Boiler_water_presentation.ppt [POWER PLANT]

BOILER WATER

1. WELCOME TO ALL FOR
PRESENTATION ON
BOILER WATER
PROBLEMS AND
SOLUTIONS

2. PROBLEMS ENCOUNTERED
IN BOILER WATER
SCALE
CORROSION
CARRY OVER
DEPOSITS

3. Boiler Water Scale

4. Introduction
Effect of Scale on Boiler Water Systems
Reduces heat transfer efficiency
Decreases unit or production capacity
Over heating of boiler tubes, tube failure
Increased down time and maintenance
Higher operating costs/decreased profits

5. Chemistry
Probable reasons for
Scale Formation
Poor operation of pretreatment
Feed water contaminanation
In adequate chemical treatment
Condensate contamination

6. Chemistry
Commonly Encountered
Boiler Water Scales
Calcium carbonate
Calcium phosphate
Iron phosphate
Iron oxides

7. Chemistry

8. Scale Inhibition
Methods
Maintain the feed water
quality
•Frequent check of feed water
for contaminants
•Use of chemicals as
recommended
•Control blow down

9. Boiler Water Corrosion

10. Consequences of Corrosion
Equpment Repair and
Replacement (Lost Revenue)
Unscheduled Shutdown (Lost
Revenue)

11. Introduction
Corrosion -
An electrochemical process in which a
metal in it’s elemental form returns to it’s
native (i.e., oxidized) state.

12. Types of Boiler Water
Corrosion
General Etch
Pitting
Caustic corrosion
Tube failures

13. Feed and Control
Continuous Feed
Routine Testing
Monitoring Program
Effectiveness
Proper Program Maintenance requires the
continuous application of the correct level of
inhibitor:

14. ImportantPropertiesinwater
chemistry
Natural Water may contain
1) Conductivity 2) Turbidity
3) Color 4) pH
5) Alkalinity 6) Solids
7) Hardness

15. ALKALINITY
• Alkalinity of water is refers to the total
amount of those substance present in water
which tend to increase the concentration of
hydroxide ions on account of dissociation
and hydrolysis in water.
It is a measure of ability of water to
neutralize acids.
Total Alkalinity =Methyl Orange Alkalinity+
Phenolphthalein Alkalinity

16. CAUSE OF ALKALINITY:
Presence of HCO
3
-
, HSiO
3
-
,SiO
3
-
:
Presence of salts of Weak acids:
Presence of Buffer forming salts:

17. CLASSIFICATION OF ALKALINITY:
IT IS OF THREE TYPES:
1) OH
-
(hydroxyl)ALKALINITY
2) CO
3
2-
(carbonate)ALKALINITY
3) HCO
3
-
(bicarbonate)ALKALINITY

18. COMBINATION POSSIBLE:
1) OH
-
(hydroxyl)ALKALINITY
2) CO
3
2-
(carbonate)ALKALINITY
3) HCO
3
-
(bicarbonate)ALKALINITY
4)OH
-
+CO
3
2-
ALKALINITY
5)HCO
3
-
+CO
3
2-
ALKALINITY

19. DETERMINATION OF ALKALINITY:
PRINCIPLE:The type and extent of alkalinity
of water sample is determined by
TITRIMETRIC METHOD.
OH
-
+ H
+
H
2O
CO
3
2-
+ H
+
HCO
3
-
P
HCO
3
-
+ H
+
H
2CO
3 M

20. STRUCTURE OF PHENOLPHTHALEIN

21. STRUCTURE OF METHYL ORANGE:

23. PROCEDURE:
KNOWN VOLUME OF WATER SAMPLE + 1 -
2 DROPS
OF Phenolphthalein.
APPERANCE OF COLOR
TITRATE WITH STD. ACID
END POINT PINK TO COLORLESS
TITRATE WITH SAME SAMPLE WITH SAME
STD. ACID BY USING Methyl Orange
INDICATOR.
END POINT YELLOWOrangeTODARK PINK
THE VOL OF ACID CONSUMED IS NOTED.

24. CALCULATIONS
FOR Phenolphthalein ALKALINITY:
N
1V
1 = N
2V
2
(AWS) (STD. ACID)
N
1 = N
2V
2/ V
1
P
ALK = N
1 X 50 X 1000 ppm
FOR METHYLORANGE ALKALINITY:
N
1V
1 = N
2V
2
(AWS) (STD. ACID)
N
1 = N
2V
2/ V
1
M
ALK= N
1 X 50 X 1000 ppm

25. Alkalinityrelationshipsasdeterminedby
titrations.
 Hydroxide Carbonate Bicarbonate
P = O O OM
P = M P O O
P = 1/2M O 2P O
P >1/2M 2P -M 2(M -P) O
P <1/2 M O 2P M -
2P
RESULT: OH
-
(hydroxyl)ALKALINITY=--------ppm
2) CO
3
2-
(carbonate)ALKALINITY=-----------ppm
3) HCO
3
-
(bicarbonate)ALKALINITY=-----------ppm

26. HARDNESS OF WATER
It is defined as a characteristic property of
water that prevents the lathering of soap.
Hardness of water may also be defined as
the soap-consuming capacity of water, or
the capacity of precipitation of soap.

