ARS | Publication request: Microfiltration of thin stillage: Process simulation and economic analyses

Submitted to: Biomass and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 4, 2010
Publication Date: December 28, 2010
Citation: Arora, A., Seth, A., Dien, B.S., Belyea, R.L., Singh, V., Tumbleson, M.E., Rausch, K.D. 2011. Microfiltration of thin stillage: Process simulation and economic analyses. Biomass and Bioenergy. 35(1):113-120.

Interpretive Summary: Nearly 14 billion gallons of corn ethanol are produced in the United States, much of it from what is termed the dry grind process. For every bushel of corn processed, 17 lbs end up as animal feed. Following fermentation, the liquids and solids are separated and the liquids (thin stillage) concentrated prior to being sprayed onto the solids and dried in a rotary dryer. The thin stillage is concentrated by evaporation. This study modeled what would happen if the evaporators were replaced with more energy efficient membrane de-watering systems. The results demonstrate a 50% reduction in operating costs for the ethanol facility and greater than two times increase in water removal capacity compared to a typical evaporator system.

Technical Abstract: In plant scale operations, multistage membrane systems have been adopted for cost minimization. We considered design optimization and operation of a continuous microfiltration (MF) system for the corn dry grind process. The objectives were to develop a model to simulate a multistage MF system, optimize area requirements and stages required for a multistage system, and perform economic analysis of a multistage MF system for a 40 million gal/yr ethanol plant. Total area requirement decreased with number of stages but there was tradeoff between higher capital costs involved at higher number of stages. To achieve thin stillage total solids concentration from 7 to 35%, a 5 stage membrane system was found to be optimum with area requirement of 655 m**2 for minimum cost. Increase in the input stream flow rate from 1.54 x 106 to 2.89 x 106 L/day significantly increased the total capital cost of the system by 47%. Compared to a single stage system, an optimal system had a 50% reduction in operating costs. Optimal system also showed potential to process more than twice the amount of thin stillage compared to a 4 effect evaporator system for given conditions.