Renewable natural gas (RNG) is a biogas that has been upgraded to a quality similar to fossil-derived natural gas. RNG has a methane concentration of at least 90%.
When biogas is sufficiently upgraded, it can be distributed to consumers using existing gas grids and then used in normal gas stoves, boilers and other gas-fuelled appliances without any need to modify them first.
Unlike the burning of fossil-derived natural gas, the burning of biogas does not add to the net greenhouse gas content in the atmosphere. That is because the greenhouse gases released by biogas come from compounds that were recently captured from the atmosphere by living organisms. Fossil fuels release compounds that were captured by living organisms a very long time ago, which is why the amount of greenhouse gas in our current atmosphere increases when we burn fossil fuels.
As mentioned above, upgraded biogas can be distributed through the existing infrastructure for fossil-derived gas and used in existing appliances. No costly upgrades are required to the gas grid, and end-users do not need modify or replace their gas stoves, boilers, etcetera to use biogas instead of fossil-gas.
In many countries, vast and well-functioning gas distribution networks already exist, and using them for the distribution of renewable fuel is better for the environment than consuming resources to create new systems.
These existing networks also allows for biogas to be transported (at low cost and low environmental impact) from places where large quantities of biomass is available, such as Russia and Scandinavia.
One of the pioneers in the field of large-scale production of upgraded biogas is Göteborg Energi in western Sweden. In December 2014, their bioSNG plant became fully operational and began supplying gas to the existing natural gas grid. The Göteborg Energi plant produced gas with a methane content over over 95%. Regrettably, it ran into financial problems and was closed down in April 2018.
From a technical perspective, the plant was a success and it performed as intended. Financially, it could not compete with the low global market price for fossil-derived gas.
In British Columbia, Canada, the gas provider FortisBC is injecting upgraded biogas into their existing gas distribution system.
The United Kingdom
The United Kingdom is a country with an extensive infrastructure for gas distribution, and the interest in replacing fossil-derived gas with upgraded biogas in this existing system is high. So far, approximately 90 biomethane injection sites have been built across the country. One of the main players is Centrica, which offers upgraded biogas where the original source material is sewage. Using sewage as the source turns something undesirable (waste) into something desirable (non-fossil fuel), and is thus tackling two issues as the same time.
Sustainable synthetic natural gas (SNG) might sound like an oxymoron, but is actually a very interesting and promising field within the renewable fuel industry.
Sustainable SNG is produced when very hot oxygen is correctly applied to suitable biomass (e.g. waste residue) at 70-75 bar pressure. Hydrogen is added to the fuel mix during the gasification process, and carbon-dioxide is removed before the final fuel product is ready for use.
A very wide range of source materials can be used to produce sustainable SNG, and a biogenic carbon content of 50-55% is enough.
If fossil-derived natural gas is used as the energy input into the gasification process, instead of simply being burned as fuel, it is possible to create 5 to 10 times more sustainable SNG than the amount of consumed fossil-gas. While this is not perfect from a greenhouse emission perspective, it is still a vast improvement.
What is power-to-gas?
Power-to-gas is a method where electrolyzed hydrogen is used to convert the carbon-dioxide and carbon-monoxide present in raw biogas into methane, thus creating a fuel with a mucher higher methane content than unprocessed biogas.
Liquefied Natural Gas (LNG)
Upgraded biogas can be converted into liquefied natural gas (LNG) for direct use as fuel in the transport sector, where vehicles designed to run on liquefied fossil-derived gas already exist.