Fulton Electric (FB-L) Steam Boiler - Manual (Page 21)

Electric IOM
Installation
17
feedwater or high corrosion rates.
In line filters, or various types of
pretreatment can be used to lower the
suspended solids level. Various polymers
assist in holding solids in suspension.
Periodic blowdowns will eliminate
suspended solids.
Alkalinity: Alkalinity is the capacity of a
water to neutralize acids. Common water
alkalinities consist of bicarbonate,
carbonates, hydroxide, phosphate, and
silicate. These alkalinities, especially
bicarbonates and carbonates, break down
to form carbon dioxide in steam, which is a
major factor in the corrosion on condensate
lines. High alkalinity also causes foaming
and carry over in boilers.
Both foaming and carry over cause erratic
boiler operation. When foaming occurs an
antifoam should be added or increased.
The reason for the high alkalinity should be
determined. It may result from lack of
sufficient blow off. Pretreated makeup
water and condensate should also be
checked. Quite often the source of alkalinity
is an overdose of alkaline internal water
treatment chemical.
pH: pH is a measure of the degree of acid
or base of solution. pH ranges of 7.5-8.0 will
have little influence on the corrosion rate of
cooling waters. If for some reason—
pollution, etc.—the pH is lowered into the
acid range, increased corrosion can be
expected. The solution lies in determining
the cause of the low pH and correcting that
condition. A low pH can result in corrosion
of metals, while a high pH can result in
scale formation. In order to control boilers
and equipment used for the external
treatment of make up water, it is essential
that reliable pH measurements be made.
RO/DI water will have a pH of 6.0 - 6.5 and
will require neutralization if used in a carbon
steel vessel.
Phosphates: Ground or surface waters
seldom contain large amounts of
phosphates. If present, it generally indicates
fertilizer runoff or pollution. Phosphate from
raw water can be the cause of scale
problems in open recirculating cooling
water systems after the water is
concentrated.
Chlorides: Chlorides are involved in
most cooling water corrosion cells. Other
factors being equal, it can be assumed the
higher the chloride content, the more
corrosive the water. When pits or cracks
occur on stainless steel or other metals,
chlorides are usually suspect. If chloride
levels are high enough to cause severe
corrosion, they can be controlled by limiting
the cycles of concentration and increasing
boiler blowdowns. Corrosion from chlorides
can also be controlled by increasing the
amount of corrosion inhibitor or changing to
a more effective inhibitor. Reverse osmosis
is another method of pretreatment to
reduce chlorides.
Oil: Oil is not a natural constituent of boiler
water; still it can frequently enter a system
through leaks in a condenser or other heat
exchanger. Oil can also enter a system
through the lubrication of steam driven
reciprocating equipment. Whatever the
source, the presence of oil in boiler water is
undesirable. Oil can act as a binder to form
scale. In high heat-transfer areas oil can
carbonize and further contribute to the
formation of scale and low pH.
Foaming is one indication of oil in boiler
water. Its presence can also be confirmed
by first shaking a bottle containing boiler
water. If oil is present foam will result. To
ensure the foaming is being caused by oil,
add a small amount of powdered activated
carbon to the bottle containing the boiler
water and shake. Little or no foam will
appear if the foaming is caused by oil. Often
oil in boiler water will originate in the
condensate. This contaminated
condensate should be directed to the sewer
until the source of the oil is determined and
corrective steps taken.
Silica: Silica in boiler deposits is usually
combined with other constitutents. Silicates
form a number of different scale complexes
with calcium, magnesium, aluminum,
sodium, and iron. Since there is at present
no effective dispersant for silicate deposits,
the scale problem can be alleviated by
maintaining close control of calcium,
aluminum, and iron as well as silica. The
usual control procedure is to maintain the
silica level in open recirculating water at 180
PPM max.
Iron (oxides): Iron in any of its oxide or
complex forms is undesirable in boiler
water. It is very difficult to disperse so that
it can be removed the bottom blowoff lines.
Iron in its various forms can originate in the
raw water makeup, condensate return
water, or form directly in the boiler as a
result of corrosion. Most iron oxide
originates outside the boiler. It does not
concentrate in the boiler and it tends to
collect in stagnant areas. If a boiler is using
raw water makeup, iron is almost certain to
be a major component of developing scale.
Water Hardness: Water hardness is the
measure of calcium and magnesium
content as calcium carbonate equivalents.
Water hardness is a primary source of scale
in boiler equipment.
Feedwater: Feedwater is the
combination of fresh makeup and returning
condensate that is pumped to the boiler.
Condensate: Condensate is condensed
steam that is normally low in dissolved
solids. Hence, it does not contribute to the
dissolved solid content of the feedwater. In
addition, condensate is very expensive to
waste. It's been chemically treated, heated,
pumped, converted to steam, and
condensed. This costs money and when
condensate is returned to the boiler, money
is saved.