Renewable natural gas

From Wikipedia, the free encyclopedia

Renewable natural gas (RNG), also known as biomethane or sustainable natural gas (SNG), is a biogas which has been upgraded to a quality similar to fossil natural gas and has a methane concentration of 90% or greater.[1] By removing CO2 and other impurities from biogas, and increasing the concentration of methane to a level similar to fossil natural gas, it becomes possible to distribute RNG to customers via existing gas pipeline networks. RNG can be used in existing appliances, including vehicles with natural gas burning engines (natural gas vehicles). Renewable natural gas is a subset of synthetic natural gas or substitute natural gas (SNG).

The most common way of collecting biogas with which to produce biomethane is through the process of anaerobic digestion. Multiple ways of methanizing carbon dioxide/monoxide and hydrogen also exist, including biomethanation, the Sabatier process and a new electrochemical process pioneered in the United States currently undergoing trials.[2]


Renewable natural gas can be produced and distributed via the existing gas grid, making it an attractive means of supplying existing premises with renewable heat and renewable gas energy, while requiring no extra capital outlay of the customer. The existing gas network also allows distribution of gas energy over vast distances at a minimal cost in energy. Existing networks would allow biogas to be sourced from remote markets that are rich in low-cost biomass (Russia or Scandinavia for example). Renewable natural gas can also be converted into liquefied natural gas (LNG) for direct use as fuel in transport sector.

The UK's National Grid believes that at least 15% of all gas consumed could be made from matter such as sewage, food waste such as food thrown away by supermarkets and restaurants and organic waste created by businesses such as breweries.[3][failed verification] In the United States, analysis conducted in 2011 by the Gas Technology Institute determined that renewable gas from waste biomass including agricultural waste has the potential to add up to 2.5 quadrillion Btu annually, being enough to meet the natural gas needs of 50% of American homes.[4][5] The Environmental and Energy Study Institute estimated that renewable natural gas could replace up to 10% of all natural gas used in the United States,[6] and a study by the National Association of Clean Water Agencies and the Water Environment Federation found that the quantity of biosolids removed from wastewater could be turned into enough biogas to potentially meet up to 12% of America's national electricity demand.[7]

In combination with power-to-gas, whereby the carbon dioxide and carbon monoxide fraction of biogas are converted to methane using electrolyzed hydrogen, the renewable gas potential of raw biogas is approximately doubled.[8]


A biomass to RNG efficiency of 70% can be achieved during the production process.[9][10] Costs are minimized by maximizing production scale and by locating an anaerobic digestion plant next to transport links (e.g. a port or river) for the chosen source of biomass. The existing gas storage infrastructure would allow the plant to continue to manufacture gas at the full utilization rate even during periods of weak demand, helping minimize manufacturing capital costs per unit of gas produced.[11]

Renewable gas can be produced through three main processes:

  • Anaerobic digestion of organic material. This can be done in dedicated anaerobic digesters or as a byproduct gas collected from landfills and wastewater treatment.
  • Production through the Sabatier reaction. With the Sabatier reaction, the gas from primary production has to be upgraded with a secondary step in order to produce gas that is suitable for injection into the gas grid.[12]
  • Thermal gasification of organic (normally dry) material

Commercial development[edit]

BioSNG from wood[edit]

Göteborg Energi opened the first demonstration plant for large scale production of bio-SNG through gasification of forest residues in Gothenburg, Sweden within the GoBiGas project. The plant had the capacity to produce 20 megawatts-worth of bioSNG from about 30 MW-worth of biomass, aiming at a conversion efficiency of 65%. From December 2014 the bioSNG plant was fully operational and supplied gas to the Swedish natural gas grid, reaching the quality demands with a methane content of over 95%.[13] The plant was permanently closed due to economic problems in April 2018. Göteborg Energi had invested 175 million euro in the plant and intensive attempts for a year to sell the plant to new investors had failed.[14]

It can be noted that the plant was a technical success, and performed as intended.[15] However, it was not economically viable, given the prices of natural gas at the time. It is expected the plant is to re-emerge around 2030 when economic conditions may be more favorable, with the possibility of a higher carbon price.[16]

