In industrial and commercial applications, the water is used as a medium for the heat transfer in boilers, cooling towers and evaporative condensers. Naturally occurring impurities in water can cause these equipment to fail due to fouling, scale formation, corrosion and growth of microorganisms.

Scale is calcium carbonate or limestone. Most underground aquifers are made of limestone, and as such these waters are high in calcium carbonate ( as well as magnesium, iron, silica etc.).

Water from lakes, rivers, & oceans evaporates and changes from a liquid to a gaseous state. Vapor rises & cools then changes state into a liquid as rain. It may further change to snow or sleet. As this rain, snow or sleet falls back to earth it collects in rivers, lakes & oceans and it also percolates into the ground to recharge underground aquifers.

Rain water contamination with these gases makes the rain slightly acidic (acid rain). Ground water is in contact with many minerals including calcium, magnesium, iron, & silicone, etc. Surface waters are frequently laden with suspended contaminants and organic matter Mineral Reactions.

“Ground waters accumulate in limestone aquifers. Limestone is a mixture of calcium and magnesium carbonate. Ground-water, which is now slightly acidic, reacts with limestone in a neutralization reaction that forms a salt and a water of
neutralization. The salt formed by this reaction is a mixture of calcium and magnesium bicarbonate which is quite soluble. It is this reaction which is the source of most of the deposition and corrosion problems we experience in industrial water usage.”

Dissolved Solids:
“Calcium bicarbonate is a water soluble salt. A solution of calcium bicarbonate is clear, because the calcium and bicarbonate are present as atomic sized ions which are not large enough to reflect light. Some soluble minerals impart a color to the solution. Soluble iron salts produce pale yellow or green solutions. Although colored, these solutions are clear.”

Virtually all dissolved solids in water disassociate into ionic species. An ion is an atom or group of atoms that have an electrical charge. Those with plus (+) charges are called cations, and those with negative (-) charges are called anions. The names are derived from the polarity of direct current electrodes immersed in a solution of dissolved solids. Since unlike charges attract, the positively charged ions will be attracted to the negatively charged electrode (the cathode) and are therefore called “cations”. Conversely, the negatively charged ions will be attracted to the positive electrode (the anode) which results in their being called “anions”.

When referring to water impurities such as calcium, magnesium, bicarbonate, chloride, sulfate, etc., it should be understood that they are not present in their neutral elemental form, but carry electrical charges associated with their outer electron shell
structure. For example, calcium and magnesium (hardness) both carry a charge of plus 2 and are represented as the divalent cations Ca++ and Mg++. They can also be shown as Ca+2 and Mg+2. In the same respect, sodium and hydrogen, the latter not necessarily being an impurity, are monovalent cations and are represented by Na+ and H+ respectively. The abbreviation Ca, Mg, Na, H Cl etc. are standard chemical nomenclature for representing the elements. For every positively charged cation there must be an anions, or group of anions, with an equivalent negative charge. Ions made up of two or more different atoms are called “radicals”.

Suspended Solids:
“Suspended solids are substances that are not completely soluble in water and are present as particles. These particles usually impart a visible turbidity to the water.“

pH “Pure H2O exists as an equilibrium between the acid
species, H+ and the hydroxyl radical, OH -. In neutral water the acid concentration equals the hydroxyl concentration and at room temperature they both are
present at 10 (-7) gram equivalents (or moles) per liter. The “p” function is used in chemistry to handle very small numbers. It is the negative logarithm of the number being expressed. Water that has 10 (-7) gram equivalents per liter of hydrogen is said to have a pH of 7. Thus a neutral solution exhibits a pH of 7.”
Special Notation: pH is logarithmic- a change of one pH unit corresponds to a ten fold change in acid concentration. pH has an inverse nature: Acid concentration increases as the pH value decreases

Alkalinity has direct bearing on the potential for scale formation in cooling waters.
Therefore, control of alkalinity is one way of preventing scale from forming.

Pure water, as rain, picks up carbon dioxide from the atmosphere. As CO2 dissolves in water it reacts chemically to form carbonic acid according to the following reaction:

CO₂ + H _2O = H₂ CO₃

This small amount of carbonic acid is enough to lower the pH slightly and cause corrosion to metal parts in cooling towers.

Due to the initial loading of CO2, as the pH is raised, a gradual transformation into the bicarbonate ion occurs (HCO3). The bicarbonate changes to carbonate as the pH increases to 8.3. The three species: carbonic acid, bicarbonate and carbonate can be converted to one another by changing the pH of the water.

• Scale Formation : Calcium Carbonate.
• Corrosion: Free oxygen.
• Growth of microbiological organisms – Anti foulant microbial control.

