Branching Out

Aemetis’ refinery will produce renewable diesel and renewable jet fuel from almond orchard and forest wood waste, which will also yield a negative carbon sugar source for ethanol. The Keyes, California, plant is also ditching fossil-based power.
By Matt Thompson | July 24, 2021

Eric McAfee, CEO of Aemetis, says the markets for sustainable aviation fuel (SAF) and renewable diesel are strong. The diesel market—and by association, the renewable diesel buildout—continued to gain momentum during the pandemic, with brisk trucking volume tied to the booming and irreversible phenomenon of consumer goods home delivery. “Renewable diesel is in high demand. Aviation fuels likewise,” he says. “It’s a 79 billion gallon market worldwide.”

And that’s good news for the company, as progress on its Carbon Zero One plant, a renewable diesel and SAF (i.e., biojet fuel) refinery continues. “We already announced the engineering for the process phase, and the engineer for the construction phase is next,” McAfee says, explaining that engineering and permitting work will continue as project financing is finalized before construction. “We’re at the end of the development phase.”

The plant will use almond orchard waste, as well as forest waste wood, from California, which McAfee says will help keep the plant’s carbon intensity (CI) score low. The unique feedstock also ends up being a benefit for Aemetis’ corn ethanol plant in Keyes, California, as sugar from the renewable diesel plant’s waste wood will be extracted for use in producing ethanol.

“If you can take sugar from a carbon negative 100 waste wood, and you have positive 50 carbon intensity sugar that comes from corn, which one are you going to make more money on, the corn or the waste wood?” McAfee says. “Then factor on top of that the waste wood is very low cost. It’s one tenth the cost of the sugar.” He adds that with the cost savings on the feedstock, and the premiums received from California’s LCFS, every 10 percent of production that uses the waste orchard wood as a feedstock generates $30 million. “That’s linear, so 20 percent is $60 million, 30 percent is $90 million, and 100 percent is $300 million. That doesn’t fade as you get more feedstock.” Those returns are possible because the feedstock is carbon negative.”

And the benefits aren’t just financial, McAfee says. “By providing an alternative use for waste wood and, ultimately, eliminating field burning of the 3 billion pounds per year of waste orchard wood in California’s Central Valley, we plan to significantly reduce greenhouse gas emissions and air pollution while displacing carbon intensive feedstock with negative carbon-intensity feedstock for the production of renewable jet and diesel fuel,” he says.

“So that’s the innovation—that it’s a jet and diesel fuel business [that also produces an input for] cellulosic ethanol using our corn ethanol plant,” McAfee explains.

Ethanol Upgrades
In addition to the lower CI the ethanol plant will enjoy from its feedstock, the 65 MMgy plant in Keyes is undergoing improvements to make it more energy efficient and lower its CI score further. “We’re basically changing the plant from being a petroleum natural gas to an electricity powered plant,” McAfee says, explaining that the electricity will be generated from on-site solar in conjunction with grid electricity from hydroelectric power.

Switching a plant from natural gas to electric power requires new equipment used in ethanol production. For example, McAfee says, the plant is using an electric-powered Mitsubishi Zebrex unit for dehydration. “It’s a unit that uses ceramic membranes instead of a vacuum and pressure system powered by natural gas,” he says. “It’s basically electric pumps, pushing ethanol water through tubes of ceramics, and the bit of tube separates out the water molecules.”

Another change the plant has seen is the use of mechanical vapor recompression, which McAfee describes as glorified fans. “They’re basically taking existing steam and compressing it again, making it hot and high pressure again,” he says. “This uses fans, rather than boiling water which uses natural gas.”

Along with high efficiency heat exchangers, the last upgrade will be the addition of on-site solar energy production, McAfee says. “Overall we’re just getting rid of 100 percent of our petroleum natural gas,” he says. “Eighty-five percent becomes electricity and 15 percent becomes biogas, which has a negative 426 CI score. All of our energy will be a zero CI, very low carbon intensity grid electricity from hydroelectric, or negative 426 CI biogas.”

That biogas comes from nearby dairy farms. “Dairy cows provide waste to the dairy digesters, thereby producing biogas that we cleanup and pressurize in an Aemetis processing unit at the dairy, then transport via the Aemetis Biogas pipeline back to our ethanol plant to use in the production of ethanol by displacing high carbon intensity petroleum natural gas,” McAfee says.

Zero Carbon Financing
The projects were funded, in part, by grants from the California Energy Commission’s Low Carbon Fuel Production program, which according to Hannon Rasool, the deputy director of the California Energy Commission’s Fuels and Transportation Division, “supports new and expanded renewable, ultra-low carbon transportation fuel production at advanced fuel production facilities, and helps the California fuel industry, vehicle manufacturers and operators work towards a low-carbon future. Funding for these projects came from the California Climate Investments program funded by the Greenhouse Gas Reduction Fund.”

Rasool says the projects at the Keyes plant were attractive because they aligned with objectives of various California agencies and programs. “This project complements the California Department of Food and Agriculture’s Dairy Digester Research and Development Program, which focuses on reducing emissions at dairies throughout the state,” Razool says. “Biogas from surrounding dairies in the region is captured in anaerobic digesters and pipelined to a central biogas upgrading facility located at Aemetis’ Advanced Fuel Production Facility in Keyes.”

While the CDFA’s funding focuses on digester installation at surrounding dairies for methane reduction, the CEC’s funding focuses on upgrading the biogas so it can be used on-site or injected into the pipeline for use as a transportation fuel. In this case, Aemetis is doing both. A fueling station will be installed on-site to help fuel trucks that come and go from the facility, while some fuel will be injected into the pipeline. A separate amount of fuel is also being allocated specifically for use in a truck fleet used by one of the surrounding disadvantaged communities to help reduce emissions.”

McAfee notes that plants shipping ethanol to California would be the main beneficiaries of such upgrades, thanks to the incentives available through the LCFS. But, he says, if regulatory changes happen, he expects more ethanol plants to take a serious look at their CI scores. “If you don’t ship your product into California, you’re not going to get any benefit from carbon intensity reduction,” he says.

McAfee adds, “I think if the Low Carbon Fuel Standard regulatory policy is adopted nationwide, which is a trend that’s definitely starting to develop, then we can see pretty much every ethanol plant in the United States adopt low-carbon production techniques.”

While Rasool says electrification is California’s main goal for light-duty vehicles, biofuels play an important role in the state’s emissions targets. “There are use cases in which zero-emission vehicles may not, in the near-term, be the best fit. Support of in-state, commercially available, low-carbon fuels are a key part of the California Energy Commission strategy and will ensure that emission reduction goals can be met and accelerated in some vehicle sectors that are more difficult to convert to zero-emission vehicles,” he says. “Low-carbon fuels are a near-term and cost-effective approach for reducing emissions in sectors that may be several years out from zero-emission options.”

Author: Matt Thompson
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