27. CAUSE OF HARDNESS
Hard water does not produce lather with soap solutions, but produces white
precipitate (scum). For example, sodium stearatereacts with calcium:
2C
17H
35COONa + Ca
2+
→ (C
17H
35COO)
2Ca + 2Na
+
calcium stearate
(insoluble in water)

28. Degree Of Hardness Of Water
Soft 0-60 mg/L
Medium 60-120 mg/L
Hard 120-180 mg/L
Very hard >180 mg/L

29. TYPES OF HARDNESS
a)TEMPORARY HARDNESS
/Carbonate/Alkaline
This hardness refers to the amount of carbonate and
bicarbonates of Ca & Mg in solution
It can be removed or precipitated by boiling.
This type of hardness is responsible for the
deposition of scale in hot water pipes and kettles.
b) Permanent/ Non-carbonate hardness/non-alkaline
This hardness is caused by sulfate, chloride or
nitrate of Ca & Mg .
This type of hardness cannot be removed by boiling.

30. UNITS OF HARDNESS:
There are several different scales used to
describe the hardness of water in different
contexts.
1)ppm
2)Mg/l
3)Clark’s Degree
4)Degree french

31. A
Parts per million (ppm)
Usually defined as one milligram of calcium
carbonate(CaCO
3) per litre of water.
Clarkdegrees (°Clark)/English degrees (°e or e)
One degree Clark is defined as equivalent of CaCO
3
per 70,000 parts of water.
French degrees (°F or f)
One degree French is defined as 10 milligrams of
calcium carbonate per litre of water, equivalent to
10 ppm.
 RELATIONSHIP:
1ppm= 1 mg/l = 0.07 °Clark =0.1 °F

32. EXPRESSION OF HARDNESS:

THE EQUIVALENT OF CaCO3 FOR A HARDNESS
CAUSING SALT IS GIVEN BY:

* EQUIVALENT OF CaCO3 = W X 50
E
W=MASS OF HARDNESS PRODUCING
SUBSTANCE
E= EQUIVALENT MASS OF CaCO3

33. DETERMINATION OF
HARDNESS:
 EDTA METHOD

34. CALCULATIONS
FOR TOTAL HARDNESS:
N
1V
1 = N
2V
2
(HWS) (STD. EDTA)
N
1 = N
2V
2/ V
1
TOT. HARDNESS = N
1 X 50 X 1000 ppm
AFTER BOILING:
N
1V
1 = N
2V
2
(HWS) (STD.EDTA)
N
1 = N
2V
2/ V
1
PERMANENT HARDNESS = N
1 X 50 X 1000
ppm
TEMPORARY HARDNESS=TOT ---PERMANENT
H

35. STRUCTURE OF
EDTA:
Molecular weight :
* EDTA 2Na:372

36. HEXADENTATE IONIC
STRUCTURE OF EDTA:
It is also represented as H
2Y
2-
it is a strong chelating
ligand,forms complex with bivalent cations like Ca &
mg ions. The complex formed are stable in alkaline
medium i.e. pH=8-10.

37. Metal-Edta complex:
Edta being a chelating
ligand react with
multivalent metal ions
to form stable complex.
In hard water, bivalent
cations like Ca & Mg
ions are present which
form complex with edta.
That`s why this method
is used to determine
hardness in water.

38. 3-D STRUCTURE OF EDTA

39. STRUCTURE OF EBT:

40. SLUDGE FORMATION IN BOILERS:
In boilers, because of continuous evaporation of water, the
concentration of salts increase progressively and after the
saturation point is reached, precipitate form on the inner
walls of boiler.
SLUDGE: Sludge is a soft,loose and slimy precipitate
formed within the boiler. It is formed at comparatively
colder portions of the boiler and collects in the area where
flow rate is slow.
These are formed by substances which have greater
solubilities in hot water than in cold-water.
E.g.. MgCO3, MgCl2, CaCl2, MgSO4.

41. Disadvantages:
a. As the sludge’s are poor conductor of
heat they cause loss of heat.
b. The working of the boiler is disturbed
because of chocking of pipes by the
sludge.
PREVENTION:
a. By using well softened water.
b. By drawing off a portion of
concentrated water frequently.

