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Renewable natural gas (RNG), also known as biomethane, is a renewable fuel and 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 via existing gas pipeline infrastructure. RNG can be used in existing appliances, including vehicles with natural gas burning engines (natural gas vehicles).
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. Renewable natural gas can also be converted into liquefied natural gas (LNG) or compressed natural gas (CNG) for direct use as fuel in transport sector.
In the United States, projections of the ultimate supply potential for RNG vary. An 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. [3] [4] 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, [5] 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. [6]
More recently, a study commissioned by the American Gas Foundation and executed by ICF in 2019 projected that between 1.6-3.78 trillion cubic feet of RNG could be produced annually for pipeline injection in the U.S. by 2030. [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:
In North America, most RNG development has historically occurred in the municipal solid waste (MSW) sector. [13] The first commercial RNG facility was launched at the Fresh Kills landfill near New York City in 1982. As of 2023, more than 300 RNG facilities are currently operational in North America, [14] with more than 70% of supplies drawn from the MSW and landfill sectors, according to the U.S. trade group RNG Coalition. [15]
Göteborg Energi opened the first demonstration plant for large scale production of bio-synthetic natural gas (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%. [16] 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. [17]
It can be noted that the plant was a technical success, and performed as intended. [18] 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. [19]
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. [20] 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. [21]
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. [22]
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. [23] [24]
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. [25] Ecotricity announced plans to supply green gas to UK consumers via the national grid. [26] Centrica also announced that it would begin injecting gas, manufactured from sewage, into the gas grid. [27]
In Canada, FortisBC, a gas provider in British Columbia, injects renewably created natural gas into its existing gas distribution system. [28]
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. [29] [30]
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, [31] 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. [32] [33] [34]
Biogas is a gaseous renewable energy source produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, wastewater, and food waste. Biogas is produced by anaerobic digestion with anaerobic organisms or methanogens inside an anaerobic digester, biodigester or a bioreactor. The gas composition is primarily methane and carbon dioxide and may have small amounts of hydrogen sulfide, moisture and siloxanes. The methane can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used in fuel cells and for heating purpose, such as in cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.
Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels such as oil. Biofuel can be produced from plants or from agricultural, domestic or industrial biowaste. Biofuels are mostly used for transportation, but can also be used for heating and electricity. Biofuels are regarded as a renewable energy source. The use of biofuel has been subject to criticism regarding the "food vs fuel" debate, varied assessments of their sustainability, and possible deforestation and biodiversity loss as a result of biofuel production.
Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principally used for producing ammonia or methanol. Syngas is combustible and can be used as a fuel. Historically, it has been used as a replacement for gasoline, when gasoline supply has been limited; for example, wood gas was used to power cars in Europe during WWII.
Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (CO2). This is achieved by reacting the feedstock material at high temperatures (typically >700 °C), without combustion, via controlling the amount of oxygen and/or steam present in the reaction. The resulting gas mixture is called syngas (from synthesis gas) or producer gas and is itself a fuel due to the flammability of the H2 and CO of which the gas is largely composed. Power can be derived from the subsequent combustion of the resultant gas, and is considered to be a source of renewable energy if the gasified compounds were obtained from biomass feedstock.
Substitute natural gas (SNG), or synthetic natural gas, is a fuel gas (predominantly methane, CH4) that can be produced from fossil fuels such as lignite coal, oil shale, or from biofuels (when it is named bio-SNG) or using electricity with power-to-gas systems.
Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the fermentation used industrially to produce food and drink products, as well as home fermentation, uses anaerobic digestion.
Landfill gas is a mix of different gases created by the action of microorganisms within a landfill as they decompose organic waste, including for example, food waste and paper waste. Landfill gas is approximately forty to sixty percent methane, with the remainder being mostly carbon dioxide. Trace amounts of other volatile organic compounds (VOCs) comprise the remainder (<1%). These trace gases include a large array of species, mainly simple hydrocarbons.
