Optimizing Control of LIquid-Liquid Extraction Columns

液-液萃取是有色金属湿法冶金生产、金属回收稀薄废液处理和危险废物消除、核燃料循环和核废料管理中铀和钚的精炼和再加工以及生化分离等新兴技术中的重要分离过程和关键步骤。这在石油工业的加氢脱硫等传统分离中都起着重要的作用。工业规模的液-液萃取设备包括柱接触器和连续流搅拌槽。柱式接触器缺乏测量技术，这是对这一过程进行的控制研究数量有限的原因之一。PI实验室的无创超声技术的发展为控制提取过程提供了一个新的倡议。此外，锡拉丘兹大学开发的现场微型相分离设备可以与浓度测量探头(如光纤、电导、折射探头等)结合使用。为多变量控制和在线优化提供了一种新的可能性。这项工作是试图利用上述技术在最佳条件下对萃取器进行安全的多变量控制。此外，这些技术是第二个目标的推动力，即开发一种用于优化操作的多变量非线性预测控制算法。设计了一种液液萃取塔的优化控制策略，其目标是(I)控制萃取器内的分散相含率，(Ii)确保在驱替或反相情况下的安全操作，(Iii)控制溶质浓度以提供最佳的萃取效率。这一过程将由(I)带有死区的一阶传递函数的线性模型和(Ii)包括液滴破裂和合并相互作用的粒子数平衡方程的非线性模型来模拟。这两个模型将按如下顺序应用于过程控制：-利用线性模型对分散相含率进行自适应增益调度控制，目的是展示超声波技术在萃取过程控制中的应用。-通过应用粒子数平衡方程对无传质的分散相含率进行非线性预测控制，以证明物理模型的有效性。-传质过程中分散相含率的非线性预测控制。-使用扩展公式中的种群平衡方程对持液率和浓度进行多变量非线性预测控制，以包括传质和浓度。

Liquid-liquid extraction is an important separation process and a key step in recently emerging technologies such as hydrometallurgical production of non-ferrous metals, treatment of dilute waste streams for metal recovery and hazardous waste elimination, refining and reprocessing uranium and plutonium in the nuclear fuel cycle and nuclear waste management, and biochemical separations. It all plays a major role in traditional separation such as hydrodesulfurization in the petroleum industry. Industrial scale equipment for liquid-liquid extraction include column contactors and continuous flow stirred tanks. There is a lack of measuring techniques for column contactors which has been one of the reasons for the limited number of control studies for this process. The development of a noninvasive ultrasonic technique in the PI's laboratory provides the opportunity of a new initiative in the control of the extraction process. Also, in situ miniature phase-separation devices developed at Syracuse University can be used in combination with concentration measuring probes (e.g., fiber optic, conductivity, refraction probes, etc.) and introduce a new possibility for multivariable control and on-line optimization. This work is an attempt to utilize the above techniques for a safe, multivariable control of the extractors at optimal conditions. Further, these techniques are the impetus for the second objective, to develop a multivariable non-linear predictive control algorithm for optimal operation. An optimizing control strategy for liquid-liquid extraction columns is planned with the objectives of (i) controlling the dispersed phase holdup inside the extractor, (ii) ensuring safe operation with respect to flooding or phase inversion, and (iii) controlling the solute concentration to provide optimum extraction efficiency. The process will be modelled by (i) linear models of first order transfer functions with dead time, and (ii) nonlinear models of population balance equations which include droplet interactions of breakage and coalescence. Both models will be applied for the control of the process in the following sequence: - Adaptive gain-scheduling control of the dispersed phase holdup by using linear models, with the objective of showing the application of the ultrasonic technique in the control of the extraction process. - Nonlinear predictive control of the dispersed phase holdup without mass transfer by applying the population balance equations, to demonstrate the usefulness of physical models. - Nonlinear predictive control of the dispersed phase holdup during mass transfer. - Multivariable nonlinear predictive control of holdup and concentration using the population balance equations in an extended formulation to include mass transfer and concentrations.