对二甲苯吸附分离装置全流程模拟及应用

【作者】 方刚；

【导师】 王健红；

【作者基本信息】 北京化工大学 ， 化学工程， 2000， 硕士

【摘要】 本论文研究的主要内容是运用流程模拟技术对PX(对二甲苯)装置进行全流程模拟，并在装置投产前用于操作技能培训及设计方案的验证与诊断。吸附分离装置是流程中的重要环节，它主要包括模拟移动床和三个精馏塔。故本文重点是研究吸附过程和精馏过程，建立其模型并选择适宜的解法。最终形成的动态模拟系统应用于实际生产装置的实时模拟，取得了很好的效果。 工业生产上利用模拟移动床吸附分离技术，能将一些沸点相近、或分子量较大、热敏性的有机混合液进行有效分离。尽管该技术已被广泛应用，但这种模拟移动床分离碳八芳烃混合物技术是美国的UOP公司和日本的东丽公司两家公司分别独有的专利技术，其技术资料难以获得。这种专利技术不仅体现在吸附剂原料的组成，更重要的是体现在它通过各股物料出入口位置不断切换来实现液相与固相之间的相对移动。因此，其机理复杂，建模有一定的难度。 本论文从探索移动床的工作原理入手，深入研究模拟移动床的工作原理，结合生产实际情况，把模拟移动床的吸附室人为分为四个区，这四个区通过它们之间的浓度、流量关系关联，建立具有轴相返混的连续活塞流稳态模型，用Laplace变换方法导出模型的解析解。稳态模型的确立，为同时建立动态模型提供了校正的模型参数，并且稳态模拟结果可用于动态流程模拟工作及优化工作。 精馏塔数学模型的推导是以物料平衡和能量平衡为基础建立的。在汽液平衡计算过程中，采用了跟踪逼近技术，即用简化模型跟踪逼近严格模型。内圈迭代采用校正克拉珀龙饱和蒸汽压方程计算平衡常数。内圈迭代收敛后，再调用严谨的热力学方法进行判敛与逼近。此法大大提高了计算效率和稳定性。通过数值实验表明，因积分时间很小，简化模型参数的变化远远小于模型误差、截段误差和舍入误差，故由此所得的计算结果与全部使用严格模型所得的计算结果几乎没有差别。 本论文工作最终形成了一套软件。该软件较好地模拟了模拟移动床的实际生产情况和精馏塔的开、停车及正常与异常工况操作，具有较好的动态特性，不仅可以用来进行仿真培训，还可用于技术人员对工艺过程的技术改造以及控制系统的研究。此研究成果成功地应用于天津石化公司二十万吨／年聚酯装置开车前的仿真培训系统，并对生产装置的优化及控制有一定的指导意义。更多还原

【Abstract】 This paper mainly dealt with the problem of using the process simulation technique to do the all-process simulation of the para-xylene equipment, and the technique could be used for the operation skill training and the verifying and diagnosis of the design program before the startup of the equipment. The separation equipment was the key role of the process. This process consisted of the simulation moving bed and three distillation columns. The main point of this paper was the research on the absorption and distillation processes, establishment of their models and the proper mathematical solutions of the models. The author established this dynamical simulation system and it could be used in the real time dynamic simulation of the practical equipment. The result was acceptable.Using the absorption extraction technique with the simulation moving bed, the organic mixtures, which had close boiling points, had a heavy molecular weight, or were thermally sensitive, could be efficiently separated. Despite of the wide use of this technology, this technique of using the simulation moving bed to extract C8A mixture was a patent dependently owned by the UOP of America and the DOLI of Japan. It was very hard to procure its technologic information. This technique was distinct not only for the composition of the absorbefacient, but also for the fact that it accomplished the relative moving of the liquid and solid by continually changing the location of the inlet and outlet of the flow. Therefore, it is difficult to found the model of the process.Author studied the operating principle of the simulation moving bed, and according to the practical production situation, divided the absorption room of the simulation moving bed into four parts. These four sections associated with each other by the thickness and flow rate relations between them. Author founded a stable state model which described the piston flow which is accompanied by an axial remixed and deduced its mathematic solution by using the Laplace transmutation method. The establishment of the stable state model provided model parameters which had been adjusted for the establishment of the dynamic model. At the same time, the results of the stable state simulation were useful for the dynamic simulation and optimization.Deducing the model of the distillation column was on the basis of the mass and energy equilibrium. The technology of trace approach was used. Author used a simplified model to approach the rigorous one in the calculation of the liquid-vapor equilibrium. In the internal iteration, author used the adjusted Clausius-Clapeyron satur-vapor pressure equation to calculate the equilibrium coefficient. After the convergence requirement of the internal iteration had been met, the strict thermodynamics theory was used in checking convergence. This method greatly increased the computation efficiency and stability. The math experiment indicated that due to the short integral time, the change of simplified model parameter was much less than modeling error, cutting error and rounding error. Therefore the calculation result by simplified model had little difference from that by strict actual model.At the end, author made a set of software. This programming has very good dynamic characteristics and can successfully simulate the practical operation situation of the simulation moving bed and the startup, shutdown, normal and abnormal operations of the distillation column. It can be used not only for the simulating training but also for the technology upgrade and control system study. This research has successfully applied in the simulating training system before polyester unit whose capacity is 2 million tons per year went into operation in Tianjin Petrochemical Corporation. The result shows that this model has guide significantly to optimization and control of production units.更多还原