Energy Reduction in the Production of Ethanol by Membrane Dehydration
Distillation/dehydration represents the largest fraction of the energy used in the production of ethanol. The SiftekTM technology introduced in this paper carries the potential of reducing energy consumption of distillation/dehydration by up to 50% through the single pass removal of water from the water/ethanol stream at the beer column outlet, using a novel membrane process. For a modern corn-based ethanol plant, this is equivalent to 7.0 US$/gal, or 1.8 US$/L. SiftekTM is a novel polymeric membrane that can operate continuously in the vapor phase and in the presence of high water concentration. The hollow fiber membranes are made of a proprietary polyimide blend that offers high water/ethanol selectivity and water permeance. The water/ethanol vapor mixture is introduced at the beer column operating pressure on the bore side of the hollow fiber module. The water permeate stream is condensed and the steam latent heat is recovered. A vacuum provides the driving force between the bore side and the shell side of the membrane. The technology has been demonstrated in the field at a capacity of 1200 kg/day (2600 lbs/day) of vapor feed with an ethanol content varying between 75 and 90 wt% at one of the Greenfield Ethanol Inc plants in Tiverton, Ontario, since August 2006. The presentation will include a detailed description of the technology, the results from the field demonstration unit, scenarios for retrofitting into existing or new green-field ethanol plants, and a summary of the energy savings and projected pay-back calculations.