Everything from the exact number of wells installed on a landfill cell, to the type of collection system, affects the selection of a cover material. Until you’ve chosen your general well system for landfill gas (LFG) collection, it’s not always easy to narrow down the right type of geomembrane to match. If you’re still in the process of choosing a landfill gas collection system, here is a brief overview of the main choices available today to help guide you.
Passive vs Active Systems
The first choice in finding the right landfill gas collection system is choosing between passive and active designs. Both require an impermeable cover material at the top to keep gas from being inappropriately released into the atmosphere. However, active gas collection requires a much more durable cover due to the pressurization of the system. Passive gas collection only works well for releasing the gas into the environment or directing it into control systems. Only active gas collection systems work well for harvesting enough gas for any reliable power generation or heating purposes. Yet, these systems are also at higher risk for a rupture or leak due to the pressurization that helps condense and collect the gases. It is essential to add redundant containment to these systems to reduce the risk of methane loss, but reinforced covers make it particularly easy to secure these collection systems regardless of their size or pressure level.
Vertical Wells
The most common type of well used for collecting and controlling gas on a landfill cell is the vertical borehole design. There’s a number of reasons for that, including the ease of installation even if the cell wasn’t built with gas collection in mind for the start. Another benefit is the ability to pack more of these wells into the same acreage for maximum extraction without overpull issues. Boreholes can easily penetrate through layers of cover material to allow gas to flow more freely, making them more versatile than other types of gas collection wells. Finally, they’re the easiest to drain if they fill inappropriately with leachate. However, they do have a few downsides. First, they cost the most to drill, which adds to the total cost substantially, especially when there are more wells per acre as well. Also, they require extensive surveying of the waste contents to ensure they’re installed in the right conditions. Boring into an area that is too finely compacted, or made of unstable materials, can cause a collapse that affects a large portion of the gas producing area.
Horizontal Wells
Horizontal wells are less common, but they generally must be installed as the landfill is packed rather than at the end. These collectors can be harder to adjust for optimal gas collection because they can stretch 500 feet or longer at a time under the layers of the waste. Wellheads are often installed at multiple points over the length of a horizontal well in order to maintain even pressure across the entire installation. These units are resistant to crushing and clogging when built correctly, but they’re difficult to maintain, especially if the leachate system fails and floods them.
No matter the type of gas collection wells you eventually choose, BTL Liners has the materials to match them. Discuss your project with us today to get custom recommendations on both liner and cover materials to match your plans.
Conclusion
Landfill gas is a valuable resource, but it’s not always the easiest source to tap due to the design of older landfill cells. Building new cells with gas production in mind from the start, makes it much easier to achieve your collection goals for power production and more.
