Does Renewable Natural Gas Have the Potential To Address Natural Gas’ Greenhouse Gas Problems?
by Bob Shively, Enerdynamics President and Lead Facilitator
Conventional natural gas is found in reservoirs deep underground and is produced by drilling wells into the reservoirs. Renewable natural gas (RNG) is gas produced by processing organic matter. Both consist primarily of methane, and RNG is sometimes called biomethane. After cleaning, RNG is pipeline-quality gas fully interchangeable with conventional natural gas. It can be injected into a natural gas pipeline to co-mingle with conventional gas, used for direct electric generation, or used as a transportation fuel as either compressed natural gas (CNG) or liquefied natural gas (LNG).
Conventional natural gas, often considered a critical bridge fuel between fossil fuels and renewable energy sources, has come under increasing criticism by some environmentalists lately due to methane emissions that occur during production, transmission, distribution, and use. Natural gas is mostly composed of methane, which is a greenhouse gas that is 20 to 80 times as potent as carbon dioxide (CO2). This means natural gas emissions add to global warming and climate change. Methane emissions can also create ozone, which can cause local air quality issues such as smog.
RNG, however, is considered carbon-neutral or even carbon negative. RNG from plant sources is considered a carbon-neutral fuel because it comes from organic sources that once absorbed carbon dioxide from the atmosphere during photosynthesis (as opposed to fossil fuels which release carbon that previously was trapped underground). RNG has even greater benefits when it's produced from organic waste that would otherwise decay and create methane emissions. When methane is converted to carbon dioxide during combustion, RNG reduces overall greenhouse gas emissions since the decaying matter would release more potent methane gas.
Digester producing RNG from cow manure
Sources of organic feedstock for RNG include:
- Agricultural residue
- Animal manure
- Crops grown specifically for energy production
- Fats, oils, and greases collected after use
- Forestry and forest product residue
- Landfill gas
- Organic municipal solid waste (MSW) separated from larger waste streams
- Wastewater treatment plants
A biogas plant in Holland that uses sugar beet pulp as a feedstock
Recent data shows the following biogas facilities in the U.S.:
- 564 operational projects at landfills around the U.S.
- 250 anaerobic digesters operating at commercial livestock facilities
- 1,300 anaerobic digesters at wastewater treatment plants.
Some gas utilities are now offering their customers the option of choosing RNG for their gas supply.
However, RNG has two key barriers to overcome, cost and insufficient amounts of organic matter to use as a feedstock. Analysis suggests that RNG costs at least three times the production cost of conventional natural gas. As use of RNG increases, competition for feedstock will drive prices even higher. Feedstock availability is limited and its use to produce RNG competes with other existing uses for the organic matter. Sufficient feedstock does not exist to displace more than a small portion of total natural gas consumption. So we can conclude that while RNG has the potential to help reduce greenhouse gas emissions associated with natural gas, it will not be capable of widely replacing conventional supplies for our overall energy needs.
Learn more about the natural gas industry in Enerdynamics' easy-to-read primer Understanding Today's Natural Gas Business or explore the many natural gas courses available online.