Argyrios I. Lygeros

Feedstock atomization effects on FCC riser reactors selectivity

Feedstock atomization affects catalytic cracking reactions that take place in an FCC riser reactor, and is considered a critical parameter especially when processing heavy fuels. A finely atomized feed allows instantaneous flash vaporization and quick quenching of the catalyst, conditions that allow the feed components to be subjected to an ideal mixing temperature. Mixing conditions at the inlet of the riser reactor also affect cracking reactions selectivity. An atomization modeling scheme has been incorporated into a CFD model developed by Theologos & Markatos (1993, A.I.Ch.E. Journal, 39(6), 1001.) and Theologos, Nikou, Lygeros & Markatos (1997, A.I.Ch.E. Journal, 43(2), 486) and has been used to evaluate atomization effects on feedstock vaporization rates, cracking reactions initiation, reactor selectivity and overall reactor performance. Cracking reactions are simulated using a simplified 3-lump model. The atomization modeling scheme takes into account the initial feed droplet size at nozzles exit, as well as droplet size reduction along with vaporization. Droplet vaporization parameters from the literature have been considered. To evaluate the degree of feedstock atomization effects on reactor performance, a parametric study is carried out considering three different initial feed droplet sizes, namely 30, 100, and 500 μm. The area where feedstock vaporization takes place inside the reactor is predicted and the evolution of atomized droplet size is illustrated. The effect of the initial degree of atomization on cracking reactions selectivity is discussed.

The selective dissolution/precipitation technique for polymer recycling: a pilot unit application

In this study, the selective dissolution/precipitation method for polymer mixture separation and recycling is evaluated. The method was successfully applied in a pilot unit designed and developed for the separation of polymer mixtures. Recycled polymers of comparable quality with that of the pre-used ones were recovered. Furthermore, the feasibility study for high-capacity units indicated the applicability of this technique from the economic point of view.

On-line PI controller tuning for integrator/dead time processes

This paper presents two new methods for tuning PI controllers for integrator plus dead time models (IPDT). The simple IPDT model was found to be a useful approximation of more complex models such as first-order plus dead time models with large time constants. The use of IPDT models can, in these cases, simplify and also accelerate the auto-tuning step especially in MIMO processes. The advantages of the proposed methods over the known tuning methods are demonstrated through simulation examples.

Variable selection and data pre-processing in NN modelling of complex chemical processes

Abstract The neural network models represent nowadays a powerful tool for complicated process identification. However, because of the fact that they belong to the category of data-driven “black box” models, they cannot avoid the consequences of the “garbage in–garbage out” rule. This work proposes a simultaneous data balancing-variable selection procedure, which is based on traditional statistical techniques and modern information theoretic approaches. It is implemented on a complicated dataset of restricted quality, which refers to a commercial aldol condensation unit (BASF). Based on the pre-processed database a neural model for the prediction of the process yield has been developed. The results verify the importance of the pre-processing stage in terms of generalization accuracy as well as of simpler network structure due to the data-variable selection procedure. Finally, an analysis of the model trends has been implemented to assess qualitative characteristics of the model, which was then used in industrial test runs and resulted in an improvement of the process operation.

Simulation and design of Fluid-Catalytic Cracking riser-type reactors

Abstract Two-phase flow, heat transfer and reaction in Fluid Catalytic Cracking riser-type reactors is studied using 3-D Computational Fluid Dynamics techniques. A model already presented in the literature (Theologos and Markatos, 1993) is further developed to incorporate a detailed 10-lump reaction kinetics scheme and account for feedstock gradual vaporization inside the reactor. A design study is carried out to illustrate that developed model is capable of predicting feed injector geometry effects on overall reactor performance. It is predicted that, by increasing the number of feed injection operating nozzles at the bottom of the reactor, selectivity to primary products is improved.

A Multiobjective Framework for the Integrated Process Design and Control

Abstract This paper presents a systematic framework for the integrated design of process and control systems. A detailed controllability analysis is performed over the entire frequency range of interest and a new method for control structure selection, based on the minimization of an overall interaction measure, is used. The trade-off between increased cost and improved controllability is resolved using the goal attainment method for solving multiobjective optimization problems. The proposed method is clarified through an application example, specifically the integrated design of a reactor-separator system with recycle.