Nonlinear Optimization Strategies for Process Separations and Process Intensification

Advanced nonlinear programming (NLP) strategies based on equation-oriented (EO) process models are leading to significant improvements in computer-aided process engineering. The EO paradigm allows the development of large, integrated optimization platforms that expand the scope of continuous optimization tasks in process engineering. In particular, these platforms deploy significantly faster NLP strategies than in commercial simulation tools. Moreover, they exploit exact derivatives and system structure in order to consider much larger and more challenging systems. Finally, they allow the incorporation of much more general models, such as multi-level optimization and complementarity constraints. For process optimization this allows the treatment of extended models for complex phase equilibrium and process separations. These advances facilitate the optimization of novel integrated systems that arise in process intensification. Several separation case studies are presented that illustrate these optimization concepts and demonstrate their effectiveness for hybrid membrane/distillation separations and reactive distillation systems that typify novel systems in process intensification.     

Simulation and assessment of manufacturing ethylene carbonate from ethylene oxide in multiple process routes

Ethylene oxide(EO) is an important raw material for producing ethylene carbonate(EC). However, the traditional method for the separation of EO from mixture gas by water in the refining process is high energy consumption. In this paper, two processes of manufacturing EC from EO mixture gas were studied by process simulation. Two processes for producing EC from EO mixture as raw materials without EO purification, called the OSAC process and the Modified OSAC process, were developed and assessed systematically. Both processes use EC as the absorbent to capture EO, avoiding the separation process of EO from solution. For comparisons, the EC producing process containing EO absorption by water, EO refinement and carbonylation process were also modeled, which was called the ERC process. Three schemes were designed for the EO absorber using EC as absorbent. Compared with the initial absorber scheme,the optimal liquid–vapor ratio is reduced from 1.66 to 1.45(mass). Moreover, the mass distribution analysis for the three processes were carried out in the form of the material chain. It was found that, compared with the ERC process, the energy consumption of the OSAC and the Modified OSAC process is reduced by 56.89% and 30.03%, respectively. This work will provide helpful information for the industrialization of the OSAC process.     

Hybrid battery-supercapacitor storage for an electric forklift: a life-cycle cost assessment

Supercapacitors, more properly named electrochemical capacitors (EC), have a great potential in constituting the premium power reserve in a variety of energy- and power-intensive applications in transport and in electricity grids. EC may be used in conjunction with electrochemical storage systems, such as the batteries of various chemistries (lead-acid, sodium-nickel chloride or sodium-sulphur, nickel-metal hydride and even lithium-based systems), in a hybrid configuration where the functions of energy and power can be conveniently separated between the two storage devices and then optimized. Recently, an electric forklift has been commercialized with such a hybrid storage system, without any demonstrated specification of the advantages achievable with this configuration. In this article, the effective technical and economical benefits of this EC integration are theoretically and experimentally evaluated, by means of a conventional electric forklift. The reference vehicle drivetrain is modified by combining a conventional traction lead-acid battery, already used in the vehicle, and a commercial EC. The performances of the modified electric forklift are simulated with already developed vehicle and components models and validated with experimental data. Simulations and electrical tests confirm the functional relationship, expressed in exponential form, between battery lifetime and peak current and demonstrate the technical and economical potentialities of the use of these hybrid configurations, such as the increased efficiency and the prolonged battery life (more than doubling the life of the battery without EC), due to the reduced battery operating stress, and an economical saving (about 30 %), able to compensate initial extra-costs for vehicle modification and battery replacement.     

固载化离子液体催化环氧乙烷和二氧化碳合成碳酸乙烯酯

用溴化1-羟乙基-3-乙烯基咪唑、甲基丙烯酸钠、丙烯酸羟乙酯、苯乙烯4种单体共聚合成了高分子离子液体催化剂,表征了其结构. 将该催化剂固载到分子筛上制成固体颗粒催化剂,催化环氧乙烷(EO)与CO2合成碳酸乙烯酯(EC)的反应,考察了反应时间、温度、压力、催化剂用量对EO转化率及生成EC选择性的影响. 结果表明,在反应时间4 h、温度403.15 K、压力2.5 MPa、催化剂与环氧乙烷质量比9%的条件下,EO转化率为95%, EC选择性为98%,催化剂在循环使用10次后,EO转化率无明显下降,EC选择性接近100%. 该反应为一级反应,动力学方程为r=-dCEO/dt=9.872×104e-52.00/(RT)CEO.     

