Minimum Total Annual Cost Research Articles

On the use of risk-based Shapley values for cost sharing in interplant heat integration programs

The heat exchanger network (HEN) is traditionally used for optimal heat recovery in a single chemical plant, while the multi-plant counterparts have been studied in recent years primarily for the purpose of reaping additional overall energy savings. Since all these works focused primarily upon minimization of the total energy cost, the resulting interplant heat integration arrangements were often infeasible due to the fact that the individual savings are not always acceptable to all participating parties. Although a few studies addressed this cost-sharing issue, the existing methodologies are still not mature enough for realistic applications. The present paper outlines a rigorous model-based two-stage procedure to handle this practical problem in the spirit of a cooperative game. The minimum total annual cost (TAC) of each and every potential coalition was first determined with a conventional MINLP model, while the core and the risk-based Shapley values of all players were then computed with explicit formulas derived in this work to settle the benefit allocation issues. A simple example is presented at the end of this paper to demonstrate the feasibility of the proposed approach.

Design and control of fully heat-integrated pressure swing distillation with a side withdrawal for separating the methanol/methyl acetate/acetaldehyde ternary mixture

In the industrial manufacturing process of polyvinyl alcohol, there is inevitably a small amount of acetaldehyde in the alcoholysis solution (methyl acetate/methanol mixture), the accumulation of which may decrease the purity of product. The effect of acetaldehyde on the separation of homogeneous azeotrope of methyl acetate and methanol via fully heat-integrated pressure swing distillation (FHI-PSD) is investigated. A PSD process with a side withdrawal is proposed and proved to avoid the accumulation of acetaldehyde in the system effectively. The optimum separation configuration conditions are based on the minimum total annual cost (TAC) analysis. In the steady-state design, the simulation reveals that the process has the minimal TAC when operating pressure of the HPC is 10atm. A conventional pressure-compensated temperature control (CS3) and a new temperature difference control (CS4) are compared in Aspen Dynamics. Both of them can eliminate the influence of pressure fluctuation on bubble points at the sensitive plates and perform well even for large feed disturbances. However, it is easier to design CS4 as CS4 doesn’t require complex bubble point temperature calculation compared with CS3. Therefore, CS4 is suggested to be another favorable and viable control scheme for PSD process, which may show superiority in industrial application.

Effect of thermodynamic parameters on prediction of phase behavior and process design of extractive distillation

Abstract Extractive distillation was investigated for separation of the minimum azeotrope of n-propanol/water, via the Aspen Plus simulation platform. Experimental data of n-propanol/water, which could pass the thermodynamic consistency test, were regressed to get suitable binary interaction parameters (BIPs) by the UNIQUAC thermodynamic model. The azeotrope system was heterogeneous in the simulation with built-in BIPs, which was contrary to the experimental data. The study focused on the effect of thermodynamic parameters on the prediction of phase behavior, and process design of extractive distillation. N-methyl-2-pyrrolidone (NMP) and ethylene glycol were used as solvents to implement the separation. Processes with built-in and regressed BIPs were explored, based on the minimum total annual cost (TAC). There were significant differences in the phase behavior simulation using different thermodynamic parameters, which showed the importance of BIPs in the design and optimization of extractive distillation.

Process design of carbon dioxide and ethane separation using ionic liquid by extractive distillation

AbstractBACKGROUNDCarbon dioxide and ethane easily form a binary azeotrope under liquefied conditions. An extractive distillation process for the separation of carbon dioxide and ethane using the ionic liquids [bmim][Tf2N], [emim][Tf2N] and [emim][EtSO4] as solvents was explored. The thermodynamic and physical property parameters of each ionic liquid and their thermo‐physical properties that correlated with the experimental data were used to create the ionic liquid components and conduct the process simulation.RESULTBased on the analysis of its physical properties and relative volatilities, [emim][Tf2N] is the best option as a solvent for extractive distillation separation compared with other ionic liquids. Based on the sensitivity analysis optimization procedure, the minimum total annual cost, carbon dioxide emissions and thermodynamic efficiency were calculated. Compared with traditional extraction distillation, the total annual cost and carbon dioxide emissions of the process using [emim][Tf2N] as a solvent decreased by 62% and 31%, respectively. The thermodynamic efficiency (η) of the electricity generated from hydropower increase by 0.7%.CONCLUSIONThe results show that an ionic liquid extractive distillation process using an ionic liquid as the entrainer performs better than a process using traditional organic solvents in terms of economics. Due to the non‐volatility of ionic liquids, a flash tank was used instead of a solvent recovery column to efficiently realize solvent recovery. © 2017 Society of Chemical Industry

