MTBE反应精馏塔的建模和应用

发布时间：2018-09-04 08:26

【摘要】：反应精馏是将化学反应与精馏过程结合在同一设备中进行的工艺。由于在反应的同时,用精馏的方法将产物移出,从而有利于提高反应转化率、降低能耗和投资,正日益得到学术和工程界的高度重视,而其中机理建模是整个问题的核心。本文首先建立了反应精馏塔的稳态机理模型,模型包括产品质量约束、质量平衡、相平衡、归一化方程、能量平衡和反应速率方程,即MESHR方程组。其中,为了准确地计算各理论板的上升气体量和下降液体量,又避免采用导致二级循环迭代的逐板计算法,减少计算负荷,本文改进了等摩尔流假设,利用各板液相潜热可算的原理,间接求出了上升气相量和下降液相量,从而使两次迭代简化为一次迭代,大大减少了计算量。本文提出了反应精馏塔稳态机理模型的求解方法,该方法由于简化了各级理论板上升气相量和下降液相量的计算,使得联立求解MESHR微分方程组成为可能。其步骤是:1)给定塔顶压力、回流比、进料状况和产品要求,进入第一次循环计算;2)设定各理论板温度和液相组成初值,用Wilson方程计算各组分的活度系数;3)计算各组分的相平衡常数初值;4)计算各理论板气相组成初值;5)采用MATLAB内置的龙格-库塔算法(ode45算法),求解各理论塔板MESHR方程组,得到修正后的塔板气液相组成;6)检验各理论板组成是否满足归一化方程,满足则输出结果,否则调整各板温度初值进行二次循环计算。编制了相应MATLAB计算程序,并将其应用于Jacobs和Krishna提出的经典MTBE案例[80],计算表明本文的计算结果与文献值高度一致,说明本文建立的反应精馏塔的稳态机理模型以及计算方法是可行的。最后,将模型应用于MTBE反应精馏塔的操作优化,通过模型内置的遗传算法,以进料温度、塔顶压力、回流比为优化变量,以体系总操作费用为目标函数,应用于Jacobs案例,发现当回流比为6.5,塔顶压力为10.7atm,甲醇进料温度为324K,C4进料温度为360K时,按年开工8000小时计算,年度总操作费用可降低947.89万元/年。
[Abstract]:Reactive distillation is a process that combines chemical reaction with distillation process in the same equipment. At the same time, the products are removed by distillation, which is beneficial to increase the conversion rate, reduce energy consumption and investment, which has been paid more and more attention by the academic and engineering circles, and the mechanism modeling is the core of the whole problem. In this paper, the steady-state mechanism model of reaction distillation column is established. The model includes product quality constraint, mass equilibrium, phase equilibrium, normalized equation, energy balance and reaction rate equation, that is, MESHR equation. In order to accurately calculate the rising gas and decreasing liquid volume of each theoretical plate, and to avoid the plate by plate calculation method which leads to two-stage cycle iteration, and to reduce the calculation load, this paper improves the isomolar flow hypothesis. Based on the principle that the latent heat of liquid phase of each plate can be calculated, the amount of rising gas phase and the amount of falling liquid phase are calculated indirectly, so that the two iterations are simplified to one iteration, and the calculation amount is greatly reduced. In this paper, a method for solving the steady-state mechanism model of the reaction distillation column is presented. The method simplifies the calculation of the ascending gas phase and the descending liquid phase of each theoretical plate, which makes it possible to solve the MESHR differential equation simultaneously. The steps are: 1) given top pressure, reflux ratio, feed condition and product requirements, enter the first cycle calculation and 2) set the initial values of each theoretical plate temperature and liquid phase composition. The Wilson equation is used to calculate the activity coefficient of each component. The initial value of phase equilibrium constant of each component is calculated. (4) the initial value of gas phase composition of each theoretical plate is calculated. (5) the Runge-Kutta algorithm (ode45 algorithm) built in by MATLAB is used to solve the MESHR equations of each theoretical tray. The modified gas-liquid composition of trays is obtained to verify whether the composition of each theoretical plate satisfies the normalized equation and the output result is satisfied. Otherwise, the initial temperature of each plate is adjusted for secondary cycle calculation. The corresponding MATLAB calculation program is compiled and applied to the classical MTBE case [80] proposed by Jacobs and Krishna. The calculation results show that the calculated results in this paper are in good agreement with the reference values. The steady-state mechanism model and calculation method of reaction distillation column established in this paper are feasible. Finally, the model is applied to the operation optimization of MTBE reaction distillation column. Through the genetic algorithm built in the model, the feed temperature, top pressure and reflux ratio are taken as the optimization variables, the total operating cost of the system is taken as the objective function, and applied in the case of Jacobs. It is found that when the reflux ratio is 6.5, the top pressure of the tower is 10.7atm, and the feeding temperature of methanol is 324kg / C4 360K, the total operating cost can be reduced by 9.4789 million yuan per year according to the 8000 hours of annual start up.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ053.5

【参考文献】