Can Biogas CHP Help Duke University Meet Aggressive Climate Goals?

April 18, 2018
Duke University is exploring what it takes to acquire and transport renewable biogas from North Carolina hog farms for what may turn out to be a new, microgrid-ready combined heat and power (CHP) plant on the university’s main campus.

Duke University is exploring what it takes to acquire and transport renewable biogas from North Carolina hog farms for what may turn out to be a new, microgrid-ready combined heat and power (CHP) plant on the university’s main campus.

The biogas project emerged after students protested plans by the university and Duke Energy to build a microgrid-ready natural gas-fired CHP plant on campus. That plan is now on indefinite hold and the utility is withdrawing the application filed with the North Carolina Utilities Commission.

Instead, the university is seeking ways to realize an alternative plan that sources renewable energy from methane-biogas produced at nearby hog, aka swine, farms.

Whether or not that plan is implemented, and if it will be microgrid-ready, is yet to be determined. In any event, sourcing renewable biogas at utility scale could enable the university to surpass its 2024, net-zero greenhouse gas emissions goal well ahead of schedule, according to university executives and staff involved in the hog farm-biogas-CHP project.

Duke University launched a strategic Climate Action Plan in 2007, an all-of-the-above strategy centered on three ways to realize greenhouse gas emissions reductions and broader sustainability goals:

  • Enhance energy productivity and energy efficiency
  • Apply green building design principles and associated technology
  • Make use of renewable energy

The university already has gone a long way towards achieving its emissions reduction goal. It has reduced on-campus greenhouse gas emissions by 24 percent to date, said Casey Collins, the university’s energy manager, during An April 10 community forum on the plan. And while Duke’s building footprint has increased 20 percent in the last decade, its energy use has increased only 1 percent, he noted.

Still, students are pushing the university to do more, faster. “We remain committed to 2024…[but] it’s going to be very hard for us to get there without making at least one more big move,” Tallman Trask III, Duke University executive vice president, told community forum attendees.

For example, the university would like to produce, or acquire, as much solar energy as it can. But state regulatory barriers prevent it from sourcing solar power at the utility scale the university requires to meet its needs and realize its 2024 net-zero emissions goal, Collins explained. The university could install solar photovoltaic (PV) panels on every feasible rooftop on campus, but doing so would only produce enough electricity to meet around four percent of the university’s energy needs.

The need for continuous baseload power

The need for lots in the way of continuous, baseload power led the university to consider acquiring biogas from swine farms, a large but untapped renewable energy resource in North Carolina. Capturing the methane gas produced by swine feces conveyed into anaerobic digesters to produce biogas would yield a double dividend, accordingto Tatjana Vujic, Duke University’s director of biogas strategy.

Methane persists in the atmosphere for a shorter time period, but it has a global warming potential 34-times greater than carbon dioxide, the primary source of emissions that drive greenhouse gas, Vujic said. Capturing the methane emissions from swine waste would eliminate a source of climate-warming emissions.

Secondly, the resulting biogas would be a renewable energy resource and it would displace use of natural gas, the extraction, refining and distribution of which is a primary source of methane emissions.

Duke University’s renewable biogas plan would also yield a third, substantial benefit: improving human and environmental health and safety by helping put the state’s hog farms and others on a healthier, safer and more sustainable pathway. In addition to reducing methane emissions, doing so would eliminate foul odors and pathogens from local community environments, Vujic said.

Duke University’s Facilities Management department is responsible for providing enough energy to serve 30,000-50,000 people on campus on any given day, Collins explained.

“We’re a small city in that regard,” he said. “It’s a bit abstract, but the university consumes an average 3.1 x 1012 BTUs a year, which really means that per annum Duke University consumes energy somewhere on the order of that needed to 34,000 typical North Carolina homes.”