A combination of pressure-swing and extractive distillation for separating complex binary azeotropic system

Methyl acetate/methanol/water mixture forms more than one different azeotrope, whereas its triangular diagram presents a distillation boundary at atmospheric pressure. The two different simulation processes of the double column pressure-swing with extractive distillation (DCPSED) and triple column pressure-swing with extractive distillation (TCPSED) were proposed to separate the complex ternary system. Furthermore, the heat integration and mechanical vapor compression (MVR) heat pump distillations were also tested (through simulation) to separate the complex ternary system to save energy. The feasibility of the processes was confirmed using vapor-liquid equilibrium curve, while rigorous steady-state simulations were implemented using Aspen Plus (version 7.1). With the goal of achieving minimum energy consumption and minimum total annual cost (TAC), the purities of methyl acetate, methanol and water were used as the constraint variables. The results show that water was a better solvent for this separation system. Compared with the TCPSED process, the energy consumption and TAC for DCPSED process could be reduced by 44.83%, and 47.74%, respectively. Compared with the DCPSED and DCPSED with heat integration processes, DCPSED with MVR process could reduce the energy consumption by 73.34% and 59.52%, while TAC was decreased by 37.64% and 11.77%, respectively. The simulation results indicated that DCPSED with MVR process has great advantage over other processes used to separate methyl acetate/methanol/water ternary mixture.

Thermo-Economic Multiobjective Optimization of a LOW Temperature Organic Rankine Cycle for Energy Recovery

In last decades the scarcity of combustible oil around the world has promoted the quest of new processes to produce power from alternative energy sources. The conventional Rankine cycle with water as working fluid, it is a good choice to convert heat into electricity but inefficient in temperatures below 350 C. Using an organic compound as working fluid the Rankine cycle (Called Organic Rankine Cycle) improves the cycle efficiency and can reduce the economy of the process for energy recovery from low temperature sources. In this work we proposed a set of organic compounds and a scenario of process to obtain simultaneously both optimum values of compositions of the mixture (used as working fluid) and operating conditions of the cycle for a given low temperature source. As design goals we set the minimization of total annual cost and the maximization of thermal efficiency. Because these two goals are in conflict the design problem was posed as a non-linear multi-objective optimization problem with thermodyn...

Effect of multi-recycle streams on triple-column pressure-swing distillation optimization

Different structures of multi-recycle triple-column pressure-swing distillation (TCPSD) are synthesized and explored. Acetonitrile/methanol/benzene ternary mixture is set as a case to identify the applicability of different multi-recycle TCPSD flowsheets. Four multi-recycle flowsheets are analyzed and compared with convention TCPSD process and rigorous steady-state simulations are implemented using Aspen Plus. Operating parameters are optimized by using the sequential iterative optimization procedure when the split fraction changes with the objective function of minimum total annual cost. Two structures are found that distillate compositions surpass the distillation boundaries at finite reflux ratios. However, the results show that different multi-recycle TCPSD processes are feasible.

Extractive Distillation Process Combined with Decanter for Separating Ternary Azeotropic Mixture of Toluene-Methanol- Water

The mixture of toluene-methanol-water is difficult to separate because of the formation of toluene-methanol and toluene-water azeotropes. Extractive distillation process with two-column decanter (EDTCD) was improved to separate the system. The process was optimized by the software named Extractive Distillation Optimization Software (EDOS) which based on the minimum total annual cost (TAC). A comparison of the EDTCD and the traditional extractive distillation with triple-column (TEDT) indicated that the former was much more economical. In this comparison, n-methyl-2-pyrrolidone (NMP) and diethylene glycol (DEG) was used as a heavy entrainer in EDTCD and TEDT. The choice of thermodynamic model was discussed in this paper, and the model of UNIQUAC was used in the two processes. The results show that high purity of toluene, methanol and water can be obtained from the process of EDTCD, and it can save 34 % TAC than the process of TEDT.

