Page 42 - Boiler plant and distribution system optimization manual
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Chapter 3
Energy Management Basics for
Boilers and Systems
ENERGY BALANCE AND LOSSES THE BTU (BRITISH THERMAL UNIT)
Understanding how energy works in sys- ———————————————————
tems is essential to an effective energy manage- “The quantity of heat required to raise the
ment program, so lets examine some basics. temperature of one pound of water one
The purpose behind managing an efficient degree Fahrenheit”
plant is to get as much energy as possible from ———————————————————
the fuel. How much would this be?
A good starting point for establishing the For scientific purposes this is measured at, or
“Ideal Scene” for an efficient plant is knowing near, its point of maximum density of water 39.1
how much energy is being delivered to the sys- Deg F [3.9C].
tem? The term used to express the energy deliv-
ered to a plant in fuel is Higher Heating Value or
(HHV—Table 3.1). INPUT-OUTPUT EFFICIENCY
The starting point for finding efficiency be-
THE HIGHER HEATING VALUE (HHV) gins with accurate knowledge of the amount of
energy “input” into the process. Two things must
——————————————————— be known, how much fuel is being fired and how
The total heat obtained from the combustion many Btu’s are in each pound of fuel. The range
of a specified amount of fuel. of heating values for various fuels is given in Ta-
——————————————————— ble 3.1.
Boiler efficiency is the percentage of the fu-
The HHV represents the total amount of heat el’s higher heating value which is converted to
energy released from the fuel when it is complete- steam. This is sometimes called the Fuel-To-Steam
ly burned, at 60 Deg F [l5.6C] when combustion Efficiency. The formula for Input-Output efficien-
starts and the combustion products of which are cy is:
cooled to 60 Deg F [15.6C] before the quantity of
———————————————————
heat released is measured.
Btu Output x 100
For practical reasons, flue gas is not cooled Efficiency= —————————
down to 60 F because acid will form which can Btu Input
cause severe corrosion problems. Stack tempera- ———————————————————
ture is kept above the acid dew point or acid for- Figure 3.1 Efficiency defined
mation temperature which wastes some of this
heat energy.
Fossil fuel heating values are expressed in Efficiencies are basically limited by the acid
terms of Btu/lb in tables and for standard calcu- dew point arid excess air. The acid dew point is
lations. the temperature at which acid begins to form on
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