Duke University, hog farms and renewable biogas

Electricity accounts for 51 percent of the university’s energy needs and natural gas 49 percent, Collins said. The former is used for lighting, HVAC (heating, ventilation and air conditioning), cooling plants and to power all the plug-in devices used on campus every day. The latter is used to produce hot water, for space heating and for humidity control. Sterilization of medical instruments, devices and apparatus is a particularly critical need on campus given the size and extent of Duke University’s healthcare and medical research activities and facilities, he noted.

Hog farms are the biggest source of methane emissions in North Carolina, a fact that the university’s energy management staff and researchers are well aware of. “We’ve been working on biogas for quite a long time,” Vujic said.

Realizing that the university would have to look outside to meet its climate and renewable energy goals, those efforts took on greater significance and gained momentum when the university introduced its first Climate Action Plan in 2007.

“We began looking for ways [we could use hog farm biogas] not only as a means of qualifying for carbon offsets, but as a means off generating renewable energy,” Vujic explained.

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Adding to that was the prospect of helping put North Carolina’s farms on healthier, more sustainable waste management pathway.

In 2011, a Duke University project team, in partnership with Duke Energy and with support from Google, began to prove the concept by deploying a methane-biogas production system at Loyd Roy Farms, an industrial-scale hog farm in eastern North Carolina. “That kind of kicked off waste-to-energy in the state,” Vujic said.

Duke University’s project team then started considering ways to to scale up from there. In 2013, the group produced a state-wide analysis of swine waste-to-energy production and use that now serves as a swine waste-to-energy road map for North Carolina.

Last year, the team began focusing on the design and engineering of a CHP plant that would be fueled by biogas produced and piped in to a central biogas production facility from local hog farms, as well as other local renewable energy resources. That set the basis for the university project planners to scale up the university’s hog farm-biogas initiative.

“We would overachieve our emissions reduction goals…if we were to power our entire campus on biogas,” Vujic said. “That would put us in a position to be a carbon sink as opposed to a source of carbon emissions…Potentially we could retire more greenhouse gas emissions, or help others reduce theirs.”

Renewable biogas production at utility-scale

Highlighting North Carolina’s national significance when it comes to methane emissions and biogas production potential, Vujic pointed out that the state is the third-largest area in the nation for bio-methane production. “All of that is greatly concentrated in eastern North Carolina. We have right now, maybe 5-20 farms that have anaerobic digesters on them. So that gives you an idea of how much more needs to be captured,” Vujic said.

North Carolina is the only US state that has set a target for renewable biogas. Utilities have not been able to meet that target to date, Vujic noted. Realization of the university’s farm-to-biogas plan could be just what’s needed to spur wider adoption and achieve the goal, not only among hog farms, but poultry farms and wastewater treatment facilities as well, she added.

“Our [market] demand signal alone…would be nearly equal to what the REPS (Renewable Energy and Power Standard] would require of the utilities,” Vujic said.

Duke Energy is following through on its own hog farm-biogas production and power generation plans. The regulated utility recently began transporting biogas from a hog farm in eastern North Carolina through 40,000 feet of pipeline to one of its natural gas power plants some 60 miles away, said Duke Energy spokesman Randy Wheeless said in an interview.

“Normally, most biogas from hog farms is captured, refined and used on site — maybe on the order of 1 MW of power generation is traditional. We do buy some renewable natural gas from Oklahoma that’s connected and shipped via pipeline, but we wanted to shift more towards sourcing from North Carolina farms,” Wheeless explained.

Cost remains an issue for biogas, especially when it is transported a long distance.

“This project is near a Duke Energy power plant, and it’s a bit of a breakthrough for us,” he said. “This is a big first step with future promise. We could scale up by collecting biogas from other farms. It’s really a matter of being able to make that interconnection to the pipeline. Right now, it’s somewhere around three times more expensive than the average cost of natural gas, but given the statewide Renewable Energy and Power Standard we believe renewable natural gas could get more cost competitive as time goes on,” Wheeless concluded.

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About the Author

Andrew Burger

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