Minimum Total Annual Cost Research Articles

Optimum design and performance analysis of heat exchanger coupling a flash dryer and parabolic trough collectors

Responding to the climate change issue, the deployment of thermal solar energy has grown remarkably. However, its use for industrial applications remains limited due to techno-economic constraints, among which the choice and optimum design of the heat exchanger allowing a profitable integration. In this context, the design of a crimped spiral fin-tube heat exchanger (CSFTHX) used to couple parabolic trough collectors and flash dryer was conducted. For this purpose, a mathematical model of CSFTHX was developed based on (ε-NTU) method and fitted to experimental data obtained in this work. The sensitivity of the model to geometrical parameters and operating variables was evaluated which results permitted to qualitatively validate this model and identify the optimum ranges of key design parameters. Then, the optimal design was carried out applying the conjugate direction optimization method considering the minimization of total annual cost as the objective function. Results showed that, at low Reynolds number (<1000), all geometrical parameters presented a significant effect on the HX thermal and hydraulic performances. Regarding the operating variables, the oil temperature and airflow rate had the most important impact on the HX required area, thus conducting to define the design point. The HX optimum design was achieved with a 20% lowered annual cost and 44% improved HX thermal performance. The designed HX was integrated within a bench scale solar flash dryer and the effect of the solar radiation intensity on the drying conditions was investigated, showing the necessity to use the back-up heating and avoid functioning under broken-clouds.

Reducing carbon footprint of deep-sea oil and gas field exploitation by optimization for Floating Production Storage and Offloading

Deep-sea oil and gas fields are acting as a vital role by providing substantial oil and gas resource, and Floating Production Storage and Offloading is an indispensable tool for the development of offshore oil and gas fields effectively. Here, Life Cycle Assessment is applied to evaluate environmental loads in the whole life cycle of the deep-sea oil and gas production. This paper explores the carbon footprint of Floating Production Storage and Offloading as the time axis. It is found that Floating Production Storage and Offloading is a conceptual product at the design stage and does not generate carbon emission, while the operational stage releases considerable emission by the fuel combustion process, accounting for 88.2% of the entire life cycle. To decrease this part of carbon emission, distributed energy system is considered as a promising choice because it integrates different energy resources and provides an economic and environmental energy allocation scheme to meet the energy demand. For the operation stage, this paper establishes a Multi-objective Mathematical Programming model to determine the selection and capacity of facilities with minimum annual total cost and carbon emissions by considering the energy balance and technical constraints. The model is validated by an example and solved by the weight method. According to designer's demand, distributed energy system can optimize economic objectives in a maximum range of 14.6%, and a maximum emission reduction of 4.53% can be expected compared with the traditional scheme. Sensitivity analysis shows that cost is more sensitive to natural gas price.

Design and control of a novel side-stream extractive distillation column for separating methanol-toluene binary azeotrope with intermediate boiling entrainer

It is innovative and important to perform complex binary azeotrope separation via single distillation column. In the article, design and control of a novel and simple side-stream extractive distillation (SSED) column with extraction and solvent recovery function is investigated for the separation of methanol and toluene binary azeotrope with intermediate boiling triethylamine (Et3N) as solvent. The steady-state design parameters of the novel SSED column are optimized and obtained with the objective of minimal total annual cost (TAC) via conventional sequential iterative procedure. On the basis of steady-state design, four single-end temperature control structures (STCS), four dual-temperature control structures (DTCS) and four dual-composition control structures (DCCS) are developed and established successively to overcome the operation and control challenges caused by the novel scheme. To seek the robust control, the dynamic performance analysis on account of the above control structures is conducted for the SSED column, which is evaluated for feed flowrates and composition disturbances. The results show that the control performance of DCCS is significantly superior to that of STCS and DTCS while the integral squared error (ISE) and energy-consuming effect are equivalent, and can take shorter time to bring the product purities back to the original steady state in coping with specified feed disturbances.

Determination of a suitable index for a solvent via two-column extractive distillation using a heuristic method

The traditional approach to solvent selection in the extractive distillation process strictly focuses on the change in the relative volatility of light-heavy components induced by the solvent. However, the total annual cost of the process may not be minimal when the solvent induces the largest change in relative volatility. This work presents a heuristic method for selecting the optimal solvent to minimize the total annual cost. The functional relationship between the relative volatility and the total annual cost is established, where the main factors, such as the relative volatility of the light-heavy components and the relative volatility of the heavy-component solvent, are taken into account. Binary azeotropic mixtures of methanol-toluene and methanol-acetone are separated to verify the feasibility of the model. The results show that using the solvent with the minimal two-column extractive distillation index, the process achieves a minimal total annual cost. The method is conducive for sustainable advancements in chemistry and engineering because a suitable solvent can be selected without simulation verification.

