decrease in alkalinity and phosphate and usually a
Feedwater
somewhat large increase in conductivity and chloride.
Feedwater is extremely important to the overall
You must locate, isolate, and correct the source of
operation of the steam plant. After all, the feed tank is
the contamination. You must continue to monitor
where the water that supplies the boilers comes from and
(sample and test) the water, add chemicals, and blow
where the water will return after it is condensed. This is
down as needed to maintain these contaminants within
why the quality of your ship's feedwater is so important.
their specified control limits. To remove high levels of
The quality of feedwater can ultimately affect the
contamination, however, the most effective method you
efficiency of your ship's engineering equipment and
can use is to secure, cool, dump, and flush the system.
systems.
Shore Water.-- The second most common
In a properly operating waste heat boiler system, the
contaminant is shore water. Shore water contamination
distillate (evaporator supply) contains the highest level
originates from a potable water supply from shore.
of contaminants. Therefore, the makeup feedwater rate
Shore water can enter the feedwater system through a
will determine the contaminate level that will enter the
leaking steam coil in a hot water heater or by the use of
boiler. High makeup rates will cause the boiler water
contaminated shore source feedwater or steam.
chloride and conductivity to increase. This condition
You can detect contaminated shore water by
will lead to higher use of treatment chemicals. Both
monitoring the condensate cooler salinity indicator or
conditions will cause greater sludge formations and an
by performing a feedwater hardness test. By reviewing
increase in the deposits on the watersides. To keep the
the logs, you should also notice an effect on water
makeup rate at a minimum, make sure all system leaks
chemistry, as indicated by a decrease in phosphate and
are corrected. In a properly maintained system, the
increase in alkalinity. In most cases, you will also see an
makeup feedwater rate should be less than 900 gallons
increase in conductivity and chloride. The corrective
per day.
actions you should take are the same ones you should
CONTAMINANTS.-- There are four primary
take for seawater contamination.
feedwater contaminants you will need to monitor: (1)
Oil.-- The third major contaminate is oil. Steam, as
seawater, (2) shore water, (3) oil, and (4) dissolved
well as feedwater, can become contaminated by oil if a
oxygen. In the following paragraphs, we will briefly
leak develops in either a fuel oil or lube oil heater. Oil
discuss the origin, detection methods, effects, and
contamination can be indicated in the feedwater or
corrective actions in regard to these contaminants.
boiler water sight glass, in feedwater or boiler water
Seawater.-- Seawater is the most common
samples, or by oily condensate in the inspection tank.
contaminant found in marine boiler water/feedwater
The effect oil contamination can have on boiler water
systems. The most routine source of intermittent
chemistry is that it can induce carryover with no effect
seawater contamination in feedwater is the distillers,
on alkalinity, phosphate, conductivity, or chloride. The
e s p e c i a l l y during start-up of the distillers.
corrective actions you should take are to find, isolate,
Contamination from the distiller air ejector drains can
and correct the source of the contamination. Surface
ultimately cause a rapid and large increase in boiler
blow the CE boiler to remove the contamination. If the
water chloride. The source of this contamination, of
boiler is steaming, treat the water as needed to keep the
course, is from concentrated seawater, more commonly
alkalinity and phosphate levels within the limits. You
called brine.
may have to secure, dump, and flush the boiler water to
Another source of seawater contamination in
remove the oil contamination. If contamination levels
feedwater that will ultimately cause an increase in boiler
are severe, clean the boiler with an alkaline boilout
water chloride are leaks in the condensate system. Small
according to the procedures in NSTM, chapter 221,
condenser leaks can cause a continual, low level
"Boilers."
increase in boiler water chloride. Tube leaks in a
Dissolved Oxygen.-- The last contaminant we will
condensate cooler or control condenser can cause
discuss is dissolved oxygen. Dissolved oxygen in the
varying levels of contamination, depending on the
feedwater as it enters the boiler will cause corrosion of
amount of leak-by. The most common methods of
the nonstainless-steel coils.
detection you can use are the salinity/conductivity
indicators or the chemical chloride test. You should
On the CE boilers and on some of the CONSECO
readily notice the effects of condensate system leaks on
boilers, a DFT is installed to reduce the oxygen level and
the boiler water chemistry. There will be a noticeable
minimize the corrosion rate. A DFT is not required on a
