F04NL.vogt Pages.nov 12-Final
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8/3/2019 F04NL.vogt Pages.nov 12-Final
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FOCUS on CFD
For Power Generation
FOCUS on CFD
For Power Generation
s2 overviewFuture Power Generation
Challenges
s3 combinedcycle powerReducing Gas Turbine
Emissions
s4 renewable powerA Powerful Wind of Change
The Wind in Spain
Aerating Water in the
Summertime
s8 nuclear powerFast Breeder Meltdown
CFD for Advanced NuclearReactor Design
s11 fossil fuel powerCoal Gasification for Future
Power Generation
Low Emissions Bluff-body
Burner
Newsletter Supplement
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8/3/2019 F04NL.vogt Pages.nov 12-Final
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Fluent Newsfall 2004 S3
combined cycle power
Reducing Gas Turbine EmissionsBy Keith C. Kaufman, Vogt Power International Inc., Louisville, Kentucky
Since 1923, the Turlock Irrigation
District (TID) has been providing
electricity to customers with a cur-
rent customer base of more than 84,000
accounts in California's Stanislaus and
Merced counties. TIDs generation
resources include large and small-scale
hydro-electric power plants and two nat-
ural gas-fired turbine generating plants.
A General Electric LM6000 engine was
recently installed to upgrade TID's
Almond Power Plant. The higher exhaust
temperature of the LM-6000 gas turbine
necessitated the replacement of both the
carbon monoxide (CO) and nitrogen
oxide (NOx) emissions control equip-
ment, upstream of an existing heatrecovery steam generator (HRSG).
The newly installed CO oxidation cat-
alyst and selective catalytic reduction
(SCR) modules are designed to react
with large volumes of gas to eliminate
CO and NOx contaminants. An ammo-
nia injection grid (AIG) upstream of the
SCR catalyst provides ammonia to com-
plete the NOx reduction reaction. TID
found, however, that the newly installed
emissions systems were not performing
at expected levels, so TID turned to Vogt
Power International Inc. (VPI), a Babcock
Power Inc. company, to help correct the
problem. Using FLUENT, VPI engineers
modeled the exhaust system from the
gas turbine through both emissions cat-
alysts to the entrance of the HRSG. In the
Almond Power unit, a collector/diffuser
spool redirects exhaust gas from the tur-
bine into an expanding inlet duct that in
turn directs gas into the catalyst modules
and HRSG. The FLUENT analysis con-
firmed what VPI engineers had anticipat-
ed: the gas velocity from the turbine was
unevenly distributed across the surfaces
of the catalyst, so only a portion of thecatalyst material was engaged.
An analysis of the existing equip-
ment showed a highly non-uniform
velocity profile at the entrance to the
CO modules. The gas exiting from the
collector/diffuser was strongly biased to
the bottom and sides of the duct, with
significant regions of backflow in some
sections of the inlet expansion. While
the CO modules acted to straighten the
flow somewhat, the flow was still large-
ly non-uniform at the plane of the AIG,
which is positioned just downstream of
the CO modules. The underperfor-
mance of the SCR was shown to be due
to non-uniform mixing of the ammonia
and exhaust streams following the AIG,
and poor gas distribution at the SCR
catalyst itself.
Using CFD as an evaluation tool, VPI
engineers designed a two-zone distribu-
tion grid that provides an improved flow
distribution entering the CO modules,
AIG and SCR. Installed just upstream of
the CO catalyst modules, the grid redis-
tributes the flow using angled perforated
plates that allow the passage of varying
amounts of air in different regions of the
plane, while limiting an increase in gas-
side pressure drop that would decreasethe gas turbine efficiency. The engineers
used CFD to adjust the design of each
grid sector, and to evaluate its influence
on each component downstream. The
resulting two-zone design provides suffi-
cient redistribution of flow top-to-bot-
tom across the unit, allows for uncertain-
ty in the gas turbine exhaust profile and
variation with gas turbine load, while
minimizing pressure drop across the
grid. The CFD results show more than a
20% improvement in velocity distribu-
tion at the CO modules and AIG plane.
With the revised design, more than 90%
of the flow upstream of the SCR falls
within +/-15% of the average velocity at
this location. Physical testing after the
grid was installed verified these results.
Most importantly, the field test values
after installation confirm that the emis-
sions systems now outperform the regu-
latory requirements.
The original designconfiguration
GT collector/diffuser
CO catalyst modules
SCR catalyst modules
Pathlines illustrate the flow inthe original configuration
Velocity contours on the AIG before (left)and after (right) the addition of thedistribution grid
The addition of a distribution grid(black) improved the flow uniformity
on the catalyst module surfaces