x x x 1 2 3 4 5 6
Concentration Factor
Customer Training WT200C Page 27
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 Customer Training WT200C Page 28
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 Customer Training WT200C Page 29
MICROBIOLOGY
Customer Training WT200C Page 30
Microbiology in Industrial Cooling Systems
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Problematic Microorganisms The Biofouling Process Water Treatment Biocides Biocide Programming Monitoring and Control
Customer Training WT200C Page 31
FUNGI
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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
Customer Training WT200C Page 32
ALGAE
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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
Customer Training WT200C
Multi cellular
Page 33
ALGAE
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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
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Plug screens, restrict flow and accelerate corrosion
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Provide excellent food source
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Exist between 5 to 65 C and pH 4 to 9
Customer Training WT200C Page 34
BACTERIA
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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
Customer Training WT200C Page 35
FACTORS CONTRIBUTING TO MICROBIAL GROWTH
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Rate of incoming contamination Amount of nutrient present pH Temperature Sunlight Availability of oxygen/carbon dioxide Water velocities
Customer Training WT200C Page 36
THE BIOFOULING PROCESS
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Bacteria prefer to colonise surfaces
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enables production of biofilm which acts to protect and entrap food sources Planktonic bacteria
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free swimming in bulk water Sessile bacteria
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attached to surfaces
Customer Training WT200C Page 37
EFFECTS OF BIOFOULING
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Fouling of: tower, distribution pipework, heat exchangers Reduction in heat transfer efficiency Lost production Under deposit corrosion Inactivation/interference with inhibitors
Customer Training WT200C Page 38
WATER TREATMENT BIOCIDES
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Oxidising Biocides
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Have the ability to oxidise organic matter eg. protein groups
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Non-Oxidising Biocides Prevent normal cell metabolism in any of the following ways :
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Alter permeability of cell wall
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Destroy protein groups Precipitate protein Block metabolic enzyme reactions
Customer Training WT200C Page 39
OXIDISING BIOCIDES
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Sodium Hypochlorite Hypobromous Acid Chlorine dioxide Ozone Hydrogen Peroxide
Customer Training WT200C Page 40
Oxidising Biocides
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Rapid kill Cost effective Tolerant of contamination e.g. Bromine, Chlorine Dioxide
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Minimal environmental impact
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e.g. Bromine, Ozone, Peroxide, Chlorine Dioxide Ineffective against SRB’s Low residual toxicity Counts approaching potable water standards possible
Customer Training WT200C Page 41
Non Oxidising Biocides
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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
Customer Training WT200C Page 42
BIODISPERSANTS
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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
Customer Training WT200C Page 43
Physical Methods
Ultra Violet and Ultra Filtration
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Only Effective At Point Of Use
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Cannot Kill Sessile Organisms
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Offer No Protection To Isolated Parts Of System (Static Areas)
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Environmentally Acceptable.
Customer Training WT200C Page 44
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 Customer Training WT200C Page 45
Customer Training WT200C Page 46
Customer Training WT200C Page 47