Ferhan Kayihan

A novel approach to full CD profile control of sheet-forming processes using adaptive PCA and reduced-order IMC design

Abstract This paper presents a new framework towards control of cross-directional profiles in sheet-forming processes. The proposed method uses adaptive principal component analysis to identify the significant disturbance modes from on-line data. To resolve the potential problems associated with large dimensional and ill-conditioned systems a low order subspace is constructed for controller design purposes. Certain projection and reduction techniques are given to systematically arrive at this design subspace. Simulations illustrate that the resulting controller is easy to design and able to isolate and reject the significant disturbance modes.

Simultaneous heat and mass transfer in binary distillation—I: Theory

Abstract Binary distillation in continuous contact equipment is modeled as a simultaneous heat and mass transfer process. In order to account for the interactions between heat and mass transfer between the two phases, the equations developed from enthalpy and material balances are analyzed simultaneously and it is revealed that the individual phase mass transfer coefficients can be evaluated rigorously by measuring liquid phase compositions and temperatures in distillation experiments. Using the theoretical relations, it is proved that the liquid phase in a distillation column will be saturated if and only if there is negligible resistance to mass transfer in the liquid film. For the case of comparable resistances in both phases, the possible amount of superheat in the liquid phase would be considerable and thus convenient to determine experimentally. The liquid phase temperatures are shown to be important in experimental analysis (i.e. in determining the individual phase transfer coefficients) but not in design applications. For the latter case, the model equations reduce to the conventional mass transfer relations which are not as sensitive to temperatures.

Reaction profile control of the continuous pulp digester

In this work, a model-based control strategy is presented for the Kappa number profile control of a continuous pulp digester. The strategy employs an empirically derived process model using subspace identification techniques. A state-space model predictive control algorithm is used to adjust five manipulated inputs in order to regulate five process outputs, in response to five randomly varying process disturbances (of which three are measurable). Profile sensitivity to closed-loop response is also explored.

Simultaneous heat and mass transfer in binary distillation—II: Experimental

Abstract A theoretical study of simultaneous heat and mass transfer in binary distillation has shown that heat and mass transfer coefficients can be appropriately evaluated if liquid phase temperatures and compositions are measured as functions of height in a column. In this study, the experiments were carried out in a wetted-wall column using a methanol-water binary system at one atmosphere. Special probes were designed to determine the state of the liquid phase. Temperatures were measured with microthermocouples and liquid samples were analyzed with a high precision refractometer. The liquid phase was found to be saturated which indicated, in accordance with the conclusions from a theoretical study, that all the resistance to mass transfer was in the vapor phase. Local transfer coefficients were calculated using the composition data as a function of column height. The results were correlated by an equation showing close agreement with the Chilton-Colburn equation. k y a m V = 0.039 Sc y − 2 3 Re y −0.20 cm −1 . It is concluded that mass transfer in the vapor phase is the controlling resistance in distillation and that there is no additional evaporation within the liquid phase caused by heat transferred from the vapor phase as proposed by some previous investigators.

Full CD Profile Control of Sheet Forming Processes using Adaptive PCA and Reduced Order MPC Design

Abstract In this paper a new approach to control full CD profiles in sheet forming processes is presented. The method consists of a sequence of dimension reductions of the input, output and external disturbance spaces, while alleviating ill-conditioning problems. SVD is used to initially condition the input-output space, and then the order of the subspace of the dominant disturbances is identified on-line through the use of the Karhunen-Loeve expansion. Subsequently the dimension of the input space is further reduced by projecting it onto the disturbance subspace. Finally, model predictive control able of handling input constraints is implemented on this space.