KORANGI THERMAL POWER PLANT

“Boiler Water Chemistry (Philosophy, Factors

affecting the Water Quality”
 QUESTIONS & ANSWERS

Q.1. What is water? Define its composition

Water is a chemical substance with the chemical
formula H2O. Its molecule made up of two
hydrogen atoms and one oxygen atom: H2O and
connected by chemical bonding. Water is also
both a weak acid and a weak base—chemical
properties that allow it to function as a universal
solvent capable of dissolving many substances.

Q.2. What is chemical bonding?

Atoms in a molecule of any substance are joined together by a
process known as chemical bonding, where two or more atoms
mutually share one or more electrons. This bonding is
particularly strong in water.

Q.3. Define weak acid

A weak acid is an acid that dissociates incompletely. It does not

release all of its hydrogen in a solution, donating only a partial amount of its protons to
the solution. These acids have higher pKa than strong acids, which release all of their
hydrogen atoms when dissolved in water.

Examples of weak acids include acetic acid (CH3COOH) and oxalic acid (H2C2O4).

Q.4. Define weak base.

In chemistry, a weak base is a chemical base that does not ionize fully in an aqueous
solution. As Bronsted-Lowry bases are proton acceptors, a weak base may also be
defined as a chemical base in which protonation is incomplete. This result in a relatively
low pH level compared to strong bases. Bases range from a pH of greater than 7 (7 is
neutral, like pure water) to 14 (though some bases are greater than 14).
Q.5. How many states of water?

Water exists naturally in three states: a liquid (its most common form), a solid (ice), and
a gas (water vapor). It is the only substance on earth in which all three of its natural
states occur within the normal range of climatic conditions, sometimes at the same
time. Familiar examples of water in its three natural states are rain, snow or hail, and
steam.

Q.6. What are the physical and chemical properties of water?

The major chemical and physical properties of water are:

Water is a liquid at standard temperature and pressure. It is tasteless and

odorless. The intrinsic color of water and ice is a very slight blue hue,
although both appear colorless in small quantities. Water vapor is
essentially invisible as a gas.

Water is transparent in the visible electromagnetic spectrum. Thus

aquatic plants can live in water because sunlight can reach them. Ultra-
violet and infrared light is strongly absorbed.

Water is a good solvent and is often referred to as the universal solvent.

Substances that dissolve in water, e.g., salts, sugars, acids, alkalis, and
some gases – especially oxygen, carbon dioxide (carbonation) are known
as hydrophilic (water-loving) substances, while those that do not mix well
with water (e.g., fats and oils), are known as hydrophobic (water-fearing)
substances.

Pure water has a low electrical conductivity, but this increases

significantly with the dissolution of a small amount of ionic material such
as sodium chloride.

The boiling point of water (and all other liquids) is dependent on the
barometric pressure. For example, on the top of Mt. Everest water boils
at 68 °C (154 °F), compared to 100 °C (212 °F) at sea level. Conversely,
water deep in the ocean near geothermal vents can reach temperatures
of hundreds of degrees and remain liquid.

At temperature below 0oC it become solid (Crystallized ice).

At 218 bar 374oC the so called “Critical point” is reached, beyond which
the liquid phase is no longer distinguishable from the vapor phase.

Water has the second highest molar specific heat capacity of any known
substance, after ammonia, as well as a high heat of vaporization
(40.65 kJ·mol−1), both of which are a result of the extensive hydrogen
bonding between its molecules. These two unusual properties allow
water to moderate Earth's climate by buffering large fluctuations in
temperature.

The maximum density of water occurs at 3.98 °C (39.16 °F). It has the
anomalous property of becoming less dense, not more, when it is cooled
down to its solid form, ice. It expands to occupy 9% greater volume in this
solid state, which accounts for the fact of ice floating on liquid water.

Water is miscible with many liquids, such as ethanol, in all proportions,

forming a single homogeneous liquid. On the other hand, water and most
oils are immiscible usually forming layers according to increasing density
from the top. As a gas, water vapor is completely miscible with air.