Sustainable Dimethyl Carbonate Production from Ethylene Oxide and Methanol

A large-scale dimethyl carbonate (DMC) production process from ethylene oxide (EO), CO₂, and methanol was simulated and optimized. Unlike most industrial processes of DMC production, the direct conversion of EO and CO₂ to ethylene carbonate (EC) and EC transesterification to DMC were performed in a single reactor. The reaction volume and the reactor operating pressure were selected as decision variables and evaluated. The key performance parameters, e.g., conversion per pass and CO₂ intensity, were compared with conventional commercialized routes or novel promising processes in the literature.     

环氧乙烷技术与市场分析

介绍了目前全球环氧乙烷（E0）的主要生产工艺、技术水平、主要工业基地、生产企业及市场供求状况等。指出了全球经济的快速发展带动化工行业朝着精细和深加工方向发展。结合中国的实际情况,重点分析了国内EO的生产和市场状况,国内EO需求的增长带动大量新项目的建设。未来EO市场有趋于缓和,价格趋向稳定。长期来看,新产能的增加一定程度上促使国内EO开工率降低,但掌握先进技术的工艺将占据绝对市场。     

Using new packages for modelling, equation oriented simulation and optimization of a cogeneration plant

The development and testing of an equation-oriented (EO) mathematical model for the optimization of heat and power systems using a new state-of-the-art sequential quadratic programming (SQP) method called filterSQP has been reported in an earlier paper. The model has been extended to include combined cycle cogeneration plants (CCCPs), the economic optimization of which involves adding equipment investment, cost functions and operating cost models to the stream and unit operation models of the earlier paper. These systems are of substantial industrial interest and are substantially larger than those in Rodríguez-Toral et al., Computers and Chemical Engineering, August 2000. Their size and complexity required the use of a new flexible modelling system (FMS) recently created within our research group. FMS can be used to set up large systems of equations, create networks to be modelled and give starting guesses easily for problems of any size. Also, FMS is able to interact with solvers for EO simulation and optimization, which have been developed here and elsewhere. A number of EO simulation and optimization examples, from simple unit operations to a whole real cogeneration plant involving a commercial gas turbine with 1275 variables and equations, are used to demonstrate the applicability of the CCCP model and the modelling package.     

Synthesis and design of new hybrid configurations for biobutanol purification

The development of new technologies for biobutanol production by fermentation has resulted in higher butanol concentrations, less by-products and higher volumetric productivities during fermentation. These new technology developments have the potential to provide a production process that is economically viable in comparison to the petrochemical pathway for butanol production. New alternative hybrid configurations based on liquid–liquid extraction and distillation for the biobutanol purification were presented. The alternatives are designed and optimized minimizing two objective functions: the total annual cost (TAC) as an economical index and the eco-indicator 99 as an environmental function. All the new configurations presented reduced the TAC compared to the traditional hybrid configuration, in particular a thermally coupled alternative exhibited a 24.5% reduction of the TAC together with a 11.8% reduction of the environmental indicator. Also intensified sequences represented a promising option in the reduction of the TAC but with some penalty in the eco-indicator.     

Performance and Energy Consumption of Membrane‐Distillation Hybrid Systems for Olefin‐Paraffin Separation

Light olefin and paraffin are commonly separated by energy‐intensive cryogenic distillation. Membrane/distillation hybrid systems constitute an economical alternative separation process. Different configurations of this hybrid system are studied for olefin‐paraffin separation with emphasis on C₃ separation. An approach based on the McCabe‐Thiele method is applied to analyze different process configurations. A facilitated transport membrane is considered as membrane type. Both new column design and augmentation of an existing distillation column by a membrane module are considered. Numerical examples are considered for the separation of propane from propylene through different hybridization shapes with facilitated transport membranes. The energy requirement can be halved using hybrid systems.     

