Most of the other components are usually removed
provide a brief discussion of these procedures that will
or replaced out of necessity because of a failure. The
pertain mostly to the major components of the WHB
only other component that will be removed according to
system.
an established time table is the boiler itself. The boiler
Cleaning. Most of the cleaning you will be
is usually replaced during a ship's major overhaul
involved in will pertain to the exterior of the system's
period.
components. For example, valve maintenance (PMS)
procedures contain cleaning as one of the first steps you
FFG-7 Class Ships
will perform.
Unless you are extremely lucky, however, there will
The FFG-7 class ship's waste heat recovery system
come a time when you will be required to assist or
does not use a WHB to supply heating for LO, FO,
perform the exhaust path cleaning of the boiler. This
potable water, and distilling. Instead it uses the waste
procedure is normally performed according to the PMS,
heat produced by the ship's service diesel generators
during an extended repair availability, or as deemed
(SSDGs) jacket water system.
necessary as a result of a boiler inspection or a casualty.
The FFG-7 waste heat circulating system contains
a total of four heat exchangers (one for each SSDG) and
Cleaning the exhaust gas path is an extremely dirty
four hot-water circulating pumps. The waste heat
and time-consuming job. In this procedure, you will be
system is pressurized by a compression tank that
required to clean the external surfaces of the boiler
maintains sufficient pressure (about 5 psig) to prevent
tubes. Soot blowing during boiler operation is the only
cavitation on the suction side of the circulating pump.
way you can perform this procedure without entering
Although high circulating water temperatures up to
the boiler. Unfortunately, soot blowing is more of a
195F can occur when the heating demand is light, the
preventive measure to lessen soot buildup. It is not as
normal operating temperature range is between 170 to
thorough a cleaning measure as entering the boiler and
175F. Sometimes there are conditions when the
cleaning the tubes.
demand for waste heat will exceed the available waste
Another painstaking cleaning procedure is cleaning
heat. When this condition occurs, there are two
the tubes in the heat exchangers (condensate cooler or
300-kilowatt supplementary electric heaters to assure a
control condenser). Technically, the work is not difficult
minimum temperature of 170F in the system regardless
but it is heavy and time consuming. It is heavy because
of the available waste heat. Normally, at sea these
you must remove the end caps of the heat exchangers to
heaters will not be needed because two or three SSDGs
allow access to the steam or water lance. It is time
will be in operation. When a SSDG is put on the line,
consuming because you must be very thorough to make
the associated hot-water circulating pump starts
sure all of the tubes are cleaned. Also, each end cap
automatically. Each pump also has a manual mode and
gasket must be hand made.
can be started or stopped manually without harming the
system or its equipment.
The last and most difficult procedure we will
Now that we have given you a brief overview of the
discuss is cleaning the internal surfaces of the boiler
waste heat recovery system's purpose and operations,
tubes. This procedure is normally scheduled and
let's discuss some of the tests, inspections, and
performed according to the PMS, as directed as a result
functional checks that you will be required to perform.
of a boiler inspection, or according to instructions in
NSTM, chapter 221. Normally, this is a chemical type of
TESTS, INSPECTIONS, AND FUNCTIONAL
cleaning that must be performed by an outside activity
CHECKS. Like the steam system in other gas
(repair facility).
turbine-powered ships, the tests, inspections, and
functional checks for the FFG-7 waste heat circulation
Removal of Components. The need for the
system are either covered in the PMS or EOSS. Some
removal and replacement of waste heat system
of the equipment items in the FFG-7 waste heat
c o m p o n e n t s depends on the PMS, NAVSEA
circulating system on which you will perform tests,
instructions, and the condition of the components. For
inspections, or functional checks are briefly described
example, the boiler's safeties will probably need to be
in the following paragraphs.
removed and replaced more frequently than any other
component. The safeties come under two guidelines for
Temperature Control Valves. All the temperature
maintenance and repair. The first guideline is the PMS;
control valves that service the waste heat circulation
system are air pilot operated valves. The tests and
the other one is NSTM, chapter 221.
