Study On Steady-state Simulation And Multi-Objective Optimization Of The Crude Distillation Unit

In petroleum refining industry,crude blending is frequently employed to improve the profit and products yields of crude distillation unit.In this paper,a running 4.5 Mt/a crude distillation unit in a refinery was taken as the research object,and its materials,products,process flow etc.were introduced briefly.Based on the calibration data,the steady-state model of whole unit was performed using process simulator Aspen Plus.The simulation results were compared with calibration data,and the errors were in reasonable range.So the built model can reflect actual production status well,and be used for the subsequent analysis and optimization work.On the basis of the steady-state model built in Aspen Plus software,the operating conditions were analyzed using the sensitivity analysis tool,and the decision variables are the crude oil blending ratio,the atmospheric furnace temperature,atmospheric bottom and side stripping team,and heat duties of pumps in the atmospheric tower and vacuum tower.Taking product quality as the constraint condition,the objective functions are the maximum economic benefit,the minimum energy consumption of heating furnace and the least amount of CO₂ emission.The software integration can be realized by developing interface toolbox to make Aspen Plus and Matlab connected.At the same time,the elitist state non-dominated sorting genetic algorithm（NSGA-II）was used to reach multi-objective optimization.Finally,three objective functions on furnace energy consumption,CO₂ emissions and economic benefits are archived optimal simultaneously.Based on the steady state model built on Aspen Plus platform,Pareto-optimal solutions were obtained.The results show that the increasing economic benefit leads to growing CO₂ emissions while keeping the product specification on the base of distribution of Pareto front.Thus,economic profit can be improved by increasing the proportion of heavy oil,but also inevitably lead to high CO₂ emissions and energy consumption.Comparing the initial condition with the optimal result,the economic benefits could be increased by 25.71%through optimizing the crude oil blending ratio and operating conditions under the same energy consumption and CO₂ emissions.This result shows that the multi-objective optimization method can solve practical problems better in refinery and bring maximum benefit.In thermodynamic analysis,energy and exergy analysis were made between before and after optimization.In energy system analysis,the grand composite curves in two conditions of the maximum and minimum economic benefits optimization results were made.The results show that more heat is recovered and the heat transfer effect is obvious by increasing the proportion of heavy oil.The exergy analysis shows that the total energy loss of the crude distillation unit decreased after optimization.