UFC 3-240-13FN
25 May 2005
3-1.5.5
Relationship Between Feedwater, Blowdown, Steam Generation, and
COC. Using the terms defined in paragraphs 3-1.5.3 and 3-1.5.4, the relationship
between feedwater, blowdown, steam generation, and COC is represented as:
a) F = B x COC, from COC, Equation (2) above
b) F = E + B, from COC, Equation (1) above
c) B x COC = E + B, replacing F in Equation (2) with
Equation (1)
d) B x COC - B = E, rearranging Equation c) above
e) B x (COC-1) = E, rearranging Equation d) above
f) B = E (COC-1), rearranging Equation a) above
3-1.5.6
Calculating Blowdown Rates. The blowdown water volume is rarely
measured by a meter. As shown below, it can be calculated if any two of the following
parameters are known: 1) feedwater; 2) COC; or 3) steam generation (E). Steam
volume is usually measured in units of meters on large boilers. The COC can be
calculated by measuring the conductivity or TDS in both the boiler water and the
feedwater. Note that the conductivity and quantity of TDS is the same for the boiler
water and the blowdown water.
COC = BTDS / FTDS
EQUATION
or
(4)
Bmhos / Fmhos3
where
COC= cycles of concentration, no units
BTDS= blowdown TDS, ppm
FTD= feedwater TDS, ppm
Bmhos= blowdown conductivity, micromhos
Fmhos= feedwater conductivity, micromhos
3-1.5.7
Determining Feedwater and Blowdown Rates. The blowdown
calculations in paragraph 3-1.5.6 can be used to determine the feedwater rate in units of
kilograms per hour (pounds per hour). Note that the term "feedwater" refers to water
that is fed to the boiler and includes the makeup water plus the condensate return and
steam from the deaerator.
EXAMPLE 3-1:
a) A 1720-kilopascal (250-pound-per-square-inch-gauge) boiler operates at a
conductivity level of 5000 mhos. The boiler feedwater has a conductivity
of 250 mhos. The COC calculation is:
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