Water is slow to heat up and slow to release heat compared to other
liquids.

Q.7. Define natural distribution of water on earth.

Water covers 71% of the Earth's surface; the

oceans contain 97.2% of the Earth's water. The
Antarctic ice sheet, which contains 61% of all
fresh water on Earth, is visible at the bottom.
Condensed atmospheric water can be seen as
clouds, contributing to the Earth's albedo.
Q.8. What are main Industrial applications of water?

There are various industrial applications of water;

Water is used in power generation.

Hydroelectricity is electricity obtained from hydropower. Hydroelectric power
comes from water driving a water turbine connected to a generator.

Pressurized water is used in water blasting and water jet cutters.

Very high pressure water guns are used for precise cutting.

It is also used in the cooling of machinery to prevent over-heating, or prevent
saw blades from over-heating.

Water is also used in many industrial processes and machines, such as the steam
turbine and heat exchanger.

In addition to its use as a chemical solvent

Industry requires pure water for many applications and utilizes a variety of
purification techniques both in water supply and discharge.

Q.9. What is water cycle? Define briefly.

The water cycle (known scientifically as the

hydrologic cycle) refers to the continuous
exchange of water within the hydrosphere,
between the atmosphere, soil water, surface
water, groundwater, and plants.
Q.10. What are the transfer processes of regional variations in water cycle?

Water moves perpetually through each of these regions in the water cycle consisting of
following transfer processes:

Evaporation from oceans and other water bodies into the air and
transpiration from land plants and animals into air.

Precipitation, from water vapor condensing from the air and falling to earth
or ocean.

Runoff from the land usually reaching the sea.

Q.11. What type of impurities and their effects in fresh water?

Q.12. How can common impurities are classified in boiler water?

The common impurities in raw water are classified as follows:

Dissolved solids

Suspended solids (Undisclosed Solids)

Dissolved gases

Scum forming substances

Hardness

Silica

pH value
Q.13. What type of dissolved solids exists in water?

The carbonates and sulphates of calcium and magnesium, which are scale-forming when
heated. For example;

CaCO3

MgCO3

NaCl

KCl. etc

Q.14. What type of suspended solids exists in water?

These are substances that exist in water as suspended particles.

CaCO3

Ca(PO4)2

CaSIO3

They are usually mineral, or organic in origin.

Q.15. What type of dissolved gases exists in water?

Oxygen, Carbon dioxide and Nitrogen can be readily dissolved by water.

These gases are aggressive instigators of corrosion

Q.16. What are Scum forming substances? Define with an example.

These are mineral impurities that foam or scum. One example is soda in the form of a
carbonate, chloride, or sulphate.

Q.17 Why hardness is caused in water?

Hardness is caused by the presence of the mineral salts of calcium and magnesium and
they are these same minerals that encourage the formation of scale. For example Ca,
Mg, Ba, Fe, Al etc.

Q.18 How water hardness is classified?

Water Hardness divided into two classes.

1. Alkaline hardness or temporary hardness.

2. Non Alkaline or permanent hardness
Q.19 What is alkaline hardness or temporary hardness? Define briefly.

Calcium and magnesium bicarbonates are responsible for alkaline hardness. The salts
dissolve in water to form an alkaline solution. When heat is applied, they decompose to
release carbon dioxide and soft scale or sludge.

Q.20. What is non-alkaline or permanent hardness? Define briefly.

This is also due to the presence of the salts of calcium and magnesium but in the form of
sulphates and chlorides. These precipitate out of solution, due to their reduced
solubility as the temperature rises, and form hard scale, which is difficult to remove.

Q.21. What is total hardness?

Temporary and permanent hardness combines to make total hardness.

Q.22. What is pH? Define briefly.

A measure of the relative acidity or alkalinity of water. Water with a pH of 7 is neutral;

lower pH levels indicate increasing acidity, while pH levels higher than 7 indicate
increasingly basic solutions.

