North Dakota-based Red Trail Energy (RTE), which since 2007 has operated an ethanol production facility with annual production of about 60 million gallons per year, is proposing sequestration of CO₂ produced from starch fermentation to lower the overall carbon intensity of the fuel for the California Low Carbon Fuel Standard (LCFS).

RTE already has two certified starch ethanol pathways under the LCFS (ETHC218 and ETHC219) for DDGS1 ethanol and MDGS ethanol. The ethanol fermentation process produces high purity CO₂ and is an ideal candidate for carbon capture and sequestration. This ethanol facility is expected to produce approximately 181,000 metric tons of CO₂ annually from starch fermentation.

RTE is now requesting approval of two design-based starch ethanol pathways which take into account sequestration of CO₂. RTE recently performed a detailed assessment of engineering designs for capturing, transporting and storing CO₂, and integrating CCS with ethanol production. The planned facility for CCS sits atop the Broom Creek Formation which is the proposed CO₂ storage site.

RTE proposes capturing the high purity CO₂ stream (>99%) from the ethanol fermentation tank via a commercially available liquefaction system. The liquefaction system includes compression, dehydration, refrigeration, distillation and a booster pump.

The high purity stream will enter the liquefaction system which will remove moisture and other non-condensable gases such as nitrogen while liquefying CO₂. The liquefaction system will be designed to minimize CO₂ losses and is expected to achieve a capture efficiency close to 99%.

The liquefied CO₂ will be transported to a sequestration and storage site located two miles away via an underground pipeline and injected into the Broom Creek Formation.

The Broom Creek Formation is a saline formation that lies approximately 6,500 ft. directly beneath the RTE facility. The formation extends over southwestern North Dakota, southeastern Montana, and northwestern South Dakota. The thickness of the formation beneath the injection site is approximately 270 ft. Shales and salts of the Opeche, Piper, and Swift Formations overlying the Broom Creek Formation form primary, secondary, and tertiary confining zones of more than 1.000 ft. in combined thickness.

RTE is proposing two ethanol with CCS pathways:

• Midwest Corn, Dry Mill; Dry DGS (DDGS), Corn oil and Syrup; Natural Gas and Grid Electricity; Starch Ethanol with CCS produced in Richardton, North Dakota; Ethanol transported by rail to California. CI = 43.00 gCO₂e/MJ.

• Midwest Corn, Dry Mill; Modified DGS (MDGS), Corn oil and Syrup; Natural Gas and Grid Electricity; Starch Ethanol with CCS produced in Richardton, North Dakota; Ethanol transported by rail to California. CI = 37 gCO₂e/MJ.

By comparison, the pathways without CCS ETCH21 (DDGS) has a CI of 82.30 gCO₂e/MJ; ETCH219 (MDGS) has a CI of 76.46 gCO₂e/MJ.