Methodological Framework for Synthesis of Multiperiod Heat Exchanger Networks with Minimum Total Annual Cost Using an Optimization Model and Area Reassignment Technique

Methodological Framework for Synthesis of Multiperiod Heat Exchanger Networks with Minimum Total Annual Cost Using an Optimization Model and Area Reassignment Technique

Comparison of heterogeneous azeotropic distillation and energy-saving extractive distillation for separating the acetonitrile-water mixtures

The separation of acetonitrile-water mixtures is a challenging and significant task due to the presence of azeotrope, for which three separation alternatives are proposed, including an energy-efficient extractive distillation strategy (ED), an pressure-swing distillation strategy (PSD) and an novel azeotropic distillation strategy (EAD). Concept design based on ternary phase diagrams of various solvents demonstrates that benzene is a suitable solvent for the newly proposed EAD scheme. The separation sequence and operating parameters are optimized via using different sequential iterative procedures based on the minimal total annual cost (TAC). Under temperature-enthalpy (T-H) diagram guidance, heat integration applied to this three sequences significantly is completed, which reduces TAC by 27.45%, 30.42%, and 46.67%, respectively. Comprehensive evaluation of the three separation alternatives from the economic and environmental perspectives indicates that the heat-integrated EAD scheme is more attractive, since its TAC decreases by 52.03% and 55.30%, respectively, and CO2 emissions decreases by 56.63% and 61.63% compared with ED and PSD schemes. It is worth noting that the conceptual design of the EAD scheme also provides an energy efficient alternative for other systems that form azeotropes with water.

Evaluation of ionic liquid separation ability for the benzene–methanol mixture by extractive distillation

AbstractBACKGROUNDBenzene–methanol azeotrope can be formed at atmospheric pressure. Extractive distillation is widely used in the separation of azeotrope. The key factor for extractive distillation is the selection of entrainer. The minimal total annual cost of extractive distillation process can be used as objective function to evaluate the separation performance of ionic liquid entrainer. Intermolecular interaction energy can be used to analyze separation mechanisms.RESULTAn Aspen Plus software database belonging to the three ionic liquids 1‐hexyl‐3‐methylimidazolium acetate, 1‐octyl‐3‐methylimidazolium acetate and 1‐decyl‐3‐methylimidazolium acetate was established. The minimal total annual costs of three extractive distillation processes for the separation of benzene–methanol mixture with different ionic liquids were obtained by sequential iterative method. The feed rate of entrainer was also obtained under the optimized conditions. Among the three extractive distillation processes with different ionic liquid, the total annual cost and the entrainer feed rate of the extractive distillation process with 1‐hexyl‐3‐methylimidazolium acetate as entrainer are the smallest. The intermolecular interaction energies in the ternary system of benzene–methanol–ionic liquid were obtained using the Gaussian 09 software package based on the density functional theory. The separation mechanisms and the extractive distillation process of benzene–methanol azeotrope with ionic liquid as entrainer was interpreted by the intermolecular interaction energy.CONCLUSIONThe results show that the separation ability of 1‐hexyl‐3‐methylimidazolium acetate is higher than that of 1‐octyl‐3‐methylimidazolium acetate or 1‐decyl‐3‐methylimidazolium acetate. Intermolecular interaction energy analysis can be used in the screening and design of ionic liquid entrainer. © 2019 Society of Chemical Industry

A novel hybrid strategy for cost-optimal heat exchanger network synthesis suited for large-scale problems

In this work optimal synthesis of heat exchanger networks (HENs) is focused on, namely the minimization of total annual costs (TAC). An efficient combination of optimization strategies for HEN synthesis is presented. A novel strategy for local optimization in the continuous space is developed and embedded in a stochastic global search with a tailored genetic algorithm using a stage-wise superstructure. The novel strategy is based on structure identification and changing the reference system for optimization. This strategy reduces the number of optimization variables and is able to simplify HEN structures thus enabling particularly well performing local search. Eight frequently studied medium- to large-scale problems from literature are investigated and evaluated. The application of the proposed algorithm was able to find configurations with consistently lower TAC compared to previously reported solutions.