Q.23. Define pH scale.

Q.24. What are Cations? Define common types present in water.

An ion or group of ions having a positive charge and characteristically moving toward
the negative electrode in electrolysis.

Mainly these cations are present in water Na+, K+, Mg2+, Ca2+ and Fe2+

Q.25 What are Anions? Define common types present in water.

An anion is a negatively charged ion, or an atom that has become negatively charged by
gaining one or more extra electrons.

Mainly these anions are present in water Cl-, So4 2- and HCO3-

Q.26 What are dissolved gases? Define common types present in water.

Dissolved gas is a situation which occurs when a gas becomes dissolved in another
solute.

Mainly these anions are present in water O2, N2 and CO2

Q.27. What is acid? Define briefly.

A substance that has a pH of less than 7, which is neutral. Specifically, an acid has more
free hydrogen ions (H+) than hydroxyl ions (OH-).

Q.28 What is alkaline? Define briefly.

Sometimes water or soils contain an amount of alkali (strongly basic) substances

sufficient to raise the pH value above 7.0 and be harmful to the growth of crops.

Q.29. What is alkalinity? Define briefly.

The capacity of water for neutralizing an acid solution.

Q.30. What is base? Define briefly.
A substance that has a pH of more than 7, which is neutral. A base has less free
hydrogen ions (H+) than hydroxyl ions (OH-).

Q.31 What is condensation? Define briefly.

The process of water vapor in the air turning into liquid water. Water drops on the
outside of a cold glass of water are condensed water. Condensation is the opposite
process of evaporation.

Q.32. What is desalination? Define briefly.

The removal of salts from saline water to provide freshwater. This method is
becoming a more popular way of providing fresh water to populations.

Q.33. What is evaporation? Define briefly.

The process of liquid water becoming water vapor, including vaporization from water
surfaces, land surfaces, and snow fields, but not from leaf surfaces.

Q.34. What is freshwater? Define briefly.

Water that contains less than 1,000 milligrams per liter (mg/L) of dissolved solids;
generally, more than 500 mg/L of dissolved solids is undesirable for drinking and many
industrial uses.

Q.35. What is hardness? Define briefly.

A water-quality indication of the concentration of alkaline salts in water, mainly

calcium and magnesium. If the water you use is "hard" then more soap, detergent or
shampoo is necessary to raise lather.

Q.36. What is maximum contaminant level (MCL)? Define briefly.

The designation given by the U.S. Environmental Protection Agency (EPA) to water-
quality standards promulgated under the Safe Drinking Water Act. The MCL is the
greatest amount of a contaminant that can be present in drinking water without causing
a risk to human health.

Q.37. What is milligram (mg)? Define briefly.

One-thousandth of a gram.
Q.38. What are milligrams per liter (mg/l)? Define briefly.

A unit of the concentration of a constituent in water or wastewater. It represents 0.001

gram of a constituent in 1 liter of water. It is approximately equal to one part per million
(PPM).

Q.39. What is million gallons per day (Mgd)? Define briefly.

A rate of flow of water equal to 133,680.56 cubic feet per day, or1.5472 cubic feet per
second, or 3.0689 acre-feet per day. A flow of one million gallons per day for one year
equals 1,120 acre-feet (365 million gallons).

Q.40. What is nephelometric turbidity unit (NTU)? Define briefly.

Unit of measure for the turbidity of water. Essentially, a measure of the cloudiness of
water as measured by a nephelometric. Turbidity is based on the amount of light that
is reflected off particles in the water.

Q.41. What is organic matter? Define briefly.

Plant and animal residues, or substances made by living organisms. All are based upon
carbon compounds.

Q.42. What is osmosis? Define briefly.

The movement of water molecules through a thin membrane. The osmosis process
occurs in our bodies and is also one method of desalinating saline water.

Q.43. What is oxygen demand? Define briefly.

