Multiobjective optimization of multiproduct batch plants scheduling under environmental and economic concerns

In batch process scheduling, production trade‐offs arise from the simultaneous consideration of different objectives. Economic goals are expressed in terms of plant profitability and productivity, whereas the environmental objectives are evaluated by means of metrics originated from the use of life cycle assessment methodology. This work illustrates a novel approach for decision making by using multiobjective optimization. In addition, different metrics are proposed to select a possible compromise based on the distance to a nonexistent utopian solution, whose objective function values are all optimal. Thus, this work provides a deeper insight into the influence of the metrics selection for both environmental and economic issues while considering the trade‐offs of adopting a particular schedule. The use of this approach is illustrated through its application to a case study related to a multiproduct acrylic fiber production plant, special attention is put to the influence of product changeovers. © 2010 American Institute of Chemical Engineers AIChE J, 57: 2766–2782, 2010     

Optimal operation of an integrated bioreaction–crystallization process for continuous production of calcium gluconate using external loop airlift columns

A kinetic model was proposed to optimize the integrated bioreaction–crystallization process newly developed for production of calcium gluconate crystals using external loop airlift columns. The optimal operating conditions in the bioreactor were determined using an objective function defined to maximize the productivity as well as to minimize biocatalyst loss. The optimization of the crystallizer was carried out by matching the crystallization rate to the optimal production rate in the bioreactor because the bioreaction was found to be the rate controlling process. The calcium gluconate productivity under the optimal conditions of the integrated process was obtained by the simulation based on the process model. The productivity of the proposed process was found to be comparable to that of the current batch fermentation process.     

Improving docosahexaenoic acid production by Schizochytrium sp. using a newly designed high‐oxygen‐supply bioreactor

A sufficiently high oxygen supply is crucial for high‐cell‐density cultivation of aerobic microorganisms, including Schizochytrium sp. We, therefore, designed a novel bioreactor enabling high‐level oxygen supply, and its relevant process parameters and fermentation‐stage characteristics were investigated. The real‐time changes of pH and nonoil biomass were monitored as proxies for the consumption of nitrogen and lipid accumulation status, which was first applied to divided fermentation process with three stages. The experimental results showed that the biomass in this porous‐membrane‐impeller bioreactor was higher than in conventional bioreactor, while docosahexaenoic acid (DHA) percentage in total lipids was lower than in conventional bioreactor. A multistage control strategy is subsequently implemented for the porous‐membrane‐impeller bioreactor, and the maximum biomass, DHA concentration, DHA percentage in biomass and DHA productivity reached 151.0 g/L, 44.3 g/L, 29.33%, 369.08 mg/(L·h), respectively. This study thus provides a highly efficient and economic bioreactor for the production of DHA by Schizochytrium sp. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4278–4286, 2017     

Effects of light quality on the accumulation of oil in a mixed culture of Chlorella sp. and Saccharomyces cerevisiae

BACKGROUND: Chlorella strains rather than terrestrial oil crops having higher oil content and shorter generation time have been considered as promising candidates for alternative biodiesel. Since the influence of light quality on oil formation of microalgae in either monoculture or mixed culture has been shown to be either inconsistent or ambiguous, a light‐emitting diode (LED) photo‐bioreactor with different light sources and intensities was used in this study to investigate a cost‐effective lipid production process. RESULTS: The oil accumulation in a mixed culture of Chlorella sp. and Saccharomyces cerevisiae was higher than that in the monoculture under the different light sources used. Results of the influence of light quality on the mixed culture indicated that the optimal light wavelength and intensity for biomass formation was red LED light at 1000 lux, whereas the optimum for oil formation was blue LED light at 1000 lux. A novel two‐stage LED photo‐bioreactor was thus proposed and the highest P_max and productivity in this study were obtained as 261 mg L^?1 and 8.16 mg L^?1 h^?1, respectively. CONCLUSION: A novel two‐stage LED photo‐bioreactor using a mixed culture to optimize microalgal oil production was proposed and successfully demonstrated in this study. Copyright © 2011 Society of Chemical Industry     

Analysis of process integration and intensification of enzymatic cellulose hydrolysis in a membrane bioreactor