Enhanced Evolutionary Sizing Algorithms for Optimal Sizing of a Stand-Alone PV-WT-Battery Hybrid System

An increase in the world’s population results in high energy demand, which is mostly fulfilled by consuming fossil fuels (FFs). By nature, FFs are scarce, depleted, and non-eco-friendly. Renewable energy sources (RESs) photovoltaics (PVs) and wind turbines (WTs) are emerging alternatives to the FFs. The integration of an energy storage system with these sources provides promising and economical results to satisfy the user’s load in a stand-alone environment. Due to the intermittent nature of RESs, their optimal sizing is a vital challenge when considering cost and reliability parameters. In this paper, three meta-heuristic algorithms: teaching-learning based optimization (TLBO), enhanced differential evolution (EDE), and the salp swarm algorithm (SSA), along with two hybrid schemes (TLBO + EDE and TLBO + SSA) called enhanced evolutionary sizing algorithms (EESAs) are proposed for solving the unit sizing problem of hybrid RESs in a stand-alone environment. The objective of this work is to minimize the user’s total annual cost (TAC). The reliability is considered via the maximum allowable loss of power supply probability ( L P S P m a x ) concept. The simulation results reveal that EESAs provide better results in terms of TAC minimization as compared to other algorithms at four L P S P m a x values of 0%, 0.5%, 1%, and 3%, respectively, for a PV-WT-battery hybrid system. Further, the PV-WT-battery hybrid system is found as the most economical scenario when it is compared to PV-battery and WT-battery systems.

Triple-column side-stream extractive distillation optimization via simulated annealing for the benzene/isopropanol/water separation

This paper proposes various side-stream extractive distillation configurations for the benzene/isopropanol/water separation with ethylene glycol as a solvent, including double side-stream extractive distillation (D-SSED), single side-stream extractive distillation (S-SSED) and conventional extractive distillation (CED). The parametric design is investigated with the minimum total annual cost (TAC) as an objective function. It is concluded that the D-SSED scheme is the best option, saving TAC by 31.52% and CO2 emission by 35.56% compared to the CED scheme. During this, one simulated annealing-based optimization procedure is firstly applied to such complex triple-column flowsheets. The accepted optimal solution is readily found through three rounds of search from one base-case. The procedure shows the advantages of time-saving, intelligence and global optimization compared to the common iterative sequential optimization method.

Design and Integration of Bio-Oil Co-Processing with Vacuum Gas Oil in a Refinery

Due to the climate change and the strong dependence on fossil fuels, biomass-derived liquid transportation fuels and energy products have been proposed to deal with such situations. Usually, the prices of the bio-diesel and bio-gasoline are much higher than those of fossil fuels. The co-processing of bio-oil and vacuum gas oil (VGO) in a fluid catalytic cracker of a refinery has been proposed to utilize the existing refinery infrastructures and decrease the prices of bio-fuels. However, the integration between the bio-oil production and the existing refinery is not clear. In this work, a superstructure model is built to design and optimize the co-processing process with minimum total annual cost which features to select the optimal bio-oil production technology (fast pyrolysis or catalytic pyrolysis) and obtain the optimal integration scheme. Furthermore, the impacts of the prices of biomass and hydrogen, the bio-oil co-processing ratio on the economics of the co-processing system are also investigated. The optimal integration scheme of the co-processing of bio-oil and VGO can be obtained by solving the proposed model.

Energy-saving investigation of hybrid reactive distillation for n-butyl acetate production from two blending feedstocks

Several reactive hybrid distillation configurations are demonstrated for the n-butyl acetate production via transesterification with two blending reactive feeds, namely MM20 (70 wt% methanol, 30 wt% methyl acetate) and MM80 (35 mol% methanol, 65 mol% methyl acetate). Pervaporation (PV) with polyoctylmethylsiloxane membrane is used to replace a methanol recovery column because what’s obtained at the retentate side is high purity methanol rather than methyl acetate. The valid mathematical model for this PV process is developed in Aspen Custom Modeler. These configurations along with conventional reactive distillation (CRD) and reactive dividing-wall distillation (RDWC) are optimized by a sequential iterative algorithm based on the minimum total annual cost (TAC). The comparison with CRD shows that RDWC + PV is the optimal alternative of two hybrid configurations for MM80, saving 40.8% operating cost, 32.6% TAC, and 48.77% CO2 emissions. However, other two hybrid configurations for MM20 are unable to achieve the desired energy-saving.

