Decision support for integrated refinery supply chains: Part 1. Dynamic simulation

Supply chain studies are increasingly given top priority in enterprise-wide management. Present-day supply chains involve numerous, heterogeneous, geographically distributed entities with varying dynamics, uncertainties, and complexity. The performance of a supply chain relies on the quality of a multitude of design and operational decisions made by the various entities. In this two-part paper, we demonstrate that a dynamic model of an integrated supply chain can serve as a valuable quantitative tool that aids in such decision-making. In this Part 1, we present a dynamic model of an integrated refinery supply chain. The model explicitly considers the various supply chain activities such as crude oil supply and transportation, along with intra-refinery supply chain activities such as procurement planning, scheduling, and operations management. Discrete supply chain activities are integrated along with continuous production through bridging procurement, production, and demand management activities. Stochastic variations in transportation, yields, prices, and operational problems are considered in the proposed model. The economics of the refinery supply chain includes consideration of different crude slates, product prices, operation costs, transportation, etc. The proposed model has been implemented as a dynamic simulator, called Integrated Refinery In-Silico (IRIS). IRIS allows the user the flexibility to modify not only parameters, but also replace different policies and decision-making algorithms in a plug-and-play manner. It thus allows the user to simulate and analyze different policies, configurations, uncertainties, etc., through an easy-to-use graphical interface. The capabilities of IRIS for strategic and tactical decision support are illustrated using several case studies.     

Toward integrated production and distribution management in multi-echelon supply chains

The effective management of multi-site systems involves the proper coordination of activities performed in multiple factories, distribution centers (DCs), retailers and end-users located in many different cities, countries and/or continents. To optimally manage numerous production and transportation decisions, a novel monolithic continuous-time MILP-based framework is developed to determine the best short-term operational planning to meet all customer requests at minimum total cost. The formulation lies on the unit-specific general precedence concept for the production scheduling problem whereas the immediate precedence notion is used for transportation decisions. To illustrate the applicability and potential benefits of the model, a challenging example corresponding to a supply chain comprising several locations geographically spread in six European countries has been solved to optimality with modest CPU times. Several scenarios with different logistics features were addressed in order to remark the significant advantages of using the integrated approach.     

Developing an integrated capacity planning framework for production processes and demand supply chains

This paper presents a new capacity planning framework integrating internal production processes and external demand supply chains. Since planning is concerned with preparing how resources are arranged before future situations are realized, the planning problem should consider the entire aspect of a company, including internal and external aspects. Most previous works focused on only one aspect by simplifying the other. The proposed framework is formulated as a mixed integer programming (MILP) problem with an aim to establishing a rigorous decision-making tool. Lessons learned during their industrial implementations are discussed with some remarks.     

Agent-based supply chain management—2: a refinery application

The refinery business involves tasks that span several departments and process large amount of data. Among others, these include crude procurement, logistics and scheduling (storage, distillation units, etc.). Current refinery decision support systems (DSSs) fail to integrate all the decision-making processes of a refinery, to interface with other systems in place, to incorporate dynamic data from various sources and to assist different departments concurrently. In part 1 of this two-part paper, we proposed an agent-based framework for supply chain DSSs. Here, we demonstrate its application through a prototype DSS, called petroleum refinery integrated supply chain modeler and simulator or PRISMS, for crude procurement. PRISMS serves as a central DSS through which all processes of a refinery can be studied and enables integrated decisions with respect to the overall refinery business. In particular, PRISMS can be used to study the effects of internal policies of the refinery and its various departments. We illustrate this through three detailed ‘what-if’ studies that provide an insight into how the business responds to changes in policies, exogenous events and plant modifications.     

Optimal operation of integrated processing systems: Part II: Closed-loop on-line optimizing control

A method for tracking the economically optimal operating conditions of a chemical process in the presence of constraints is developed. The technique is based on an on-line search rather than a fundamental model. The most profitable operating point is found by fitting a dynamic model of the process based on data obtained from experimental moves on the plant. This model is used to compute gradients of the economic objective and of the constraints so that a direction of economic improvement inside the allowed operating region of the plant is always obtained. Constraint violations during the transients are prevented by a multivariable regulator. A new regulation method (Internal Model Control) is used which permits explicit handling of constraints and which can be made robust against modelling errors. This combined optimization/regulation approach is tested in a demonstrative simulation example and shown to be reliable for following a moving optimum and safely handling complex constraint moves.     

An integrated flow reactor-membrane filtration system for heterogeneous photocatalysis. Part II: Experiments on the ultrafiltration unit and combined operation

A batch-recirculated photoreactor was combined with a hollow-fibre membrane ultrafiltration (UF) unit for heterogeneous photocatalysis applications. This paper focuses on the operation and modelling of the UF process component and on the performance of the integrated photoreactor–UF process assembly. Methylene blue and titanium dioxide (Degussa P-25) were used as the test pollutant and photocatalyst, respectively. The influence of cross-flow velocity, transmembrane pressure, and TiO₂ dose on the permeate flux through the hollow fibre membrane is described. These data are modelled on the basis of concentration polarization and gel layer formation at the membrane surface/feed slurry boundary. The operation of the integrated photoreactor–UF assembly over ten repeat cycles is described. Photocatalyst separation was complete as gauged by nephelometric turbidity measurements. However, a systematic degradation in the photocatalyst performance was noted with each repeat cycle. Dynamic laser light scattering data are consistent with agglomeration of the TiO₂ particles as a result of the UF process, and suggest a possible factor in the degraded photocatalytic activity. Possible solutions to this problem are finally presented.     

