【作者】 罗春鹏；

【导师】 荣冈；

【作者基本信息】 浙江大学 ， 控制理论与控制工程， 2008， 博士

【摘要】 生产调度在流程工业企业中起着承上启下的关键作用,是生产经营的核心,它决定了生产过程是否能够顺利进行,影响到企业的生产成本和资源的合理利用。炼油生产企业是流程工业的典型代表,激烈的市场竞争促使炼油企业提高利润和减小成本的压力越来越大。由于炼油企业生产调度优化方案能减少原油采购、运输、加工和存储成本,充分利用生产加工能力,提高资源利用效率,增加生产收率,满足需求和最大化利润,因而生产调度问题成为研究的热点问题。但由于炼油企业生产调度问题具有复杂性、不确定性、非线性、多目标和多约束等特点,而成为研究的难点问题。以往的研究一般以炼油企业中某一生产环节如罐区存储、装置加工、原油和成品油调和等作为调度对象,而没有从全厂角度整体考虑调度目标,但局部生产优化不等于全厂最优,因而无法达到全局优化。本文对炼油企业调度问题的研究主要包括以下几个方面:(1)从炼油企业整体建模角度出发,将构建炼油企业生产流程模型所需的各种模型元素抽象出来,通过对这些元素的数学描述,来剖析炼油企业流程建模的特点,通过这些抽象出的模型元素可以为灵活构建整个生产网络奠定基础。并着重描述了这些不同模型元素在多操作方案下,物料平衡计算及物性计算的特点。(2)详细讨论了炼油企业操作约束建模以及如何构建高效数学模型的问题。论述了如何通过逻辑角度来理解和描述生产操作规则的建模,以及如何将逻辑描述转化为数学模型。同时还阐述了许多建立高效混合整数线性规划模型的技巧,如:何时将0-1变量视作0-1连续性变量、将高维离散变量分解为低维离散变量等。(3)通过所介绍的物流框架模型和逻辑建模方法,通过实例揭示如何建立一个完整的调度模型。通过该实例展示,用一个单一的数学优化模型来刻画企业调度细节,特别是刻画与储罐相关的物流分配操作,如:同时接收物料的储罐数目、同时输送物料的储罐数目、储罐的多操作方案、储罐接收物料后的静置时间等,不仅会导致模型规模庞大,而且会导致大量的离散变量,从而极大影响了模型的运行时间。(4)针对单一优化模型求解困难的难点,提出了一种分层建模与求解策略。上层优化模型用来决定装置宏观的调度策略:装置各加工方案的时刻和顺序、进出厂管线输送物料的时间及顺序、并决定各装置在各时间周期内生产或消耗的物料数量及种类。在上层的优化模型中只涉及企业的集合罐,即由当前储存相同物料的物理罐组合而成的逻辑罐。下层系统将应用启发式规则去调整集合罐内多用途的操作方案,以调节集合罐的存储能力。另外下层系统也通过启发式规则来管理物理罐接收和输送物料的顺序。这样的分层策略能大大减少上层优化模型离散变量的数目,加快模型的求解速度。(5)在分层策略的基础上,提出了一种不确定条件下具有鲁棒特性的计划与调度整合的策略。由于生产过程数据测量不准确,或未预知事件的发生,可能会使模型找到的优化解不再是可行解,为了缓解这种不确定因素的影响,介绍了一种鲁棒建模策略。同时为了探索计划与调度整合问题,在分层策略的基础上,提出了基于滚动优化的计划/调度整合模型。更多还原

【Abstract】 Scheduling is the key of Manufacturing Executing System (MES), which links process control system and business management system in process industry. It determines whether production process is running smoothly, influences production cost and reasonable utilization of resources. It is oil refinery that is one of the typical representatives of process industry. The refineries have to make great efforts to increase profits while decrease costs under market competition. The optimal solution of refinery production scheduling can reduce the costs of purchase, transportation, storage, and make the best of production capacity, improve efficiency of resource utlization and capacity ratio, meet demands and maximize profits, the refinery production scheduling problem receives significant attention in recent year. However, the refinery scheduling problem is difficult to solve for its complexity, uncertainty, nonlinearity, multi-objectives and multi-contraints. In many literatures, scheduling object was one section of production process in refinery such as tank farm storage, production unit process, crude oil or products blending, but entire refinery was not considered as the scheduling target. It is obvious that local production optimization does not achieve global refinery optimization. The main works of this dissertation are as follows:(1) A general modeling framework and modeling approaches for scheduling in refineries are proposed. Modeling frameworks of processing units, storage tanks, and pipelines, which are introduced for operational planning (Neiro and Pinto), are extended for operational scheduling. The most important extension is that operation modes for these entities are considered. And at the same time, another framework for perimeter unit is introduced to control raw material supplies and product demands. A complex production topology can be built by these grouped elementary entities that are interconnected by intermediate streams.(2) We reveal that many modeling problems in refineries can be understood from a logic and qualitative view. This work will shed light on the logic essential of many mathematical formulations presented in the literature. And, how to convert logic expressions to mathematical formulations is also presented. The application of the approach to some modeling problems is elaborated. These modeling problems include: modeling some important operation rules in refineries, decomposing large- index binary variables to small-index binary variables and linearization of some nonlinear formulations.( 3 ) Based on the modeling framework and the logic modeling methods, a scheduling optimization model for refineries is built. This example shows how to build scheduling models by using the modeling framework, and how to model operation rules by using the logic inference. The computational results show that the operation rules, such as a minimum amount of time to allow the settle of tanks after receiving materials, that just one tank receives the same kind of material at the same time and a tank cannot receive and send material at the same time, that one mode of a tank can only hold one kind of material, will lead to a large number of 0-1 variables that would make the model solution unattainable within reasonable time.( 4 ) A hierarchical approach with two decision levels for short-term scheduling problems in refineries is proposed. This approach includes two levels: the optimization model at the upper level and the heuristics and rules adopted in simulation system at the lower level. The optimization model is used to decide sequencing and timing of the operation modes of processing units and pipelines, and to determine the quantities of materials consumed/produced by each operation mode of a unit. Only aggregate tanks are used at the upper level, and the simulation system at the lower level uses a heuristic to adjust the operation modes of some actual multipurpose tanks within aggregate tanks. The iteration procedure between the upper level and the lower level is used to find optimal solution under new aggregate storage capacities. The simulation system also uses some heuristics and rules to arrange actual tanks to receive/send materials with logic operation constraints (operation rules) on tanks respected.( 5 ) A methodology for the integration of production planning and scheduling in refineries is proposed. This method also relies on the two-level hierarchical approach. In this paper, uncertainties are also considered, and, two robust optimization approaches presented for optimization problems under uncertainty are integrated to cope with uncertain parameters with continuous and discrete probability distribution respectively.更多还原