Energy saving alternatives for renewable ethanol production with the focus on separation/purification units: A techno-economic analysis

The bioethanol production process includes energy-demanding units with high operating costs, i.e., separation, dehydration, and stillage evaporation units. The present study attempts to reduce energy consumption and, ultimately, ethanol price through industrially feasible methods. These methods include adopting thermally-coupled columns, dividing-wall columns, single/multi-stage pervaporation process, and evaporators. Nine scenarios were studied and compared with an industrial process case using heat-integration and thermal vapor recompression system. Each scenario was simulated with Aspen Plus® and analyzed with Aspen Process Economic Analyzer. The pervaporation process with a hydrophilic polymer membrane was modeled with MATLAB using sorption-diffusion theory and three-conservation law. Then, the required membrane area and the temperature drop during the pervaporation process were estimated. The dividing-wall column reduced the separation unit's energy consumption by 67% and the capital costs by 19%. The energy consumption decreased by 49% by adopting thermally-coupled and heat-integrated columns, and capital costs were reduced by 17%. Moreover, the four-stage pervaporation process for ethanol dehydration proved to be more profitable than the pressure swing adsorption. The proposed and investigated methods reduce the cost associated with the processes' energy consumption and decrease bioethanol's overall production cost.