Sequential Modular Solution Techniques Versus

SEQUENTIAL MODULAR SOLUTION TECHNIQUES VERSUS SIMULTANEOUS SOLUTION TECHNIQUES 

Care should be taken when embarking on a modeling effort to choose the modeling environment and method, which assure that the model is solved efficiently when its complete scope and level of fidelity are reached. 

A significant part of developing a model used for other than determining static sets of heat and material balances (which are sufficient for some model objectives, such as providing the basis for new plant design) is specifying which variables are independent and which are dependent. Far more variables are dependent variables than are independent in essentially all models. For simulation and optimization 

It is important to have the correct set of variables specified as independent and dependent to meet the modeling objectives. For monitoring objectives observed conditions, including the aforementioned independent variables (FICs, TICs, etc.) and many of the normally (for simulation and optimization cases) dependent variables (FIs, TIs, etc.) are specified as independent, while numerous equipment performance parameters are specified as dependent. These equipment performance parameters include heat exchanger heat transfer coefficients, heterogeneous catalyst activities (representing the relative number of active sites), distillation column efficiencies, and similar parameters for compressors, gas and steam turbines, resistance-to-flow parameters (indicated by pressure drops), as well as many others. These equipment performance parameters are independent in simulation and optimization model executions. 

The aforementioned specifications reflect the control system in a plant (existing or under development). The importance of having a model appropriately specified cannot be overstated. 

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