Decision support for integrated refinery supply chains: Part 2. Design and operation

Supply chain management has continually attracted much attention as companies are constantly looking into areas where they can cut costs and improve profit margin while maintaining customer satisfaction. Optimizing design and operation of the supply chain is vital for this purpose. Simulation models that capture the dynamics and uncertainties of the supply chain can be used to effectively conduct design and operation optimization studies. In Part 1 of this two-part paper, we proposed an integrated refinery supply chain dynamic simulator called Integrated Refinery In-Silico (IRIS). Here, we demonstrate the application of IRIS to provide decision support for optimal refinery supply chain design and operation based on a simulation–optimization framework. Three case studies are presented: identifying the optimal strategy to deal with supply disruptions, optimization of design decisions regarding additional capacity investments, and optimization of policies’ parameters. These decisions are optimized for two objectives: profit margin and customer satisfaction. The framework consists of a linkage between IRIS and a non-dominated sorting genetic algorithm, implemented in a parallel computing environment for computational efficiency. Results indicate that the proposed framework works well for supporting policy and investment decisions in the integrated refinery supply chain.     

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.     

Fleet sizing in chemical supply chains using agent-based simulation

Fleet sizing is an essential element of chemical supply chain management. It is expensive to purchase and maintain tank cars. Further, the sizing decision is not an isolated one and is closely linked to fleet routing, inventory management and other aspects of logistics and supply chain management. Traditional methods to determine the size of fleets rely on coarse models of the supply chain. In this paper, we present a detailed agent-based simulation model of a multisite chemical supply chain that brings out the intricacies of the tank car fleet sizing problem. The model explicitly takes into account the independent decision making of the different entities as well as the interactions across operations such as replenishment planning and order assignment. Our simulation studies show that different fleet sizes and routing policies can have significant impact on the overall performance of the supply chain including on customer satisfaction and plant performance.     

Decision support for the development,simulation and optimization of dynamic process models

Simulation is besides experimentation the major method for designing,analyzing and optimizing chemical processes.The ability of simulations to reflect real process behavior strongly depends on model quality.Validation and adaption of process models are usually based on available plant data.Using such a model in various simulation and optimization studies can support the process designer in his task.Beneath steady state models there is also a growing demand for dynamic models either to adapt faster to changing conditions or to reflect batch operation.In this contribution challenges of extending an existing decision support framework for steady state models to dynamic models will be discussed and the resulting opportunities will be demonstrated for distillation and reactor examples.     

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.     

Advances on modeling and simulation of alcoholic distillation. Part 1: Thermodynamic modeling

Several studies done in the literature on the simulation of distillation processes of interest in the alcoholic food industry are reviewed, with emphasis on the advances done by the authors group on the thermodynamic modeling of water + ethanol + congener mixtures. In wine and must distillation the presence of polar substances found in the mixture to be distilled and the very low concentration of many components (different from ethanol and water), called congeners, make it difficult to model these mixtures, for simulation and design purposes. This is probably the main cause for the little progress done in obtaining accurate simulation of alcohol distillation processes. This review discusses the availability of appropriate data for modeling these processes, analyzes the different models available and their capabilities. Conclusions on the accuracy of the most appropriate models and recommendations for current and future studies are provided.     

Economic model predictive control for inventory management in supply chains

In this paper, we propose economic model predictive control with guaranteed closed-loop properties for supply chain optimization. We propose a new multiobjective stage cost that captures economics as well as risk at a node, using a weighted sum of an economic cost and a tracking stage cost. We also demonstrate integration of scheduling with control using a supply chain example. We integrate a scheduling model for a multiproduct batch plant with a control model for inventory control in a supply chain. We show recursive feasibility of such integrated control problems by developing simple terminal conditions.     

