Study On Modeling And Optimization Of The Process For Fuel Ethanol By Raw Fermentation

Since 1970s, as alternative and renewable energy resources, fuel ethanol using biotechnology has become a research focus of many countries. Fuel ethanol research is important in the sense that it can converse biomass energy, relieve energy crisis, and reduce atmosphere pollution and so on. In China, most processes for ethanol dehydration have high-energy consumption due to the lack of deep heat integrations for distillation processes. Especially for large-scale fuel ethanol processes, energy consumption is still a key concern not only because it is the main factor influential to product cost, but also as the price of the fuel ethanol should be competent to fossil fuel.Raw fermentation is the process of liquescence, saccharification and fermentation conducting at the same time. By cutting the cook process, besides energy saving, the deoxidized sugar in the broth is in the low level during the whole process, which has the advantage of avoiding the fermenting material to be infected by other bacteria and being suitable for high gravity fermentation. With low viscidity, the broth by raw fermentation flows well in the distillation column. By contrast with American, who has corn as the main fermentation material for fuel ethanol, lots of first-crop paddy in south china can be new raw material for ethanol production, so raw fermentation for ethanol using paddy is suitable for the situation of China.This paper presents a design of a new process scheme of ethanol production by raw fermentation. The process model is developed and the heat integration problem is studied. We simulated the process using rigorous models under different condition, and obtained the variation of energy consumption to columns' pressures and the optimal solution by adjusting the reflux ratio of the prefractionator. For distillation, heat is supplied to the prefractionator's reboiler and taken away from the second column's condenser and absorb column, and heat balance is achieved by adjusting the reflux ratio of the prefractionator. For verifying the feasibility for the lower pressure operation of prefractionator using as feed the paddy by raw fermentation, experiment on low pressure distillation is performed. In the experiment, compared to atmosphere distillation, low-pressure distillation is proved to be able to save more nourishment, remain more yeast for the fermentation with cornstalk and finally give more energy saving.