1.
What are the sources of Boiler feed water?
River,
Underground water (bore well), pond water and sea water.
2.
What is make up water?
Raw
water, softened water or demineralized water used for steam generation is
generally called as make up water.
3. What are the various impurities present in untreated or
natural water?
- Undissolved
suspended materials: mud, sand, sediments etc.
- Dissolved salts and minerals:
Carbonate, bicarbonate, sulphates, silicate and nitrate of calcium &
magnesium.
- Dissolved
gases such as oxygen, carbon dioxide.
- Other
minerals, mineral acid (HCL & H2SO4) oil and grease.
4.
What is condensate water?
When the steam transfers
its heat to process or heat exchanger, it reverts to liquid phase called
condensate.
5.
What is blow down water?
Part of water that is
drained to limit the impurity level to an acceptable level.
6.
What is feed water?
Feed water is the sum of
condensate that is returned from process or heat exchanger and make up water.
7.
What is a total solid in water?
It is the sum of dissolved
and suspended solids in water.
8.
What is turbidity?
It
is the final suspended matter, which does not settle and imparts cloudy or
muddy color to water. It is measured in NTU.
9.
What is conductivity?
It is the ability of water
to conduct electricity in water. It indicates the amount of dissolved minerals
in water. It is measured in micro-seimen/cm. Conductivity of water increases
with increase in temperature. For example if water of conductivity 100 μS/cm at
25 °C increase to approx. 440 μS/cm at 100 °C
10.
What is pH of a solution?
- pH is the measure of
degree of acidity or basicity of a solution. pH range is 0 to 14, zero being
most acidic and 14 is most alkaline.
Key indicators of pH:
- A change of one pH value represents
the change of 10 times in relative acidity or alkalinity. For example a pH of 4
is 10 times more acidic than pH 5.
- In general, when the pH is less than
recommended ranges, then there will be chances of corrosion and if more then
there will be chances of scale formation.
- According to ASME standards, boiler
water pH level is maintained above 9.5 to ensure the proper reaction between
calcium and magnesium ions & phosphate molecules.
- Acids and alkalis have effect of
increasing the conductivity of water above the neutral value, for example a
water of pH 12 has more conductivity than that of pH 7.
11.
What is alkalinity of water?
It is the measure of
carbonates (Co3),
bicarbonates (HCO3)
and hydroxyl ions (OH).
12.
What is M alkalinity?
It is the sum of
carbonate, bicarbonate and hydroxyl alkalinity.
13.
What is Phenolphthalein or P alkalinity?
It is the sum of hydroxyl
alkalinity and half of carbonates alkalinity.
14.
What are Cation & anions?
Positively charged ions
like calcium Ca+, Magnesium
Mg+, Sodium Na+ and Potassium K+ are called cations.
Anions are negatively
charged ions such as nitrates, sulphates and chlorides.
15.
What is temporary hardness and permanent hardness?
Hardness caused due to
carbonate and bicarbonate salts is temporary hardness as it is soft scale which
can be removed easily.
Hardness due to sulphates
and nitrates is permanent hardness, such hardness is very hard to remove.
Hardness is measured in parts per million (ppm).
16.
What is Biological/Biochemical Oxygen Demand (BOD)?
Biochemical oxygen demand
(BOD) is a measure of the amount of oxygen that bacteria will consume while
decomposing organic matter under aerobic conditions. Biochemical oxygen demand
is determined by incubating a sealed sample of water for five days and
measuring the loss of oxygen from the beginning to the end of the test.
17.
What is chemical oxygen demand (COD)?
It is a measure of the
total quantity of oxygen required to oxidize all organic material into carbon
dioxide and water. COD values are always greater than BOD values, but COD
measurements can be made in a few hours while BOD measurements take five days.
18.
What does silica cause in Boiler water?
Silica causes hard scale,
it reacts with calcium and magnesium salts, which can form a scale and inhibit
heat transfer.
19.
How do you remove the hardness from water?
Hardness of water can be
removed by a process called “ion exchange” it is carried out in DM plant.
20.
How does scale effects on the performance of Boiler?
