Modelling Fundamentals

Models are an integral part of any sort of human activity. Yet, we are largely unaware of this. Most models are qualitative in nature and are not formulated explicitly. Such models are not reproducible and cannot conveniently be verified or confirmed to be false. Models guide our activities, and throughout our complete life we are continually modifying those models that affect our everyday behavior. The most scientific and technically useful varieties of models are expressed in mathematical terms. The use of models in chemical engineering is nicely established, but the use of dynamic models, as opposed to the more classic use of steady-state models for chemical plant analysis, is significantly more recent. This is reflected in the development of new strong commercial software program packages for dynamic simulation, which has arisen owing t o the increasing pressure for style validation, method integrity and operation research for which a dynamic simulator is an necessary tool.

Indeed it is conceivable to envisage dynamic simulation becoming a mandatory condition in the security assessment of plant, with consideration of such elements as start out up, shutdown, abnormal operation, and relief conditions assuming an increasing importance. Dynamic simulation can thus be observed to be an necessary part of any hazard or operability study, both in assessing the consequences of plant failure and in the mitigation of conceivable effects. Dynamic simulation is thus of equal importance in large scale continuous method operations, as in other inherently dynamic operations such as batch, semi-batch and cyclic manufacturing processes. Dynamic simulation also aids in a really positive sense in enabling a much better understanding of method overall performance and is a strong tool for plant optimization, both at the operational and at the style stage. Moreover steady-state operation is then observed in its rightful spot as the end outcome of a dynamic method f or which rates of change have become ultimately zero.

Substantial scale commercial software program packages for chemical engineering dynamic simulation are now really strong and contain extremely sophisticated mathematical procedures, which can resolve both for the initial steady-state condition as nicely as for the following dynamic changes. They also contain extensive standard model librates and the implies of synthesizing a complete method model by combining standard library models. Other necessary aspects are the provision for external data interfaces and built-in model identification and optimization routines, together with access to a physical property data package. An necessary stage in the development of any model is the formulation of the appropriate mass and energy balance equations. One particular of the most necessary characteristics of modeling is the frequent require to reassess both the fundamental theory, and the mathematical equations, representing the physical model, in order to reach agree ment, among the model prediction and actual method behavior.

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