Minimum Total Annual Cost Research Articles

Design and optimization of dimethyl ether production from crude glycerol in a reactive distillation

Methanol in crude glycerol from biodiesel production is considered to be a raw material for dimethyl ether production. In this work, the production of dimethyl ether from the dehydration reaction of methanol in a reactive distillation is studied. A model of the reactive distillation is developed using a process simulator and used to analyze its performance by considering both the methanol conversion and the total annual cost. The effect of key operating parameters on conversion of methanol is reported. The optimal process design is determined in terms of the minimization of total annual cost.

Optimization of Pressure-Swing Batch Distillation with and without Heat Integration for Separating Dichloromethane/Methanol Azeotrope Based on Minimum Total Annual Cost

Pressure-swing batch distillation was investigated to separate the binary azeotrope of dichloromethane/methanol. Based on the robust control of a composition–flow rate cascade control structure, minimum total annual cost, instead of conventional energy consumption, was studied to optimize the process. Different cooling mediums of cooling water and refrigerated water were applied and compared based on a 323 K reflux-drum criterion. Heat integration was also studied to realize further reduction of total annual cost. The results show that the difference of the costs is small when the lower-pressure column was operated at 1 and 1.6 atm. However, heat integration reduces the cost by 11.3% and shows advantage in energy consumption, which is 53.8% lower than that of the process without heat integration.

Step-wise synthesis of work exchange networks involving heat integration based on the transshipment model

Abstract Due to the deterioration of serious energy dilemma, energy-conservation and emission–reduction have been the strategic target in the past decades, thus people have identified the vital importance of higher energy efficiency and the influence of lower carbon development. Since work exchange network is a significant part of energy recovery system, its optima design will have dramatically significant effect on energy consumption reduction in chemical process system. With an extension of the developed transshipment model in isothermal process, a novel step-wise methodology for synthesis of direct work exchange network (WEN) in adiabatic process involving heat integration is first proposed in this paper, where a nonlinear programming (NLP) model is formulated by regarding the minimum utility consumption as objective function and optimizing the initial WEN in accordance with the presented matching rules to get the optimized WEN configuration at first. Furthermore, we focus on the work exchange network synthesis with heat integration to attain the minimal total annual cost (TAC) with the introduction of heat-exchange equipment that is achieved by the following strategies in sequence: introducing heat-exchange equipment directly, adjusting the work quantity of the adjacent utility compressors or expanders, and approximating upper/lower pressure limits consequently to obtain considerable cost savings of expanders or compressors and work utility. Finally, a case taken from the literature is studied to illustrate the feasibility and effectiveness of the proposed method.

Comparative analysis of extractive and pressure swing distillation for separation of THF-water separation

In the present work, extractive and pressure-swing distillation methods are analyzed in detail through steady state ASPEN Plus simulations to propose the most economic method for separation of equimolar mixture of THF-Water. Various solvents were evaluated and DMSO was identified as the most appropriate solvent, as it gave minimum Total Annual Cost (TAC) for desired purity. In case of pressure swing distillation, various pressure ranges were explored to achieve minimum TAC. Configurations for extractive and pressure swing distillation with heat integration were also worked out. The optimum designs of extractive and pressure swing distillation with and without heat integration were compared on a common basis of feed conditions and purity constraints. Results indicate that TAC of extractive distillation with heat integration is 5.2% less than that of PSD with partial heat integration.

Design and optimization of dimethyl oxalate (DMO) hydrogenation process to produce ethylene glycol (EG)

In this work, the steady state design of ethylene glycol (EG) production process by the dimethyl oxalate (DMO) hydrogenation is investigated. In comparison with the conventional ethylene oxide hydration process for EG production, this novel process provides better conversion and selectivity. The DMO hydrogenation process is comprised of a reaction section and a sequence of distillation columns as separation section. In reaction section, DMO is dissolved in methanol, and this DMO solution is then reacted with hydrogen to become EG and side products. Then, the raw product stream is fed into the sequence of distillation columns to obtain the EG product stream at the specified purity. After the initial process design is completed, the DMO hydrogenation process is optimized to obtain the optimal design with the minimum total annual cost (TAC). During process optimization, it is found that the mole ratio of hydrogen to DMO (HDMR) has global influences on TAC, and thus it is the last variable to be optimized. In this paper, the optimal case with HDMR=40 is obtained through optimization.

