Page 32 - Boiler Operator’s Handbook

Operating Wisely 17

gas-fired boiler where the gas head pressure is 16 inches and by observing nature we can get a better under-
of water column at full load. What’s the pressure going standing of what’s going on. Steam is generated and
to be at three-fourths load? Squaring three-fourths gives condensed by nature, we experience it by rain falling
you nine-sixteenths which permits you to answer the and noticing the puddles disappear when it’s dry. Fire
question by saying 9 inches of water column. Note that occurs naturally and we can see what happens when the
nine-sixteenths is much closer to one-half than it is to fuel and air are mixed efficiently (as in a raging forest
three-fourths. If the firing rate is decreased to one-half fire) and not so efficiently (our smoldering campfire).
then the pressure drop is one-fourth and the gas head We can observe the hawks spinning in close circles in a
pressure would be only 4 inches of water column. At rising column of air heated by a hot spot on the ground
one tenth load the pressure drop is one one-hundredth or air deflected by wind hitting a mountain. Even
of full load. That should help explain why many of your though we can’t see the air, can understand buoyancy or
flow instruments fail to record accurately at flows less how an air stream is diverted.
than 10%; the pressure drop is so small that its value Buoyancy is also evident in a block of wood float-
is lower than the pressure fluctuations associated with ing on water. The wood is not as dense as the water so
noise in the piping. I trust you can now see that, if you it is lifted up. The hot air the hawks ride is not as dense
don’t understand this fact of nature, you can make some as cold air so it floats up in the sea of colder air around
very erroneous decisions about your operation. it. The movement of air and gases of different densities
The square root chart in the Appendix is provided is important in a boiler plant, we refer to it as “natural
so you can use percentages to obtain more precise val- draft,” movement of air that naturally occurs because air
ues. Divide the full load pressure drop you note on gag- or gas of higher temperatures is lighter than colder sur-
es between two points in a system (actually using the roundings and rises.
same gage connected at two points would be better, so We can see the leaves and twigs in a stream spin off
you can eliminate gage calibration error) to get a 100% to the side indicating the water is deflected by a rock in
(full load) pressure drop value. For any other pressure the stream. We can see the level of the water increase be-
drop divide it by that full load value to get a percent side the rock revealing the increase in static pressure as
pressure drop. The result of the division will always be the velocity pressure is converted when it hits the rock.
less than one and more than zero. Then draw a horizon- That conversion of velocity pressure to static pressure is
tal line from that value to the intersection of the curve how our centrifugal fans and pumps work.
and a vertical line down to the bottom scale to read the When something happens that doesn’t make sense
percent of full load flow. To compare one state to another try to relate it to what you observe happening in nature.
use the one with the higher pressure drop as if it was full That’s how I arrive at many solutions to problems.
load and perform the math again to determine the flow
at the lower pressure drop in percent of the value of flow
at the higher pressure drop. WATER, STEAM AND ENERGY

At almost every hearing for the installation or ex-
WHAT COMES NATURALLY pansion of a new boiler plant there is the proverbial little
old lady in tennis shoes claiming we don’t need the plant
Observing everything in nature helps you under- because it’s much easier and cleaner to use electricity. We
stand what’s going on in the boiler plant. Most of our have to explain to her that almost all the electricity is gen-
engineering is based on learning about what happens erated using boilers, even nuclear power. Each time I’m
naturally then using it to accomplish purposes like mak- questioned about why the facility needs a boiler plant I
ing steam. The formation of clouds, fog, and dew all think of how history was shaped by the use of boilers. If it
conform to rules set up by nature. By observing them were not for the development of boilers, we could still be
we learn cause and effect and can make it work for us. heating our homes with a fireplace in each room; imagine
We can be just like Newton, sitting under the apple tree the environmental consequences of that!
and being convinced, by an apple dropping, that there’s Most people know so little about the use of water
such a thing as gravity and we can use it to do some and steam for energy that it’s important to establish an
work for us. You can see how it works, then relate it to understanding of the very simple basics, which is what
what’s happening in the boiler plant. I’ll attempt to do in this section. Although you may feel
Many natural functions occur in the boiler plant you understand the basics you want to read this section