Lowered Drying Costs from Corn Oil Removal Impact Carbon Accounting Managing carbon intensity values under California’s LCFS By James M. Ramm
California’s Low Carbon Fuel Standard allows an ethanol plant to submit a Method 2B petition to the California Air Resource Board requesting a lower carbon intensity (CI) number. Jan. 8, CARB
issued guidance for ethanol producers seeking a lower CI number based on distillers grains dryness levels. The new guidance makes clear that use of default drying energy values is no longer acceptable because it may overestimate CI reductions. Going forward, petitions must be based on plant-specific, operational information on drying or overall plant energy. The proliferation of advanced technologies for corn oil extraction systems (COES) and the increasing use of nonfood-grade (NFG) corn oil for biodiesel production contributed to the latest guidance. CARB also states it cannot prescribe a single approach because drying systems and processing parameters can vary widely from one plant to the next. Over the past two years, the use of NFG corn oil for biodiesel production has grown tremendously. Corn oil biodiesel is eligible for a D4 RIN (renewable identification number) under the renewable fuels standard and the LCFS has assigned it a CI value of 4 grams of CO2 equivalent per megajoule of biodiesel produced. Biodiesel made from NFG corn oil is eligible for the CI value of 4 because the energy required to dry the DDGS at the ethanol plant after the corn oil is extracted is considerably lower. This energy saving is credited to the corn oil and subsequently to the biodiesel made from it. The low CI value for NFG corn oil biodiesel assumes the DDGS is dried fully at the ethanol plant, for if the distillers grains were not dried, there would not be any energy savings to be allocated to the corn oil. Second,
it assumes that the ethanol plant selling the corn oil is not submitting a Method 2 pathway and lowering the CI of its ethanol based on lower energy consumption, as this would be double counting. Third, it assumes that the actual energy savings from installing COES is 3,070 Btu per gallon of ethanol.
A regulated party using the CI value of 4 for corn oil biodiesel must demonstrate that the net energy savings from the extraction of corn oil at the ethanol facility is greater than or equal to the value used in the Californiaadapted model for greenhouse gases, regulated emissions, and energy use in transportation (CA-GREET) calculation: 3,070 Btu per gallon of ethanol. If the net energy savings at the ethanol plant from corn oil production is less than this value, the biodiesel producer must use the Method 2A/2B pathway option of the LCFS. In the CA-GREET default scenario for a dry mill corn ethanol plant, CARB assumes a default drying energy of 9,900 Btu per gallon of ethanol. This number is calculated from a 1998 study, which stated that the total energy consumption at an average dry mill plant is 36,000 Btu per gal of thermal energy, and 27.5 percent of that is used for drying DDGS. The assumptions that go into using the default value include: • Sensible heat effects are ignored. • The wet cake must contain approximately 65 percent water. • The syrup (solubles) must contain approximately 65 percent water. • The dry DDGS must contain approximately 10 percent water. • The drying process must be approximately 91 percent efficient. In the latest guidance, CARB admits that
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