pwr_may-2024 - 26

MARNIE SURFACEBLOW
2. With so many variables to consider, Mr.
Rao needed Maya's encouragement. Source:
POWER
" I have been reading a copy of your
findings in our Surfaceblow intranet archives.
I was amused seeing you wrote
equations on Christmas cards and
scanned those in, " said Maya as she
smiled. " It seems a festive way to calculate,
yes? "
Marnie shrugged, " I was hit by inspiration,
grabbed a pen, and wrote on whatever
was nearby. Have you reached the
conclusions yet? "
Maya shook her head. " It is nearly 600
pages of technical references, equations,
sketches of dragons, and goth song lyrics.
I will require the night to finish, " she
surmised.
Marnie nodded. " It's worth the read.
I could drop hints and tease you until
you worked the problem out yourself,
but you have nothing to prove to me, my
friend. Today's lesson is: 'If someone's
already blazed an academic trail through
the jungle surrounding you, try that path
first before making a new one.' Read,
learn, and tell me if you think that one
song on page 252 is any good? The one
about the vampire cat café. "
The video ended. Maya pinched the
bridge of her nose and shook her head. " I
fear someday I must describe these things
to a therapist, " she muttered to herself.
Highly Variable Conditions
It took Maya two days digesting Marnie's
ammonia magnum opus, but it paid off.
She called a meeting for the following
day to report her conclusions.
Facing the assembled plant staff in the
canteen (the coolest spot in the morning),
Maya began, " I have no concise
solution, for I do not believe such exists.
Instead, I can tell you how to find potentially
several parallel solutions, praise be
to Ms. Surfaceblow and her persistent,
passionate problem-solving. "
She continued:
" Mr. Rao, your
26
spreadsheets, neural networks, and
databases are powerful tools. With respect,
you are not correctly employing
them. First is the problematic assumption
that coal-based empirical relationships
for ash resistivity can be used for
predictions with biomass. The ash mineral
analysis is deceptive in this case.
For example, silica in coal points to the
presence of hard-rock minerals, or even
clays and shales, with melting points
above 1,600C. In biomass, however, silica
may take on glassy, alkali-lime forms,
melting below 1,100C. This is why it is
not proper to attempt predicting slagging
and fouling in the boiler by using
coal-based indices for biomass fuels. To
assist you so you need not repeat her
effort, she has provided many research
papers to guide you, which I e-mailed to
you just before this meeting. "
A minute later, Mr. Rao nodded as he
found Maya's e-mail on his laptop. " This
all may be true-I will need to examine
the research-but what is the reason for
our varying ESP performance? " he asked.
" Potentially many reasons, " Maya responded.
" Here is my conclusion after
studying a multivariate
solution.
First,
there is a misperception that ammonia
changes ash resistivity. Aside from some
unusual cases, ammonia has the effect
of combining with sulfur and forming ammonium
bisulfate. This is the very sticky
substance found in air heaters downstream
of ammonia injection grids. But
ammonium bisulfate requires sulfur to
combine with, and thus, for low-sulfur fuels,
ammonia's impact can be even less. "
" Then why does adding more ammonia
cause the ESP performance to
decrease sometimes? " asked one of the
operators.
" Because when your ammonia concentration
is high relative to sulfur, ammonium
sulfate, which is less sticky than
its bisulfate auntie, begins to form, " explained
Maya.
" You are saying ammonia does not reduce
ash resistivity. That is different than
we were told, " Mr. Mankar said dubiously.
" It depends on the type of ash, "
Maya countered. " In most cases, no-
the effect is reducing the resistivity of
the flue gas, also called the space resistivity.
This reduced space resistivity
allows an increased effective operating
voltage, giving improve charging of
ash particles. " Maya paused, then said,
" Humidification of the flue gas, via
burning higher-moisture fuels or fuels
with more hydrogen in them, will also
reduce space resistivity. However, the
www.powermag.com
moisture and ammonia are not additive
in effect. Higher flue gas moisture has
been found to reduce ammonia's effectiveness
via several methods, which depend
upon the specific fuel being fired.
And there's still more impacts to consider,
which can be strongly influenced
by changes in the flue gas velocity, temperature,
and other mineral compounds
in the ash. Namely, every different fuel
you burn may require a set of customized
ammonia injection curves. "
Despite having been given powerful
clues to help them solve their ash emissions
problem, none of the engineers
seemed happy upon learning there was
not a single, simple trendline to draw.
" What are we to do? " cried Mr. Rao, as
he sat and held his head (Figure 2).
Mr. Mankar walked up and placed a
hand on his shoulder, speaking reassuringly
to him, the station manager said,
" You will do what you have always done.
You will collect the data, arrange it, and
develop those ammonia injection curves. "
" Mr. Rao, by using your very clever
RFID fuel tracking system, I am certain
you shall be able to correlate the fuel
data with many other operations variables
of the ESP system and find the
multivariate equations to develop your
own set of curves. And given your capabilities,
I feel confident you can incorporate
these seamlessly into the
power station emissions control systems, "
Maya reassured the young engineer.
" May I now share with the group
some outlines of the path forward I developed
this morning? " she asked.
A Delightful Day, but Clouds on the
Horizon
Saturday morning found Maya resting on
her father's porch, sipping orange juice
with her auntie Komal. Her father joined
them, and the three sat in comfortable
silence, looking across the orange fields
at the stack of the biomass power station
in the distance. While not completely
clear, the ash was already much less
visible as the station operators and engineers
diligently worked to find the best
way to balance their emissions.
It was a perfect, idyllic day. Yet, Maya
frowned. She remembered Marnie's final
words at the end of their video call
the previous night: " Rest well, so you're
in top form kiddo. Our next job is going to
be one of the hardest ever. " Even in the
heat of a Nagpur May, Maya shivered. ■
-Una Nowling, PE is an adjunct professor
of mechanical engineering at the
University of Missouri-Kansas City.
POWER | May 2024
http://www.powermag.com
pwr_may-2024

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