42. scales
SCALES: Scales are hard, adhering precipitates formed on
the inner walls of the boilers. They stick
very firmly on to the inner wall surface and are difficult to
remove with chisel and hammer.
causes of scale formation: Following are the causes
a. decomposition of calcium bicarbonate:
Ca(HCO3)2CaCO3 + H2O + CO2
In low pressure boilers,CaCO3 causes scale formation.
In High pressure boilers,CaCO3 becomes soluble.
CaCO3 + H2OCa(OH)2 + CO2

43. b. Decomposition of calcium sulphate:
The solubility ofCaSO4 in water decreases with
rise of Temperature. In super heated water CaSO4
is insoluble.This is the main cause in high-
pressure boilers.
c. Hydrolysis of Magnesium salts:
Dissolved Magnesium salts undergo hydrolysis
formingMg(OH)2 preci

44. SCALES:
Scales are hard,adhering precipitates formed on the
inner walls of the boilers. They stick very firmly on
to the inner wall surface and are difficult to remove
with chisel and hammer.
causes of scale formation: Following are the causes
a. decomposition of calcium bicarbonate:
Ca(HCO3)2 CaCO3 +H2O + CO2
In low pressure boilers,CaCO3 causes scale
formation.
In High pressure boilers,CaCO3 becomes soluble.

45. b. Decomposition of calcium sulphate:
The solubility of CaSO4 in water decreases with rise
of Temperature. In super heated water CaSO4 is
insoluble.
This is the main cause in high-pressure boilers.
c. Hydrolysis of Magnesium salts:
Dissolved Magnesium salts undergo hydrolysis
forming Mg(OH)2 precipitate.
MgCl2 + 2H2O Mg(OH)2 + 2 HCl
Mg(OH)2 so found by hydrolysis of Magnesium
salts is a soft type of scale.

46. Disadvantages of scale:
wastage of fuel: The scale formation causes
decreases of heat transfer. As a result over
heating is required this causes consumption of
fuel.
Danger of Explosion: The hot scale cracks
because of expansion and water suddenly
comes in contact with overheated Iron plates.
This causes in formation of large amount of
steam suddenly. This results high pressure
causing boiler to burst.
Bagging: distortion of boiler material
Reduce efficiency of boiler.

47. PREVENTION:
a.External treatment: Efficient softening
of water is to be carried out.
b.Internal treatment: Suitable chemicals
are added to the boiler water either to
precipitate or to convert scale in to
compounds.

48. INTERNAL TREATEMENT:
Internal treatment of boiler water is carried
out by adding proper chemicals to
precipitate the scale
forming impurities in the form of sludge
and to convert the scale forming chemicals
into compounds
which will stay in dissolved form in water.

49. CONDITIONING:
COLLODIAL CONDITIONING:The addition of organic
substances such as Kerosene, tannin, Geletc., to the surface
in low pressure boilers may prevent the scale formation.
These substances gets coated over the scale forming
precipitates and gives a loose and non-sticky precipitates
which can be removed by using blow-down operation.
PHOSPHATE CONDITIONING: The addition of sodium
phosphatein hard water reacts with the hardness causing
agents and gives calcium and magnesium phosphates which
are soft and non-adhere and can be removed easily by blow-
down operation. In this way, scale formation is removed in
high-pressure boilers.
3CaCl2 + 2 Na3PO4 →Ca3(PO4)2 + 6NaCl

50. CARBONATE CONDITIONING: In low-pressure
boilers, scale-formation can be avoided by adding
sodium carbonate to boiler water, when CaSO
4is
converted into calcium carbonate in equilibrium.
CaSO
4+ Na
2CO
3→ CaCO
3+ Na
2SO
4
Consequently, deposition of CaSO
4as scale doesn’t
take place and calcium is precipitated as loose sludge
of CaCO
3which can be removed by blow-down
operation.

51. CALGON CONDITIONING: Involves in
adding calgon to boiler water. It prevents the
scale and
sludge formation by forming soluble complex
compound with CaSO
4.
Calgon = Sodium hexa Meta phosphate
Na
2[Na
4(PO
3)
6]→ 2Na+ + [Na
4P
6O
18]
2-
2CaSO
4+ [Na
4P
6O
18]
2-
→ [Ca
2P
6O
18]
2-
+
2Na
2SO
4

52. SODIUM ALUMINATE:
Sodium aluminate gets hydrolyzed yielding NaOH and a
gelatinous precipitate of aluminum hydroxide.
NaAlO2 + 2H2O→ NaOH + Al (OH)3
The sodium hydroxide, so-formed, precipitates some of the
magnesium as Mg (OH)2.
MgCl2 + 2NaOH → Mg (OH)2 + 2NaCl
The flocculent precipitate of Mg (OH)2 plus aluminum
hydroxide, produced inside the boiler, entraps finely suspended
and colloidal impurities, including oil drops and silica. The loose
precipitate can be removed by pre-determined blow-down
operation.

