| The process intensification technologies have been analyzed with four drivers for innova-tion in the chemical process industry:feedstock cost reduction, capital expenditure reduction, energy reduction and safety risk reduction.This contribution studied a complex heat-integrated process(DDE), combining dividing wall column, double-effect distillation and reutilizing waste heat, which is used to separate a certain quaternary mixture from a synthetic process in industry. The data from practical applica-tion showed this DDE process was able to largely reduce energy consumption. However, it also increased the difficulties in controlling due to its highly coupled degree. The current control strategies were sufficient in handling±10%in feed flow/concentration disturbances, notwith-standing human meddling still existed in dealing with large-scale feed load change, startup and shutdown events. Therefore, this study focuses on the aforementioned problems in order to pro-vide guidance for industry. Specific contents are listed as follows:(1) Employed Aspen Plus Dynamics to build up models for this DDE process, established a heat-integrated network, made rectifications of models according to industrial data, took considerations of heat transfer across the dividing wall and vapor split ratio.(2) Based on the understanding of process as well as the results of Singular Value De-composition and stability analysis, chose6representative feedback control strategies and applied them into the large-scale feed load change; analyzed dynamic behaviors, obtained temperature and composition responses versus time; compared steam con-sumption, time required and off-grade products of different strategies. Temperature and composition responses showed that using reflux to control temperature lead the system unstable, as well as using steam flow and side draw to control temperature was unable to make the system back to desired status. All these feedback strategies presented lim-ited performances and produced large quantities of off-grade products.(3) Analyzed the reasons that caused bad performance of feedback control strategies; In order to conquer the defects of conventional strategies, proposed an advanced strategy integrating temperature difference control, feed forward control, model predictive con- trol and feedback control; Further improved the controllers from simulating results with sectional relation of feed flow and targets; Compared to conventional feedback control strategy, the optimal advanced control strategy could reduce77%energy con-sumption, shorten79%unproductive time and produce no off-grade products; Applied the final optimal control strategy to conduct shutdown process, reducing54%methylal products and78%methanol products while increasing35%required time over con-ventional shutdown strategy. The novel strategy is not applicable in emergy stops.(4) Thoroughly analyzed the startup process and divided it into three periods; Discussed the strategies for each period respectively; Compared different startup procedures with different bottom initials. For the first and second period, startup with water and with feed consumed the same quantity of steam, but the former shorten6.9%time and pro-duced no off-grade products; The latter produced a large number of methnol products containing much methylal. For the third period, applied the same strategy as load re-duction process into load increase process, which achieved the consistent comparison results of different strategies.However, this thesis has not considered the strategies to deal with other events, such as the disturbance of feed composition, emergency stops without feed and steam, equipment break-down and so on. These problems will be studied in future. |
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