Download - Water Treatment Training
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Water Treatment Training
Dakhni Ex ansion Pro ect
Sulfur Recovery Unit
Oil & Gas Development Company Limited
Dakhni Gas Processin Plant
Dakhni, Pakistan
November 2010
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Typical Water Cycle
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Impurities in water
CATIONS:
a c um a
Magnesium Mg
Sodium Na
Bicarbonates HCO3
ar ona esChlorides Cl
Sulfates SO4
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Impurities in water
PROBLEMS IN BOILER SYSTEMS DUE TO WATER
IMPURITIES:
These impurities/salts make hard / non-conductive
scales inside boiler and on heat transfer surfaces.
Scales are very hard to remove.
Heat transfer rates are decreased so energy is lost. O O .
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Soft & Hard Water
SOFT WATER:
o wa er con a ns on y -car ona es.
HARD WATER:
Hard water contains carbonates, chlorides and sulfates.
When soft water is heated, bicarbonates are converted in
carbonates.
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Steam System Requirements
Boiler Operating
PressureTotal Dissolved Solids
Total Alkalinit Total Sus ended Solids
(psig)
(bar)
- -
(ppm)
(ppm)
(ppm)
0 - 50
0 - 3.52500 500
50 - 300
3.5 - 203500 700 15
300 - 45020 - 30 3000 600 10
450 - 600
30 - 402500 500 8
600 - 750
40 - 501000 200 3
750 - 90050 - 60
750 150 2
900 - 1000
60 - 70625 125 1
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Soft & Hard Water
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Soft & Hard Water
-(scale + carbonic acid)
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Total Dissolved Solids (TDS)
When a boiler generates steam, impurities in the feed water
will concentrate. When the concentration of impurities
ecomes g er, oam s genera e an e vo ume o e
boiling water increases, resulting in more and more lowquality wet steam generated.
The concentration of impurities is often termed TDS - Total
conductivity or density method.
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Total Dissolved Solids (TDS)
Measuring TDS with the density method:
-. -
where
TDS = Total Dissolved Solids (ppm)
= relative density of the boiler water at 15.5oC
This is a manual method and requires measuring a cooled down
sample with a very sensitive hydrometer.
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Total Dissolved Solids (TDS)
Measuring TDS with the conductivity method:
T .
where
= conductivity (s/cm)
This method can be used with an automatic resistance meter
controlling the blow down cycles of the boiler. Note that electrolytic
polarization of the probe may be a problem and that an ac (amplitude
current) resistance meter normally is used. Be also aware that
the conductivity increases with temperature.
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Components of Steam System
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Deaerator
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Blow Down Rate
BLOWDOWN RATE :
e ow own ra e epen s on e
Steam consumption (steam used in the process and not
returned as condensate to the boiler)
Concentration of impurities in the feed water
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Blow Down Rate
BLOWDOWN RATE :
e ow own ra e can e ca cu a e as
qBD = qS fc / (bc - fc)
where
qBD= blowdown rate (kg/h)=
fc= Total Dissolved Solids - TDS - in the feed water (ppm)bc= maximum allowable Total Dissolved Solids - TDS - in
e o er wa er ppm
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