基于分子矩阵的炼油过程全厂模拟与优化

利用物流分子矩阵对多个生产单元过程进行建模,将单元过程的分子矩阵模型和全厂模拟优化相结合,采用分解优化策略对原料、产品和操作参数等进行优化.分子矩阵为模拟优化提供了更详尽的信息,尤其加强了对环境影响和产品质量的考虑.结果表明分子信息有助于掌握物质在炼油过程中的变化情况,基于分子矩阵模型的优化可以在满足产品质量和环境要求的条件下最大程度地提高企业的效益.     

Options analysis for long-term capacity design and operation of a lignocellulosic biomass refinery

The growth of the lignocellulosic fuels has been hindered by technological and market uncertainty. This paper optimizes strategic investment decisions by prospective biobased fuel and chemical enterprises. A real options-based stochastic integer programming model is developed in this paper. We model a hypothetical, vertically integrated lignocellulosic enterprise that produces cellulosic ethanol and biosuccinic acid. Uncertainty is represented in bioproduct demands and prices. Strategic options including investment in research and development, investments in a flexible production platform and deferral of project investment are modeled. A hypothetical market model is also developed to correlate crude oil prices with the evolution of bioproduct markets. The discounted value of equity free cash flows is optimized. The optimal results include multiple capacity design plans based on the long term evolution of bioproduct markets. Monte Carlo simulations are also conducted to quantify the risk adjusted NPV's and returns on investment for the optimal capacity design trajectories.     

Resume of total operation of waste treatment facility for animal and vegetable oil refinery

A 2 year study in cooperation with the U.S. Environmental Protection Agency has been conducted to define and treat effluent from one of Swift’s edible oil refineries. As a result of this study, the existing treatment system was modified to produce effluent suitable for discharge to the Kankakee, Ill., sanitary district and at the same time eliminate surcharges and the need for a lagoon. The treatment system consists of a skim tank which is cathodically protected, automatic pH and chemical addition control, and an air flotation cell also cathodically protected. Provisions also were made to recover the inedible oil for sale as a by-product. The skimmings from the skim tank and from the air flotation cell are acid treated, heated, and centrifuged to recover 7–10,000 lb/day of inedible oil. Sale of recovered inedible oil can cover 60–80% of the direct costs of operation of the waste treatment system. Recent improvements in the system have reduced the cost of treatment even further and rasied effluent quality. With impressed current and chemicals, the biochemical oxygen demand is reduced from 3300 to 150, fats, oils, and greases from 2500 to 75, and suspended solids from 3000 to 150 ppm. One of seven papers presented in the symposium, “Ecology-Practical Solutions to Environmental Problems as Practiced in the Fats and Oils Industry” at the AOCS Spring Meeting, Mexico City, Mexico, April 1974.     

供应链优化技术研究及应用--润滑油企业物流优化

当前供应链管理和优化已成为一个企业最根本、最核心的竞争力,引起世界各国工业界和学术界的重视.但供应链优化与供应链管理的不同之处在于优化是要去除供应链流程中的非增值环节.为了降低生产成本、提高产品质量,根据润滑油企业物流特点和存在问题,提出在加强库存管理的基础上,实现物流优化.以中国石化供应链管理软件为例,论述了在21世纪全球一体化的知识经济浪潮中,供应链优化是石化流程企业立于不败之地的必由之路.     

Fair profit allocation in supply chain optimization with transfer price and revenue sharing: MINLP model and algorithm for cellulosic biofuel supply chains

A mixed‐integer nonlinear programming (MINLP) formulation to simultaneously optimize operational decisions as well as profit allocation mechanisms in supply chain optimization, namely material transfer prices and revenue share policies among the supply chain participants is proposed. The case of cellulosic bioethanol supply chains is specifically considered and the game‐theory Nash bargaining solution approach is employed to achieve fair allocation of profit among the collection facilities, biorefineries, and distribution centers. The structural advantages of certain supply chain participants can be taken into account by specifying different values of the negotiation‐power indicators in the generalized Nash‐type objective function. A solution strategy based on a logarithm transformation and a branch‐and‐refine algorithm for efficient global optimization of the resulting nonconvex MINLP problem is proposed. To demonstrate the application of the proposed framework, an illustrative example and a state‐wide county‐level case study on the optimization of a potential cellulosic bioethanol supply chain in Illinois are presented. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3211–3229, 2014     

Decision support framework for coordinated production and transport scheduling in SCM

The efficient coordination of production and distribution systems becomes a challenging problem as companies move towards higher collaborative and competitive environments. Focusing on the operational level of supply chain management (SCM), a framework is proposed to address the interrelated production and transport scheduling problems from the perspective of a production plant of a multi-site system that owns, or leases on a long-term basis, a fleet of vehicles to distribute the products. This framework aims to support the coordination of production and transport activities to properly manage the inventory profiles and material flows between sites. Both production and transport problems are defined as detailed scheduling problems, and different algorithms, either mathematical or heuristic-based, can then be used for their resolution. The flexibility and applicability of the proposed modeling framework is illustrated through two different case studies, which highlight the benefits of coordinating both activities in such a complex supply chain (SC) environment.     