Strategic optimisation of biomass-based energy supply chains for sustainable mobility

The identification of alternative and sustainable energy sources has been one of the fundamental research goals of the last two decades, and the transport sector plays a key role in this challenge. Electric cars and biofuel fed vehicles may contribute to tackle this formidable issue. According to this perspective, a multi-echelon supply chain is here investigated considering biomass cultivation, transport, conversion into bioethanol or bioelectricity, distribution, and final usage in alternative bifuel (ethanol and petrol) and electric vehicles. Multiperiod and spatially explicit features are introduced in a Mixed Integer Linear Programming (MILP) modelling framework where economic (in terms of Net Present Value) and environmental (in terms of Greenhouse Gases emissions) objectives are simultaneously taken into account. The first and second generation bioethanol production supply chain is matched with a biopower production supply chain assessing multiple technologies. Both corn grain and stover are considered as biomass sources. In the environmental analysis, the impact on emissions caused by indirect Land Use Change (iLUC) effects is also assessed. Results will show the efficacy of the methodology at providing stakeholders with a quantitative tool to optimise the economic and environmental performance of different supply chain configurations.     

Advances on modeling and simulation of alcoholic distillation. Part 2: Process simulation

Several studies developed by the authors on the application of process simulators to the distillation processes of alcoholic mixtures are analyzed and discussed in this second part of the series on advances on modeling and simulation of alcoholic distillation. Three study cases are presented and discussed to show the usefulness of simulation packages, and in particular of ChemCAD: (i) production of whisky in a sequence of double batch distillation; (ii) production of brandy in a single continuous column; and (iii) production of neutral spirits in a sequence of multiple columns (concentrator, light component separator, and rectification column). In all cases the selection of the thermodynamic models considered previous studies as discussed in Part 1 of the series in which the NRTL model was recommended for phase equilibrium modeling. Applications of two industrial and pilot plant cases are presented, so the validity of the simulations and the appropriateness of the thermodynamic and process simulation studies presented in this series of papers. The main conclusion of the study is that simulators can play an important role in understanding alcoholic distillation processes, in optimizing resources and in making distillation of wine and musts a more efficient process.     

A heuristic-based algebraic targeting technique for aggregate planning in supply chains

Process integration techniques have seen its establishment in many non-conventional applications in the last decade. One of the newest applications of process integration technique is in the area of supply chain management. The well-established pinch analysis tools of composite curves and grand composite curves have been demonstrated their adaptability in this new area. Although the graphical tools provide many important insights for production planners, the common limitations of these graphical tools such as inaccuracy and being cumbersome need to be overcome. This calls for an algebraic targeting approach presented in this paper, known as the supply chain cascade analysis to supplement the various graphical tools. The cascade analysis technique sets targets for a supply chain. Besides, other new insights such as minimum and maximum inventory as well as the scheduling of process shut down are being introduced in this paper. Two industrial case studies are presented to illustrate the proposed method.     

Hot plate welding of polypropylene. Part II: Process simulation

A volume of fluid finite difference method based computer code was developed to simulate the heat transfer and squeezing flow in the hot-plate welding process. The simulation results include melt displacement, temperature distribution, and stress build-up and relaxation. By implementing the crystallization kinetic model developed in Part I, the formation of stress-induced crystal structure in the heat affected zone can be revealed.     

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.     

Enzyme immobilization: Part 1. Modified bentonite as a new and efficient support for immobilization of Candida rugosa lipase

Immobilization of Candida rugosa lipase onto modified and unmodified bentonites is described. The effect of hydrophilic or hydrophobic nature of the support, the reuse efficiency, and kinetic behavior of immobilized lipase were studied. The modified bentonite with monolayer surfactant (BMS), was the best support, for immobilization. The activity of the immobilized enzyme was examined under varying experimental conditions. The effect of various factors such as concentration of enzyme solution, pH and temperature, stirring and various thermodynamic parameters were also evaluated. The activity of lipase on Na-bentonite, on BMS and on bentonite with bilayer surfactant (BBS) at the optimum pH was 7.2%, 56.6% and 3.6%, respectively. The adsorption isotherm was modelled by the Langmuir equation. The amounts of immobilized lipase on Na-bentonite, BMS and BBS at the highest activity were 42.6%, 61.2% and 28.3%, respectively. The effect of substrate concentration on enzymatic activity of the free and immobilized enzymes showed a good fit to the Michaelis–Menten plots. The immobilized enzyme exhibited an activity comparable to the free enzyme after storage at 30 °C. The thermal stability of free and immobilized lipase were also studied.     