Optimal heat exchanger network synthesis with detailed shell and tube heat exchanger design based on superstructure model

The shell and tube heat exchanger (SHE) is the most common type of heat transfer equipment used in heat exchanger networks (HENs) in the field of chemical process industries. Both counter-current flow and co- current flow may be involved in the shell and tube heat exchangers. To calculate the temperature difference, the correction factor FT is generally used for multi-pass heat exchanger optimization. For synthesis of heat exchanger networks, a lot of researchers use the correction factor FT as a constraint condition, and the HEN with minimum number of shells is optimized by iterative calculation based on a stage-wise superstructure model. However, in these studies the heat transfer temperature difference correction factor FT are used to avoid temperature crossing without considering the optimization of shell and tube number. In this paper, a method of HEN synthesis with the optimization of the number of shells and tubes for each SHE based on superstructure model is presented. Firstly, the heat transfer process of counter-current and co-current flow in SHE is studied. The correction factor of heat transfer temperature difference FT is calculated based on the mechanism of heat transfer process. Then, each tube of heat exchanger instead of a SHE is defined as a single unit and the energy balance function is established for each unit to minimize the total cost of HEN in the proposed superstructure model of HEN. By using the methodology of mixed integer nonlinear program (MINLP), the HEN synthesis and the correction factor of heat transfer temperature difference FT are optimized simultaneously. The proposed methodology allows for proper handling of the trade-offs involving energy consumption, number of units, number of shells and tubes, and network area to provide a network with the minimum total annual cost. Finally, the case study results demonstrate the effectiveness of this proposed method, and the total cost of HEN are lowered as well as the number of tubes and shells for each SHE is optimized simultaneously.

Separation of acetone/isopropyl ether/water ternary mixture via hybrid azeotropic-extractive distillation

An industrial ternary mixture of acetone/isopropyl ether/water forms two binary azeotropes and a ternary azeotrope at atmospheric pressure and conventional distillation processes cannot achieve efficient separation. A hybrid azeotropic-extractive distillation (HAED) process is proposed for the separation of acetone/isopropyl ether/water. In this process, isopropyl ether is chosen as a light entrainer aimed to form a binary azeotrope with acetone, so that water can be separated from the bottom of azeotropic distillation column (ADC) at 0.3 atm. Then extractive distillation for the separation of binary azeotrope of acetone/isopropyl ether is investigated with ethylene glycol (EG) as an entrainer. On the basis of minimum total annual cost (TAC), a sequential iterative optimization procedure is performed to optimize the economy of two processes with two different feeding ways of light entrainer. The results demonstrate that both processes can make three products purities achieve 99.5 wt% with three columns. Additionally, compared with the process in which light entrainer is blend with the fresh feed, the process in which the light entrainer is added in the upper of the ADC can reduce the TAC and energy consumption by 9.3 % and 9.21 %.

Control of extractive distillation process for separating heterogenerous ternary azeotropic mixture via adjusting the solvent content

Abstract The existence of heterogeneous azeotrope of toluene-water and homogenous azeotrope of toluene-methanol makes it difficult to separate the toluene-methanol-water mixture. Two methods of three column extractive distillation and two column extractive distillation using decanter were explored to separate the ternary azeotrope. Diethylene glycol and N-methyl-2-pyrrolidone were used as heavy solvent in the two processes, respectively. The UNIQUAC physical model was used in both simulations. Based on the minimum total annual cost, variables of the two processes were optimized and the results indicated the two column extractive distillation using decanter can save 51.4% of total annual cost than three column extractive distillation. The dynamics of two column extractive distillation using decanter was studied due to its superiority of economics. Several common control schemes were used to investigate the controllability of two column extractive distillation using decanter and all schemes showed poor controllability on feed composition disturbances. An improved control structure was designed to achieve better control of the process. In the improved control scheme, the temperature controller of column C1 was replaced by a proportional controller, and a certain amount of solvent flow rate was increased. The integral squared error was calculated to compare the dynamic performances of the improved control structure with different solvent flow rate, and a suitable amount of solvent was found in view of the controllability and economy.

Heat-integrated pressure-swing distillation process for separating the minimum-boiling azeotrope ethyl-acetate and ethanol

Abstract Design and control of the forward integration of pressure-swing distillation processes is explored with the aid of the tools of Aspen plus and Aspen dynamics taking the separation of the minimum-boiling azeotrope ethyl acetate and ethanol as an example. The optimized separation configuration is obtained by taking the minimization of total annual cost (TAC) as an objective function. The two key performance indicators of second law efficiency (η) and carbon dioxide emissions are employed to evaluate the three operations, which consist of conventional non-heat integration and the corresponding partially and fully heat integration processes. Compared to the non-heat integration process, the fully heat integration process is more attractive since it can achieve 33.33% energy consumption saving, reduction of 31.33% CO 2 emissions and 26.64% TAC. Furthermore, the control of the PSD processes with heat integration are explored since the interaction of parameters are complicated for this neat configuration. The effectiveness of the single-end control strategy is evaluated and determined by method of the feed composition sensitive analysis, and a series of control structures are devised and assessed by the perturbations of the feed flow rate and feed composition. It is concluded that the small disturbances are addressed for fully heat integration in comparison with the partially heat integration owing to the degree of freedom reduction. In addition, the efficient control strategy with the ratio scheme to manipulate the cascade flow controller is developed to eliminate the snowball effect for PSD with partially case.

