Generating Electricity with Biomass Fuels at Ethanol Plants

Vance Morey, Professor
Douglas Tiffany, Research Fellow, Applied Economics
Dennis Hatfield, Ethanol Team Leader, RMT, Inc., Madison, WI

Funding Sources

Xcel Energy Renewable Development Fund

Objective

Answer technical and economic questions related to using biomass to produce combined heat and power at ethanol plants.

Need or Impact

Biomass can provide electricity and process heat at dry-grind ethanol plants to both reduce costs and improve the renewable energy ratio of ethanol production. Distillers dried grains and solubles (DDGS), which are coproducts of ethanol production, can potentially be used for energy. Current prices of DDGS compared to the price of natural gas suggest that the DDGS may be more valuable as fuel than as feed. Cornstover is another potential biomass energy source for ethanol plants. Cornstover is available in the vicinity of most ethanol plants. Also, many ethanol plants are owned by farmers who produce the corn and cornstover, so the process of procuring the material is potentially simplified if technical issues can be solved.

Recent research indicates that the renewable energy output/input ratio for corn ethanol is 1.67 to 1. This means that 1.67 units of renewable ethanol energy are produced for each unit of fossil energy input. Using renewable biomass energy to produce electricity and process heat in a combined heat and power configuration has the potential to improve the renewable output/input ratio for corn ethanol to as much as 5 to 1.

Project Status

The project officially started in October 2005. Our analysis shows that corn dry-grind ethanol production using biomass (DDGS or cornstover) to meet process energy needs and generate electricity achieves net energy values in the range of 72,000 to 108,000 Btu/gal of ethanol, which equals or exceeds previous estimates for biomass ethanol production. There are significant annual energy cost savings/returns for a 40 million gallon per year plant capacity over a range of natural gas and biomass prices to apply to additional capital and operating costs required for a biomass energy system. Electricity generation is potentially an important contributor to the annual energy cost savings/returns because of the ability to effectively use waste heat from electricity generation to meet process energy needs.

The next steps are to 1) analyze co-product streams from ethanol plants as well as cornstover to determine energy, emission, and ash characteristics; 2) evaluate options for combustion, electricity generation, steam production, emission control, and ash utilization; 3) develop capital and operating costs for required technologies; and 4) perform an overall economic analysis for biomass-based combined heat and power at ethanol plants.