Johnson Controls York YHAU-C, Installation, Operation And Maintenance Manual

Page: 163 / 180

Table 31: Tendency of generation of scales and corrosion by quality of cooling water
General tendency Quality of cooling
water
Scale and its color Corrosion and its color
Low water PH
Hard scales are
generated and iron
bacteria propagate
Bad corrosion of iron and
copper
Dark brown -
pale greenish
blue
High PH water
Calcium carbonate
scales are
generated easily.
Pale yellow ──
Water contains many
calcium ions (Ca
2+
) and
magnesium ions (Mg
2+
)
Sulfuric ion SO
4
2-
,
silica SiO
2
and 2
carbonate ion CO
3
2-
combine together
to generate hard
scales.
Pale yellow ──
Water contains many
chlorine ions (Cl
-
)
──
Iron and copper tubes are
corroded badly.
Water contains many
sulfuric ions (SO
4
2-
) and
silica (SiO
2
)
Calcium sulfide
(CaSO
4
) and calcium
silicate (CaSiO
3
)
combine together
to generate hard
scales.
Gray
SO
4
2-
corrodes copper
tubes badly.
Greenish blue
Factors of water
quality
Water contains many
iron (Ferrous ion
(Fe
2+
),ferric ion (Fe
3+
))
Fe
3+
becomes
ferric hydroxide
(Fe(OH)
3
) to make
red water and sets
red rust of ferric
dioxide (Fe
2
O
3
). Iron
bacteria propagate.
Reddish
brown-Black
Fe
3+
corrode iron and
copper tubes badly.
Reddish
brown - black
Water smells bad
(Contains compounds
of sulfur, hydrogen
sulfide (H
2
S),
ammonium ion (NH
4
+
),
methane, and other
compounds.)
Scales are
generated easily,
and slime is
generated.
Greenish Blue
– Dark brown
H
2
S and NH
4
+
corrodes
copper tubes badly.
Black –
greenish blue
Water contains organic
matter (High COD and
BOD)
Scales are
generated easily,
and slime is
generated.
──
Exhaust gases
(Sulfurous acid gas
(SO
2
), nitrogen oxide
(NO
2
), hydrogen
chloride (HCl),
ammonia (NH
3
), and
other exhaust gases)
mixed in water in
cooling tower
If organic nitrogen
and inorganic
nitrogen are
contained, algae
propagate. SO
2
becomes SO
4
2-
and
combines with
Ca
2+
and Mg
2+
to
generate scales.
Algae: Green
Pale yellow
Exhaust gas from
automobiles, factories,
sewage plants, ammonia
refrigerating machine,
and other environments,
lower or heighten PH
number. As SO
4
2-
, Cl
-
and
NH
4
+
are increased, tubes
are corroded and pitted
very quickly.
Solid matter (mud,
sand, fibers, dust,
insects, and so on) in
water in cooling tower
Scales are
generated easily.
Solid matters set.
Slime is generated.
────
Environmental
factors
Sea wind (district by
sea)
Scales are
generated easily.
Tubes are corroded badly. Reddish
brown - black
161 YHAU-C Single Effect Steam-Fired Absorption Chiller