Water impurities like
magnesium, calcium and silica at higher temperatures precipitate and form a scale
on heat exchanger surfaces.
- Scale reduces heat transfer.
- Scale
reduces the internal diameter of pipe/tube.
- Scale
causes fuel wastage of water tube boiler by 2% and fire tube boiler by 5%.
- Scale increases the tube metal
temperature to rise, which increases the flue gas temperature and in extreme
condition tube may fail.
21. What are the principle factors cause scale formations in
boiler?
- Presence
of calcium, magnesium and silica salts in water.
- Insufficient
blow down.
- Alkalinity
of water (pH > 7).
- Higher
TDS.
- Low
condensate circulation.
22.
What is meant by cycle of concentration?
It is the ratio of makeup
water to the blow down rate.
23.
What are internal and external water treatments?
If the feed water chemical
and mechanical treatment is done outside the boiler by engaging filtration,
clarification, osmosis and demineralization process, then it is called as
external treatment.
If the feed water chemical
treatment is done inside the boiler by chemical dosing, then it is called
internal treatment.
24.
Write the sequence of water treatment in external water treatment?
Sedimentation, clarification,
sand filtration, ultra filtration, reverse osmosis, degassing and
demineralization.
25.
How does the internal chemical treatment work?
Two methods
used to control the hardness in internal treatment, one is carbonate cycle and
phosphate cycle. Carbonate cycle is employed in the boiler operating pressure
125 PSIG (up to 9 k/cm2)
and Phosphate cycle for above 125 PSIG.
26.
How does the scale conditioning work?
Scale conditioner modifies
the crystal structure of scale creating a bulky transportable sludge instead of
hard deposit.
27.
What causes the corrosion of Boilers?
Dissolved gases like
oxygen, carbon dioxide and ammonia are the major sources of corrosion. Of these
oxygen is most aggressive.
28.
What type of corrosion exists in boiler water systems?
The most common type of
corrosion is “Pitting” attack, the main source of pitting is oxygen. These
cause small pin type holes that penetrate into the wall of tubes and eventually
lead to tube failure.
29.
What water characteristics affect the corrosion?
Following factors affect
the corrosion.
- Oxygen/other dissolved gases
- Total
dissolved and suspended solids
- Acidity
(pH < 7)
- Fluid
velocity
- Temperatures
30.
How does the velocity of fluid influences the rate of corrosion?
High velocity of fluid
increases the corrosion rate by transferring the oxygen to metal and carrying
away the corrosion byproducts at the faster rate.
Low velocity of fluid
causes the deposition of suspended solids can establish localized corrosion
cells, thereby increasing the corrosion rate.
31.
Which inhibitors are commonly used to remove oxygen from feed water?
Sodium sulphite,
hydrazine, carbohydrazide and diethyl hydroxide amine are the commonly used
oxygen scavengers.
32.
What inhibitors are used to remove carbon dioxide from feed water?
Amines (Filming amines
& neutralizing amines).
33.
What is hard water?
When water is
referred to as ‘hard’ this simply means, that it contains more minerals than
ordinary water. These are especially the minerals of calcium and magnesium. The
degree of hardness of the water increases, when more calcium and magnesium
dissolves. Magnesium and calcium are positively charged ions. Because of their
presence, other positively charged ions will dissolve less easily in hard water
than in water that does not contain calcium and magnesium.
34-How is regeneration
process is accomplished in demineralization plant?
Regeneration
Process:
Back
Wash: Flow of water through mineral bed is reversed. The mineral bed is
loosened and accumulated sediments wash out to drain by upward flow of water.
Brine/Acid
Draw and Slow Rinse: Ordinary salt (NaCl) and hydrochloric acid (HCl) of concentration
33% have the capacity to restore the ion exchange capacity of resins. A given
amount of salt or acid is rinsed with the resin bed. The rinsing of resin will
continue till all the salt/acid is removed from bed.
Generally 3 to 5% of acid
is used for strong acid cation (SAC) regeneration.
Fast Rinse: In fast rinse small traces of salt and acid will get remove.
35-What
is the significance of degasser unit?
