精馏过程的新逐板计算法 (Ⅳ)多元精馏过程的设计型计算

对于精馏过程的模拟计算,大都已有严格算法适用于操作型计算.操作型方法虽可用于设计型计算,但增长计算时间.本文则提出用于直接设计型计算的新逐板法.设计型新逐板法选择比值为迭代变量.对于理想系统和与之相近系统,比值是指塔上部各板上各重组分分流量之比和塔下部各板上各轻组分分流量之比.对于萃取精馏系统,比值是指各板上各被分离组分的浓度之比.与操作型的新逐板法”相比,强回路不再存在,迭代回路全部由弱回路构成,因此具有更快的收敛速度.由于这是逐板计算法,故各股进料和侧线出料的最优位置可以方便地确定,而不必应用最优化判据或作最优化计算.

A New Plate-to-plate Method for Calculating Distillation Processes (Ⅳ) Design calculation of multicomponent distillation processes

As to multicompoent distillation calculation, most available methods were proposed for operating problems. Although these methods can also be used for design problems, more computer time is needed, since the plate numbers are regarded as iterative variables. In this paper, the authors develop a new plate-to-plate method, which can directly be applied for design purpose and can be used for providing a rigorous solution. Ratios of molar flow rates and mole fractions are chosen as iterative variables. As to ideal systems and those close to ideal ones, these ratios refer to either ratios of molar flow rates of the heavy components or to those of the light components in various plates. As to extractive distillation processes, these ratios refer to the ratios of mole fractions of the components to be seperated in various plates. In comparison with the new plate-to-plate method for performance prediction1,2] design calculation involves only week loops and more rapid convergence can be achieved without any acceleration or relexation, owing to the disappearance of the strong loop. As a plate-to-plate method, optimal location of feed plates and side-stream plates can easily be determined and no more optimization and any thumb criteria are needed.