Analysis of Combustion Processes Using Computational Fluid Dynamics - A Tool and Its Application

摘要

Numerical simulation by means of Computational Fluid Dynamics (CFD) has developed over recent years to a valuable design tool in engineering science. In the beginning mainly applied to address fluid dynamic questions it is nowadays capable to predict in detail conditions in various complex technical processes. State of the art commercial CFD codes are almost always set up as multi-purpose tools suitable for a wide variety of applications from automotive industry to chemical processes and power generation. However, since not highly specialized in all possible fields of application, CFD codes should be rather seen as a collection of basic models that can be compiled and extended to individual tools for special investigations than as readily applicable tools. In power generation CFD is extensively used for simulation of combustion processes in systems like utility boilers, industrial furnaces and gas turbines. The purpose of these simulations is to analyze the processes, to optimize them with regard to efficiency and safety and to develop novel techniques. Since combustion processes have been the target for CFD software for long, also standard models available in the codes are of high quality as long as modelling of conventional combustion systems is concerned. However, as soon as characteristics of novel combustion systems or fuels or detailed effects within a certain process are of interest, the limits of these standard models are reached easily. At this point extension of standard models by process specific knowledge is required. This paper presents some of the opportunities CFD offers when applied to analyse different combustion systems. Practical examples presented are ash deposition predictions on heat exchanger surfaces and walls in a bubbling fluidised bed furnace and detailed nitrogen oxide emission predictions for the same furnace type. Furthermore, the extension of a standard model using process specific data is presented for the fuel conversion process in a black liquor recovery furnace.