OCR Text |
Show EQUILIBRIUM AND EXPERIMENTAL NOx COMPARISONS· ABSTRACT C.E. Baukal, A.G. Slavejkov and P.l . Valianatos Air Products and Chenlica/s, Inc. Copyright, 1992 This paper shows how adiabatic equilibrium calculations for methane combustion can be used to predict trends for nitrogen oxides formation . Equilibrium calculations show that NOx emissions should increase rapidly as the oxygen concentration in the oxidizer decreases below 100%. NOx should also increase at fuel lean conditions (excess oxygen) and decrease under fuel rich conditions. A comparison of the calculations to a set of experimental data shows similar trends. However, the calculations over predict the data by about an order of magnitude. INTRODUCTION The prediction of nitrogen oxides emissions in industrial combustion systems has received much attention in the last 10 years due to their detrimental effects on the environment including smog and acid rain. Modeling actual combustion processes is extremely difficult because it must include complicated fluid dynamics (usually 3-dimensional turbulent flow) , heat transfer, and chemistry. Full treatment of the reaction kinetics would include dozens of species and hundreds of chemical reactions. In addition, many of the rate constants needed for the reactions are not known with a high degree of certainty at this time. Assuming a model does accurately represent the combustion process, these types of problems require very large amounts of computer memory and CPU time. This makes it difficult to do parameter studies to determine the effects of different variables. The Gas Research Institute (Chicago, IL) has been funding the development of combustion models since the late 1980's. Their ultimate goal is to provide burner and furnace designers with a tool for simulating and optimizing various combustion configurations for high energy efficiency and low pollutant emissions. They recognized the complexity of the problem at the outset and adopted a strategy looking at two approaches to the problem. The first approach attet:npts to model the combustion process using fairly simple fluid dynamics, but very complicated reaction kinetics. The second approach uses complicated fluid dynamics and simplified kinetics. Both approaches are attempting to siInplify the problem enough so that it can be solved in a reasonable amount of time without the need for a supercomputer, but with • Presented at the American Fbme Research Committee 1992 Fall International Symposium, Cambridge, MA, October 19-21, 1992. |