Eduardo M. Queiroz

Supercritical carbon dioxide extraction of macadamia (Macadamia integrifolia) nut oil: experiments and modeling

Supercritical CO2 extraction of macadamia nut oil was carried out in a flow apparatus at the following operational conditions: pressures of 10, 15 and 18 MPa; and temperatures of 313 and 353K; a volumetric flow of 1.64 x 10-7 m3.s-1 was used for one hour in each experiment. The efficiency of the extraction process showed to be low. The behaviors of the extraction curves were very similar at all temperatures and the best efficiency value was obtained at 10 MPa. Chromatographic analysis demonstrated the ability of supercritical CO2 to remove some of the main components of the oil: myristic (C14:0), palmitic (C16:0), oleic (C18:1) and linoleic (C18:2) acids, and that higher pressures favoured the removal of lighter components. The extraction process was represented by a simple model based on Langmuir Isotherm, showing a good data fitting.

Supercritical carbon dioxide extraction of pigments from Bixa orellana seeds (experiments and modeling)

Supercritical CO2 extraction of the pigments from Bixa orellana seeds was carried out in a flow apparatus at a pressure of 200 bar and a temperature of 40 oC at two fluid flow rates (0.67g/min and 1.12g/min). The efficiency of the extraction was low (only about 1% of the pigment was extracted). The increase in flow rate led to a decrease in pigment recovery. A large increase in recovery (from 1% to 45%) was achieved using supercritical carbon dioxide with 5 mol % ethanol as extraction fluid at pressures of 200 and 300 bar and temperatures of 40 and 60 oC. Although the increase in temperature and pressure led to an increase in recovery, the changes in flow rate did not seem to affect it. Furthermore, two plug flow models were applied to describe the supercritical extraction of the pigments from annatto seeds. Mass transfer coefficients were determined and compared well with those obtained by other researchers with similar models for the supercritical extraction of solutes from plant materials.

Parameter Estimation of Fouling Models in Crude Preheat Trains

Several fouling mitigation techniques depend on the capacity of predicting fouling rates. Therefore, the identification of accurate fouling rate models is an important task. Crude fouling rates are usually evaluated through empirical or semiempirical models. In both alternatives, there are parameters that must be determined through laboratory or process data. In this context, the article presents an analysis of the parameter estimation problem involving fouling rate models. A proposed procedure for addressing this problem is described through the development of a computational routine called HEATMODEL. An important aspect of this study is focused on the obstacles associated to the search for the optimal set of parameters of the Ebert and Panchal models and its variants. This optimization problem may present some particularities that complicate the utilization of traditional algorithms. In the article, the performance of a conventional optimization algorithm (Simplex) is compared with a more modern numerical technique (a hybrid genetic algorithm) using real data from a Brazilian refinery. The results indicated that, due to the complexity of the parameter estimation problem, the Simplex method may be trapped in poor local optima, thus indicating the importance of the utilization of global optimization techniques for this problem.

Design and Economic Evaluation of Alternatives to Effluents Treatment on Biodiesel Production from Soybean Oil and Palm Oil

Abstract Biodiesel production by homogeneous alkali catalysis was simulated in PRO/II ® from crude soybean oil and crude palm oil at industrial level, with ethanol. Actual compositions were assumed and thermodynamic properties were estimated by a group contribution method. The main effluents from biodiesel production are streams rich in unreacted oil, water, ethanol and glycerine. Some alternatives to the treatment of these effluents were proposed, including hydrous or anhydrous ethanol production, production and recycle of pure glycerol and unreacted oil recycle. An economic evaluation was done to find out the potential of each treatment possibility. It was demonstrated that, in the case of Brazil in mid-2014, it was not profitable to produce biodiesel from these oilseeds and ethanol without tax reductions or subsidy, but it is possible to reduce production costs and biodiesel prices with effluents treatment, generating more economical and sustainable plants.

AUTOMATIC EVOLUTION OF HEAT EXCHANGER NETWORKS WITH SIMULTANEOUS HEAT EXCHANGER DESIGN

Recently, a new software (AtHENS) that automatically synthesizes a heat exchanger network with minima consumption of utilities was developed. This work deals with the next step, which represents the evolution of the initial network. Hence, new procedures to identify and break loops are incorporated, for which a new algorithm is proposed. Also, a heat exchanger design procedure which uses the available pressure drop to determine the film coefficient on the tube side and shell side is added, providing the utilization of more realistic heat exchangers in the network during its optimization. Results obtained from a case study point to the possibility of equipment design having a strong influence on the network synthesis.

