The RWE Generation SE operates a coal-fired power plant in Ibbenbüren under increasingly difficult economic conditions. Possibly, in order to increase the contribution margin, a part of the normal used anthracite from Ibbenbüren can be substituted by Rhenish lignite. Both coals differ in the form of a basically identical structure of all coals, which can affect the combustion process in different ways. The task of this thesis is to discuss, on the basis of corresponding numerical flow simulations, how the corresponding coal mixtures in the steam generator of the power plant in Ibbenbüren would ignite and burn off. The flow simulations are made by means of a relevant evolution of AIOLOS, a computer code specially developed for the simulation of pulverized coal combustion processes at the Institute of Combustion and Power Plant Technology of the University of Stuttgart. (see chapter 1)
In the power plant in Ibbenbüren a slag-tap furnace is installed to handle the combustion process. This includes, inter alia, eight vertical roller mills in which the coal is ground and dried simultane- ously before it enters two combustion chambers via respective burners. In the combustion chambers the conversion of the coal is induced by the mixing of the coal dust-carrier gas mixture with flue gas and the radiant heat exchange. At first, adsorptively bound gases escape. Then the solid particle struc- ture changes and combustion processes begin. The flue gases flow from the combustion chambers into a common radiation section. At the end of the radiation space the convective heating surfaces are installed. (see chapter 2)
The flow simulations created are based on the modeling of the general coal dust combustion process. This process is described in the depth of detail of the molecular motion through a balance equation for the mass of a component, the momentum of each phase, the total energy of each phase and the change of the spectral radiation. From this process description the process description is derived in the lesser depth of detail of the flow movement, which among other things includes a modeling of different unknown terms. (see chapter 3)
The modeling of the general pulverized coal combustion process leads to a under-determined system of equations. Its closure takes place by means of the modeling of various application-specific processfeatures. These include boundary conditions regarding the design of the simulation space and the state of the incoming material flows as well as properties that describe the substance, radiation and con- version behavior. (see chapter 4)
The resulting system of equations cannot be solved analytically. A corresponding preparation of the equation system makes it possible to calculate an approximation of the process state at discrete posi- tions. The processing includes the subdivision of the simulation space in control volumes, the trans- formation of the balance equations established for each control volume and the approximation of quantities at the boundaries of the control volumes. (see chapter 5)
The characteristics of two application-specific process features are not known, why their determina- tion is based on a corresponding sensitivity analysis. Due to these and other simplifications, the entire procedure is validated with the result that the influence of co-firing of Rhenish lignite on the ignition and combustion behaviour can be reliably analysed. The analysis shows that the structure and position of the flames only change insignificantly due to the lower heat absorption of the combustion chamber walls. The loss on ignition at the end of the radiation space increases slightly when Rhenish lignite is co-fired. Co-firing of Rhenish lignite with a proportion of rated thermal input of up to 40% is harm- less, but the influence on production operations, in particular due to the changed heat absorption of the various heating surfaces, needs to be discussed in more detail. (see chapter 6)