The need for molecular oxygen to meet the needs of biological and chemical
processes in water. Even though very little oxygen will dissolve in water, it is extremely
important in biological and chemical processes.

Q.44. What is particle size? Define briefly.

The diameter, in millimeters, of suspended sediment orbed material. Particle-size

classifications are:

1. Clay—0.00024-0.004 millimeters (mm);

2. Silt—0.004-0.062 mm;
3. Sand—0.062-2.0 mm; and
4. Gravel—2.0-64.0 mm.
Q.45. What are parts per billion? Define briefly.

The number of "parts" by weight of a substance per billion parts of water. Used to
measure extremely small concentrations.

Q.46. What is parts per million? Define briefly.

The number of "parts" by weight of a substance per million parts of water. This unit is
commonly used to represent pollutant concentrations.

Q.47. What is saline water? Define briefly.

Water that contains significant amounts of dissolved solids.

Here are our parameters for saline water:

1. Fresh water - Less than 1,000 parts per million (ppm)

2. Slightly saline water - From 1,000 ppm to 3,000 ppm
3. Moderately saline water - From 3,000 ppm to 10,000 ppm
4. Highly saline water - From 10,000 ppm to 35,000 ppm

Q.48. What is sediment? Define briefly.

Usually applied to material in suspension in water or recently deposited from

suspension. In the plural the word is applied to all kinds of deposits from the waters of
streams, lakes, or seas.

Q.49. What is solute? Define briefly.

A substance that is dissolved in another substance, thus forming a solution.

Q.50. What is solution? Define briefly.

A mixture of a solvent and a solute. In some solutions, such as sugar water, the
substances mix so thoroughly that the solute cannot be seen. But in other solutions,
such as water mixed with dye, the solution is visibly changed.

Q.51. What is solvent? Define briefly.

A substance that dissolves other substances, thus forming a solution. Water dissolves
more substances than any other, and is known as the "universal solvent".
Q.52. What are suspended solids? Define briefly.
Solids that are not in true solution and that can be removed by filtration. Such
suspended solids usually contribute directly to turbidity. Defined in waste
management, these are small particles of solid pollutants that resist separation by
conventional methods.

Q.53 What is turbidity? Define briefly.

The amount of solid particles that are suspended in water and that cause light rays
shining through the water to scatter. Thus, turbidity makes the water cloudy or even
opaque in extreme cases. Turbidity is measured in nephelometric turbidity units
(NTU).

Q.54. What is water cycle? Define briefly.

The circuit of water movement from the oceans to the atmosphere and to the Earth and
return to the atmosphere through various stages or processes such as precipitation,
interception, runoff, infiltration, percolation, storage, evaporation, and transportation.

Q.55. What is water quality? Define briefly.

A term used to describe the chemical, physical, and biological characteristics of water,
usually in respect to its suitability for a particular purpose.

Q.56. What are common water measurements in boiler water?

Water temperature

pH

Specific conductance

Turbidity

Dissolved oxygen

Hardness

Suspended sediment

Q.57. What is Acidity? Define briefly.

The quantitative capacity of water to neutralize a base, expressed in ppm or mg/L

calcium carbonate equivalent. The number of hydrogen atoms that are present
determines this. It is usually measured by titration with a standard solution of sodium
hydroxide.
Q.58. What is Activated coal? Define briefly.

This is the most commonly used adsorption medium, produced by heating

carbonaceous substances or cellulose bases in the absence of air. It has a very porous
structure and is commonly used to remove organic matter and dissolved gases from
water. Its appearance is similar to coal or peat. Available in granular, powder or block
form; in powder form it has the highest adsorption capacity.

Q.59. What is Activated sludge? Define briefly.

Oxygen dependent biological process that serves to convert soluble organic matter to
solid biomass, that is removable by gravity or filtration.

Q.60. What is Bicarbonates? Define briefly.

Salts containing the anion HCO3-. When acid is added, this ion breaks into H2O and CO2,
and acts as a buffer.