Enzymatic cellulose hydrolysis has been studied for many years, generating rich literatures and knowledge in respect to the underlying reaction mechanism, reaction kinetics, and bioreactor systems. This paper attempts to offer some additional information and new understanding of how reaction kinetics and reactor productivity can be improved in a process involving simultaneous reaction and product separation using a purpose‐built membrane reactor with a single combined reaction zone and separation zone. Different operating strategies of batch, fed batch and continuous cellulose hydrolysis were investigated with intermittent or simultaneous removal of products (reducing sugars) to reduce enzyme inhibition and improve reactor productivity. The effect of continuous and selective product removal, reduced enzyme inhibition and higher enzyme concentration in retention were examined for the potential benefit in process integration and intensification in order to lower the high process cost of the enzymatic hydrolysis process, mainly due to slow reaction kinetics and expensive enzymes. A mathematical model was offered to account for the effect of selective product (reducing sugars) separation, permeate flux, reduced cellulase inhibition, dynamic structural change of the solid substrate and possible shear deactivation of the enzyme. Computer analysis was also carried out to analyse the quasi‐steady state of the reaction intermediates in order to gain an insight into the reaction mechanism in simultaneous reaction and separation systems. Some original analysis and simulation of the effect of membrane separation parameters on the overall reactor performance is offered, including the effect of membrane selectivity (rejection coefficient) and flux. Copyright © 2005 Society of Chemical Industry     

Characterization of sodium cellulose sulphate/poly‐dimethyl‐diallyl‐ammonium chloride biological capsules for immobilized cultivation of microalgae

BACKGROUND: Microalgae continue to be a focus of industrial bioprocess sustainability practice owing to the numerous biofuels and bioproducts that can be obtained with simultaneous environmental bioremediation applications. However, the extremely dilute nature of large volume microalgal cultures and the small particle size of single‐cell microalgae present technological and economic problems of effective dewatering, thus affecting the application of microalgae in process industries. Microalgae immobilization using biocompatible polymeric systems has proved to be an effective strategy to circumvent the heavy dewatering requirement, as this approach provides physical separation between the solid microalgal cells and the liquid medium. RESULTS: In this work, a novel microalgae immobilization carrier, sodium cellulose sulphate/poly‐dimethyl‐diallyl‐ammonium chloride (NaCS‐PDMDAAC) capsule, was synthesized and the resulting polymeric capsules were characterized using physicochemical techniques such as Fourier transform infrared spectroscopy (FT‐IR), scanning electron microscopy equipped with energy dispersive X‐ray spectroscopy (SEM‐EDX) and nuclear magnetic resonance spectroscopy (NMR). Experimental results showed that the unique properties of NaCS‐PDMDAAC capsules, such as pore size, capsule size, mechanical strength, and structural and compositional homogeneity, relevant to microalgae cultivation with batch or continuous nutrient removal can be accurately controlled. CONCLUSION: These polymeric capsules find applications not only with microalgae cultivation but also for other microorganisms. © 2012 Society of Chemical Industry     

The release of the blue biological pigment C‐phycocyanin through calcium‐aided cytolysis of live Spirulina sp.

C‐phycocyanin is a light‐harvesting phycobiliprotein found in, amongst other species, the cyanobacterium Spirulina sp. C‐phycocyanin is bright blue in colour and can be used as a natural blue colorant for a variety of applications. Various cell disruption methods exist to cause the lysis of the cyanobacterial cells and release of phycocyanin, but these methods have significant drawbacks, such as cost, difficulty in scale‐up, bacterial contamination, or risk of degrading the protein. This article outlines an alternative method for cell disruption based on the use of Ca(II), which lyses live Spirulina biomass, releasing phycocyanin at a range of concentrations (0.1–0.8 m ) over varying time periods, depending on the conditions. In comparison with other ionic species tested, Ca(II) performed best by a significant margin. Bead milling of biomass was used to quantify the maximum phycocyanin in the biomass, and the greatest was found to be ca. 90% released into solution after 48 h under 0.5 m Ca(II) in a 0.35 m acetate buffer at pH 6. Exposing Spirulina to sodium azide revealed that the mechanism of Ca(II) ion‐aided cytolysis is likely based on a metabolically driven process. This study demonstrates a potential processing option for the release of phycocyanin from live Spirulina, paving the way for the development of a novel bioprocess for the industrial production of the biological pigment.     