Waste-to-energy (WtE) or energy-from-waste (EfW) is the process of generating energy in the form of electricity and/or heat from the primary treatment of waste, or the processing of waste into a fuel source. WtE is a form of energy recovery. Most WtE processes generate electricity and/or heat directly through combustion, or produce a combustible fuel commodity, such as methane, methanol, ethanol or synthetic fuels, often derived from the product syngas.
A mechanical biological treatment (MBT) system is a type of waste processing facility that combines a sorting facility with a form of biological treatment such as composting or anaerobic digestion. MBT plants are designed to process mixed household waste as well as commercial and industrial wastes.
The United States produces mainly biodiesel and ethanol fuel, which uses corn as the main feedstock. The US is the world's largest producer of ethanol, having produced nearly 16 billion gallons in 2017 alone. The United States, together with Brazil accounted for 85 percent of all ethanol production, with total world production of 27.05 billion gallons. Biodiesel is commercially available in most oilseed-producing states. As of 2005, it was somewhat more expensive than fossil diesel, though it is still commonly produced in relatively small quantities, in comparison to petroleum products and ethanol fuel.
Biodegradable waste includes any organic matter in waste which can be broken down into carbon dioxide, water, methane, compost, humus, and simple organic molecules by micro-organisms and other living things by composting, aerobic digestion, anaerobic digestion or similar processes. It mainly includes kitchen waste, ash, soil, dung and other plant matter. In waste management, it also includes some inorganic materials which can be decomposed by bacteria. Such materials include gypsum and its products such as plasterboard and other simple sulfates which can be decomposed by sulfate reducing bacteria to yield hydrogen sulfide in anaerobic land-fill conditions.
On April 25, 2006, Executive Order S-06-06, the Bioenergy Action Plan was issued by the then governor of California, Arnold Schwarzenegger, outlining a set of target goals which would establish the increasing use and production of biofuels and biopower for both electricity generation and substitution of natural gas and petroleum within the state of California. The plan asked multiple state agencies to work towards the advancement of biomass programs in California. The order would also help provide statewide environmental protection, mitigation and economic advancement. The plan was passed on July 7, 2006, with progress reports issued in 2007 and 2009.
Biofuels are renewable fuels that are produced by living organisms (biomass). Biofuels can be solid, gaseous or liquid, which comes in two forms: ethanol and biodiesel and often replace fossil fuels. Many countries now use biofuels as energy sources, including Sweden. Sweden has one of the highest usages of biofuel in all of Europe, at 32%, primarily due to the widespread commitment to E85, bioheating and bioelectricity.
Second-generation biofuels, also known as advanced biofuels, are fuels that can be manufactured from various types of non-food biomass. Biomass in this context means plant materials and animal waste used especially as a source of fuel.
Methanation is the conversion of carbon monoxide and carbon dioxide (COx) to methane (CH4) through hydrogenation. The methanation reactions of COx were first discovered by Sabatier and Senderens in 1902.
A biogas upgrader is a facility that is used to concentrate the methane in biogas to natural gas standards. The system removes carbon dioxide, hydrogen sulphide, water and contaminants from the biogas. One technique for doing this uses amine gas treating. This purified biogas is also called biomethane. It can be used interchangeably with natural gas.
Power-to-gas is a technology that uses electric power to produce a gaseous fuel. When using surplus power from wind generation, the concept is sometimes called windgas.
Iona Capital Ltd is a fund management institution that specializes in the management of equity and debt investments for private and institutional clients. Its investment strategy focuses on seeking out promising start-up companies that align with the UK Government's goal of reducing waste sent to landfills. In addition to its environmental objectives, the company also places a significant emphasis on identifying and partnering with strong management teams.
Digeponics (pronounced die-jeh-ponics, as in digestion) is a method of agriculture which integrates the products of anaerobic digestion, including CO2 and digestate, with greenhouse cultivation of vegetables.
Lutispora saccharofermentans, is an anaerobic bacteria. Lutispora saccharofermentans was first isolated from methanogenic enrichment cultures derived from a material collected from a lab-scale methanogenic landfill bioreactor.