Structure-based modelling is an alternative knowledge representation technique, where the problem is formulated as the structure of connected but autonomous elements instead of a mathematical construction (e.g. differential equation). Taking the opportunity that the structural elements can directly be accessed a new method for the solution of large scale stiff problems is presented. The example is the oxidative coupling of methane in gas phase with a kinetic model of 164 elementary reactions and 27 components. The method is based on a runtime model reduction carried out simultaneously with the dynamic simulation considering the actual rate of reactions and the actual concentrations of components. Coarse and fine, as well as irreversible and reversible transformation strategics are introduced and compared.