Synthesis of More Sustainable Total Site

Heat recovery between different streams of Total Site (TS) can significantly decrease external utility consumption. Decreased utility consumption leads to decreased impact on the environment resulting from lower GHG emissions produced by fuel. The optimal rate of heat recovery can be determined by establishing an appropriate trade-off between utility consumption and investment in heat transfer equipment. Therefore, it can be concluded that both economic and environmental pillars of sustainability encourage the goal of constructing TSs. However, the social pillar of sustainability should also be considered in order to ensure the overall sustainability of a TS. The social pillar is usually not included in the synthesis because different aspects of social performance are quite difficult to quantitatively determine. Safety is an important social aspect when considering TS, especially when TS complexes are located across areas with high population density where any failure is a potential source of events with catastrophic consequences. In order to construct a safe TS, one option is to perform risk assessment before the synthesis and forbid highly risky matches at the synthesis step or to perform the synthesis and the risk assessment simultaneously. In this study, risk assessment was performed simultaneously during the synthesis in order to design TSs with as low risks as are socially acceptable. The synthesis was performed in two steps. In Step 1 a globally optimal solution was obtained based on a simplified trade-off between investment and operating cost while simultaneously considering risk assessment using a mixed-integer linear programming (MILP) TransGen model, while in Step 2 a detailed synthesis considering risk assessment was performed on a reduced superstructure obtained in Step 1 with a mixed-integer nonlinear programming (MINLP) model called Total Site Synthesis model, which explicitly considers risk limits during optimization. The risk depends on the frequency of failures and the severity of the consequences. The former can be reduced by the selection of more suitable equipment and the latter by selecting indirect rather than direct heat transfer, selecting smaller sizes and safer operating conditions. The minimization of total annual costs (TAC) is a primary objective of this synthesis. There are significant differences in the results obtained when safety is not considered and when lower risk limits are set in order to obtain safer designs. It can be concluded that by performing TS synthesis using the proposed synthesis model, the inherent safety of the TS is significantly increased; however, this incurs economic expense.

Optimal design of plate-fin heat exchanger by combining multi-objective algorithms

In this paper, a multi-objective optimization method is proposed which is a combination of Genetic algorithm, Differential Evolution and Adaptive Simulated Annealing algorithms. This technique is intended to generalize and improve the robustness of the three population based algorithms. In optimization problems, it is essential to keep the balance between local and global search abilities of algorithms. In the current method, DE, GA and ASA algorithms are linked in the variation stage to enrich the searching behavior and enhance the diversity of the population. The performance of the proposed DE-GA-ASA is tested against benchmark problems for multi-objectives and compared with two widely recognized vector optimizers. Next, the proposed technique is successfully implemented to optimize the design of plate-fin heat exchanger. The effectiveness of the present method is illustrated by comparing with various case studies. Some of the earlier case studies violated the constraints and/or only focused on single objective optimization. Results show that DE-GA-ASA method can be used effectively for the optimal design of plate-fin heat exchanger. Moreover, the effect of variation of fin and heat exchanger parameters on the optimal design is also investigated. Hot, cold and no-flow length of the heat exchanger, fin offset length, fin height and fin length are introduced as the optimization variables to obtain maximum heat transfer rate and minimum total annual cost. The investment cost and operating costs are independently optimized to provide a detailed investigation on the effect of fin and heat exchanger geometry parameters on their variation. Furthermore, a multi-criteria decision making method, TOPSIS is introduced for the selection of final optimal solution from the set of non-dominated solutions.

Two-stage MINLP algorithm for the optimal synthesis and design of networks of CHP units

This paper proposes a Mixed Integer Non Linear Programming (MINLP) model and two-stage optimization algorithm for determining the most profitable synthesis and design of Combined Heat and Power units within a district heating network with heat storage while taking into account the optimal scheduling of the units over the year. A two-stage algorithm for tackling the challenging MINLP problem is devised: at the upper level the selection and sizing of the units is optimized by means of specifically selected evolutionary algorithms, while at the lower level the operational scheduling problem is linearized and optimized with a commercial Mixed Integer Linear Programing solver. Three different approaches, based on two different evolutionary algorithms and discrete variable relaxation, are devised and compared to tackle the upper level problem. Moreover a bounding technique is proposed to limit the computational time required to solve the lower-level problem. The overall algorithm is tested on an industrial scale problem to find the two system designs leading to the minimum energy consumption and the minimum total annual cost. Computational results indicate that the continuous relaxation of the plant sizes significantly helps to improve the convergence rate of the tested evolutionary algorithm and to find improved solutions. For the considered test case, the design optimized for the minimum energy consumption allows to save 64% of primary energy compared to the minimum total annual cost solution, but with a 28% higher total annual cost.

