2 replies to this topic

[Olof Persson]

Hello gents

My question is this; if I have high conductivity in the feed water to a steam generator (850 - 1000 µS/cm) will that automaticly translate to high conductivity in the steam produced? I know we'd normaly not talk about conductvity in steam but I hope you'll understand what I mean.

Will the resulting conductivity be dependant on what kinds of dissolved material are in the feed water? In my head inorganic dissolved content would stay in the steam generator, causeing fouling, but not actually affect the quality of the steam?

Gratefull for any insight and help!

Best Regards

Olof Persson

[Pilesar]

If you mean by 'fouling' a lowering of heat transfer
coefficient, the lower heating efficiency is not the only
reason for concern about poor feed water quality. Minerals
in water tend to fall out of solution as the water
temperature increases. This causes scale which clings to
metal walls in hot areas. Scale also forms where there is active
evaporation such as where the liquid and vapor phase meet in
steam drums. Between the scale and the metal wall is an
anaerobic interface that is no longer exposed to water and
this is the area where corrosion begins in the metal wall --
sort of like tooth decay under areas of plaque.

Some of the minerals in the water do get into the steam. A
common impurity in water which becomes volatile and makes
its way into steam is silica. Silica tends to fall out and
form a glass plating on the wheels of steam turbines. High
pressure steam driven turbines are most susceptible to
silica. High speed turbines can become dangerously
unbalanced if some of the silica buildup breaks loose.

Even 'pure' water usually has more than one component in
trace amounts. As steam generation pressure increases, the
standard for water purity is tightened. Water that would be
completely unacceptable in a high pressure steam system may
be just fine in a low pressure system.

The steam condensate will have a measurable conductivity
different from the boiler feed water. Some of this
conductivity may be due to material picked up from the walls
of the piping and equipment.

[Olof Persson]

Wow, thank you for a very long and informative anwser. That was pretty much everything I needed to know!