Carlo Edgar Torres-Ortega

The importance of the sequential synthesis methodology in the optimal distillation sequences design

Abstract The sequential design method is presented as a complementary tool of the systematical synthesis procedure that allows to define a clear connection among the different types of distillation column sequences. In particular, the connection with the simple column subspace is considered, since this subspace represents the comparison reference for all the alternatives considered. The sequential design procedure, based on the correspondence between the functionality of the columns section among the simple columns and the derived sequences, is compared with a mathematical based optimization algorithm. The separations of a four-component near ideal mixture and the azeotropic ethanol–water mixture are considered as case studies and the designs obtained applying both methods have been compared. The results confirmed that the sequential design method is a fast and reliable tool in the optimal design of the column sequence.

Design and optimization of modified non-sharp column configurations for quaternary distillations

Abstract The possible structural changes of a non-sharp quaternary distillation configuration are considered. For the reference configuration composed of four columns, different alternatives are generated following the process intensification principle to reduce the number of equipment units. The intensified systems with three or two columns are obtained, including the dividing wall columns. Simulator Aspen Plus V8.0 was used to design and simulate all the systems for a hydrocarbon mixture. The intensified structures showed relevant energy savings compared to the reference case. The most promising alternatives were optimized by means of the differential evolution (DE) method minimizing the total annual cost (TAC). It was observed that the intensified systems were able to reduce both the energy consumption and the number of equipment units. The best intensified system has a TAC of 11.98% lower than the optimized reference case.

Design and Optimization of Thermally Coupled Distillation Sequences for Purification of Bioethanol

An important problem in the bioethanol production process is the purification of ethanol from a dilute solution, i.e., approximately 10% ethanol in water. The key factor in the purification process is the formation of the ethanol-water binary homogeneous azeotrope, and an additional process is required to obtain high purity ethanol that can be used in motor vehicles. This study examines the design and optimization of three extractive distillation options (two with thermal coupling) for the purification of a representative mixture of ethanol and water. These extractive arrangements can produce ethanol as distillate with the required purity and energy savings, reduction in CO2 emissions, high thermodynamic efficiencies and good control properties.

Optimal synthesis of integrated process for co-production of biodiesel and hydrotreated vegetable oil (HVO) diesel from hybrid oil feedstocks

Abstract Current vehicles use biodiesel and diesel’s blends to minimize engine modifications while encouraging the use of renewable fuels. Biodiesel combustion reduces CO 2 emissions but has poorer fuel properties than diesel. A promising renewable diesel alternative is hydrotreated vegetable oil (HVO) diesel with diesel-like fuel properties, overcoming the biodiesel limitations. However, HVO diesel processing requires higher capital expenses than biodiesel. In the present work, we defined a synthesis network superstructure to optimize the integrated production of biodiesel and HVO diesel. We identified processing blocks inside the superstructure and defined equipment, operating conditions and yields of each processing block based on literature. After that, we performed individual rigorous simulations in Aspen Plus V8.8 and Aspen Process Economic Evaluator V8.8 for the processing blocks to store conversion, separation, energy and equipment parameters for a fixed processing flowrate. Then, we defined a superstructure as a mixed integer non-linear programming (MINLP) problem coded in GAMS 24.4.6, that minimized the total manufacturing costs per gasoline gallon equivalent under different scenarios, computing also the water used and CO 2 -Equiv. for comparison purposes. The results showed that the optimal integrated production synthesis path, including hydrogen in-situ production as integration factor, reduced the total manufacturing costs in around 24% in comparison to the co-production without integration. The novelty of the present work relies on two main points: the process synthesis of a new integrated biodiesel-HVO diesel production superstructure, and the use of a combined rigorous simulation and MINLP-using-simplified-models evaluation approach to relax the rigorous search for the optimal synthesis path.

Superstructure-based Rigorous Simulation for Synthesis and Evaluation of Lignocellulosic Biofuels Processes

Abstract In the present work, a process synthesis framework for the conversion of softwood biomass to liquid (BtL) transportation fuels was developed. We defined processing blocks out of promising thermochemical and upgrading technologies, and performed individual blocks rigorous simulations in Aspen Plus® V8.8. The simulations and experimental data taken from the literature were used to predict conversions, recovery factors, capital and energy costs of the processing blocks. From the simulations, it was found that Gasification-Low Temperature Fischer-Tropsch (LTFT) followed by fractional upgrading and fractionating units (BC-GLTUF), was the most cost-effective, in terms of total annual cost (TAC) and liquid fuels production. Then, given the preliminary results, the possibility of combining blocks between the thermochemical routes, as well as mass and energy integration were explored. A superstructure was proposed and defined as a Mixed Integer Non-Linear Programming (MINLP) problem coded in GAMS 24.5.6, which sets the objective to minimize the TAC’s of BtL fuels under different cases and integration scenarios. The results showed that a combined alternative of Gasification followed by simultaneous high and low temperature FT reactions (CA-GLTHT) could increase the liquids fuels production and product distribution from 87 % to 90 % (wt) and reduce the TAC in around 26 % if mass and energy integration are considered.

