Date of Award

1987

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

First Advisor

Armando B. Corripio

Abstract

The design of a reliable control scheme and efficient computer control algorithm for the double effect heat integrated distillation columns under floating pressure operation to control four product compositions on setpoint specifications has been studied. The system includes a pair of distillation columns with the vapors of one column providing the heat source for the other column. The economic profitabilities of four different configurations of the double effect heat integrated distillation columns for the methanol and water system have been investigated using the ASPEN PLUS process simulation program. Three of the four configurations of the double effect heat integrated columns have been shown to be very profitable because the payout time to invest in an additional column is less than one year. The energy balance control scheme, the material balance control scheme, the modified material balance control scheme, and Ryskamp's control scheme have been compared using the feedback PI control algorithm and the multivariable Dynamic Matrix Control (DMC) algorithm based on simulation. The dynamic simulation program, which has features to calculate the thermodynamic properties using nonideal solution models and which allows the column pressure to vary with time, has been constructed employing Gear's implicit integrator. When the feedback PI control algorithm is used, the rank of the performance of the control schemes is, in descending order, Ryskamp's control scheme, the energy balance control scheme, the modified material balance control scheme, and the material balance control scheme. When the DMC control algorithm is applied, the performance of the energy balance control scheme is superior to that of Ryskamp's control scheme and the material balance control scheme. The DMC control algorithm has been proved to work well even though the dynamic matrix does not accurately represent the process.

Pages

233

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