Controllability of separate heat pump distillation for separating isopropanol-chlorobenzene mixture

The isopropanol-chlorobenzene mixture is separated via separate heat pump distillation (SHPD) to achieve significant energy savings. Rigorous steady state and dynamic characteristics for this SHPD process are simulated using Aspen Plus and Aspen Plus Dynamics. Optimized operation conditions including vapor flow rate to compressor are developed on the condition of minimum total annual cost. Two control strategies are proposed to solve feed disturbance issues and the improved structure with Q Re /F (lower column reboiler duty/feed flow rate) ratio scheme can maintain the two product purities requirement with smaller transient deviation and shorter settling time.

Optimal synthesis and design of the number of cycles in the leaching process for surimi production

Water consumption required during the leaching stage in the surimi manufacturing process strongly depends on the design and the number and size of stages connected in series for the soluble protein extraction target, and it is considered as the main contributor to the operating costs. Therefore, the optimal synthesis and design of the leaching stage is essential to minimize the total annual cost. In this study, a mathematical optimization model for the optimal design of the leaching operation is presented. Precisely, a detailed Mixed Integer Nonlinear Programming (MINLP) model including operating and geometric constraints was developed based on our previous optimization model (NLP model). Aspects about quality, water consumption and main operating parameters were considered. The minimization of total annual costs, which considered a trade-off between investment and operating costs, led to an optimal solution with lesser number of stages (2 instead of 3 stages) and higher volumes of the leaching tanks comparing with previous results. An analysis was performed in order to investigate how the optimal solution was influenced by the variations of the unitary cost of fresh water, waste treatment and capital investment.

Effect of feed temperature on economics and controllability of pressure-swing distillation for separating binary azeotrope

The mixture of methyl acetate and methanol created a minimum-boiling azeotrope which can be separated by pressure-swing distillation. The designs and optimizations of eight processes with eight different feed temperatures were studied to explore the effect of feed temperature on economics. Total annual cost (TAC) as the objective function reduced first and then increased with feed temperature increasing. Dynamic control of three typical temperature points was made. The designed process with feed temperature at 334.15K (vapor-liquid) had the minimum TAC, while the best dynamic control performance was found for the design process with feed temperature at 323.15K (cold). The choice of feed temperature should be considered from the perspectives of both TAC and the dynamic control performance.

NLP modeling for the optimization of LiBr-H2O absorption refrigeration systems with exergy loss rate, heat transfer area, and cost as single objective functions

Based on a nonlinear mathematical programming model, the sizes and operating conditions of the process units of single-effect absorption refrigeration systems operating with a LiBr–H2O solution are optimized for a specified cooling capacity by minimizing three single objective functions: the total exergy loss rate, the total heat transfer area, and the total annual cost of the system.It was found that the optimal solution obtained by minimization of the total exergy loss rate provides “theoretical” upper bounds not only for the total heat transfer area of the system but also for each process unit and all stream temperatures, while the optimal solution obtained by minimization of the total heat transfer area provides the lower bounds for these model variables, to solve a cost optimization problem.The minimization of the total exergy loss rate by varying parametrically the available total heat transfer area between these bounds was also performed, allowing to see how the optimal distribution of the available total heat transfer area among the system components, as well as the operating conditions (stream temperature, pressure, composition, and mass flow rate) and heat loads, vary qualitatively and quantitatively with increasing available total heat transfer area. These optimization results allowed to find a “practical” value of the total heat transfer area, i.e. no benefits can be obtained by increasing the available total heat transfer area above this value since the minimal total exergy loss value cannot be significantly improved by distributing additional heat transfer area among the process units. The optimal solution corresponding to this practical value significantly improves the upper bounds for an economic optimization problem with respect to the optimal solution corresponding to the theoretical value.The optimal solutions corresponding to the theoretical and the practical upper bound values for the total heat transfer area (100m2 and 61m2, respectively) as well as the optimal solution obtained by minimization of the total annual cost are discussed for a case study considering a cooling capacity of 50kW, upon the model assumptions made and a given cost model. Around three-quarters of the minimal total annual cost correspond to capital expenditures and the rest to operating expenditures. The generator and evaporator represent together around 70% of the capital expenditures. The absorber is the largest contributor to both the total heat transfer area and the total exergy loss rate, with around 33.19 and 39.16%, respectively, when the total annual cost is minimized.

