Superheated Steam Drying Technology in an Ethanol Production Process

Abstract

Superheated steam drying (SHSD) is a process that uses steam heated beyond its boiling point, in lieu of air, in a direct contact dryer to remove moisture from the wet material. Moisture removed in the form of superheated steam is readily condensed to provide heat for other applications and to recover the liquid water. A SHSD model was developed in Aspen Plus to determine energy and water recovery for drying the co-products, distillers wet grains (DWG) or DWG and syrup, in a corn ethanol plant. The SHSD model was integrated into a biomass integrated gasification combined cycle (BIGCC) model to produce heat and generate power at an ethanol plant. Results were compared to estimates for a steam tube dryer (STD), which uses air to remove moisture. Energy consumed for the SHSD ranged from 760 to 805 kJ/kg of water removed, and 1.3 liters of water was recovered per liter of ethanol produced. Energy consumption for the STD was 2660 to 2690 kJ/kg of water removed with no water recovery. However, using superheated steam drying with a BIGCC system to provide heat and power at a fuel ethanol plant resulted in lower thermal efficiency and less power to the grid than steam tube drying because the more efficient drying process provided a smaller heat sink in which to discharge the waste heat from the power generation cycle.