Environmental Engineering Reference
In-Depth Information
pollutants emission with a combustor design incorporating swirl
flow in the com-
bustor. Experimental investigations have outlined the importance of
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eld
design and the relationship between the fuel jet location and resulting pollutants
emission. Novel premixed combustion design along with swirling
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ow
flow has yielded
low pollutants emission. At a rather high equivalence ratio of 0.6, the resulting
pollutants emissions were 4 PPM of NO and 11 PPM of CO with inlet air preheat
temperature of 600 K to the combustor. Such performance demonstrates the ability
of this combustor design to produce minimal pollutants emission at a moderate
thermal intensity of 27 MW/m
3
-atm.
Novel non-premixed combustion design, which is of great interest to eliminate
premixed combustion instabilities,
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flashback, and other risks associated with
premixed combustion have shown the ability to achieve low pollutants emission.
The results have shown that
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ame
fl
field design and mixture preparation in non-
premixed combustion is critical. The results showed that a change in fuel injection
location greatly affects pollutants emission. For instance, NO emission decreased
dramatically from 21 PPM (for coaxial air/fuel injection, case
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ow
“
CA
”
) to 10 PPM
(for non-premixed, case
). CO emission variation was minimal between the
different cases due to the fact that inlet air preheats dramatically decreased CO
emission due to faster reaction kinetics and complete conversion to CO
2
.
The experimental data on emissions and numerical predications revealed that
high NO emissions recorded for cases
“
CA
”
and
“
NP0
”
can be attributed to poor
mixing of air, fuel, and hot recirculated reactive gases. Numerical simulations
showed that high temperature rise (indicating ignition) was found in areas where
only air and fuel existed with minimal amounts of recirculated gases. Such ignition
occurring in oxygen-rich mixture fosters thermal NO formation which should be
avoided. In order to achieve distributed reaction the air, fuel and hot recirculated
reactive gases should be thoroughly mixed prior to ignition and that mixing time to
be less than ignition delay. Such good mixing can be found in premixed case
“
NP1
”
“
PR
”
and non-premixed case
”
The interaction between jet mixing ability and the combustor
“
NP1.
field is also of
importance. Coaxial injection has been reported to yield favorable mixing between
the center jet and surrounding annulus jet. However, in the present case where
mixing is required between air, fuel, and recirculated gases, coaxial injection
yielded high pollutants emission due to improper mixing between the air/fuel jet
and the recirculated
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ow
flow, leading to the ignition of air/fuel mixture only.
Novel air and fuel mixing, where fuel is diluted with air while portion of the fuel
is introduced in the main air jet, demonstrated NO emission comparable to those
encountered in premixed combustion mode. These emissions were about 40 % of
the NO emissions under non-premixed combustion mode. Fuel dilution, charac-
terized by high cross jet momentum, not only demonstrated NO emission reduction
compared to non-premixed mode with comparable emissions to the of premixed
mode combustion, but also lower CO emissions compared to non-premixed com-
bustion. Such novel mixing technique eliminates the possibility of
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fl
ame
fl
ashback
as the equivalence ratio in the jets is outside the methane air
flammability limit.
OH* intensity distribution showed that the combustion zone is affected by the cross
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