A Dual Methodology for Synthesis of Woody Biomass to Liquid (BtL) Thermochemical Conversion Routes and Bio-oil Upgrading

Abstract Among the different biomass conversion technologies, biomass to liquid (BtL) process, using cheap lignocellulosic materials, can produce high quality fossil-like fuels. Thermochemical conversion processes consist mainly in pyrolysis, gasification, liquefaction and supercritical fluid processing, by which biomass can be converted into syngas, bio-oil, char and gaseous products. From these, bio-oil can be used as an intermediate step to convert it into higher energy-dense transportation liquid fuels such as diesel and gasoline. In this study, we introduced a process synthesis framework for the conversion of woody BtL transportation fuels, where we evaluated promising thermochemical and upgrading technologies and adapted into a superstructure based on experimental data from literature. In the model, woody biomass was represented by Spruce. The process simulator Aspen Plus V8.8 and Aspen Economic Evaluation V8.8 were used to predict the energy consumption and equipment cost of the unit operations. From the multiple paths, the process flowsheet of Gasification-Low Temperature Fischer-Tropsch-hydrotreating-hydrocracking and final fractionating units was among the most cost-effective under different scenarios. The novelty of this work relies on the synthesis of a superstructure of the combined thermochemical conversion and upgrading technologies specifically for woody BtL fuels, as well as the use of rigorous simulations to predict thermodynamic properties, energy consumption and equipment designs and costs for the superstructure’s units operations.

Design and Optimization of Intensified Non-sharp Distillation Configurations

Abstract For an N-component mixture, a separation sequence with only sharp splits needs the minimum number of N-1 simple columns with 2(N-1) heat exchangers to achieve N pure products. As the number of columns and heat exchangers are the dominant criteria to evaluate a distillation configuration, traditional distillation configurations with only sharp splits have been the preferred alternatives. However, sharp split separations present intrinsic thermodynamic inefficiencies, and one way to reduce these inefficiencies is by means of non-sharp splits. This refers to the possibility of obtaining one product in more than one stream. Moreover, the increasing in both the number of columns and heat exchangers due to the non-sharp splits can be reduced by combining the individual columns and by introducing thermal couplings. In this work, the non-sharp distillation sequence for the separation of a four component mixture of hydrocarbons is considered. Using the aforementioned method, different alternative sequences were designed by the rigorous method with Aspen PlusV8.0, going from 4 to 3 and to 2 columns; then optimized by minimizing the total annual cost by means of a platform consisting in Aspen PlusV8.0 (rigorous simulation) and Visual Basic (stochastic optimizer Differential Evolution), to finally compare the sequences. Moreover, the synthesis methodology used allows deriving two types of intensified systems, the systems with less column sections or the systems with dividing wall columns.

The Integration of the Synthesis Methodology in the Design of a Five-Component Distillation Sequence

Abstract The separation of a multicomponent stream by distillation represents a common problem in the industrial field. The possibility to realize the same separation task by means of different sequences have opened an unique research topic focused on the definition of a complete searching space that includes all the possible alternatives. The searching space can be generated following different approaches based on a mathematical background, like superstructures, or based on the connection of the simple column sequences with the alternatives generated. The correspondence between simple column sequences and the alternatives predicted is the principle of the generation method followed in the present work. Using this type of approach the generation and the design method used to screen and evaluate the alternative’s performance are deeply related. The correspondence between the functionality of the column’s sections of the simple columns and the corresponding alternatives was used to get the initialization parameters, then these parameters were optimized by a sensitivity analysis. The proposed design method was called Sequential Design Method (SDM). The method was applied for a five component separation sequence considering a particular class of alternative configurations called Modified Simple Column (MSC) sequences. In order to test the proposed methodology, the same sequences were designed using an optimization procedure based on a hybrid multi-objective (HMO) algorithm. It was found that the SDM is a fast and reliable design procedure that allows the user to easily define the column sequences‘ parameters. Moreover the SDM can be used to correctly initialize the multi-objective algorithm. When the HMO algorithm is initialized with the design parameters obtained from the SDM, the computational time is reduced by 21 % compare to a random initialization.