tailieunhanh - Modeling of Combustion Systems A Practical Approach 13

Tham khảo tài liệu 'modeling of combustion systems a practical approach 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 5 Semiempirical Models Chapter Overview In Chapter 2 we discussed the mechanical energy balance and implications it had for flow of air and fuel in burners. This allowed us to make good physical models requiring one or no adjustable parameters. In this chapter the physics become more complicated and involve thermodynamic chemical and kinetic quantities. For this reason our semiempirical models will require more adjustable parameters. Notwithstanding such expressions will be capable of correlating complicated behavior with engineering accuracy. With the techniques the reader has already learned he will be able to regress such semiempirical models handily from facility data or planned experiments. We begin the chapter with a discussion of various NOx formation mechanisms. Along the way we introduce the reader to whatever thermodynamics or kinetics the situation may require. NOx formation naturally progresses to NOx reduction so here we discuss nearly a dozen such strategies. These lead to a generic semiempirical model for NOx and NOx reduction. We then develop a parallel approach for CO. Throughout we focus on the practical. The heat flux profile from a combustion system has now gained importance. Modeling of such profiles is important for certain reactors such as ethylene cracking units ECUs and hydrogen and ammonia reformers. We develop the general three-parameter equation from a simplified analysis of fuel jets and the heat balance. We can reduce this to a two-parameter model by normalizing the heat flux. Such a model also allows us to consider the qualitative response of heat flux to various operational factors. Two important responses we consider are run length between decoking cycles and process efficiency. The heat flux model also allows us to develop a similarity criterion for test and field units. 421 2006 by Taylor Francis Group LLC 422 Modeling of Combustion Systems A Practical Approach Next we consider how one may .