basic cooling water treatment principles john cowpar area manager ge water and process technologies
TRANSCRIPT
Basic Cooling Water Basic Cooling Water Treatment principlesTreatment principles
John CowparArea Manager
GE Water and Process Technologies
USING WATERUSING WATER
POTENTIAL PROBLEMSPOTENTIAL PROBLEMS
CORROSION
DEPOSITION - Fouling Biofouling Scaling
Scale Formation 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
CorrosionCorrosion
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
FoulingFouling 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 Objectives of Water TreatmentTreatment MINIMISE SCALE MINIMISE CORROSION MINIMISE FOULING MINIMISE BIOFOULING MAXIMUM SAFETY MAXIMUM EFFICIENCY NON-POLLUTING
WHAT CAUSES OUR PROBLEMS?
DISSOLVED SOLIDSDISSOLVED SOLIDS
e.g. CALCIUM MAGNESIUM SODIUM CHLORIDE BICARBONATE SULPHATE SILICA IRON
DISSOLVED GASESDISSOLVED GASES
e.g. OXYGEN CARBON DIOXIDE NITROGEN SULPHUR DIOXIDE
SUSPENDED MATTERSUSPENDED MATTER
DUST/DIRT CONTAMINANTS e.g. OIL BIOLOGICAL e.g. ALGAE,
FUNGI, BACTERIA
TYPICAL WATER ANALYSIS CHARTTYPICAL WATER ANALYSIS CHART
Water Analysis ResultpH 7.7Colour 3.00 HAZENTurbidity 9.00 F.T.U.Solids - Suspended 5 mg/lChloride as Cl 44 mg/lAlkalinity as CaC03 144 mg/lAmmoniacal Nitrogen as N 0.140 ug/lIron (Total) as Fe 311 ug/lManganese (Total) as Mn 65 ug/lNitrate as N 4.0 mg/lTotal Hardness as CaC03 207 mg/lSulphate as S04 62.3 mg/lSilica - Reactive as Si02 6.9 mg/lSulphide as S 0.015 mg.lCarbon Dioxide - Free 2.50 mg.lSolids - Total Diss. at 180C 347 mg/lD.O. Concentration (Field Det.) 10.7 mg/lColiforms <10 /100mlE. Coli <10 /100mlFaecal Streptococci <1 /100mlSulphite Red. Clostridia 300 /20ml
HardnessHardness
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
EVAPORATION
WINDAGE
BLEED
MAKE UP
M = E + W + B
Useful EquationsUseful 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 FORMATIONSCALE FORMATION
SCALE CAN BE CONTROLLED BY:
PRE-TREATMENT
CHEMICALS
CONCENTRATION FACTOR
CORROSIONCORROSION
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 CORROSION CAN BE CONTROLLED BY:CONTROLLED BY:
REMOVAL OF OXYGEN ?
ADDITION OF CHEMICALS
CONTROL OF pH
BiofoulingBiofouling
What is Biofouling caused by?
• FUNGI
• ALGAE
• BACTERIA
FOULING/BIOFOULINGFOULING/BIOFOULING
Can be controlled by
Filtration Control of Concentration Factor (bleed) Dispersants Biocides
Customer Training WT200C Page 23
Open CoolingOpen 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 24
Cooling WaterCooling Water
WATER DROPLET COOLS BY:
EVAPORATION
RADIATION
CONVECTION
Customer Training WT200C Page 25
Control of ConcentrationControl 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 26
Bleed ControlBleed 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 27
1 2 3 4 5 6
xxx
x
x
Concentration Factor
WaterUse
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
Customer Training WT200C Page 28
Non-biological Fouling 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 29
Non-biological FoulantsNon-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 30
MICROBIOLOGYMICROBIOLOGY
Customer Training WT200C Page 31
Microbiology in
Industrial Cooling Systems
• Problematic Microorganisms
• The Biofouling Process
• Water Treatment Biocides
• Biocide Programming
• Monitoring and Control
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
Customer Training WT200C Page 33
ALGAE
• Classified as plants as they grow byphotosynthesis
• Range in size from unicellular microscopic organisms to plants that can be up tp 50m in length
Single cells Multi cellular
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
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
Customer Training WT200C Page 36
FACTORS CONTRIBUTING TOMICROBIAL GROWTH
• Rate of incoming contamination
• Amount of nutrient present
• pH
• Temperature
• Sunlight
• Availability of oxygen/carbon dioxide
• Water velocities
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
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
Customer Training WT200C Page 39
WATER TREATMENT BIOCIDES
• Oxidising Biocides– Have the ability to oxidise organic matter eg. protein
groups
• Non-Oxidising BiocidesPrevent normal cell metabolism in any of the following
ways :
– Alter permeability of cell wall
– Destroy protein groups
– Precipitate protein
– Block metabolic enzyme reactions
Customer Training WT200C Page 40
OXIDISING BIOCIDES
• Sodium Hypochlorite
• Hypobromous Acid
• Chlorine dioxide
• Ozone
• Hydrogen Peroxide
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 SRB’s
• Low residual toxicity
• Counts approaching potable water standards possible
Customer Training WT200C Page 42
Non Oxidising BiocidesNon 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
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
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.
Customer Training WT200C Page 45
Control of ConcentrationControl 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 46
Customer Training WT200C Page 47