Why does scale form in a recirculating cooling system?
1. Calcium becomes less soluble as water temperatures increase with-in the system.
2. Calcium becomes less soluble as the alkalinity increases with-in the system.
Notation #1 Precipitation occurs when a mineral becomes insoluble
Notation #2 Carbonate means, the mineral is in its raw state when precipitation occurs. Special Note: When we perform chemical tests, we are measuring and identifying only dissolved minerals not visible to the naked eye.

What is the cause of corrosion in a recirculated cooling system?

• Oxygen becomes less soluble as the water temperatures increase with-in the system.
• As the oxygen becomes insoluble, it then is released. It takes the shape of a bubble of air. This bubble of air will then attach its self to the piping & wetted surfaces, allowing a corrosion cell to develop.

Notation: Oxygen becomes entrapped in the system’s circulated water in the form of a free agent and as such will attack metal surfaces.

Polymers: are used synergistically with both yellow metal and mild steel corrosion inhibitors for greater extension of corrosion protection.
Azoles: used primarily as yellow metal corrosion inhibitors.
Molybdates: used primarily for mild steel corrosion protection.
Zinc & Zinc Phosphate combinations: also excellent mild steel corrosion inhibitors.

Polyacrylic Acids: Prevents any settling of suspended solids due to calcium-phosphate precipitation, as well as material brought into the system via airborne contamination.

Chlorine & Bromine are oxidizing agents and are used most effectively when systems are operating on pH control or alkalinity control [pH ranges between 6.8 to 7.8] Broad spectrum biocides are most effective in systems that are operating on total polymer control. Such systems will establish pH ranges between 8.35 to 9.0. All microbiocide dosages are based on system’s capacity and not on system’s evaporation ratio.

PPM = Method used to measure chemical levels in water
MMHOS= [Micromos/cm] another term used for measuring total dissolved solids [TDS] one can convert MMHOS to PPM by using the multiplier 0.9 to get PPM. the term milligrams per liter {MGPL} is equal to PPM

“P” ALKALINITY = Refers to the test indicator for alkali in water [phenolphtalein] a pink color will develop if pH is above 8.29] if a pink color develops there are carbonates present, if no color develops only bicarbonates are present”.

CYCLES OF CONCENTRATION = as water is evaporated, city water is added to keep the system’s water level in tact. Cycles are the number of times the water was replaced during the evaporation process. The method used is either test for chlorides and or TDS.
“M” ALKALINITY = (total alkalinity) refers to test indicator for alkali in water (methyl orange) after testing for “P” alkalinity the test is continued on the same sample to determine total alkalinity.

EVAPORATION = Water is broken into droplets by distribution plates or fill, or it is sprayed through a series of spray nozzles. Air is forced through the spray causing the water to be cooled by evaporation.

1. The all Polymer Treatment Program(pH levels in the system = 8.5 to 8.8) rely totally on polymers for both scale and corrosion control.ADVANTAGES:
   1. Can be controlled via a single product that can be fed into system “neat” directly from the container.
   2. If controlled properly it can be reasonably effective and is safer than pH control.DISADVANTAGES:
   1. Will cause an increase of water to be bled from the system due to the system’s demand for lower allowable cycles to concentrate within the system.
   2. Due to certain chemical limitations, it will require a greater effort and cost to control microbiological problems.
2. pH or alkalinity control program. (the pH levels reached in the system = 6.9 to 7.5)ADVANTAGES:
   1. Will allow much higher concentrations to develop within the cooling system.
   2. Will reduce operating cost: Both Water & Sewer Charges
   3. Will maintain cleaner heat transfer surfaces, assuring low energy cost.DISADVANTAGES:
   1. May require additional safety precautions.
   2. Requires much closer monitoring.
   3. Loss of control could cause damage to the system.

The Langlier Saturation index can predict how to balance the system’s water chemistry in a way that will prevent scale from forming on the system’s heat transfer surfaces. It allows you to change either the scale or corrosion potential of the cooling water. It will also allow you to determine precisely how many cycles of concentrations the system can hold. It can show you how to save millions of gallons of water every year at your plant.

The number of allowable cycles of concentrations of total dissolved solids permitted within the cooling water system is of utmost importance. We will learn how to employ the Langlier Saturation index to make these determinations.

