Price of Methane:
The value of landfill gas (LFG) depends on a number of factors, including methane content, gas quality, the current market price for natural gas or electricity, and whether carbon credits, tax credits or renewable energy credits for electricity or alternate fuel generation are also applicable. The value of LFG may also be affected by site-specific issues such as proximity of the landfill to potential users, and state or regional requirements for public utilities to provide electricity from renewable energy sources (Renewable Portfolio Standards, or RPS).
Natural Gas Values
The market price of natural gas varies greatly depending on location and type of consumer. The residential price varies from 50-300% more than the wholesale price. On February 25, 2014, the Henry Hub natural gas spot price* was $5.21 per million British thermal units (mmBtu).
Utilization of LFG – Types of Projects
Based on the factors above, a site may choose to collect LFG for use in one of several ways:
- Direct use to heat buildings, power a boiler or kiln, produce biofuels such as ethanol or biodiesel, or evaporate leachate or liquid wastes (also known as “medium Btu projects”)
- Landfill gas to energy (LFGTE or LFGE), running engines or turbines to produce electricity, or combined heat and power (CHP) projects that generate electricity and capture the energy value of waste heat from the engine or turbine.
- High Btu projects, where the gas is cleaned and compressed for use as pipeline gas, compressed or liquefied natural gas (CNG or LNG) for vehicle fuel, or as feedstock to produce methanol
The low current value of natural gas per mmBtu may make direct use projects less viable unless an end user places an additional value on the gas as a “green” resource. Credits may be available based on offsetting another fuel source, such as heating oil, coal or natural gas. Of course, future pricing for natural gas could increases significantly over current prices, driving the opportunity for direct use projects. These projects can have a lower capital cost than other types of LFG projects with minimal permitting issues.
LFGE and CHP projects can generate greater revenue than direct use of LFG. In addition to the value of the electricity that can be sold, Renewable Energy Certificates (RECs) can be earned for each megawatt of electricity produced from a renewable fuel source such as LFG. These RECs range in value depending on state or region, but can easily be worth more than the value of the power generated. Historically, RECs from LFGE projects in the U.S. have been sold in the range of $5 to $45 per megawatt. LFGE and CHP projects have a higher capital cost than direct use, and also require air quality permits that can take as much as a year or more to obtain.
High Btu projects can be the most lucrative of all LFG uses. Gas can be sold to the pipeline as a renewable fuel at a premium above the spot price for natural gas. Where LFG is converted to CNG or LNG for use as a vehicle fuel, offsetting the use of gasoline or diesel fuel, Renewable Identification Numbers (RINs) can be earned in addition to the value of the fuel. High Btu pipeline gas and LNG projects generally need to be larger to be viable, at least 1,500 CFM and preferable as much as 2,000-3,000 CFM. Conversion of LFG to CNG can be from large to very small, with small projects in the range of 50-200 CFM allowing sites to use “excess” gas from LFGE or flare systems to make vehicle fuel for site vehicles. High Btu projects typically have the highest capital cost but have fewer permitting requirements than LFGE projects and can be quicker to implement.
Maintaining High LFG Quality Ensures Project Success
Whether LFG is used to generate electricity or is used as a medium or high Btu fuel, maintaining the highest gas quality can result in meeting or exceeding revenue expectations in your LFG project. The heat content of the fuel is directly related to the methane content, which is typically 50-55%. If the methane content drops significantly below this value, more gas volume would be needed to make up for lost heat content. However, increasing gas flow typically results in even lower methane content. Higher vacuum applied to the well to increase gas flow can result in “over pulling” on the well, and air leaks into the gas collection system through the landfill cap, gas collection piping and well cap. It also potentially affects future gas quality by pulling air into the anaerobic zone of the landfill where methane is generated. Air leaks can also raise both oxygen and nitrogen content in the gas. While direct use projects may be minimally affected by air leaks, LFGE and high Btu projects are less tolerant of high oxygen and nitrogen. When pipeline gas quality specifications need to be met, removing excess nitrogen from LFG can be very costly, adding as much as $1 million or more to the cost of the gas treatment system. Simply stated, it’s cheaper to keep the air out of the system through better well field management practices than to remove it later.
Dewatering LFG wells can help to maintain high gas quality. Dewatering to keep the well perforations exposed creates greater area for gas flow, minimizing the vacuum needed to maintain the desired gas flow at high methane content. Keeping the vacuum lower will also help to reduce air leaks through the landfill cap and piping system that would otherwise occur at higher vacuum levels. It also reduces the energy required to operate the collection blower, a direct cost savings. An added benefit is control of fugitive LFG emissions, maintaining regulatory compliance and reducing odors.
Using a LFG wellhead with precise gas flow control and accurate flow measurement can also help to maintain high gas quality at the highest possible flow rates. With the limited flow control available in a gate valve, the vacuum applied to a well often exceeds the rate at which the well will yield gas without over pulling. Using a precision flow control valve designed specifically for LFG gives the operator the ability to make smaller incremental adjustments in flow at each well to achieve the perfect balance between gas flow and methane content. Having accurate flow measurement that allows the operator to truly measure small changes in flow goes hand-in-hand with improved flow control, maximizing the value generated from the gas collection system.
* The Henry Hub is a natural gas pipeline located in Erath, Louisiana that serves as the official delivery location and pricing point for natural gas futures contracts on the New York Mercantile Exchange. Spot and future prices set at Henry Hub are denominated in $/mmBtu and are generally seen to be the primary price set for the North American natural gas market.