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PREVENTION OF SCALE FORMATION IN
FEED,BOILER & STEAM SYSTEMS.
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PREVENTION OF CORROSION IN THE
ABOVE SYSTEM.
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TO MAINTAIN STEAM’S PURITY IN
STEAM CYCLE.
2
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WITH RISE IN OPERATING PRESSURE FAILURES
OF SYSTEM MATERIALS DUE TO CORROSION
AND LOSS IN SYSTEM EFFECIENCY DUE TO
HEAVY SCALING INCREASES.
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BOILER WATER TREATMENT IS ALSO CALLED STEAM-WATER
CYCLE TREATMENT
FOR PRODUCING HIGH QUALITY STEAM DM WATER IS USED
BUT, DM WATER IS ALSO CORROSIVE AT pH 6.8 TO 7.2.
HENCE, THIS WATER IS TREATED WITH LIQUOR NH3 TO RAISE
pH to 9.0 to 9.2 NORMALLY BUT, pH REQUIREMENT OF FEED
WATER VARIES UPON PRESSURE RATING AND METALLURGY OF
BOILER.
NH3 DOSING IS NORMALLY DONE AT CEP OR CPU DISCHARGE.
IN DM WATER OR MAKE UP TO HOTWELL DISSOLVED O2 IS
AROUND 7600 ppb. THIS COMES DOWN TO 10 TO 40 ppb IN
CONDENSATE
THIS DO IS REMOVED IN DEARATOR BY PHYSICAL MEANS TO
AVOID METAL CORROSION.
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DEARATOR O/L REMAINS 5 ppb DO. THIS RESIDUAL
DO IS NEUTRALIZE BY DOSING HYDRAZINE
SOLUTION BY A POSITIVE DISPLACEMENT PUMP AT
BFP SUCTION / CEP DISCHARGE.
O2 + N2H4 - N2 + H2O
THE DOSING OF NH3 AND N2H4 IS CALLED LP
DOSING.
TO MAINTAIN pH IN DRUM TSP OR NaOH SOLUTION IS
DOSED WITH HIGH PRESSURE POSITIVE
DISPLACEMENT PUMP. THIS IS CALLED HP DOSING.
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A)MAKE UP WATER CONTAMINATION
MAY BE DUE TO IMPROPER
REGENENRATION OF RESIN.
B) CONDENSOR TUBE LEAKAGE :
EVEN MINOR LEAKAGE THROUGH
EXPANDED JOINT WILL SEEP RAW WATER
CONTINUOSLY & CONSTANTLY INJECT
IMPURITIES INTO STEAM CONDENSATE.
Ca & Mg ARE SCALE FORMING SALTS
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ALKALANITY CONTROL :- CARBON STEEL
HAS MINIMUM CORROSION IN THE p H
RANGE 9-10.
NaOH CAN BE ADDED TO BOILER.
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HYDRAZINE
N2H4+O2 = 2H2O +N2
6Fe2O3 +N2H4 = 4Fe3O4 +2H2O+N2
4CuO+N2H4= 2 Cu2O+ 2H2O+N2
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PHOSPHATE CONTROL :TSP, DSP OR MSP CAN BE ADDED TO BOILER.
Na3PO4 + H2O  NaOH + Na2HPO4
Na2HPO4 + H2O  NaOH + NaH2PO4
NaH2PO4+ H2O  NaOH + H3PO4
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TSP REACTS WITH SCALE FORMING SALTS (CaSO4,MgSO4)
TO FORM INSOLUBLE PO4 DERIVATIVES WHICH FORM
SLUDGE .
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SOLUBILITY OF TSP INCREASES WITH TEMP UPTO
120 0C THEN GRADUALLY DECREASES.AFTER 220
0C DECREASE IS RAPID, WHEREAS ABOVE 350 0C
SOLUBILITY IS EXREAMELY LOW,SO AT BOILER
CONDITION THE EXCESS PHOSPHATE FROM BOILER
WATER PRECIPATES OUT & THUS DISAPPEARS FROM
SOLUTION.
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DECREASE IN PRESSURE OR TEMP OF BOILER WILL
REDISSOLVE PRECIPITATED PHOSPHATE.
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HIDDEN PHOSPHATE ATTACKS MAGNETITE LAYER.
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HIGHLY SOLUBLE
 CAN NEUTRALISE ACIDITY
BUILD UP DURING
CONDENSOR TUBE LEAKGE.