Energy demand management for process systems through production scheduling and control

Demand response (DR) is an integral part of the Smart Grid paradigm, and has become the focus of growing research, development, and deployment in residential, commercial and industrial systems over the last few years. In process systems, energy demand management through production scheduling is an increasingly important tool that has the potential to provide significant economic and operational benefits by promoting the responsiveness of the process operation and its interactions with the utility providers. However, the dynamic behavior of the underlying process, especially during process transitions, is seldom taken into account as part of the DR problem formulation. Furthermore, the incorporation of energy constraints related to electricity pricing and energy resource availability presents an additional challenge. The goal of this study is to present a novel optimization formulation for energy demand management in process systems that accounts explicitly for transition behaviors and costs, subject to time‐sensitive electricity prices and uncertainties in renewable energy resources. The proposed formulation brings together production scheduling and closed‐loop control, and is realized through a real‐time or receding‐horizon optimization framework depending on the underlying operational scenarios. The dynamic formulation is cast as a mixed‐integer nonlinear programming problem based on a proposed discretization approach, and its merits are demonstrated using a simulated continuous stirred tank reactor where the energy required is assumed to be roughly proportional to the material flow. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3756–3769, 2015     

The FluxMax approach for simultaneous process synthesis and heat integration: Production of hydrogen cyanide

Resource and energy efficiency are essential in process synthesis of chemical plants as they combine economic with ecological benefits. The two main targets of the process synthesis problem—mass and energy flux optimization—are typically split into two steps: single unit optimization and subsequent energy integration preventing the identification of the globally optimal solution. This article presents a single-step procedure for resource-efficient process synthesis through simultaneous heat and mass flux optimization called FluxMax approach (FMA), which is demonstrated for the production of hydrogen cyanide (HCN). The impact of simultaneous heat integration on the optimal process structure is demonstrated and two resource-optimal processes for HCN production are identified consisting of a combination of different reactor and recycling strategies reducing total variable cost by 68%. For convex objective functions, the globally most resource-efficient process is identified highlighting the potential of the FMA for site planning and retrofitting of existing plants.     

Strategies of valorization of sludge from wastewater treatment

Sludge is regarded as a potential source to achieve valorization via strategies such as resource recovery, sludge based adsorbents preparation, bioflucculants production, sludge manufacturing construction materials preparation, sludge composting and thermal valorization, which are currently common and effective strategies. Appropriate treatment strategies of sludge are of great importance worldwide for the fast growing population and rapidly increasing waste. This mini review summarized some widely used and effective strategies to achieve sludge valorization based on whether the strategy would utilize or reuse the potential of sludge to obtain valuable product and eliminate secondary pollution. Anaerobic digestion of sludge is perceived as a potentially cost‐effective method to achieve sludge reduction and resource recovery including carbon, nitrogen, phosphorus resource recovery coupled with other technologies. Utilizing sludge as raw material for preparation of valuable products including sludge based adsorbents, bioflocculants and construction materials is another aspect to achieve sludge valorization. Sludge composting and thermal valorization are also introduced in the mini review since the two strategies could also achieve sludge valorization. In addition, the strategies mentioned were discussed and analyzed in the mini review from environmental and economic aspects. © 2017 Society of Chemical Industry     

Quantitative Risk Assessment for Process Design Modification and Maintenance Optimization in Refineries and Petrochemical Plants

Quantitative risk assessment is methodology based on calculating probabilities and frequencies of sequential events using Boolean algebra, and it is normally used to perform safety assessments for complex interacting systems. Although quantitative risk assessment has been commonly used in aerospace and nuclear industries, it can also be used for quantifying economic risk and for estimating possibilities of potential production losses in a petrochemical or a manufacturing plant. In developing quantitative risk assessment models for petrochemical plants, component failures as well as human (operator) errors are taken into consideration in developing the plant's fault‐tree logic, in which is used to predict probabilities of future plant upsets. This paper shows how the quantitative risk assessment can be used to rank the economic importance of the production units in a refinery for prioritizing maintenance activities. In addition, two case studies are compared to demonstrate how a quantitative risk assessment model can be used as an invaluable tool in process design optimization. The quantitative risk assessment methodology developed in this work relates production losses to the performance of the major components and the process design. This application of the quantitative risk assessment provides a basis for the risk‐informed decision‐making and optimizing allocation of plant resources in support of plant operation and maintenance activities.     

