UFC 3-240-13FN
25 May 2005
Figure 3-14. Water Boiler Mist Formation
Stage 1
Stage 2
Stage 3
Surface
Indentation
Droplet
After
Formation
Bubble
Bubble
Formation
(Mist)
Release
3-2.8.2
Foaming Carryover. The term "foaming carryover" refers to boiler water
foam and the carryover of foam into the steam. A variety of conditions can cause foam.
Excessive levels of alkalinity, TDS, SS, and at times water treatment chemicals can
interact to create foam in the boiler. Normally, maintaining the total alkalinity at less than
20% of the TDS and the total suspended solids (TSS) at less than 8% of the TDS can
control foaming to a reasonable level. In addition, adding antifoam agents to the boiler
water can control foaming. Polyamides and polyglycols are examples of antifoam
agents.
3-2.8.3
Priming Carryover. The term "priming" refers to boiler water in the steam
when, due to liquid level variations and surges in the steam drum, water is mixed with
the steam and is subsequently carried into the steam header. A mechanical problem or
mechanical properties, such as oversensitive feedwater controls, large steam demands,
or incorrect blowdown procedures, always cause priming. There is no chemical control
method available, although the addition of antifoam chemicals may help reduce the
extent of this occurrence. Boiler operations should be reviewed and modified if priming
carryover is occurring.
3-2.8.4
Silica Carryover. The term "silica carryover" refers to a situation that
occurs when silica in the boiler water volatilizes and enters the steam independently of
water carryover. The silica can then form a deposit in the condensate lines and in
process equipment when the silica condenses from the steam. When steam turbines
are used, silica deposition can be very serious, resulting in unbalancing of the steam
66
Previous Page
