Energy, Water and Process Technologies Integration for the Simultaneous Production of Ethanol and Food from the entire Corn Plant

This contribution presents the simultaneous integration of different technologies for converting different parts of the corn plant, and integration of energy, water and feedstocks. The traditional dry-grind process is used for obtaining ethanol from corn grains, whilst for the conversion of corn stover to ethanol, gasification using two different paths of syngas conversion is taken into account: syngas fermentation (thermo-biochemical path) and catalytic mixed alcohol synthesis (thermo-chemical path). These processes are modelled in the Mixed-Integer Process Synthesizer (MIPSYN) using mass and energy balances and conversion constraints. Short cut models for the more complex process units are obtained from the detailed ones, as developed by Martin and Grossmann (2011). The results show that the best integrated process when using the entire corn plant is a combination of the dry-grind process and thermo-chemical conversion. For the base case (18 kg/s of grain and 10.8 kg/s of stover), the optimal scheme is comprised of dry-grind and thermo-chemical conversion technologies. The best integrated process requires only 17 MW of energy, 50 MW of cooling and 1.56 L/L of freshwater, with an ethanol production cost of 0.41 $/kg. In the thermal conversion, the integration of energy plays the more important role when reducing production costs. Since the thermo-chemical path enables better heat integration, it is preferred over the thermo-biochemical in spite of the higher yield and sharing of equipment, when using the syngas fermentation path.