Dynamic Simulation And Advanced Control Of Ethylbenzene Plant

Ethylbenzene is an important aromatic compound in petrochemical industry supply chains,which is mostly used to make styrene.An interesting feature of the benzene alkylation process for the production of ethylbenzene is that the by-products can be separated and then recycled to trans-alkylation reactions converting into ethylbenzene,thus improving the full process selectivity.However,the nonlinear characteristics of this reaction-separation-recycle system can generate the snowball effect,where a large recycle flowrate change is caused by a small load change.The snowball effect leads to complex dynamic effects.Therefore,it is necessary to design a suitable control scheme to achieve smooth operation.In this paper,the liquid-phase benzene alkylation process is analyzed to establish the physical and thermodynamic model,unit operation model,process structure model,and process control model and then implement the dynamic simulation.The accuracy of the simulation is confirmed by comparing the simulation results with the design values.The snowball effect of the ethylbenzene process is reproduced based on the simulation.For improving the efficiency of designing and verifying control schemes,program hotspots and dependencies between unit operation models are analyzed,a parallel computation method considering unit operation model solving sequences is designed,and the upper limit of speedup ratios is estimated.The general dynamic simulation & optimization system is rewritten at both granularities using multi-threaded parallelism and vectorized parallelism.A5-hour test is conducted on the established ethylbenzene dynamic simulation program,and the results showed that the highest speedup ratio was up to 261%compared to the original program,and the simulation was completed in 70.98 seconds wall-clock time.In order to cope with the complex dynamic effects caused by the snowball effect,a supervisory control layer control scheme based on dynamic matrix control is designed to achieve cooperative control.This control scheme utilizes multiple unit operations within the cycle to synergistically attenuate the fluctuation of the recycle flowrate.The new control scheme with ethylene feed flowrate as disturbance variables,the new control scheme without disturbance variable,and the traditional control scheme are compared.The results show that the control scheme without disturbance variable has the best recycle flowrate stabilization effect.