Q.61. What is Biochemical Oxygen Demand (BOD)? Define briefly.

The amount of oxygen (measured in mg/L) that is required for the decomposition of
organic matter by single-cell organisms, under test conditions. It is used to measure the
amount of organic pollution in wastewater.

Q.62. What are Biological contaminants? Define briefly.

Living organisms such as viruses, bacteria, fungi, and mammal and bird antigens that can
cause harmful health effects to humans.

Q.63. What is Boiling point? Define briefly.

The temperature at which the vapour pressure of a liquid equals the pressure of its
surface. The liquid will than vaporize If the pressure of the liquid varies, the actual
boiling point varies. For water the boiling point is 100 degrees Celsius.
Q.64. What is Breakpoint chlorination? Define briefly.

Addition of chlorine to water until there is enough chlorine present for disinfection of
water.

Q.65. What is Brine? Define briefly.

Highly salty and heavily mineralised water, containing heavy metal and organic
contaminants.

Q.66. What is Buffer? Define briefly.

A substance that reacts with hydrogen or hydroxyl ions in a solution, in order to prevent
a change in pH.

Q.67. What is Carbonates? Define briefly.

Chemical compounds related to carbon dioxide.

Q.68. What is Carbonate hardness? Define briefly.

Hardness of water caused by carbonate and bicarbonate by-products of calcium and

magnesium.

Q.69. What is Catalysts? Define briefly.

Chemical that increases the rate of a reaction but does not take a direct part in the
reaction, so that it is still intact after the reaction has taken place.

Q.70. What is Chemical Oxygen Demand (COD)? Define briefly.

The amount of oxygen (measured in mg/L) that is consumed in the oxidation of organic
and oxidasable inorganic matter, under test conditions. It is used to measure the total
amount of organic and inorganic pollution in wastewater. Contrary to BOD, with COD
practically all compounds are fully oxidized.
Q.71. What is Chlorination? Define briefly.

A water purification process in which chlorine is added to water for disinfection, for the
control of present microrganisms. It is also used in the oxidation of compound
impurities in water.

Q.72. What is Conductivity? Define briefly.

The amount of electricity the water can conduct. It is expressed in a chemical

magnitude.

Q.73. What is Cooling tower? Define briefly.

Large tower used to transfer the heat in cooling water from a power or industrial plant
to the atmosphere either by direct evaporation or by convection and conduction.

Q.74. What is Corrosivity? Define briefly.

Ability of water to dissolve or break down certain substances, particularly metals.

Q.75. What is Desalination? Define briefly.

The removal of salt from seawater or brackish water to produce drinking water, using
various techniques.

Q.76. What is Dissolved oxygen? Define briefly.

The amount of oxygen dissolved in water at a certain time, expressed in ppm mg/L.

Q.77. What is dissolved solids? Define briefly.

Solids material that totally dissolves in water and can be removed by means of filtration.

Q.78. What is Distillation? Define briefly.

Water treatment method where water is boiled to steam and condensed in a separate
reservoir. Contaminants with higher boiling points than water do not vaporize and
remain in the boiling flask.
Q.79. What is Effluent? Define briefly.

The outlet or outflow of any system that deals with water flows, for an oxidation pond
for biological water purification. It is the product water of the given system.

Q.80. What is Electrical charge? Define briefly.

The charge on an ion, declared by its number of electrons. A Cl- ion is in fact a Cl atom
which has acquired an electron, and a Ca++ ion is a Ca atom, which has lost two
electrons.

Q.81. What is Electrolyte? Define briefly.

Substance that dissociates into ions when it dissolves in water.

Q.82. What is Electrolysis? Define briefly.

Process where electrical energy will change in chemical energy. The process happens in
an electrolyte, a watery solution or a salt melting which gives the ions a possibility to
transfer between two electrodes. The electrolyte is the connection between the two
electrodes, which are also connected to a direct current. If you apply an electrical
current, the positive ions migrate to the cathode while the negative ions will migrate to
the anode. At the electrodes, the cations will be reduced and the anions will be
oxidated.

