Simulation And Optimization Of Semi-continuous Simultaneous Saccharification And Fermentation In Fuel Ethanol Production

Fuel ethanol is a renewable and environmental friendly fuel, which can effectively solve the problem of the energy shortage and environment pollution. The cost of raw materials and energy consumption are the main factors restricting the development of fuel ethanol. Optimization of fermentation process, which can improve the utilization rate of raw materials and reduce energy consumption, thereby lowering the production cost, is an important way to sovle the bottleneck of fuel ethanol development. In this thesis, dynamic simulation method was utilized to simulate and optimize semi-continuous simultaneous saccharification and fermentation process.Continuous fermentation is the initial stage of semi-continuous fermentation. Optimization of continuous fermentation can provide basic information for semi-continuous fermentation. The major parameters were investigated using Aspen Sensitivity Analysis tools. The calculation results showed that continuous fermentation achieved 11.13%wt. of ethanol with 100U/g glucoamylase and 30% yeast inoculum size after 80 h by 8 fermenters.Continuous fermentation is the second stage of semi-continuous fermentation. Batch fermentation was simulated by Aspen Dynamics, and then the results were compared with those of Aspen Plus. Thus, the interaction effect of saccharification and fermentation was studied and the number of batch fermenter and charging strategy was optimized. The obtained results showed that dynamics module was more proper due to the consideration of charging. The saccharification rate reached its maximum after 16 h. When the yeast inoculum size was less than 5%, there would be accumulation of glucose. The optimum charging time was 12.5h, and fermenter volume was 1800m3. After 67.5h,the mass fraction of ethanol was reached to 11.28%, and the productivity was 1.275g/L?h. The process needed 7 heat exchangers and total heat exchanger area of 889 m2.The fermenter number, fermentation time and the heat exchange system of semi-continuous process were investigated and optimized. The simulation results demonstrated that with two 1500 m3 continuous fermenters and five 1800 m3 batch fermenters, after 48 h, the mass fraction of ethanol was reached to 11.20%, and the productivity was 1.332g/L?h. The process needed 7 heat exchangers and total heat exchanger area of 378 m2.By comparing three different fermentation methods(the continuous, batch and semi-continuous), the ethanol concentration obtained from the semi-continuous fermentation is higher than that from continuous fermentation, and the ethanol productivity is higher than batch fermentation. The semi-continuous fermentation is superior to batch fermentation in the fermentation equipment investment and is better than continuous fermentation in the fermentation index. Therefore, using semi-continuous simultaneous saccharification and fermentation for mass production of fuel ethanol is fairly promising for development and good economic benefits.