2. This Presentation includes :
Cooling Water Sources
Canal & Raw Water Chemistry
Chemistry Control Limits
Consequences of Disturbed Chemistry
Major Cooling Water Problems
Chemical Treatment of Cooling Water
Working of Added Chemicals.
3. 1- Canal Water
•Contain high Suspended Solids
•Contain low Dissolved Solids
2- Well Water
•Contain high TDS
•Contain Low Suspended Solids
4. • Basic Chemistry of Make-up water can be
summarized in the table below.
5. Following are the significant factors that must be
controlled in the prescribed range of concentration for
proper working of cooling tower.
1-CaCo3 Maximum 500 ppm
2-Total Chloride 250 ppm
3-Sulphates lesser than 585 ppm
4-Iron 2 ppm
5-Alkalinity 100-200 ppm
6-pH must be controlled between 7.5-8.2
7-Total Hardness 600-1000ppm
8-Conductivity 1000 -4000 microsiemen/cm
6. Calcium Carbonate: If concentration increases
beyond 500ppm can cause severe scaling resulting in
subsequent loss of heat transfer .
Chloride: If concentration increases beyond 250ppm
can result in stress corrosion on steel and iron metal
surfaces.
pH: If prescribed limit disturbs it aids corrosion as at low
pH zinc hydro oxide will results in corrosion and at higher pH
Zn will precipitate in water causing scales.
Suspended Solids: If exceeds 40ppm then
1-Deactivate the scale inhibitors and cause fouling.
2-Provide site for the growth of micro organisms
resulting higher consumption of biocides.
7. Alkalinity: If exceeds beyond 100-200ppm will
result in scaling and higher acid consumption.
Conductivity: It is the measure of total ions
present in the system it increases the electrolysis
potential of water consequently more corrosion and
scaling if limit exceeds.
Ammonia: Its control limit is less than 20ppm .In
presence of ammonia the microbial control become
very tedious .Nitrifying bacteria uses ammonia and
form nitrates nitrites and nitric acid thus reducing
the pH of the system enhancing corrosion
damaging the passivation layer.Also chlorine reacts
with ammonia to form chloramines. Chloramines
are poor biocides and more stable than chlorine
thus harmful to environment.
8. Major cooling water problems are
1-Corrosion
2-Scaling
3-Biofouling
4-Fouling
Corrosion:
Main reasons of corrosion in cooling water operation are
1-pH
2-Dissolved gases like CO2,O2,H2S,NH3
3-Dissolved and Suspended solids
4-Water velocity
5-Temperature
9. For corrosion to occur, there must be
1-A difference in potential between two metals or
between different parts of a single metal- a driving
force for the electrons
2-A corrodable surface(ANODE) - one with
electrons to loose
3-An electron acceptor(CATHODE) - a place for
the electrons to go
4-An electrolyte, to close the circuit - conditions
conducive for electron flow
11. In Cooling tower we are adding Bulab 9063 for
corrosion inhibition
Working :
Bulab 9063 is Zinc Phosphate Zn3(PO4)2 corrosion
inhibitor.It serves as
Anodic inhibitor (suppresses metal dissolution at anode)
Cathodic inhibitor (interferes with oxygen reduction)
12. Zinc Phosphate ionizes in water to give Zn+2 and PO4-3
ions.
Zinc being more electropositive will lose more electron
and form Zinc Hydro oxide thus acting as Cathodic
inhibitor.
Orthophosphate acts as Anodic inhibitor forming a
passive iron phosphate film .Thus retarding the corrosion.
Calculated amount of zinc phosphate must be added to
cooling tower because this added phosphate if excess in
quantity results in scaling of heat exchange surfaces.
14. Any of these materials deposited where they
shouldn’t be in the cooling system
Calcium carbonate
Calcium phosphate
Iron phosphate
Iron oxides
Manganese oxides
Calcium sulfate
Magnesium silicate
Silica
Zinc phosphate
Zinc carbonate, hydroxide
Aluminum phosphate
Calcium fluoride
16. Major contribution in scale formation is of Calcium
and magnesium precipitated salts which are quite
adherent and difficult to remove .They are also
effective heat insulator thus reduces the efficiency of
heat transfer equipments.