An extended logical analysis of data approach to fault detections of industrial hybrid systems

It is difficult to deal with industrial hybrid systems involving both continuous and discrete variables using conventional data-driven fault detection methods. While logical analysis of data (LAD) methods are able to effectively explore hidden rules in discrete and continuous data by means of logical analysis for variable associations. However, conventional LAD has the problem of losing trend change information when extracting features of continuous variables. And when processing industrial data with high-dimensional, multivariate features, it will cause a lot of redundancy in the extracted rules. Motivated by these observations, this paper presents an extended logical analysis of data (ELAD) approach to fault detections of industrial hybrid systems. Therein, correlated variables are selected according to the association degree with key variables and additive variable trends are employed to characterize process status changes, creating an explicable fault detection model. The proposed method is applied to the steam drum process of an industrial coal gasification plant in detecting the influence of key hybrid variables on the fault of steam drum level. The results verify the feasibility and effectiveness of the contribution.     

面向工业混杂系统故障检测的扩展数据逻辑分析方法

常规的数据驱动故障检测方法难以处理同时包含连续和离散变量的工业混杂系统,数据逻辑分析(logical analysis of data, LAD)方法通过对历史数据中变量组合的逻辑分析,能够有效地挖掘离散和连续变量数据中存在的隐含规则。然而,常规的LAD在提取连续变量特征时存在对趋势变化信息丢失的问题,并且在处理具有高维度、多变量特征的工业数据时会导致提取的规则存在大量冗余。为此,本文提出一种基于扩展数据逻辑分析(extended logical analysis of data, ELAD)的工业混杂系统故障检测方法,根据与关键变量的关联度选取相关变量,增加变量的趋势信息以进行过程状态变化的表征,生成可解释的故障检测模型。应用于工业煤气化汽包过程,有效地检测了关键混杂变量对汽包液位故障的影响,实验结果验证了所提方法的可行性和有效性。     

Landfill leachate treatment using hybrid coagulation-nanofiltration processes

In this study, treatment of landfill leachate using a novel electrocoagulation - nanofiltration (EC-NF) hybrid system was investigated. Leachate sample was collected from Whytes Gully landfill in Wollongong, Australia. The performance of electrocoagulation (EC) using aluminium electrodes as a pretreatment step for the nanofiltration process was compared against a conventional chemical coagulation (CC) process. Results reported here indicate that electrocoagulation is superior over the conventional coagulation process with respect to total organic carbon (TOC) and turbidity removal. At the optimum reaction time, TOC and turbidity removals by the electrocoagulation process were 67% and 80%, respectively. In comparison, at the optimum dosage of Al₂(SO₄)₃ obtained by a standard jar testing procedure, TOC and turbidity removals by the chemical coagulation process were only 10% and 65%, respectively. It is noteworthy that the amount of aluminium released by the electrocoagulation process to the solution was significantly higher than the optimum dosage of the chemical coagulation process. Therefore, better performance of the electrocoagulation process can possibly be explained by the higher coagulation concentration and the formation of polymeric aluminium which is known to be more effective for small organic compounds which are prevalent in landfill leachate. A remarkable difference between electrocoagulation and chemical coagulation pretreatment was also observed with respect to fouling mitigation in a subsequent nanofiltration process. For the two different nanofiltration membranes (NF 270 and SR2) used in this study, severe membrane fouling was evident when filtering raw landfill leachate or chemical coagulation pretreated landfill leachate. In contrast, fouling was not observed with an electrocoagulation pretreated feed solution. However, the use of electrocoagulation pretreatment did not result in any improvement in treated effluent quality by the hybrid system. Over all, there was no discernible variation between the EC - NF and CC - NF hybrid systems in their TOC and turbidity removals, which were approximately 92% and 99%, respectively. The reported results demonstrate that an EC - NF hybrid system can be a promising candidate for landfill leachate treatment, particularly for small and decentralised landfills where simplicity and robustness are required.     