Study of three-dimensional polystyrene networks containing linear chains: 2. Relaxation spectrum of linear chains

A study of the relaxation phenomenon in polystyrene networks containing linear polystyrene chains of high molecular weight has been carried out using measurements in methylcyclohexane and in the dry state by dynamic sinusoidal deformation and static stress relaxation. It is shown that the relaxation of the free chains contained in the network is (i) proportional to (1 ? v²₂) where v₂ is the volume fraction of the crosslinked network in the dry state, and (ii) depends very little on their concentration in the network. The distribution of relaxation time shows a peak related to the glass transition of the networks and a second peak corresponding to the spectrum of the linear chains of high molecular weight.     

knowledge-based expert system for dyeing of cotton. Part 1: Design and development

Artificial intelligence-based computer programs, called expert systems, have received a great deal of attention and have been used to solve an impressive array of problems in a variety of fields. Diagnosis was one of the first subjects to be investigated after the availability of digital computers, with the advent of artificial intelligence as well as the expert system technology. A knowledge-based expert system for diagnosing problems in the dyeing of cotton has been designed and developed. The performance of the system has been tested and evaluated by human experts and is deemed to be highly satisfactory. This provides a starting point for further improvements in the system.     

A learning feedforward control strategy for the concentration control of recycle reactors. Part III: Implementation and operation

In order to verify its performance, the learning feedforward control strategy was applied to the catalytic methanation of CO-rich synthesis gas. Details of the implementation in hardware as well as in software are discussed. The experimental results confirm the functionality of the learning feedforward control. Suggestions are given for further improvement of the control strategy.     

An integrated flow reactor-membrane filtration system for heterogeneous photocatalysis. Part I: Experiments and modelling of a batch-recirculated photoreactor

A two-part study was undertaken to examine the feasibility of combining a batch-recirculated photoreactor with a hollow-fibre membrane based ultrafiltration unit for heterogeneous photocatalysis applications. Methylene Blue (MB) and titanium dioxide (Degussa, P-25) were used as the test substrate and photocatalyst respectively for this study. This paper, which forms Part I of this study, describes the influence of MB concentration, recirculation flow rate, TiO2 dose, solution volume in the reservoir and solution pH on the photocatalytic reaction rate. The dark adsorption of MB on the TiO2 particle surface was also analysed. The combination of the reservoir and the annular reaction vessel could be modelled as a continuous flow stirred tank in series with a plug-flow reactor. This model predicts that the reaction rate should increase with a decrease of solution volume in the reservoir, both in the low and high substrate concentration regimes of the Langmuir–Hinshelwood kinetics formalism. This prediction was borne out by the experimental data for the low concentration regime. Part II of this series will describe experiments and modelling of the UF unit, and the operation of the combined system, respectively.     

Polycarbonate nanocomposites: Part 2. Degradation and color formation

Polycarbonate nanocomposites were prepared using two different twin screw extruders from a series of organoclays based on sodium montmorillonite, with somewhat high iron content, exchanged with various amine surfactants. It seems that a longer residence time and/or broader residence time distribution are more effective for dispersing the organoclay. The effects of organoclay structure on color formation during melt processing were quantified using colorimeter and UV-Vis spectroscopy techniques. Color formation in the PC nanocomposites depends on the type of organoclay and the type of pristine clay employed. Double bonds in the hydrocarbon tail of the surfactants lead to more darkly colored materials than saturated surfactants. The most severe color was observed when using a surfactant containing hydroxy-ethyl groups and a hydrocarbon tail derived from tallow. Molecular weight degradation of the PC matrix during melt processing produces phenolic end groups which were tracked by UV-Vis spectroscopy. Greater dispersion of the clay generally led to higher reduction in molecular weight due to the increased surface area of clay exposed; however, for color, the situation is far more complex. Hydroxy-ethyl groups and tallow unit on the surfactant lead to more degradation. A selected series of organoclays based on synthetic clay Laponite^® and calcium montmorillonite from Texas (TX-MMT) were also prepared to explore the effects of the clay structure. Laponite^® and TX-MMT produce less color formation in PC nanocomposites than montmorillonite probably due to lower content of iron. Dynamic rheological properties support the trends of molecular weight degradation and dispersion of clay.     

电厂补给水反渗透系统的优化运行与清洗

反渗透膜污染是电厂补给水反渗透系统应用中最大的问题之一。对反渗透膜的污染及其化学清洗方法进行了综述,主要内容包括反渗透膜污染物的种类、污染物形成的原因以及清洗时机的选取、清洗药品的选择、影响清洗效果的主要因素、清洗系统构成、清洗方法和清洗效果的评价,并提出了几种防护措施。