POWER September 2023 - 34

MARNIE SURFACEBLOW
Bowing Under Pressure
Just because something hasn't failed doesn't mean it won't-especially when an
" old dog " of a plant is taught new tricks.
Una Nowling, PE
wo women wearing personal protective
equipment waited impatiently
in the shade of a guard hut
on an unusually warm Canadian summer
morning. Slapping her forearm to
kill a mosquito that had started drilling
for blood like a tiny oil derrick, Marnie
Surfaceblow, vice president of Surfaceblow
& Associates International, was at
her wits' end. " They say there are two
seasons in Canada, my faithful apprentice-winter
and mosquito. I think that
makes bite number 500 from these Lilliputian
vampires. And how come they
aren't bothering you? " she remarked to
her assistant.
Maya shrugged. " I am Indian. Our
strength and honor cannot be overcome
by mere mosquitos. Also, insect repellent. "
Marnie nodded. " Your foresight favors
T
fortune. And Saint Sara be praised, our
hosts have arrived to rescue us! "
They were greeted very warmly by the
plant manager, Preston McDonald, and
the chief engineer, Annik Ivanoff, who offered
the mercy of an air-conditioned ride
to the old coal power station (Figure 1),
which was having some problems converting
to biomass fuel. As they made
the usual pre-work small talk, Maya
asked Annik, " By your family name, Ivanoff,
are you Russian? "
" Inuit, and two-spirit, " replied Annik.
" Many from Alaska have Russian names
from the occupation. My chosen name
means 'grace.' "
" Well that's fairly fortuitous! " announced
Marnie with glee. " My name and
Maya's mean joy, and with yours meaning
grace, hopefully we'll all have good luck!
Preston, what does your name mean? "
Preston smiled, " Oh, shoot, I don't
know. Maybe 'he who has more problems
than mosquitos,' eh? "
" Well, I can't do anything about the
mosquitos-darn it, speak of the devil! "
Marnie slapped her arm again, claiming
another insect victim, " but I'll bet we can
help get rid of your problems. "
Unveiling the Plant Puzzle
The morning briefing was well-attended
by friendly and highly engaged plant staff,
who were clearly hoping for good news
from the visiting consultants. The usual
introductions were made and business
cards exchanged. Marnie took a four-liter
carton of Tim Hortons' coffee from her
backpack and started pouring a cup.
" Well, thank you so much for bringing
us all coffee, ma'am. I'll go get some
more cups, " said one of the engineering
interns. Marnie sat in mute horror,
until Maya leaned over and whispered,
" Ma'am, it will work out. I anticipated
such, and have hidden an extra liter of
coffee in my backpack for you. " Marnie
turned and stared at Maya, and whispered,
" Remind me to give you a raise
when we get back to the office. "
When all had taken a cup of Marnie's
figurative lifeblood, and Maya had surreptitiously
passed the full liter carton to
Marnie under the table, Preston started
the meeting.
" We started burning local coal in
1. Marnie and Maya are greeted by Preston
and Annik at the coal plant's front gate.
Source: POWER
34
1949, sending 400 MW almost 24/7 onto
the grid. The plants mostly standard design-subcritical
balanced-draft, five mills
with one kept spare, each mill feeds one
burner level. We have two electrostatic
precipitators, no other emissions control
systems. And the plant was reliable,
running smooth until the powers that be
said we had to stop burning coal within
eight years. We're natural gas poor in this
province an' no pipelines to bring enough
in. There's local hydroelectric power, see,
but some energy trader sold all the extra
to the States for a decade! If this plant
shuts down, we can't make it through
www.powermag.com
the winter without brownouts or shutting
down industries, " he explained.
Maya flipped through some briefing
pages, and commented, " And while you
could deploy demand-side management
plans, my research shows two aluminium
smelters are your largest contracted
customers. Those customers often require
baseload power, so your flexibility
is limited. "
" Well, we found a white knight, "
Preston replied. " There's a wood pellet
producer nearby using partial thermal upgrading
to make pellets we can get by
on. We derate by 200 MW from poor mill
grindability, but they're relatively cheap. "
Marnie, flipping through fuel quality
data sheets, replied, " Hmph. Maybe. Given
the cost per tonne, I mean, you could
truck pellets from elsewhere cheaper. "
" We looked, " replied Annik, " but you
know what the pellet market looks like?
There's waiting lists two years out for
pellets we could use. "
Marnie shrugged. " So ... they're not
carbonizing the pellets very much, and
their bulk density implies a worn pelletizer.
This bulk density of 550 kilograms
per cubic meter [kg/m3] wouldn't pass
muster in some countries. Your local
coals have a density of about, what,
800 to 850 kg/m3? No way that doesn't
cause problems. "
" Nope, it's definitely part of the problem, "
Annik shook her head and continued,
" Just lightly cooking the pellets
doesn't really help energy density, so
the pellet heating value is two-thirds
that of coal. At 200 MW, we burn eight
more tonnes of pellets per hour than we
burn of coal at 400 MW. Being mostly
small cylinders, the pellets have more
void space than coal. Our two main plant
feed conveyors have a 27-degree hoist,
and pellets roll back down the belt and
spill-being small cylinders on moving
equipment. We started water misting to
increase pellet adhesion, and it genuinely
helped, but not near enough to reach
more than half capacity. "
Jeff Clinton, a grizzled fuel-handling
engineer, spoke up. " We have separate
silos per mill, rather than a single divided
bunker. Since the pellets don't grind
good, we send them to the three middle
POWER | September 2023
http://www.powermag.com
POWER September 2023

Table of Contents for the Digital Edition of POWER September 2023
