A new report has identified two ways Burlington could reduce carbon emissions from its wood-burning power plant without significantly raising electricity rates.
The report commissioned by the Burlington Electric Department examined 12 potential ways the McNeil Generating Station could lower its emissions, but found only two made economic sense: carbon capture and wood pyrolysis.
Carbon capture is just what it sounds like, capturing the CO2 from the burning of wood chips before the planet-warming gas is released into the atmosphere. Chilling the gas to turn it into a sellable liquid could then create a lucrative new revenue stream, the consultants found.
Wood pyrolysis is more obscure but potentially even more beneficial, the report found. Instead of burning wood chips to create the heat to generate the steam used at McNeil, the chips would be cooked at high temperatures in a low-oxygen chamber.
Under such conditions, the wood decomposes into two byproducts: syngas, which is short for synthetic gas, and biochar, a charcoal-like substance. The syngas could then be burned to generate the McNeil’s steam more efficiently, while the biochar could be sold as a soil amendment, the consultants found.
Most of the other technologies the consultants reviewed were either too expensive or resulted in too few emissions reductions or both.
“We’ve identified what we would say are the leading horses in the race on this type of initiative,” Ben Bradshaw, the founder of Massachusetts-based consulting firm Velerity, told city leaders Tuesday.
Bradshaw presented the firm’s findings to the Burlington City Council’s Transportation, Energy and Utilities Committee.
The council in 2023 ordered the report in response to the growing scientific consensus and public realization that burning biomass to generate electricity, which McNeil has done for more than 40 years, is bad for the planet.
That summer the city hosted a symposium about biomass energy at which climate scientists explained that while some label biomass energy as “renewable” or “carbon neutral” because the chips come from trees grown in sustainably managed forests, the trees take decades to reabsorb the carbon.
Following the conference, the council told BED to explore ways to reduce emissions from the plant by 25 percent in 5 years and 50 percent in 10 years. It also asked for options for power generation if McNeil were to close.
“Today’s release of the Velerity report marks an important moment for our efforts toward a just transition for the McNeil Generating Station, including our journey toward improved efficiency and reduced stack emissions,” BED General Manager Darren Springer said in a news release.
During the meeting, however, Springer stressed that Burlington owns only half of the McNeil plant. Green Mountain Power, the state’s largest utility, has a 31 percent share and the Vermont Public Power Supply Authority owns 19 percent.
BED began negotiations to buy out those partners last year. Talks are on hold until the utility gets clarification about whether Connecticut will continue to buy renewable energy credits from McNeil.
During the meeting, Springer stressed that having partners limits what McNeil can do.
“We remain in joint ownership of McNeil, so we’re not able to immediately or unilaterally implement anything,” Springer told councilors.
The carbon capture and wood pyrolysis technologies rose to the top because they are not only capable of producing major emissions reductions, but they essentially pay for themselves because of the potentially lucrative sale of byproducts, the consultants found.
The liquid CO2 could be sold for industrial processes, and the biochar could be offered to farmers as a soil amendment.
Carbon capture could slash emissions by a third but only increase rates by half a percent. Wood pyrolysis, meanwhile, was estimated to have a similar carbon reduction while lowering rates by 1 percent.
Drying the wood chips was rejected. The chips are green, meaning they are full of water, which makes the combustion process less efficient. One idea was to capture excess heat from McNeil to dry the wood chips before burning them. The consultants found that there wasn’t enough excess heat to make the process worth the cost.
Two other ideas, adding renewable natural gas or ammonia to the combustion process, were rejected as too expensive. Two processes the consultants identified were already performed at McNeil.
Another process called an organic Rankine cycle involves using the waste heat to generate additional electricity. The heat causes an organic fluid to expand, turn into a gas, and run a electric turbine. The consultant concluded there was likely not enough waste heat to make this process worth it, either, but Springer said it might merit additional analysis.
The report also outlined a number of options for providing electricity to Burlington and the grid if McNeil were to close. Options include expanding hydropower contracts and installing large batteries to store power at the site or elsewhere in the community.
The report will be taken up by the Burlington Electric Commission in coming weeks.