| Fluidized catalytic cracking(FCC) is the main way to convert heavy oil in China.The target product yield and energy consumption of separation system are the main factors affecting the profits of FCC unit.Unit optimization is one way to improve unit profits.The process simulation software has enriched the means for optimization.In order to maximize unit profits,it is important to apply process simulation software to simulate and optimize the FCC unit.Therefore,in this thesis,based on the production data of a 0.65 Mt/a heavy oil FCC unit,I apply the software HYSYS to perform a process simulation of the unit to optimize the reactionregeneration system and separation system respectively with accurate models.For the reaction-regeneration system,with the optimization objective of improving the unit revenue and liquid yield,sensitivity analysis was first performed on regular operating variables in terms of products distribution and quality.Then multivariate optimization was carried out using the OPTIMIZER module based on the actual situation of the unit.The results show that the operating variables has different influence degrees on product distribution,property and optimization objectives.The reaction temperature has the greatest influence,while the feed preheating temperature has the least influence.The multivariate optimization results show that the unit revenue and liquid yield increase by 11.82 yuan/t and 0.92 percentage points,respectively,under the working conditions in the case of maximizing unit revenue;and the unit revenue and liquid yields increase by 7.41 yuan/t and 1.76 percentage points,respectively,under the working conditions in the case of maximizing liquid yield.For the separation system,multi-objective optimization of operating variables was first performed.With the optimization objectives of maximizing target product(gasoline + LPG)yields and minimizing separation system energy consumption,the modified non-dominated sorting genetic algorithm(NSGA-Ⅱ)was used for the multi-objective optimization of the FCC separation system.A multi-objective optimization method was established through the selective selection of decision variables,the study of optimal algorithm parameters(including population,Pc,Pm adaptive strategy,and generation),and the decision of optimal point.The results show that for this optimization model,the optimal population is 125,the adaptive strategy is set for the optimal Pc and Pm of this model,and the optimal solution set of this model is obtained under the generation of 200.The optimization results corresponding to the optimal point show that the yield of the target product(gasoline + LPG)is an increase of 4.93 percentage points,and the energy consumption of the separation system is reduced by 16.88%.In addition,process optimization of the absorption-stabilization system in the separation system was also performed in this thesis.The two-steps condensation process,the process with an intermediate reboiler,and the pre-equilibrium process were applied in simulation analysis respectively under similar criteria of product quality index.The results show that there is no significant change in product yields,while the energy consumption of the absorptionstabilization system is reduced by 4.67% to 9.85%.Therefore,a composite process with the advantages of the three above mentioned processes was proposed and conducted simulation analysis.The results show that the product yields and product qualities of the composite process are slightly higher than those of the working process,and the energy consumption of the absorption-stabilization system is reduced by 22.47%.Simultaneously,the desorption gas amount is approximate one-third lower than that of the working process,and the gas phase load of the desorption tower is lower than that of the working process.The simulation and optimization work in this thesis gives optimized operating parameters and variables for different parts of FCC unit as well as a more comprehensive optimization analysis,which provides important data support and optimization ideas for optimization in this FCC unit,and also provides a case reference for the optimization of other FCC units. |
