| As a renewable energy,fuel ethanol has gradually received widespread attention in today’s society with huge energy demand and increasingly depleted fossil energy.In this paper,two different separation processes are designed for the distillation process of cellulose to fuel ethanol:three-tower differential pressure distillation plus molecular sieve adsorption and extractive distillation.The details are as follows:(1)This article takes ethanol-water,the main substance in the fermented mash,as the main research object.The reliability of the vapor-liquid equilibrium data obtained from the literature was tested,and then the set of experimental data and the regression module in Aspen Plus were used to fit and regression the binary interaction parameters of the three models of NRTL,Wilson and UNIQUAC.Finally,the average error of NRTL was found to be the smallest by analyzing the calculated and experimental values of the three models,so the NRTL model is determined to be the physical property method of this paper.(2)For the production of fuel ethanol,a three-tower differential pressure distillation plus molecular sieve adsorption process is adopted.Because the composition of distillation tower top has an effect on the energy consumption and cost of distillation section and adsorption section,the relationship between the mass composition of distillation tower top and the reflux flow rate of weak liquor in adsorption section is obtained by formula derivation.The simulation calculation and optimization were carried out with 0.5%step size for the mass composition of tower top in the range of 88%～93%by Aspen Plus software.Through the comprehensive analysis of energy consumption and TAC,the optimal mass composition of tower top recovery is determined to be 90%.Then,multi-effect distillation and heat pump distillation were introduced to strengthen the process design.After evaluation,it was found that multi effect distillation had more advantages.Compared with the original process,its energy consumption and TAC were reduced by 25.29%and 19.03%respectively.(3)The extractive distillation separation process with ethylene glycol as extractant was proposed.Based on the sequential iterative optimization method,the optimal operation parameters of each tower were determined,and then the process intensification design was carried out by using variable pressure heat exchange and direct heat exchange between towers.Compared with the original process,the first strengthening scheme reduces energy consumption by 17.80%and TAC by 9.64%.The second strengthening scheme reduces energy consumption by 26.53%and TAC by 18.62%.(4)A comprehensive evaluation of all separation processes was conducted in terms of economy,environment,and exergy loss.The results show that the TAC of three tower differential pressure distillation combined with molecular sieve adsorption separation process is 7.7471 million U.S.dollars per year,the CO2 emission is 6381.11 kg/h,and the exergy loss is 4162.23 kW.The three evaluation indexes of this separation process are the smallest among all separation processes,so it can be determined that this separation process is the most economical,environmentally friendly and has more application potential.In summary,this paper designs two separation processes for the cellulose-to-fuel ethanol distillation process,selects a suitable thermodynamic model,and completes the process simulation optimization,process enhancement design and comprehensive evaluation,thereby determining the optimal separation process in order to provide a reference for actual production. |
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