POWER August 2016 - 28

REINVENTION AWARD
Table 1. Primary vendors involved in the rehabilitation project. Source:
Longview Power
Vendor
Babcock and Wilcox
Black and Veatch
Emerson Process Management
Foster Wheeler North America
Howden
Siemens
Equipment
Third-party engineering review
Owner's engineer and assistance with project and outage management
Distributed control system
Supercritical boiler, bottom ash system, and air quality control system
Bottom ash system
Turbine generator
There were logic glitches, hardware issues,
and software bugs. And to make matters worse,
the plant didn't feel it was getting the support it
needed to resolve the troubles. But the plant's
owners demonstrated their commitment to the
cause by making another bold decision: They
chose to completely replace the DCS.
" It was probably the single most important
thing we did, " said Nelson. " It was our biggest
risk, but it also caused our greatest reward. "
The plant installed an Emerson Ovation
system. It was a 12,000-input/output
point replacement (Figure 3). Fortunately,
most of the field instruments could be left
in place, but a very detailed logic review
had to be conducted and a lot of logic was
ultimately recreated.
" Because the DCS is the central nervous
system for the whole plant, and there were
some pretty serious issues, we needed to start
with a fresh slate to assure ourselves that
we would end up with a fully viable control
system, " Nelson said. " It was a pretty large
undertaking, but it was well worth it because
the results were significant. "
Emerson turned out to be a great partner
for Longview on that project. The plant also
hired Black and Veatch as its owner's engineer.
Nelson noted that Black and Veatch
was not only instrumental in the successful
DCS replacement, but it also provided
Longview with " deep bench strength " in
other project and outage management areas
(Table 1).
" Teaming with Black and Veatch allowed
us to bring in air quality control, boiler, and
other system subject matter experts, " Nelson
said. " In fact, our key outage manager was a
Black and Veatch employee. "
Solving Vibration Issues
Siemens supplied an SST6-6000 steam turbine
and an SGen6-3000W generator for the
plant. At the time of installation, it was the
company's latest design for that frame size.
The machine had an acceptable track record
in 50-Hz applications, running at some of
the most efficient plants in the world, but
Longview's unit was Siemens' first 60-Hz
machine, and it had a few glitches.
Although the turbine ran flawlessly, the
generator did not. The most significant issue
was vibration, but there was also a problem
with excessive hydrogen leaking through the
generator seals. However, Siemens committed
to fixing the machine under warranty.
The solution basically amounted to a major
overhaul of the generator. The unit was
fully disassembled, and Siemens completed
shop repairs and modifications. Some field
modifications were also required, including
to the foundation. The results were excellent.
The generator vibration readings are now
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POWER August 2016

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