John Preston, a mechanical engineer with Tetra Tech’s renewable biogas team, discusses how to optimize landfill gas (LFG) collection and infrastructure for improved performance and reliability.
How is the shift to renewable natural gas (RNG) changing LFG projects?
Current natural gas market prices have made it more attractive to sell RNG on the open market than to use LFG to generate electricity, especially with the ability of third-party electrical generators to obtain regulatory credits for using biogas to produce renewable electricity. These regulatory credits, known as electricity renewable identification numbers (eRIN), can be bought and sold in a market to meet regulatory requirements and can provide the primary economic incentive for biogas and RNG projects.
The advent of eRINs and current natural gas market prices have made it more attractive to sell RNG on the open market than to use LFG to generate electricity. Because RNG projects now have higher performance expectations for gas quality and methane capture, landfill operators must be more disciplined about how they manage the wellfield and the waste going into the landfill.
For example, minimizing oxygen intrusion into the gas collection and control system (GCCS) reduces the demand on the deoxygenation system, if such a system is required. Additionally, reducing the volume of waste components into the input stream allows a higher volume of revenue generating methane to be processed.
What technical challenges arise when converting LFG systems to RNG?
The conversion of an LFG system to RNG changes what was once treated as a waste byproduct into a revenue stream. Every step, from gas collection and refinement to final transmission, must be evaluated in terms of its impact on the quality and quantity of the final product.
One key challenge is managing non-uniform inlet conditions. LFG composition and flow rates can vary over time, so the system must be designed with sufficient flexibility to handle those fluctuations, including considerations such as injection point location, required boost pressure, and pipeline access features like pigging stations. Without proper flexibility and integration, variability in the gas stream can affect system performance.
How should owners evaluate retrofit versus new RNG infrastructure?
Owners should begin by evaluating their LFG collection system. Without sufficient gas collection, there is no RNG and therefore no revenue. The strength and reliability of the existing vacuum and gas collection infrastructure are critical starting points.
In some cases, existing infrastructure with strong vacuum performance and gas collection can be used to reduce capital costs when installing a new RNG system. In other situations, temporary improvements, such as installing jumper lines between the existing system and a new system, can help during a transition period.
However, if a large area lacks any gas collection system, new infrastructure must be installed throughout that area to support RNG production. The decision ultimately depends on the condition and performance of the existing system and the long-term goals of the project.
How can system optimization improve RNG reliability and revenue?
System optimization improves both the quantity and quality of the collected gas. By increasing overall gas capture and, more importantly, increasing methane recovery, RNG production becomes more reliable and consistent.
When collection systems are optimized, less gas gets flared off or lost due to poor capture, which increases the amount of gas available for processing and sale. Reducing flaring also minimizes methane emissions into the atmosphere.
Tetra Tech can assist clients in evaluating whether to expand collection infrastructure to capture additional gas or allow additional gas to be safely combusted in the flare.
How does Tetra Tech help clients reduce risk in RNG projects?
Tetra Tech provides landfill gas emissions modeling that serves as an accurate tool for planning expansions, monitoring existing conditions, and addressing potential issues—such as production declines or quality problems—before they impact operations.
We also evaluate proposed gas upgrading technologies based on current landfill conditions and projected future performance. By analyzing anticipated return on investment and lifecycle costs, we help clients select technologies that align with their long-term goals.
About the expert
John Preston
John Preston has more than 30 years of experience in mechanical and process engineering focused on energy and waste infrastructure systems.
His background in root cause analysis and continuous process improvement helps clients improve their RNG operations.
John specializes in RNG feasibility studies, LFG system optimization, performance testing, and facility upgrades and has integrated new technologies into existing infrastructure and improved gas collection efficiency for his clients. He also has provided owner’s engineer services for system design projects and technical due diligence.
John holds a Master of Science in Mechanical Engineering from the University of Tennessee, Knoxville, a Bachelor of Science in Mechanical Engineering from Clemson University, and is a registered Professional Engineer in five states.