Cooling water Chemistry & Chemical TreatmentPresented By: M Abbas Mahar

Engro Fertilizers limited

ContentsThis Presentation includes :

Cooling Water SourcesCanal & Raw Water ChemistryChemistry Control LimitsConsequences of Disturbed ChemistryMajor Cooling Water ProblemsChemical Treatment of Cooling Water Working of Added Chemicals.

Make-Up Sources For Cooling Water

1- Canal Water •Contain high Suspended Solids•Contain low Dissolved Solids

2- Well Water •Contain high TDS•Contain Low Suspended Solids

Make-Up Water Chemistry• Basic Chemistry of Make-up water can be summarized in the table below.

Control Limits Of Cooling water Chemistry

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 ppm2-Total Chloride 250 ppm3-Sulphates lesser than 585 ppm4-Iron 2 ppm5-Alkalinity 100-200 ppm6-pH must be controlled between 7.5-8.27-Total Hardness 600-1000ppm8-Conductivity 1000 -4000 microsiemen/cm

Threats Posed by Disturbed Chemistry

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.

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.

Chemistry related major cooling water problems

Major cooling water problems are1-Corrosion2-Scaling3-Biofouling4-Fouling

Corrosion:Main reasons of corrosion in cooling water operation are1-pH2-Dissolved gases like CO2,O2,H2S,NH33-Dissolved and Suspended solids4-Water velocity5-Temperature

Conditions for corrosion to occur

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 electrons2-A corrodable surface(ANODE) - one with electrons to loose3-An electron acceptor(CATHODE) - a place for the electrons to go4-An electrolyte, to close the circuit - conditions conducive for electron flow

Corrosion

4Fe ð 4Fe2+ + 8e-

2O2

Anode

8OH-

8e- + 2O2 + 4H2O ð 8OH-

4H2O

Cathode

4Fe2+ + 8OH- ð 4Fe(OH)2

O2 + 4Fe(OH)2 ð 2Fe2O3 + 4H2O

O2

Corrosion ControlIn 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)

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.

Corroison Inhibition

Anodic Inhibitors

Cathodic Inhibitors

ScalingAny of these materials deposited where they shouldn’t be in the cooling system

Calcium carbonateCalcium phosphateIron phosphateIron oxidesManganese oxidesCalcium sulfate Magnesium silicateSilicaZinc phosphateZinc carbonate, hydroxideAluminum phosphateCalcium fluoride

Factors Promoting Scale formation

Concentration Of SpeciesBulk Water TemperatureSkin TemperatureSystem pHIon PairsHeat FluxVelocity

Major ContributorMajor 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.

Scale Formation Steps

Scale Formation is a Series of Steps from the Soluble State to a Solid, Crystalline Scale

Scaling Remedy 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.

Bulab9067Bulab9067 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 velocityLower Heat FluxMetallurgy

Bio FoulingBio fouling is caused by:

AlgaeBacteriaFungi

Problem Caused by Bio Fouling

Slime & Bio Film formationCorrosion H2S Produced By SRB (Sulfate Reducing Bacteria) Under-deposit CorrosionScaling (Scale Nucleation Sites Created By Bio-film)Fouling(Entrapment of Suspended Solid And Debris By Slime And Bio-

film)

Treatment 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

Hypobromous acid is preferred over hypochlorous acid due to greater efficiency at high PH. and because of its lower environmental impacts

Reasons for using the Target Bromination concept

Dissociation Constants Bromamines as BiocidesCostBromamines 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.

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.

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

It is used to remove biofilm from heat transfer surfaces caused by trapped phosphates, silicates, metallic oxides, silt .