Q.83. What is Ion? Define briefly.

An atom in a solution that is charged, either positively (cations) or negatively (anions).

Q.84. What is Ion exchange? Define briefly.

The replacement of undesirable ions with a certain charge by desirable ions of the same
charge in a solution, by an ion-permeable absorbent.

Q.85. What is Maximum Contaminant Level (MCL)? Define briefly.

The maximum level of a contaminant allowed in water by federal law. Based on health effects
and currently available treatment methods.
Q.86. What is Membrane? Define briefly.

A thin barrier that allows some compounds or liquids to pass through, and troubles. It is
a semi-permeable skin of which the pass-through is determined by size or special nature
of the particles. Membranes are commonly used to separate substances.

Q.87. What is Neutralization? Define briefly.

The addition of substances to neutralize water, so that it is neither acid, nor basic.
Neutralization does not specifically mean a pH of 7.0, it just means the equivalent point
of an acid-base reaction.

Q.88. What is Physical and chemical treatment? Define briefly.

Processes generally used in wastewater treatment facilities. Physical processes are for
instance filtration. Chemical treatment can be coagulation, chlorination, or ozone
treatment.

Q.89. What is Titration? Define briefly.

An analytical technique to determine how much of a substance is present in a water

sample by adding another substance and measuring how much of that substance must
be added to produce a reaction.

Q.90. What is TDS? Define briefly.

Total Dissolved Solids. The weight per unit volume of water of suspended solids in a
filter media after filtration or evaporation

Q.91. What is Viscosity? Define briefly.

The syrupiness of water and it determines the mobility of the water. When the temperature
rises, the viscosity degrades; this means that water will be more mobile at higher temperatures.
Q.92. What is VOC? Define briefly.

Volatile Organic Compound. Synthetic organic compounds which easily vaporize and are
often carcinogenic.

Q.93. What is Zero discharge water? Define briefly.

The principle of “zero discharge” is recycling of all industrial wastewater. This means
that wastewater will be treated and used again in the process. Because of the water
reuse wastewater will not be released on the sewer system or surface water.

Q.94. What are the properties, their effects and corrective action of feed water
treatment? Define each briefly.

1. pH
 Controlling the PH of water is the first step towards boiler treatment.
 We all know that if PH is below 7 the solution is acidic and above 7 it's alkaline.
 For boiler water PH is maintained between 11-11.8 and that of feed water
between 7-9.

Effects

If either of the values increases, water will accordingly become acidic or alkaline, leading
to detrimental effects caused due to acidic attack or caustic embrittlement. This may
damage the boiler completely.
2. Hardness

 The main purpose of controlling hardness is to prevent scale formation building

on the interior surface. This can be done by keeping hardness values low.
 Standard hardness value is kept less than 1 mg of CaCo3/liter.
 Hardness can be removed by using various phosphoric acid based chemicals in
the blow-down process of boiler.

Effects

In case layers of scales keeps on building inside the boiler, the insulation layer will
reduce, this in turn will prevent the heating of water and generation of steam. This will
lead to overheating and damage to the internal parts of the boiler, reducing the overall
efficiency.

3. Oil and fats

 Oil-in-water emulsion is quite common on ship. Proper care should be taken to
prevent any ingression of oil in the feed water.
 This is done in order to prevent carbonization of oil and formation of scales due
to boiler heat.
 Accumulation of oil will reduce the capability of heat transfer surfaces, thus
reducing the overall efficiency.
Effects

Carbonization and scale formation will lead to overheating of the boiler material and
parts, which may lead to serious damage to the boiler.

4. Dissolved oxygen
 When oxygen reacts with metal of the boiler, it causes corrosion. Thus it is
imperative to remove this dissolved oxygen. This can be done by adding
additives such as hydrazine to water.
 Standard value of hydrazine in water should be 0.1-03mg/l.

