Installation
18
WATER TREATMENT
The thermal system water must comply with the Laws in force, therefore it is good practise to use treatment units when the line
water is particularly rich in calcium carbonate, which causes scale build-ups and corrosion.
The table includes some indicative values:
Characteristics
Scale
Filling water
Circuit water
pH*
-
7-8
Hardness (CaCo2)
°Fr
< 15
-
Iron (Fe)**
mg/kg
-
< 0.5
Copper (Cu)**
mg/kg
-
< 0.1
Oxygen (O
2
)
mg/l
< 0.05***
-
Appearance
Clear
Possibly clear
* 8 is the maximum acceptable pH value in case of radiators in aluminium or light alloys.
** Higher values indicate on-going corrosion phenomena.
*** In case of agents which form oxygen film and/or surplus, do not observe this value with intermittent operation or operation
without deaerator, but use the additive.
LIMESTONE BUILD-UPS
Limestone build-ups reduce the heat exchange between the combustion gases and water, leading to an abnormal increase of
temperature of the parts exposed to the flame and thus to a significant reduction of the service life of the boiler.
Limestone gathers in the points where the wall temperature is higher and the best defence against it, at the construction level,
is to eliminate the superheating areas.
Scale build-ups form an insulating layer which decreases the heat exchange of the boiler, penalising its efficiency. This means that
a significant part of the heat obtained from the combustion is not fully transferred to the system water, but is lost through the
chimney.
LIMESTONE DIAGRAM
Lost heat
0
5
10
15
20
30
10
20
30
%
limestone mm
CORROSION ON WATER SIDE
The corrosion of the metal surfaces of the boiler on the water side is due to the iron transit into the solution through its ions (Fe+).
In this process, the presence of dissolved gases, in particular oxygen and carbon dioxide, is very important. Corrosion phenomena
often occur with softened and/or demineralised water, which by nature is more aggressive against iron (acid water with Ph < 7);
in these cases, even when scale build-ups are prevented, corrosions can occur and it is necessary to treat the water with corrosive
process inhibitors.
Cooke Industries - Phone: +64 9 579 2185 Email: [email protected] Web: www.cookeindustries.co.nz
