Water Treatment - CleaverBrooks CEJS Installation, Operation And Maintanance

3 - Water Treatment

The KW output of the boiler is determined by the conductivity of the water in the system. Water
conductivity is determined by its chemical makeup. General water hardness, pH, alkalinity, iron,
oxygen, and total dissolved solids all have an effect on boiler operation. The water required for CB
boilers should be non-scale forming, non-corrosive, non-foaming, and should have the following
chemical characteristics:
• pH of boiler water should be between 8.5 and 11.0
• Total alkalinity of boiler water should not exceed 400 ppm
• Oxygen content of feedwater should not exceed 0.005 ppm
• Iron content of boiler water should not exceed 0.5 ppm
• Makeup water hardness should not exceed 0.5 ppm - preferably 0 ppm
• Boiler water hardness should be 0 ppm
Correct conductivity varies with the boiler voltage and temperature. This information is supplied by CB
for each boiler installation. Conductivity must be high enough to allow development of the required
KW output of the boiler at its designed operating pressure, and should not exceed that amount by more
than 10%.
In electrode steam boilers, water conductivity must be carefully controlled. If conductivity
is allowed to increase without limits, it will result in damage to the boiler shell and
electrodes and could also result in high voltage surface arc-over in the boiler itself.
The control of alkalinity and CO2 content of the steam or hot water is important because these factors
can affect the porcelain insulators which are used as lead-through bushings to bring the electric power
into the boiler. With porcelain insulators, total alkalinity should be held below 400 ppm.
It is normally recommended that boiler water conductivity be kept as low as will enable the boiler to
continue at full load operation without being unduly sluggish. Chemical additives commonly used in
electrode steam boilers include sodium hydroxide, sodium sulfite, sodium sulfate, sodium tri-
phosphate, and hydrazine for oxygen control. There are of course other compounds which could be
used in the boiler for various purposes - for example, control of sludge fluidity. Each additive would
need to be evaluated on an individual basis with attention to its effect on conductivity as well as to its
intended purpose.
Any chemicals or compounds which tend to induce foaming should be avoided.
Particularly in high voltage boilers, foaming will cause boiler shutdowns and
could lead to serious disruptions of supply circuits and switchgear. Impurities or
contaminants from elsewhere in the system should also be avoided.
750-272
Important
!
Caution
!
Electrode Boiler
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