No More Feeding the Flare at This Oregon Clean-Water Facility

A renewable natural gas process replaces CHP at an Oregon clean-water plant, making use of what had been surplus biogas and generating revenue

No More Feeding the Flare at This Oregon Clean-Water Facility

Aerial view of the Metropolitan Wastewater Management Commission plant shows equipment for purifying biogas. The Greenlane Biogas pressure swing adsorption system in the center foreground.

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The Metropolitan Wastewater Management Commission was producing more biogas than its equipment could use to generate electricity and heat. As a result, the plant was flaring about 40% of the biogas it produced.

The regional facility, which serves the cities of Springfield and Eugene and Lane County, Oregon, could have added more generating capacity. Instead, the commission invested in a new system to turn the biogas into renewable natural gas to be sold into the natural gas grid.

The decision required a substantial investment in equipment, and a receiving point for the natural gas utility to accept the RNG. “A number of factors went into the decision,” says Mark Van Eeckhout, project manager.

A fiscal decision

“We looked at a cost-benefit analysis with a consultant. Ultimately, we decided that between the capital cost of adding generators, the price we would receive for the increased power production, and the offset from additional energy credits, it made more sense to go with the RNG system.”

Steven Barnhardt, operations manager, notes that market incentives made RNG a better choice: “In the 1990s and early 2000s, there was quite a bit of revenue from Renewable Energy Credits for the electricity, but then the RECs went away. We were basically getting just the kilowatt value for the energy produced versus the RECs on top of that.”

However, credits in the form of Renewable Identification Numbers are available for RNG. Now the utility sells the RNG to gas supplier NW Natural and receives energy credits marketed by a broker, ANEW, which sells them mainly to fuel refiners. The RNG facility was connected to the gas grid in November 2021.

CHP as backup

The commission still maintains its CHP system powered by an 800 kW generator (Jenbacher). “It’s available when we have issues with the RNG facility or if there are other issues,” Van Eeckhout says. “We use the CHP to produce power if we’re offline for some reason, because RNG systems don’t always run seamlessly.”

The wastewater treatment plant, in Eugene, has a design capacity of 49 mgd and an average flow of 28 mgd. The biological nutrient removal plant has a standard primary and secondary treatment and a tertiary system that uses fuzzy filter technology (Schreiber, a Parkson brand). Effluent disinfected with sodium hypochlorite and dechlorinated with sodium bisulfide is discharged to the Willamette River.

Biosolids from four anaerobic digesters are pumped to a commission-owned Biosolids Management Facility about 6 miles away and stored in stabilization lagoons. The material is dewatered on belt filter presses and further dried on site before land application on a poplar tree plantation owned by the commission and on grass seed farms.

Biogas was treated for the CHP system, but RNG requires much more purification. The process uses a pressure swing adsorption system (Greenlane Biogas). In addition, gas chromatographs in the production facility and the gas grid monitor the RNG to make sure it meets specifications.

After a little more than a year of operating the system, Van Eeckhout is encouraged by the results: “Generally, when we’re injecting, it’s been quite successful. We have had issues with certain contaminants, and we go back to flaring until we get it figured out.”

Dedicated operator

One decision that helped the project go smoothly was to dedicate one operator to the new process from the beginning. “That was one of the keys to the operation, to have a resident expert who could do the problem-solving and troubleshooting we needed,” Barnhardt says.

“It’s not something that’s easily handed off to the rest of the people in the operations group. It takes quite a bit of time to work the bugs out of the system and to train people on it during startup. It was like a full year of startup where things were changing all the time.”

Spencer Goodro is the lead operator of the RNG facility. As a result of his work during the new facility’s first year, he was named 2022 Oregon Treatment Plant Operator of the Year by the Pacific Northwest Clean Water Association.

While RNG production has been successful, Van Eeckhout says it might not fit every treatment plant: “The decision would be unique to any facility. From an environmental standpoint, I think it’s the right way to go, and financially it is paying us back. We’re not having to flare, and the environmental credits are hopefully offsetting geologically produced natural gas.”

Another environmental plus is that in the Pacific Northwest, most power is generated at hydroelectric dams. Although the commission now produces RNG instead of electricity, the power it buys off the grid is generally carbon-free hydro power.

Even though the biogas flare still gets used from time to time, Van Eeckhout is satisfied with progress at the RNG facility. “My expectations are high, so we really have a way to go, but we’re heading in the right direction,” he says.

“We’re always going to have that flare as a safety outlet. There are always issues. There is always maintenance. There are always things going on, but we’re trying to minimize the amount of flaring.”


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