Default Control Structure and Simplified Heat Transfer Models

3 Default Control Structure and Simplified Heat Transfer Models 

Aspen Dynamics automatically installs some control loops on the flowsheet. This default control stmcture can be modified as required. In our flash-tank example, a pressure controller is automatically installed that controls the pressure in the vessel by manipulating the valve in the vapor line. If we had not placed a pump on the liquid line and only had a valve. Aspen Dynamics would automatically install a level controller that controls the hquid level in the tank by manipulating the valve in the hquid line. 

A similar simplification is made for the heat input in the reboiler. If steam is the heating medium used, reboiler heat input is determined by position of a valve in the steam line feeding steam into the reboiler. Opening the steam valve puts more steam into the shell or mbe side of the heat exchanger, which increases the steam pressure and increases the steam temperature, thus increasing heat transfer. Aspen Dynamics simplifies the model by specifying heat transfer directly. 

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