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 -
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
 increased
of plant
maintenance costs
 Fouling
 loss
of efficiency due to increased pumping
costs
 loss of heat transfer efficiency
 Increased
 fouling
Biological Nutrients
and health implications
Fouling
 Loss
of heat transfer efficiency
 increase
 Under
in running costs
deposit corrosion
 increase
in maintenance requirements
 Increased
 health
biological nutrients
implications
 Blockages
 increased
in system
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
pH
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
Sulphate as S04
Silica - Reactive as Si02
Sulphide as S
Carbon Dioxide - Free
Solids - Total Diss. at 180C
D.O. Concentration (Field Det.)
Coliforms
E. Coli
Faecal Streptococci
Sulphite Red. Clostridia
Result
7.7
3.00
9.00
5
44
144
0.140
311
65
4.0
207
62.3
6.9
0.015
2.50
347
10.7
<10
<10
<1
300
HAZEN
F.T.U.
mg/l
mg/l
mg/l
ug/l
ug/l
ug/l
mg/l
mg/l
mg/l
mg/l
mg.l
mg.l
mg/l
mg/l
/100ml
/100ml
/100ml
/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
EVAPORATION
WINDAGE
MAKE UP
M=E+W+B
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?
• FUNGI
• ALGAE
• 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
 Too
of too much or too little bleed:
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
x
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
x
x
1
2
3
4
x
x
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
filter
Customer Training WT200C
with the bleed or via a side stream
Page 28
Non-biological Foulants
 Silt
 Rust
 Process
 all
contamination
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
•
•
•
•
•
Problematic Microorganisms
The Biofouling Process
Water Treatment Biocides
Biocide Programming
Monitoring and Control
Customer Training WT200C
Page 31
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 32
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
Customer Training WT200C
Multi cellular
Page 33
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 34
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 35
FACTORS CONTRIBUTING TO
MICROBIAL GROWTH
•
•
•
•
•
•
•
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
• 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 37
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 38
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
Customer Training WT200C
Page 39
OXIDISING BIOCIDES
•
•
•
•
•
Sodium Hypochlorite
Hypobromous Acid
Chlorine dioxide
Ozone
Hydrogen Peroxide
Customer Training WT200C
Page 40
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 41
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
Customer Training WT200C
Page 42
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 43
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 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