Design and control of entrainer-assisted reactive distillation for N-propyl propionate production

An entrainer-assisted reactive distillation process is proposed to produce high-purity N-propyl propionate from propionic acid and N-propanol. The E-RD process can take advantages of both the heterogeneous azeotropic distillation (HAD) and reactive distillation (RD). Cyclohexane is selected as the proper entrainer in the E-RD process. And the E-RD process is optimized by calculating the minimum total annual cost (TAC). The optimal results reveal that the E-RD process can save 46.11% of TAC and 41.40% of reboiler duty compared with the two-column process. Furthermore, two control structures for the E-RD process are considered. The dynamic performances demonstrate that the improved control structure (CS2) can solve the problem of disturbances and maintain the product purities close to the set points with small deviations and short settling times.

Design of thermally coupled reactive distillation schemes for triethyl citrate production using economic and controllability criteria

This work describes a systematic process design for triethyl citrate production by direct esterification of citric acid with ethanol via simultaneous reaction-separation technologies. The design methodology includes simultaneous optimization of controllability and profitability criteria. With a novel approach, the conceptual feasibility analysis of the intensified processes was carried out by extending the reactive residue curve maps (RRCM) to mixtures with six components by implementing a substitution degree parameter. The RRCM have been also extended to the conceptual design of dividing wall columns. The configuration of both, traditional and dividing wall reactive distillation columns, were obtained from the conceptual analysis. The processes were simulated using experimentally validated models, and further optimized using a nature inspired multi-objective algorithm. A triethyl citrate production capacity of 10kTon/yr was used as process specification. Final designs evidenced citric acid conversions above 99.9%, energy consumption from 3-5MJ/kg, and a TEC production costs of c.a 1.5USD/kg. Controllability assessment was performed by evaluating the condition number of the proposed operating schemes. Pareto diagrams indicate that the minimization of total annual costs and controllability are conflicting goals in both production schemes. Nevertheless, both alternatives withstand large perturbations over the main process variables. The reactive dividing wall column scheme results in large energy and cost savings over a traditional reactive distillation process.

DESIGN OF WATER NETWORK PIPE SYSTEM OF SPRINKLER IRRIGATION FOR MINIMUM COST

To optimize the life-cycle cost of pressurized irrigation system, we must find the set of pipe sizes that gives the minimum sum of fixed plus operating costs. If a very small pipe sizes are used, fixed costs will be low, but the operating (power) cost of overcoming friction losses in the pipes will be relatively high. As the pipe diameters increase, the fixed cost will also increase. The optimum pipe sizes are that minimizes the sum of fixed plus the operating costs. A linear programming model was developed for the design of water network of a hand moved sprinkler system of 2 main lines supply 10 fields each contains a submain and two portable hand move sprinkler laterals. The system comprises junctions or nodes and pipe sections between adjacent nodes. The objective function is to minimize total cost subject to three groups of constraints. The first group concerned about pressure head at each node. The second were to limit the water velocity in the pipe sections between 1m/s to 2 m/s. The last, involves the non negativity of the various decision variables. The results showed that the minimum total annual cost to operate the system is 1135 L.E/year. fed. at 1.6 m/s average water velocity in pipes. The head loss gradient was 1.9 m/100m and the total area was 110 feddan, The system operating time 1440 hour/season to add 3400 mm/ season. The sprinkler discharge is 1.4 m3/h operate at 3 bar pressure head spaced 7m by 7 m. Linear programming method results were verified by two other methods, namely, water velocity and unit head loss (head loss gradient). Comparing results of the linear programming method with the other two methods showed faster and more accurate results, especially when applied by Microsoft EXCELL spreadsheet.

