Numerical Simulation of Utility Boilers with Advanced Combustion Technologies

This paper presents calculations of a pulverized coal flame and a coal-fired utility boiler with advanced combustion technologies. A combustion model based on an extended Eddy Dissipation Concept (EDC) combined with finite rate chemistry is described and some applications are shown. This model can be regarded as an extension of the previously used Eddy Breakup model (EBU) where infinite fast chemistry is assumed. It is part of a 3D-prediction code for quasi-stationary turbulent reacting flows which is based on a conservative finite-volume solution procedure. Equations are solved for the conservation of mass, momentum and scalar quantities. A domain decomposition method is used to introduce locally refined grids. Validation and comparison of both combustion models are made by comparison with measurement data of a swirled flame with air staging in a semi-industrial pulverized coal combustion facility. The application to three-dimensional combustion systems is demonstrated by the simulation of an industrial coal-fired boiler. INTRODUCTION Prediction of utility boiler performance becomes an important tool for the development of new combustion methods. But advanced combustion modifications require more detailed modeling of turbulent combustion when, e.g., the formation and destruction processes of carbon monoxide are to be predicted in order to reduce harmful concentrations near the furnace walls. The recent development in computer hardware and numerical methods rises the possibility to use more complex combustion models in three-dimensional predictions of utility boilers. In most three-dimensional simulation codes of pulverized coal combustion for practical systems the infinite-fast-chemistry assumption is used to model the gas phase combustion. Chemical kinetics, however, have a major influence on pollutant formation, especially in combustion systems equipped with air or fuel staging. The use of a detailed description of turbulent combustion, even if available, would be extremely time and memory consuming and therefore not be applicable to practical three-dimensional calculations. Thus simplifications in the description of the turbulence behavior and the chemical reaction mechanisms are necessary. The application of a combustion model which is able to handle finite rate chemistry in turbulent combustion is presented in this paper.