A novel simultaneous optimization model with efficient stream arrangement for heat exchanger network synthesis

This study aims to explore a new simultaneous synthesis method for heat exchanger network synthesis (HENS) problems to achieve the minimum total annual cost (TAC). A proposed efficient process stream arrangement strategy is used to reduce the search region for the optimal stream match and a stage-wise chessboard model expands the new feasible search region as well as avoiding missing optimal matches of other stream arrangements. Thus, the proposed stage-wise chessboard model combined with the arranged streams is a good improvement for managing the feasible search region for the heat exchanger network (HEN). Moreover, a recent stochastic algorithm called random walking algorithm of compulsory evolution (RWCE) is considered and used to optimize the heat transfer area directly. Finally, an ideal combination of the stage-wise model and the stochastic algorithm is applied to four different benchmark cases to show its effectiveness and the results show that simpler and more economic networks are found while using less computational time, which are all encouraging.

Path-set based optimal planning of new urban distribution networks

This paper presents a method for optimal planning of new urban distribution networks based upon the selection of the best subset of paths providing back feed from the entire path set generated for the available cable routes. The optimal solution is the path subset providing minimum total annual cost including capital recovery, loss and undelivered energy costs while satisfying all technical constraints. The impacts of distributed generator units, if available, can be also taken into account in the optimization flow. The reliability requirements are additionally assured by introducing SAIFI and SAIDI constraints. The method allows for common trenches for cables and different sizes of feeders depending on their loads. The planner is allowed to choose the concept of back feed, through only feeders interconnecting source nodes, ring feeders or by the best combination of these two structures. During the optimization process the optimal distribution system trees are generated providing minimum loss operation. The search for the optimal network is conducted using the simulated annealing algorithm.

Reduce Distillation Column Cost by Hybrid Particle Swarm and Ant Colony Optimization Technique

A novel method for optimum design of plate type distillation column integrating the equilibrium, hydraulic and economic calculations is presented in the present paper. The present study explores the use of non-traditional optimization technique: called hybrid Particle swarm optimization (PSO) and Ant colony optimization (ACO), for design optimization of plate type distillation column from economic point of view. The optimization procedure involves the selection of the major plate geometric parameters such as hole diameters, ratio of downcomer area to tower area, weir height, fractional hole area in tray, tray spacing, tower diameter etc. and minimization of total annual cost is considered as design target subjected to operational constraints like flooding, weeping entrainment, quality specifications etc. The solution space of such type of problem is very complex due to presence of various nonlinear constraints and multiple minima. Hybrid Particle swarm optimization and Ant colony optimization (PSACO) technique is applied to deal with such complexity. The particle swarm optimization applies for global optimization and ant colony approach is employed to update positions of particles to attain rapidly the feasible solution space. Ant colony optimization works as a local search, wherein, ants apply pheromone-guided mechanism to update the positions found by the particles in the earlier stage. The presented hybrid Particle swarm optimization and Ant colony optimization (PSACO) technique is simple in concept, few in parameters and easy for implementations. Furthermore, the PSACO algorithm explores the good quality solutions quickly, giving the designer more degrees of freedom in the final choice with respect to traditional methods. One case study is presented to demonstrate the effectiveness and accuracy of proposed algorithm. The PSACO approach is able to reduce the total cost of distillation column as compare to cost obtained by commercial simulator.

EVALUATION OF TOTAL ANNUAL COSTS OF HEAT EXCHANGER NETWORKS USING MODIFIED PINCH ANALYSIS

This study presents pinch analysis of some heat exchanger networks (HENs) problems using Hint integration (HINT) software. Three examples reported to have been solved using different approaches by various researchers to obtain the least possible total annual cost (TAC) were solved using the Hint software. In this work, the use of remaining problem analysis (RPA) contained in the heat integration software was used to carry out matching and the general optimization of the networks for minimum TAC for the three problems solved. The results obtained after solving the first problem using RPA based heat integration gave a minimum total annual cost (TAC) of $237, 510 /yr. which is the fourth when compared with the lowest solution that shows the minimum TAC of $235.400 /yr. in that example. However, the TAC obtained in solving problem 2 and 3 were $562, 333 /yr. and $2.881 M/yr. respectively and they are the least total annual cost obtained when compared with what have been obtained using mathematical programming and non-RPA based Hint software. The overall assessment of the various approaches used to solve these problems when compared with the results obtained in this study shows that HINT software is able to obtain TAC that are within the same range as those obtained using mathematically based technique. http://dx.doi.org/10.4314/njt.v35i3.10

