(635a) Process Simulation of a Hybrid Gasification-Syngas Fermentation Plant for Production of Ethanol from Switchgrass

Production of renewable energy is part of the overall solution regarding crude oil depletion, release of harmful pollutants to the environment, and energy security. Ethanol can be produced from agricultural and waste materials using the hybrid gasification-syngas fermentation technology described in this work. The hybrid conversion platform has the potential to provide 35% more biofuel from the same amount of biomass compared to other available conversion technologies due to the utilization of all components of biomass including cellulose, hemicellulose, and lignin. In this process, biomass is first converted to synthesis gas via gasification, and the gases (mainly CO, CO₂ and H₂) are then fermented to alcohols and organic acids using acetogenic bacteria at mild temperatures and pressures. While this process has gained interest during the past decade, there is a lack of tools for modeling and process simulation required for techno-economic and sensitivity analyses toward designing large scale syngas fermentation processes. A process flow diagram for ethanol production via the hybrid gasification-syngas fermentation was established using Aspen Plus® software. The simulation illustrates a biorefinery facility to produce anhydrous ethanol from 1,080 metric tons of switchgrass (dry basis) per day. The process model consists of a gasification unit, a bioreactor, and a distillation and molecular sieve purification step.  Sensitivity analyses were performed to show how the main gasification parameters such as air-to-fuel ratio and steam-to-biomass ratio effect the syngas composition. These analyses also assess the effect of the fermenter dilution rate on ethanol production. The results of the work revealed a potential production of approximately 30 million gallons of anhydrous ethanol per year. This work provides a basis for a detailed economic analysis of the process, and it facilitates optimization of the process flow diagram for large scale biorefineries.