Editor's note: This story has been changed to correct the planned capacity of the initial landfill gas generator.
The Kenai Peninsula Borough Assembly faces a funding decision in plans to generate energy from methane gas created by decomposing garbage in Central Peninsula Landfill.
At the Kenai Peninsula Borough Assembly’s Tuesday meeting, Mike Salzetti, Manager of Fuel Supply and Renewable Energy Development for Homer Electric Association (HEA) — the local electrical cooperative that would participate in the landfill gas project as a power buyer — gave assembly members a rundown of where the landfill gas project presently stands.
In a June 2016 feasibility study for the project, engineering firm CH2M Hill analyzed the cost efficiencies of six possible uses of landfill gas. HEA and then-borough Mayor Mike Navarre entered an agreement in August to spend $200,000 on advancing a landfill gas project, with each party contributing half. The agreement is contingent on the borough assembly appropriating funding for it.
“Basically what that agreement will do would allow us to do a series of feasibility studies, really come up with a conceptual design detailed enough to do a good cost estimate,” Salzetti said. “Based upon that cost estimate we could actually run the financial feasibility of the project. It looks great, but we would need to do our due diligence to make sure it looks as good as we think it does on the napkin here.”
HEA and the borough would then draft schedules, sales agreements for gas or electricity, an operation and maintenance agreement, and contract outlining the terms of the partnership for the project’s design and construction.
Microbes digesting buried trash create gas as a waste product — a roughly 50-50 mix of carbon dioxide and methane that Salzetti said is “typically considered a liability because of its odor and explosive nature.”
Both its primary components are also strong greenhouse gases that contribute to atmospheric warming. Methane’s warming effect can be up to 35 times greater, according to the U.S Environmental Protection Agency, but it is also the combustable component of natural gas, creating the possibility of burning landfill gas for heat and electricity instead of venting it into the atmosphere.
One use would help to handle another landfill byproduct — water carrying dissolved particles of waste, known as leachate, created by precipitation trickling through the mass of buried garbage. In unlined waste deposits — such as that in which Central Peninsula Landfill buried trash between 1969 and 2005 — leachate drains into the ground. After environmental regulations required Central Peninsula Landfill to lay a liner of clay, plastic, or composite material under their waste masses to prevent leachate draining, landfill staff have pumped out leachate and recirculated it through the garbage mass to speed decomposition.
When heavy rains or snowfall create an excess of leachate, the landfill stores it in a lagoon and boils its moisture into the atmosphere with a gas-fired evaporator. In 2015, the landfill burnt 21.95 million cubic feet of natural gas, purchased from regional gas utility ENSTAR, to boil leachate in its evaporator.
CH2M Hill calculated that the flow of landfill gas will accelerate as trash decomposes, peaking in 2035 at 435 cubic feet of gas per minute. The cells whose decomposition is quickened by leachate recirculation would produce the majority, while the older unlined portion of the landfill will produce less.
Salzetti said the project is designed to scale up as the gas flow from decomposition increases, with the intial landfill gas supply being supplemented with purchased gas.
“Right now the estimates are that there’s only about 500 kilowatts worth of gas,” Salzetti said. “We don’t know for sure, but that’s what the modeling shows. We’d be looking at about a two megawatt project, so there’s quite a bit of supplemental gas at first. But then, as the next landfill closes, you get more gas, and with the next you get more gas.”
According to CH2M Hill’s report, the landfill used 948,915 kilowatt hours of electricity in 2015, a demand that the landfill gas would more than meet by the time it peaks. Waste heat from the generator could also be used to boil leachate, offsetting another natural gas requirement. The generator that CH2M Hill used in their modeling would be able to evaporate 4,000 gallons of leachate a day, according to the report — about a third of the 12,000 gallons the landfill needs to evaporate daily.
Under this option, excess energy not used by the landfill’s offices and facilities would be sold to HEA.
Another option would be using the gas for heat and energy at the closest borough facility — Skyveiw Middle School, about 1.4 miles down the Sterling Highway from the landfill — where it could be used for either heat or electricity. Skyview in 2015 used 1.5 million kilowatt hours of electricity, according to the feasibility study. CH2M Hill concluded that trucking the gas offsite would be cost-prohibitive, and so only examined the option of piping the gas to the school.
Based on the feasibility study, Salzetti said plans to run the landfill on a landfill-gas fired generator were “clearly the best options based on net present value — in fact, they’re almost two times better than the next potential option studied.” CH2M Hill calculated that using the gas for electricity would add a net value of about $7 million over a 20 year operational life, with an additional $421,154 value if the generator’s waste heat also evaporates leachate. This option would have a $3.5 million capital cost.
Another option would be selling landfill gas to the regional gas utility ENSTAR. This would require the landfill gas to be compressed and cleaned of its carbon dioxide and moisture, as well as the construction of a 0.2-mile pipeline between the landfill and the existing ENSTAR line following the Sterling Highway. Though this would be the cheapest option, with a $823,141 capital cost, CH2M Hill concluded it would also bring the borough the lowest returns.
Though its report states that directly burning landfill gas in a boiler “is common and often the most cost-effective use of (landfill gas)” CH2M Hill concluded that doing so at Central Peninsula Landfill or Skyview would likely be a money-losing project. Since landfill gas is only half methane, the existing boilers at these facilities would need to be modified to burn twice as much of it, versus pure methane fuel gas. Impurities in landfill gas would also require annual cleaning and the replacement of present boiler components with corrosion-resistant stainless steel. Annual operations and maintenance costs would be almost as great as the savings, giving these projects negative value in CH2M Hill’s analysis.
Reach Ben Boettger at firstname.lastname@example.org