Installation
25
WATER CHARACTERISTICS
The values in the following tables are extracted from tables 5.1 and 5.2 in EN 12953-10 (requirements concerning the quality of
water supply and the water in the generator).
Even for generators that are not covered by the aforementioned provision it is however necessary to adopt at least the indicated
limits and however, to refer to the specialised companies that manage selecting the type of treatment to be carried out on the
basis of a thorough analysis of the water available.
5.1 Water supply - Threshold values (in input)
CHARACTERISTICS
u.m.
Steam generator water with pressure up to 20 bar
Appearance
Clear, limpid, without foam or suspended solids
Direct conductivity at 25°C
μS/cm
See table values "Operating water - threshold values"
pH at 25°C (
a
)
---
> 9,2
[b]
Total hardness (Ca+Mg)
mmol/l
< 0,01
[c]
Iron (Fe)
mg/l
< 0,3
Copper (Cu)
mg/l
< 0,05
Silica (SiO
2
)
mg/l
See the "Maximum acceptable silica content in the generator water up to 20 bar pressures" table
Oxygen (O
2
)
mg/l
< 0,05
[d]
Oily substances
mg/l
< 1
Concentration of organic substances
-
See note
[e]
[a]
With copper alloys in the system the pH value must be kept within 8.7 and 9.2.
[b]
With a softened water pH value > 7.0, the pH of the generator water should be provided according to table 5.2.
[c]
At operating pressure <1 bar, a maximum total hardness of 0.05 mmol/l must be acceptable.
[d]
Instead of respecting this value with intermittent operation or operation without deaerator, in case of agents forming the film
and/or excess of oxygen, the additive must be used.
[e]
Organic substances are generally a mixture of various different compounds. The composition of such mixtures and the
behaviour of their individual components under the steam generator operating conditions, are difficult to predict. Organic
substances can be decomposed to form carbonic acid or other acid decomposition products that increase acid conductivity and
cause corrosion and deposits. They can also lead to the formation of foam and/or production of steam with suspended water, that
must be kept as low as possible.
Maximum acceptable silica content in the generator water up to 20 bar pressures
Alkalinity
Silica
0,5 mmol/l
80 mg/l
5 mmol/l
105 mg/l
10 mmol/l
135 mg/l
15 mmol/l
160 mg/l
NOTE
These values are valid assuming the presence of a thermal deaerator. In the absence of the deaerator, it is appropriate, however,
to raise the temperature of the water contained in the tank to at least 80°C to reduce the content of dissolved gas (O
2
and CO
2
).
It is, in any case, appropriate to use chemical conditioning to de-oxygenate the water supply completely and to minimise the
corrosive CO
2
effects.
