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Vol. 22, No. 9 Week of February 26, 2017
Providing coverage of Alaska and northern Canada's oil and gas industry

Landfill gas grows

Anchorage municipal waste system generates power for JBER from 5 engines

ALAN BAILEY

Petroleum News

A project involving power generation using gas derived from the decomposition of trash in the Anchorage Regional Landfill is already producing more power than had originally been anticipated and is looking to expand further, Mark Madden, manager of engineering and planning for the Municipality of Anchorage Solid Waste Services, told the Alaska Forum on the Environment on Feb. 9.

Nearly 60 wells

The power generation system now has nearly 60 gas wells drilled through the pile of garbage that in places is 180-feet deep. The system delivers gas to a dedicated power plant operated by Doyon Utilities LLC in adjacent Fort Richardson, the army section of Joint Base Elmendorf-Richardson. Much of the trash consists of organic material which bacteria devour, producing a gas consisting of about a 50-50 mix of methane and carbon dioxide, plus small quantities of contaminants. Apparently the bacterial feeding frenzy is so intense, that the temperature deep in the dump remains at some 140 to 150 F year round.

A processing facility at the landfill site condenses out water and associated contaminants from the gas coming from the wells, before warming the treated gas and compressing it into a pipeline for delivery to the power plant. The retrieved water is delivered to the Anchorage wastewater treatment plant.

At the power plant, a line of General Electric Jenbacher engines, fueled by the landfill gas, generate power for the army base. Although the engines are dual fuel, designed to run on natural gas or landfill gas, they actually operate more efficiently on landfill gas, Madden commented. That is because the landfill gas has a lower Btu content than the nearly pure methane of natural gas, thus enabling the engines to run cooler than with regular city gas, he explained.

Currently the system runs on between 2,000 to 2,800 cubic feet of gas per minute, outputting more than 44,000 megawatt hours of electricity in 2016. Peak annual production so far, close to 55,000 megawatt hours, came in 2015, Madden said. Revenue from the project helps fund the running and the expansion of the landfill, he said.

Once trash is put into the Anchorage landfill, gas production peaks after some five to 10 years. Gas production would then continue for another 30 or 40 years, presumably supporting the landfill gas power project.

The power generation system came on line in 2012, partly in response to a regulatory requirement under the Clean Air Act to destroy methane generated in the landfill. Funding for the development came from an Alaska Energy Authority grant and from financing arranged by Doyon Utilities, Madden said.

At that time the power plant had four engines. So, with each engine capable of a power output of 1.4 megawatts, the plant had a nameplate capacity of 5.6 megawatts. But the facility had been built with a future expansion of up to six engines in mind - modeling of the anticipated landfill gas production suggested the possibility of adding a fifth engine in 2018 and a sixth engine in 2024.

In fact, soon after the system went into operation it became apparent that gas production was much higher than anticipated. Consequently, Doyon Utilities added that fifth engine in 2014 and there is already sufficient gas production to support a sixth engine. Furthermore, discussions are underway to add capacity beyond the original six-engine concept, perhaps as a larger engine, or perhaps by expanding the powerhouse to accommodate more engines, Madden commented.

Expanding demand

A key parameter in this situation is the power demand that the landfill gas power station supports. The facility, originally conceived as an auxiliary power plant, can now supply more power than Fort Richardson needs during the summer, and can meet about 60 percent of the army base’s electricity load in the winter. An obvious area of expansion would be to supply power for Elmendorf Air Force Base, thus supplying the entire JBER. However, the Elmendorf and Fort Richardson electrical systems are not interconnected, although moves are afoot to link them, said Travis Smith, Solid Waste Services principal information officer.

Routine maintenance must also be factored into the system economics. Each engine will need to be taken offline periodically, with one of the factors being the buildup of a hard glassy material called siloxane on the engine parts, a buildup that will require component cleaning or replacement. Siloxane is a silica based material that ends up in a landfill because it is commonly used in cleaning products such as shampoo and detergent, Madden explained. Curiously, and helpfully, the Anchorage landfill contains much less siloxane than is typical in landfills elsewhere, he commented.

Other applications

Given the success of the Anchorage project, the question arises of finding other applications for similar technologies. For example, could the trash dumps in Alaska’s rural communities be used a source of energy? Dan Smith from the Alaska Energy Authority commented that, although all communities produce waste, the challenges in rural Alaska would be the small scale of the trash facilities and the cold climate. A particular challenge for a small-scale application is the economics of a small project, especially given the high cost of building infrastructure at a remote Alaska site, he said.

Madden commented that, when the municipality had originally published a request for proposal for the Anchorage landfill gas project, one entity had filed a proposal to use the gas as a boiler fuel. Some places outside Alaska have implemented systems that purify the landfill gas to pipeline quality, although that approach to using the gas tends to be somewhat expensive, he said. There are a couple of landfills that have facilities for converting the gas into liquid fuels for use in vehicles and other liquid-fuel applications. In fact, the municipality had received one proposal for a pilot project for liquid fuel production at the Anchorage landfill - unfortunately, when fuel distribution costs were added to the fuel production costs, the project did not appear viable, Madden said.



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