1. Complete Water Analysis
   a) Total alkalinity or “M” alkalinity
   b) Total calcium hardness
   c) Total dissolved solids (TDS)
   d) Determine the system’s highest water temperature
   e) Calculate the system’s actual pH
2. Saturation Index chart

Langelier Calculations
Example:
Temperature : 140 Degrees F
pH: 7.8
Ca Hardness: 200 ppm
M Alkalinity: 160 ppm
TDS: 400

pCa = 2.70
pAlk = 2.50
C @ 120 = 1.56
Sum pH = 6.76 (pHs)
Actual pH = 7.80
LSI = +1.04
LSI: Best Range: Under + 1.9
Corrosive Water < 2.0 < 1.0 -0- 1.0 > 2.0 > Scale Forming Water

PROCEDURE:
To determine the RSI, first the pHs, (saturation pH) is calculated as follows: pHs = (9.3+A+B) – (C+D) Where A, B, C, and D are obtained from the table above, based on water analysis.

Then, using the actual pH of the water, calculate the RSI using this equation: RSI = (2 X pHs) – Actual pH.

For example, calculate the RSI of the following water: pH=8.5, TDS=1,000 ppm, Calcium=200 ppm Alkalinity=250 ppm, Temp=100 degrees F.
From the chart above, A=0.2, B=1.7, C= 1.95, D=2.45
The pHs = (9.3+0.2+1.7) – (1.95+2.45) = 6.8
The RSI = (2 x 6.8) – 8.5 = 5.1: a moderately scaling water

More Scaling 4.5   Target   6.5 More Corrosive

Work by professor W.F. Langelier, published in 1936 deals with the conditions at which water is in equilibrium with calcium carbonate. An equation developed by Langelier makes it possible to predict the tendency of calcium carbonate either to precipitate or to dissolve under varying conditions. The equation expresses the relationship of: pH, calcium, total alkalinity, dissolved solids, and temperature as they relate to the solubility of calcium carbonate in waters with a pH of 6.5 to 9.5. The result is known as the pHs. The difference between the actual pH of the sample water and the pHs is called the Langelier Saturation Index. If the index is positive, calcium carbonate tends to deposit. If the number is negative, calcium carbonate tends to dissolve. Zero indicates equilibrium. The Langelier Index was originally developed for water storage tanks.

The Stability Index developed by Ryzner uses the Langelier Index as a component in a new formula, which makes it possible to reliably predict the tendency of water to precipitate or dissolve calcium carbonate. This Index is based on normal operating conditions found in cooling water systems. The formula is:

Ryzner Stability Index = 2 (pHs) – actual pH system water

Where water has a Stability Index of 6.0 or less, scaling increases. Where the Stability Index exceeds 7.0, scaling may not occur at all. As the Stability Index rises above 7.5 the probability of corrosion increases. Use of the LSI and Ryzner together contributes to a more accurate prediction of the scaling or corrosive tendencies of water.

Maintain Scaling Index
LSI below 1.9 ppm.
RSI above 4.5 ppm.

Scale Inhibition: Organo phosphonate levels should be
maintained between 6.0 & 10.0 ppm.

Corrosion Inhibition: Molybdate levels should be
maintained between 0.5 ppm and 1.0 ppm.

Dispersants: Poly Acryllic acid levels should be
maintained at 4.0 ppm.
Yellow Metal Inhibitors: Azoles should be maintained at
1.8 ppm.
Tower Cleaning: Every 60 to 90 days
Pressure wash: tube bundle , sump, eliminators
Pull spray nozzles and flush manifold, clear all spray nozzles.

CORROSION: destruction of a metal by a chemical or Electro -chemical reaction.

CRYSTALLINE: having the properties of crystals such as definite geometrical configuration.

DEFOAMER: a chemical that reduces foaming in boiler, cooling or process water.

DEPOSIT: any one or combination of materials that have formed on the surface of tubes, headers or drums. The deposit may consist of corrosion products, scale, sludge or even water soluble salts left behind by evaporation of water.

DISPERSIVE: a material possessing surface active properties that interferes with the normal process of crystalline growth to prevent precipitates from forming in water. The dispersive must have the same electrical charge as the material tending to precipitate so that the charge on each ion or molecule is increased and the particles tend to repel each other.

END POINT: the point at which titration reactions are completed and the color of the indicator changes.

EROSION: the mechanical wearing away of metal by the action of a liquid or gas.

EXCESS: the quantity of chemical added over and above the theoretical amount necessary to produce a chemical reaction, to provide a driving
force that makes it proceed to completion more quickly, also used to refer to the amount maintained in the water to act as reservoir or emergency supply.
.
FREE CO₂: a term used to designate the carbon dioxide gas dissolved in water and not combined in the form of bicarbonates or carbonate ions.

GHOST POINT (GP): an intermediate end point in the soap hardness test of raw water occurring when the soap has reacted with all the calcium salts present. True end point occurs when the soap has reacted with magnesium as well as the calcium salts.

