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Show • • • • To define design and operating conditions for the prototype burner; To optimize fuel staging, flue gas recirculation, and air flow to achieve low NOx emissions, low CO emissions, and flame characteristics compatible with chiller combustion chamber geometry; To identify key variables for the experimental burner development; and To interpret the experimental test results and to guide burner design refinements. Chemical Kinetic Modelling Approach. The latest versions of Sandia National Laboratories' Chemkin-n package were used to perform the chemical kinetics analyses. This package is a comprehensive system for modelling gas-phase chemical kinetics and is described by Kee et ale [Ref 1]. The Chemkin plug-flow reactor model was modified at Arthur D. Little to include convective and radiative heat transfer to the walls. Chemkin provides a solution methodology and framework for kinetics calculations; the user must provide appropriate elementary chemical reaction specifications and reaction rate data. For this analysis, the latest version of the comprehensive methane oxidation and NOx formation mechanism of Miller and Bowman [Ref. 2] was used. Thermal NOx' prompt NOx and fuel NOx mechanisms are included. For purposes of kinetic analysis, the burner flowfield was divided into a well-stirred zone (modelled by the Chemkin Perfectly-Stirred Reactor (PSR) model) followed by a plug-flow zone (modelled by the Chemkin Plug-Flow Reactor (PFR) model). This scheme is illustrated in Figure 2. In this approach, the "lean pre-mixed" stage of the burner is modelled as the PSR, and the secondary fuel is introduced at the start of the PFR, which serves to simulate the second "bum-out" stage of the burner. Flue gas recirculation to either the PSR or the PFR was included, as was heat loss from either the PSR or the PFR. Table 1 shows the range of parameters considered in the kinetics analysis. Table 1. Range of Parameters for Chemical Kinetics Analysis f y:;'r:~ " ·,,3 ~~ ,.~Patamete.r; . ·;~4;}~:. j;'y, ., fl~lJgeJ~:· .Q~}"tf:': .;: " . Flue Gas Recirculation Rate o - 200/0 of total flow Fuel Staging 20 - 40% of total fuel Firing Rate 33- 1000/0 of design PSR Heat Loss 0- 10% of heat input Flue Gas Injection Location PSR or PSR+PFR Results. The NOx-control advantages of operating a lean-premixed primary zone are illustrated in Figure 3, in which predicted NOx levels at the exit of the PSR are plotted as a function of equivalence ratio for two cases: no flue gas recirculation and 5 |
