André L.H. Costa

Competitive biosorption of cadmium(II) and zinc(II) ions from binary systems by Sargassum filipendula

The present work describes our study on the competitive biosorption of Cd(II) and Zn(II) ions onto Sargassum filipendula from single component and binary systems. Results showed that S. filipendula was an efficient biosorbent for the removal of Cd(II) and Zn(II) ions from an aqueous solution. The equilibrium experimental data for the single component system for the two metallic species fitted well to Langmuir and Langmuir-Freundlich isotherm models. Seven isotherm models were tested with the equilibrium data for modeling of the binary system. Based on the sum of squares error, the Langmuir-Freundlich isotherm model showed the best fit to the binary adsorption data. The influence of the additional cation on the behavior of the biosorption of Cd(2+) and Zn(2+) was analyzed comparing single component and binary isotherms. It was observed that Zn(2+) had a relevant effect on the Cd(2+) biosorption, but the interference of Cd(2+) on the sorption of Zn(2+) was considerably less intense.

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.

Multi-objective design optimization of natural gas transmission networks

Abstract This paper proposes the multi-objective optimization of the design of natural gas transmission networks to support the decision of regulatory authorities. The problem formulation involves two objective functions: the minimization of the transportation fare and the maximization of the transported gas volume. These design parameters of the pipeline project must be previously established by the regulatory agency, considering an attractive return on the investment for the entrepreneurs and the demands of current and future consumers. The solution of this problem without an optimization tool may imply in unfair gas prices or the lack of investors interest. The proposed analysis is focused on growing markets, associated to a continuous increase of the natural gas consumption. Constraints associated to gas flow and compressor stations guarantee the feasibility of the set of design options found. Aiming to illustrate the performance of the proposed approach, the tool was applied to a typical trunkline example.

Global optimization of water distribution networks through a reduced space branch-and-bound search

A branch-and-bound approach to the problem of optimal design of water distribution networks is presented. Global optimum is reached through the generation of convergent sequences of upper and lower bounds. The relaxations responsible for the lower bounds correspond to linear programming problems formulated through the enlargement of the original feasible region by outer approximations of the constraints. Although formulated within an arc-based framework, the proposed scheme does not apply the branching process to all flow variables; by utilizing the mass conservation principle, only a reduced set of variables is assigned for branching. The algorithm was applied to three variants of a classical problem from the literature. Comparisons with previous results indicates a faster convergence to the optimum (fewer linear programming problems solved) in several situations.

Development and evaluation of a new DGA diagnostic method based on thermodynamics fundamentals

The dissolved gas analysis (DGA) is a well-accepted power transformer predictive maintenance technique. However, despite the importance of the technique, classical diagnostic methods were developed from observations of simplified thermodynamic and compositional models. This paper presents the development of a DGA diagnostic method based on a thermodynamic model that includes a contribution inspired on the kinetics of the process. The performances of the new phenomenological proposition and of classical DGA diagnostic methods are compared and discussed. Also, a general procedure for the application of the new diagnostic method is described.

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.

Influence of Metal Oxides Impregnated on Silica-Alumina in the Removal of Sulphur and Nitrogen Compounds from a Hydrotreated Diesel Fuel Stream

The environmental legislation of many countries imposes severe restrictions on the emissions of gaseous pollutants, including NOx and SOx. Efficient alternatives for the removal of nitrogen and sulphur contaminants are required to obtain increasingly cleaner fuels. In this regard, adsorption is economically promising, because it requires less energy than the traditional hydrotreating processes due to mild conditions of temperature and pressure required. The objective of this study was to evaluate the influence of nickel, cerium, molybdenum and cobalt oxides impregnated on silica–alumina in removing nitrogen and sulphur compounds from a hydrotreated diesel. The incorporation of metal oxides increased the density of acid sites and promoted the removal of nitrogen and sulphur compounds, especially the one impregnated with molybdenum oxide. The influence of molybdenum oxide loading was also studied. It was observed that this synthesis parameter affected acid sites density and contaminant removal.

A MATRIX APPROACH FOR OPTIMIZATION OF PIPE NETWORKS IN COOLING WATER SYSTEMS

This article addresses the design problems associated with pipe networks in cooling water systems. The objective is to determine the lowest cost network that can supply the heat exchangers with cooling water at the flow rates previously established in the thermal design. The solution to the problem provides the diameter for each section of pipe in the network together with the corresponding pump alternative. The objective function and constraints are organized in a matrix formulation where the solution consists of a set of linear programming problems. The basic structure of the optimal design problem also extends to the solution for revamp problems. The comparison of the proposed approach to the traditional solution based on economical velocities indicates that the optimization scheme can make pipe network designs less expensive and more reliable for supplying cooling water.

Heat Exchanger Design Optimization Considering Threshold Fouling Modelling

Abstract In heat exchangers, fouling is the undesired accumulation of deposits over the equipment thermal surface. This phenomenon causes a gradual reduction of the overall heat transfer coefficient. The traditional approach to handle the fouling problem during the design consists in the introduction of fouling factors in the evaluation of the (dirty) overall heat transfer coefficient. However, this approach ignores the fact that the fouling rate is dependent on the flow velocity and temperature. Aiming to fill this gap, this paper investigates the optimization of the design of heat exchangers including fouling modelling. Among the many fouling manifestations, this investigation focuses on chemical reaction fouling in crude oil streams associated to the presence of asphaltenes, modelled by a threshold model (Ebert Panchal model and its variants). According to this model, there are conditions of surface (or film) temperature and flow velocity where there is no fouling. The developed formulation of the design problem employs a mixed integer linear programing approach, where the geometry-related design variables are defined based on standard values. The results are compared with a traditional approach with fixed fouling factor, which indicates a potential reduction of capital costs.

An extended techno-economic analysis of the utilization of glycerol as an alternative feedstock for methanol production

Glycerol is a by-product of biodiesel production and may become an environmental problem. This paper investigates the utilization of glycerol as alternative feedstock for methanol production. A mathematical model of the methanol plant encompassing the steam reforming and methanol synthesis units is employed to generate data for an economic analysis involving two comparative cases: the conventional operation of the plant using only natural gas and the operation with partial substitution of the natural gas by glycerol. The results indicate that the glycerol injection can reduce the total natural gas consumption by about 11% for a given fixed methanol production. A breakeven analysis procedure is applied to determine the limit price of glycerol that makes this operation economically feasible. Based on a natural gas price of 10.13 US