Effects

Prolonged corrosion leads to damage of boiler material and even rupture of internal
parts.
5. P alkalinity
 This is standard value of hydroxyl ion (OH) and carbonate ion (CO3) in water.
 The higher the value of P alkalinity, higher the probability of scales formation.
 The conventional boiler water test finds only the presence of OH and half of CO3.
 Standard value of P alkalinity in Boiler Water is between 50-300mg CaCO3/l.

Effects

Higher value of P alkalinity leads to scale formation and overheating of the inside of the
boiler causing internal damage.

6. Chloride ion
 It causes generation of scale formation. The more the chloride ions, the more
the scale formation.
 Therefore, it is necessary to limit it as low as possible. The problem with chloride
ions is that high degree of dissolution makes it difficult to remove them at a later
stage.
 It also serves as a standard of boiler water concentration together with total
solids.
 Formation of chloride ions can be done by controlling the amount and time of
boiler blow down.
 Standard value of chloride ion is less than 300 mg Cl/l.

Effects

The more chloride ions, the more the scale formation.

7. Phosphates

 Proper check on phosphates reserve of boiler water should be kept because it

reacts with calcium and forms calcium phosphates, which is a major scale
forming component
 When calcium phosphates are formed it precipitates on the water surface and
can be easily removed by blow down.
 Phosphates also contribute to the prevention of alkali corrosion and caustic
embrittlement.
 Standard value of Phosphate is 20-40 mg PO4/l.

Effects

It reacts with calcium and form calcium phosphate, which is major component.

8. Total Solids and electrical conductivity.

 The increase of total solids promotes deposition of scales in the boiler as well as
in the equipment consuming steam due to carry over.
 More amounts of dissolved solids also lead to more scale formation and carrying
over.

Effects

Carry-over of solids is a dangerous issue as it can leads to steam using machinery such as
high speed turbines etc.
Q.95. What is the principal of water chemistry control system in boiler water?

Minimizing metal corrosion / impurities in the system.

Controlling the formation of sludge in the system.

Minimizing calcium and magnesium scale formation on heat transfer surfaces.

Minimizing the potential for the formation of free caustic or acid in the system.

Maintaining less than 0.005 ppm (expected value) dissolved oxygen level in the feed
water system.

Q.96. What is the Importance of chemical dosing system in Power Industries?

1. Prevention of scale in the system

2. Prevention of corrosion in the system.

Q.97. How we can prevent the system from the scale and corrosion?

Through! External Water Treatment and Internal Water Treatment System.

Q.98. What is an External Treatment?

Treatment of water that is done outside of the boiler is called pre-boiler or external
treatment. The main physical methods for improving quality of water for boiler include
flocculation, clarification, deaeration, oil removal, colour removal, suspended solids
removal and blow down. When preparing water for boilers operated at less than 150
psi, all necessary chemical treatments can be accomplished in a clarifier, but as pressure
increases; the quality of feed water must improve. The purpose of external treatment is
to reduce suspended solids, demineralize the feed water and remove silica. This
purpose can be achieved by

Coagulation with chemicals

Demineralization/ Reverse osmosis/ Electrodialysis (cold lime, soda process,
hotlime-soda process, mixed bed exchange)

Silica removal (coagulation with chemical, Demineralization, Reverse Osmosis,
Electrodialysis)

Q.99. What is an Internal Treatment?

There are number of treatments that are made within the boiler to minimize the
adverse effects of small concentration of components that remain in the feed water
after the external treatment. In spite of various external treatments, it is not possible to
attain an absolute perfect quality of boiler feed water. Chemical treatment or internal
 treatment of water inside the boiler is essential to take care of various impurities
entering into the boiler such as hardness, dissolved solids, oxygen, and silica.

In many cases, external treatment of water supply is not necessary specifically in low or
moderate pressure boilers or where large amount of condensed streams are used or
when raw water available is of very good quality.

