In this work a rough overview of the possibilities of denitrification of exhaust gases is given by means of end-of-pipe off-gas treatment. Especially the method of selective catalytic reduction (SCR) is investigated. As a method for flow simulation of process engineering plants Computational Fluid Dynamics (CFD) finds broad application. For the first time it is possible to simulate combinations of 3D-fluid dynamics and chemical processes in SCR-systems with the CFD-program SWIFT 3.1 and the inserted modules Porosity, Aftertreatment, and Species Transport. The CFD related fundamentals and the theoretical background of the individual modules for simulating the heat exchanger and catalysts in SCR-systems are presented. Further on the basis of the domestic garbage combustion plant Lauta the applicability of the CFD-program SWIFT 3.1 was demonstrated and documented.