This paper aims at demonstrating the possible improvement of currently used control concepts for steam turbines. A model-based control is designed for a condensation turbine with steam extraction, which is used to drive a compressor on the chemical process side. The turbine is part of a sophisticated steam system of a chemical high-duty plant. Modeling of the steam system with the turbine leads to a system of two nonlinear differential equations. Taking advantage of the flatness property of the given nonlinear system model, a flatness-based control approach involving nonlinear feedforward and feedback control is employed. Remaining model uncertainties as well as nonlinear friction can be counteracted by an observer-based disturbance compensation. Simulation results show an excellent control performance with small control errors.