Dynamics of a distillation column with distributed and conventional approach using multivariable control with adjustment based on multiple errors

In this study, an application of a multivariable conventional control structure of the continuous tray distillation columns is compared to a new distributed proposal. This was done considering the process dynamics, more specifically the transition time when the process is disturbed. As the conventional approach, the top and bottom product temperatures of the distillation column were selected as controlled variables and the reflux ratio and reboiler heat supply as manipulated variables. These loops plus an intermediate temperature column stage controlled using the heat supply of one tray as the manipulated variable comprised the distributed control structure. The regulator problem was considered for the experimental control studies. Feed temperature was chosen as the load variable. It is important to notice that this study focuses on the response process and does not address the development or design of the control structure. The main aim is to compare the time response of the process when subject to an expected disturbance using two different approaches (conventional and distributed). Experiments were carried out with multivariable PI controllers and the multiple errors (desired controller variable and the corresponding measured output) of each controlled variable were used together to computed the control actions (interactions were considered). Better performance in relation to transition time was observed with the distributed approach, indicating that this is an interesting strategy which could be used to minimize the transients in a distillation column.