Integrated campaign planning and resource allocation in batch plants

Operational planning in batch plants has been studied extensively in the literature. However, the focus has largely been on developing better formulations and solution approaches for large examples. This work attempts to capture the key aspects of the industrial planning activity such as interactions among the planner and other stakeholders and the effect of resource allocation on process performance. We present a simple mathematical formulation for integrated resource allocation and campaign planning in multiproduct batch plants. Our model enables decision support pertaining to campaign scheduling, sequence-dependent changeovers, key resource allocations, scheduled maintenance, inventory profiles with safety stock limitations, and new product introductions. To demonstrate the performance of our mathematical model, we consider a case study from a typical specialty chemical plant from the lube industry. We validate our approach using a series of dynamic business and market scenarios with planning horizons of up to 2 years.     

Design and operation of a stochastic hydrogen supply chain network under demand uncertainty

The design of a future hydrogen supply chain (HSC) network is challenging due to the: (1) involvement of many echelons in the supply chain network, (2) high level of interactions between the supply chain components and sub-systems, and (3) uncertainty in hydrogen demand. Most of the early attempts to design the future HSC failed to incorporate all these challenges in a single generic optimization framework using mathematical modeling approach. Building on our previous multiperiod MILP model, the model presented in this paper is expanded to take into account uncertainty arising from long-term variation in hydrogen demand using a scenario-based approach. The model also adds another echelon: fueling stations and local distribution of hydrogen. Our results show that the future HSC network is somewhat similar to the existing petroleum infrastructure in terms of production, distribution, and storage. In both situations, the most feasible solution is centralized production plants with truck and rail delivery and small-to-large storage facilities. The main difference is that the future hydrogen supply has the benefits of using distributed forecourt production of hydrogen at local fueling stations via several production technologies. Finally, the performance of the studied models was evaluated using sensitivity and risk analyses.     

Robust policies for a multi-stage production/inventory problem with switching costs and uncertain demand

In this paper, we seek robust policies for a multi-stage production/inventory problem to minimise total costs, including switching, production, inventory or shortage costs. While minimising switching costs often leads to non-convexity in the model, 0–1 variables are introduced to linearise the objective function. Considering the impossibility of obtaining the exact distribution of uncertain demand, we study the production/inventory problem under worst cases to resist uncertainty. In contrast to traditional inventory problems, unexpected yields in production are considered. Robust support vector regression is developed to approximate the yields of each unit. A mixed-integer linear programming is proposed, employing the duality theory to address the min–max model. A practical case study from cold rolling is considered. Experiments on the actual steel production data are reported to illustrate the validity of the proposed approach.     

冷热电联供微网优化调度通用建模方法

在分析典型冷热电联供(combined cooling,heat and power,CCHP)系统的基础上,提出描述其组成和结构的母线式结构,并围绕该系统结构设计了微网调度优化模型构架。在该结构中,选取电气、烟气、蒸汽、热水、空气作为基本母线,与源、负荷、储能和转换装置联接形成微网。使用该结构对各设备进行独立建模,有助于 CCHP 系统的灵活配置和通用建模。围绕该结构,建立联供型微网日前动态经济调度的0-1混合整数线性规划模型,最后通过测试算例证实了所提框架的合理性和有效性。     

含电动汽车换电站的微电网孤岛运行优化

由于风电、光伏等可再生能源具有间歇性,独立运行的微电网会经常出现功率缺额或过剩,给系统运行带来不利影响。对微电网内重要单元,如电池储能电站、电动汽车换电站、可中断负荷等分别进行了分析并建模,结合系统功率平衡、备用需求等约束,建立微电网独立运行优化模型,利用CPLEX软件求解该混合整数规划问题。算例中对以电动汽车换电站和电池储能电站作为储能单元的微电网分别进行讨论,结果表明,相比传统电池储能电站,电动汽车换电站作为储能装置,通过协调优化,可以提高微电网的可再生能源接纳能力,提高微电网可靠性,并更具经济性。     

Demand side management and operational mode switching in chlorine production

Demand side management (DSM) gains importance due to penetration of renewable energy in energy provision. A promising candidate is the chlor-alkali process as it is an energy-intensive process with a high installed capacity and high penetration worldwide. In this article, we consider DSM for the purpose of chlorine production via membrane electrolysis. We allow for switching between two different operational modes with different respective electrical power demands on a per ton of produced chlorine (Cl₂) basis and different modulation of production rate. Switching necessitates a cleaning procedure leading to downtimes of the Cl₂ production, while a constant provision of Cl₂ for downstream processes is necessary. The optimal operation of a variable and switchable chlor-alkali process under aforementioned constraints is determined by formulation as a mixed integer linear program. The results demonstrate that oversizing, in combination with switching, leads to substantial savings, especially in future scenarios for the electricity price. © 2018 American Institute of Chemical Engineers AIChE J, 65: e16352 2019     

An MILP model for optimization of byproduct gases in the integrated iron and steel plant

In iron and steel industry, byproduct gases are important energy. Therefore it is significant to optimize byproduct gas distribution to achieve total cost reduction. In this paper, a dynamic mixed integer linear programming (MILP) model for multi-period optimization of byproduct gases is used to optimize byproduct gas distribution. Compared with the previous optimization model, the proposed model simultaneously optimizes the distribution of byproduct gases in byproduct gas system, cogeneration system and iron- and steel-making system. Case study shows that the proposed model finds the optimal solution in terms of total cost reduction.     

Energy optimization in a pulp and paper mill cogeneration facility

Alarmingly low pulp prices in early 2009 left pulp and paper mills across North America desperate for any way to improve thin profit margins. One solution that continues to gain popularity among the industry is improved energy management systems for cogeneration systems, which use steam for two purposes – to provide heat for the pulping process and to generate electricity for sale to regional providers. This paper presents an energy optimization algorithm for use in a pulp and paper mill cogeneration system. The algorithm is applicable to a number of popular mill configurations, power sale contracts, and fuel purchasing scenarios. The method is also extended to address weather-dependent cooling limitations encountered by a mill cogeneration facility, in which case an iterative solution is proposed in order to maintain convexity of the optimization problem. Results are presented in the form of three case studies.     

纸卷分切与库存管理的集成优化

对造纸过程大规模的纸卷分切和库存管理问题进行了集成和优化求解。首先建立新的纸卷分切与库存综合优化的混合整数线性规划（MILP）模型;其次,提出一套合理的优化求解策略,有效地降低模型复杂程度,提高求解效率,实现切纸过程的全局优化。案例研究表明：采用新的模型和方法得到的方案既满足客户要求（产品多样、需求量大、交货期短）,又能降低其生产成本（纸边废料最少、库存成本最低、产品交货时间最短、生产切换费用最低）。     

Production planning under a working time accounts scheme

Working time accounts (WTAs) provide flexibility to a company to adjust the capacity to the demand by planning, for each period and each worker, an appropriate number of working hours. Under this scheme, every worker has a balance that can be positive (the company owes hours to the worker), zero or negative (the worker owes hours to the company). Credit (or debit) hours are compensated by working less (or more) hours than the reference value in the subsequent periods. This scheme is especially useful for companies dealing with demand fluctuations, because WTA balances can take any value, provided that these belong to a given bounded interval. Other conditions that affect the number and distribution of working hours may be established either in law or in the WTA agreement. This paper proposes a new mathematical model for planning production, inventory levels, working time and temporary closures in a manufacturing company operating under a standard WTA scheme. The results of the computational study show that the model is an appropriate tool not only for planning but also for helping in the bargaining process (different WTA scheme configurations could be evaluated with the model).