Syngas 101
January 1, 2008

All ethanol is not created equal. Even with corn-based ethanol, a variety of production processes and energy sources is used in biorefineries, with widely differing...

Producing Ethanol for Low-Carbon Fuel Markets

by Richard Plevin and Steffen Mueller

Ethanol Producer Magazine, May, 2007

All ethanol is not created equal. Even with corn-based ethanol, a variety of production processes and energy sources is used in biorefineries, with widely differing greenhouse gas balances. Price volatility in the natural gas markets has led many ethanol producers to consider alternative thermal energy sources, including agricultural residues, distillers grains and syrup, biogas, manure, wood chips and coal. Despite a wide range of climate benefits, domestic biofuels policies have treated ethanol largely as a homogenous product, but not for long.

New Fuels Regulations

On Jan. 9, a new regime was ushered in when California Gov. Arnold Schwarzenegger signed an executive order requiring that state agencies develop a “low-carbon fuel standard” to reduce the carbon intensity of transportation fuels by at least 10 percent by 2020. Within weeks, European Union regulators and the Canadian province of British Columbia proposed a similar standard. Other states are reportedly considering similar measures.

Although the details are still being worked out, the low-carbon fuel standard is likely to use a lifecycle approach and judge each fuel production pathway on its own merits. This will likely involve differentiating ethanol production on a facility-by-facility basis. Carbon regulations will increase the demand for—and relative value of—biofuels offering the greatest greenhouse gas reductions (GHG) relative to gasoline.

Figure 1 shows the range of lifecycle GHG emissions per megajoule of ethanol produced with different energy sources in new dry-grind facilities. Producing ethanol with coal results in a fuel that is just as hard on the climate as gasoline.

Blending climate-friendly grades of ethanol with gasoline may be a primary strategy for reducing the carbon intensity of transport fuels. Without significant adjustments to current operating practices, ethanol produced by coal-fired plants will be of little value to refineries and blenders seeking to lower the carbon intensity of their petroleum-based fuels.

The Way Forward

Existing corn-based ethanol plants have several options for improving their GHG profiles. These include selling wet cake to avoid the GHG emissions and cost of drying distillers grains, like Pacific Ethanol is doing with its 35 MMgy facility in Madera, Calif. Existing plants could also implement a no-cook fermentation system, which avoids energy use for heating and subsequently cooking the mash.

Other plants could integrate with a cattle feedlot similar to what E3 BioFuels has done in Nebraska. E3’s energy needs are met with biomethane from digested manure and thin stillage. Panda Ethanol Inc. plans to gasify cattle manure for process heat at its Hereford, Texas, facility that is currently under construction.

Existing producers could also gasify wood waste or combust syrup, like Central Minnesota Ethanol Co-op and Corn Plus, respectively. These producers have reduced their exposure to natural gas price volatility while lowering the carbon intensity of their product. Under low-carbon fuel standards, the plants will be rewarded by the market.

Retrofitting a natural gas dry-grind plant to use a range of biomass feedstocks may be an option for many existing plants. For example, the Chippewa Valley Ethanol Company (CVEC) plans to bring its 75-ton-per-day biomass gasification system on line in the fall of 2007. According to CVEC General Manager Bill Lee, the total capital costs for a gasification system installed at a 40 MMgy dry-grind plant is about $18 million.

Coal-fired plants can also utilize biomass, either by co-firing the two fuels or by switching to biomass. Co-firing biomass in coal-fired fluidized bed boilers has shown significant promise in large-scale demonstration projects. This practice could allow facilities to approximate the GHG impact of current natural-gas-fired plants.

Under low-carbon fuel standards, the market will demand these adjustments from existing coal-fired ethanol plants. Of course, if the plants are closer to the coal than to biomass sources, their options may be limited.

Carbon sequestration may eventually provide another option for coal-fired ethanol plants to adjust to low-carbon fuel standards.

In the near term, the most readily available biomass source for producers in the Corn Belt is stover. For any quantity of corn, only about 25 percent of the stover is required to provide enough thermal energy to convert the corn to ethanol, an amount that is likely to be harvestable in a sustainable way under conservation tillage. Researchers are actively pursuing improved methods for collecting and storing stover, including preprocessing it in the field (e.g., pelletization) to reduce transport costs and increase storability.

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