RESEARCH: Reduction in energy usage during dry grind ethanol production by enhanced enzymatic dewatering of whole stillage: Plant trial,process model,and economic analysis

Abstract

A plant trial was conducted at a 54 MGPY dry grind fuel ethanol facility to evaluate the use of enhanced water removal from whole stillage by enzyme addition during fermentation. Laboratory data had previously shown significant improvements in water removal that could potentially result in significant energy and water savings during ethanol production. Plant baseline data was collected for normal operating conditions before and after the enzyme addition and statistically compared to the results collected during the enzyme-treatment period. The results showed a significant increase in the amount of water removed during centrifugation, resulting in a lower-moisture cake. The firing rate of the drier was decreased during the enzyme-addition period, resulting in a 12% reduction in the amount of natural gas required to produce 1 gal of ethanol. DDGS composition was unaffected. Process model simulations developed using the plant trial results showed a decrease in utility consumption for the enzymatic treatment model compared to the conventional model. Sensitivity analysis showed a tradeoff between the enzyme cost and drier’s natural gas savings. Additional sensitivity simulations with enzyme dosing show energy, water, and economic benefits for a wide range of enzyme and natural gas costs. Water use was reduced by up to 14% for processing and 10% overall. Total energy reductions were calculated with the 54 MGPY process model and found to reduce greenhouse gas emissions by approximately 7.2 million kg of CO₂ equivalents/yr.