POWER April 2023 - 26

MARNIE SURFACEBLOW
will lead to disaster. "
" As well you should be, " Marnie sternly
replied. " Mill fires lead to not only
damaged equipment, but the potential
for an explosion, which could very easily
be fatal. "
Valentina nodded her head. " Indeed,
we have had one small pressure spike
from combustion ... "
" I just heard 'explosion,' not 'pressure
spike,' " Marnie interrupted.
" OK, then, expert lady, explosion from
fuel deposits in a fuel pipe, " Valentina
scowled.
Luis Phillipe stepped in, " Let us tell our
guests about the CO measurements. "
Marnie noticed Maya immediately tensing,
her full attention riveted on a wizened
plant engineer. Looking as if he
carried more years of plant experience
than the rest of the room combined, a
gentleman introduced with reverence
as Señor Franco shakily stood up, and
with the help of Miguel called up another
screen onto the display.
" I always have doubts about this new
fuel, so I walk the power station and
monitor gases-explosive, poison, suffocating.
I walk the station and always
watch, " the seasoned plant veteran explained.
" So, this week I walk the floor
over the silos, and I find CO. And, I put
monitors over each silo. " Señor Franco
paused, while Miguel typed a few buttons
and highlighted CO reading trends.
" Sir, I admire very much your dedication
to safety. These CO measurements
are very low, one to eight parts per million,
and mostly under five. Is there not
always some CO near the fuel handling
system? " Maya asked.
Señor Franco shrugged, " Never have
I seen any CO above the fuel silos. It is
small, but my instruments are calibrated
daily. "
" That ... does warrant notice, sir, "
agreed Maya. " I wish to examine all historical
data since operation on biomass
began. "
" And I want to examine the fuel silos
and the mills, " added Marnie. " Maya, can
I borrow your collection of gas sensors? "
Silo Operation and CO Monitoring
The plant was dark and relatively quiet,
save for occasional distant clangs and
conversation as the staff took advantage
of the unplanned outage to perform
some repairs and preventive maintenance
activities. Marnie, Señor Franco,
Miguel, and Valentina gathered around
the steel grating covering the fuel silos.
After tying off for safety, Marnie leaned
26
over to peer through the grating on top
of the silos, but her flashlight couldn't
penetrate the lingering biomass dust
cloud. Not to be defeated, she produced
her high-powered hand-held green laser
and shone it down through the dust to
gauge the height of the fuel pile in each
silo. After a moment's observation, she
asked, " Why are silos one and four nearly
full of fuel, but silos two and three are
less than half full? "
" We have raised the plant capacity
with pellets step by step, starting with
the middle two mills. We were going to
start three-mill operation soon, but then,
well, the CO, " Miguel said. Then turning
to Señor Franco, he asked, " Señor,
where was the CO most concentrated? "
Señor Franco pointed to the number
two and three silos, and replied, " Mostly
these, but a trace in the others. It drifts,
as you know. "
" And when did you install the permanent
CO monitors? " asked Marnie.
Miguel checked his notes and replied,
" Last month. We didn't notice the CO in
the control room because it was under the
alarm point for worker safety, but not for
impending or slow combustion. We have
since corrected that error and are grateful
Señor Franco checked this himself. "
" Look, I know every safety agency has
exposure limit curves, but really now, CO
is like mercury-there is no lower limit
that is truly safe. And if it implies a fire,
then we have a serious problem. Where
are your temperature sensors on the silos? "
Marnie asked.
Miguel pointed to one sensor mounted
in the grating and replied, " Also there
is one sensor every three meters until
above the bottom cone, there we have
four sensors. "
" Why at the bottom of the silo? Why
not near the top? The heat would rise to
the top, " Marnie said.
Miguel and Señor Franco shrugged.
Valentina offered, " I believe we thought
that would be the wettest area and prone
to more heating from the moisture. "
" I see, " said Marnie. " I noticed water
standing up here. Your roof is in terrible
condition, and here, right here, " she highlighted
a tiny rivulet wending from the
wall, " it's leaking into silo number two
right now! "
Valentina and Miguel both sighed.
Miguel responded, " We have spent
much on roof repairs, but our budget is
continually reduced. We do what we can,
but ... "
" I know, but you also know this isn't
good. Let's examine the feeders and
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2. Marnie and Señor Franco inspect a mill.
Source: POWER
mills, " Marnie said, leading the way and
shaking her head.
Feeders and Mills
The number two and three feeders and
mills were currently open for inspection,
and it was clear there was water actively
draining in a slow drip from the bottom of
the silo cone. " How does your biomass
even flow when it's that wet? " Marnie
asked.
" We have pluggage at first, and then
it will start to flow. Señor Franco says we
should redesign the bottom cone to be, I
think, a hyperbola? But we have not the
time, and we have the hot biomass and
CO to be concerned about, " answered
Miguel.
" You only have a small amount of
spilled biomass, but some of it looks
slightly charred. " Marnie frowned to herself,
and then took her thermal camera
from her latest Prada purse and started
scanning the area. " I'm not seeing much
in the way of heat right now. And the CO
readings were low, despite the wet fuel
that should be self-heating. So, why ...
let's examine the mills, " she said.
Descending to the next level where
the mills sat open for inspection as
well, Marnie examined each in turn as
much as possible without requiring site
confined space certification (Figure 2).
" There's some sign of wet fuel buildup
here, and in the pulverized fuel pipes,
and the downspout, and ... everywhere, "
she noted.
" Señora, " said Señor Franco quietly,
" often the reject spouts are blocked
when the fuel is wet, and sometimes the
POWER | April 2023
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POWER April 2023

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