Fulton Electric (FB-L) Steam Boiler - Manual (Page 20)

Electric IOM
Installation
16
Water Supply
1. The quality of the water used in the boiler
will affect the life of the elements and it
is strongly recommended that a
competent water treatment concern be
consulted prior to the installation of the
boiler. They should be advised that
treatment will be used on an electric
boiler. Certain chemicals may attack or
attach to boiler heating elements and
shorten their life span. Elements
damaged due to adverse water
conditions will not be replaced under
warranty.
2. Natural feedwater supplies contain solids
and dissolved gases. These may
promote incrustation or scale, foaming,
solids in steam, corrosion, and/or
caustic embrittlement. To prevent this,
feedwater must be studied individually
and treated accordingly. The treatment
should provide quality feedwater to the
boiler such that corrosion and deposition
in the boiler will be minimized. Dissolved
oxygen, high chloride levels and low pH
can all be major causes of corrosion.
Untreated hardness is the major cause
of deposits. Poor quality feedwater
requires increased blowdown and
increased chemical treatment costs to
prevent boiler corrosion and scaling.
3. One way to lower the amount of
dissolved oxygen 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 from the water.
Oxygen is a corrosive.
4. 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
have 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.
5. Electric boiler pressure vesselsmade
from carbon steel that use RO/DI water
for the supply water will require pH
neutralization for vessel longevity.
Electric boilers with stainless steel
pressure vessels. ASME Code allows
electric boilers to be manufactured with
stainless steel pressure vessels
provided RO/DI water only is used as
the water supply. The use of RO/DI
water must be listed on the nameplate of
the boiler. The use of RO/DI water with
stainless steel pressure vessels does
not require pH neutralization.
6. The Fulton Warranty does not cover
damage or failure that can be attributed
to corrosion, scale or dirt accumulations.
Oxygen is corrosive.
Recommended Water
Treatment
1. Following are recommendations for feed
water and boiler water. Contact your
local water treatment professional for
testing and treatment recommendations.
It is very important that a strict water
treatment program be followed.
Feedwater:
Dissolved Oxygen.....less than 0.03 ppm
pH Value...........................................9-11
*Hardness....................less than 70 ppm
in terms of calcium carbonate
Oil....................................................none
Suspended Solids............................none
Organic Matter............less than 5.0 ppm
Chloride.............less than 50.0 ppmTotal
Dissolved Solids..............less than 300ppm
Temperature........................less than 120°F
Boiler Water:
Phosphate..........................30 to 50 ppm
expressed as PO4 (Phosphate)
Alkalinity.....................less than 300 ppm
as CACO3 (Calcium Carbonate)
Chloride......................less than 500 ppm
pH Value.....................................9 to 11
(measured at room temperature)
Total Dissolved Solids....less than 2,000 ppm
Iron...............................1 ppm maximum
Silica......................180 ppm max. as SIO2
Hardness..................less than 50.0 ppm
Dissolved Oxygen...........................none
ppm = parts per million
*1 Grain Hardness = 17.118 ppm
Therefore: 70 ppm = 4.10 grains hardness
2. It is critical that the boiler pH be alkaline
(9-11) whenever water is in the boiler.
This is traditionally maintained through a
combination of sodium hydroxide,
bicarbonate and phosphate. The
phosphate has the additional benefit of
removing any hardness that may leak
past the softener. Solids that enter in
with the feed water concentrate in the
boiler. A regular schedule of boiler
blowdown must be maintained to
prevent high salt concentrations
(chloride and sulfate) from corroding the
boiler or forming deposits.
Glossary of Water Supply
Corrosives and Inhibitors
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 y 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 heaters, and
feedwater lines.
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 slightly more than
enough sodium sulfite to consume all of the
dissolved oxygen that slips through the
deareating equipment. When sodium sulfite
is not fed continuously, protection of the
boiler against oxygen attack must depend
on the reserve of sodium sulfite that is
present in the boiler water. In this case, it is
important that the feedwater and the boiler
water are mixed thoroughly and as quickly
as possible so that boiler water sodium
sulfite may consume feedwater oxygen
before the latter can cause damage to the
boiler. Sulfite as a treatment represents the
second line of defense against oxygen
corrosion. Primary protection against this
type of attack requires adequate facilities for
mechanical deareation of the feed-water
plus a vigorous maintenance program to
safe guard against oxygen leakage into the
pre-boiler system.
Suspended Solids: Suspended solids are
the undissolved matter in water, inc-luding
dirt, silt, vegetation, iron oxides, and any
other insoluble matter. Normally suspended
solids are expressed in terms of turbidity.
The presence of suspended solids in
cooling water can increase impingement
type corrosion. Suspended solids may also
deposit in low velocity areas and create
differential aeration cells. Pitting can result.
The most common cause of high
suspended solids is high hardness