Scrubber Additions and Booster Fans
Today, more than ever, you must consider energy efficiencies
when installing new machinery. The PAM Motor design enables you
to save a significant amount of energy by switching to an optimum
low speed when high-speed operation is not required.
The chart below, of a typical ID fan, Illustrates how a reduction
in motor operating speed will in turn reduce horsepower. This
lowers the motor's energy consumption and increases your dollar
savings.
By observing the fan laws we see that:
- Volume varies with speed.
- Static pressure varies as the speed squared.
- HP varies as the speed cubed.
In this example, changing speeds results in saving 1200HP.
If energy is evaluated at $1700/KW x 1200HP x .746KW/HP, the savings
are $1,521,840.
In this example, to attain high unit availability, the fundamental
requirement is to size the ID fan such that the boiler will not
become ID fan limited. Yet, care is taken not to increase the
potential for problems with draft controllability and implosion
because of over-sizing. Sufficient margin is added to the gas
flow rate estimated from the boiler manufacturer's predicted MCR
heat input so that the ID fans can handle the gas flow at the
maximum demonstrated heat input without difficulty.
Additional margins are provided for increased air leakages, boiler
gas path fouling, air-heater fouling, fan performance deterioration,
and other uncertainties.
To account for all these allowances, typically a 15% mass flow
margin and a 32% static pressure margin is applied to the MCR
values to obtain the Test Block conditions.
Some fans are specified to be designed for initial base load
operation with provisions for future cyclical duty. Additional
revised design conditions due to scrubber and balanced draft conversion
affect the ID fan size.
These requirements are shown in the Pressure / HP vs. Volume
curve.
Thus the fans and motors are designed for Test Block requirements
but normal operation is a MCR. This sets the stage for two-speed
conditions.
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