Numerical Simulation of Advanced Coal-Fired Combustion Systems with In-Furnace NO{sub}X Control Technologies

摘要

A general 3D combustion code for turbulent reacting flows is presented. Sub-models for fluid flow, turbulence, combustion and heat radiation are included. Equations for the conservation of mass, momentum and scalar quantities are solved. Turbulence closure is done with a k, ε-model or a Reynolds stress model. Radiation is considered by a discrete-transfer method. Coal combustion is described by a reduced four-step reaction scheme. For the gaseous reactions, the interaction between turbulence and chemistry is modelled using an advanced Eddy-Dissipation-Concept. The code is based on a conservative finite-volume formulation with all variables defined at the centres of the control volumes. In order to reduce numerical diffusion the convection terms are discretized with higher order schemes. A domain decomposition method is used to realize local grid refinements in regions with steep gradients of the variables. Parallel application of the code is realized using data distribution. The validation of the models is done with data of velocity, temperature and species concentrations gained at a semi-industrial pulverized coal combustion facility. After thorough inspection of the physical models and the numerical methods, the code is applied to the simulation of industrial pulverized coal-fired boilers with wall fired systems using swirl burners and tangentially fired units for the combustion of bituminous and brown coal. The presented furnaces are characterized by the application of advanced low-NO{sub}x combustion technologies, e.g. low-NO{sub}x burners and multiple air-staging. Comparisons between measured and predicted species concentration and temperature profiles show generally good agreement. Thus it may be concluded that the simulation of coal combustion processes in power plants is an attractive tool for the design and assessment of modern combustion technologies.