Determination of NOx emissions from strong swirling confined flames with an integrated CFD-based procedure

Abstract The present work is focused on a new procedure for the determination of NO x emission from combustion processes, which allow using very detailed and comprehensive reaction schemes, on the basis of the results obtained from CFD computations. This procedure is validated in the case of high swirled confined natural gas diffusion flames. The experimental data refer to the work developed within the German TECFLAM cooperation concerning a swirl burner ( 0.6 S 1.4 ) fed with natural gas characterized by 150 kW thermal load and 0.8 equivalence ratio (TECFLAM webpage, www.tu-darmstadt.de/fb/mb/ekt/tecflam ; Schmittel et al., Proceedings of the Combustion Institute 28 (2000) 303–309). The CFD analysis represents a useful technology to provide the flow and temperature fields. The high swirling configuration makes the solution an interesting and difficult task for commercial codes. In particular, previous attempts of predicting the flow and temperature fields with the FLUENT code failed (Meier et al., Applied Physics B 71 (2000a) 725–731). Only a careful attention to the boundary conditions and converging strategy allows to reach a satisfactory modeling of the main characteristics of the flame. The numerical calculation was performed using the commercial code FLUENT6.0. NO x formation is a chemical process whose time-scale is of the same order of mixing fluid dynamics. For this reason, comprehensive modeling of NO x reaction processes in combustion systems requires simulation of both the turbulent fluid dynamics and chemical kinetics in the system being modeled. Hundreds of elementary reactions are required to provide a detailed description of the formation and depletion of oxides of nitrogen in combustion systems. However, it is not currently feasible to use such detailed reaction mechanisms to model a turbulent reacting system in which large reaction kinetics schemes are coupled with the turbulent fluid dynamics. Consequently, the difficulties in coupling detailed chemistry and detailed fluid dynamics force to adopt proper simplifications. The prediction of NO x formation is then obtained by postprocessing the flow and temperature fields, as predicted by CFD, and lumping together computational cells similar in terms of NO x formation. The resulting macrocells are assumed to be a network of ideal reactors, which are simulated adopting a detailed kinetics. The characteristics and operating conditions of each reactor are defined by a procedure already developed for furnaces and named SFIRN (Faravelli et al., Computers and Chemical Engineering 25 (2001) 613–618). The predictions have been tested on flames at different swirl numbers. Both the CFD and the chemical analysis show a satisfactory agreement with the measured data.

[1]  B. Hjertager,et al.  On mathematical modeling of turbulent combustion with special emphasis on soot formation and combustion , 1977 .

[2]  A. Brink,et al.  Possibilities and limitations of the Eddy Break-Up Model , 2000 .

[3]  Johannes Janicka,et al.  Prediction of swirling confined diffusion flame with a Monte Carlo and a presumed-PDF-model , 2002 .

[4]  P. Cheng.  Two-dimensional radiating gas flow by a moment method , 1964 .

[5]  R. Barlow,et al.  Scalar profiles and NO formation in laminar opposed-flow partially premixed methane/air flames , 2001 .

[6]  G. J. Sturgess,et al.  Importance of inlet boundary conditions for numerical simulation of combustor flows , 1983 .

[7]  Sanjay M. Correa,et al.  Measurements and modeling of a bluff body stabilized flame , 1992 .

[8]  Influence of inlet conditions on the flowfield in a model gas turbine combustor , 1992 .

[9]  Leonardo Tognotti,et al.  A new procedure for predicting NOx emissions from furnaces , 2001 .

[10]  Wolfgang Rodi,et al.  Computation of strongly swirling axisymmetric free jets , 1984 .

[11]  M. Pinar Mengüç,et al.  Thermal Radiation Heat Transfer , 2020 .

[12]  C. Westbrook,et al.  Simplified Reaction Mechanisms for the Oxidation of Hydrocarbon Fuels in Flames , 1981 .

[13]  Wolfgang Leuckel,et al.  Turbulent swirling flames: Experimental investigation of the flow field and formation of nitrogen oxide , 2000 .

[14]  L. Tognotti,et al.  Modelling practical combustion systems and predicting NOx emissions with an integrated CFD based approach , 2002 .

[15]  P. Bradshaw,et al.  Turbulence Models and Their Application in Hydraulics. By W. RODI. International Association for Hydraulic Research, Delft, 1980. Paperback US $15. , 1983, Journal of Fluid Mechanics.

[16]  A.M.O. Smith,et al.  Turbulence models and their application in hydraulics: W. Rodi, University of Karlsruhe, International Association for Hydraulic Research, Rotterdamseweg 185, 2600 MH Delft, The Netherlands , 1981 .

[17]  Leonardo Tognotti,et al.  CFD+reactor network analysis: an integrated methodology for the modeling and optimisation of industrial systems for energy saving and pollution reduction , 2002 .

[18]  Tiziano Faravelli,et al.  Lumping procedures in detailed kinetic modeling of gasification, pyrolysis, partial oxidation and combustion of hydrocarbon mixtures , 2001 .

[19]  D. Wilcox.  Turbulence modeling for CFD , 1993 .

[20]  Winfried Stricker,et al.  Investigations in the TECFLAM swirling diffusion flame: Laser Raman measurements and CFD calculations , 2000 .

[21]  Philip J. Smith,et al.  Modeling of swirl in turbulent flow systems , 1986 .

[22]  Tiziano Faravelli,et al.  Kinetic modeling of the interactions between NO and hydrocarbons in the oxidation of hydrocarbons at low temperatures , 2003 .

[23]  B. Launder,et al.  Lectures in mathematical models of turbulence , 1972 .

[24]  Raman/Rayleigh and mie-scattering measurements in a reverse flow reactor close to extinction , 1989 .

[25]  Frederick L. Dryer,et al.  High-temperature oxidation of CO and CH4 , 1973 .

[26]  D. Fletcher,et al.  A CFD based combustion model of an entrained flow biomass gasifier , 2000 .

[27]  H. Naji.  The prediction of turbulent swirling jet flow , 1986 .

[28]  David G. Lilley,et al.  Primitive Pressure-Velocity Code for the Computation of Strongly Swirling Flows , 1976 .

[29]  D. Spalding.  Mixing and chemical reaction in steady confined turbulent flames , 1971 .

[30]  Tiziano Faravelli,et al.  Kinetic modeling of the interactions between NO and hydrocarbons at high temperature , 2003 .

[31]  S. Patankar.  Numerical Heat Transfer and Fluid Flow , 2018, Lecture Notes in Mechanical Engineering.