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Show [N0J = J^"?[5]"^ (3) where A, b, and n are constants; T is absolute temperature; S is a reactant species, andf is a reaction coordinate of interest (e.g., time, conversion, etc.). For the thermal-NOx mechanism3 ln[NOx] is proportional to \n(yw). Though the model proceeds from kinetic theory, experimental data1 comprising hundreds of observations from a score of combustion sources validate Equation (1). Response Surface Methodology (RSM) If one understands R S M , one may easily apply it to a predetermined equation form ( M R S M ) . The statistical literature describes R S M in detail.4'5 For readers unfamiliar with the method, this paper overviews it here. RSM is a mathematical French curve in several dimensions. One regresses it from a statistically cognizant experimental design. Figure 1 shows one such surface along with its contour representation. Here a municipal solid waste ( M S W ) boiler uses S N C R to control NOx. In the subject system, carrier air pushes N H 3 into a furnace where it reacts with N O x to destroy it. The important variables are the N H 3 injection rate and the carrier air pressure. The maximum allowable N O x emissions are 34 lb/h. One would like to minimize the compressor horsepower and reagent cost. Generating the response surface is essential to achieving these goals. H o w do w e do it? Deriving the Response Surface One generates the response surface using a particular experimental design known as a central-composite. It comprises corner, axial, and center points. For two dimensions this would include four corner points (a square), four axial points (a cross or star) and several replicate points at the design center (Figure 2). Central composite designs readily extend to higher dimensions. N O x Response Surface 43Ib/hN0x -^ 8 lb/h NOx N O x Contours for N H 3 and Carrier Air 10 20 30 40 50 Carrier Air Pressure Figure 1, N O x Response Surface & Contour Diagram 3 |
