【作者】 李锋；

【导师】 罗祎青； 梁万义；

【作者基本信息】 天津大学 ， 化学工程， 2020， 硕士

【摘要】 精馏塔的经济性受其结构和操作变量影响,需严格而可靠的方法找到这些变量的最优值。尽管基于严格平衡级模型的模拟在精馏中已被广泛应用,由于收敛问题和塔板数优化问题,基于此模型对精馏塔连续操作变量和设备结构离散变量的同时优化仍是存在困难的。为使问题简化,现有优化设计方法中通常忽略或简化塔内水力学性能的计算,仅根据经验将塔板压降取为固定值。然而,准确描述塔内压力分布对精馏塔优化设计是至关重要的,在考虑精馏塔内水力学的同时,实现精馏塔所有决策变量的同时优化目前是一个需要深入研究的开放性问题。本研究基于严格的MESH方程(质量平衡方程、相平衡方程、加和方程和能量平衡方程),建立了考虑塔板水力学的严格精馏模型。采用绕流效率法将因优化塔板数导致的MINLP问题转化为非线性规划(NLP)问题,有效解决了连续变量与整数变量的同时优化问题;基于虚拟瞬态延拓方法,建立了考虑塔板水力学的虚拟瞬态(PT)精馏模型,有效解决了面向方程(EO)建模环境下NLP问题的每个优化步中牛顿型算法求解非线性模型方程的收敛问题。通过PT模型辅助的稳态优化算法,实现了考虑塔板水力学的精馏塔结构变量和操作变量的同时优化。使用本研究建立的严格精馏塔模型,针对传统精馏塔和隔板塔(DWC)两个研究案例,分别进行了不考虑塔板水力学和考虑塔板水力学的优化设计。对比两种方法的优化设计结果,证明了塔内压力分布对精馏塔决策变量优化结果有重要影响。发现按照不考虑水力学的设计结果操作的精馏塔不能达到产品分离要求,这一影响对于DWC更为明显。最后,提出了考虑塔板水力学的DWC严格优化框架,并对进料组成波动时DWC的操作柔性进行了研究,发现限制其操作柔性的因素主要为塔径,因此DWC塔径的确定需操作柔性和经济性的权衡。更多还原

【Abstract】 The economic performance of a distillation column is affected by its structure and operating variables,a rigorous and reliable method to find the optimal values of these parameters is needed.Although the rigorous equilibrium stage model has been widely used in distillation,it is still difficult to optimize the continuous operating variables and discrete structural variables of the column simultaneously based on the model due to the convergence problem and the integer optimization for stage number.To alleviate the problem,the hydraulic equations are usually ignored or simplified in the existing optimal design method,and the tray pressure drop is taken as a fixed value based on experience.Accurately describing the pressure profile,however,is crucial to the optimal design of the column.While considering the hydraulics in the column,the simultaneous optimization of all the decision variables remains an open question that needs an in-depth study.In present study,a rigorous distillation model considering stage hydraulics was established based on the rigorous MESH equations(material balance,equilibrium,summation,and heat balance).The mixed-integer nonlinear programming(MINLP)problem caused by the optimization of trays was converted into a traditional nonlinear programming(NLP)problem by the bypass efficiency method,which effectively solved the simultaneous optimization problem of continuous variables and integer variables;A pseudo-transient(PT)distillation model considering stage hydraulics was established based on pseudo-transient continue method,which effectively solved the convergence problem of the Newton-type algorithms for solving the nonlinear model equations in each optimization step of the NLP problem under equation-oriented environment.By applying the steady-state optimization algorithm assisted by the PT models,the simultaneous optimization of structural variables and operating variables was completed.Using the rigorous distillation model established in this study,for two cases of a traditional distillation column and a dividing wall column(DWC),optimal designs without considering stage hydraulics and considering stage hydraulics were carried out.Comparing the results of the two methods,it was proved that the pressure profiles in the column have the impact on the optimization results of the decision variables.The distillation column operated according to the design results without considering the hydraulics cannot meet the product requirements.This effect is more obvious on DWC.Finally,an optimization framework for DWC was proposed,which can consider stage hydraulics.And the operating flexibility of DWC was studied.It was found that the main factor limiting the operating flexibility was the column diameter,and thus the diameter requires a trade-off between operating flexibility and economy.更多还原