Modern systems for basic automation and process visualization are becoming more and more complex and extensive. To realize modernization measures failure-free and efficiently, process simulation tools are used more and more frequently. Process simulation familiarizes the users with the new technology, helps to identify and debug failures before ramp-up. Using the example of a steel plant and a continuous caster at ThyssenKrupp Steel Europe AG in Duisburg, options and extensiveness of different process simulation methods are illustrated and schedule of modernization is analyzed. Block diagrams of the process simulation with Simit and of the structure of test converter for automatic operation are shown. Example of a control picture in the control system is displayed.