Equation‐oriented flowsheet simulation and optimization using pseudo‐transient models

Tight integration through material and energy recycling is essential to the energy efficiency and economic viability of process and energy systems. Equation‐oriented (EO) steady‐state process simulation and optimization are key enablers in the optimal design of integrated processes. A new process modeling and simulation concept based on pseudo‐transient continuation is introduced. An algorithm for reformulating the steady‐state models of process unit operations as differential‐algebraic equation systems that are statically equivalent with the original model is presented. These pseudo‐transient models improve the convergence of EO process flowsheet simulations by expanding the convergence basin. This concept is used to build a library of pseudo‐transient models for common process unit operations, and this modeling concept seamlessly integrates with a previously developed time‐relaxation optimization algorithm. Two design case studies are presented to validate the proposed framework. © 2014 American Institute of Chemical Engineers AIChE J 60: 4104–4123, 2014     

Simulation of a hybrid pervaporation–distillation process

This study explores the possibility of simulating a hybrid pervaporation membrane process with the help of Aspen Plus? (Aspen Tech) flowsheeting. Because Aspen Plus does not contain membrane modules in its Model Library, the pervaporation membrane is simulated within Excel Visual Basic for Applications (VBA). Excel VBA is then linked with Aspen Plus to perform the hybrid simulation. In this way, the user can control the simulation even during the calculations.Case studies, in which industrially relevant hybrid distillation–pervaporation processes are simulated, are used to test the program. First, the dehydration and recycling of ethanol in an industrial plant is looked at, to explore whether an economic improvement can be established with a hybrid process. Secondly, the same is done for the purification of acetic acid in an industrial plant. The results presented here indicate the value of this software as a design tool.     

环氧乙烷与CO2合成碳酸乙烯酯动力学研究

环氧乙烷与CO2合成法是一种具有工业应用价值的碳酸乙烯酯生产方法,有必要对其反应机理和动力学加以研究。文中假设CO2与环氧乙烷合成碳酸乙烯酯的反应按照亲核加成反应机理分3步进行,其中催化剂溴化四乙铵作为亲核试剂。在一定温度和一定的压力下,碳酸乙烯酯的合成反应速率正比于催化剂和环氧乙烷浓度。提出了动力学方程,通过实验对假设机理进行了验证,并回归得到动力学方程参数。所得合成碳酸乙烯酯的反应动力学方程对大规模工业化生产具有一定参考价值。     

Enhanced UV- and visible-light driven photocatalytic performances and recycling properties of graphene oxide/ZnO hybrid layers

Light induced catalytic processes have attracted significant attention during the last years for wastewater treatment due to their efficiency in decomposition of organic contaminants. In this study we report the synthesis of graphene oxide (GO)/ZnO hybrid layers with high photocatalytic efficiency using laser radiation. The results show that the hybrid layers exhibit much improved photodecomposition efficiency as compared to pure GO or ZnO both under UV and visible-light irradiation. The enhanced photocatalytic efficiency of the hybrid as compared to the reference pure ZnO and GO layers was attributed to the contribution of GO to the separation and transport of the photogenerated charge carriers. Additionally, under visible light irradiation the organic molecules can act as first sensitizers in the degradation process. The recyclability of the layers was also investigated through repetitive photodegradation cycles under UV- or visible-light irradiation. After consecutive degradation runs, the hybrid photocatalyst layers were still stable and retained high degradation efficiency, ensuring reusability. The photocatalytic activity of the layers was correlated with the gradual change of their chemical structure during consecutive degradation cycles. Owing to the high photodegradation efficiency, reusability, and ease of recovery the synthesised hybrid layers consisting of easily available materials are suitable for environmental purification applications.     

