Process Optimization Study On The Key Units In Aromatics Complex

Aromatics are important and basic raw materials in chemical industry, and large-scale production of aromatic is fullfiled by modern aromatic complex. The processes involved in aromatic production include hydrocracking, hydrotreating, catalytic reforming, extraction and et al. Each process mentioned is finished in separate unit. Besides, hydrogen production plant is also included in the complex, which provides hydrogen to other hydrogen consumption processes. Aromatic complex is a complicated system composed by these sepatate units, most of which have the problem of high energy consumption and high waste emission in operation. It is of great significance to reduce the energy consumption and waste emission in the operation of aromatic complex through process optimization from both scientific research and practical indusrial operation aspects.The hydrogen production plant, aromatic extraction plant and catalytic reforming plant are selected as the objects of this study, as they are the key units in the complex and have the highest energy consumtion and waste emission. The process optimization of the3units is performed by focusing on energy consumption, product quality and environmental influence aspects. For each object, simulation is first carried out based on real industrial data. Exergy analysis, mathematical programming and methematic statistics are applied to analyze the process energy utilization, material consumption and the relationship between the product quality and operation parameters. This study focus on3main scientific problems, which are (1) the relationship between efficiencis of system and its subsystems,(2) the solution of multi-objective optimization,(3)the distribution of energy consumption among products. The process optimization of hydrogen production plant, aromatic extraction plant and catalytic reforming plant are the three main parts of this thesis, and the main results can be summarized as follows: Firstly, the steam metane reforming is investigated from both energy consumption and environmental aspects usting exergy analysis. The system efficiency is identified for the base case, as well as the distribution of exergy loss and CO2emissions for unit hydrogen produced. The sensitivity analysis indicates that the optimal S/C ratio will decrease with Tr, and both the optimum S/C ratio and Tr are around the critical point.The exergy load distribution analysis indicates that the most improvement lies in increasing the efficiency of furnace without increasing its relative load. Finally, evaluation of the promising integration of OEC and SMR indicates that the OEC can increase the system efficiency significantly when the reformer operates above its critical point, while in other cases the system efficiency may decrease.Secondly, a multi-objective optimization model is developed to maximize the product purity and minimize the energy consumption in the process optimization on aromatic extraction plant. The flow rate of distillation in stripper colum, steam in recovery column and distillation in benzene column are chosen as the operation variables.An improved adaptive weighted sum method is proposed and used to solve the model. The results show that the proposed method can improve the efficiency without decreasing the uniformity of distribution of Pareto optimal solutions. The optimal operation parameters are given for different purity levels, and the comparison between the optimum operation results and the existing results indicates that the flowratae of distillation in stripper column should be reduced while the flowrate of steam in recovery column and distillation in benzene column should be increased.Thirdly, the catalytic reforming is simulated using the "Catalytic reformer" model embedded in ASPEN Hysys package. The influence of inlet temperature of the4reactors on the liquid yield, hydrogen production, hydrogen purity, aromatic productivity, RON of reformate and catalyst coke. The energy consumption in the operation are distributed to reformate and hydrogen through the proposed dynamic energy consumption distribution method on the basis of product relative benefit, which is the ratio of the product benefit to the specified value in the reference state. Three operation conditions when the inlet temperature is set to480℃,520℃and530℃are selected as the reference states. The product benefit of hydrogen is measured by the mass flowrate or lower heating value (LHV), and the product benefit of reformate is measured by mass flowrate, LHV, aromatic productivity or RON. Comparison between the results obtained by the dynamic energy consumption distribution method and normal method indicates that the former can provide more reasonable and accurate product energy consumption.