POWER May 2022 Intl - 32

MARNIE SURFACEBLOW
erative air heater bearing oil temperature. And while we go
on that journey into mystery, my assistant Maya is going to
try killing off some of your false DCS alarms to make life a
little quieter for everyone. "
" Sure ma'am, but we don't get bothered too much by the
alarms, " Brad responded.
" I respectfully must disagree Mr. Clinton, " interjected
Maya. " In the eight minutes we have been in this room,
there have been 29 audible alarms, none of them serious.
That is every 17 seconds, and this is resulting in great distraction
for you. " Marnie nodded in agreement, adding, " And
the constant hurly-burly of these alarms is keeping you from
hearing a cry for help from your air heater. For months, temperatures
trended from about 80-120F, but yesterday, they
jumped to 160F and started cycling from 120F to 160F and
back again. What are they right now? "
Brad clicked quickly through the DCS screens and produced
a trendline of air heater lube oil temperatures.
" Great. Now, add the air heater inlet and outlet temperatures,
and flowrates over the last six months. " Brad nodded,
and a minute later the screen was filled with a tangle of
colored trendlines.
" Maybe it's just got hotter because this week's been a
scorcher, " Brad suggested. Marnie scanned the screen and
frowned. " But temperatures were stable for six months-
winter, spring, and summer. What changed? " she asked.
" Sir, what is your alarming point? " asked Maya. Brad replied,
" We alarm at 180F and trip at 200F, but we've never
even come close to an alarm. We leave the system alone,
and it just works. "
Marnie suddenly came to attention. " Show me the trends
on every single tag you have on the air heater lube oil system,
quick! " Rapid mouse-clicks led to a skein of trendlines
appearing on the DCS screens. Marnie focused on the
trends, green eyes shining in the light as she watched the
patterns form and reform in her mind. " So, my young assistant,
why would the lube oil temperature jump when nothing
else changed? Air and gas temperatures don't trend with it,
flowrates are independent, the air heater rotation's a little
slower, sure, and the oil pump amps are ... oh ... "
Maya looked over at her boss, one eyebrow raised in question.
" I heard an 'oh.' That means you locked the keys in the
rental car, again, or you have found evidence of a problem. "
" Yes ... to both. By the way, I hope you have the rental
company number; I can't even remember their name. Something
that sounds like ... food? " During the awkward silence
that followed, Maya patted her pocket to confirm her spare
keys were safely tucked away. Stan and Brad looked askance
at Maya, who held one finger up to her lips and shook her
head. The silence was split with a whoop from Marnie.
" I got it! Brad! Take me to the lube oil tank! Someone, get
me a shop rag! And then some coffee, with enough cream
and sugar you can make pancakes with it! " Grabbing their
personal protective gear, the four left the cool of the control
room and trekked into the hot din of the plant.
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Solving the Issue in the Field
" That was a close one, Maya, " said Marnie as they journeyed
toward the parking lot. " The oil level was just low enough
that the pump was cycling from liquid to air. The clue was
the oil pump amp readings-when the pump couldn't draw
oil, the amps cycled down and the bearing temperatures increased.
Then, when enough oil returned to the tank, the
amps cycled up and the bearing temperatures dropped. Also
note, Brad said they basically left the system alone, telling
me that with all the other planned and unplanned emergencies
each day, they probably forget to check the oil. The good
news is the monitoring system did its job, and they avoided
a lengthy and expensive outage. For goodness' sake, the air
heater bearing alone can cost upwards of $20,000-and if
you don't have a spare handy, the whole plant could be down
for a couple of weeks. "
Maya stopped to lean against a car, removed her hard
hat and shook out her hair. " I must respectfully disagree
ma'am. The monitoring system should also have noted the
oil pump amperage and informed operations of the root
cause. I will add logic to the system tomorrow so this will
never happen again. "
Marnie nodded, and added, " Don't forget, you were going
to kill some dead DCS tag alarms. Or are they really undead?
Oh great, next thing they'll tell us is the plant is haunted.
Grandpa Marmaduke would have gotten a kick out of that! "
" I have great certainty, ma'am, that even were the plant
haunted, you and I would exorcise it together, " Maya retorted.
" Of course we would! " Marnie beamed at her assistant.
" Now, do you have great certainty you can find our rental
car? I'll bet you dinner you can't find it in five minutes. "
Maya smiled smugly, flourishing the spare key set,
pressed a button on the fob, and the trunk of the car she
was leaning against opened slowly. ■
-Una Nowling, PE is an adjunct professor of mechanical
engineering at the University of Missouri-Kansas City.
32
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