What is Renewable Natural Gas (RNG)?

Posted by Jon Snyder on Tuesday, January 18, 2022

Renewable Natural Gas (RNG) is generally made up of the same molecules (about 95% methane, CH4) as “traditional” natural gas (NG) that is recovered from underground rock formations and is delivered to homes and businesses via pipeline. While the chemical makeup of pipeline-quality NG and RNG are very similar, the difference between the two lies in the way they are sourced and processed prior to use. The chart below provides an overview of the differences between NG and RNG with more detail provided below.

	Natural Gas (NG)	Renewable Natural Gas (RNG)
Source	Underground geologic formations.	Biogas captured from decomposing organic material at landfills, wastewater treatment plants, dairy farms, etc.
Processing Requirements	Removal of heavier hydrocarbons and water vapor.	Removal of sulfur compounds, carbon dioxide, water vapor, and other contaminants.
Delivery	Pipeline infrastructure and systems.	Same delivery as NG.
Supply	Currently an abundant supply, but a supply that is finite.	Continuous sources exist in our current waste streams, but capturing RNG requires investment and likely incentives.
Uses	Heating, transportation, electric generation, manufacturing, etc.	Can be used for the same uses as NG.

Sourcing

There are at least three main sources of biogas, which is common shorthand for unprocessed RNG:

1. Anaerobic digestion at wastewater treatment plants.
2. Landfill gas that is captured from decomposing waste.
3. Anaerobic digestion of animal waste (think farming).

As you can imagine, we have numerous potential biogas sources around us in the form of reliable waste streams, hence RNG is considered “renewable.” Traditional NG is trapped (sometimes with crude oil) in underground layers of sandstone and shale, which is usually a few hundred feet to two miles underground. The NG is recovered by drilling a well into the producing rock formation allowing the pressurized gas to flow into a pipeline. The differing sources lead to different raw products requiring separate processing methods.

Processing Requirements

Where NG from a gas well is processed to remove heavier hydrocarbons and water vapor before being compressed and sent to a high-pressure pipeline, RNG usually needs to be processed to remove nitrogen, sulfur compounds, carbon dioxide, water vapor, and some other contaminants before compression. However, after processing, both sources produce essentially the same fuel.

End Uses & Subsidies

While chemically very similar, RNG and traditional NG are generally burned by different end users. A producer of traditional NG generally sells their gas into a “midstream” company’s pipelines near the well head where the gas comes out of the ground. From there, the gas is treated as described above, compressed, and injected into a transmission pipeline where the NG is transported to the end user (power plant, industrial facility, utility distribution network, etc.).

RNG is sometimes distributed using the traditional method, but it is often used more locally. A landfill may treat their biogas on site and build a vehicle fueling facility for Compressed Natural Gas (CNG). A wastewater treatment plant may improve the efficiency of their anaerobic digester by burning RNG to pre-heat sludge as it enters the digester. RNG from any source may be compressed into specialized pressure vessels as CNG and trucked to another location for use.

The U.S. EPA’s Renewable Fuel Standard (RFS) program provides a market-driven subsidy for renewable fuel sources used for ground transport (cars, trucks, and buses). The program applies to renewable liquid and gaseous fuels, including RNG. The RFS program can be generalized as follows: an RNG producer sells the gas into the traditional NG pipeline network, at which point a Renewable Identification Number (RIN) is created. An end user wishing to use a renewable fuel source purchases fuel for their vehicle including an extra fee to retire the RIN, with the price of the RIN being paid indirectly to the RNG producer.

California and Oregon are two states in the U.S. that have additional subsidy programs for RNG. California has ambitious goals to reduce their greenhouse gas emissions, and according to SoCalGas/ADG&E, RNG directed to individual homes for residential use can be one piece of the puzzle that will help California reach its climate goals.

What’s Next for RNG?

I hope this post has answered the question: “What is RNG?” The natural follow-up questions are: “What is the future of RNG?” and “Will it completely replace NG from fossil sources?” The International Energy Agency forecasts that with current government policies, the global consumption of RNG will more than double by 2040 when compared to 2018 consumption (75 Mtoe in 2040 vs. 35 Mtoe in 2018). Even if all this RNG growth takes place in the US, the quantity of RNG would still be dwarfed by natural gas's share of the domestic energy market (about 780 Mtoe consumed in the US in 2018). And in some cases there are other cost-effective and efficient uses of the waste by-products, such as animal waste applied to nearby farm fields as a nutrient-rich slurry or compost.

That said, there are continual technological advancements in RNG capture and processing. Sustainable energy initiatives grow stronger every day. All types of end-user equipment (such as household appliances, vehicle engines, boilers, and generators) that utilize RNG are already in service using traditional NG as the fuel.

The economics of RNG are still not appealing on their own in most markets, but when coupled with corporate sustainability goals and government subsidies, many are willing to pay up for RNG. All in all, the future looks promising for RNG, and we plan to be a part of that future.

Categories: Oil & Gas Infrastructure

Tagged: Energy Planning & Management  |  Natural Gas