 DOESN’T REMOVE SCALE
FORMING SALTS.
 HIGHLY VOLATILE ABOVE
160KSC
 MAY LEAD TO CAUSTIC
EMBRITTLEMENT.
 EASILY BOOST UP
pH
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SOLUBILITY CONSTRAINT
HIDEOUT PHENOMENON
REMOVES SCALE FORMING
SALTS INCLUDING SILICA
LOW VOLATILE
RESTRICT p H to 12.5 so NO
EMBRITTLEMENT.
BOOST UP OF p H IS BIT
SLOW.
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1.
2.
3.
4.
SILICA
CHLORIDE
METAL OXIDES
CO2
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VOLATILE AT 65 KSC & SOLUBILY IN STEAM IS
PROPORTIONAL TO PRESSURE.
CAN CARRIED AWAY TO STEAM TO FORM DEPOSIT
ON TURBINE BLADES AT LOW PRESSURE STAGES.
UNEVEN DEPOSITION ON BLADES WILL RESULT IN
ROTOR IMBALANCE .
BLOW DOWN CAN CHECK SILICA LEVEL IN BOILER.
DISTRIBUTION RATIO OF SILICA
=SILICA IN STEAM / SILICA IN WATER
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S No
Drum Pr(KSC)
SiO2 ppm
1
60
8.2
2
80
3.8
3
100
1.9
4
120
0.9
5
130
0.7
6
140
0.52
7
145
0.48
8
150
0.4
9
155
0.37
10
160
0.3
11
165
0.27
12
170
0.25
13
176
0.22
14
186
0.2
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CONDENSOR LEAKAGE IS MAIN SOURCE OF
CHLORIDE.
CHLORIDE IS CORROSIVE IN NATURE & CAN
GENERATE ACIDITY IN THE BOLIER WHICH MAKES IT
FATAL.
FeCl 2 + 2 H20  Fe (OH) 2 + 2HCl
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CHLORIDE IONS CATALYSES RATE OF CORROSION
IN HP BOLIERS.
IMPROPER REGENERATION OF CPU MAY RISE THE
LEVEL OF CHLORIDE.
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METAL OXIDES ARE CORROSION PRODUCTS LIKE
CuO,FeO,Fe2O3.
CAN SET UP GALVANIC CELL INTO SYSTEM SO
DETRIMENTAL.
FEED WATER CONTAINS MORE OXIDES DUE TO
CORROSION IN CONDENSOR.
CONDENSATE POLISHING UNIT CAN TAKE CARE OF
CRUD & ALL METAL OXIDES.
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MAIN SOURCE OF INGRESS IS CARBONATE &
BICARBONATE SALTS INTO BOILER DUE TO
CONDENSOR TUBE LEAKAGE.
ABOVE SALTS GET DISSOCIATED AT BOILER
CONDITIONS.
MAKE UP WATER COULD BE SATURATED WITH
CO2 IF DM STORAGE TANKS DO NOT HAVE CO2
ARRESTERS (BREATHERS).
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S.N
Description
sample
Parameter/Date
Limit
St.I
1 Boiler Water
pH
9.2-9.5
9.1-9.4
<0.2
<0.1
Phosphate (ppm)
<4
<2
Sp. Cond.(ms/cm)
<30
<20
Chloride (ppb) Dt.
<1000
<500
pH
8.8-9.0
9.0-9.2
K (uS/cm )
3-4
5
AMMONIA (ppm)
.5
1.0
Silica (ppb)
<20
<10
DO (ppb)
<40
<40
<5
<5
Silica (ppm)
2 Condensate
St.II
Sodium (ppb)
18
Feed Water
Steam
pH
8.8-9.0
9.0-9.2
Silica (ppb)
<20
<10
Sp. Cond.(ms/cm)
<5
<10
ACC (ms/cm)
0.2
0.2
DO ppb On Line
<5
<5
Hydrazine (ppb)
10-20
10-20
8.8-9.0
9.0-9.2
Silica (ppb)
<20
<10
ACC (ms/cm)
<0.2
<0.2
Sodium (ppb)
-
<5
PH
19
Flue Gas
Oxygen (%)
Stator Water
pH
Gen. H2
2-4
2-4
6.5-7.0
8.5-9.0
Cond. (ms/cm)
<5
1.8-2.2
DO (ppm)
>1
<0.1
Copper (ppb)
N/A
<20
Purity (%)
>97
>97
Dew Point (oC)
<7.8
<11.3
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Thanks
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