Rafael de Pelegrini Soares

Assessing the production of first and second generation bioethanol from sugarcane through the integration of global optimization and process detailed modeling

Abstract There is a worldwide effort to make economically feasible the use of lignocellulosic biomass for production of biofuels. In sugarcane industry, cane juice (sucrose) is fermented for bioethanol production. Sugarcane bagasse is used as fuel in cogeneration systems, to produce steam and electric power to the plant, and the surplus of electric power may be delivered to the grid. The hydrolysis of bagasse to produce second generation ethanol poses a challenge: how much bagasse can be diverted, since the process must continue energetically self-sufficient. This work presents a computational tool developed within an equation-oriented process simulator that couples the simulation of first and second generation bioethanol production with a global optimization algorithm. The tool was robust, optimizing the steady state process in any economic scenario and for different process configurations. Four case studies are presented, and their implications on process internal demands and on the surplus electrical power are discussed.

Teaching chemical reaction engineering using EMSO simulator

Nowadays, the use of computational tools in classroom is quite habitual and important by making the learning process more constructive and dynamic. The objective of this work is to introduce a support didactic material for use in computational classes of Chemical Reaction Engineering. The development of the work is based on a direct implementation of examples of the well‐known Foglers textbook “Elements of Chemical Reaction Engineering” in an equation‐based dynamic simulator: EMSO. The problems were implemented in a way to preserve the structure of the problem as described in the textbook. The results are illustrated by graph plots generated in the simulator, allowing comparisons with the results presented in the textbook and detailed analyses for effects of variables in the problem. The problems are easily modified, allowing the student to analyze several possibilities, changing equations and values of variables, for example, and observing the results.

Assessing the reliability of predictive activity coefficient models for molecules consisting of several functional groups

Currently, the most successful predictive models for activity coefficients are those based on functional groups such as UNIFAC. In contrast, these models require a large amount of experimental data for the determination of their parameter matrix. A more recent alternative is the models based on COSMO, for which only a small set of universal parameters must be calibrated. In this work, a recalibrated COSMO-SAC model was compared with the UNIFAC (Do) model employing experimental infinite dilution activity coefficient data for 2236 non-hydrogen-bonding binary mixtures at different temperatures. As expected, UNIFAC (Do) presented better overall performance, with a mean absolute error of 0.12 ln-units against 0.22 for our COSMO-SAC implementation. However, in cases involving molecules with several functional groups or when functional groups appear in an unusual way, the deviation for UNIFAC was 0.44 as opposed to 0.20 for COSMO-SAC. These results show that COSMO-SAC provides more reliable predictions for multi-functional or more complex molecules, reaffirming its future prospects.

Modeling, simulation, and optimization of a front-end system for acetylene hydrogenation reactors

The modeling, simulation, and dynamic optimization of an industrial reaction system for acetylene hydrogenation are discussed in the present work. The process consists of three adiabatic fixed-bed reactors, in series, with interstage cooling. These reactors are located after the compression and the caustic scrubbing sections of an ethylene plant, characterizing a front-end system; in contrast to the tail-end system where the reactors are placed after the de-ethanizer unit. The acetylene conversion and selectivity profiles for the reactors are optimized, taking into account catalyst deactivation and process constraints. A dynamic optimal temperature profile that maximizes ethylene production and meets product specifications is obtained by controlling the feed and intercoolers temperatures. An industrial acetylene hydrogenation system is used to provide the necessary data to adjust kinetics and transport parameters and to validate the approach.

Direct initialisation and solution of high-index DAE systems

Differential-algebraic equations (DAE) systems arise naturally from modelling many dynamic systems and are more difficult to handle than ordinary differential equation (ODE) systems. For instance, it is well known that difficulty arises when DAEs are solved with inconsistent initial values. Furthermore, the solution of high-index problems requires specially designed integration methods or index reduction, which are usually limited. In this work, alternatives for initialising and solving general high-index DAE systems are studied and a new algorithm for index analysis and reduction is introduced.

Modifications, simplifications, and efficiency tests for the CAPE-OPEN numerical open interfaces

Abstract The CAPE-OPEN (CO) project have published CORBA and COM open interfaces in order to enable native components of a process simulator to be replaced or plugged from those of independent sources. Until now the major effort of this project is regarded with sharing thermodynamic and unit operation packages. For this reason, the set of interfaces for numerical solvers is not mature yet. In this work the set of CORBA interfaces for sharing numerical solvers is treated. Some inconsistencies found at the original CO set of interfaces were corrected and simplifications were proposed. The performance impact in using the interfaces was studied and the usability of the simplified set of interfaces was tested.

Integrated tool for simulation and optimization of a first and second generation ethanol-from-sugarcane production plant

Abstract An integrated first and second generation ethanol production plant was simulated and optimized in an equation-oriented process simulator. Two optimization methods were used: ipopt, a deterministic algorithm, and PSO, a stochastic one. The optimization of cash flow and of ethanol production was carried out for three different pretreatments. PSO was able to solve the optimization problems, while ipopt did not converge. The objective functions exhibited opposite behavior, i.e. ethanol maximization leaded to lower cash flows for the considered economic scenario.

Reliability vs. Efficiency When Solving Multiphase Equilibrium Problems with Hybrid Optimization Codes

Abstract Computation of phase equilibrium is a very important and frequently encountered problem in process systems engineering. Accurate and robust flash routines are at the core of the major part of chemical engineering design applications, ranging from pipelines to distillation columns, chemical reactors, and oil and gas production. The multiphase equilibrium calculation by the direct minimization of the Gibbs free energy has some potential advantages over classical methods, mainly because the equality of chemical potentials is a necessary but not a sufficient condition for equilibrium. Recent developments in global optimization and the availability of very fast computers have stimulated the research on the direct minimization approach. In this work, a hybrid method (genetic algorithm for the global search and interior point for refinement) was implemented and the efficiency/reliability relation was studied. For some systems the global minimum can be found in a NFE compatible with the methods currently available in process simulators. But, it was also found that, for some systems, there is an asymptotic behavior. Apparently, a reliability of 100 %, when using global search algorithms with some random nature, would be found only for an infinite number of function evaluations.

Analysis of equations of state for polymers

In the literature there are several studies comparing the accuracy of various models in describing the PvT behavior of polymers. However, most of these studies do not provide information about the quality of the estimated parameters or the sensitivity of the prediction of thermodynamic properties to the parameters of the equations. Furthermore, there are few studies exploring the prediction of thermal expansion and compression coefficients. Based on these observations, the objective of this study is to deepen the analysis of Tait, HH (Hartmann-Haque), MCM (modified cell model) and SHT (simplified hole theory) equations of state in predicting the PvT behavior of polymers, for both molten and solid states. The results showed that all equations of state provide an adequate description of the PvT behavior in the molten state, with low standard deviations in the estimation of parameters, adequate sensitivity of their parameters and plausible prediction of specific volume, thermal expansion and isothermal compression coefficients. In the solid state the Tait equation exhibited similar performance to the molten state, while HH showed satisfactory results for amorphous polymers and difficulty in adjusting the PvT curve for semicrystalline polymers.

Design and Implementation of a Real Time Optimization Prototype for a Propylene Distillation Unit

Abstract The design of a steady state RTO system prototype to be tested in an industrial unit is presented. A software architecture (SA) approach is carried out proposing an objectoriented software framework. SA patterns are used in the architecture design. The framework aims to allow the implementation of different RTO approaches. A RTO system prototype is being developed using the framework integrating EMSO (Soares and Secchi, 2003) as the modeling and optimization engine. The framework opens opportunities for academic uses and deeper researches on the field.