Renewable natural gas (RNG) is defined as methane gas derived from organic materials and waste streams.

Feedstock & Technologies

Pipeline–grade RNG has been upgraded (also called conditioning) to remove water, carbon dioxide, hydrogen sulfide, and other trace elements. This meets natural gas pipeline specifications, and also meets those set for natural gas vehicles by engine manufacturers.

The primary “feedstocks” for producing RNG are:

  • Agricultural and agri-food sources such as unused crop residues, animal manure and food processing waste;
  • Forestry bi-products such as wood waste generated during harvest operations;
  • Municipal solid waste and bio-solids from wastewater.
  • RNG can be produced using either anaerobic digestion, an established technology best suited for producing RNG from relatively wet feedstock or gasification, which is a rapidly developing technology best suited for producing RNG from relatively dry feedstock.

Anaerobic Digestion (microbial process)

Anaerobic digestion (AD) is a natural process of decomposition of organic materials by microbes in the absence of oxygen, in which biogas is produced. Anaerobic digestion occurs in landfills and sewage treatment and in industrial processes to convert manures, agri-food residues, industrial by-products and sorted municipal wastes to biogas.

The resulting biogas contains a much lower methane concentration than conventional natural gas and can be used on-site with minor processing for its heating value or to run an electricity generator. However, upgrading technologies are available that can produce a clean, high energy RNG suitable for direct injection into existing natural gas pipeline infrastructure and able to be mixed with conventional natural gas.

Gasification (thermal process)

Biomass gasification is a high temperature (>500 °C) process in which organic material is converted into syngas in the presence of oxygen and/or steam. The syngas can be converted into RNG through a process called methanation and then be introduced into the natural gas pipeline infrastructure and mixed with conventional natural gas.

Gasification has the advantages over anaerobic digestion that a wider variety of non-homogeneous feedstocks can be utilized. Almost any type of organic material can be used as gasification feedstock, including forestry and agriculture residues, and sorted municipal waste.

RNG Infrastructure

The extensive Canadian pipeline and underground gas storage network and the interchangeability of RNG with conventional natural gas means that in many cases, RNG can be introduced at its point of production, and transported to the end user without a significant modification to pipeline infrastructure or to the end user’s natural gas burning equipment.
Sources: CANMET Technology Roadmap / AFDC

Applications

Like conventional natural gas, RNG can be used as a transportation fuel in the form of compressed natural gas (CNG) or liquefied natural gas (LNG). RNG qualifies as an advanced biofuel under the US Renewable Fuel Standard.