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Studies On Process Modeling And Its Application Of Aromatics Transformation In Aromatics Combination Unit

Posted on:2008-01-30Degree:DoctorType:Dissertation
Country:ChinaCandidate:O G XuFull Text:PDF
GTID:1101360212989561Subject:Control Science and Engineering
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It is well known that aromatics are key raw materials and important starting materials for many intermediates and petrochemicals, playing an important role in the modern national economy, benezene, toluene and xylenes in particular. The commercial production of aromatics is achieved by modern aromatics combination unit with complex processes accompanying transformation between aromatics. The modern aromatics combination unit is assembled properly with many processes together including process of C8-aromatics hydroisomerization and process of toluene disproportionation and transalkylation with C9-aromatics. The process of C8-aromatics hydroisomerization is to transform isomers such as o-xylene, m-xylene and ethylbenzene to more valuable p-xylene and the process of toluene disproportionation and transalkylation with C9-aromatics is a convenient way to get more valuable and widely used benzene and xylenes from surplus toluene (C7) and trimethylbenzenes(C9).Modeling is a key issue in petrochemical industry, and more and more attentions are payed to the integrated automation technologies based on process model such as soft sensor, advanced process control, process simulation and optimization, process scheduling and planning in modern petrochemical industry.The dissertation takes the practical commercial unit, unit of C8-aromatics hydroisomerization and unit of toluene disproportionation and transalkylation in aromatics combination unit, in petrochemical industry as the research background, focusing on several typical theory and engineering issues in petrochemical process modeling and its applications. Two main parts are involved in the dissertation, one relating to process modeling of two aromatics transformation processes, namely process of C8-aromtics hydroisomerization and process of toluene disproportionation and transalkylation with C9-aromatics, and the other dealing with applications of the two established models, off-line simulation and on-line application. The contents discussed here are the foundation of functional modules for special process simulationand optimization softwares and the details are arranged as follows,1. Based on the reported reaction networks, new kinetic models for commercial unit of C8-aromtics hydroisomerization and unit of toluene disproportionation and transalkylation with C8-armatiocs are developed for process monitor, process optimization and prediction. A time based empirical catalyst deactivation function considering hydrogen partial pressure (Ph) and weight hourly space velocity (WHSV) is incorporated into the models, accounting for the loss in activity because of coke formation on the catalyst surface during the long-term operation. As to the difficulty of simultaneous estimation for frequency factors (k0) and activation energies (Ea) as well as the difficulty of many parameters to be estimated at the same time, the activation energies of the same kind catalyst and empirical activation energies are adopted, hence the number of parameters is reduced to half. The kinetic parameters are benchmarked with several sets of balanced plant data and estimated by the differential variable metric optimization method (BFGS), while the ordinary differential equations of the models are solved by the Runge-Kutta method and the errors introduced are inevitably accumulated to the frequency factors. The kinetic models are validated by industrial units with sets of plant data at different operating conditions and simulation results show a good agreement between the model predictions and plant observations, which means that the developed model are suitable for off-linesimulation and on-line soft sensor application of industrial units.2. The off-line applications of the developed models about process of C8-aronaticshydroisomerization and process of toluene disproportionation and transalkylation with C9-aromatics are discussed in detail including model verification, process simulation and sensitivity analysis of operating variables. First of all, large number of balanced plant data are simulated with the developed models, and the comparisons of key components concentration and technologic indexes between model predictions and plant observations are made for the warranty of modelmaintenance; then the distribution of the components inside the reactor is simulated by the models and its rationality is showed in detail; at last, the effect of operating variables such as reaction temperature, weight hourly space velocity, molar ratio of hydrogen-to-hydrocarbons and reaction temperature on the process performances is investigated. In fact, off-line simulation involves model verification and process simulation, and process analysis incorporates simulation of the reactor and sensitivity analysis. The above-mentioned discussion and analysis point out functional modules of the special process simulation and optimization softwares for two aromatics transformation processes.3. The on-line applications of the first principle process models are studied for domestic industrial units about aromatics transformation processes, C8-aromatics hydroisomerization and toluene disproportionation and transalkylation with C8-aromatics. The key problems about practical operation of on-line soft sensors system based on process models are discussed and the strategy of on-line model rolling-revision is proposed for the warranty of model prediction accuracy. On-line computation is applied to the industrial units with APC-Sensor soft and the results show that the model predictions agree well with plant data observed. The high performance of the model predicting many indexes simutaneously is presented and its successful on-line application guarantees the operation of advanced process control and optimized process control. The dissertation is concluded with a summary and perspectives of someimportant issues for further investigation.
Keywords/Search Tags:Aromatics combination unit, C8-aromatics hydroisomerization, Toluene disproportionation and transalkylation with C9-aromatics, First principle process model, Parameter estimation, BFGS optimization method, off-line simulation, on-line application
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