POWER July 2023 - 28

MARNIE SURFACEBLOW
High Anxiety at Low Loads
Ultra-low loads may be necessary for large coal plant survival, but they represent
uncharted territory for operations and maintenance staff. Stay informed on the
latest trends for success and expect the unexpected.
Una Nowling, PE
This is ... coffee? " Marnie Surfaceblow,
vice president of Surfaceblow
& Associates International, stared
balefully at the weak concoction in her
paper cup. " My dear friend, Mary, this is
simply atrocious! No wonder you have
so many problems here. With coffee like
this, your staff likely just ... loses their
will to live. " Shaking her head, Marnie
continued, " We were roommates in the
engineering dorms, and yet, you disrespect
me like this? "
Mary Short, day manager of the Cot "
tonwood
Power Plant and a friendly rival
of Marnie's since university, smiled wanly.
" Remember that funny sign at the coffee
shop we worked at? 'Don't complain
about our coffee-someday you may be
old and weak yourself!' "
Marnie could not suppress her shudder.
" It was by Upton Sinclair, and like
most things he wrote, it was highly
misunderstood. Like how every single
high school teacher thinks The Jungle
was about the meatpacking industry. It
was about socialism! Not hot dogs, but
socialism! "
Maya Sharma, Marnie's lead field engineer,
tapped notes into her computer
while adding, " Ma'am, let us focus upon
this problem. Or, perhaps, we can continue
with topics not of importance. I
could relate to Ms. Short your attempt to
create an ultrasupercritical coffee maker,
and what happened to our laboratory ... "
" Another time, " interrupted Marnie,
her fair Scottish face blushing slightly. " It
looks like the meeting is about to start. "
Operations Evolve
As the clock showed 7:00, the plant lead
staff filed into the conference room.
There was the traditional confusion of
handshakes, business cards, and finding
seats, and then with a clearing of her
throat, Mary kicked the meeting off and
addressed the Surfaceblow duo.
" I told you most of the situation in our
last call. The plant was commissioned
in 1998, and like all of us, it's starting to
show its age. " Only Maya heard Marnie's
muttering of " speak for yourself, " and
gently kicked her boss's leg under the ta28
ble.
" We're the last operating coal plant
in our system, mainly because we're still
paying off the loan. "
" But the world has changed, and
those who do not adapt shall perish, "
Marnie noted. " Somehow you managed
to keep mostly baseload operation going
until five years past, and I see that when
you moved to deep cycling operation,
you did your best to accommodate the
new regime. "
Walt, the maintenance lead, spoke
up. " We started seeing really bad sulfur
corrosion as the flue gas temperatures
dropped, so we started blending in lowsulfur
Central Appalachian coal and then
eventually switched away from our design
high-sulfur Illinois Basin coal. Our
ash content went up, but at the lower
loads, fly ash erosion wasn't so much a
problem anymore, " he said.
Mary continued, " When the Cowskin
project came online
Creek solar
last
year, we shifted to parking at the lowest
load possible-about 45% of MCR
(maximum continuous rating)-to supply
constant low baseload generation.
But even that sometimes put us out of
the money because it was too much
power at the wrong time. We'd already
changed the low-pressure turbine section
to improve final steam quality, and
after we upgraded our control systems,
and swapped the main plant fans and
the boiler feed pumps to VFDs (variable
frequency drives), we could reduce our
minimum stable load all the way down
to 20% of MCR. "
" Ma'am, with your boiler being natural
circulation, was that not a problem? "
inquired Maya.
Mary nodded toward Keith, their water-side
lead, who answered, " We added
an electric booster pump to help out at really
low loads, and after some trial by fire,
it seems to work. " Pausing and frowning
deeply, he continued, " I doubt we could
go too much lower though, even without
all the other problems we've had. Did
you tell them everything? "
Mary walked to the whiteboard and
started listing bullet-items of pain for the
plant operators. " Number one, we started
noticing about six months ago that we
www.powermag.com
were clogging the underflow lines in the
wet limestone scrubber from high fly ash
carryover. We fully oxidize our scrubber
sludge to make gypsum. We don't make
much money from it, but it's a lot better
than paying $30 a ton for landfilling. But
the problem was a moving target. Once
every couple of months we would see
serious scrubber fly ash carryover, so
bad we had to blow the system down for
days, AND we were paying $100,000 a
month to landfill contaminated gypsum. "
Maya raised her hand, and asked,
" Ma'am, when this event occurs, do you
have high unburned carbon in the ash?
And do you have opacity monitors downstream
of the precipitator? "
Mary shook her head. " No problem
with fly ash LOI (loss on ignition), and we
aren't regulated on opacity. We pass every
particulate emissions test pretty easily
though. Our limit is 0.1 lbm/MMBtu,
and we've never tested above half that. "
An 'Unhealthy' System
Kelly, the scrubber lead, added, " Don't
forget what else happens with that fly
ash in the scrubber. It starts to line the
inside of the pipes, like arteries clogging,
and last fall a big piece of fly ash
concrete came loose and destroyed a
recycle pump. "
" Like a blood clot suddenly breaking
free, to carry on the cardiac analogy, "
added Marnie, with a somber look. After
a minute's thought, she added, " I really
should eat healthier, but they lock the
yogurt fridge before I even get down to
breakfast at the hotel ... "
" That is not an acceptable excuse
ma'am, " interjected Maya. " You are
merely attempting to justify your traditional
morning sausage and biscuits. "
As Marnie looked open-mouthed at her
assistant, unable to develop a defense,
Maya carried on. " I see there is an unplanned
outage this morning. What is
the root cause? "
" We had another scrubber recycle
line clog and pump damage, but also
we didn't see much of a fly ash upset
this time. That's another strange thing
that's been happening. " Mary paused
and spoke into her plant radio, " Jessica,
POWER | July 2023
http://www.powermag.com
POWER July 2023

Table of Contents for the Digital Edition of POWER July 2023
