pwr_january-2025 - 27

MARNIE SURFACEBLOW
ladies are warm enough. Even I'm feeling
this
weather. The nighttime low
could get to -40F. Hey, Ms. Sharma, you
use the metric system in India right?
What's -40F in Celsius? "
Forcing her teeth to stop chattering,
Maya replied, " It is the same temperature,
-40C, sir. "
" Huh, " Wayne replied. " Then, why do
they call it two different names? Why not
just Fahrenheit? "
Marnie was about to say something
she believed would be very humorous
and clever, when Maya cleared her
throat in a way that expressed, " Ma'am,
do not take the bait. "
After arriving at the primary reformer,
Claude began the situation narrative.
" The plant was built in 1979 and
uses steam methane reforming feeding
a Haber process to make ammonia.
A small scrubber just upstream
removes sulfur and other contaminant,
sending cleaned gas to the primary reformer
here. This module mixes steam
with the cleaned natural gas, passing
them both down catalyst tubes inside
a containment shell. Natural gas burners
add heat to help the process, firing
down in parallel flow to the gas inside
the tubing. The burner exhaust gas
goes to the primary reformer stack,
and gas exiting the catalyst tubes is
now called syngas, comprised of about
50% hydrogen by volume, along with
water, carbon monoxide (CO), and carbon
dioxide (CO2). "
" Excuse me, " Maya interjected. " The
data you sent indicates the primary reformer
has been in service thrice its
design lifespan. Yet, your reliability was
quite good until the last two years, when
equipment failures increased markedly. "
Claude nodded. " We see the same
trends, but we're not sure exactly why
it's worse, " he admitted.
Maintenance
manager Ron
ance, although we didn't always have
a failure as a result. Once we see the
hot spot form, a failure will occur at that
point. It may be delayed by a couple of
days, but it always happens. "
Wayne added, " No one's been able to
explain why these hot spots form near the
reformer exit, instead of near the burners
at the entrance. Why would they form at
the furthest point from the burners? "
Marnie and Maya gave each other
" the look " with perfect timing.
More Unsolved Mysteries
" Here's something maybe you can help
fix, " said Ron Sorrel as he began describing
the next part of the process.
" We have exhaust gas cooling tubes
downstream of the primary reformer
shell, intended to circulate glycol to
recover heat and cool down the stack.
Over time, severe leaks formed in the
long underground runs for the cooling
water lines. We didn't lose much water.
The problem was soil and sand ingress
when the water stopped flowing. The
soil clogged the heat exchanger piping,
and the sand scored the pipes, valves,
and water pumps. "
" We tried to replace them, " Wayne
added. " But there's a lot of underground
utilities here, and very few of them are
marked. These water lines aren't very
deep, maybe 18 to 24 inches, but the
plastic they used not only doesn't show
up with conventional locater tools, even
ground penetrating radar had trouble
seeing them. If we know where they ran,
maybe we could fix them and restore the
system to full operation. "
" Doesn't your chimney suffer damage
from the elevated exhaust temperatures? "
asked Maya.
Ron replied, intending to be humorSorrel
chimed
in. " When tube failures started
increasing, we thought maybe burner
flames were impinging on the tubes. We
spent weeks tuning the burners, then replaced
about half of them that had dodgy
performance, but the failure rates stayed
high, " he reported.
" Are there any indicators that a failure
is imminent? " asked Maya.
" According to
our
thermocouple
probes, hot spots form in concentrated
locations on the tubes, " Claude replied.
" The reformer is designed for steadystate
operation, and even when it was
newer, hot zones would sometimes
form when something was out of balJanuary
2025 | POWER
ous, " Our exit dampers melted stuck
open, half our stack lining is gone, and
the concrete outer stack is spalling off
from the heat. So, yes. "
" Could you add a water mist curtain
just upstream of the stack to cool it
down? " asked Marnie. Ron, Claude, and
Wayne looked at each other, then Ron
noted, " The only problem I might see is
freezing in the winter. But if we can stop
the erosion three seasons of the year,
that's pretty good! "
They walked to the secondary reformer,
and Claude continued his narrative.
" This system is called air-fired, because
we take our nitrogen from bleeding in
air, as opposed to pure nitrogen. This reacts
with some remaining natural gas.
After that, the syngas passes through
www.powermag.com
high-temperature and low-temperature
water-shift reactors to oxidize CO into
CO2, " he said.
Ron took over at this point, adding,
" If there are problems with the secondary
reformer system, it's that we
think too much CO is passing through
the system. This causes two problems.
First, the CO isn't captured by the MEA
carbon capture system just after the water
shift reactors. Then, after the carbon
capture system, we have the Methanator.
That uses a catalyst to remove the
last of the CO and CO2
. The problem is
CO catalyzation releases a bit of heat,
and if the CO concentration entering the
Methanator is too high, the catalyst can
undergo a runaway reaction, where the
temperatures can get high enough to
melt the catalyst. "
" I have concerns, " said Marnie. " Catalyst
temperature runaways aren't rare in
the industry, but your plant has experienced
them at more than double the
maximum expected rate. I agree with
you on the CO issue, but your DCS data
shows even though the CO is all over the
map, the DCS says the CO entering das
Methanator (which Marnie pronounced
in an awful Schwarzenegger Austrian accent)
is under your limit? "
" So, are you thinking maybe the highor
low-temperature catalyst is worn
out? " asked Wayne.
" Maybe both? " Ron supposed.
Marnie shrugged, adding, " Or contaminated. "
" Or
your CO sensor is suspect, " Maya
opined.
Consistently Missing Marks
A condenser was located downstream
of the Methanator to remove as much
water as possible from the syngas. Asbuilt,
it worked very well, but decades of
use led to so many major tube failures
that nearly a third of the condenser tubes
were plugged over.
" We're missing that condenser capacity,
and we're losing efficiency and reliability
by adding dryers to the system, "
commented Ron. " I don't think Wayne
wants to pay for re-tubing or a new condenser,
so we're stuck with it for now. "
The last area of concern for the plant
staff was the syngas compressors.
Compressor rebuilds had increased from
once every decade to once every two
to three years. The two steam-driven
compressors were undergoing service
during the current outage, and the compressor
area was covered by a giant
maintenance tent.
27
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