OCR Text |
Show 2 be quite versatile and provide the means to simulate not only flow, but combustion, heat transfer, emissions, and their interrelationships (Fiveland and Wessel, 1988; Fiveland and Wessel, 1991). The models vary in complexity between three-dimensional (3-~) models that require expert users and workstation computers to one-dimensional (1-0) models that can be run on personal computers. The extensive capabilities of the models provide the means to evaluate and understand the changes that occur when low NOx combustion systems are applied to furnaces. The models continue to be used on a day-to-day basis for the analysis and design of staged systems. The 3-D flow and combustion models are being used in the development of low NOx combustion systems. Elements of the system and/or the entire system can be evaluated and optimized. The models are useful as screening tools for evaluating low NOx burner design concepts. Results reveal not only the effectiveness of the concept, but provide insight into the operation of the concept's unique features. The predictions are compared with subsequent experimental test data and observations for model validation (Fiveland and Jessee, 1994). The 3-D models are used routinely to investigate potential changes that may occur when a low NOx combustion system is applied to a boiler. Altering the combustion system to limit the mixing between the air and fuel may cause changes to the characteristic heat release patterns and gas temperature distributions in the furnace. The altered heat release and the presence of incomplete combustion products can affect the absorption and scattering of radiation, changing the distribution of the heat absorbed within the furnace. These changes can affect tube metal temperatures, heating surface performance, and water-side circulation. The models provide not only the capability to minimize deleterious effects on the gas side, but they can be used along with existing techniques to ensure that the water-side performance of the boiler is maintained. ® High Temperature-Fuel Rich Devolati llzatlon Zone ® Production of Reducing Species © NO. Decomposition Zone @ Char Oxidizing Zone Figure 1 Controlled Air and Coal Mixing With the DRB-XCL® Burner |