CARB accepts innovative Trestle Energy coproduct pathway

By Sue Retka Schill | January 29, 2016

California-based Trestle Energy LLC has received a favorable carbon intensity (CI) rating from the California Air Resources Board that puts it one step closer to commercializing a new approach to reducing the carbon intensity of ethanol. The new energy pathway would shave 18 points off an ethanol plant’s CI rating, according the CARB staff summary of the pathway approval.

James Rhodes, co-founder and president of Trestle Energy, said the new approach creates a new coproduct credit from using corn stover for electric generation, either at an ethanol plant with biomass boilers or at a partnering utility cofiring biomass with coal. “By being very careful about the way we structure those supply chains and working with producers to integrate those supply chains, we’re able to engineer the integrated production of solid coproducts from the stover and liquid biofuels from the grain.”   

Data for the life cycle analysis of the pathway was collected in a demonstration project conducted in 2012 and 2013 with Iowa-based Golden Grain Energy and a local utility. The utility, Rhodes explained, has been evaluating the possible use of biomass in one of its coal-fired boilers for several years. The life cycle analysis used for the CARB CI score took into consideration the additional use of farm equipment for stover removal, additional inputs to offset nutrients removed and feedstock transportation, among other factors. The biggest CI reduction was the result of avoided emissions from using the crop residues.

Coproduct credits are common in life cycle analyses, Rhodes added. A common coproduct credit in biodiesel CI pathways, for example, comes from the feed produced at the soybean mill. Another example would be California crude oil that is produced with enhanced oil recovery using steam. The production of that steam includes an electricity coproduct which is credited to the fuel. 

The CARB summary said that Trestle Energy’s pathway would reduce Golden Grain’s CI to 70.65 with 100 percent DDGS. The calculation was done under CARB’s original modeling, so under the revised CA-GREET 2.0 modeling, the CI score would drop another 10 points due to the adjustment in indirect land use. Rhodes pointed out the low CI score would make Midwestern corn ethanol competitive with Brazilian sugarcane ethanol, where the coproduct credit for generating electricity from bagasse is a big part of the fuel’s low carbon intensity score.

Rhodes reports the company is currently in discussions with a network of ethanol plants to implement the strategy. “The reality of the number of steps and development work that has to take place means this is not something we can do overnight,” Rhodes added. Besides creating the new partnerships with ethanol plants, the feedstock supply chain for stover-based solid fuels has to be established with cooperating utilities.  “We are aiming to ramp up commercial deployment in 2017,” he said.

The company has also received approval under the British Columbia low carbon program and is in discussions with the staff implementing the new Oregon program. Trestle Energy also has filed a petition with the U.S. EPA for consideration of its pathway.