GRAINS PER GALLON (GPG): a unit of concentration equivalent to 17.14 parts per million.

HARDNESS: hardness of water is due to its calcium and magnesium content. Quantities are reported in terms of calcium carbonate. Hardness of raw water may be referred to as carbonate and non-carbonate hardness. Carbonate hardness is that portion of the total hardness, which combines with carbonate and bicarbonate ions. The remainder of the total hardness is that portion which combines with sulfate or other anions and this is known as non-carbonate hardness. Formerly it was customary to refer t carbonate hardness as temporary hardness and non-carbonate hardness as permanent hardness. The terms calcium hardness and magnesium hardness are occasionally used to differentiate the hardness due to one or the other of these elements.

INDICATOR: substances, which undergo a color, change when the end or equivalent point of a titration has been reached.

INHIBITOR: a material that reduces a normal tendency to cause scale or corrosion. Usually used to describe chemicals that almost eliminate corrosion through formation of protective films on a base metal.

PARTS PER MILLION (PPM): a measure of proportion by weight. One part per million means one part in a million parts as for example, one pound in one million pounds of water. 17.14 ppm equals 1 gpg.

pH: a numerical indication of the intensity of acidity or alkalinity present in a solution. Precisely defined, pH is the logarithm of the reciprocal of the hydrogen ion concentration.

POLYELECTROLYTE: a chemical that makes available very highly electrically charged ions in solution, used as a coagulant aid by increasing the charges on the coagulate which attract the materials to be removed from the water.

PRECIPITATE: a substance separated from a solution in a solid state because of a chemical or physical change as by the action of a reagent or a change in temperature.

REAGENT (ANALYTICAL): any substance which from its capacity for certain reactions is used in detecting, examining, or measuring other substances.

SATURATED SOLUTION: a solution which contains its normal capacity of a dissolved substance at a given temperature and pressure.

SCALE: a deposit on surfaces caused by actions or reactions at the point of deposition. Scale caused by corrosion results from corrosive attack at that point. Scale caused by salts precipitated from the water results in a direct crystalline growth on tube surface as the solubility limit is reached for various materials as concentrations and temperature are increased.

SEQUESTRING AGENT: any complexing or chelating agent which forms a water-soluble metal complex compound.

STANDARD SOLUTION: a solution that contains more of a substance than can normally be held in solution at a given temperature.

SUSPENDED SOLIDS: insoluble dispersed particles of greater than colloidal size. Suspended solids may be separated from the supporting liquid by filtration or sedimentation.

SYNERGIST: a substance added to increase the effect of another material. Normally the total effect is greater than that of the sum of the individual materials.

TRESHHOLD TREATMENT: the process of adding minute amounts of polyphosphate to inhibit precipitation of hardness by means of a surface-active action that prevents normal crystalline growth.

TITRATION: a volumetric method of analysis to determine the strength of a solution or the concentration of substances involving an indicator and the addition of measured increments of a standard reagent until an end point is reached.

TOTAL DISSOLVED SOLIDS (TDS): the total quantity of substances in solution stable to evaporation.

TREATED WATER: water which has had its chemical characteristics altered by a water conditioning process; usually a raw water which has been softened for feedwater make-up.

TURBIDITY: the quantity of finely divided particles suspended in a solution as measured by the optical obstruction of light rays.

WETTING AGENT: a chemical that reduces the surface tension of water, allowing it to penetrate into smaller crevices than normal

ALKALINITY: the capacity of a water for neutralizing acid.

ANION: an ion possessing a negative charge, which would be attracted to a positive pole (anode). Always the after part of a chemical compound such as the CO3 in CaCO3.

BLOWDOWN: the releasing of water from a system, such as a boiler or cooling tower, to decrease the concentration of suspended and/or dissolved solids.

CATALYST: a material added to influence the speed or completion of a chemical reaction without entering into the reaction itself.

CATION: an ion possessing a positive charge, which would be attracted to a negative pole (cathode). Always the front part of a chemical compound such as the Ca in CaCO3.

CHELATING AGENT: a compound which will inactivate a metallic ion with the formation of an inner ring structure in the molecule, the metallic ion becoming part of the ring.

COAGULANT: a material added to water containing silt, color, suspended or colloidal material for the purpose of collecting the particles into a heavier mass that settles more quickly. The coagulant must possess an opposite electrical charge from the suspended matter so that the mutual attraction results in a larger and heavier floc.

COLLOID: a insoluble substance dispersed in such a fine state of subdivision that will not readily settle and cannot be removed by ordinary filtration.

COMPLEXING AGENT: a compound that will inactivate a metallic ion

CONDUCTIVITY: a measurement of the electrical conductance of a solution.