GOALI: Low-Order Dynamic Modeling and Nonlinear Model Predictive Control of Cryogenic Gas Separation Plants

该NSF GOALI项目是马萨诸塞州/阿默斯特大学和普莱克斯公司的一项共同努力，旨在开发和实施用于低温空气分离装置的非线性模型预测控制（NMPC）技术。 计划中的方法包括建设低阶蒸馏塔模型的基础上非线性波理论。 本文将波动模拟方法应用于分离氮、氧、氩的三塔装置。 低阶模型将与使用动态模拟工具的白杨技术套件开发的严格低温工厂模拟器进行比较。 非线性波建模框架将用于开发专门为低温空气分离装置设计的NMPC技术。 计划的控制策略将利用白杨模拟器作为实际低温分离装置的替代物进行评估。 该项目最终将在德克萨斯州普莱克斯拉波特工厂实施三柱NMPC控制器。低温气体分离装置为化工和钢铁制造业生产大量液体和/或气体产品。 据估计，工业气体生产商每年的国内用电量超过7亿美元。 对电力行业的持续放松管制将导致电力成本的更频繁和不可预测的变化。 这将决定气体分离装置的操作原理的根本变化。 为了充分利用随时间变化的公用事业成本，将需要大的生产率变化和更频繁的启动/关闭。 因此，在自动过程控制方面的微小改进有可能带来巨大的经济效益。 对一个代表性工厂的初步经济分析表明，所提出的控制技术有可能在启动期间每年回收12万美元的产品损失。 该研究将为普莱克斯在美国的60个低温空气分离装置提供控制系统原型，并将为其他国内气体供应商实施非线性控制技术提供动力。

This NSF GOALI project is a joint effort between the University of Massachusetts/Amherst and Praxair aimed at the development and implementation of nonlinear model predictive control (NMPC) technology for cryogenic air separation plants. The planned methodology involves the construction of low-order distillation column models based on nonlinear wave theory. The wave modeling approach will be applied to the problem of triple column plant used to separate nitrogen, oxygen and argon. The low-order models will be compared to a rigorous cryogenic plant simulator developed using the Aspen Technology suite of dynamic simulation tools. The nonlinear wave-modeling framework will be used to develop NMPC technology specifically designed for cryogenic air separation plants. The planned control strategy will be evaluated utilizing the Aspen simulator as a surrogate for an actual cryogenic separation plant. The project will culminate with the implementation of the triple column NMPC controller at the Praxair Laporte, Texas plant site.Cryogenic gas separation plants produce large quantities of liquid and/or gaseous products for the chemical and steel manufacturing industries. Domestic consumption of electricity by industrial gas producers is estimated to be over $700 million per year. Continued deregulation of the electric utility industry will lead to more frequent and unpredictable changes in electricity costs. This will dictate fundamental changes in the operating philosophy of gas separation plants. Large production rate changes and more frequent startups/shutdowns will be required to take full advantage of time-varying utility costs. Consequently, small improvements in automatic process control have the potential for substantial economic benefits. Preliminary economic analysis for a representative plant indicates that the proposed control technology has the potential to recover $120,000/year of products lost during startups. The research will provide Praxair with a control system prototype for the 60 cryogenic air separation plants in the United States and will provide impetus for other domestic gas suppliers to implement nonlinear control technology.