Optimizing the insulation thickness of walls of existing buildings with CHP-based district heating systems

The heat demand of existing buildings can be reduced by improving the thermal properties of building envelope. Moreover, the heat medium temperature of district heating (DH) systems may also be influenced by adding insulation materials. An optimization model used to determine the optimum economic insulation thickness of walls (OEITW) of existing buildings with combined heat and power (CHP)-based DH systems was established based on energy grade and amount of energy. An existing residential building in Beijing, China, was used as the basis of the case study. The impact of insulation thickness (IT) on energy grade and amount of energy was studied. Sensitivity analysis method was used to investigate the impact of electricity price, interest rate, insulation material price and absorption heat pump price on the OEITW and minimum annual total cost (MATC). Results show that the OEITW and MATC can be obtained by using the optimization model. The heat demand and heat medium temperature can be lowered through adding insulation materials, resulting in the reduction of energy grade and amount of energy. Sensitivity analysis results show that the impact of sensitivity factors on the OEITW and MATC are different.

Separation of propylene oxide-methanol-water mixture via enhanced extractive distillation: Design and control

The ternary azeotropic mixture of propylene oxide-methanol-water generally occurs in the direct oxidation of hydrogen peroxide and needs to be separated effectively. This paper explores two energy-efficient configurations with water as solvent, namely extractive dividing-wall column (EDWC) and side-stream extractive distillation (SSED), in terms of the potential economic advantages compared to conventional extractive distillation (CED) and the dynamic control. Several steady-state designs with the minimum total annual cost (TAC) by using a sequential iterative optimization method are achieved and compared. Regarding the controllability, four control structures for the SSED are developed and examined via introducing the feed flow and composition disturbances as well as one control structure for the EDWC. Similar to the EDWC, the SSED can be well controllable via an optimal control structure relying on only temperature measurements.

Energy-efficient extractive pressure-swing distillation for separating binary minimum azeotropic mixture dimethyl carbonate and ethanol

An energy-efficient extractive pressure-swing distillation process is proposed for separating binary minimum azeotropic mixture ethanol and dimethyl carbonate. It can be observed that the minimum amount flow rate of entrainer will be decreased when the operating pressure of extractive distillation column is increased via the thermodynamic feasibility insights (i.e., residue curve map and isovolatility lines). Therefore, an extractive pressure-swing distillation process with 4 bar for the extractive distillation column is designed. Process variables of the proposed design are optimized by combining the sensitivity analysis and sequence quadratic program approaches with minimum total annual cost as objective function. Total annual cost, CO2 emissions, and exergy loss of the optimized extractive pressure-swing distillation with 4 bar for the extractive distillation column is reduced by 44.09%, 44.16% and 41.54%, respectively when compared with the existing process with 1 bar for the extractive distillation column, which mainly attributing the flow rate of entrainer decreasing from 200.020 kmol/h to 44.963 kmol/h. Furthermore, the extractive pressure-swing distillation with heat integration is studied to further reduce energy cost because the enough heat transfer temperature difference could be provided by increasing operation pressure.

Solvent Recovery System for a CO2-MEA Reactive Absorption-Stripping Plant

The solvent recovery section from the exhaust gas represents an important auxiliary part for an industrial CO2 post-combustion capture plant by the reactive absorption-stripping process. In this work, a partial condenser and a water-wash section configuration were designed to reach 1 ppm of solvent in the exhaust gas, and compared using the Total Annual Cost (TAC) as economic index. Both the configurations ensured the required recovery performance. The results highlighted that the partial condenser alternative is more convenient in terms of capital annualized costs and water make-up, but at the same time it is strongly penalized by the high operating costs for the cooling water. Therefore, the configuration in which the absorber is equipped with the water-wash section resulted the option with the minimum TAC.