CaCo3 Scaling:
Calcium carbonate is probably is the most recognized scale
forming component in water. It originates from Calcium
bicarbonate .At higher temperature and sharp rise in pH
cause Bicarbonate to decompose into carbonate and CO2.
17. Scale Formation is a Series of Steps from the Soluble State
to a Solid, Crystalline Scale
18. BULAB-7024 (Scale and Deposit Inhibitor)
It is a combination of scale inhibiting and dispersing
compounds for control of scale and suspended solids.
It is effective in controlling a variety of scale forming
substances, such as calcium carbonate, calcium
sulfate, barium sulfate and manganese oxides. It is
highly resistant to hydrolytic decomposition, even at
elevated temperatures and both high and low PH.
Calcium carbonate scale is primarily inhibited using
phosphonates and polymers in Bulab 7024.
It actually distort the crystal and acts as dispersant
not allowing it to get agglomerate and adhere.
19. Bulab9067 is high performance co-polymer providing
excellent Calcium Phosphate Scaling control. It is also
very effective in controlling the scale formation by Iron
Magnesium and slit.It works by crystal modification that
prevents Calcium Phosphate crystal from growing into
large fouling scale.
Other methods to control scaling are:
Increase velocity
Lower Heat Flux
Metallurgy
20. Bio fouling is caused by:
Algae
Bacteria
Fungi
Problem Caused by
Bio Fouling
Slime & Bio Film formation
Corrosion
H2S Produced By SRB (Sulfate Reducing Bacteria)
Under-deposit Corrosion
Scaling (Scale Nucleation Sites Created By Bio-film)
Fouling
(Entrapment of Suspended Solid And Debris By Slime And Bio-
film)
21. Following Chemicals are being added to control Bio
fouling in our Cooling tower:
Bulab-6041 (oxidizing Biocide)
(Aqueous Solution of Bromide)
Sodium bromide is a salt and has no oxidizing
capability until it is “activated”. It must be activated to
provide active bromine to a cooling water system. It is
activated by reacting it with hypoclorous acid (HOCL)
to yield hypobromous acid (HOBr) which is a strong
oxidizing biocide. Hypochlorous acid is generated
through addition of sodium hypochlorite or chlorine.
NaOCl + H2O → HOCl + NaOH
HOCl + NaBr → HOBr + NaCl
22. Hypobromous acid is preferred over hypochlorous acid
due to greater efficiency at high PH. and because of its
lower environmental impacts
23. Reasons for using the Target Bromination concept
Dissociation Constants
Bromamines as Biocides
Cost
Bromamines are more effective than chloramines in
the control of bacteria.
Bromamines break down more quickly than
Chloramines in the Environment.
Lower long term environmental toxicity.
At higher pH, reduction in chlorine consumption.
>Efficacy of bromamines over chloramines can
reduce total halogen needs.
24. BULAB-3847 (Non Oxidizing Biocide)
It is a non oxidizing biocide that can provide
broad- spectrum micro-organism control in
cooling water applications. It is a non foaming
water based product that is readily biodegradable.
Bulab- 3847 is very effective in controlling the
growth of nitrifying bacteria, which convert
nitrite into nitrate,Nitric acid and causes dips
in PH of cooling water.
It contains dispersing agents that ensure good
distribution through the system and efficient
penetration into the slime masses.
25. Bulab-3847 depends upon daily Nitrite (NO2) / Nitrate
(NO3) test. If these are greater than 30 PPM then shock
dose of bulab-3847 is fed to the cooling water.
BULAB-8006 (Bio dispersant and Bio
penetrant)
BULAB 8006 - Penetrant, Dispersant, Biodispersant is an
efficient penetrating and dispersing agent. It has
combined hydrophobic and hydrophilic nature.
It controls deposits caused by parafins,oils,pitch and
micro-organisms.
As biodispersant it enhance the performance of any
biocide including chlorine,Bromine etc.
It penetrates to bacterial colonies and expose them to
biocide
26. It is used to remove biofilm from heat transfer
surfaces caused by trapped phosphates,
silicates, metallic oxides, silt .
