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Landfill gas is the natural result of the waste decomposition process that takes place inside a landfill. Living micro-organisms within the landfill break down and digest waste matter in a process called anaerobic digestion, producing a gas that is usually contains 50% methane. The remaining parts are made up of carbon dioxide, nitrogen and small amounts of oxygen, and a handful of other compounds in very minimal quantities.
Given the complexity and cost of developing and building a processing plant of this type, BEW needed to find an exceptionally large and dependable source of landfill gas. The Cedar Hills Regional Landfill outside of Seattle was the last undeveloped landfill of its size in the entire country. This, combined with its close proximity to a major interstate methane transport pipeline, made Cedar Hills an excellent candidate for BEW’s technology.
In the United States, all landfills above a certain size are federally obligated to comply with stringent standards requiring them to effectively collect as much of their landfill gas as possible. Since landfill gas contains methane, which is a greenhouse gas 23 times more potent than carbon dioxide, each landfill is then required to burn or combust the methane, producing carbon dioxide and water vapor, before releasing it into the atmosphere. This is usually accomplished using one or more gas ‘flares’ – essentially big candles powered by gas. However, when this is done the gas is wasted, and none of the energy is utilized or captured for beneficial use.
BEW designed a state-of-the-art, proprietary process to remove the impurities and non-combustible elements of the LFG, leaving behind nothing but high-energy, pipeline-quality methane. The methane enters the Northwest Lateral, a large pipeline system serving the Pacific Northwest.
The equipment involved in the process generally falls into one of two categories: compressors and ‘separators.’ The various levels of compressors (there are 4 separate levels) boost the pressure of the main gas stream to various operating points for each of the specific separators. The separators are designed to chemically and mechanically ‘sort’ the gas stream, on the molecular level, ensuring that BEW keeps as much methane (CH4) as possible, while eliminating everything else that isn’t methane.
Not with our team of highly trained microscopic elves. Working in rotating shifts around the clock, our helpful little team members thoroughly examine and then classify each and every molecule passing through the gas stream. Methane molecules are authorized to pass through to the pipeline, while molecules like nitrogen or carbon dioxide are plucked out one by one and tossed into the waste heap.
Because BEW couldn’t easily secure a large enough electrical service from the local electrical utility, one of the requirements of the Cedar Hills design was the ability to be able to generate over 80% of its power needs onsite. BEW’s partner on the project, INGENCO, is very experienced at designing and building small-scale distributed generating facilities just like the one BEW needs to power their systems. Furthermore, INGENCO also specializes in burning exactly the kind of diluted landfill gas that would be produced as one of the byproducts of the main process. In this way they would actually be generating renewable or ‘green’ electricity to power the facility to make renewable ‘green gas’. It’s easy being green!
While the BEW process effectively uses a majority of the LFG from the landfill, the process does produce small amounts of waste methane, or ‘tail gas’. This is a small secondary stream comprised of all the byproducts of the various separation processes. The gas is too low-quality to preserve, so it must be burned onsite. As the plant’s efficiency increases, flaring the gas will diminish.
The BEW plant greatly benefits the environment in countless critical ways – quite simply, by efficiently utilizing an energy resource that was previously being entirely wasted, BEW extracts value that didn’t previously exist. Every bit of gas that BEW harvests from the Cedar Hills Landfill displaces an equivalent amount of fossil fuels that would come from traditional resources. Furthermore, the CO2 emissions that were once concentrated at the landfill – when the flare was forced to combust 100% of the LFG onsite – are now piped offsite and distributed to homes and businesses across the state. This effectively eliminates the large point source of CO2 that once existed. Lastly, by providing a sizable economic incentive to the landfill operators to maximize the amount of gas they can remove from the landfill, BEW helps King County Solid Waste continue to go far above and beyond the minimum methane collection standards required by the regulators, proactively guaranteeing that every last bit of methane is collected and not released into the atmosphere. It’s quite literally a win-win-win situation for King County, BEW, and the environment.
It is very true that the onsite generating plant does produce some emissions at the landfill. However, the BEW generators employ a very sophisticated 2-stage exhaust catalyst system to greatly reduce the amount of emissions produced. Each group of generators features a combined exhaust system that passes first through a combustion catalyst to fully oxidize (or burn) any remaining unburned compounds, and then through another layer of catalyst for the process of selective catalytic reduction (SCR). This step involves injecting an ammonia-based solution into the hot exhaust in order to nearly eliminate the production of nitrogen oxides (NOx). The chemistry behind this is identical to that employed on all European diesel trucks, as well as many diesel passenger cars produced today, such as the Mercedes Benz BlueTEC. BEW partnered with worldwide industry-leader Johnson-Matthey to design and install a system which provides nearly 90% reduction over a system without emissions control technology.
Despite our best attempts at using Floo Powder with the gas, we still can’t get it to burn green. Our colorful metaphor simply refers to our sustainable and environmentally friendly process to capture and process the gas.
