POWER August 2016 - 29

REINVENTION AWARD
4. More bags needed. Longview's pulse jet fabric filter required expansion because the
original design was based on the wrong fuel specification. Courtesy: Longview Power
POWER POINTS
Winning Attributes
Best net unit heat rate (highest
efficiency) in the U.S. coal fleet:
8,999 Btu/kWh.
Completed rehabilitation project
addressing major design errors in
only 18 months.
Equivalent availability factor of
98.5% since project completion.
jection system could also be modified, so that
too was a step in the right direction.
However, the baghouse and scrubber were
simply too small. The baghouse needed to be
expanded by about 30% (Figure 4) to accommodate
the necessary flue gas flow, while a
second dual-flow tray was required in the
scrubber. The scrubber's original design did
not include a method for removing fines
from the liquor either, so Longview added a
decanting basin to handle that task and improved
the dewatering system too.
" There were a lot of other things-a lot
of other equipment-we ended up adding to
that scrubber system, but in short, what we
did was we 'hot-rodded' the scrubber, and
we're getting 99.5% removal out of it now, "
said Nelson. " We're pretty proud of what we
got out of that. "
Much like the scrubber and baghouse,
the boiler bottom ash system was smaller
than required. The original design was also
very complicated. When slag fell, it often
caused structural damage, or it would plug
up the system.
Longview worked with Foster Wheeler
more typical of a new machine, and hydrogen
leakage is well under limits.
" The steam turbine generator is a great Siemens
machine that is extremely efficient and
reliable, " said Chad Hufnagel, Longview's
reliability and performance manager. " It is a
significant contributor to our extremely low
heat rate. "
Improving the AQCS
As a plant conceived in the mid-2000s,
Longview had advanced pollution controls
integrated into its original design. The air
quality control system (AQCS) consisted of
a pulse jet fabric filter (baghouse) to remove
particulate matter, a wet flue gas desulfurization
system (scrubber) for SO2
low-NOx
control, and
burners and a selective catalytic
August 2016 | POWER
reduction system with ammonia injection to
limit NOx
emissions. Acid was removed from
the flue gas using a hydrated lime injection
system, which combined with the wet scrubber
and baghouse also controlled mercury.
But the AQCS was not without its flaws
either. The catalyst was handled incorrectly,
so it got wet, which caused it to degenerate
quickly. It had to be fully replaced.
The AQCS was also sized incorrectly. The
design was based on the wrong fuel specification,
so at the end of the day, everything on
the back end was too small.
Longview completed some modeling to
determine how things could be improved.
Combustion tuning resulted in a reduction in
thermal NOx
www.powermag.com
and Howden to design and fabricate simpler,
more robust equipment. In the end, the
plant replaced the entire bottom ash system.
Like all of the other changes, the results
made it worthwhile.
" It's just a world of difference down there
now. We don't have the problems we had,
and to be honest with you, we don't have
problems that a lot of other bottom ash systems
have, " said Nelson.
Adding Autonomy
Although Longview is a coal-fired plant, the
unit starts up using natural gas. That fact has
also allowed the plant to capitalize on the
low price of natural gas. Earlier this year, the
plant cofired up to 20% of its heat input using
natural gas simply because it was cheaper.
The surprising thing about that is that
, so at least that was a plus. The
control scheme and logic for the ammonia inLongview
is a mine-mouth facility. The
plant is fully integrated with Mepco LLC,
29
http://www.powermag.com
POWER August 2016

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