Process Control: Modeling, Design, and Simulation

M13.2. Open-Loop Behavior

Response to Reflux Change

Here, we consider open-loop step changes in the manipulated inputs, with additional time delays of 2 minutes in the concentration measurements. The responses to step changes of ±0.01 kmol/minute in reflux at t = 10 minutes, while keeping vapor boil-up constant, are shown in Figure M13-3. The response to a positive reflux flow change are shown as solid lines, while responses to a negative reflux change are shown as dashed lines; also, we have chosen to plot mole percent rather than mole fraction (the unit used in the transfer function matrix). The responses are symmetric because we are using a linear model. Naturally, the bottoms composition cannot decrease below 0, as obtained with a step decrease ...