水热电催化氧化法处理高浓度苯酚模拟废水的研究

结合催化湿式氧化法和电催化氧化法为水热电催化氧化法处理高浓度苯酚模拟废水((ρCOD)为7500mg/L):以C/Ru作催化剂(w(Ru)为0.5%),自制DSA阳极(釜体为阴极),加入NaCl作支持电解质(w(NaCl)为1%),充入氧气使PO2为3.5MPa,升温至设定温度后:开初0.5h进行苯酚的催化湿式氧化,后0.5h进行电催化氧化,并改变条件进行苯酚的单一催化湿式氧化和电催化氧化。结果表明:85℃时水热电催化氧化条件下,苯酚去除率为100%,COD去除率达92.34%,而单一催化湿式氧化和电催化氧化的COD去除率却依次为68.46%、39.73%,可见水热电催化氧化法利用了催化湿式氧化法和电催化氧化法的协同作用,取得了更佳的效果。该方法是一种新型、低温、高效的废水处理技术,为处理苯酚废水提供了另一种可能途径。     

Solar thermal systems in industry

A significant portion of the demand for industrial process heat can be met with solar energy. Whether this energy source is widely used will depend not only on its economic attractiveness, but also on the ease with which solar thermal systems interface with the remainder of the industrial plant. Foster Wheeler has recently designed solar thermal systems to supply hot water and process steam to industry and has nearly completed the construction of one of these. Drawing on this experience, this paper discusses selection of solar technologies that can best satisfy the user’s energy requirements and minimize interfacing problems.     

Hybrid systems in seawater desalination—practical design aspects, present status and development perspectives

Ever since seawater desalination has been applied on an industrial scale, and particular in the countries of the Arabian Gulf, the application of desalination processes in dual-purpose facilities—water and power—as a hybrid configuration has been discussed in many feasibility investigations and also planning concepts. It is above all the combination of reverse osmosis with thermal processes that has found increasing interest with the aim of ensuring, as economically as possible, uniform water supplies under the specific, greatly varying load conditions in the Gulf countries. Such design concepts for hybrid configurations encompass straightforward structures with a low degree of coupling between membrane and thermal desalination processes, but range up to very complex configurations with strong interconnections on both the water side and thermally, as well as with several desalination processes connected in series or in parallel. Classical hybrid concepts in which the permeate from an RO desalination component is mixed with distillate from thermal desalination have already been implemented in Saudi Arabian dual-purpose plants, like Jeddah and Yanbu-Medina. Although hybrid systems of greater complexity have been addressed in many design studies and publications, up to now none has been brought to fruition. Coming into consideration asthe design basis for determining the capacity shares of the various desalination processes operated in a hybrid configuration are: arrangement of thermal cycle of the power plant component; water/power ratio of the dual-purpose seawater desalination and power plant; provision of undiminished water production of the desalination plant as electricity generation varies; provision of a specified drinking water quality with regard to composition and salt content; combination of all these aspects. Also gaining in importance are concerns of environmental pollution and sustainable development when selecting seawater desalination and power plant configurations, as well as their optimization when considering desalination and electricity generation as a whole. In the practical design of hybrid membrane and thermal systems, aspects come to light, though, that restrict linking of the two systems and joint utilization of facilities, as conceived in studies and conceptual design investigations. This applies both for common utilization of intakes and the use of heated up cooling water from thermal processes as a feed stream for the RO part of the desalination process. Additionally, requirements of drinking water composition, particularly chloride content, TDS and compliance with a specific residual content of boron, influence specifically the design of the membrane process part and its share in the total desalination capacity. Such practical aspects have greatly influenced the design and configuration of the Fujairah hybrid plant for which, from a total desalination capacity of 100 MIGD (454,600 m³/d), the share of 37.5 MIGD (170,500 m³/d) makes its seawater RO plant the biggest currently being constructed anywhere in the world. From the findings of the engineering of this plant and the idea that, by increasing interconnection between the two processes on the water side, it is possible to advance a hybrid configuration of this type with regard to cost optimization in the membrane installation, but also by joint utilization of the intake equipment, perspectives result for applied research efforts over the near and long terms, for example: long-term behavior of membranes at elevated temperatures; tendency for biofouling in membrane process with common utilization of cooling water and brine; influences of such interconnections on the overall availability of the facility. But also for the operation and maintenance organization of such large facilities, consequences can be foreseen for the future development of hybrid plants, particularly for operation management and organisation of the interplay of the different power plant and desalination systems, monitoring of SWRO membrane replacement and cleaning, as well as controlling water quality.