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Finite-rate entrainment effects on nitrogen oxide (NOx) emissions in staged combustors
- Source :
- Combustion and Flame. 230:111434
- Publication Year :
- 2021
- Publisher :
- Elsevier BV, 2021.
-
Abstract
- Axially staged combustors offer the potential for achieving low NO x emissions from gas turbines at the elevated temperatures required to achieve at least 65% combined cycle efficiencies. While there is evidence that premixing between the main burner products and secondary stream reduces NO x , it is important to characterize the specific requirements needed to achieve low emissions at gas turbine conditions. This study examines the sensitivity of NO x to finite-rate, large-scale entrainment of the main and secondary streams under the simplifying assumption of infinitely-fast small-scale mixing. Essentially, this allows us to isolate the effects of limited large-scale entrainment rates by using a homogeneous/uniform condition for the entrained and reacting gases. We use a reduced-order reactor network model to examine a generic staged-combustor whose inputs are physical time scales that embody the finite-rate entrainment characteristics. With simulations conducted over a large parameter space at typical operating conditions (25 atm, 650 K air), the results show that, even when small-scale mixing is infinitely fast and the reaction zone is uniform, entrainment significantly affects NO x emissions due to its influence on the equivalence ratio — and thus the temperature and time — at which the entrained mixture ignites. Fuel-air staging is shown to be vital to NO x reduction in most practical cases where entrainment times exceed roughly 1 ms and the secondary stream finishes entraining before the main burner products. A constrained NO x minimization indicates that using the leanest possible main burner and re-routing as much air as possible to the secondary stage is key to low NO x with finite-rate entrainment; for example, less than 10 ppm NO x can be achieved if the secondary stage contains 20% of the total mass flow.
- Subjects :
- 010304 chemical physics
Combined cycle
General Chemical Engineering
Mass flow
Mixing (process engineering)
General Physics and Astronomy
Energy Engineering and Power Technology
02 engineering and technology
General Chemistry
Mechanics
Parameter space
01 natural sciences
law.invention
chemistry.chemical_compound
Fuel Technology
020401 chemical engineering
chemistry
law
0103 physical sciences
Combustor
Environmental science
Nitrogen oxide
0204 chemical engineering
Entrainment (chronobiology)
NOx
Subjects
Details
- ISSN :
- 00102180
- Volume :
- 230
- Database :
- OpenAIRE
- Journal :
- Combustion and Flame
- Accession number :
- edsair.doi...........5ac7abb1c5d14f26a298f594e6dfc43f