Renewable Natural Gas (RNG) – What It Is, Where It Comes From & Benefits
August 24, 2020 Welcome
A recent trend in the energy industry is an increased focus on recyclable sources of energy. Among the sources of renewable energy being touted as the future of clean power is renewable natural gas (RNG).
While the power generated from RNG is cleaner than other sources, it isn’t perfect. The focus of this article will be to identify the definition, benefits, and relevance of renewable natural gas as a low carbon fuel for heating and electricity generation.
Is Natural Gas Renewable?
The commonly known “natural gas” is a natural, non-renewable mixture of hydrocarbon compounds that was generated underground over the course of millennia. However, RNG is a subset of natural gas that is renewable.
Generally, when someone says, “natural gas,” they are referring to the non-renewable gas rather than the family of gases that includes RNG (renewable natural gas).
What Is Natural Gas?
Natural gas is a non-renewable hydrocarbon mixture of methane (a primary constituent), some negligible percentages of other alkanes, carbon dioxide, nitrogen, hydrogen sulfide, and helium. Natural gas is also known as a fossil fuel formed by natural processes involving the decomposition of dead plant and animal matter subjected to intense heat and pressure beneath the earth’s surface over millions of years.
This very useful fuel is frequently recovered by petroleum exploration efforts and must undergo refining processes into safe and useful forms for both domestic and industrial use.
What Is Renewable Natural Gas?
Renewable natural gas (frequently referred to as biogas) is derived from the breakdown of organic materials (plants and animal materials) as well as other sources of degradable carbon like paper, wood, and cardboard materials.
While RNG fuel bears a lot of similarities to natural gas in terms of composition (RNG is largely methane gas) and substrate required for synthesis, the creation of RNG is a man-made process typically done at a landfill site or a wastewater treatment facility. Further, the duration of processing required to generate biogas is significantly shorter than that of natural gas (typically within weeks to months).
Where Does RNG Come From
The major component of renewable natural gas is methane which is produced when organic matter undergoes decomposition. As a result, any large source of organic waste can produce useful quantities of renewable gas.
Key sources of RNG energy include:
- Landfill gas (LFG) systems
- Methane from livestock waste
- Wastewater digester gas
Landfill gas systems are usually sited away from residential areas on large swathes of land where organic wastes can be safely stored without posing a health risk to the population. A landfill system is a collection of contained pits filled with organic waste that decomposes to produce a methane-rich gas mixture.
Once sufficient biogas has accumulated within the cells, it is recovered using horizontal trenches or vertical wells sunk into the pits. The recovered gas is then subjected to a primary treatment process that converts it to renewable natural gas before being channeled to various end processes including electricity generation, and heating.
Methane from Livestock Waste
Animal manure is a major source of organic substrate required for biogas fuel production. Collected animal waste can be channeled to anaerobic digester plants that produce a steady stream of methane which is converted into RNG. Biogas generated from livestock waste can be used in electricity production or to power natural gas vehicles.
Wastewater Digester Gas
Biogas can be generated during the breakdown of solids in a wastewater treatment process. This microbiologic activity can be harnessed by integrating an anaerobic wastewater digester in the treatment process. The biogas is collected as a by-product of the water treatment cycle and converted into useful RNG.
Renewable Natural Gas Production Process
The production of RNG involves a three-stage process:
- Biogas collection
- Gas conditioning
- Consumption of biomethane by utilities and consumers
Biogas from multiple sources including landfill gas systems, livestock waste, and wastewater treatment plants is collected and transported to a biomethane processing plant. Biogas can also be collected from other sources like industrial users but these are less economically feasible alternatives.
After collection, biogas must undergo a conditioning process that converts it into useful RNG. This process can be efficiently facilitated by the use of a skid-mounted fuel gas conditioning membrane system. This setup eliminates excess moisture and other non-methane compounds (carbon dioxide, helium, hydrogen sulfide) from the gas mix resulting in biomethane (pipeline-quality RNG) which is interchangeable with conventional natural gas.
Consumption of Biomethane by Utilities and Consumers
This is technically not a real step in RNG production but rather it represents the potential applications of the newly synthesized gas. As earlier stated, well-conditioned RNG is essentially the same as conventional pipeline natural gas and can be safely delivered directly to utility companies and end-users.
Common applications of RNG include
- Industrial manufacturing
- Power generation
- Powering natural gas vehicles
- Residential space heating
Is Renewable Natural Gas Carbon Neutral?
The answer is yes. According to the American Gas Association, renewable natural gas can be considered a carbon-neutral fuel because it harnesses methane that would otherwise have been released into the environment when organic material decays. By capturing the methane from matter decomposition and converting it into a useful source of energy, RNG synthesis helps to significantly reduce greenhouse gas emissions.
Can Biogas Replace Natural Gas?
At present, the goal of biogas production is not to replace natural gas recovered from oil exploration efforts which are still a useful source of energy. However, biogas generation has created a viable, more environmentally-friendly, and renewable alternative to natural gas which is a finite resource.
If natural gas reserves are ever depleted to a point at which recovery is no longer economically feasible, RNG will prove to be a very efficient substitute.
IFS Has Fuel Gas Conditioning Solutions Suitable for Biogas
At Integrated Flow Solutions, we are dedicated to providing our clientele with turnkey modular process skids for all their Air Quality, Power Generation, and O&G applications. IFS has high-quality fuel gas treatment systems for use by biogas processing plants.
Please contact us online today to learn more about the full range of industrial solutions we offer at IFS.