Investigation on Thermodynamics in Separation for Ethylene Glycol + Neopentyl Glycol System by Azeotropic Distillation

The isobaric vapor–liquid equilibrium (VLE) data for two binary systems of ethylene glycol (EG) + neopentyl glycol (NPG) and NPG + para-xylene (PX) have been measured under pressure of 101.3 kPa, respectively. The thermodynamic consistency of the experimental isobaric VLE data was tested by means of Herington area test. Meanwhile, the experimental isobaric VLE data have been satisfactorily correlated with Wilson, NRTL, and UNIQUAC models. A conventional azeotropic distillation process has been designed to achieve high-purity products based on preceding results. The product purities of EG and NPG can both achieved at 99.9 mol % with minimal total annual cost (TAC) through sequential iterative optimization procedure.

Separation of acetonitrile/methanol/benzene ternary azeotrope via triple column pressure-swing distillation

Abstract Acetonitrile/methanol/benzene mixture forms more than one different azeotropes and its triangular diagram presents several distillation boundaries at atmospheric pressure. A process named as triple column pressure-swing distillation (TCPSD) was proposed to separate this complex ternary system. The feasibility of the process was confirmed using residue curve maps and rigorous steady-state simulations were implemented on Aspen Plus. On basis of minimum total annual cost, several operating parameters were optimized by pressure-swing optimization software using the sequential iterative optimization procedure and the economics of TCPSD were compared with four different separation configurations. The results demonstrated that the A-M-B separation configuration was the most optimal column sequence in global optimization to separate acetonitrile/methanol/benzene azeotropic mixture using TCPSD. TCPSD may arouse the interest of researchers in various fields and can assist engineers to select the optimal separating process.

Optimal reservoir sizing in on-demand irrigation networks: Application to a collective drip irrigation network in Spain

Optimal reservoir sizing in on-demand irrigation networks with a minimum cost was obtained, taking into account the variability of pressure and flow rate demanded by the network during the irrigation season. With this aim, a model called DRODIN (Design of Reservoirs of regulation in On-Demand Irrigation Networks) was developed under a holistic approach. That obtain the optimal design and management (minimum total annual cost, CT) of the water abstraction systems in an integrated manner to include the aquifer along with the pumping station, reservoir and pumping and distribution pipes in a collective irrigation network. This tool has been applied to an on-demand irrigation network located in Spain with 171 ha of drip irrigation in vineyard and olive crops. The optimal reservoir volume is approximately 5000 m3, and the CT for water lift (WL) = 100 m (the most common case for this aquifer) is 325 € ha−1 yr−1. The energy cost is the primary component of CT, both in the abstraction and the water supply to the irrigation network, representing between 57% and 80%. The operation of the pumping station determines the size of the reservoir and the annual costs of the water supply to the network for a given water supply guarantee. The CT increases linearly with the WL, primarily because of the increase in energy costs (Ce), although there is a clear relation between the investment costs (Ca), Ce and the reservoir size, which is only possible to analyse with tools such as DRODIN.

Sequential synthesis of heat integrated water networks: A new approach and its application to small and medium sized examples

This paper presents a new step-wise sequential solution strategy for the synthesis of heat integrated water networks (HIWNs) comprising of two mathematical models. The first model minimizes water and energy costs. The optimal freshwater and water flow rates within the HIWN are determined from this model. Using these optimal flow rates, different configurations of HIWN are evaluated for the purpose of heat integration. The second model is the stage-wise heat exchanger network (Yee and Grossmann, 1990), which is solved for each of the evaluated network configuration in a sequential manner. Using this proposed strategy, a set of locally optimal HIWNs are produced and the best one is chosen based on the minimum total annual cost (TAC). The proposed sequential strategy is applied to small and medium sized examples in the literature. The results show that the proposed new sequential solution strategy can be successfully applied to small and medium sized HIWN problems.