NDLI: NOx Reduction by Air-Side vs. Fuel-Side Dilution in Hydrogen Diffusion Flame Combustors

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Nathan, T. Weiland Peter, A. Strakey
Copyright Year	2009
Abstract	Lean-Direct-Injection (LDI) combustion is being considered at NETL as a means to attain low NOx emissions in a high-hydrogen gas turbine combustor. Integrated Gasification Combined Cycle (IGCC) plant designs can create a high-hydrogen fuel using a water-gas shift reactor and subsequent CO2 separation. The IGCC’s air separation unit produces a volume of N2 roughly equivalent to the volume of H2 in the gasifier product stream, which can be used to help reduce peak flame temperatures and NOx in the diffusion flame combustor. Placement of this diluent in either the air or fuel streams is a matter of practical importance, and has not been studied to date for LDI combustion. The current work discusses how diluent placement affects diffusion flame temperatures, residence times, and stability limits, and their resulting effects on NOx emissions. From a peak flame temperature perspective, greater NOx reduction should be attainable with fuel dilution rather than air or independent dilution in any diffusion flame combustor with excess combustion air, due to the complete utilization of the diluent as a heat sink at the flame front, although the importance of this mechanism is shown to diminish as flow conditions approach stoichiometric proportions. For simple LDI combustor designs, residence time scaling relationships yield a lower NOx production potential for fuel-side dilution due to its smaller flame size, whereas air-dilution yields a larger air entrainment requirement and a subsequently larger flame, with longer residence times and higher thermal NOx generation. For more complex staged-air LDI combustor designs, dilution of the primary combustion air at fuel-rich conditions can result in full utilization of the diluent for reducing the peak flame temperature, while also controlling flame volume and residence time for NOx reduction purposes. However, differential diffusion of hydrogen out of a diluted hydrogen/nitrogen fuel jet can create regions of higher hydrogen content in the immediate vicinity of the fuel injection point than can be attained with dilution of the air stream, leading to increased flame stability. By this mechanism, fuel-side dilution extends the operating envelope to areas with higher velocities in the experimental configurations tested, where faster mixing rates further reduce flame residence times and NOx emissions. Strategies for accurate CFD modeling of LDI combustors’ stability characteristics are also discussed.
Sponsorship	International Gas Turbine Institute
Starting Page	877
Ending Page	887
Page Count	11
File Format	PDF
ISBN	9780791848838
DOI	10.1115/GT2009-60128
e-ISBN	9780791838495
Volume Number	Volume 2: Combustion, Fuels and Emissions
Conference Proceedings	ASME Turbo Expo 2009: Power for Land, Sea, and Air
Language	English
Publisher Date	2009-06-08
Publisher Place	Orlando, Florida, USA
Access Restriction	Subscribed
Subject Keyword	Water Temperature Stability Diffusion flames Computational fluid dynamics Hydrogen Carbon dioxide Plant design Combustion Fuels Separation (technology) Nitrogen Diffusion (physics) Flow (dynamics) Modeling Emissions Air entrainment Flames Integrated gasification combined cycle power stations Gas turbines Nitrogen oxides Combustion chambers Heat sinks Diluents
Content Type	Text
Resource Type	Article

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