Degasser is an
integral part of any demineralization plant, where it is generally placed
between cation and anion exchanges and removes Carbon Dioxide, which is
generated by dissociation of carbonic acid at cation outlet water. In this
Degassing processes, Degasser Tower is utilized, which is made from either FRP
or Mild Steel with rubber lined or epoxy coating. Low air pressure is generated
at the bottom of the tower that drives out CO2 and the degassed water is
collected in a sump beneath the tower.
36-What is the
conductivity and silica of water at mixed bed outlet?
Conductivity 1–2 mico
siemens/cm and silica 0.01 to 0.02 ppm.
37.
What is meant by output between regeneration (OBR)?
OBR is the mean time
between two successive regeneration process. Generally it is expressed in M3 or
in hour. OBR depends on water quality and resin quality.
38.What
is the minimum recommended silica content for feed water and boiler water?
Feed water: 0.015 to 0.02
ppm.
Boiler water: 1.5 to 2 ppm.
39. What is the
recommended Hydrazine residual in feed water?
It is 0.01 to 0.02 ppm.
40.
What is the recommended Tri sodium phosphate (TSP) residual inboiler drum
water?
It is 5 to 10 ppm.
41. Why
HCl is more preferred for the regeneration of cation than Sulphuric acid?
Hydrochloric
acid is more efficient than sulphuric acid to regenerate a strongly acidic
cation exchange resin (SAC) initially in the Na1 form. With 50 g HCl per litre
of resin, a conversion of 60% to the H1 form is achieved. With 50 g H2SO4, a
conversion of only 40% is achieved. Even expressed as equivalents, hydrochloric
acid is more efficient: 36.5 g HCl (1 eq) will convert the resin to 45%,
whereas 49 g H2SO4 (1 eq) convert only 39%.
42. List out the
hazardous chemicals used in Water treatment plant.
Most hazardous chemicals are Hydrochloric
acid, Sulphuric acid, Caustic soda & Ferric chloride.
43. What is jar test?
The purpose of
the laboratory jar test is to select and quantify a treatment program for
removal of suspended solids or oil from raw water or a dilute process or waste
stream. Jar tests are conducted on four or six-place gang stirrer, which can be
utilized to simulate mixing and settling conditions in a clarifier. Jars
(beakers) with different treatment programs or the same product at different
dosages are run side-by-side, and the results compared to an untreated jar, or
one treated with the current program.
44. What are the
different parameters of coals which are analyzed in lab?
Proximate
Analysis: Ash, moisture, fixed carbon, volatile matter.
Ultimate
Analysis: Percentage of carbon, hydrogen, oxygen, sulphur and nitrogen.
Other
Analysis Includes: GCV (by calculation), GCV by Bomb calorimeter, sieve analysis.
45.
What are the different moisture levels of coal that are analyzed in lab?
Surface moisture, inherent moisture and total
moisture.
46. What is ARB and ADB
based GCV?
ARB: It is the
GCV of coal on “As received basis.” That is coal GCV is calculated as soon as
it received in laboratory.
ADB: It is the GCV of coal on: “Air dried basis.” That is coal GCV is
calculated by allowing the coal to dry at room temperature for 24 hours.
47.
What is Spectrophotometer? And what parameters are analyzed with this
instrument?
Spectrophotometry is a
method to measure how much a chemical substance absorbs light by measuring the
intensity of light as a beam of light passes through sample solution. The basic
principle is that each compound absorbs or transmits light over a certain range
of wavelength. This measurement can also be used to measure the amount of a
known chemical substance.
Following water parameters
are analyzed in Spectrophotometer
- Silica: Wavelength 815 nm
- Phosphate: 720 nm
- Iron: 510 nm
- Chloride: 463 nm
- Hydrazine: 450 nm
48-What chemicals are used in clarifier?
Ferric chloride,
Polyelectrolyte & Sodium hypochlorite
49-What is the function of anti-scalent & SMBS in RO system?
Antiscalent especially
polymer based antiscalent are used to inhibit the precipitation of calcium
carbonate
50-What do you mean by ORP in RO system?
ORP is the term used to
measure of the cleanliness of the water & its ability to break down
contaminants. Its range is -2000 to 2000 millivolts