A Sliding Mixed-Integer Linear Programming Approach for the Optimization of the Cleaning Schedule of Crude Preheat Trains

The fuel consumption in the fired heaters of atmospheric distillation columns for petroleum refining increases during the refinery operation. This effect is a consequence of fouling in the heat exchangers of the crude preheat train. The application of a cleaning schedule to the crude preheat train can reduce fouling costs. However, the management of the cleanings for the entire set of interconnected heat exchangers is a complex problem. Aiming to contribute to the solution of this problem, this paper presents an optimization approach based on the resolution of a sequence of mixed-integer linear programming problems. Each problem indicates the set of heat exchangers that must be cleaned in a certain time instant. The structure of the crude preheat train is described using an incidence matrix, encompassing supply and demand nodes, heat exchangers, mixers, splitters, and desalters. The sequence of problems is associated to a sliding horizon, where the concatenation of the solutions composes the complete heat exchanger cleaning schedule. Although the present approach cannot guarantee the global optimality of the solution, the linear structure avoids nonconvergence problems. The performance of the proposed approach is illustrated through its application in an example of a crude preheat train from a Brazilian refinery.

A Novel Approach to Predict Violations and to Define the Reference Contaminant and Operation in Water Using Networks

Abstract The development of new techniques to the management of industrial water resources has become increasingly necessary in the last years. Many efforts in the field of algorithmic approaches have been made to achieve the minimum fresh water consumption. A common issue to most of those methods is the determination of a reference contaminant when dealing with processes presenting multiple contaminants. An assertive choice of it is crucial, because the calculations of all other contaminants are based on the reference contaminant and all of them require the same flow rate to meet the process constrains. Not only that, but the structure obtained based only on the reference contaminant can lead to violations of concentration limits. One of those techniques is the Water Source Diagram (WSD), which also requires a reference contaminant to deal with multiple contaminants. This work presents a novel and robust algorithm to determine the reference contaminant when applying WSD in Water Using Networks (WUN) problems. The proposed approach can also be used in conjunction with other methods based on the Water Pinch Analysis (WPA). We also present a violation prediction method that informs which contaminant violates (or may violates) the concentration limits and its respective operation. The presented results show the effectiveness and robustness of the algorithm when applied to a process plant example from the literature with four operations and three contaminants.

A Software for the Calculation of the Exergetic Efficiency in Distillation Columns

Abstract Many processes in chemical industries consume a lot of energy and often operate inefficiently. This implies high operation costs, which can be reduced through improvements in the use of energy in the process. Distillation is an important unit operation that is widely used in industry and requires an excessive energy demand. The exergetic analysis, which is based on the second law of thermodynamics, is an alternative to minimize this demand. Exergy or availability is the measure of the maximum amount of stream energy that can be converted into shaft work if the stream is taken to the reference state. This property may be applied to measure the quality of energy employed in a process. Therefore, the purpose of this study is to develop a program to calculate the exergetic efficiency and suggest, if necessary, possible operational changes that lead to the reduction of energy losses by irreversibilities in distillation columns. The preliminary conclusion is that exergy analysis is vital for evaluating inefficiencies in industrial processes and thus the exergetic analysis can be used as an important tool not only for process synthesis but also for process optimization activities.

Analysis of self-aspirating combustion systems

We present an analysis of self-aspirating combustors in which the induced mass-flow rate of air is derived as a function of the average combustion-gas temperature. The effects of pressure drop along the internal wall of the combustor and through the fixed combustion bed were considered. An implicit equation for the mass-flow rate and a computer program to solve it were developed and applied to a particular case. The formulation is general and useful for the design of large combustion units.

Systematic Procedure for the Removal of Violations in Water Sources Diagrams

Abstract Over the years, the Water Sources Diagram (WSD) has become a consolidated approach to determine the minimum freshwater consumption and simultaneously generate the system structure in water networks in many kinds of industrial processes. Some efforts have been employed to, for example, automatically determine the reference contaminant and reference operation and to predict in which operation(s) violations will occur, before the beginning of the calculations. Those violations are then removed as part of the last step of the method and it is currently performed by hand. Seeking to improve this step and to create an automated procedure that can be linked with the MINEA software was the motivation of this research.