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- Engineered for the lowest emissions with "F" & "G" class
turbines
- Optimum performance during turbine power augmentation modes.
- Proven field performance
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The Coen PowerPlus ,
built on three years of R&D and extensive field experience, introduces
a new generation of duct burners to the power industry. Designed
to handle the most challenging "Advanced Technology Turbines", PowerPlus provides
unparalleled performance, quality, and reliability. The PowerPlus is the most reliable duct burner system in
the world.
Duct Burner Design Fundamentals
Today's "Advanced Technology Turbine" has a lower O2, and
higher H2O exhaust composition than previous gas turbine designs.
This shift in exhaust temperature and composition reduces local flame
temperatures and as a result has a significant impact on the duct burner
stability range and CO contribution. Further, CO emission limits
have been decreasing in recent years. As a result, Coen initiated
a duct burner improvement program in R&D. The objectives were
to identify CO formation pathways and develop reduction methods,
while maintaining low NOx levels.
Through Computational Fluid Dynamics (CFD) modeling, coupled with
Coen test facility experiments and field data, the following were established:
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- Mixing rates and chemical kinetics were identified as the controlling
factors in the modeling effort
- CO formation was identified as cooling of flame partial products
with upstream turbine exhaust gas (TEG) prior to complete oxidation
- Reduction of CO, UBHC's (Unburned Hydrocarbons) and Volatile
Organic Compounds (VOC's) was proven to be directly related to
increasing residence time in the flame stabilizer recirculation
zone and decreased mixing rates in the near field zone
- Residence time can be increased with controlled flow baffle/flame
stabilizer geometry, increased with reduced TEG velocity (until
buoyancy limited) and increased with reduced turbulence
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Tradeoffs of the above became obvious. Simple increases in flame
stabilizer size and associated recirculation size resulted in the beneficial
increased residence time, but was also offset by increased TEG velocity
and turbulence.& Simple bluff bodies provided excessive turbulence
and mixing rates in the near field, so streamlined flame stabilizers were
desired for reduced pressure drop. How to increase residence time
without increases in turbulence, pressure drop or TEG velocity?
Reacting CFD models indicated that it was desired to obtain a long narrow
recirculation zone that minimized mixing of TEG until complete oxidation.
Hundreds of configurations were modeled and analyzed.
| The answer was our PowerPlus flame stabilizer arrangement. It resulted
in twin recirculation zones or as we have labeled "Dual Recirculation
Technology". This dual recirculation pattern provides for
increased residence time in a narrow "corridor" without excessive
blockage or undesirable flame patterns. Typical residence times
with ordinary stabilizers of any shape were approximately
50 milliseconds in the recirculation zone. The PowerPlus design increases this residence time
by 3 times compared to current duct burner designs. Further
TEG flow is diverted to the flame ends where oxidation is nearly complete.
This concept has been modeled extensively, lab tested and field confirmed.
Reduction in CO emissions of approximately 50% over previous flame
stabilizer designs was achieved. |
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The NOx emissions in duct burner systems are relatively low
in comparison to ambient air fired burners. This is partially due
to lower thermal NOx generation as a result of lower flame temperatures
when firing with TEG as an oxidizer. Computational using only the
extended Zeldovich mechanism, suggest that NOx emissions from duct burner
systems should be lower than experimental data indicates. These
computational results indicate that the ratio of prompt NOx to thermal
NOx is higher in duct burner systems. A common passive method of
total NOx reduction in duct burner systems is the utilization of re-burn.
Re-burn is the concept of reducing incoming NOx (from the TEG) by reverse
reactions from NOx to N2 in UHC rich flames. These reverse reaction
rates are kinetically slow, therefore the limitation of re-burn
NOx reduction is the amount of residence time in the re-burn zone.
For duct burners the re-burn zone is the flame zone. Coen's PowerPlus
duct burner has significant increases in residence time in the flame zone
and as a consequence NOx reduction via re-burn.
The end result is our new PowerPlus
duct burner. It produces
the lowest NOx, CO, UBHC's and VOC emissions possible under any turbine
exhaust condition!
For more information about this product, talk to your nearest Coen Sales Representative.
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