MIL-HDBK-1003/6
a)
Continuous or intermittent blowdown,
b)
Internal treatment,
c)
Ion exchanger (sodium cation, chloride anion, hydrogen cation),
d)
Lime-soda softening, cold or hot,
e)
Demineralization (cation and anion exchangers).
Selection Guide. Table 18 is a general guide to raw water
7.2.3.2
treatment of boiler makeup and the conditions under which each method or
combination should be used. For more specific recommendations, retain a
specialized consultant.
For the effectiveness of different treatment
7.2.3.3
Effect of Treatment.
processes, refer to Table 19.
For Pier Side Ships. For boilers providing steam to pier side
7.2.3.4
ships, it will generally be necessary to utilize demineralizers to treat
boiler feedwater to meet NAVSEASYSCOM requirements outlined in NAVSEA
technical manual NSTM Chapter 220.
7.3
Blowdown
7.3.1
General. Essentially pure water vapor is generated in a boiler and
the impurities (dissolved solids) of the boiler feedwater remain and become
concentrated. The concentration of dissolved solids can be controlled by
discharging boiler water with a high dissolved solids concentration as
blowdown and replacing the discharged amount of boiler water with feedwater of
low mineral concentrations. The blowdown must be adjusted so that the
dissolved solids entering the boiler will equal those leaving and the maximum
concentration of dissolved solids is limited to or maintained at a
predetermined value.
Types. Every boiler system has two types of blowdowns. The upper
7.3.2
blowdown is either intermittent or continuous operation. It is used to
control concentrations of dissolved solids. This blowdown is generally
connected to the steam drum of a water tube boiler in a location which will
minimize the inclusion of feedwater, chemical feed and steam entrainment. The
other blowdown is from the mud drum or the water walls. It is an intermittent
or mass blowdown which removes accumulated solids and sludge from stagnated
areas of the boiler. This blowdown is usually performed at reduced steam
loads. Blowdown in firetube boilers is located near the point of highest
concentration of dissolved solids in the water, i.e., near the bottom of the
boiler.
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