乙烯复杂精密精馏塔动态模拟中的平衡常数和热焓的分析与处理

Analysis and treatment of equilibrium constant and enthalpy in dynamic simulation of complicated close-boiling ethylene-ethane fractionation

复杂精密精馏塔是典型的多变量系统,而且各变量之间关联严重,对其进行建模和模拟,可以为多变量先进控制奠定基础。由于其动态机理模型十分复杂,计算精度要求极高,在其系统建模、模型求解中存在气、液相热焓和气液平衡常数的准确性对精密精馏动态模拟结果的影响突出等问题。本文以乙烯精馏塔为例,利用准确度相当高的BWR状态方程来计算气、液相焓和气液平衡常数,对能量平衡方程中热焓的时间导数项作了适当合理的简化,从而既提高了计算效率又保证了计算精度。乙烯精馏塔的动态模拟结果表明,经修正后的动态模型及模拟方法不仅能较好地描述其动态特性,而且其模拟精度高,反映了实际生产效果。

Ethylene-ethane rectifier is a typical complicated close-boiling fractionation system,which includes product side-draw,several middle reboilers and strict product requirement.As a typical multivariable system,close-boiling fractionation system is very complicated,and these variables are seriously connected each other.Dynamic model establishment and system simulation will help to coordinate the relations between variables and to implement advanced control plan.However,the complication of actual system leads to many problems in the process of obtaining exact mechanic model and solving related mathematical equations.For example,the accuracy of enthalpy and equilibrium constant can greatly influence the dynamic simulation of close-boiling fraction.An ethylene distillation column was selected as a case to propose strategies dealing with these problems better.BWR state equations were used to calculate the enthalpy and equilibrium constant,the model accuracy was improved,and the enthalpy derivatives in the energy equation were reasonably simplified.Simulation results showed reasonable computational efficiency and accuracy.Such improved model for ethylene distillation column has a high precision,and can predict the dynamic behaviors better.