Robust modeling of a microalgal heterotrophic fed-batch bioreactor

Microalgal feedstocks have shown potential for the production of biofuels and fine chemicals. Recently, an optimal experimental input profile for the identification of parameters of a microalgal bioreactor, containing 6 states and 12 unknown parameters has been proposed. In this work, the proposed design is implemented and parameters are estimated. It was found that the parameter estimation procedure can be made more computational efficient by the use of a novel iterative non-linear model reparameterization algorithm. By applying the proposed algorithm to experimental data, a good degree of output prediction was achieved along with bounds on the parameter values. The final, validated, model can be used for optimal control and process simulation.     

Practical application of aqueous two‐phase systems for the development of a prototype process for c‐phycocyanin recovery from Spirulina maxima

A novel process for the recovery of c‐phycocyanin from Spirulina maxima exploiting aqueous two‐phase systems (ATPS), ultrafiltration and precipitation was developed in order to reduce the number of unit operations and benefit from an increased yield of the protein product. The evaluation of system parameters such as PEG molecular mass, concentration of PEG as well as salt, system pH and volume ratio was carried out to determine under which conditions the c‐phycocyanin and contaminants concentrate to opposite phases. PEG1450–phosphate ATPS proved to be suitable for the recovery of c‐phycocyanin because the target protein concentrated in the top phase whilst the cell debris concentrated in the bottom phase. A two‐stage ATPS process with a phase volume ratio (V_r) equal to 0.3, PEG1450 7% (w/w), phosphate 20% (w/w) and system pH of 6.5 allowed c‐phycocyanin recovery with a purity of 2.4 (estimated as the relationship of the 620 nm to 280 nm absorbances). The use of ultrafiltration (with a 30 kDa membrane cut‐off) and precipitation (with ammonium sulfate) resulted in a recovery process that produced a protein purity of 3.8 ± 0.1 and an overall product yield of 29.5% (w/w). The results reported here demonstrated the practical implementation of ATPS for the design of a prototype recovery process as a first step for the commercial purification of c‐phycocyanin produced by Spirulina maxima. © 2001 Society of Chemical Industry     

Hybrid simulation-optimization based approach for the optimal design of single-product biotechnological processes

In this work, we present a systematic method for the optimal development of bioprocesses that relies on the combined use of simulation packages and optimization tools. One of the main advantages of our method is that it allows for the simultaneous optimization of all the individual components of a bioprocess, including the main upstream and downstream units. The design task is mathematically formulated as a mixed-integer dynamic optimization (MIDO) problem, which is solved by a decomposition method that iterates between primal and master sub-problems. The primal dynamic optimization problem optimizes the operating conditions, bioreactor kinetics and equipment sizes, whereas the master levels entails the solution of a tailored mixed-integer linear programming (MILP) model that decides on the values of the integer variables (i.e., number of equipments in parallel and topological decisions). The dynamic optimization primal sub-problems are solved via a sequential approach that integrates the process simulator SuperPro Designer^® with an external NLP solver implemented in Matlab^®. The capabilities of the proposed methodology are illustrated through its application to a typical fermentation process and to the production of the amino acid L-lysine.     

Simultaneous mixed-integer dynamic optimization for environmentally benign electroplating

Hoist scheduling, especially cyclic hoist scheduling (CHS), is used to maximize the manufacturing productivity of electroplating processes. Water-reuse network design (WRND) for the electroplating rinsing system targets the optimal water allocation, such that fresh water consumption and wastewater generation are minimized. Currently, there is still a lack of studies on integrating CHS and WRND technologies for electroplating manufacturing. In this paper, a multi-objective mixed-integer dynamic optimization (MIDO) model has been developed to integrate CHS and WRND technologies for simultaneous consideration of productivity and water use efficiency for environmentally benign electroplating. The orthogonal collocation method on finite elements is employed to convert the MIDO problem into a mixed-integer nonlinear programming (MINLP) problem. The efficacy of the methodology is demonstrated by solving a real electroplating example. It demonstrates that the computational methods of production scheduling, process design, and dynamic optimization can be effectively integrated to create economic and environmental win-win situations for the electroplating industry.     