SNG is of particular interest in countries with extensive natural gas distribution networks. Core advantages of SNG include compatibility with existing natural gas infrastructure, higher efficiency that Fisher-Tropsch fuels production and smaller-production scale than other second generation biofuel production systems.[17] The Energy Research Centre of the Netherlands has conducted extensive research on large-scale SNG production from woody biomass, based on the importation of feedstocks from abroad.[18]

Renewable natural gas plants based on wood can be categorized into two main categories, one being allothermal, which has the energy provided by a source outside of the gasifier. One example is the double-chambered fluidized bed gasifiers consisting of a separate combustion and gasification chambers. Autothermal systems generate the heat within the gasifier, but require the use of pure oxygen to avoid nitrogen dilution.[19]

In the UK, NNFCC found that any UK bioSNG plant built by 2020 would be highly likely to use "clean woody feedstocks" and that there are several regions with good availability of that source.[20][21]

RNG development by region[edit]

In the UK, using anaerobic digestion is growing as a means of producing renewable biogas, with nearly 90 biomethane injection sites built across the country.[22] Ecotricity announced plans to supply green gas to UK consumers via the national grid.[23] Centrica also announced that it would begin injecting gas, manufactured from sewage, into the gas grid.[24]

In Canada, FortisBC, a gas provider in British Columbia, injects renewably created natural gas into its existing gas distribution system.[25]

A company called Divert, which also reduces food waste through donation, says it will use a $1 billion investment from Canadian pipeline operator Enbridge to scale its existing network of food waste anaerobic digesters to cover all major markets of North America.[26][27]

Sustainable synthetic natural gas[edit]

Sustainable SNG is produced by high temperature oxygen blown slagging co-gasification at 70 to 75 bar pressure of biomass or waste residue. The advantage of a wide range of feedstocks is that much larger quantities of renewable SNG can be produced compared with biogas, with fewer supply chain limitations. A wide range of fuels with an overall biogenic carbon content of 50 to 55% is technically and financially viable. Hydrogen is added to the fuel mix during the gasification process, and carbon dioxide is removed by capture from the purge gas "slip stream" syngas clean-up and catalytic methanation stages.

Large scale sustainable SNG will enable the UK gas and electricity grids to be substantially de-carbonized in parallel at source, while maintaining the existing operational and economic relationship between the gas and electricity grids. Carbon capture and sequestration can be added at little additional cost, thereby progressively achieving deeper de-carbonization of the existing gas and electricity grids at low cost and operational risk. Cost benefit studies indicate that large scale 50% biogenic carbon content sustainable SNG can be injected into the high pressure gas transmission grid at a cost of around 65p/therm. At this cost, it is possible to re-process fossil natural gas, used as an energy input into the gasification process, into 5 to 10 times greater quantity of sustainable SNG. Large scale sustainable SNG, combined with continuing natural gas production from UK continental shelf and unconventional gas, will potentially enable the cost of UK peak electricity to be de-coupled from international oil denominated 'take or pay' gas supply contracts.


Environmental concerns[edit]

Biogas creates similar environmental pollutants as ordinary natural gas fuel, such as carbon monoxide, sulfur dioxide, nitrogen oxide, hydrogen sulfide and particulates. Any unburned gas that escapes contains methane, a long lived greenhouse gas. The key difference from fossil natural gas is that it is often considered partly or fully carbon neutral,[28] since the carbon dioxide contained in the biomass is naturally renewed in each generation of plants, rather than being released from fossil stores and increasing atmospheric carbon dioxide.

A major concern is that the potential biogas yield would only represent a small percentage of existing supplies of fossil gas (also called natural gas). This fact has led existing natural gas suppliers to push back against measures to increase the use of electricity as an energy supply - decreasing demand for gas. This reality prompted Southern California Gas Company (SoCalGas) to covertly support the creation of a nonprofit: Californians for Balanced Energy Solutions (C4Bes) which then went on to lobby for the gas sector and against the momentum in favor of electrification. The Sierra Club exposed the hand of SoCalGas in the formation of C4Bes (astroturfing) and so C4Bes curtailed its lobbying activities, although it continued to promote demand for gas.[29][30][31]

See also[edit]


