Cleaning Up In California

In the lower Central Valley, Calgren Renewable Fuels makes three biofuels—ethanol, biodiesel and renewable natural gas—and the latter operation just keeps growing.
By Tom Bryan | April 19, 2022

As out-of-state ethanol producers strive for lower carbon intensity scores to make good in California’s market, one legacy low-CI producer in the Golden State is ironically more focused on a different output—renewable natural gas. 

“We’ve been at this—dairy digester, manure-derived biogas production—for some time now, and it’s worked out really well,” says Lyle Schlyer, president of Calgren Renewable Fuels LLC in Pixley, California. “The bulk of our biogas doesn’t power our biofuel plants. It goes to RNG, which is a more profitable end use. It earns us a D3 RIN, which we don’t receive when the biogas is used for energy onsite.”

Calgren, a 58 MMgy corn dry mill built in 2009, primarily rails in corn from the Midwest. Schlyer says the plant is currently running at a relaxed pace. “I’d like to say we we’re at full capacity,” he says, “but that’s seldom the case.”

To be clear, Schlyer says, the ethanol plant is in nice shape and running well—partially powered by biogas—as is Calgren’s co-located 5 MMgy biodiesel plant, which utilizes brown grease (trap grease, animal waste, etc.) and distillers corn oil (DCO) at about a 50/50 ratio. “We initially thought we’d use less brown grease—maybe 20%—but ended up hitting a higher number,” he says, adding that the biodiesel plant has been a “challenging but fruitful” part of Calgren’s biorefining experience since it came online in 2019. “We’ve had to learn a lot over the past few years, but it’s worked out nicely. The brown grease aspect has been especially good.”

Calgren, which operates another ethanol plant of the same size and design in south-central Kansas (Pratt Energy LLC), has morphed its Pixley biorefinery into what it is today—an integrated ethanol/biodiesel/RNG complex—through stages of layered investment. It’s onsite anaerobic digester, paired with a combined-heat-and-power plant, came online in 2015 and can produce up to 11 MW of power. Its biodiesel and RNG ventures started a few years later.

Schlyer describes Calgren’s biogas involvement as two separate but related operations: (1) biogas production for onsite energy; and (2) biogas production and conversion to pipeline-quality RNG, or as he calls it, RCNG. The biogas digester on the Pixley campus, a modified plug-flow design, produces an industrial-grade biomethane derived from dairy manure, biodiesel wash water and other substrates. “We primarily use slurry from the nearest dairy in that digester, but it is permitted for a wide range of feedstocks,” Schlyer says. “Because it’s not exclusive to dairy manure, however, we can’t use that biogas for D3 RIN generation through RNG, so we use it as a process fuel to make ethanol and biodiesel.”

The way Calgren utilizes its onsite biogas for energy is as unique as the raw materials it comes from. Schlyer says the biogas is typically not used to generate electricity alone, but rather process heat and power. “We have just generated electricity from time to time, but because of the way we have to allocate electricity under the California Low Carbon Fuel Standard, the more prudent approach for us is to use biogas to generate thermal energy.”

By using biogas to help fire its thermal utility—which requires the biomethane to be cleansed of sulfur but not CO2—Calgren lowers the CI score of its ethanol and biodiesel by about two points each. Calgren’s current ethanol CI score is just under 59, a number based on the plant’s biogas utilization, ultra-efficient steam utilization (its distillation-dehydration-evaporation system designed by Thermal Kinetics uses steam four times) and selling all of its distillers grains wet, among other factors.

Calgren’s two cogen units run more efficiently when they are “pedal to the metal,” Schlyer says, so the company typically runs them at full rate and sells any excess power back to the grid through a feed-in tariff with the regional utility, Southern California Edison.

The site of the biorefinery is as distinctive as Calgren’s business model, with the entire complex packed into a relatively small triangular lot between a two-lane county road to the west and a rail line and busy freeway (Route 99) to the east. “We’ve squeezed a lot into this little site plan,” Schlyer says. “There’s so much here—a digester, biogas cleanup, ethanol, biodiesel, cogen and even a collocated CO2 liquefaction plant.”

The branch of the biorefinery getting the most attention right now, however, is the biogas cleanup facility, which upgrades raw dairy digester biogas into pipeline-grade RNG. While Calgren’s original digester remains on site, subsequent digesters have been set up miles away at area dairies. Since late 2018, Calgren has been processing biogas from several dairies in the area. “We pipeline biogas from those sites to our facility and clean it up,” Schlyer says. “The newer digesters—we’re up to 14, plus another three that we [receive] from, and building more—are primarily covered lagoon digesters, and we capture the methane and CO2 that would otherwise be emitted, so we get a credit for that. More importantly, we get a cellulosic RIN for the RNG that we produce.”

