A methodology for generating problem specific "local" simulators from a base (modular) simulator is presented. Based on an analysis of the process flowsheet and the simulation problem, the flowsheet is decomposed into parts that are solved with the modular approach and parts that are solved with the equation oriented approach. Also, the use of optimization techniques has been investigated to solve a part of the flowsheet. The application of the methodology has been tested in terms of an existing modular steady state simulator. Numerical examples of solution of parts of flowsheets with the equation oriented approach or the optimization technique from within the modular simulator are presented.