  1. ^ Al Mamun, Muhammad Rashed; Torii, Shuichi (2017). "Enhancement of Methane Concentration by Removing Contaminants from Biogas Mixtures Using Combined Method of Absorption and Adsorption". International Journal of Chemical Engineering. 2017: 1–9. doi:10.1155/2017/7906859. ISSN 1687-806X.
  2. ^ "SoCalGas and Opus 12 Successfully Demonstrate Technology That Simplifies Conversion of Carbon Dioxide into Storable Renewable Energy". (Press release). PR Newswire. Retrieved 3 May 2018.
  3. ^ The Guardian 'Food waste to provide green gas for carbon-conscious consumers'
  4. ^ "Natural Gas Can Come From Renewable Sources". Sempre Energy. Retrieved 3 May 2018.
  5. ^ Minter, George. "SoCalGas's Minter on Renewable Natural Gas as a Foundational Fuel". David Abel. Retrieved 3 May 2018.
  6. ^ "Fact Sheet | Biogas: Converting Waste to Energy | White Papers | EESI". Retrieved 9 December 2021.
  7. ^ "Alternative Fuels Data Center: Renewable Natural Gas Production". Retrieved 9 December 2021.
  8. ^ Marija, Saric; Dijkstra, Jan Wilco; Haije, Wim G. (July 2017). "Economic perspectives of Power-to-Gas technologies in bio-methane production". Journal of CO2 Utilization. 20: 81–90. doi:10.1016/j.jcou.2017.05.007.
  9. ^ Cornerstone environmental group, LLC 'Biomethane / Natural Gas Interconnection Opportunities'
  10. ^ Kachan & Co. 'The Bio Natural Gas Opportunity'
  11. ^ Energy Research Centre of the Netherlands 'Heat from Biomass via Synthetic Natural Gas'
  12. ^ Danish Gas Technology Centre 'Sustainable Gas Enters the European Gas Distribution System'
  13. ^ "GoBiGas". Retrieved 10 November 2017.
  14. ^ Nyheter, S. V. T.; Youcefi, Fouad (3 April 2018). "Investerade nästan två miljarder i Gobigas – nu läggs projektet ner". SVT Nyheter. Retrieved 25 April 2018.
  15. ^ "Professor: "The Gobigas Project A Technical Success"". 19 April 2018. Retrieved 2 May 2018.
  16. ^ LUNDIN, KIM (4 April 2018). "Biogasflow in Gothenburg provides the taxpayer with an environmental standard". SVT Nyheter. Retrieved 2 May 2018.
  17. ^ Åhman, Max (2010). "Biomethane in the transport sector—An appraisal of the forgotten option". Energy Policy. 38 (1): 208–217. doi:10.1016/j.enpol.2009.09.007.
  18. ^ "BioSNG: Synthetic Natural Gas". Retrieved 27 December 2012.
  19. ^ Van der Meijden, C.M. (2010). Development of the MILENA gasification technology for the production of Bio-SNG (PDF). Petten, Netherlands: ECN. Retrieved 21 October 2012.
  20. ^ 'Potential for BioSNG Production in the UK, NNFCC 10-008'
  21. ^ New Energy Focus 'BioSNG could be economically attractive for renewable heat'
  22. ^ "AD map – biomethane plants". ADBA. The Anaerobic Digestion & Bioresources Association. Retrieved 12 June 2018.
  23. ^ The Guardian 'Food waste to provide green gas for carbon-conscious consumers'
  24. ^ The Guardian 'Human waste turned into renewable gas to power homes'
  25. ^ Kachan & Co.'New Bio Natural Gas May Assist In Adding Solar and Wind to Utility Renewable Power Generation, Study Finds'
  26. ^ Divert Inc. Announces $1B Infrastructure Deal with Enbridge Inc. to Tackle Food Waste and Combat Climate Change
  27. ^ Enbridge commits $1 billion to company turning food waste to energy
  28. ^ Dr. Ann C. Wilkie (16 December 2019). "Biogas – Frequently Asked Questions (Biogas FAQ)". University of Florida – Soil and Water Sciences Department. Retrieved 2 September 2022.
  29. ^ David Roberts (20 February 2020). "The false promise of "renewable natural gas" - It's no substitute for shifting to clean electricity". Vox. Retrieved 2 September 2022.
  30. ^ Sammy Roth (4 April 2019). "California's next frontier in fighting climate change: your kitchen stove". Los Angeles Times. Retrieved 2 September 2022.
  31. ^ Susie Cagle (26 July 2019). "US gas utility funds 'front' consumer group to fight natural gas bans". The Guardian. Retrieved 2 September 2022.

External links[edit]