Q.100. When and why external treatment is required?

External treatment is required only in case where the impurity content in the water is
unacceptable high for the proper functioning of Cooling and Boiler system.

Q.101. What are the impurities which can be removed by external water treatment?

Some impurities, which can be removed by External Water Treatment include

suspended Solids, dissolved gases, dissolved salts, organic matter etc.

Q.102. How many processes are used in external / internal water treatment?

The various processes used in external / internal Water Treatment.

Clarification

Coagulation and Flocculation

Filtration

Ion Exchange Method (Demineralization )

Deaeration

Softening System (Lime Softening)

Softening System (Sodium Zeolite)

Reverse Osmosis (RO Plant)

Q.103. How many types of filtration process?

There are two types of filtration process.

1. Activated carbon filters

2. Ion Exchange Method (Demineralization)

Q.104. What is Activated carbon filters?

It is a physical process to remove any remaining suspended particles from water.

Q.105. What is Ion Exchange Method or Demineralization?

Removal of all kind of salts from the water is called demineralization.

Q.106. How many types of ion exchangers?

There is different type of ions exchangers:

Strong Acid Cation exchanger.

Weak Acid Cation exchange.

Strong Base Anion exchange.

Weak Base Anion exchange.

Q.107. Define deaeration process?

Dissolved gases in water can cause corrosion in the system. A Deareator is used to expel
the dissolved gases in particular oxygen. This also reduces the need for oxygen
scavengers.

Q.108. Sketch the flow diagram of routine water analysis.

Q.109. Sketch the flow diagram of demineralizing plant.

Q.110. What is the role of Ammonia / Morpholine in boiler water treatment?

1. Ammonia / Morpholine is injecting into the Condensate system.

2. To make the water alkaline side by increasing the pH (8.5- 9.0).
3. To minimize the corrosion or deposition of Iron & Copper in the Boiler drum.

Q.111. What is the role of Hydrazine / Sodium Sulphite in boiler water treatment?

1. Hydrazine is injected into the Feed Water System.

2. In spite of proper Deaeration Feed water also contain 5-10 ppb of dissolved O2
that can produces corrosion.
3. It is necessary to inject the Hydrazine to scavenge the Oxygen completely from
the water.
4. Dual phenomenal of Hydrazine: Oxygen itself reacts with hydrazine and produce
nitrogen and water
N 2 H4 + O 2 N2 + 2H2O

5. Theoretically 1 ppm of Hydrazine is required to react with 1 ppm dissolved

Oxygen.
6. A Hydrazine reserve in the boiler water is maintained in the range of 0.1 to 0.3
ppm.
7. Any excess hydrazine decomposes to form ammonia (NH3).
Q.112. Why Boiler Need Tri Sodium Phosphate Treatment?

Feed water contains slight amount of dissolved salts like Calcium and Magnesium

Constant evaporation in the boiler drum (steam production) causes increase dissolved
Solids in the boiler drum water.

These accumulated salts eventually create problems in terms of deposits, corrosion
& Carry over.

Q.114. Why (Phosphate) is being injected in the boiler drums?

(Phosphate) is being injected in the boiler drums in order to precipitate

Calcium & Magnesium salts As soluble phosphates in the water, which are eventually
removed from the system through CBD.

Na3PO4+ H2O Na2HPO4 + NaOH

3 Ca(HCO3)2 + 2 Na3PO4 Ca3(PO4)2 + 3 Na2CO3 + 3 CO2 + 3 H2O

Q.115. What causes in case of over dosing of PO4?

Over dosing of PO4 may cause severe corrosion carry problem.

Q.116. What is Blowing Down?

In many plants the amount and frequency of blowing down is determinated from a
chemical analysis of the water from the boiler. The amount of blow down depending
upon the quality of feed water and the amount of steam generated.

Q.117. What is the concentration of pure water?

The concentration of pure water is about 55 moles per liter.