Page 262 - Boiler plant and distribution system optimization manual

Chapter 13

Steam System Optimization

STEAM SYSTEM OPTIMIzATION, water up to boiling temperature. This sensible
A HUGE OPPORTUNITY FOR SAVINGS energy may be lost through a phenomena known
as “Flashing” when hot condensate is formed at
According to the Department of Energy, a high pressure and escapes to a lower pressure
nearly 160 billion dollars is spent creating steam through the steam trapping system.
in a single year. Steam generation accounts for Figure 13.2 shows what happens to the con-
fully one half of the industrial and commercial en- densate when it escapes from a higher pressure
ergy dollar. When you consider that steam plays to a lower pressure. Illustrated here is a trap for
a major role in generating electricity this number a heat exchanger which is forming condensate
can be much higher. Energy conservation mea- at the rate of 100 pounds per hour. The system
sures described in this chapter can play a signifi- pressure is 100 psi and the corresponding steam
cant role in saving over 15 billion dollars annually temperature is 353°F. This 100 lb of condensate
which is lost in steam distribution systems. contains 32,500 Btu.
The cost of operating a steam system in- On the low pressure side of the trap, which
cludes: is atmospheric pressure in this case, the satura-
tion temperature is 212°F. Of the 100 pounds of
a. Boiler operating costs condensate, 14.8 lb will form flash steam with
b. Steam distribution system losses a heat value of 17,100 Btu. The remaining 85.2
c. Trapping system losses pounds of condensate formed will contain 180
d. Condensate return system losses Btu per pound for a total heat content of 15,400
e. Operation and maintenance of the systems Btu. Notice that the 32,500 Btu in the condensate
involved. on the high pressure side of the trap has formed
steam and water with the same total heat content
Boiler Plant Optimization of 32,500 Btu.
Boiler plant operating costs and losses have Table 13.1 shows the percentage of steam
been covered in the earlier chapters of this book. that will form at the new lower pressure. This
An important fact to keep in mind is that every low pressure flash steam will, in fact, contain
Btu wasted in the steam distribution system has more heat than the condensate. There is a great
to be replaced by the boiler and the boiler has potential for half of the energy going through the
large losses of its own. If a boiler is 80% efficient, trapping system to be lost as flash steam, espe-
then at least 20% of the original fuel used to gen- cially in condensate recovery systems that vent to
erate steam for the distribution system is lost and atmosphere.
does no useful work. The higher the steam system pressure, the
higher this flash steam loss will be, so one im-
getting the Most Energy from portant factor that should be examined is how to
Steam Systems reduce this loss.
Energy in steam consists of sensible and la- Table 13.2 shows that the higher the steam
tent heat (Figure 13.1). It is apparent that a sig- system pressure, the less latent heat is available in
nificant amount of heat is invested in bringing the steam. This latent heat is what does the work,
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