The implementation of inter-plant heat integration among multiple plants. Part II: The mathematical model

It is a challenging task to solve a large-scale Inter-Plant Heat Integration (IPHI) problem, especially for simultaneous optimization for intra- and inter-plant heat integration. In the companion paper (Part I), a novel screening algorithm named Nearest and Largest Qrec-based Screening Algorithm (NLQSA) was proposed. It can be used to divide a large-scale IPHI problem into several small ones, each of which includes two or three plants, while keeping the theoretical maximum inter-plant heat recovery potential Qrecmax almost unchanged. NLQSA provides a prior solution before determination of inter-plant Heat Exchanger Network (HEN) configuration for each achieved small IPHI scheme. In this paper, a modified MINLP model with an objective of minimum Total Annual Cost (TAC) is proposed to determine the final inter-plant HEN configurations of achieved segregated IPHI schemes. With the addition of stream data extraction method and NLQSA which were proposed in Part I of this paper series, a complete three-step strategy is established in order to solve the large-scale IPHI problem. Theoretically, a large-scale IPHI problem can be solved no matter how many plants involved. A case study with seven plants is introduced to illustrate the feasibility and effectiveness of the proposed method.

Optimization of municipal pressure pumping station layout and sewage pipe network design

ABSTRACTAccelerated urbanization places extraordinary demands on sewer networks; thus optimization research to improve the design of these systems has practical significance. In this article, a subsystem nonlinear programming model is developed to optimize pumping station layout and sewage pipe network design. The subsystem model is expanded into a large-scale complex nonlinear programming system model to find the minimum total annual cost of the pumping station and network of all pipe segments. A comparative analysis is conducted using the sewage network in Taizhou City, China, as an example. The proposed method demonstrated that significant cost savings could have been realized if the studied system had been optimized using the techniques described in this article. Therefore, the method has practical value for optimizing urban sewage projects and provides a reference for theoretical research on optimization of urban drainage pumping station layouts.

Many-objective optimization of cross-flow plate-fin heat exchanger

This paper presents a rigorous investigation of many-objective (four-objective) optimization of cross flow plate-fin heat exchanger and its comparison with multi-objective (two-objective) optimization. Maximization of effectiveness and minimization of total annual cost, total weight and number of entropy generation units are considered simultaneously as objective functions during many-objective optimization. Multi-objective heat transfer search (MOHTS) algorithm is introduced and applied to obtain a set of Pareto-optimal points of many-objective problem. Application example of plate-fin heat exchanger is presented to demonstrate the effectiveness and accuracy of proposed algorithm. Many objective optimization results form a set of solutions in four dimensional hyper objective space and for visualization it is represented on a two dimension objective space. Thus, results of four-objective optimization are represented by six Pareto fronts in two dimension objective space. These six Pareto fronts are compared with their corresponding two-objective Pareto fronts. Different decision making approaches such as LINMAP, TOPSIS and fuzzy are used to select the final optimal solution from Pareto optimal set of the many-objective optimization. Finally, to reveal the level of conflict between these objectives, distribution of each design variables in their allowable range is also shown in two dimensional objective spaces.

Novel reactive distillation process with two side streams for dimethyl adipate production

Reactive distillation presents a distinct advantage for the combination of reaction and separation. However, when reactants are the lightest and the heaviest components and products are the intermediate ones, the configuration should be well designed to maintain the merits of the reactive distillation. In this work, two new processes, whose reactive distillation column with one side stream (RDC-S1) and with two side streams (RDC-S2) are proposed for dimethyl adipate production by the esterification of adipic acid with methanol. The two new processes are simulated using Aspen Plus and analyzed with minimum total annual cost (TAC) as the objective function. Then the carbon dioxide emissions of the proposed processes are calculated. The RDC-S1 and RDC-S2 processes are compared with the conventional reactive distillation process and the reactive distillation column with a top-bottom external recycle process. The results show that RDC-S2 process requires the lowest energy and has the smallest carbon dioxide emissions when compared with other processes. Thus considering the remarkable economic and environmental benefits, RDC-S2 is an attractive configuration for the production of dimethyl adipate.

Targeting of heat integrated water allocation networks by one-step MILP formulation

Heat integrated water allocation networks (HIWAN) is a system where water and energy are highly interconnected. Well arranged nexus between water allocation networks and heat exchanger networks would reduce the water and energy consumption significantly. The aim of this study is to develop a novel mathematical programming model for targeting minimum simplified total annual cost of HIWAN. A new transshipment type of heat exchanger networks (HEN) representation is proposed, with features of stream splitting, stream by-pass, non-isothermal mixing, and isothermal mixing. Constraints are added to follow up on the flowrate consistency when stream splitting or mixing happens. Furthermore, a new formulation is presented to count heat exchanger units. The proposed model is formulated as a mixed-integer linear programming (MILP) problem. It is much easier to get feasible solutions than mixed-integer non-linear programming (MINLP) problems, especially for large-scale problems. Three examples including an industrial example and a large-scale case are solved by the proposed model. It is shown that the proposed model is suitable for the synthesis of HIWAN, and more importantly, the obtained results are better than literature records.