The process of upgrading raw biomethane to RNG involves, among other things, removing hydrogen sulfide and carbon dioxide. California has tight specifications for RNG. Ironically, though, diary digester biogas is not hard to purify. “Biogas from dairy manure, funny enough, is pretty clean,” Schlyer says. “It really has just a little bit of hydrogen sulfide and some CO2 in it, as opposed to landfill gas, which has more siloxanes and other bad actors to clean up.”

Schlyer estimates that Calgren’s RNG production is close 500,000 MMBtu per year. “It’s a lot of gas,” he says. “And we just keep adding to it.” 

While Calgren’s RNG production has little or nothing to do with its ethanol and biodiesel plants, the company views the three production flows as parts of an integrated biorefining operation with synergies that make each branch more efficient. “We think of everything as essentially connected, and we have incredibly talented operators running the whole system. They all work together to run the various operations,” Schlyer says, explaining the company’s early plan. “We always envisioned a renewable fuel complex, and we initially envisioned using more biogas to run the biofuel plants—and we still may—but biogas today can be turned into RNG, not just for use as a transportation fuel but for any number of uses. It could be used to make electricity for Teslas. We’re just not sure what tomorrow will bring.” The RNG produced at Calgren's facility is mostly used as a carbon-negative fuel for heavy-duty vehicles like transit buses and long-haul trucks, but it can also be delivered to customers to generate clean electricity and heat homes and businesses, which is what Southern California Gas Co. plans to eventually do. 

Just a few years ago, it was reported that Calgren’s affiliated dairy digesters represented the manure waste from over 65,000 cows in the Pixley area, but Schlyer says that number is over 100,000 today. “Candidly, our diary digester work has been so successful that it’s hard to not keep building more,” he says, describing how the company sells RNG to SoCalGas, which has committed to replacing 20 percent of its traditional natural gas supply with RNG by 2030.

By some accounts, Calgren is one of the largest producers of RNG derived from dairy digester biogas in the world, but Schlyer says he isn’t keeping tabs on other producers. “I’m really not sure if we’re one of the largest, but it wouldn’t surprise me,” he says. “We are building out more digesters now, and we’ve been continuously expanding for some time. We’ve got another half dozen digesters under development today, and we’ll likely add a few more after that.”

Under state law in California, dairies and other sources of methane emissions must reduce their emissions by 40 percent by 2030. If they don’t, they could be mandated to do so without the benefit of remaining eligible for environmental credits. But Schlyer says it’s not the stick, but the carrot, that’s driving California dairies  to capture biogas.

“We write them checks,” he says. “Those dairies end up with another revenue source, and they become part of something really unique and right; they become little energy producers. With our help, and sometimes by themselves, they’re capturing biomethane that would otherwise be released into the atmosphere. It’s a good deal for everybody.”

Aemetis also Going All-In on Biogas/RNG
In Keyes, California, Aemetis Inc. has optimized its unique geographic location in a way that truly highlights the benefits of biogas integration and usage. Starting roughly a year and half ago, the 60 MMgy advanced biofuel producer began using biogas to directly power a boiler at the plant. Doing so allowed Aemetis to expand its dairy-based biogas business.

“We are in the middle of the world’s largest dairy shed,” says Eric McAfee, CEO of Aemetis. With a $4.1 million grant to construct a biogas upgrading facility, Aemetis was able to utilize a pipeline already delivering biogas from more than a dozen anaerobic digesters at dairies in two California counties.
This January, the company also completed a biogas pipeline spanning 36 miles across multiple dairy digester sites. The California Air Resource Board, through the California Energy Commission, supplied grant money for the pipeline.

In early April, Aemetis successfully completed testing of its biogas-to-RNG upgrading and compression facility. Pacific Gas & Electric is now conducting final tests of the utility gas pipeline interconnection—already constructed—which will enable the injection of RNG into PG&E’s pipeline. Ultimately, Aemetis would like to grow the operation to include more than 60 dairies and capture more than 1.6 million MMBtu of biomethane per year.

For ethanol facilities looking at biogas integration, McAfee says the opportunity is two-fold. Producers can produce and sell RNG while also integrating biogas power into their ethanol operation, which reduces the plant’s CI score (the CI of biogas is negative 426 compared to natural gas at plus 100). “I think people should be trying as hard as possible to get into dairy or swine biogas,” he says.

-Luke Geiver


Author: Tom Bryan