典型炼化一体化企业生产低硫船用燃料油的重油加工方案比较

基于低硫重质船用燃料油生产需要以及炼厂最大化生产重整原料和乙烯裂解原料转型升级背景,本文针对典型炼化一体化企业生产低硫船用燃料油,分别采用沸腾床和浆态床的不同重油加工方案从产品分布、产品性质及后续加工路线等进行经济性分析。结果表明,相比于浆态床加氢方案,尽管沸腾床渣油加氢转化率低于浆态床,但由于转化后的产品中干气收率低、各种馏分油的氮含量显著低于浆态床方案,且可以直接生产低硫船用燃料油、不存在废渣处理等优势,此外,耗氢较低,同时航煤、石脑油及芳烃产量增量明显,以50美元效益测算价测算,沸腾床方案扣消费税毛利较浆态床方案高16.13亿元。可见,对于有低硫船用燃料油生产需求的炼化企业,采用沸腾床重油加工路线在经济性方面更具竞争力。     

城镇给水厂集约化设计实例

基于全流程、全立体、全厂界的给水厂集约化理念,针对城镇中心城区超大型水厂原址的升级改造工程,采取了高效工艺优化、功能的拓展集成、紧凑的总图布置、空间的三维利用等方法,各个单元之间组合出叠合式、组团式、合建式等综合池型,有效提高了土地利用率,万吨水占地面积指标为1 600 m2。建成运行后,出厂水水质指标达到GB 5749—2006《生活饮用水卫生标准》,其中浊度≤0.1 NTU、色度≤5倍、ρ（CODMn）≤1.5mg/L、ρ（NH3-N）≤0.3 mg/L、ρ（Mn）≤0.05 mg/L。     

Integrated safety stock management for multi-stage supply chains under production capacity constraints

In the petrochemical, chemical and pharmaceutical industries, supply chains typically consist of multiple stages of production facilities, warehouse/distribution centers, logistical subnetworks and end customers. Supply chain performance in the face of various market and technical uncertainties is usually measured by service level, that is, the expected fraction of demand that the supply chain can satisfy within a predefined allowable delivery time window. Safety stock is introduced into supply chains as an important hedge against uncertainty in order to provide customers with the promised service level. Although a higher safety stock level guarantees a higher service level, it does increase the supply chain operating cost and thus these levels must be suitably optimized.The complexities in safety stock management for multi-stage supply chain with multiple products and production capacity constraints arise from: (1) the nonlinear performance functions that relate the service level, expected inventory with safety stock control variables at each site; (2) the interdependence of the performances of different sites; and (3) finally the margin by which production capacity exceeds the uncertain demand. Given the complexities, the integrated management of safety stocks across the supply chain imposes significant computational challenges. In this research, we propose an approach in which the evaluation of the performance functions and the decision on safety stock related variables are decomposed into two separate computational frameworks. For evaluating the performance functions, off-line computation using a discrete event simulation model is proposed. A linear programming based safety stock management model is developed, in which the safety stock control variables (the target inventory levels used in production planning and scheduling models, base-stock levels for the base-stock policy at the warehouses) and service levels at both plant stage and warehouse stages are used as important decision variables. In the linear programming model, the nonlinear performance functions, interdependence of the performances, and the safety production capacity limits in safety stock management are properly represented.To demonstrate the effectiveness of the proposed safety stock management model, a case study of a realistically scaled polymer supply chain problem is presented. In the case problem, the supply chain is composed of two geographically separated production sites and 3–8 warehouses supplying 10 final products to 30 sales regions.     

Scenario-based dynamic negotiation for the coordination of multi-enterprise supply chains under uncertainty

A novel scenario-based dynamic negotiation approach is proposed for the coordination of decentralized supply chains under uncertainty. The relations between the involved organizations (client, provider and third parties) and their respective conflicting objectives are captured through a non-zero-sum and non-symmetric roles SBDN negotiation. The client (leader) designs coordination agreements considering the uncertain reaction of the provider (follower) resulting from the uncertain nature of the third parties, which is modeled as a probability of acceptance function. Different negotiation scenarios are studied: (i) cooperative, and (ii) non-cooperative and (iii) standalone cases. The use of the resulting models is illustrated through a case study with different vendors around a “leader” (client) in a decentralized scenario. Although the usual cooperation hypothesis will allow higher overall profit expectations, using the proposed approach it is possible to identify non-cooperative scenarios with high individual profit expectations which are more likely to be accepted by all individual partners.