Simultaneous optimization strategies for heat exchanger network synthesis and detailed shell-and-tube heat-exchanger design involving phase changes using GA/SA

A simultaneous optimization approach for heat exchanger network (HEN) synthesis and detailed shell-and-tube heat exchanger (HE) design including phase changes is proposed based on a genetic/simulated annealing algorithm (GA/SA). Firstly, a model for HEN synthesis considering utility HEs with phase change is established by combining the improved stage-wise superstructure model of HEN synthesis with non-isothermal mixing of splits and detailed design models of HEs involving phase change, the minimum total annual cost accounting for pumping cost is set as the key objective. Secondly, two alternative connection schemes for HEs, which are referred to as one-stream series-wound and one-stream parallel in the stage-wise superstructure of the HEN, were applied. Thirdly, a simultaneous optimization strategy is proposed. Required areas of HEs obtained by stage-wise superstructure, overall heat-transfer coefficients and pressure drops based on the dimension parameters of HEs are used to connect HEN synthesis and the detailed design of each HE. Finally, a flowchart of optimization procedures using GA/SA was presented to solve the problem, and an inner iterative loop of the area of HE is used to guarantee the feasibility of the solution. Two examples results are used to illustrate the availability of the proposed model and algorithm.

Cost-saving and control investigation for isopentyl acetate ionic liquid catalyzed synthesis through conventional and dividing-wall reactive distillation

The reactive distillation process regarding ionic liquid-catalyzed transesterification for iso-pentyl acetate production is attracting increasing attention owing to outstanding properties of green homogeneous catalysts. This work investigates the economics and controllability of conventional reactive distillation (CRD) and dividing-wall reactive distillation (RDWC) configurations for this reaction. The optimizations of both configurations are carried out based on the minimum total annual cost (TAC) by the sequential iterative procedures. Their effective control structures are proposed and verified when either feed flow or feed composition disturbances are introduced. The results show that the RDWC process permits the reduction of up to 22.8% in the TAC compared to the CRD process. Furthermore, it is justified in view of the integral squared errors calculated that both control structures represent good dynamic performances in regard to resisting two kinds of feed disturbances.

Process analysis of extractive distillation for the separation of ethanol–water using deep eutectic solvent as entrainer

Deep eutectic solvents (DESs) as novel entrainers can be used for the separation of azeotropic mixture, and have received much attention in recent years. However, the researches about DESs mainly focus on vapor–liquid equilibrium (VLE) and extractive distillation experiment. In this work, an overall extractive distillation process for ethanol dehydration using ChCl/Urea (1:2) as entrainer is investigated. The physical properties of the DES are defined by correlating the experimental data. Three thermodynamic methods are employed to describe the phase behavior of ethanol–water–ChCl/Urea (1:2) system. COSMO-based theory is adopted to explain the differences in separation performance among ChCl/Urea (1:2), glycerol and [EMIM][BF4]. The design parameters of extractive distillation process are optimized by multi-objective generic algorithm (MOGA) with minimum total annual cost (TAC), minimum CO2 emissions ECO2 and maximum efficiency indicator of extractive section (EExt) as objective functions. In addition, the control structure of extractive process is studied by Aspen Dynamics, and the proposed control structure could resist fresh feed flow rate and composition disturbances. The results show that ChCl/Urea (1:2) exhibits better separation performance in ethanol dehydration compared with glycerol and [EMIM][BF4]. Both COSMOSAC model relying on molecular information and NRTL model based on experimental data can well describe the vapor–liquid behavior containing ChCl/Urea (1:2). Entrainer purity plays an important role in extractive distillation process, and a proper concentration rather than nearly pure entrainer should arouse our attention in extractive distillation process. DESs as promising novel entrainers can be used in extractive distillation industrial for separating azeotrope.

Exploration of the effects of pressure on the controllability of extractive distillation for separating pressure-sensitive azeotropes

Exploring the influence of steady-state process parameters on dynamic control structures is receiving increasing attention from researchers. In this work, the effects of pressure on dynamic control structures and anti-disturbance were discussed based on the minimal total annual cost. Ethanol-benzene and ethanol-ethyl acetate, two binary azeotropic systems, were used to investigate the influence of pressure on the dynamic controllability. For ethanol-benzene, the control structures with two solvents, 1,2-propanediol and p-xylene, under the optimal pressure were both more complex than that under normal pressure. In addition, when the deviation from the initial set value was small, a slight increase in the purity of the product could be adopted instead of introducing a component controller. The optimal pressure needs to be determined by balancing cost and control. For ethanol-ethyl acetate, the influence of pressure on the dynamic controllability was not obvious, and the optimal pressure can be only determined by economy. The results showed that pressure had different effects on the dynamic controllability of different systems.