Fulton Ancillary Equipment SteamPac Unfired Steam Generators - Manual (Page 18)

Fulton Thermal Corp.*SteamPac Unfired Steam Generators Manual* Version 2010-0201
Page 18
c) One way to lower the amount of dissolved gases in the boiler feed water is to preheat the
feedwater. This option injects live steam into the feedwater to increase the water
temperature to 180 degrees F or higher which removes oxygen and carbon dioxide from
the water.
d) RO/DIWater: Reverse Osmosis / Deionized water is water that all dissolved solids have
been removed. Osmosis is a process that uses a semi-permeable membrane, under
pressure, to reject dissolved salts and allow water to pass through. When a solution of
salt and water is separated by a membrane, the osmotic pressure forces the water
through the membrane, diluting the salt solution. When pressure greater than osmotic
pressure is applied to the salt solution, the membrane allows the water from the salt
solution to pass into the water solution and rejects the dissolved salts. The osmotic
process is reversed, hence, reverse osmosis. RO/DI water has no buffering capacity and
a pH of <6.5. It is corrosive to carbon steel, however, not to stainless steel. Very high
purity steam quality can be obtained with RO/DI water.
e) Electric boiler and unfired steam generators’ pressure vessels made from carbon steel
that use RO/DI water for the supply water will require pH neutralization for vessel
longevity. Electric boilers and unfired steam generators with stainless steel pressure
vessels do not require pH neutralization. ASME Code allows electric boilers to be
manufactured with stainless steel pressure vessels provided RO/DI water is used as the
water supply.
f) The Fulton Warranty does not cover damage or failure that can be attributed to corrosion,
scale or fouling.
12. Glossary of Water Supply Terms
a) Dissolved Oxygen: Oxygen that is dissolved in the feedwater will cause the steel in the
boiler and the feedwater system to be attacked by the water in a manner described as
“pitting”. The pits that are produced can vary from tiny depressions to holes large enough
to penetrate the boiler metal and are usually covered with tubercles of iron oxide. Once
pitting starts, it may be extremely hard to arrest. Pitting can proceed at a surprisingly
rapid rate and can occur not only in the boiler proper, but also in pre-boiler equipment
such as ecomomizers, feedwater tanks, and feedwater lines.
b) Sodium Sulfite: Its purpose is to chemically remove the dissolved oxygen left in the
feedwater after the feedwater has been mechanically deareated. Sodium Sulfite reacts
chemically with dissolved oxygen, producing sodium sulfate. Since it is desirable to
remove dissolved oxygen from the feedwater before it reaches a boiler. Sodium sulfite is
best introduced continuously at some suitable point in the feedwater system (the storage
section of the feedwater heater or deareator, six inches below the water line). Chemical
residual control is based on the maintenance of a specific excess of sodium sulfite in the
boiler water. The essential requirement being to maintain in the feedwater at all times