53. Diagrams of scale and sludge:

54. Boiler Corrosion:
The chemical or electro chemical eating
away of metal by its environment in a boiler
is known as boiler corrosion. The main
reason for this problem is the presence of
excess of oxygen in water. It can be
prevented by mechanical de-aerator, pre-
heating and chemical treatment.

55. Effect of corrosion
Metal losses.
Efficiency losses.

56. Caustic Embrittlement:
The formation of brittle and incrystalline cracks in
the boiler shell is called caustic embrittlement.
It is a type of boiler corrosion and the main
reason for this, is the presence of alkali-metal
carbonates and bicarbonates in feed water and
also the presence of sodium sulphate.
In lime-soda process, it is likely that, some
residual Na2 CO3 is still present in the softened
water. ThisNa2CO3decomposes to give NaOH
and CO2, due to which the boiler water becomes
“Caustic”.
Na2CO3+ H2O → NaOH+ CO2

57. -
This caustic water flows inside the boiler
and causes some minutes hair-cracks, by
capillary action.
On evaporation of water, the dissolved
caustic soda increases its concentration
which attacks the surrounding area, thereby
dissolving Iron of boiler as Sodium ferrate.
This causes embrittlement of boiler parts
such as bends, joints, reverts etc, due to
which the boiler gets
fail.

58. -
Therefore, caustic embrittlement can be
prevented.
a. By maintaining the pH value of water
and neutralization of alkali.
b. By using Sodium Phosphate as
softening reagents, in the external
treatment of boilers.
c. Caustic embrittlement can also be
prevented by adding Tannin or Lignin
or Sodium sulphate which prevents the
infiltration of caustic-soda solution
blocking the hair-cracks

60. . Boiler Blow Down
•Controls ‘total dissolved solids’ (TDS) in the water that is
boiled
•Blows off water and replaces it with feed water
•Conductivity measured as indication of TDS levels
•Calculation of quantity blow down required:
Blow down (%) =Feed water TDS x %
Make up water
Maximum Permissible TDS in Boiler
water

61. continue
Two types of blow down
•Intermittent
•Manually operated valve reduces TDS
•Large short-term increases in feed water
•Substantial heat loss
•Continuous
•Ensures constant TDS and steam purity
•Heat lost can be recovered
•Common in high-pressure boilers

64. When blow down required
If boiler drum water quality increase
Conductivity, TDS, silica, Phosphate level
high.

65. Boiler drum water quality
PH 9.0-9.3
Conductivity 30 µs/cm
TDS 15 ppm
Silica as Sio2 0.1 ppm
Phosphate as Po4 2-4 ppm

66. Boiler Blow Down
Benefits
•Lower pretreatment costs
•Less make-up water consumption
•Reduced maintenance downtime
•Increased boiler life
•Lower consumption of treatment
chemicals

67. Boiler Feed Water
Treatment
•Quality of steam depend on water treatment
to control
•Steam purity
•Deposits
•Corrosion
•Efficient heat transfer only if boiler water is
free from deposit-forming solids

68. Boiler feed water quality
PH @ 25°C 8.8-9.2
Conductivity 0.2 µs/cm
Total hardness NIL
Silica as Sio2 0.01 ppm
Copper as cu 0.002 ppm
Iron as Fe 0.005 ppm
Dissolved oxygen 0.007 ppm
Sodium as Na 0.005 ppm
Residualhydrazine 0.01-0.02 ppm
Chloride as cl 0.003 ppm

69. Steam purity
PH@25°C 8.8-9.2
Silica as Sio2 0.01 ppm
Copper as cu 0.002 ppm
Iron as Fe 0.005 ppm
Chloride as Cl 0.003 ppm
Sodium asNa 0.005 ppm

70. Boiler Feed Water Treatment
Deposit control
•To avoid efficiency losses and reduced heat
transfer
•Hardness salts of calcium and magnesium
•Alkaline hardness: removed by boiling
•Non-alkaline: difficult to remove
•Silica forms hard silica scales

71. Boiler Feed Water Treatment
Internal water treatment
•Chemicals added to boiler to prevent scale
•Different chemicals for different water types
•Conditions:
•Feed water is low in hardness salts
•Low pressure, high TDS content is tolerated
•Small water quantities treated
•Internal treatment alone not recommended

72. External Water Treatment
Mechanical de-aeration
•O2 and CO2 removed by heating feed water
•economical treatment process
•Vacuum type can reduce O2 to 0.02 mg/l
•Pressure type can reduce O2 to 0.005 mg/l

73. External Water Treatment
Chemical de-aeration
•Removal of trace oxygen with scavenger
•Sodium sulphite:
•Reacts with oxygen: sodium sulphate
•Increases TDS: increased blow down
•Hydrazine
•Reacts with oxygen: nitrogen + water
•Does not increase TDS: used in high pressure
boilers