Flash Steam
Explanation
and
Calculation
Flash Steam
When hot condensate above the saturation
temperature under pressure, is released to
atmospheric pressure, the excess heat is
given off by reevaporation or what is common-
ly referred to as flash steam.
Flash steam is important because it contains
heat which can often be utilized for economy.
It is necessary to know how it is formed and
how much will be formed under given condi-
tions.
The Btu values given in the Properties of
Saturated Steam tables provide the neces-
sary data for calculating energy loss due to
flash steam.
Float and thermostatic traps, bucket traps,
and disc traps discharge condensate at
approximately saturation temperature.
Thermostatic traps discharge condensate 10°
to 30°F. below the saturation temperature.
Flash Steam Heat Loss Calculation
The form provided to the right will allow you to
easily calculate the flash steam loss and
associated energy cost.
Lines A, B, C, D, and E are based on the actu-
al operating conditions. It may be necessary
to estimate the average conditions when
loads fluctuate.
Lines F, G, H and I can be filled in using the
values from the Properties of Saturated
Steam table.
The calculation for flash loss may now be
made with the annual loss determined.
The calculation of energy cost may now be
made to determine the flash loss and
required heating of make-up water to replace
the flash loss.
The amount of make-up water and water cost
can also be determined using this form.
How to Calculate Your Own Flash Steam
and Energy Loss
List Operating Conditions:
A. ____Initial Saturation Pressure.
B. ____Reduced Pressure.
C. ____System Load in Lbs. Per Hr..
D. ____Cost of Steam Per 1,000 Lbs.
E. ____Make-up Water Temperature ° F.
From Properties of Saturated Steam Table:
F. ____Btu/Lb. in Condensate at Initial
F. ____
Pressure.
G. ____Btu/Lb. in Condensate at Reduced
G. ____
Pressure.
H. ____Btu/Lb. Latent Heat in Steam at
H. ____
Reduced Pressure.
I. _____Btu/Lb. in Make-up Water.
Calculation of Flash Steam Loss
F – G x 100 = % flash loss
______ x 100 = ______% of flash loss
C x % flash loss = lbs. per hr. loss
To obtain annual loss multiply Ibs. per hr.
Ioss x hr. per day x days per year process
operates = Ib. of flash steam annually.
Calculation of Energy Loss:
This calculation must take into consideration
that, not only are we reducing the tempera-
ture of the returns, but that the condensate
removed in the form of flash steam must be
replaced with cooler make-up water.
% of returns x system load Ibs./hr. x (F - G)
= Btu/hr. condensate cooling.
% of flash loss x system load Ibs./hr. x (F - I)
= Btu/hr. make-up water loss.
Btu condensate c make-up loss
= Btu/hr. Ioss.
Btu/hr. Ioss x hr. per day x days per year
= annual Btu loss.
Btu annual loss ÷ H = equivalent Ib./yr. Ioss.
Lb./hr. Ioss ÷ 1,000 x D
= annual cost of flash steam loss.
Lb./Year Flash Loss ÷ 8.33
= Gallons per year make-up water.
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