State‐of‐the‐art and progress in the optimization‐based simultaneous design and control for chemical processes

Significant progress in the area of simultaneous design and control for chemical processes has been achieved and various methodologies have been put forward to address this issue over the last several decades. These methods can be classified in two categories (1) controllability indicator‐based frameworks that are capable of screening alternative designs, and (2) optimization‐based frameworks that integrate the process design and control system design. The major objective is to give an up‐to‐date review of the state‐of‐the‐art and progress in the challenging area of optimization‐based simultaneous design and control. First, motivations and significances of simultaneous design and control are illustrated. Second, a general classification of existing methodologies of optimization‐based simultaneous design and control is outlined. Subsequently, the mathematical formulations and relevant theoretical solution algorithms, their merits, strengths and shortcomings are highlighted. Last, based on the recent advances in this field, challenges and future research directions are discussed briefly. An attempt is made with the help of this review article to stimulate further research and disseminate the simultaneous design methods to challenging problem areas. In particular, the application of optimization‐based simultaneous design and control methods to large‐scale systems with highly inherent nonlinear dynamics often the case in industrial chemical processes remains a challenging task and yet to be solved. © 2012 American Institute of Chemical Engineers AIChE J, 58: 1640–1659, 2012     

Dynamic real‐time optimization with closed‐loop prediction

Process plants are operating in an increasingly global and dynamic environment, motivating the development of dynamic real‐time optimization (DRTO) systems to account for transient behavior in the determination of economically optimal operating policies. This article considers optimization of closed‐loop response dynamics at the DRTO level in a two‐layer architecture, with constrained model predictive control (MPC) applied at the regulatory control level. A simultaneous solution approach is applied to the multilevel DRTO optimization problem, in which the convex MPC optimization subproblems are replaced by their necessary and sufficient Karush–Kuhn–Tucker optimality conditions, resulting in a single‐level mathematical program with complementarity constraints. The performance of the closed‐loop DRTO strategy is compared to that of the open‐loop prediction counterpart through a multi‐part case study that considers linear dynamic systems with different characteristics. The performance of the proposed strategy is further demonstrated through application to a nonlinear polymerization reactor grade transition problem. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3896–3911, 2017     

Optimal processing pathway for the production of biodiesel from microalgal biomass: A superstructure based approach

In this study, we propose a mixed integer nonlinear programming (MINLP) model for superstructure based optimization of biodiesel production from microalgal biomass. The proposed superstructure includes a number of major processing steps for the production of biodiesel from microalgal biomass, such as the harvesting of microalgal biomass, pretreatments including drying and cell disruption of harvested biomass, lipid extraction, transesterification, and post-transesterfication purification. The proposed model is used to find the optimal processing pathway among the large number of potential pathways that exist for the production of biodiesel from microalgae. The proposed methodology is tested by implementing on a specific case with different choices of objective functions. The MINLP model is implemented and solved in GAMS using a database built in Excel. The results from the optimization are analyzed and their significances are discussed.     

双极膜电渗析技术在工业高含盐废水中的应用

双极膜电渗析（BMED）作为新型膜分离技术,可将盐转变为相应的酸和碱,围绕BMED技术在工业高含盐废水领域的应用已逐渐成为热点,但在实际应用中还存在一些亟需解决的难点。本文主要介绍了近年来BMED技术在处理工业高含盐废水领域的研究现状,提出和探讨了限制BMED技术在该领域大规模工业化应用的3个关键性问题,即与酸碱浓度和纯度有关的技术问题、与过程成本有关的技术经济性问题以及与投资成本有关的经济性问题。针对这3个问题,指出BMED技术未来发展方向应致力于降低双极膜成本,减弱或消除离子交换膜同离子泄漏及水迁移过程。对于现阶段而言,将制备的酸碱回用于系统内部,是解决酸碱品质较低而未能商品化的主要途径,同时该过程可节省酸碱外购费用,弥补BMED技术投资成本过高问题。     

A bioprocessing mode for simultaneous fungal biomass protein production and wastewater treatment using an external air‐lift bioreactor

A pilot plant investigation for bioprocessing has been undertaken to develop a simple, non‐aseptic, low‐cost single process for production of fungal biomass protein (FBP) and wastewater treatment using starch processing wastewater. It has been confirmed that the newly developed external air‐lift bioreactor was very suitable for bioconversion of starch materials and FBP production by the microfungi Aspergillus oryzae and Rhizopus arrhizus. Bioproduct yields of 8.5 g dm^?3 of FBP that contained 46–50% protein were obtained within a comparatively short retention time. A fungal biomass productivity in a range of 0.85–0.92 g dm^?3 h^?1 and removals of total suspended solids and 95% COD were achieved in batch, semi‐continuous and continuous processes. The operation modes of the semi‐continuous and continuous processes demonstrated a high biological dynamics in fungal biomass productivity and COD reduction. The semi‐continuous process appeared to be the most practical mode. © 2001 Society of Chemical Industry